X chromosomal mutations and spermatogenic failure

Biochimica et Biophysica Acta 1822 (2012) 1864–1872

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Review

X chromosomal mutations and spermatogenic failure☆ Katrien Stouffs ⁎, Willy Lissens Center for Medical Genetics, Universitair Ziekenhuis Brussel, Laarbeeklaan 101, 1090 Brussels, Belgium Research Group Reproduction and Genetics, Vrije Universiteit Brussel, Laarbeeklaan 101, 1090 Brussels, Belgium

a r t i c l e

i n f o

Article history: Received 6 November 2011 Received in revised form 24 February 2012 Accepted 14 May 2012 Available online 23 May 2012 Keywords: X chromosome Spermatogenesis Infertility

a b s t r a c t The X and Y chromosomes, the sex chromosomes, are important key players in germ cell development. Both chromosomes contain genes that are uniquely expressed in male spermatogenesis. Furthermore, these chromosomes are special because men only have a single copy of them. These features make the sex chromosomes interesting for studying in view of spermatogenesis defects. The role of the Y chromosome, together with the presence of Yq microdeletions, in male infertility is well established. Less well-understood are the X-linked genes, their expression patterns and potential impact on male infertility. This review provides an overview of the current knowledge on potential spermatogenesis genes that are located on the mouse and human X chromosomes. A summary is given on knock-out mice models in which X-linked genes have been shown to alter spermatogenesis, and on genes that have been studied in humans. Finally, new research areas like miRNA analysis, Genome Wide Association Studies (GWAS) and array comparative genomic hybridisation (CGH) studies are discussed. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure. © 2012 Elsevier B.V. All rights reserved.

1. Introduction — why study the X chromosome? The X and Y chromosomes, the sex chromosomes, are special since men only have a single copy of these chromosomes. Women, on the other hand, have two copies of the X chromosome and lack the Y chromosome. These sex chromosomes are derived from an autosomal chromosome pair 300 myr ago [1]. While the Y chromosome decreased to ~ one third the size of the X chromosome, the X chromosome remained more or less stable in size. However, the gene content of the X chromosome has changed largely. Under various selection processes, the sex chromosomes have obtained their current content. It is well known that both sex chromosomes play a pivotal role in sex determination. The major functions of the Y chromosome are related to sex determination and spermatogenesis. Mutations of, or alterations in the SRY gene on the short arm of the Y chromosome lead (in most cases) to sex reversal [2]. The long arm of the Y chromosome is involved in male infertility: deletions of one or more azoospermia factor (AZF) regions lead to spermatogenic failure. Abnormalities in/of X linked genes are causing a much wider range of diseases/syndromes. The X chromosome is enriched for genes expressed in brain, skeletal muscle, and as explained later, in sexand reproduction-related tissues [3]. Therefore, it is not surprising

☆ This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure. ⁎ Corresponding author at: Center for Medical Genetics, Universitair Ziekenhuis Brussel, Laarbeeklaan 101, 1090 Brussels, Belgium. Tel.: +32 2 4749149; fax: +32 2 4776860. E-mail address: [email protected] (K. Stouffs). 0925-4439/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.bbadis.2012.05.012

that the X chromosome is associated with syndromes involving mental retardation or muscle disorders. Typically, X-linked disorders are more common in men. One of the most common X-linked recessive disorders, is congenital color blindness, affecting ~ 8% of males, but only 0.5% of females [4]. The increased frequency of recessive disorders in males is caused by hemizygous exposure: men only have a single copy of the X chromosome, and therefore compensation by a second, normal allele is not possible. Keeping in mind the hemizygous presence of the X chromosome in men, it is also interesting to study this chromosome in view of male infertility. Changes in X-linked spermatogenesis genes can be passed on through women for several generations: the “effect” or phenotype will only become visible in males. Since infertility is affecting 10–15% of couples, and a male factor is responsible for about half of the cases, it is worthwhile to study the origin of male infertility. For infertile men producing a few spermatozoa, intracytoplasmic sperm injection (ICSI) with the patient's own sperm might be a solution to overcome the fertility problems. In many cases where genetic causes of infertility would be selected out naturally, the introduction of artificial reproductive technologies such as ICSI might circumvent this natural selection, and consequently genetic alterations might be transmitted to subsequent generations. Therefore it is important to identify genetic causes of male infertility for both diagnostic purposes and genetic counseling. 2. Testicular genes on the X chromosome There has been, and still is, much debate on the gene content of the X chromosome. While some authors claim that the X chromosome has

K. Stouffs, W. Lissens / Biochimica et Biophysica Acta 1822 (2012) 1864–1872

a small number of male-specific genes, others believe that the X chromosome is rather enriched for spermatogenesis genes. The gain/loss of male-specific genes can be explained by different evolutionary strategies. Evolutionary selection processes that are leading to demasculinization of the X chromosome (i.e. causing a decrease in the number of spermatogenesis genes on the X chromosome) include the sexual antagonism driven X inactivation (SAXI) hypothesis and meiotic sex chromosome inactivation (MSCI). MSCI, also referred to as meiotic silencing of unsynapsed chromatin (MSUC), is a process through which the X chromosome is inactivated during male meiosis. The process behind this inactivation is not well understood. MSCI is different from X chromosome inactivation (lyonization) in women by which one of the X chromosomes is inactivated, and is independent of the XIST gene. Due to the MSCI, the majority of genes on the X chromosome are repressed from meiosis onwards. This makes the X chromosome an unlikely place for meiotic and post-meiotic genes. As a consequence, part of the genes involved in meiosis has changed their location by retroposition from the X to an autosomal chromosome [5]. The SAXI hypothesis suggests that sexual antagonism is determining the chromosomal localization of genes: since the X chromosome is present twice as much in females, X-linked mutations that are of benefit to females are much more likely to accumulate, even if they are deleterious for men. In contrast to the SAXI theory, the hemizygous exposure theory predicts an accumulation of spermatogenesis genes on the X chromosome. This theory suggests that recessive mutations with a positive or beneficial effect for men will accumulate on the X chromosome. Men have only one copy of the X chromosome, and therefore the beneficial effect will immediately become visible. For women, two mutations would then be necessary in order to be beneficial. If deleterious for women, these effects would initially be masked since two mutations need to be present in women in order to have a negative effect. This would lead to masculinization of the X chromosome. This theory is also referred to as Rice's hypothesis [6]. The origin of the different theories concerning the gene content of the X chromosome is a result of the selection of the species under examination and the gene pool studied. Experimental data in mice suggested that testis-enriched genes are 2.5 times less dense on the X chromosome compared to autosomal chromosomes [7]. These authors further examined Spo11 −/− testes that show an arrest at meiosis [7]. Therefore, post-meiotic cells are depleted, and premeiotic cells are relatively enriched. This experiment showed that testis genes are enriched on the X chromosome, confirming that especially pre-meiotic genes are present on the X chromosome. Similarly, these authors analyzed 15 day old mice, a time where the first wave of spermatogenesis reaches meiosis. This study confirmed the enrichment of pre-meiotic genes on the X chromosome. Also Wang et al. suggested that among the spermatogonial genes, the X-linked genes are far more abundant [8]. They identified nine new genes that are expressed in spermatogonia (Table 1). In Drosophila melanogaster and Caenorhabditis elegans, however, male-biased genes are underrepresented on the X chromosome [9,10]. Sturgill et al. showed that, besides post-meiotic cells, also genes expressed in mitotic germ cells and male-biased somatic testes are depleted from the X chromosome [11]. Presumably, the difference in the gene content of the X chromosome might be explained by differences in the impact of different evolutionary selection processes. Another way of defining the gene content of the X chromosome is to look at the age of genes. Zhang et al. noticed that young (i.e. primate-specific) genes are enriched on the X chromosome in contrast to ‘older’ male-biased genes [12]. Interestingly, these young genes are detected throughout all stages of spermatogenesis, indicating that they escape MSCI. It was estimated that 70% of these genes are expressed in post-meiotic stages [12]. The majority of these genes, however, are multi-copy genes. In another study, it has been suggested that the more copies of a gene, the higher the chance to escape from X inactivation [13]. Warburton et al. proposed that the

