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A novel type of gene interaction in D. melanogaster
Mutation Research 795 (2017) 27–30
Contents lists available at ScienceDirect
Mutation Research/Genome instability and disease journal homepage: www.elsevier.com/locate/molmut Community address: www.elsevier.com/locate/mutres
A novel type of gene interaction in D. melanogaster B.F. Chadov ∗ , E.V. Chadova, N.B. Fedorova Institute of Cytology and Genetics, Siberian Department of Russian Academy of Sciences, Novosibirsk 630090, Russian Federation
a r t i c l e
i n f o
Article history: Received 7 September 2016 Received in revised form 19 November 2016 Accepted 4 January 2017 Available online 11 January 2017 Keywords: Drosophila Conditional mutations Gene interaction Parental effect
a b s t r a c t The genes interact according to classical mechanisms, namely, complementation, modification, polymery, and epistasis, in the cells and organisms carrying these genes. Here we describe a novel type of gene interaction when the interacting genes reside in parents, whereas the interaction event takes place in their progenies lacking these genes. The conditional mutations in the D. melanogaster male X chromosome caused the “prohibition on producing daughters” in its offspring. The chromosomal rearrangements in chromosomes 2 and 3 of its female partner removed the prohibition. The phenomena of “prohibition” and “removal of prohibition” appeared as a parental effect in both the male and female. Both phenomena ensued from the presence of the studied mutations in parents rather than their unviable or survived progenies. Thus, the gene interaction when the genes themselves are absent at the site of interaction and during the interaction event takes place in drosophila. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Following G. Mendel, the modern genetic theory regards the genes as independent hereditary factors. However, genes occasionally interact via (1) complementation, (2) modification, (3) polymery, and (4) epistasis. It is believed that the gene products do interact in these cases rather than the genes themselves. This interpretation allows the principle of independent genetic units to be reconciled with the existence of interaction. Characteristic of the gene interaction in a classical variant is the presence of effect in a cell or an organism carrying the corresponding genes. As a rule, this fact is left unnoted since a basic principle of the classical genetics is the integrity of gene and its trait. The edifice of genetics rests and is further constructed on this foundation. As has emerged, the interaction of genes in their “presence” is only one of the variants of their interaction. It is possible that the genes are able to interact in the case when they are absent at the moment of interaction event and at in the site of interaction. The research into a novel class of mutations in the drosophila referred to as conditional mutations [1] has demonstrated the existence of the interaction that fundamentally differs from the classical variant. The genes interacted in the body of a progeny lacking the genes that were the subject of interaction, while the parents
∗ Corresponding author at: Detskij Proezd Str. 9, App. 5, Novosibirsk 630090, Russian Federation. E-mail addresses: boris [email protected], [email protected] (B.F. Chadov). http://dx.doi.org/10.1016/j.mrfmmm.2017.01.002 0027-5107/© 2017 Elsevier B.V. All rights reserved.
of these progenies carried the corresponding genes. Find below the description of three experiments that demonstrate this new type of interaction. 2. Materials and methods The conditional mutations in the D. melanogaster X chromosome were produced earlier using a special technique for selecting mutants [2,3]. Males of wild phenotype (+) were gamma-irradiated and crossed with the attached − X females. Sons of the parents were individually crossed to yellow females. Sons that gave no female progeny from this cross were chosen as mutants. These sons contained the conditional mutation in the X chromosome. The mutation did not affect their viability. However, once in the female yellow/+ genome, it became a dominant lethal: daughters died at the embryonic stage, and the adult progeny was composed of sons only. In this exemplary case, the conditional mutation is a dominant lethal. It is called conditional because manifest as lethal in mutant females heterozygous for yellow (restrictive genotype) and not in mutant males (+) of normal phenotype (permissive genotype) [1,4]. The conditional mutations are maintained in the last genotype as laboratory cultures. The restrictive genotype is the daughter genotype y/+ produced by crossing a mutant male (+) to yellow females. The y/+ daughters die at the stage of embryo [5] (“prohibition on producing adult daughters in the progeny”). In the first experiment, the (+) males of 21 mutant strains (nos. 1–38) were repeatedly examined for the absence of daughters in their progenies as well as assessed for the male fertility. The ratio
