151
|
Fung JC, Marshall WF, Dernburg A, Agard DA, Sedat JW. Homologous chromosome pairing in Drosophila melanogaster proceeds through multiple independent initiations. J Cell Biol 1998; 141:5-20. [PMID: 9531544 PMCID: PMC2132734 DOI: 10.1083/jcb.141.1.5] [Citation(s) in RCA: 173] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The dynamics by which homologous chromosomes pair is currently unknown. Here, we use fluorescence in situ hybridization in combination with three-dimensional optical microscopy to show that homologous pairing of the somatic chromosome arm 2L in Drosophila occurs by independent initiation of pairing at discrete loci rather than by a processive zippering of sites along the length of chromosome. By evaluating the pairing frequencies of 11 loci on chromosome arm 2L over several timepoints during Drosophila embryonic development, we show that all 11 loci are paired very early in Drosophila development, within 13 h after egg deposition. To elucidate whether such pairing occurs by directed or undirected motion, we analyzed the pairing kinetics of histone loci during nuclear cycle 14. By measuring changes of nuclear length and correlating these changes with progression of time during cycle 14, we were able to express the pairing frequency and distance between homologous loci as a function of time. Comparing the experimentally determined dynamics of pairing to simulations based on previously proposed models of pairing motion, we show that the observed pairing kinetics are most consistent with a constrained random walk model and not consistent with a directed motion model. Thus, we conclude that simple random contacts through diffusion could suffice to allow pairing of homologous sites.
Collapse
Affiliation(s)
- J C Fung
- Graduate Group in Biophysics, University of California, San Francisco, California 94143-0554, USA
| | | | | | | | | |
Collapse
|
152
|
Jin Q, Trelles-Sticken E, Scherthan H, Loidl J. Yeast nuclei display prominent centromere clustering that is reduced in nondividing cells and in meiotic prophase. J Cell Biol 1998; 141:21-9. [PMID: 9531545 PMCID: PMC2132713 DOI: 10.1083/jcb.141.1.21] [Citation(s) in RCA: 152] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/1997] [Revised: 02/04/1998] [Indexed: 02/07/2023] Open
Abstract
Chromosome arrangement in spread nuclei of the budding yeast, Saccharomyces cerevisiae was studied by fluorescence in situ hybridization with probes to centromeres and telomeric chromosome regions. We found that during interphase centromeres are tightly clustered in a peripheral region of the nucleus, whereas telomeres tend to occupy the area outside the centromeric domain. In vigorously growing cultures, centromere clustering occurred in approximately 90% of cells and it appeared to be maintained throughout interphase. It was reduced when cells were kept under stationary conditions for an extended period. In meiosis, centromere clusters disintegrated before the emergence of the earliest precursors of the synaptonemal complex. Evidence for the contribution of centromere clustering to other aspects of suprachromosomal nuclear order, in particular the vegetative association of homologous chromosomes, is provided, and a possible supporting role in meiotic homology searching is discussed.
Collapse
Affiliation(s)
- Q Jin
- Institute of Botany, University of Vienna, A-1030 Vienna, Austria
| | | | | | | |
Collapse
|
153
|
Abstract
Imprinting is a genetic mechanism that determines expression or repression of genes according to their parental origin. Some imprinted genes occur in clusters in the genome. Recent work using transgenic mice shows that multiple cis-acting sequences are needed for correct imprinting. Mutation analysis in a normal chromosomal context reveals the importance of imprinting centres for regional establishment or maintenance of imprinting in a cluster. Elements that contribute to the function of imprinting centres and regional propagation of the imprints are CpG-rich differentially methylated regions (that during development retain germline imposed methylation or demethylation), direct repeat clusters, and unusual RNAs (antisense, non-translated etc.). The interaction of these cis elements with transacting factors such as methylase and chromatin factors establishes a hierarchical control system with local and regional effects.