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presence of inverted repeats on the X chromosome could protect genes in these regions from X inactivation [14]. The X chromosome carries 24 of these repeats, containing a large part of the cancer-testis (CT) genes [13]. These genes are in normal conditions only expressed in testis, but are also detected in multiple cancers (Table 2). Based on these ‘characteristics’, the genes on the X chromosome can be subdivided into two major groups: single copy and multicopy genes (Table 1 and Table 2). One further group of genes that we will consider here are X-linked genes with a homologue on the Y chromosome (Table 4). 3. Differences between mice and humans From Tables 1 and 2, it is obvious that especially for multicopy genes, large differences are observed between mice and humans. This can probably be explained by the fact that these genes arose late in evolution and are presumably still actively changing. Furthermore, part of the human ‘single’ copy genes is present in multiple copies in mice and vice versa (Table 2). Gmcl1 and Zfp161-rs1 are located on the X chromosome in mice, but are autosomal in humans. The Tsga8 gene is a testis-specific gene expressed in post-meiotic germ cells. This gene is present only in mice, although a potential homologue was found in rat [15,16]. It has been shown, however, that this gene is evolving rapidly, even within different mouse subspecies. It should be noted that the list of CT genes is increasing rapidly, and that probably not all CT genes are listed in Table 2. Presumably, the number of genes having different copy numbers in human and mouse will also increase as more genomic research will be performed. For part of these genes, a more specific function in spermatogenesis or a role in male infertility has already been reported. These results are described in the next paragraphs. We focus on X-linked genes that are uniquely or preferentially expressed in testicular tissues. 4. X-linked testis-specific or testis-enriched genes studied by generating knock-out mice (Tables 1 and 2) 4.1. AKAP4 The mouse Akap82 gene (later renamed Akap4 — A kinase anchor protein 4) was first identified by Carrera et al. [17]. This gene belongs to a family of A kinase anchor proteins. These proteins are tethering protein kinase A to subcellular locations and are crucial for tyrosine phosphorylation, which is essential for sperm capacitation. Miki et al. disrupted the Akap4 protein in mice [18]. They noticed that the sperm production was normal in terms of the number of sperm cells produced. However, the fibrous sheath was not completely developed and the flagellum was shortened. Consequently, these spermatozoa were immotile and the mice were infertile. 4.2. NXF2 The nuclear export factor 2 gene belongs to a family of proteins involved in the export of RNA from the nucleus to the cytoplasm [19]. In mice, four Nxf genes are present (Nxf1, Nxf2, Nxf3 and Nxf7) of which the latter three are located on the X chromosome [20]. The Nxf2 gene was first thought to be testis-specific, after which Tan et al. suggested that its major site of expression was brain tissue (although mRNA was detected in testis and brain) [21]. Lai et al. described the expression of mouse NXF2 proteins in brain and testis [22]. Recently, Zhou et al. confirmed this expression pattern [23]. The impact of the expression in both tissues remained uncertain until Pan et al. examined Nxf2 −/− and Nxf2 −/Y mice [24]. They noticed that all mice developed grossly normal and that part of the male mice were infertile. The observed fertility problems were very heterogeneous and were partly dependent on the genetic background of the mice. Inbred (C57BL/6J) mice were infertile with reduced semen parameters and impaired motility.

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K. Stouffs, W. Lissens / Biochimica et Biophysica Acta 1822 (2012) 1864–1872

Table 1 Single copy X-linked genes specifically expressed in testis, or enriched in testis. Human gene

Mouse gene

Mouse region

Mouse expression

Function

References

Genes with homologues in human and mouse AKAP4/AKAP82 Xp11.2 Testis, tumor cell lines ARPT1/ACTRT1 Xq25 Testis

Akap4 Arp-T1

A1.1 A3.1

Testis Testis

[18,32,33] [65]

CPXCR1

Xq21.3

Cpxcr1

E1

Testis

DMRT8

Xq13

Testis, tumor cell lines + multiple fetal tissues Multiple tissues

Sperm fibrous sheath protein Cytoskeletal calyx of the mammalian sperm head NDY

D

Testis

Transcription factor

DMRT8

Xq13

Multiple tissues

Transcription factor

[68]

Xq22.1 Xq28

Testis, placenta Testis, tumor cell lines

D, 12 copies F1 A7.3

Testis

ESX1L/ESR1 FATE1

Dmrtc1a/ Dmrt8.1 Dmrtc1b/ Dmrt8.2 Esx1 Fate1

Testis, placenta NA

[69] [37,38]

FMR1NB

Testis, tumor cell lines

Fmr1nb

A7.1

Testis, brain

LUZP4 NUDT10

Xq27.3q28 Xq23 Xp11.23

Homeobox gene, transcription factor Testicular differentiation/germ cell development NDY

Testis, tumor cell lines Brain, liver + multiple tissues

Luzp4 Nudt10

F3 A1.1

Xp11.23

Testis, brain, pancreas

Nudt11

A1.1

PABPC1L2A/B

Xq13.2

Pabpc1l2a/b

D/2 copies

Testis

PAK3

Xq23

Ovary, prostate, brain, kidney (Unigene) Testis, brain, lung

NDY Diphosphoinositol polyphosphate phosphohydrolase Diphosphoinositol polyphosphate phosphohydrolase NDY

[70] [71–73]

NUDT11

NDY Liver, kidney, testis Brain

Xq24 Xq24

Several

Ovary, testis

Homeobox gene, transcription factor

[76]

Testis, tumor cell lines Testis Not expressed

PEPP (Rhox) subfamily PEPP (Rhox) subfamily Taf7l Tex11 (Zip4h) Tex13

Several

RHOXF2

Testis, ovary, epididymis, tumor cell lines Testis, tumor cell lines

Cell migration, differentiation, or survival Homeobox gene, transcription factor

[74,75]

RHOXF1

Testis, brain, kidney Ovary, testis

E3 C3 F1

Testis Ovary, testis Testis

Transcription factor Meiotic recombination NDY

[8,25,26,43,44] [8,28] [8]

Xq21.3

Testis

Tgif2lx1/Tex1

Testis

Transcription factor

[78]

TKTL1/TKR

Xq28

Testis

Tktl1

2 copies/ E1 A7.3

Thiamine dependent enzyme

[8,79]

USP26

Xq26.2

Testis

Usp26

A5

Multiple tissues, tumor cell lines Testis

Deubiquitination

[8,45–49]

– – – – – – –

– – – – – – –

– – – – – – –

NDY NDY Metabolism of glutamate Testis-specific histone variant NDY (proto-oncogene) NDY NDY

[53] [80] [81–83] [39] [84] [85] [86]

Testis Testis Testis

NDY Chromatin condensation NDY

[8] [15,16] [87,88]

TAF7L TEX11 TEX13A TEX13B TGIF2LX

Human region

Xq22.1 Xq13.1 and Xq22.3

Human expression

Genes present only in human cXorf61 Xq23 DDX53/CAGE Xp22.11 GLUD2 Xq25 H2BFWT Xq22.2 MYCL2 Xq22-23 PASD1 Xq28 SAGE1 Xq26

Testis, tumor Testis, tumor Testis, brain Testis Testis, tumor Testis, tumor Testis, tumor

Genes present only in mice – – – – – –

– – –

cell lines cell lines

cell lines cell lines cell lines

Pak3

Tex16 E1 Tsga8/Halap-X C1 Tsx D

[66,67]

[67]

[71–73] [13]

[76,77]

The NXF3 gene is also part of the nuclear export factor family. Zhou et al. examined its expression in testicular tissues and found that the NXF3 protein is expressed in Sertoli cells [23]. The generation of Nxf3 −/Y and Nxf3 −/− mice showed that these mice were grossly healthy and fertile, even on a mixed genetic background. Consequently, this study showed that the Nxf3 gene is not essential for spermatogenesis, at least in mice.

inactivation during meiosis, it was shown that the TAF7L protein is expressed in the cytoplasm before meiosis and in the nucleus in post-meiotic cells [25]. Taking into consideration the function of the protein as a transcription factor, it is expected that the function of the TAF7L protein will be post-meiotic. The autosomal TAF7 protein, on the other hand, is expressed in the nucleus of pre-meiotic cells [25]. It is thus likely that the function of TAF7 is replaced by TAF7L from meiosis onwards. Cheng et al. generated Taf7l −/Y mice to further examine the function and relevance of the TAF7L protein [26]. They noticed that all mice were healthy and female mice were fertile. Male mice, however, showed decreased sperm production with abnormally shaped and immotile sperm cells [26].

4.4. TAF7L

4.5. TEX11

The TATA box binding protein associated factor 7 like was first identified by Wang et al. [8]. This gene has an autosomal homologue: Taf7, which is ubiquitously expressed. Unexpectedly in view of X

The testis expressed 11 gene is another gene isolated in 2001 from mice spermatogonia [8]. The authors noticed that the Tex11 gene is mainly expressed before meiosis, although transcripts remain

It was also noticed that the proliferation of spermatogonial stem cells was decreased, causing germ cell loss in aged mice. 4.3. NXF3

K. Stouffs, W. Lissens / Biochimica et Biophysica Acta 1822 (2012) 1864–1872

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Table 2 Multicopy X-linked genes specifically expressed in testis, or enriched in testis. Human gene

Human region

Mouse gene

Mouse region

Mouse expression

Function

Genes with homologues in the human and mouse FTHL17 Xp21, 4 copies Testis, tumor cell lines GMCL1L 5q35.3 NDY H2AFB1 Xq28, 3 copies Testis/sperm MAGE family >24 copies Testis, tumor cell lines

Fthl17 Gmcl1l H2A.Bbd Mage

A1.1/6 copies ~ 21 copies/A1.1 E2/4 copies > 16 copies

Iron metabolism NDY Histone Cell cycle regulation

[8,13,65,89] [13] [90]

NXF

4 copies

Nxf

2 copies

Nuclear export

[8,21–24]

PRAME SPANX genes

22q11.22 9/11 copies

Pramel3 Spanx

9 copies/F1 A6

Testis Testis

Cell death NDY

[8,91] [92,93]

SSX family

Xp11.2/> 10 copies

Testis, brain, tumor cell lines Testis, tumor cell lines Testis, prostate, placenta, lung, tumor cell lines Testis, tumor cell lines

Testis Testis Testis/sperm Testis, tumor cell lines Testis, brain

13 copies

Testis

NDY

[13,94]

ZFP161

18p11.21

Multiple tissues

Ssxa + SSXb family Zfp161-rs1

2 copies

Testis

[13,95]

ZXDa/b

Xp11.1/Xp11.21

Multiple tissues

Zxda/b

2 copies/C3

Testis

Zinc finger protein; transcriptional repressor Zinc finger protein

Testis, tumor cell lines Testis, tumor cell lines Testis, low in placenta and brain, tumor cell lines Testis, ovary, tumor cell lines Testis, tumor cell lines Testis, tumor cell lines Testis, tumor cell lines Testis, tumor cell lines