28
B.F. Chadov et al. / Mutation Research 795 (2017) 27–30
Table 1 The progeny and fertility of the mutant males (+) in crosses with yellow females. Male strain
1 2 3 4 5 6 7 9 10 27 29 30 31 32 33 34 26 35 36 37 38
Cross: 2♀y × ♂+
Cross: 6♀ y × ♂+
Male fertility
Total number of progenies
Share of daughters
Total number of progenies
Share of daughters
119 650 112 114 50 47 47 182 162 68 15 122 106 81 144 88 92 102 95 52 54
0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.07 0.03 0.00 0.07 0.00 0.00 0.00 0.00 0.00 0.03 0.03 0.00 0.02 0.06
191 435 180 293 303 283 100 529 297 93 61 115 83 117 90 110 89 115 110 68 84
0.00 0.00 0.00 0.00 0.02 0.02 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.04 0.01 0.04 0.01
of the number of adult progenies that emerged from the eggs laid by yellow females to the number of laid eggs was determined. The sample comprised 500–700 eggs. In the second experiment, the effect of inverted chromosomes 2 and 3 in the maternal yellow genome on the “prohibition of daughters” phenomenon was studied. The inversions In(2LR)CyO, In(2LR)Pm, and In(3LR)D/Sb were used [6]. In this experiment, the mutant (+) males of 11 strains (nos. 1–34) carrying conditional mutations in the X chromosome were crossed to four genotypes of yellow females, namely, y/y; + / + ; + / + ;
(1)
y/y; In(2LR)CyO/ + ; + / + ;
(2)
y/y; In(2LR)Pm/ + ; + / + ; and
(3)
y/y; + / + ;In(3LR)D/ + .
(4)
The females of these genotypes were produced so that the differences between the genomes (1–4) would be minimal and involved only the chromosome carrying rearrangements. For this purpose, the yellow females y/y; +/+; +/+, earlier used to test the conditional mutations in chromosome X, were crossed with the In(2LR)Pm/In(2LR)CyO; In(3LR)D/Sb males. The males y; In(2LR)Pm/+; In(3LR)D/+ and y; In(2LR) CyO/+; In(3LR)D/+ were again crossed to the females of the initial strain y/y; +/+; +/+. The progeny of this cross contained yellow females of all target genotypes. The females differed only by the rearranged chromosomes. Females (1) were identical to the female that had been used for selecting the mutants; females (2) differed from the latter by the presence of CyO inverted chromosome 2; females (3) by the presence of Pm inverted chromosome 2; and so on. The third experiment examined the effect of In(2LR)CyO, also present in mutant males. Yellow females were crossed with males of ten strains (nos. 2–36) carrying conditional mutations and In(2LR)CyO as well as with their brothers that lacked the inversion in question (control) [7]. 3. Results and discussion The cross to yellow females is the key stage in isolation of conditional mutations in the X chromosome [2,3]. Repeated crossing to yellow females (Table 1) involved the males of mutant cultures. It
0.02 0.15 0.12 0.07 0.14 0.14 – 0.40 0.09 0.18 0.14 0.19 0.15 0.13 0.16 0.12 – 0.35 0.14 0.14 0.10
is evident that the crossing results are well reproducible. Although a mutation in the permissive genotype allows the males to survive and give progeny, such males still cannot be regarded as normal. The fertility of mutant males is drastically decreased with some minor exceptions. Theoretically, a complete absence of daughters in the progeny should mean a 50% decrease in male fertility. The fertility of mutant males was even lower. This suggests the death of not only the y/+ daughters, but also part of y sons. The latter die despite that they do not receive the X chromosome (which is mutant in this case) from their father. Thus, the mutation carried by the father is the cause of lethality for part of the progenies; however, the death of a progeny is not directly associated with inheritance of the mutant chromosome (parental inheritance). The death of a progeny is the result of the fact that the mutation was present in the parent rather than in the progeny itself. A drastic decrease in the fertility of a mutant male following a parental type means that the absence of y/+ daughters, which allows for