Collapse
Affiliation(s)
- W Reik
- Laboratory of Developmental Genetics and Imprinting, Babraham Institute, Cambridge, UK.
| | | |
Collapse
|
154
|
Mitsuya K, Meguro M, Sui H, Schulz TC, Kugoh H, Hamada H, Oshimura M. Epigenetic reprogramming of the human H19 gene in mouse embryonic cells does not erase the primary parental imprint. Genes Cells 1998; 3:245-55. [PMID: 9663659 DOI: 10.1046/j.1365-2443.1998.00183.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Genomic imprinting in mammals is thought to result from epigenetic modifications to chromosomes during gametogenesis, which leads to differential allelic expression during development. There is a requirement for an appropriate experimental system to enable the analysis of the mechanisms of genomic imprinting during embryogenesis. RESULTS To develop a novel in vitro system for studying the molecular basis of genomic imprinting, we constructed mouse cell lines containing either a paternal or maternal human chromosome 11, by microcell-mediated chromosome transfer. Allele-specific expression and DNA methylation studies revealed that the imprinting status of the human H19 gene was maintained in mouse A9 mono-chromosomal hybrids. Each parental human chromosome was introduced independently into mouse near-diploid immortal fibroblasts (m5S) and two embryonal carcinoma (EC) cell lines (OTF9-63 and P19). The paternal allele of human H19 remained in a repressed state in m5S cells, but was de-repressed in both EC cells. The paternal H19 allele was demethylated extensively in OTF9-63 cells, whereas the only alteration in P19 hybrids was de novo methylation on both alleles in the 3' region. Following in vitro differentiation, the expressed paternal H19 allele was selectively repressed in differentiated derivatives of EC hybrids. CONCLUSION These results indicated that human imprint marks could function effectively in mouse cells, and that the imprinting process was epigenetically reprogrammed in embryonal carcinoma cells, without erasure of the primary imprint that marked the parental origin. Therefore, these mono-chromosomal hybrids could provide a valuable in vitro system to study the mechanisms involved in the regulation of imprinted gene expression.
Collapse
Affiliation(s)
- K Mitsuya
- Department of Molecular and Cell Genetics, School of Life Sciences, Faculty of Medicine, Tottori University, Yonago, Japan
| | | | | | | | | | | | | |
Collapse
|
155
|
LaSalle JM, Ritchie RJ, Glatt H, Lalande M. Clonal heterogeneity at allelic methylation sites diagnostic for Prader-Willi and Angelman syndromes. Proc Natl Acad Sci U S A 1998; 95:1675-80. [PMID: 9465075 PMCID: PMC19144 DOI: 10.1073/pnas.95.4.1675] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are developmental disorders resulting from the absence of the paternal or maternal contribution to the 15q11-13 region, respectively. Allele-specific methylation at D15S63 (PW71) has routinely been used as a diagnostic indicator of PWS and AS in DNA samples derived from peripheral blood. Extensive variation in allele-specific methylation patterns, however, has been observed at this site in different tissues, but the frequency or mechanism of this variation has remained uncharacterized. Herein, we have investigated the cellular basis of variation in methylation patterns at four sites of allelic methylation near SNRPN by using DNA samples derived from a panel of primary T lymphocyte clones. Interclonal variability was observed at three of these sites, including the diagnostic PW71 site. Changes in allele-specific methylation patterns occurred at a frequency of about one change in 50% of the cells every 22-25 doublings. In contrast, stable allele-specific methylation was observed in these clonal populations at exon 1 of SNRPN and the androgen receptor locus on the inactive X chromosome, suggesting that methylation at some CpG sites is more faithfully maintained than others. Clonal heterogeneity at PW71 was not an artifact of cell culture because the absence of allelic methylation was also observed in about 20% of the alleles in unstimulated peripheral blood. These results demonstrate that variation in allele-specific methylation at PW71 and other sites in the PWS/AS region appear to depend on the clonal complexity of the particular tissue and on the lack of strict maintenance of methylation within clones.
Collapse
Affiliation(s)
- J M LaSalle
- Howard Hughes Medical Institute, Genetics Division, Children's Hospital; and Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
| | | | | | | |
Collapse
|
156
|
Robinson WP, Dutly F, Nicholls RD, Bernasconi F, Peñaherrera M, Michaelis RC, Abeliovich D, Schinzel AA. The mechanisms involved in formation of deletions and duplications of 15q11-q13. J Med Genet 1998; 35:130-6. [PMID: 9580159 PMCID: PMC1051217 DOI: 10.1136/jmg.35.2.130] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Haplotype analysis was undertaken in 20 cases of 15q11-q13 deletion associated with Prader-Willi syndrome (PWS) or Angelman syndrome (AS) to determine if these deletions arose through unequal meiotic crossing over between homologous chromosomes. Of these, six cases of PWS and three of AS were informative for markers on both sides of the deletion. For four of six cases of paternal 15q11-q13 deletion (PWS), markers on both sides of the deletion breakpoints were inferred to be of the same grandparental origin, implying an intrachromosomal origin of the deletion. Although the remaining two PWS cases showed evidence of crossing over between markers flanking the deletion, this was not more frequent than expected by chance given the genetic distance between proximal and distal markers. It is therefore possible that all PWS deletions were intrachromosomal in origin with the deletion event occurring after normal meiosis I recombination. Alternatively, both sister chromatid and homologous chromosome unequal exchange during meiosis may contribute to these deletions. In contrast, all three cases of maternal 15q11-q13 deletion (AS) were associated with crossing over between flanking markers, which suggests significantly more recombination than expected by chance (p = 0.002). Therefore, there appears to be more than one mechanism which may lead to PWS/AS deletions or the resolution of recombination intermediates may differ depending on the parental origin of the deletion. Furthermore, 13 of 15 cases of 15q11-q13 duplication, triplication, or inversion duplication had a distal duplication breakpoint which differed from the common distal deletion breakpoint. The presence of at least four distal breakpoint sites in duplications indicates that the mechanisms of rearrangement may be complex and multiple repeat sequences may be involved.