– – –

– – –

– – –

NDY NDY NDY

[67] [97,98] [98,99]

–

–

–

NDY

[100]

– – – –

– – – –

– – – –

[67] [101] [12] [102,103]

Testis, tumor cell lines Testis Testis, tumor cell lines

– – –

– – –

– – –

NDY Homologuos to SYCP3 NDY Differentiation and survival of germ cells NDY Ribosome assembly NDY

Genes present only in mice – –

–

Cypt

7 copies

Testis

[106]

–

–

–

Ott genes

Testis, ovary

–

–

–

Slx/Xmr

~ 12 copies/F1F3 > 25 copies

Remodeling of spermatid nucleus Meiosis

[13,108,109]

– –

– –

– –

Srsx Sstx

~ 14 copies 3 copies

Testis Testis

Meiosis, homologuos to SYCP3 NDY NDY

Genes present only in humans CSAG Xq28/4 copies CT45 Xq26.3/6 copies CT47 Xq24/> 13 copies CTAG/NY-ESO1 CXorf48 FAM9 FAM47B/C GAGE family PAGE family VCX XAGE family

3 copies Xq26.3/3 copies Xp22/3 copies Xp21.1/2 copies Xp11.2-11.4, 13–39 copies Xp11.23/7 copies Xp22.3/4 copies Xp11.21-Xp11.22/14 copies

Human expression

Testis

[13,96]

[67] [102,104] [105]

[107]

[13] [13]

detectable during and after meiosis, indicating that this gene escapes MSCI [27]. Two consequent studies have examined the role of the Tex11 gene during meiosis by examining the expression pattern of the TEX11 protein and by generating knock-out mice [28,29]. The conclusions on the function of the TEX11 protein were consistent: the Tex11 gene is essential for the formation of crossovers during meiosis. However, both studies came to different conclusions concerning the phenotype of the Tex11 −/Y mice. Yang et al. concluded that male mice were infertile due to a meiotic arrest [29]. Although female Tex11 −/− mice were fertile, the litter sizes were reduced. Similar results were also observed for autosomal genes (for instance Sycp3: [30,31]). Adelman and Petrini, on the other hand, concluded that both female and male knock-out mice were fertile with the production of normal litter sizes [28].

[32,33]. For both patient groups, no differences were observed in the expression, location or function of the AKAP4 proteins compared to normal controls. The gene was partially sequenced in five patients with fibrous sheath dysplasia and the patient with stump sperm tails. No mutations were detected in the region encoding for the AKAP3 binding site. Bacetti et al. noticed partial deletions in the AKAP3 and AKAP4 genes in the DNA of a single patient with fibrous sheath dysplasia [34,35]. Visser et al. examined 30 infertile men for the presence of mutations in nine genes presumably involved in asthenozoospermia [36]. Among multiple potential disease-causing mutations that were only detected in the patient group and absent in 90 controls studied, one was located in AKAP4 (c.887G>A; p. Gly296Asn). Although not located in a functional domain, the authors concluded that this change might be related to the infertility problems of the patient.

5. Mutation analyses in human X-linked genes with a testis-specific or testis-enriched expression pattern (Tables 1, 2 and 3)

5.2. FATE1

5.1. AKAP4 Based on the observations by Miki et al. multiple studies in humans have been performed to identify defects in the human protein/gene [18]. Turner et al. have looked at the AKAP4 protein in nine patients with fibrous sheath dysplasia and one patient with stump sperm tails

The FATE1 (fetal and adult expressed 1) gene was found to be mainly expressed in testicular tissues and to a lesser extent in brain, lung, adrenal gland, heart and kidney [37]. The cytoplasmic-expressed protein was found in spermatogonia and primary spermatocytes, but was absent in spermatids and spermatozoa. Expression was also observed in Sertoli cells [38]. It belongs to the family of cancer-testis genes [38]. However, at present only a single copy has been identified in humans.

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Table 3 Overview of alterations with an amino acid change or predicted to have functional consequences observed in infertile patients and control groups.

AKAP4 FATE FATE H2BFWT TAF7L TAF7L TAF7L USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26 USP26

Nucleotide change

Protein change Patients Controls References

887G>A (exon6) 185T>C 459C>G –9C>T 922A>G 10471052GGATGAdel 1371G>A 370_371insACA, 494T>C, 1423C>T 370_371insACA 370_371insACA, 460G>A 370_371insACA, 494T>C 468T>G 494T>C 508G>A 520T>G 565T>G 1037T>A 1044T>A 1090C>T 1274C>T 1423C>T 1498G>A 1549C>T 1609C>G 1737G>A 1976C>T 2144A>T 2182A>T 2195T>C 2202A>C 2204T>G 2239A>T 2247A>C

G296N I34T S125R – S308G D350_E351del

1/30 1/144 1/144 204/442 9/41 4/41

0/90 0/100 0/100 77/213 9/80 15/80

R458H T123_124ins, L165S, H475Y T123_124ins T123_124ins, V154I T123_124ins, L165S Q156H L165S G170R E174* E189* L346H F348L L364F P425L H475Y E500K L517F Q537G M579I T659M N715I I128F F732S K734N V735G I747F E749D

3/41 51/ 1437 2/1091 8/791

1/80 [43,44] 87/2445 Reviewed in [47] 0/767 [46,110–115] 0/480 [46,110–114]

9/1091

2/767

[46,108–115]

1/791 40/1091 2/791 1/791 1/791 1/791 4/791 25/1091 1/791 6/1091 1/791 0/791 1/791 85/1091 1/791 1/791 1/791 1/791 1/791 1/791 1/791 1/791

0/480 36/767 0/480 0/480 0/480 0/480 2/480 21/767 0/480 4/767 0/480 1/480 0/480 31/767 0/480 0/480 0/480 0/480 0/480 0/480 0/480 0/480

[46,108–114] [46,108–115] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–115] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–115] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–114] [46,108–114]

[36] [37] [37] [41] [43,44] [43,44]

Olesen et al. looked for the presence of mutations in 144 infertile men [37]. One potential mutation was detected (c.185T>C or p.I34T). A second change that was uniquely detected in the patient group (c.459C>G or p.S125R) was inherited from the mother of the patient, who has a fertile brother with the same (hemizygous) change. This change therefore does not seem to be involved in male infertility. 5.3. H2BFWT The H2B histone family, member W, testis-specific (H2BFWT) gene encodes for a testis-specific histone. This gene is conserved among primates, but absent in rodents [39]. H2BFWT and the somatic protein H2B show 43% identity [39]. Boulard et al. showed that H2B and H2BFWT can be exchanged without changing the overall structure of the nucleosome [40]. However, the NH2 tail of both proteins is different. In the somatic protein, this tail is essential for the assembly of mitotic chromosomes. Churikov et al. suggested that the H2BFWT protein is enriched in the telomeric regions of the chromosomes [39]. Lee et al. identified a variant in the 5′UTR of the H2BFWT gene that might be associated with sperm numbers and sperm viability [41]. The authors could also show differences at the translational level.

[42]. However, in this study only patients with Sertoli cell-only syndrome have been examined. As mentioned above, male mouse models defective for this gene are infertile though the phenotype of the examined mice is very heterogeneous. Therefore, the human phenotype in case of a mutation in the NXF2 gene might be heterogeneous as well, and possibly Sertoli cell-only syndrome might not be linked with mutations in the NXF2 gene in humans. 5.5. TAF7L Two studies have on the reported molecular analysis of the TAF7L gene in humans [43,44]. In one of the studies, patients with maturation arrest of spermatogenesis were analyzed, while the second paper focused on non-obstructive azoospermic men (including men with a spermatogenic arrest). The choice of the patient groups was based on the observed expression pattern (see above): the TAF7L protein shows a reallocation from the cytoplasm to the nucleus in spermatocytes and this process coincides with the absence of expression of the TAF7 protein. Presumably, the protein function starts from the spermatocyte stage onwards. All observed changes were also present in control groups. Akinloye et al. found that one of the changes (c.1371G>A, p.R458H) was detected more often in the patient groups than in the control groups, and therefore suggested that this change might be a risk factor [44]. However, the expected phenotype might not be azoospermia but oligozoospermia. This observation is supported by mice knock-out studies showing oligoasthenoteratozoospermia [26]. 5.6. USP26 The Usp26 gene was first identified by Wang et al. in mouse spermatogonia [8]. In a more recent study, the specific localization of the protein was investigated in mice testicular tissues [45]. The authors noticed that the USP26 protein is present at the blood-testis barrier. It is also present in the acrosomes of round spermatids and spermatozoa, in the region where the sperm cells are attached to the Sertoli cells. Multiple variations in the human USP26 gene have been reported of which three changes have been investigated more intensively: c.370_371insACA, c.494T>C, c.1423C>T. This cluster of changes has first been reported in 2005, where a link with spermatogenesis defects was suggested [46]. A small meta-analysis performed on eight publications showed that these changes are probably not involved in male infertility [47]. Presumably, the frequency of the presence of this cluster of changes is dependent on the geographic location of the patients under investigation [48]. Dirac and Bernards (2010) have performed functional analyses of the USP26 gene [49]. By looking at proteins involved in the regulation of ubiquitination of the androgen receptor, the USP26 gene was the most promising gene. Both proteins interact and this causes a change in the function of the androgen receptor. These authors have investigated the impact of the variants c.494T>C, c.1037T>A, c.1090C>T and c1423C>T on the transcriptional activity of the androgen receptor. No differences were observed compared to the wild type USP26 protein. Unfortunately, a large number of changes have been detected in the USP26 gene — including two nonsense mutations — for which no functional analyses have been performed [Table 3, 47]. Consequently, it remains unsure whether these rare changes might be involved in male infertility by changing the androgen receptor or potentially by disrupting the blood-testis barrier or through a still unknown mechanism [45].