isolation of conditional mutations, represents only part of the larger scale lethality, also covering other classes of progeny. The fact that the lethality in a progeny is induced without passing the mutant chromosome to it means that (1) the gene responsible for induction of lethality is active in the male germline cells and (2) the lethal effect of mutation is passed to the zygote (3) with the delivered chromosome set of the sperm cell; however, (4) this is not associated with passing of the mutant gene itself. The chromosome rearrangements from the maternal side removed the “prohibition on daughters” (Table 2). This prohibition was removed to different degrees depending on the type of inversion in the mother and the mutation carried by the father. Quite expectable, the yellow mothers without rearrangements (control) gave no daughters. Daughters were most abundant in the mothers carrying a Cy inversion, somewhat fewer in the mothers with a Pm inversion, and even fewer in the case of a D inversion. The removal of the “prohibition on daughters” also followed a parental type, maternal one in this case. Although a rearrangement in a yellow mother resulted in appearance of daughters, this was not associated with receiving of the rearranged chromosome from the mother. The emerged daughters were not only Cy, but also Cy +; not only Pm, but also Pm+; and so on. The above briefed conclusions on the induction of the “prohibition on daughters” trait is applicable to the liquidation of this trait
B.F. Chadov et al. / Mutation Research 795 (2017) 27–30
29
Table 2 Suppression of “prohibition on daughters” effect of conditional mutations by rearrangements in chromosomes 2 and 3. Male mutant strain
Female y/y; +/+ Daughter +
1 2 4 5 27 29 30 31 32 33 34
– – – – 2 4 – – – – –
Female y/y; +/Cy Son y
230 230 270 197 167 163 184 242 197 209 140
Daughter +
Female y/y; + /Pm Son y
Female y/y; +/D Son y
Daughter +
Daughter + +
Son y
Cy+
Cy
Cy+
Cy
Pm+
Pm
Pm+
Pm
D
D
D+
D
– 14 9 23 1 32 15 32 22 20 11
– 13 4 21 0 27 13 20 10 18 14
178 127 185 80 102 71 81 127 90 95 88
163 134 159 95 113 56 76 102 77 101 101
– 4 1 6 2 26 9 5 9 11 25
– 3 7 4 1 24 12 4 17 8 20
107 70 86 47 53 55 60 28 36 87 68
57 72 81 48 65 20 47 29 32 47 54
– – – – – 6 – – – 24 –
– – – – – 6 – – – 2 10
115 42 162 37 9 88 38 70 48 85 103
8 7 7 3 2 10 6 6 2 12 3
Table 3 The lack of influence of the Cy inversion in the mutant male (+) on “prohibition” effect. Male mutant strain
Phenotypes of progeny Cross: ♀ y x ♂+ (control)
2 4 5 26 30 31 32 33 34 36
Cross: ♀ y x ♂ +; Cy
♀+
♂y
♀+
♂y
– – – – – – – – – –
59 125 95 56 77 114 55 66 41 89
– 1 – – – – – – – –
14 137 144 43 49 137 82 54 14 140
as a result of chromosome rearrangements: (1) the gene responsible for the removal of daughter lethality is active in the (female) germline cells and (2) the lethal effect of mutation is passed to the zygote (3) with the delivered chromosome set of the oocyte; however, (4) this is not associated with passing of the mutant gene itself. The data on the interaction between conditional mutations and chromosome rearrangements give the pattern of interaction that is different from a classical one. The classical pattern implies that the interaction takes place in the presence of the interacting genes versus the described situation, when these genes are absent. The former can be referred to as a short-range effect and the latter, as a long-range effect. In the second case, the genes providing the effect in question function in the germline cells of the parents. The changes caused by the genes involved in this effect are passed to the zygote together with the chromosome sets rather than the genes themselves. The interaction event takes place in the zygote when the maternal and paternal sets meet. Formally, this can be referred to as an epigenetic interaction if it were not for the fact that we speak about the genetic events of a classical type caused by damages (mutations) of the DNA material. Some of them (conditional mutations) bring about the “prohibition on daughters” and the other (chromosome rearrangements) remove this prohibition. Both mutations (conditional mutation and Cy inversion) in the mutant males carrying this inversion (Table 3) reside in the same genome. This is the case when the mutations could apparently interact in the most efficient manner. However, the interaction is absent: the males ♂ +; Cy have no daughters as well as their brothers, ♂+; Cy+ , lacking the inversion. Classical genetics has an example of inheritance of the traits without inheriting genes, referred to as maternal effect [8]. This