Collapse
Affiliation(s)
- W P Robinson
- Department of Medical Genetics, University of British Columbia, Vancouver, Canada
| | | | | | | | | | | | | | | |
Collapse
|
157
|
Abstract
A handful of autosomal genes in the mammalian genome are inherited in a silent state from one of the two parents, and in a fully active form from the other, thereby rendering the organism functionally hemizygous for imprinted genes. To date 19 imprinted genes have been identified; 5 are expressed from the maternal chromosome while the rest are expressed from the paternal chromosome. Allele-specific methylation of CpG residues, established in one of the germlines and maintained throughout embryogenesis, has been clearly implicated in the maintenance of imprinting in somatic cells. Although the function of imprinting remains a subject of some debate, the process is thought to have an important role in regulating the rate of fetal growth.
Collapse
Affiliation(s)
- M S Bartolomei
- Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia 19104, USA
| | | |
Collapse
|
158
|
Baylin SB, Herman JG, Graff JR, Vertino PM, Issa JP. Alterations in DNA methylation: a fundamental aspect of neoplasia. Adv Cancer Res 1998. [PMID: 9338076 DOI: 10.1016/s0065-230x(08)60702-2] [Citation(s) in RCA: 1202] [Impact Index Per Article: 46.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Neoplastic cells simultaneously harbor widespread genomic hypomethylation, more regional areas of hypermethylation, and increased DNA-methyltransferase (DNA-MTase) activity. Each component of this "methylation imbalance" may fundamentally contribute to tumor progression. The precise role of the hypomethylation is unclear, but this change may well be involved in the widespread chromosomal alterations in tumor cells. A main target of the regional hypermethylation are normally unmethylated CpG islands located in gene promoter regions. This hypermethylation correlates with transcriptional repression that can serve as an alternative to coding region mutations for inactivation of tumor suppressor genes, including p16, p15, VHL, and E-cad. Each gene can be partially reactivated by demethylation, and the selective advantage for loss of gene function is identical to that seen for loss by classic mutations. How abnormal methylation, in general, and hypermethylation, in particular, evolve during tumorigenesis are just beginning to be defined. Normally, unmethylated CpG islands appear protected from dense methylation affecting immediate flanking regions. In neoplastic cells, this protection is lost, possibly by chronic exposure to increased DNA-MTase activity and/or disruption of local protective mechanisms. Hypermethylation of some genes appears to occur only after onset of neoplastic evolution, whereas others, including the estrogen receptor, become hypermethylated in normal cells during aging. This latter change may predispose to neoplasia because tumors frequently are hypermethylated for these same genes. A model is proposed wherein tumor progression results from episodic clonal expansion of heterogeneous cell populations driven by continuous interaction between these methylation abnormalities and classic genetic changes.