5.4. NXF2 6. Genes with a homologue on the Y chromosome In humans, six copies of the nuclear export factor gene family are present of which four genes are located on the X chromosome in the order Xcen-NXF5-NXF2-NXF4-NXF3-Xqter. Mutation analysis of the NXF2 gene has been reported in a single study, but failed to identify mutations related to male infertility

Another group of genes that are interesting to study are genes with a homologue on the Y chromosome. Besides genes located in the pseudo-autosomal regions of the X and Y chromosomes, a number of genes ‘still’ have a homologue on the Y chromosome. The

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majority of these are escaping X inactivation in women (Table 4; [50]). It was suggested that two copies of these genes are essential for their proper function and consequently that these genes might play a role in the phenotypical appearance of Turner syndrome. Two of the genes are only expressed in the testis (VCX and TGIF2LX), and therefore they are potentially interesting to study in view of spermatogenesis defects. The Y-homologues of these genes are located at positions Yq11.221 and Yp11.2, respectively. Mutation studies have not been performed neither for the X nor the Y copy. However, in 2005, a potential role in mental retardation was suggested for the VCX gene [51]. This study stresses the need to re-investigate the expression pattern of these genes. It is highly unlikely that a testisspecific gene is involved in the etiology of mental retardation.

7. Other genes studied in human (GWAS, CNV) Besides these studies focusing on a single gene or a few genes, large-scale studies have also been performed to identify genetic causes of male infertility. Although the main focus of the majority of these studies was not on the X chromosome, X-linked defects could also be detected. Aston and Carrell have performed a first genome wide association study (GWAS) in male infertility [52]. In this study, 20 single nucleotide polymorphisms (SNPs) were significantly associated with azoospermia or oligozoospermia. None of these SNPs were located on the X chromosome. In a subsequent study, 172 interesting SNPs, including nine on the X chromosome, were further examined in larger patient and control groups. These SNPs include polymorphisms in the androgen receptor (AR), TEX11, USP26 and ZFX. Two SNPs (rs5911500 located in a gene of unknown function cXorf61 and rs35397110 in USP26) were found to be significantly associated with azoospermia or oligozoospermia. The cXorf61 gene (also referred to as CT83; KKLC1; KK-LC-1) is probably a cancer-testis gene [53]. Further research is necessary to examine the function of this gene and to determine its role in male infertility. Tüttelmann et al. were the first to examine copy number variations (CNVs) in infertile men [54]. They focused on patients with Sertoli cell-only syndrome or idiopathic severe oligozoospermia. The authors noticed significantly more X-linked CNVs in patients with Sertoli cellonly syndrome. The authors detected one duplication in the cXorf48 gene that was detected in two oligozoospermic men and 23 ‘private’ CNVs that were detected in only a single patient. The cXorf48 gene also belongs to the family of cancer-testis genes [55]. Among the private X-linked CNVs are several cancer-testis genes.

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8. X-linked miRNA and spermatogenesis Non-coding RNAs are playing an important role in many different regulatory events [56]. Among the non-coding RNAs, microRNAs (miRNAs) are presumed to be especially involved in the regulation at the post-transcriptional level. In the ‘mature’ form these miRNAs are 21 to 25 nucleotides long. In testicular tissues, several miRNAs are essential for the progress of spermatogenesis (reviewed in [57]). In 2007, two studies were published in which the miRNA profile of murine testis was established [58,59]. In one of these studies, it was already suggested that a large part of the X-linked miRNAs are highly expressed in pachytene spermatocytes which are undergoing meiosis [58]. The same group further examined the X-linked miRNAs. They could show that around 38% of X-linked miRNAs show a testisspecific or testis-enriched expression pattern [60]. A similar finding was described by Guo et al. who demonstrated that, at least in mammals, the X chromosome has the highest density of miRNAs and that these are mostly present in the testis [61]. Song et al. further described that 86% of the X-linked miRNAs escape from X inactivation during meiosis, and that the majority of these are expressed from meiosis onwards [60]. It was therefore suggested that the miRNAs might be involved in MSCI and/or might be crucial for the regulation of gene expression in later stages of spermatogenesis. Guo et al. [61] suggested that X-linked miRNAs might be involved in cell cycle control, possibly in the regulation of spermatogonial stem cell renewal or meiosis. Both studies suggested that X-linked miRNAs might be involved in meiosis. Consequently, it might be interesting to study the impact of miRNAs in meiosis, and in meiotic arrest. Although most of the detected miRNAs are well-conserved among different species, at least one X-linked cluster is evolving rapidly, and its presence is restricted to primates. This cluster containing 10 miRNAs preferentially expressed in testicular tissues was first identified by Bentwich et al. and further examined by Zhang et al. [62,63]. Also Guo et al. [61] could show that, when comparing mouse and human miRNAs, miRNAs on the X chromosome have a much higher substitution rate compared to autosomes. So far, no mutations have been detected in human miRNAs involved in male infertility. In mouse, a few miRNAs have been investigated in view of infertility. Yet, at present, no Xlinked miRNA has been knocked-out. In an interesting study, Dicer, an RNase III endonuclease essential for the synthesis of mature miRNAs, has been selectively knocked-out in spermatogonia [64]. This study showed reduced numbers of post-meiotic germ cells, along with a high number of apoptotic spermatocytes. This study, again, showed that miRNAs might be essential to complete meiosis.

Table 4 X-linked genes with an homologous copy on the human Y chromosome. NA = not assessed; NR = not relevant; for testis-specific genes, it is impossible to test X-inactivation. Gene name

Human location

Mouse location

Expression

Function

Escape X inactivation

Reference

AMELX DDX3X EIF1AX KDM5C/SMCX KDM6A/UTX NLGN4X PCDH11X PRKX RBMX RPS4X SOX3 TBL1X TGIF2LX TMSB4X TSPYL2 TXLNG/CXORF15 USP9X VCX ZFX

Xp22.31–p22.1 Xp11.3–p11.23 Xp22.12 Xp11.22–p11.21 Xp11.2 Xp22.23 Xq21.3 Xp22.3 Xq26.3 Xq13.1 Xq27.1 Xp22.3 Xq21.31 Xq21.3–q22 Xp11.2 Xp22.2 Xp11.4 Xp22.3/4 copies Xp21.3

F5 A1.1 F4 F2–F4 A1.2–A1.3 NA E2 A7.3 A5 D A7.3–B B-CPRKX E1 F5 F2 F4 A1.1 – D

Tooth Ubiquitous Ubiquitous Ubiquitous Ubiquitous Ubiquitous Brain Kidneys Ubiquitous Ubiquitous Ubiquitous Ubiquitous Testis Ubiquitous Testis, Brain + others NA Ubiquitous Testis Ubiquitous

Part of enamel RNA helicase Translation initiation Transcriptional repressor Demethylation Cell-adhesion molecule at synapse Cell surface molecule Serine/threonine kinase Regulation of splicing Ribosomal protein Transcription factor Protein–protein interactions Transcription factor Actin sequestering

NA Yes Yes Yes Yes Yes Yes Yes No Yes No Yes NR Yes No Yes Yes NR Yes

[116] [117–119] [120] [121] [122] [123,124] [125] [126] [127] [128] [129] [130,131] [76] [132] [133,134] [135] [136] [108,110] [137]

Intracellular vesicle trafficking Ubiquitin-specific proteases Regulation of ribosome assembly Transcriptional regulation

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9. Conclusion The X chromosome is particularly interesting to study in view of male infertility first of all because of its hemizygous exposure in men, and secondly because of the presence of a relatively high number of testis-specific genes and non-coding RNAs. Due to this hemizygous exposure, the X chromosome is particularly prone to evolutionary selection processes. As described before, the consequences of these forces might be advantageous or disadvantageous for men. In humans, it appears that the X chromosome is (slightly) enriched for male specific genes. A further consequence is that the X chromosome is evolving very quickly, giving rise to new genes or gene family members in humans. As can be seen from Tables 1 and 2, a lot of differences in the gene content of the X chromosome from mice and human can be detected, at least for testis-specific genes. Moreover, the function of the majority of the CT genes has not been investigated yet. Possibly, the copy number of the genes, as well as their function might be different in mice and humans. This, again, stresses that extrapolation of data obtained from mouse studies to humans will not always be possible (or might be incorrect). So far, the number of mutations detected on the X chromosome in infertile men remains small. This can partly be explained by the low number of genes that have been studied at present (Table 3). The development of new molecular techniques (f.i. next generation sequencing) will allow the examination of all X-linked genes in a single analysis. Consequently, the analysis of X-linked genes in association with male infertility will be less time consuming, and it is likely that more mutations will be detected. However, at present, the interpretation will be cumbersome since the function of part of the genes needs to be determined. Here again, the development of large scale analysis methods at ‘array format’ (RNA arrays, protein arrays,…), will enhance the study of these genes. Yet, again, the interpretation of these studies might be difficult and could cause some biases: part of the ubiquitously expressed genes might only affect spermatogenesis when deleted in knock-out mice models. In other tissues, the function of the gene could be compensated by alternative genes (‘genetic redundancy’). Overall, we believe that within the next decade our current understanding of the genes on the X chromosome in all its aspects (which genes, expression patterns, evolutionary aspects,…) will strongly expand.