type of inheritance is explainable with the RNA templates passed to the progeny with the egg cell cytoplasm. However, this explanation does not work in our case. The parental effect of conditional mutations appears in male, which excludes any possibility to pass a gene effect via the cytoplasm. The absence of interaction between a conditional mutation and the In(2LR)CyO inversion present in the same genome (Table 3) is even more eloquent. There is no interaction at all despite the conditions providing implementation of the interaction at any of the possible levels (DNA, RNA, and protein) and at any developmental stage (embryonic tissue and soma): the structural mutation, Cy, fails to manifest itself as a suppressor of “prohibition on daughters”. It is clear that the long-range effect is unexplainable with the fact that RNA templates or proteins merely enter the zygote, even if this really takes place. 3.1. The mechanism of the long-range effect The obtained data demonstrating (1) the effect of conditional mutations as a “prohibition on daughters”, (2) removal of the effect by chromosome rearrangements when a rearrangement and a conditional mutation are carried by different parents, and (3) the absence of the effect of chromosome rearrangements when the rearrangement and conditional mutation reside in the same parent (Table 3) suggest that emergence of the long-range effect requires that two differently changed parental chromosome sets meet in the zygote. We assume that one chromosome set with the genome advance along the germline is altered because of the presence of a conditional mutation and the other, because of the presence of a rearrangement. These changes are of an epigenetic nature and affect the overall genome. It is not necessary that the mutations that induced the epigenetic changes are present in the zygote.
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B.F. Chadov et al. / Mutation Research 795 (2017) 27–30
This novel type of interaction between genes is a remarkable but not the only characteristic of the genes responsible for conditional mutations. Our review [1] comprehensively describes the overall set of unusual features of the mutants for these genes. It is assumed [5,9] that the studied genes follow a DNA–short RNA scheme rather than a DNA–mRNA–protein pattern, characteristic of the Mendelian genes. As is mentioned above, the long-range gene interaction takes place when two genomes meet in the zygote. This meeting has two outcomes depending on the specificities of these genomes, namely, implementation of development or its cessation (dominant lethality). In essence, this is the conditionality appearing in the name of such mutations. The “encounter” of genomes accompanies every event of fertilization. That is why the insight into the mechanism underlying “the mutual recognition of parental developmental programs”, which is the particular event marking the start of a newly formed diploid genome, is of the paramount importance. References [1] B.F. Chadov, N.B. Fedorova, E.V. Chadova, Conditional mutations in Drosophila melanogaster: On the Occasion of the 150th Anniversary of G. Mendel’s Report in Brünn, Mutat. Res./Rev. Mutat. Res. 765 (2015) 40–55, http://dx.doi.org/10. 1016/j.mrrev.2015.06.001.
[2] B.F. Chadov, E.V. Chadova, S.A. Kopyl, N.B. Fedorova, 2000 A new class of mutations in Drosophila melanogaster, Dokl. Biol. Sci. 373 (2000) 423–426. [3] B.F. Chadov, Mutations in the regulatory genes in Drosophila melanogaster, in: Proc. Intern. Conf. Biodiversity and Dynamics of Ecosystems in North Eurasia, IC@G, Novosibirsk, Russia, 2000, pp. 16–18. [4] B.F. Chadov, N.B. Fedorova, E.V. Chadova, E.A. Khotskina, Conditional mutations in Drosophila, J. Life Sci. 5 (2011) 224–240. [5] B.F. Chadov, N.B. Fedorova, E.V. Chadova, Conditional Mutations in Drosophila melanogaster, 2016, http://dx.doi.org/10.13140/RG.2.1.2585.5606. [6] D.L. Lindsley, E.H. Grell, Genetic Variations of Drosophila melanogaster, Carnegie Inst., Washington, 1967 (Publ. no. 627). [7] B.F. Chadov, Mutations capable of inducing speciation Evolution Biology, Vol. 1, Tomsk State University Press, 2001, pp. 138–162 (In Russian) http://www. evolbiol.ru/. [8] R. Sager, Cytoplasmic Genes and Organelles, Elsevier, 1972. [9] N.B. Fedorova, E.V. Chadova, B.F. Chadov, Genes and Ontogenes in Drosophila: The Role of RNA Forms // Transcriptomics 4, 2016, pp. 137, http://dx.doi.org/ 10.4172/2329-8936.1000137.
