- Email: [email protected]
Dosage effects on gene expression in a maize ploidy series
MONITOR A gene (RPGR)withhomology to the RCCl gtuniae nucleoti& exchange
Fatient MO with a 75kb deletion approximately 380 kb proximal to the
factoris mutated in X-linked retinitis BB breakpoint altered the region of search IA. Meindl et al. (1995) Htrsr. pigmentosa (RP3) Mol. Genet. 4. 2339-23461. This paper
Over the past decade linkage analysis of X-linked retinitis pigmentosa CURPI has revealed at least two loci on the short arm of the X chromosome. The most cormnon fornl of Xl&P (RP3) was fine mapped with the aid of the renowned BB deletion patient (which led to the cloning of the DMD and CGD Renes), who also suffered from RI’. Positional cloning efforts for many years focused near the proximal deletion breakpoint without any success, but the recent identification of W
Dosage effectson geneexpression in a
maizeploidyseries
The phenotypic effects of variations in the total genomic complement (pl&iy) and the copy number of individual chromosomes (aneuploidy) have been known for some tane. Guo et nl. analysed the levels of specific tran-
scripts in a complete ploidy series of matze. The levels of 18 different transcripts were studied in leaves from mono&id, diploid. triploid and tetraplaid plants. Expression of most genes
displayed direct gene dosage effects; that is, transcript levels per cell increased proportionally wah ploidy and
also describes the SRPX gene abundantly expressed in the retina, which is partially deleted in patient MO. The same gene had been is&ted by K. Dty er nl. I(1995) HflS?. Mol. GcI?e/. 4, 2347-23531 but neither group could identify disease, causing murarions in their RP3 families. A timely collaborative effort between the two groups has since resulted in the cloning of RPGR, encoding a guanine nucleotide exchange factor, which has a very low level of expression in the retina This very low level of expression explains why the gene was not isolated through direcT sreening of retina cDNA libraries. The gene was eventually identified
gene copy number. However, in Edceptional cases gene expression was negatively con&ted with ploldy, or showed a positive correlation greater than expected from the number of gene copies. This general relationship between gene dosage and overali ploidy levels contrdsti with the resulw of a previous study, by the same group, on aneuploid lines of maize. In that study addition of individual chromosomes or segments of chromosomes
resulted mainly in dosage compcnsation effects, in which the overall expression of genes present on the aneuploid chromosome remained unaltered, even though gene copy number had increased. Taken together, these results susest that dosage effects on gene expression are the result of
stoichiometric
utterartions
Meeting reportsin Td 7I’Gfeatures regular meeting tepow, which developmental biologists. We generally widespread interest. The reports are around and rhe controversies at the meeting
bv aenomic seauencincc of cosmkls frbnywithin the i40 dele%on, followed by GRAIL analysis for predicting the prewnce of axons, and finally the gene structure was verified rhrough cDNA sequencing and expression studies. Mutations were found that .seRregate with dlsea.se in seven XLRI’ families from a pool of 74 unrelated XLRI’ patients, which is surprisingly low because RI’3 accoilnts for approximately 70% of all XLRP cases. We must assume that either further e?~onb are still to be identified (although transcript size corresponds well with the cDNA sequence), or that the major locus for RP3 has yet to be investigated, suggesting microheterogeneity. Either xvay, the important question remains, what is the precise function of this rare gene in the rerima and how do mutations in this gene cause retinal degeneration? h
frrrrts-acting factors and their target genes. In the ploidy series, the stoichiomrtty is the same in each case, and for the most pan gene expression is proponional to copy number. In aneuplaid lines, perturbation
of chromo-
sotnal balance resulw in a change in stoichiomety and, thus, the dosage compensation of gene expression. 2%
Monitor contributors this month Simon Dowell,
Frank Conlon,
Stephen Wilson. Jonathan Hodgkin, Shomi Bhattachatya, Lisa Hall
betwc-en
in tAm?tks
provide highlights of meetings of interest to geneticists and cover smaller meetings, althottgb the topics should be of 500 words, and should focus on the sutpti.ses, rhe excitement rather tin attctiipi io StriiiiiadZe ilir: Whole mr+-iing.
If you know about a meeting tbat we should cover, or if you would lice to w&e a report for us, then please get in touch. MarkF&terson Trerzds in Genetics, Trends JoumaIs, 68 Hills Road, Cambridge, UK CB2 ILA.