Acknowledgements Katrien Stouffs is a postdoctoral fellow of the Fund for Scientific Research Flanders (Belgium) (FWO-Vlaanderen). The work was supported by grants from the Fund for Scientific Research Flanders (Belgium), from the Research Council of UZ Brussel and a Concerted Action of the Vrije Universiteit Brussel (VUB).

References [1] J.A. Graves, E. Koina, N. Sankovic, How the gene content of human sex chromosomes evolved, Curr. Opin. Genet. Dev. 16 (2006) 219–224. [2] T. Wang, J.H. Liu, J. Yang, J. Chen, Z.Q. Ye, 46, XX male sex reversal syndrome: a case report and review of the genetic basis, Andrologia 41 (2009) 59–62. [3] E.J. Vallender, B.T. Lahn, How mammalian sex chromosomes acquired their peculiar gene content, Bioessays 26 (2004) 159–169. [4] M.P. Simunovic, Colour vision deficiency, Eye 24 (2010) 747–755. [5] P.J. Wang, X chromosomes, retrogenes and their role in male reproduction, Trends Endocrinol. Metab. 15 (2004) 79–83. [6] W.R. Rice, Sex-chromosomes and the evolution of sexual dimorphism, Evolution 38 (1984) 735–742. [7] P.P. Khil, N.A. Smirnova, P.J. Romanienko, R.D. Camerini-Otero, The mouse X chromosome is enriched for sex-biased genes not subject to selection by meiotic sex chromosome inactivation, Nat. Genet. 36 (2004) 642–646. [8] P.J. Wang, J.R. McCarrey, F. Yang, D.C. Page, An abundance of X-linked genes expressed in spermatogonia, Nat. Genet. 27 (2001) 422–426.

[9] M. Parisi, R. Nuttall, D. Naiman, G. Bouffard, J. Malley, J. Andrews, S. Eastman, B. Oliver, Paucity of genes on the Drosophila X chromosome showing male-biased expression, Science 299 (2003) 697–700. [10] V. Reinke, I.S. Gil, S. Ward, K. Kazmer, Genome-wide germline-enriched and sex-biased expression profiles in Caenorhabditis elegans, Development 131 (2004) 311–323. [11] D. Sturgill, Y. Zhang, M. Parisi, B. Oliver, Demasculinization of the X chromosomes in the Drosophila genus, Nature 450 (2007) 238–242. [12] Y.E. Zhang, M.D. Vibranovski, P. Landback, G.A. Marais, M. Long, Chromosomal redistribution of male-biased genes in mammalian evolution with two bursts of gene gain on the X chromosome, PLoS Biol. 8 (2010) e1000494. [13] J.L. Mueller, S.K. Mahadevaiah, P.J. Park, P.E. Warburton, D.C. Page, J.M. Turner, The mouse X chromosome is enriched for multicopy testis genes showing postmeiotic expression, Nat. Genet. 40 (2008) 794–799. [14] P.E. Warburton, J. Giordano, F. Cheung, Y. Gelfand, G. Benson, Inverted repeat structure of the human genome: the X-chromosome contains a preponderance of large, highly homologous inverted repeats that contain testes genes, Genome Res. 14 (2004) 1861–1869. [15] M.M. Taketo, Y. Araki, A. Matsunaga, A. Yokoi, J. Tsuchida, Y. Nishina, M. Nozaki, H. Tanaka, M. Koga, K. Uchida, K. Matsumiya, A. Okuyama, J.M. Rochelle, Y. Nishimune, M. Matsui, M.F. Seldin, Mapping of eight testis-specific genes to mouse chromosomes, Genomics 46 (1997) 138–142. [16] J.M. Good, D. Vanderpool, K.L. Smith, N.W. Nachman, Extraordinary sequence divergence at Tsga8, an X-linked gene involved in mouse spermiogenesis, Mol. Biol. Evol. 28 (2011) 1675–1686. [17] A. Carrera, J. Moos, X.P. Ning, G.L. Gerton, J. Tesarik, G.S. Kopf, S.B. Moss, Regulation of protein tyrosine phosphorylation in human sperm by a calcium/calmodulin-dependent mechanism: identification of A kinase anchor proteins as major substrates for tyrosine phosphorylation, Dev. Biol. 180 (1996) 284–296. [18] K. Miki, W.D. Willis, P.R. Brown, E.H. Goulding, K.D. Fulcher, E.M. Eddy, Targeted disruption of the Akap4 gene causes defects in sperm flagellum and motility, Dev. Biol. 248 (2002) 331–342. [19] A. Herold, M. Suyama, J.P. Rodrigues, I.C. Braun, U. Kutay, M. Carmo-Fonseca, P. Bork, E. Izaurralde, TAP (NXF1) belongs to a multigene family of putative RNA export factors with a conserved modular architecture, Mol. Cell. Biol. 23 (2000) 8996–9008. [20] M. Sasaki, E. Takeda, K. Takano, K. Yomogida, J. Katahira, Y. Yoneda, Molecular cloning and functional characterization of mouse Nxf family gene products, Genomics 85 (2005) 641–653. [21] W. Tan, A.S. Zolotukhin, I. Tretyakova, J. Bear, S. Lindtner, S.V. Smulevitch, B.K. Felber, Identification and characterization of the mouse nuclear export factor (Nxf) family members, Nucleic Acids Res. 33 (2005) 3855–3865. [22] D. Lai, D. Sakkas, Y. Huang, The fragile X mental retardation protein interacts with a distinct mRNA nuclear export factor NXF2, RNA 12 (2006) 1446–1449. [23] J. Zhou, J. Pan, S. Eckardt, N.A. Leu, K.J. McLaughlin, P.J. Wang, Nxf3 is expressed in Sertoli cells, but is dispensable for spermatogenesis, Mol. Reprod. Dev. 78 (2011) 241–249. [24] J. Pan, S. Eckardt, N.A. Leu, M.G. Buffone, J. Zhou, G.L. Gerton, K.J. McLaughlin, P.J. Wang, Inactivation of Nxf2 causes defects in male meiosis and age-dependent depletion of spermatogonia, Dev. Biol. 330 (2009) 167–174. [25] J.C. Pointud, G. Mengus, S. Brancorsini, L. Monaco, M. Parvinen, P. Sassone-Corsi, I. Davidson, The intracellular localisation of TAF7L, a paralogue of transcription factor TFIID subunit TAF7, is developmentally regulated during male germ-cell differentiation, J. Cell Sci. 116 (2003) 1847–1858. [26] Y. Cheng, M.G. Buffone, M. Kouadio, M. Goodheart, D.C. Page, G.L. Gerton, I. Davidson, P.J. Wang, Abnormal sperm in mice lacking the Taf7l gene, Mol. Cell. Biol. 27 (2007) 2582–2589. [27] P.J. Wang, D.C. Page, J.R. McCarrey, Differential expression of sex-linked and autosomal germ-cell-specific genes during spermatogenesis in the mouse, Hum. Mol. Genet. 14 (2005) 2911–2918. [28] C.A. Adelman, J.H. Petrini, ZIP4H (TEX11) deficiency in the mouse impairs meiotic double strand brak repair and the regulation of crossing over, PLoS Genet. 4 (2008) e1000042. [29] F. Yang, K. Gell, G.W. van der Heijden, S. Eckardt, N.A. Leu, D.C. Page, R. Benavente, C. Her, C. Höög, K.J. McLaughlin, P.J. Wang, Meiotic failure in male mice lacking an X-linked factor, Genes Dev. 22 (2008) 682–691. [30] L. Yuan, J.G. Liu, J. Zhao, E. Brundell, B. Daneholt, C. Höög, The murine SCP3 gene is required for synaptonemal complex assembly, chromosome synapsis, and male fertility, Mol. Cell 5 (2000) 73–83. [31] L. Yuan, J.G. Liu, M.R. Hoja, J. Wilbertz, K. Nordqvist, C. Höög, Female germ cell aneuploidy and embryo death in mice lacking the meiosis-specific protein SCP3, Science 296 (2002) 1115–1118. [32] R.M. Turner, J.A. Foster, G.L. Gerton, S.B. Moss, P. Patrizio, Molecular evaluation of two major human sperm fibrous sheath proteins, pro-hAKAP82 and hAKAP82, in stump tail sperm, Fertil. Steril. 76 (2001) 267–274. [33] R.M. Turner, M.P. Musse, A. Mandal, K. Klotz, F.C. Jayes, J.C. Herr, G.L. Gerton, S.B. Moss, H.E. Chemes, Molecular genetic analysis of two human sperm fibrous sheath proteins, AKAP4 and AKAP3, in men with dysplasia of the fibrous sheath, J. Androl. 22 (2001) 302–315. [34] B. Baccetti, G. Collodel, M. Estenoz, D. Manca, E. Moretti, P. Piomboni, Gene deletions in an infertile man with sperm fibrous sheath dysplasia, Hum. Reprod. 20 (2005) 2790–2794. [35] B. Baccetti, G. Collodel, L. Gambera, E. Moretti, F. Serafini, P. Piomboni, Fluorescence in situ hybridization and molecular studies in infertile men with dysplasia of the fibrous sheath, Fertil. Steril. 84 (2005) 123–129.