Contents lists available at ScienceDirect
Mutation Research/Genome instability and disease journal homepage: www.elsevier.com/locate/molmut Community address: www.elsevier.com/locate/mutres
A novel type of gene interaction in D. melanogaster B.F. Chadov ∗ , E.V. Chadova, N.B. Fedorova Institute of Cytology and Genetics, Siberian Department of Russian Academy of Sciences, Novosibirsk 630090, Russian Federation
a r t i c l e
i n f o
Article history: Received 7 September 2016 Received in revised form 19 November 2016 Accepted 4 January 2017 Available online 11 January 2017 Keywords: Drosophila Conditional mutations Gene interaction Parental effect
a b s t r a c t The genes interact according to classical mechanisms, namely, complementation, modification, polymery, and epistasis, in the cells and organisms carrying these genes. Here we describe a novel type of gene interaction when the interacting genes reside in parents, whereas the interaction event takes place in their progenies lacking these genes. The conditional mutations in the D. melanogaster male X chromosome caused the “prohibition on producing daughters” in its offspring. The chromosomal rearrangements in chromosomes 2 and 3 of its female partner removed the prohibition. The phenomena of “prohibition” and “removal of prohibition” appeared as a parental effect in both the male and female. Both phenomena ensued from the presence of the studied mutations in parents rather than their unviable or survived progenies. Thus, the gene interaction when the genes themselves are absent at the site of interaction and during the interaction event takes place in drosophila. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Following G. Mendel, the modern genetic theory regards the genes as independent hereditary factors. However, genes occasionally interact via (1) complementation, (2) modification, (3) polymery, and (4) epistasis. It is believed that the gene products do interact in these cases rather than the genes themselves. This interpretation allows the principle of independent genetic units to be reconciled with the existence of interaction. Characteristic of the gene interaction in a classical variant is the presence of effect in a cell or an organism carrying the corresponding genes. As a rule, this fact is left unnoted since a basic principle of the classical genetics is the integrity of gene and its trait. The edifice of genetics rests and is further constructed on this foundation. As has emerged, the interaction of genes in their “presence” is only one of the variants of their interaction. It is possible that the genes are able to interact in the case when they are absent at the moment of interaction event and at in the site of interaction. The research into a novel class of mutations in the drosophila referred to as conditional mutations [1] has demonstrated the existence of the interaction that fundamentally differs from the classical variant. The genes interacted in the body of a progeny lacking the genes that were the subject of interaction, while the parents
∗ Corresponding author at: Detskij Proezd Str. 9, App. 5, Novosibirsk 630090, Russian Federation. E-mail addresses: boris [email protected], [email protected] (B.F. Chadov). http://dx.doi.org/10.1016/j.mrfmmm.2017.01.002 0027-5107/© 2017 Elsevier B.V. All rights reserved.
of these progenies carried the corresponding genes. Find below the description of three experiments that demonstrate this new type of interaction. 2. Materials and methods The conditional mutations in the D. melanogaster X chromosome were produced earlier using a special technique for selecting mutants [2,3]. Males of wild phenotype (+) were gamma-irradiated and crossed with the attached − X females. Sons of the parents were individually crossed to yellow females. Sons that gave no female progeny from this cross were chosen as mutants. These sons contained the conditional mutation in the X chromosome. The mutation did not affect their viability. However, once in the female yellow/+ genome, it became a dominant lethal: daughters died at the embryonic stage, and the adult progeny was composed of sons only. In this exemplary case, the conditional mutation is a dominant lethal. It is called conditional because manifest as lethal in mutant females heterozygous for yellow (restrictive genotype) and not in mutant males (+) of normal phenotype (permissive genotype) [1,4]. The conditional mutations are maintained in the last genotype as laboratory cultures. The restrictive genotype is the daughter genotype y/+ produced by crossing a mutant male (+) to yellow females. The y/+ daughters die at the stage of embryo [5] (“prohibition on producing adult daughters in the progeny”). In the first experiment, the (+) males of 21 mutant strains (nos. 1–38) were repeatedly examined for the absence of daughters in their progenies as well as assessed for the male fertility. The ratio