Collapse
Affiliation(s)
- S B Baylin
- Johns Hopkins Comprehensive Cancer Center, Baltimore, Maryland, USA
| | | | | | | | | |
Collapse
|
159
|
Duvillié B, Bucchini D, Tang T, Jami J, Pàldi A. Imprinting at the mouse Ins2 locus: evidence for cis- and trans-allelic interactions. Genomics 1998; 47:52-7. [PMID: 9465295 DOI: 10.1006/geno.1997.5070] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The mouse gene encoding preproinsulin 2 (Ins2) is located on the distal end of chromosome 7 in a region of several hundred kilobases that contains several imprinted genes. The exclusive expression of the Ins2 paternal allele in the visceral yolk sac during the last part of gestation indicates that Ins2 also is imprinted. However, in other tissues in which Ins2 is expressed, both alleles are active at all developmental stages. Taking advantage of two mouse strains carrying different null mutations introduced at the Ins2 locus via homologous recombination in ES cells, we examined whether genes inserted at the Ins2 locus become imprinted and have the same restricted pattern of monoallelic expression. In the first null allele, Ins2 was replaced by LacZ, under the control of the endogenous Ins2 promoter, and a Neo cassette with its own promoter was inserted 3' to LacZ (Zneo allele). In the second null allele, Ins2 and its promoter were replaced by the same Neo cassette (Neo allele). Expression of the maternally and paternally inherited genes was monitored by RT-PCR performed on various reciprocal crosses involving the two mutants and the wildtype alleles. In (Zneo x wildtype) F1 embryos, the pattern of LacZ expression was similar to that of Ins2; i.e., LacZ is expressed in the yolk sac only when paternally inherited, while its expression in the embryo proper is independent of its paternal or maternal origin. For both of the mutant alleles, Neo was transcribed only when paternally inherited, in the yolk sac as well as in the embryo. Unexpectedly, we found that LacZ transcription on the maternal chromosome varied depending on the nature of the allele on the paternal chromosome. While fully expressed in the embryo when the paternal chromosome carries the wildtype allele, the maternally inherited LacZ is extinguished when the paternal allele is the Neo allele. The major conclusion from our results is that individual genes introduced into an imprinted chromosomal domain can become imprinted, indicating the influence of long-range cis-acting effects. In addition, our data suggest that the two parental alleles may "communicate" with each other and influence the transcription at the locus.
Collapse
Affiliation(s)
- B Duvillié
- Institut Cochin de Génétique Moléculaire, INSERM U257, Paris, France
| | | | | | | | | |
Collapse
|
160
|
Sullivan KF, Shelby RD. Chapter 12: Using Time–Lapse Confocal Microscopy for Analysis of Centromere Dynamics in Human Cells. Methods Cell Biol 1998. [DOI: 10.1016/s0091-679x(08)61956-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
161
|
Janevski J, Park PC, De Boni U. Changes in morphology and spatial position of coiled bodies during NGF-induced neuronal differentiation of PC12 cells. J Histochem Cytochem 1997; 45:1523-31. [PMID: 9358854 DOI: 10.1177/002215549704501109] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Interphase nuclei are organized into structural and functional domains. The coiled body, a nuclear organelle of unknown function, exhibits cell type-specific changes in number and morphology. Its association with nucleoli and with small nuclear ribonucleo-proteins (snRNPs) indicates that it functions in RNA processing. In cycling cells, coiled bodies are round structures not associated with nucleoli. In contrast, in neurons, they frequently present as nucleolar "caps." To test the hypothesis that neuronal differentiation is accompanied by changes in the spatial association of coiled bodies with nucleoli and in their morphology, PC12 cells were differentiated into a neuronal phenotype with nerve growth factor (NGF) and coiled bodies detected by immunocytochemical localization of p80-coilin and snRNPs. The fraction of cells that showed coiled bodies as nucleolar caps increased from 1.6 +/- 0.9% (mean +/- SEM) in controls to 16.5 +/- 1.6% in NGF-differentiated cultures. The fraction of cells with ring-like coiled bodies increased from 17.2 +/- 5.0% in controls to 57.8 +/- 4.4% in differentiated cells. This was accompanied by a decrease, from 81.2 +/- 5.7% to 25.7 +/- 3.1%, in the fraction of cells with small, round coiled bodies. SnRNPs remained associated with typical coiled bodies and with ring-like coiled bodies during NGF-induced recruitment of snRNPs to the nuclear periphery. Together with the observation that coiled bodies are also present as nucleolar caps in sensory neurons, the results indicate that coiled bodies alter their morphology and increase their association with nucleoli during NGF-induced neuronal differentiation.