K. Stouffs, W. Lissens / Biochimica et Biophysica Acta 1822 (2012) 1864–1872 [36] L. Visser, G.H. Westerveld, F. Xie, S.K. van Daalen, F. van der Veen, M.P. Lombardi, S. Repping, A comprehensive gene mutation screen in men with asthenozoospermia, Fertil. Steril. 95 (2011) 1020–1024. [37] C. Olesen, J. Silber, H. Eiberg, E. Ernst, K. Petersen, S. Lindenberg, N. Tommerup, Mutational analysis of the human FATE gene in 144 infertile men, Hum. Genet. 113 (2003) 195–201. [38] X.A. Yang, X.Y. Dong, H. Qiao, Y.D. Wang, J.R. Peng, Y. Li, X.W. Pang, C. Tian, W.F. Chen, Immunohistochemical analysis of the expression of FATE/BJ-HCC-2 antigen in normal and malignant tissues, Lab. Invest. 85 (2005) 205–213. [39] D. Churikov, J. Siino, M. Svetlova, K. Zhang, A. Gineitis, E.M. Bradbury, A. Zalensky, Novel human testis-specific histone H2B encoded by the interrupted gene on the X chromosome, Genomics 84 (2004) 745–756. [40] M. Boulard, T. Gautier, G.O. Mbele, V. Gerson, A. Hamiche, D. Angelov, P. Bouvet, S. Dimitrov, The NH2 tail of the novel histone variant H2BFWT exhibits properties distinct from conventional H2B with respect to the assembly of mitotic chromosomes, Mol. Cell. Biol. 26 (2006) 1518–1526. [41] J. Lee, H.S. Park, H.H. Kim, Y.J. Yun, D.R. Lee, S. Lee, Functional polymorphism in H2BFWT-5′UTR is associated with susceptibility to male infertility, J. Cell. Mol. Med. 13 (2009) 1942–1951. [42] K. Stouffs, H. Tournaye, J. Van der Elst, I. Liebaers, W. Lissens, Is there a role for the nuclear export factor 2 gene in male infertility? Fertil. Steril. 90 (2008) 1787–1791. [43] K. Stouffs, A. Willems, W. Lissens, H. Tournaye, A. Van Steirteghem, I. Liebaers, The role of the testis-specific gene hTAF7L in the aetiology of male infertility, Mol. Hum. Reprod. 12 (2006) 263–267. [44] O. Akinloye, J. Gromoll, C. Callies, E. Nieschlag, M. Simoni, Mutation analysis of the X-chromosome linked, testis-specific TAF7L gene in spermatogenic failure, Andrologia 39 (2007) 190–195. [45] Y.W. Lin, T.H. Hsu, P.H. Yen, Localization of ubiquitin specific protease 26 at blood-testis barrier and near Sertoli cell-germ cell interface in mouse testes, Int. J. Androl. 34 (2011) e368–e377. [46] K. Stouffs, W. Lissens, H. Tournaye, A. Van Steirteghem, I. Liebaers, Possible role of USP26 in patients with severely impaired spermatogenesis, Eur. J. Hum. Genet. 13 (2005) 336–340. [47] K. Stouffs, H. Tournaye, I. Liebaers, W. Lissens, Male infertility and the involvement of the X chromosome, Hum. Reprod. Update 15 (2009) 623–637. [48] C. Ravel, B. El Houate, S. Chantot, D. Lourenço, A. Dumaine, H. Rouba, A. Bandyopadahyay, U. Radhakrishna, B. Das, S. Sengupta, J. Mandelbaum, J.P. Siffroi, K. McElreavey, Haplotypes, mutations and male fertility: the story of the testis-specific ubiquitin protease USP26, Mol. Hum. Reprod. 12 (2006) 643–646. [49] A.M.G. Dirac, R. Bernards, The deubiquitinating enzyme USP26 is a regulator of androgen receptor signaling, Mol. Cancer Res. 8 (2010) 844–845. [50] L. Carrell, H.F. Willard, X-inactivation profile reveals extensive variability in X-linked gene expression in females, Nature 434 (2005) 400–404. [51] H. Van Esch, K. Hollanders, L. Badisco, C. Melotte, P. Van Hummelen, J.R. Vermeesch, K. Devriendt, J.-P. Fryns, P. Marynen, G. Froyen, Deletion of VCX-A due to NAHR plays a major role in the occurrence of mental retardation in patients with X-linked ichthyosis, Hum Mol Genet 14 (2005) 1795–1803. [52] K.I. Aston, D.T. Carrell, Genome-wide study of single-nucleotide polymorphisms associated with azoospermia and severe oligozoospermia, J. Androl. 30 (2009) 711–725. [53] T. Fukuyama, T. Hanagiri, M. Takenoyama, Y. Ichiki, M. Mizukami, T. So, M. Sugaya, T. So, K. Sugio, K. Yasumoto, Identification of a new cancer/germline gene, KK-LC-1, encoding an antigen recognized by autologous CTL induced on human lung adenocarcinoma, Cancer Res. 66 (2006) 4922–4928. [54] F. Tüttelmann, M. Simoni, S. Kliesch, S. Ledig, B. Dworniczak, P. Wieacker, A. Röpke, Copy number variants in patients with severe oligozoospermia and Sertoli-cell-only syndrome, PLoS One 6 (2009) e19426. [55] G. Tomiyoshi, A. Nakanishi, K. Takenaka, K. Yoshida, Y. Miki, Novel BRCA2-interacting protein BJ-HCC-20A inhibits the induction of apoptosis in response to DNA damage, Cancer Sci. 99 (2008) 747–754. [56] M.A. Matzke, J.A. Birchler, RNAi-mediated pathways in the nucleus, Nat. Rev. Genet. 6 (2005) 24–35. [57] M.D. Papaioannou, S. Nef, microRNAs in the testis: building up male fertility, J. Androl. 31 (2010) 264–272. [58] S. Ro, C. Park, K.M. Sanders, J.R. McCarrey, W. Yan, Cloning and expression profiling of testis-expressed microRNAs, Dev. Biol. 311 (2007) 592–602. [59] N. Yan, Y. Lu, H. Sun, D. Tao, S. Zhang, W. Liu, Y. Ma, A microarray for microRNA profiling in mouse testis tissues, Reproduction 134 (2007) 73–79. [60] R. Song, S. Ro, J.D. Michaels, C. Park, J.R. McCarrey, W. Yan, Many X-linked microRNAs escape meiotic sex chromosome inactivation, Nat. Genet. 41 (2009) 488–493. [61] X. Guo, B. Su, Z. Zhou, J. Sha, Rapid evolution of mammalian X-linked testis microRNAs, BMC Genomics 10 (2009) 97. [62] I. Bentwich, A. Avniel, Y. Karov, R. Aharonov, S. Gilad, O. Barad, A. Barzilai, P. Einat, U. Einav, E. Meiri, E. Sharon, Y. Spector, Z. Bentwich, Identification of hundreds of conserved and nonconserved human microRNAs, Nat. Genet. 37 (2005) 766–770. [63] R. Zhang, Y. Peng, W. Wang, B. Su, Rapid evolution of an X-linked microRNA cluster in primates, Genome Res. 17 (2007) 612–617. [64] H.M. Korhonen, O. Meikar, R.P. Yadav, M.D. Papaioannou, Y. Romero, M. Da Ros, P.L. Herrera, J. Toppari, S. Nef, N. Kotaja, Dicer is required for haploid male germ cell differentiation in mice, PLoS One 6 (9) (2011) e24821. [65] H.W. Heid, U. Figge, S. Winter, C. Kuhn, R. Zimbelmann, W.W. Franke, Novel actin-related proteins Arp-T1 and Arp-T2 as components of the cytoskeletal calyx of the mammalian sperm head, Exp. Cell Res. 279 (2002) 177–178.