28
B.F. Chadov et al. / Mutation Research 795 (2017) 27–30
Table 1 The progeny and fertility of the mutant males (+) in crosses with yellow females. Male strain
1 2 3 4 5 6 7 9 10 27 29 30 31 32 33 34 26 35 36 37 38
Cross: 2♀y × ♂+
Cross: 6♀ y × ♂+
Male fertility
Total number of progenies
Share of daughters
Total number of progenies
Share of daughters
119 650 112 114 50 47 47 182 162 68 15 122 106 81 144 88 92 102 95 52 54
0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.07 0.03 0.00 0.07 0.00 0.00 0.00 0.00 0.00 0.03 0.03 0.00 0.02 0.06
191 435 180 293 303 283 100 529 297 93 61 115 83 117 90 110 89 115 110 68 84
0.00 0.00 0.00 0.00 0.02 0.02 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.04 0.01 0.04 0.01
of the number of adult progenies that emerged from the eggs laid by yellow females to the number of laid eggs was determined. The sample comprised 500–700 eggs. In the second experiment, the effect of inverted chromosomes 2 and 3 in the maternal yellow genome on the “prohibition of daughters” phenomenon was studied. The inversions In(2LR)CyO, In(2LR)Pm, and In(3LR)D/Sb were used [6]. In this experiment, the mutant (+) males of 11 strains (nos. 1–34) carrying conditional mutations in the X chromosome were crossed to four genotypes of yellow females, namely, y/y; + / + ; + / + ;
(1)
y/y; In(2LR)CyO/ + ; + / + ;
(2)
y/y; In(2LR)Pm/ + ; + / + ; and
(3)
y/y; + / + ;In(3LR)D/ + .
(4)
The females of these genotypes were produced so that the differences between the genomes (1–4) would be minimal and involved only the chromosome carrying rearrangements. For this purpose, the yellow females y/y; +/+; +/+, earlier used to test the conditional mutations in chromosome X, were crossed with the In(2LR)Pm/In(2LR)CyO; In(3LR)D/Sb males. The males y; In(2LR)Pm/+; In(3LR)D/+ and y; In(2LR) CyO/+; In(3LR)D/+ were again crossed to the females of the initial strain y/y; +/+; +/+. The progeny of this cross contained yellow females of all target genotypes. The females differed only by the rearranged chromosomes. Females (1) were identical to the female that had been used for selecting the mutants; females (2) differed from the latter by the presence of CyO inverted chromosome 2; females (3) by the presence of Pm inverted chromosome 2; and so on. The third experiment examined the effect of In(2LR)CyO, also present in mutant males. Yellow females were crossed with males of ten strains (nos. 2–36) carrying conditional mutations and In(2LR)CyO as well as with their brothers that lacked the inversion in question (control) [7]. 3. Results and discussion The cross to yellow females is the key stage in isolation of conditional mutations in the X chromosome [2,3]. Repeated crossing to yellow females (Table 1) involved the males of mutant cultures. It
0.02 0.15 0.12 0.07 0.14 0.14 – 0.40 0.09 0.18 0.14 0.19 0.15 0.13 0.16 0.12 – 0.35 0.14 0.14 0.10
is evident that the crossing results are well reproducible. Although a mutation in the permissive genotype allows the males to survive and give progeny, such males still cannot be regarded as normal. The fertility of mutant males is drastically decreased with some minor exceptions. Theoretically, a complete absence of daughters in the progeny should mean a 50% decrease in male fertility. The fertility of mutant males was even lower. This suggests the death of not only the y/+ daughters, but also part of y sons. The latter die despite that they do not receive the X chromosome (which is mutant in this case) from their father. Thus, the mutation carried by the father is the cause of lethality for part of the progenies; however, the death of a progeny is not directly associated with inheritance of the mutant chromosome (parental inheritance). The death of a progeny is the result of the fact that the mutation was present in the parent rather than in the progeny itself. A drastic decrease in the fertility of a mutant male following a parental type means that the absence of y/+ daughters, which allows for isolation of conditional mutations, represents