Elsevier
Tel: 44 1223 315961, fax: 44 1223 464430, email: [email protected] TIG AUGUST1996 VOL. 12 No. 8
293
Fatient MO with a 75kb deletion approximately 380 kb proximal to the
factoris mutated in X-linked retinitis BB breakpoint altered the region of search IA. Meindl et al. (1995) Htrsr. pigmentosa (RP3) Mol. Genet. 4. 2339-23461. This paper
Over the past decade linkage analysis of X-linked retinitis pigmentosa CURPI has revealed at least two loci on the short arm of the X chromosome. The most cormnon fornl of Xl&P (RP3) was fine mapped with the aid of the renowned BB deletion patient (which led to the cloning of the DMD and CGD Renes), who also suffered from RI’. Positional cloning efforts for many years focused near the proximal deletion breakpoint without any success, but the recent identification of W
Dosage effectson geneexpression in a
maizeploidyseries
The phenotypic effects of variations in the total genomic complement (pl&iy) and the copy number of individual chromosomes (aneuploidy) have been known for some tane. Guo et nl. analysed the levels of specific tran-
scripts in a complete ploidy series of matze. The levels of 18 different transcripts were studied in leaves from mono&id, diploid. triploid and tetraplaid plants. Expression of most genes
displayed direct gene dosage effects; that is, transcript levels per cell increased proportionally wah ploidy and
also describes the SRPX gene abundantly expressed in the retina, which is partially deleted in patient MO. The same gene had been is&ted by K. Dty er nl. I(1995) HflS?. Mol. GcI?e/. 4, 2347-23531 but neither group could identify disease, causing murarions in their RP3 families. A timely collaborative effort between the two groups has since resulted in the cloning of RPGR, encoding a guanine nucleotide exchange factor, which has a very low level of expression in the retina This very low level of expression explains why the gene was not isolated through direcT sreening of retina cDNA libraries. The gene was eventually identified
gene copy number. However, in Edceptional cases gene expression was negatively con&ted with ploldy, or showed a positive correlation greater than expected from the number of gene copies. This general relationship between gene dosage and overali ploidy levels contrdsti with the resulw of a previous study, by the same group, on aneuploid lines of maize. In that study addition of individual chromosomes or segments of chromosomes
resulted mainly in dosage compcnsation effects, in which the overall expression of genes present on the aneuploid chromosome remained unaltered, even though gene copy number had increased. Taken together, these results susest that dosage effects on gene expression are the result of
stoichiometric
utterartions
Meeting reportsin Td 7I’Gfeatures regular meeting tepow, which developmental biologists. We generally widespread interest. The reports are around and rhe controversies at the meeting
bv aenomic seauencincc of cosmkls frbnywithin the i40 dele%on, followed by GRAIL analysis for predicting the prewnce of axons, and finally the gene structure was verified rhrough cDNA sequencing and expression studies. Mutations were found that .seRregate with dlsea.se in seven XLRI’ families from a pool of 74 unrelated XLRI’ patients, which is surprisingly low because RI’3 accoilnts for approximately 70% of all XLRP cases. We must assume that either further e?~onb are still to be identified (although transcript size corresponds well with the cDNA sequence), or that the major locus for RP3 has yet to be investigated, suggesting microheterogeneity. Either xvay, the important question remains, what is the precise function of this rare gene in the rerima and how do mutations in this gene cause retinal degeneration? h
frrrrts-acting factors and their target genes. In the ploidy series, the stoichiomrtty is the same in each case, and for the most pan gene expression is proponional to copy number. In aneuplaid lines, perturbation
of chromo-
sotnal balance resulw in a change in stoichiomety and, thus, the dosage compensation of gene expression. 2%
Monitor contributors this month Simon Dowell,
Frank Conlon,
Stephen Wilson. Jonathan Hodgkin, Shomi Bhattachatya, Lisa Hall
betwc-en
in tAm?tks
provide highlights of meetings of interest to geneticists and cover smaller meetings, althottgb the topics should be of 500 words, and should focus on the sutpti.ses, rhe excitement rather tin attctiipi io StriiiiiadZe ilir: Whole mr+-iing.
If you know about a meeting tbat we should cover, or if you would lice to w&e a report for us, then please get in touch. MarkF&terson Trerzds in Genetics, Trends JoumaIs, 68 Hills Road, Cambridge, UK CB2 ILA.
Elsevier
Tel: 44 1223 315961, fax: 44 1223 464430, email: [email protected] TIG AUGUST1996 VOL. 12 No. 8
293