1871

[66] C. Braybrook, G. Warry, G. Howell, V. Mandryko, A. Arnason, A. Bjornsson, M.T. Ross, G.E. Moore, P. Stanie, Physical and transcriptional mapping of the X-linked cleft palate and ankyloglossia (CPX) critical region, Hum. Genet. 108 (2001) 537–545. [67] B.J. Stevenson, C. Iseli, S. Panji, M. Zahn-Zabal, W. Hide, L.J. Old, A.J. Simpson, C.V. Jongeneel, Rapid evolution of cancer/testis genes on the X chromosome, BMC Genomics 8 (2007) 129. [68] A.M. Veith, J. Klattig, A. Dettai, C. Schmidt, C. Englert, J.N. Volff, Male-biased expression of X-chromosomal DM domain-less Dmrt8 genes in the mouse, Genomics 88 (2006) 185–195. [69] L.E. Fohn, R.R. Behringer, ESX1L, a novel X chromosome-linked human homeobox gene expressed in the placenta and testis, Genomics 74 (2001) 105–108. [70] O. Tureci, U. Sahin, M. Koslowski, B. Buss, C. Bell, P. Ballweber, C. Zwick, T. Eberle, M. Zuber, C. Villena-Heinsen, G. Seitz, M. Pfreundschuh, A novel tumour associated leucine zipper protein targeting to sites of gene transcription and splicing, Oncogene 21 (2002) 3879–3888. [71] K. Hidaka, J.J. Caffrey, L. Hua, T. Zhang, J.R. Falck, G.C. Nickel, L. Carrel, L.D. Barnes, S.B. Shears, An adjacent pair of human NUDT genes on chromosome X are preferentially expressed in testis and encode two new isoforms of diphosphoinositol polyphosphate phosphohydrolase, J. Biol. Chem. 277 (2002) 32730–32738. [72] N.R. Leslie, A.G. McLennan, S.T. Safrany, Cloning and characterisation of hAps1 and hAps2, human diadenosine polyphosphate-metabolising Nudix hydrolases, BMC Biochem. 3 (2002) 20. [73] L.V. Hua, K. Hidaka, X. Pesesse, L.D. Barnes, S.B. Shears, Paralogous murine Nudt10 and Nudt11 genes have differential expression patterns but encode identical proteins that are physiologically competent diphosphoinositol polyphosphate phosphohydrolases, Biochem. J. 373 (2003) 81–89. [74] P.D. Burbelo, C.A. Kozak, A.A. Finegold, A. Hall, D.M. Pirone, Cloning, central nervous system expression and chromosomal mapping of the mouse PAK-1 and PAK-3 genes, Gene 232 (1999) 209–215. [75] M. Kohn, P. Steinbach, H. Hameister, H. Kehrer-Sawatzki, A comparative expression analysis of four MRX genes regulating intracellular signalling via small GTPases, Eur. J. Hum. Genet. 12 (2004) 29–37. [76] C.M. Wayne, J.A. MacLean, G. Cornwall, M.F. Wilkinson, Two novel human X-linked homeobox genes, hPEPP1 and hPEPP2, selectively expressed in the testis, Gene 301 (2002) 1–11. [77] C. Geserick, B. Weiss, W.D. Schleuning, B. Haendler, OTEX, an androgen-regulated human member of the paired-like class of homeobox genes, Biochem. J. 366 (2002) 367–375. [78] P. Blanco-Arias, C.A. Sargent, N.A. Affara, The human-specific Yp11.2/Xq21.3 homology block encodes a potentially functional testis-specific TGIF-like retroposon, Mamm. Genome 13 (2002) 463–468. [79] J.F. Coy, S. Dubel, P. Kioschis, K. Thomas, G. Micklem, H. Delius, A. Poustka, Molecular cloning of tissue-specific transcripts of a transketolase-related gene: implications for the evolution of new vertebrate genes, Genomics 32 (1996) 309–316. [80] B. Cho, Y. Lim, D.Y. Lee, S.Y. Park, H. Lee, W.H. Kim, H. Yang, Y.J. Bang, D.I. Jeoung, Identification and characterization of a novel cancer/testis antigen gene CAGE, Biochem. Biophys. Res. Commun. 292 (2002) 715–726. [81] I. Zaganas, K. Kanavouras, V. Mastorodemos, H. Latsoudis, C. Spanaki, A. Plaitakis, The human GLUD2 glutamate dehydrogenase: localization and functional aspects, Neurochem. Int. 55 (2009) 52–63. [82] C. Spanaki, I. Zaganas, K.A. Kleopa, A. Plaitakis, Human GLUD2 glutamate dehydrogenase is expressed in neural and testicular supporting cells, J. Biol. Chem. 285 (2010) 16748–16756. [83] A. Plaitakis, H. Latsoudis, C. Spanaki, The human GLUD2 glutamate dehydrogenase and its regulation in health and disease, Neurochem. Int. 59 (2011) 459–509. [84] N.G. Robertson, R.J. Pomponio, G.L. Mutter, C.C. Morton, Testis-specific expression of the human MYCL2 gene, Nucleic Acids Res. 19 (1991) 3129–3137. [85] A.P. Liggins, P.J. Brown, K. Asker, K. Pulford, A.H. Banham, A novel diffuse large B-cell lymphoma-associated cancer testis antigen encoding a PAS domain protein, Br. J. Cancer 91 (2004) 141–149. [86] V. Martelange, C. De Smet, E. De Plaen, C. Lurquin, T. Boon, Identification on a human sarcoma of two new genes with tumor-specific expression, Cancer Res. 60 (2000) 3848–3855. [87] M.C. Simmler, D.B. Cunningham, P. Clerc, T. Vermat, B. Caudron, C. Cruaud, A. Pawlak, C. Szpirer, J. Weissenbach, J.M. Claverie, P. Avner, A 94 kb genomic sequence 3′ to the murine Xist gene reveals an AT rich region containing a new testis specific gene Tsx, Hum. Mol. Genet. 5 (1996) 1713–1726. [88] D.B. Cunningham, D. Segretain, D. Arnaud, U.C. Rogner, P. Avner, The mouse Tsx gene is expressed in Sertoli cells of the adult testis and transiently in premeiotic germ cells during puberty, Dev. Biol. 204 (1998) 345–360. [89] A. Loriot, T. Boon, C. De Smet, Five new human cancer-germline genes identified among 12 genes expressed in spermatogonia, Int. J. Cancer 105 (2003) 371–376. [90] T. Ishibashi, A. Li, J.M. Eirín-López, M. Zhao, K. Missiaen, D.W. Abbott, M. Meistrich, M.J. Hendzel, J. Ausió, H2A.Bbd: an X-chromosome-encoded histone involved in mammalian spermiogenesis, Nucleic Acids Res. 38 (2010) 1780–1789. [91] N. Tajeddine, J.L. Gala, M. Louis, M. Van Schoor, B. Tombal, P. Gailly, Tumor-associated antigen preferentially expressed antigen of melanoma (PRAME) induces caspase-independent cell death in vitro and reduces tumorigenicity in vivo, Cancer Res. 65 (2005) 7348–7355. [92] M. Salemi, A.E. Calogero, R. Castiglione, D. Tricoli, P. Asero, R. Rosa, G. Rappazzo, E. Vicari, Expression of SpanX proteins in normal testes and in testicular germ cell tumours, Int. J. Androl. 29 (2006) 368–373. [93] N. Kouprina, V.N. Noskov, A. Padvlicek, N.K. Collins, P.D. Schoppee Bortz, C. Ottolenghi, D. Loukinov, P. Goldsmith, J.I. Risinger, J.H. Kim, V.A. Westbrook, G. Solomon, H. Sounders, J.C. Herr, J. Jurka, V. Lobanenkov, D. Schlessinger, V.

1872

[94]

[95]

[96]

[97]

[98]

[99]

[100]

[101]

[102] [103]

[104]

[105]

[106]

[107] [108]

[109]

[110]

[111]

[112]

[113]

[114]