only part of the larger scale lethality, also covering other classes of progeny. The fact that the lethality in a progeny is induced without passing the mutant chromosome to it means that (1) the gene responsible for induction of lethality is active in the male germline cells and (2) the lethal effect of mutation is passed to the zygote (3) with the delivered chromosome set of the sperm cell; however, (4) this is not associated with passing of the mutant gene itself. The chromosome rearrangements from the maternal side removed the “prohibition on daughters” (Table 2). This prohibition was removed to different degrees depending on the type of inversion in the mother and the mutation carried by the father. Quite expectable, the yellow mothers without rearrangements (control) gave no daughters. Daughters were most abundant in the mothers carrying a Cy inversion, somewhat fewer in the mothers with a Pm inversion, and even fewer in the case of a D inversion. The removal of the “prohibition on daughters” also followed a parental type, maternal one in this case. Although a rearrangement in a yellow mother resulted in appearance of daughters, this was not associated with receiving of the rearranged chromosome from the mother. The emerged daughters were not only Cy, but also Cy +; not only Pm, but also Pm+; and so on. The above briefed conclusions on the induction of the “prohibition on daughters” trait is applicable to the liquidation of this trait
B.F. Chadov et al. / Mutation Research 795 (2017) 27–30
29
Table 2 Suppression of “prohibition on daughters” effect of conditional mutations by rearrangements in chromosomes 2 and 3. Male mutant strain
Female y/y; +/+ Daughter +
1 2 4 5 27 29 30 31 32 33 34
– – – – 2 4 – – – – –
Female y/y; +/Cy Son y
230 230 270 197 167 163 184 242 197 209 140
Daughter +
Female y/y; + /Pm Son y
Female y/y; +/D Son y
Daughter +
Daughter + +
Son y
Cy+
Cy
Cy+
Cy
Pm+
Pm
Pm+
Pm
D
D
D+
D
– 14 9 23 1 32 15 32 22 20 11
– 13 4 21 0 27 13 20 10 18 14
178 127 185 80 102 71 81 127 90 95 88
163 134 159 95 113 56 76 102 77 101 101
– 4 1 6 2 26 9 5 9 11 25
– 3 7 4 1 24 12 4 17 8 20
107 70 86 47 53 55 60 28 36 87 68
57 72 81 48 65 20 47 29 32 47 54
– – – – – 6 – – – 24 –
– – – – – 6 – – – 2 10
115 42 162 37 9 88 38 70 48 85 103
8 7 7 3 2 10 6 6 2 12 3
Table 3 The lack of influence of the Cy inversion in the mutant male (+) on “prohibition” effect. Male mutant strain
Phenotypes of progeny Cross: ♀ y x ♂+ (control)
2 4 5 26 30 31 32 33 34 36
Cross: ♀ y x ♂ +; Cy
♀+
♂y
♀+
♂y
– – – – – – – – – –
59 125 95 56 77 114 55 66 41 89
– 1 – – – – – – – –
14 137 144 43 49 137 82 54 14 140
as a result of chromosome rearrangements: (1) the gene responsible for the removal of daughter lethality is active in the (female) germline cells and (2) the lethal effect of mutation is passed to the zygote (3) with the delivered chromosome set of the oocyte; however, (4) this is not associated with passing of the mutant gene itself. The data on the interaction between conditional mutations and chromosome rearrangements give the pattern of interaction that is different from a classical one. The classical pattern implies that the interaction takes place in the presence of the interacting genes versus the described situation, when these genes are absent. The former can be referred to as a short-range effect and the latter, as a long-range effect. In the second case, the genes providing the effect in question function in the germline cells of the parents. The changes caused by the genes involved in this effect are passed to the zygote together with the chromosome sets rather than the genes themselves. The interaction event takes place in the zygote when the maternal and paternal sets meet. Formally, this can be referred to as an epigenetic interaction if it were not for the fact that we speak about the genetic events of a classical type caused by damages (mutations) of the DNA material. Some of them (conditional mutations) bring about the “prohibition on daughters” and the other (chromosome rearrangements) remove this prohibition. Both mutations (conditional mutation and Cy inversion) in the mutant males carrying this inversion (Table 3) reside in the same genome. This is the case when the mutations could apparently interact in the most efficient manner. However, the interaction is absent: the males ♂ +; Cy have no daughters as well as their brothers, ♂+; Cy+ , lacking the inversion. Classical genetics has an example of inheritance of the traits without inheriting genes, referred to as maternal effect [8]. This
type of inheritance is explainable with the RNA templates passed to the progeny with the egg cell cytoplasm. However, this explanation does not work in our case. The parental effect of conditional mutations appears in male, which excludes any possibility to pass a gene effect via the cytoplasm. The absence of interaction between a conditional mutation and the In(2LR)CyO inversion present in the same genome (Table 3) is even more eloquent. There is no interaction at all despite the conditions providing implementation of the interaction at any of the possible levels (DNA, RNA, and protein) and at any developmental stage (embryonic tissue and soma): the structural mutation, Cy, fails to manifest itself as a suppressor of “prohibition on daughters”. It is clear that the long-range effect is unexplainable with the fact that RNA templates or proteins merely enter the zygote, even if this really takes place. 3.1. The mechanism of the long-range effect The obtained data demonstrating (1) the effect of conditional mutations as a “prohibition on daughters”, (2) removal of the effect by chromosome rearrangements when a rearrangement and a conditional mutation are carried by different parents, and (3) the absence of the effect of chromosome rearrangements when the rearrangement and conditional mutation reside in the same parent (Table 3) suggest that emergence of the long-range effect requires that two differently changed parental chromosome sets meet in the zygote. We assume that one chromosome set with the genome advance along the germline is altered because of the presence of a conditional mutation and the other, because of the presence of a rearrangement. These changes are of an epigenetic nature and affect the overall genome. It is not necessary that the mutations that induced the epigenetic changes are present in the zygote.
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This novel type of interaction between genes is a remarkable but not the only characteristic of the genes responsible for conditional mutations. Our review [1] comprehensively describes the overall set of unusual features of the mutants for these genes. It is assumed [5,9] that the studied genes follow a DNA–short RNA scheme rather than a DNA–mRNA–protein pattern, characteristic of the Mendelian genes. As is mentioned above, the long-range gene interaction takes place when two genomes meet in the zygote. This meeting has two outcomes depending on the specificities of these genomes, namely, implementation of development or its cessation (dominant lethality). In essence, this is the conditionality appearing in the name of such mutations. The “encounter” of genomes accompanies every event of fertilization. That is why the insight into the mechanism underlying “the mutual recognition of parental developmental programs”, which is the particular event marking the start of a newly formed diploid genome, is of the paramount importance. References [1] B.F. Chadov, N.B. Fedorova, E.V. Chadova, Conditional mutations in Drosophila melanogaster: On the Occasion of the 150th Anniversary of G. Mendel’s Report in Brünn, Mutat. Res./Rev. Mutat. Res. 765 (2015) 40–55, http://dx.doi.org/10. 1016/j.mrrev.2015.06.001.
[2] B.F. Chadov, E.V. Chadova, S.A. Kopyl, N.B. Fedorova, 2000 A new class of mutations in Drosophila melanogaster, Dokl. Biol. Sci. 373 (2000) 423–426. [3] B.F. Chadov, Mutations in the regulatory genes in Drosophila melanogaster, in: Proc. Intern. Conf. Biodiversity and Dynamics of Ecosystems in North Eurasia, IC@G, Novosibirsk, Russia, 2000, pp. 16–18. [4] B.F. Chadov, N.B. Fedorova, E.V. Chadova, E.A. Khotskina, Conditional mutations in Drosophila, J. Life Sci. 5 (2011) 224–240. [5] B.F. Chadov, N.B. Fedorova, E.V. Chadova, Conditional Mutations in Drosophila melanogaster, 2016, http://dx.doi.org/10.13140/RG.2.1.2585.5606. [6] D.L. Lindsley, E.H. Grell, Genetic Variations of Drosophila melanogaster, Carnegie Inst., Washington, 1967 (Publ. no. 627). [7] B.F. Chadov, Mutations capable of inducing speciation Evolution Biology, Vol. 1, Tomsk State University Press, 2001, pp. 138–162 (In Russian) http://www. evolbiol.ru/. [8] R. Sager, Cytoplasmic Genes and Organelles, Elsevier, 1972. [9] N.B. Fedorova, E.V. Chadova, B.F. Chadov, Genes and Ontogenes in Drosophila: The Role of RNA Forms // Transcriptomics 4, 2016, pp. 137, http://dx.doi.org/ 10.4172/2329-8936.1000137.