K. Stouffs, W. Lissens / Biochimica et Biophysica Acta 1822 (2012) 1864–1872 Larionov, Evolutionary diversification of SPANX-N sperm protein gene structure and expression, PLoS One 4 (2007) e359. Y.T. Chen, B. Alpen, T. Ono, A.O. Gure, M.A. Scanlan, W.H. Biggs III, K. Arden, E. Nakayama, L.J. Old, Identification and characterization of mouse SSX genes: a multigene family on the X chromosome with restricted cancer/testis expression, Genomics 82 (2003) 628–636. I. Sobek-Klocke, C. Disque-Kochem, M. Ronsiek, R. Klocke, H. Jockusch, A. Breuning, H. Ponstingl, K. Rojas, J. Overhauser, U. Eichenlaub-Ritter, The human gene ZFP161 on 18p11.21-pter encodes a putative c-myc repressor and is homologous to murine Zfp161 (chr 17) and Zfp161-rs1 (X chr), Genomics 43 (1997) 156–164. G.M. Greig, C.B. Sharp, L. Carrel, H.F. Willard, Duplicated zinc finger protein genes on the proximal short arm of the human X chromosome: isolation, characterization and X-inactivation studies, Hum. Mol. Genet. 2 (1993) 1611–1618. Y.T. Chen, M. Hsu, P. Lee, S.J. Shin, P. Mhawech-Fauceglia, K. Odunsi, N.K. Altorki, C.J. Song, B.Q. Jin, A.J. Simpson, L.J. Old, Cancer/testis antigen CT45: analysis of mRNA and protein expression in human cancer, Int. J. Cancer 124 (2009) 2893–2898. Y.T. Chen, M.J. Scanlan, C.A. Venditti, R. Chua, G. Theiler, B.J. Stevenson, C. Iseli, A.O. Gure, T. Vasicek, R.L. Strausberg, C.V. Jongeneel, L.J. Old, A.J. Simpson, Identification of cancer/testis-antigen genes by massively parallel signature sequencing, Proc. Natl. Acad. Sci. U. S. A. 102 (2005) 7940–7945. Y.T. Chen, C. Iseli, C.A. Venditti, L.J. Old, A.J. Simpson, C.V. Jongeneel, Identification of a new cancer/testis gene family, CT47, among expressed multicopy genes on the human X chromosome, Genes Chromosomes Cancer 45 (2006) 392–400. Y.T. Chen, A.D. Boyer, C.S. Viars, S. Tsang, L.J. Old, K.C. Arden, Genomic cloning and localization of CTAG, a gene encoding an autoimmunogenic cancer-testis antigen NY-ESO-1, to human chromosome Xq28, Cytogenet. Cell Genet. 79 (1997) 237–240. I. Martinez-Garay, S. Jablonka, M. Sutajova, P. Steuernagel, A. Gal, K. Kutsche, A new gene family (FAM9) of low-copy repeats in Xp22.3 expressed exclusively in testis: implications for recombinations in this region, Genomics 80 (2002) 259–267. B.T. Lahn, D.C. Page, A human sex-chromosomal gene family expressed in male germ cells and encoding variably charged proteins, Hum. Mol. Genet. 9 (2000) 311–319. M.W. Killen, T.L. Taylor, D.M. Stults, W. Jin, L.L. Wang, J.A. Moscow, A.J. Pierce, Configuration and rearrangement of the human GAGE gene clusters, Am. J. Transl. Res. 3 (2011) 234–242. S.W. Zou, J.C. Zhang, X.D. Zhang, S.Y. Miao, S.D. Zong, Q. Sheng, L.F. Wang, Expression and localization of VCX/Y proteins and their possible involvement in regulation of ribosome assembly during spermatogenesis, Cell Res. 13 (2003) 171–177. S. Sato, Y. Noguchi, N. Ohara, A. Uenaka, M. Shimono, K. Nakagawa, F. Koizumi, T. Ishida, T. Yoshino, Y. Shiratori, E. Nakayama, Identification of XAGE-1 isoforms: predominant expression of XAGE-1b in testis and tumors, Cancer Immun. 7 (2007) 5. M.A. Hansen, J.E. Nielsen, M. Tanaka, K. Almstrup, N.E. Skakkebaek, H. Leffers, Identification and expression profiling of 10 novel spermatid expressed CYPT genes, Mol. Reprod. Dev. 73 (2006) 568–579. S.M. Kerr, M.H. Taggart, M. Lee, H.J. Cooke, Ott, a mouse X-linked multigene family expressed specifically during meiosis, Hum. Mol. Genet. 5 (1996) 1139–1148. A. Calenda, B. Allenet, D. Escalier, J.F. Bach, H.J. Garchon, The meiosis-specific Xmr gene product is homologous to the lymphocyte Xlr protein and is a component of the XY body, EMBO J. 13 (1994) 100–109. L.N. Reynard, J.M. Turner, J. Cocquet, S.K. Mahadevaiah, A. Touré, C. Höög, P.S. Burgoyne, Expression analysis of the mouse multi-copy X-linked gene Xlr-related, meiosis-regulated (Xmr), reveals that Xmr encodes a spermatidexpressed cytoplasmic protein, SLX/XMR, Biol. Reprod. 77 (2007) 329–335. G.L. Christensen, J. Griffin, D.T. Carrell, Sequence analysis of the X-linked USP26 gene in severe male factor infertility patients and fertile controls, Fertil. Steril. 90 (2008) 851–852. I.W. Lee, L.C. Kuan, C.H. Lin, H.A. Pan, C.C. Hsu, Y.C. Tsai, P.L. Kuo, Y.N. Teng, Association of USP26 haplotypes in men in Taiwan, China with severe spermatogenic defect, Asian J. Androl. 10 (2008) 896–904. D.A. Paduch, A. Mielnik, P.N. Schlegel, Novel mutations in testis-specific ubiquitin protease 26 gene may cause male infertility and hypogonadism, Reprod. Biomed. Online 10 (2005) 747–754. Y.C. Shi, L. Wei, Y.X. Cui, X.J. Shang, H.Y. Wang, X.Y. Xia, Y.C. Zhou, H. Li, H.T. Jiang, W.M. Zhu, Y.F. Huang, Association between ubiquitin-specific protease USP26 polymorphism and male infertility in Chinese men, Clin. Chim. Acta 412 (2011) 545–549. J. Zhang, S.D. Qiu, S.B. Li, D.X. Zhou, H. Tian, Y.W. Huo, L. Ge, Q.Y. Zhang, Novel mutations in ubiquitin-specific protease 26 gene might cause spermatogenesis impairment and male infertility, Asian J. Androl. 9 (2007) 809–814.

[115] I. Ribarski, O. Lehavi, L. Yogev, R. Hauser, B. Bar-Shira Maymon, A. Botchan, G. Paz, H. Yavetz, S.E. Kleiman, USP26 gene variations in fertile and infertile men, Hum. Reprod. 24 (2009) 477–484. [116] Y. Nakahori, O. Takenaka, Y. Nakagome, A human X–Y homologous region encodes ‘amelogenin’, Genomics 9 (1991) 264–269. [117] B.T. Lahn, D.C. Page, Functional coherence of the human Y chromosome, Science 278 (1997) 675–680. [118] S.H. Park, S.-G. Lee, Y. Kim, K. Song, Assignment of a human putative RNA helicase gene, DDX3, to human X chromosome bands p 11.3–p11.23, Cytogenet. Cell Genet. 81 (1998) 178–179. [119] Q.P. Vong, Y. Li, Y.F. Lau, M. Dym, O.M. Rennert, W.Y. Chan, Structural characterization and expression studies of Dby and its homologs in the mouse, J. Androl. 27 (2006) 653–661. [120] T.V. Pestova, V.G. Kolupaeva, I.B. Lomakin, E.V. Pilipenko, I.N. Shatsky, V.I. Agol, C.U. Hellen, Molecular mechanisms of translation initiation in eukaryotes, Proc. Natl. Acad. Sci. U. S. A. 98 (2001) 7029–7036. [121] L. Carrel, P.A. Hunt, H.F. Willard, Tissue and lineage-specific variation in inactive X chromosome expression of the murine Smcx gene, Hum. Mol. Genet. 5 (1996) 1361–1366. [122] A. Greenfield, L. Carrel, D. Pennisi, C. Philippe, N. Quaderi, P. Siggers, K. Steiner, P.P. Tam, A.P. Monaco, H.F. Willard, P. Koopman, The UTX gene escapes X inactivation in mice and humans, Hum. Mol. Genet. 7 (1998) 737–742. [123] T. Nagase, K. Ishikawa, R. Kikuno, M. Hirosawa, N. Nomura, O. Ohara, Prediction of the coding sequences of unidentified human genes. XV. The complete sequences of 100 new cDNA clones from brain which code for large proteins in vitro, DNA Res. 6 (1999) 337–345. [124] M.F. Bolliger, K. Frei, K.H. Winterhalter, S.M. Gloor, Identification of a novel neuroligin in humans which binds to PSD-95 and has a widespread expression, Biochem. J. 356 (2001) 581–588. [125] P. Blanco, C.A. Sargent, C.A. Boucher, M. Mitchell, N.A. Affara, Conservation of PCDHX in mammals; expression of X/Y genes predominantly in brain, Mamm. Genome 11 (2000) 906–914. [126] X. Li, H.-P. Li, K. Amsler, D. Hyink, P.D. Wilson, C.R. Burrow, PRKX, a phylogenetically and functionally distinct cAMP-dependent protein kinase, activates renal epithelial cell migration and morphogenesis, Proc. Natl. Acad. Sci. 99 (2002) 9260–9265. [127] P.A. Lingenfelter, M.L. Delbridge, S. Thomas, H.E. Hoekstra, M.J. Mitchell, J.A. Graves, C.M. Disteche, Expression and conservation of processed copies of the RBMX gene, Mamm. Genome 12 (2001) 538–545. [128] E.M. Fisher, P. Beer-Romero, L.G. Brown, A. Ridley, J.A. McNeil, J.B. Lawrence, H.F. Willard, F.R. Bieber, D.C. Page, Homologous ribosomal protein genes on the human X and Y chromosomes: escape from X inactivation and possible implications for Turner syndrome, Cell 63 (1990) 1205–1218. [129] M. Stevanovic, R. Lovell-Badge, J. Collignon, P.N. Goodfellow, SOX3 is an X-linked gene related to SRY, Hum. Mol. Genet. 2 (1993) 2013–2018. [130] C.M. Disteche, M.B. Dinulos, M.T. Bassi, R.W. Elliott, E.I. Rugarli, Mapping of the murine Tbl1 gene reveals a new rearrangement between mouse and human X chromosomes, Mamm. Genome 9 (1998) 1062–1064. [131] V. Perissi, C. Scafoglio, J. Zhang, K.A. Ohgi, D.W. Rose, C.K. Glass, M.G. Rosenfeld, TBL1 and TBLR1 phosphorylation on regulated gene promoters overcomes dual CtBP and NCoR/SMRT transcriptional repression checkpoints, Mol. Cell 29 (2008) 755–766. [132] S.P. Yang, H.J. Lee, Y. Su, Molecular cloning and structural characterization of the functional human thymosin beta4 gene, Mol. Cell. Biochem. 272 (2005) 97–105. [133] Z. Chai, B. Sarcevic, A. Mawson, B.-H. Toh, SET-related cell division autoantigen-1 (CDA1) arrests cell growth, J. Biol. Chem. 276 (2001) 33665–33674. [134] L.L. Ozbun, L. You, S. Kiang, J. Angdisen, A. Martinez, S.B. Jakowlew, Identification of differentially expressed nucleolar TGF-beta-1 target (DENTT) in human lung cancer cells that is a new member of the TSPY/SET/NAP-1 superfamily, Genomics 73 (2001) 179–193. [135] S. Nogami, S. Satoh, S. Tanaka-Nakadate, K. Yoshida, M. Nakano, A. Terano, H. Shirataki, Identification and characterization of taxilin isoforms, Biochem. Biophys. Res. Commun. 319 (2004) 936–943. [136] M.H. Jones, R.A. Furlong, H. Burkin, I.J. Chalmers, G.M. Brown, O. Khwaja, N.A. Affara, The Drosophila developmental gene fat facets has a human homologue in Xp11.4 which escapes X-inactivation and has related sequences on Yq11.2, Hum. Mol. Genet. 5 (1996) 1695–1701. [137] M.S. Palmer, P. Berta, A.H. Sinclair, B. Pym, P.N. Goodfellow, Comparison of human ZFY and ZFX transcripts, Proc. Natl. Acad. Sci. 87 (1990) 1681–1685.