Collapse
Affiliation(s)
- J Janevski
- Department of Physiology, Faculty of Medicine, University of Toronto, Ontario, Canada
| | | | | |
Collapse
|
162
|
Meguro M, Mitsuya K, Sui H, Shigenami K, Kugoh H, Nakao M, Oshimura M. Evidence for uniparental, paternal expression of the human GABAA receptor subunit genes, using microcell-mediated chromosome transfer. Hum Mol Genet 1997; 6:2127-33. [PMID: 9328477 DOI: 10.1093/hmg/6.12.2127] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We have constructed mouse A9 hybrids containing a single normal human chromosome 15, via microcell-mediated chromosome transfer. Cytogenetic and DNA-polymorphic analyses identified mouse A9 hybrids that contained either a paternal or maternal human chromosome 15. Paternal specific expression of the known imprinted genes SNRPN (small nuclear ribonucleoprotein-associated polypeptide N gene) and IPW (imprinted gene in the Prader-Willi syndrome region) was maintained in the A9 hybrids. Using this system, we first demonstrated that human GABAAreceptor subunit genes, GABRB3 , GABRA5 and GABRG3 , were expressed exclusively from the paternal allele and that E6-AP (E6-associated protein or UBE3A ) was biallelically expressed. Moreover, the 5' portion of the GABRB3 gene was found to be hypermethylated on the paternal allele. Our data imply that GABAAreceptor subunit genes are imprinted and are possible candidates for Prader-Willi syndrome, and that this human monochromosomal hybrid system enables the efficient analysis of imprinted loci.
Collapse
Affiliation(s)
- M Meguro
- Department of Molecular and Cell Genetics, School of Life Sciences, Faculty of Medicine, Tottori University, Nishimachi 86, Yonago, Tottori 683, Japan
| | | | | | | | | | | | | |
Collapse
|
163
|
Bennett ST, Wilson AJ, Esposito L, Bouzekri N, Undlien DE, Cucca F, Nisticò L, Buzzetti R, Bosi E, Pociot F, Nerup J, Cambon-Thomsen A, Pugliese A, Shield JP, McKinney PA, Bain SC, Polychronakos C, Todd JA. Insulin VNTR allele-specific effect in type 1 diabetes depends on identity of untransmitted paternal allele. The IMDIAB Group. Nat Genet 1997; 17:350-2. [PMID: 9354805 DOI: 10.1038/ng1197-350] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The IDDM2 type 1 diabetes susceptibility locus was mapped to and identified as allelic variation at the insulin gene (INS) VNTR regulatory polymorphism. In Caucasians, INS VNTR alleles divide into two discrete size classes. Class I alleles (26 to 63 repeats) predispose in a recessive way to type 1 diabetes, while class III alleles (140 to more than 200 repeats) are dominantly protective. The protective effect may be explained by higher levels of class III VNTR-associated INS mRNA in thymus such that elevated levels of preproinsulin protein enhance immune tolerance to preproinsulin, a key autoantigen in type 1 diabetes pathogenesis. The mode of action of IDDM2 is complicated, however, by parent-of-origin effects and possible allelic heterogeneity within the two defined allele classes. We have now analysed transmission of specific VNTR alleles in 1,316 families and demonstrate that a particular class I allele does not predispose to disease when paternally inherited, suggestive of polymorphic imprinting. But this paternal effect is observed only when the father's untransmitted allele is a class III. This allelic interaction is reminiscent of epigenetic phenomena observed in plants (for example, paramutation; ref. 17) and in yeast (for example, trans-inactivation; ref. 18). If untransmitted chromosomes can have functional effects on the biological properties of transmitted chromosomes, the implications for human genetics and disease are potentially considerable.
Collapse
Affiliation(s)
- S T Bennett
- Wellcome Trust Centre for Human Genetics, Nuffield Department of Surgery, University of Oxford, UK
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
164
|
Ashe HL, Monks J, Wijgerde M, Fraser P, Proudfoot NJ. Intergenic transcription and transinduction of the human beta-globin locus. Genes Dev 1997; 11:2494-509. [PMID: 9334315 PMCID: PMC316561 DOI: 10.1101/gad.11.19.2494] [Citation(s) in RCA: 292] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/1997] [Accepted: 08/13/1997] [Indexed: 02/05/2023]
Abstract
We have identified novel nuclear transcripts in the human beta-globin locus using nuclear run-on analysis in erythroid cell lines and in situ hybridization analysis of erythroid tissue. These transcripts extend across the LCR and intergenic regions but are undetectable in nonerythroid cells. Surprisingly, transient transfection of a beta-globin gene (epsilon, gamma, or beta) induces transcription of the LCR and intergenic regions from the chromosomal beta-globin locus in nonerythroid cell lines. The beta-globin genes themselves, however, remain transcriptionally silent. Induction is dependent on transcription of the globin gene in the transfected plasmid but does not require protein expression. Using in situ hybridization analysis, we show that the plasmid colocalizes with the endogenous beta-globin locus providing insight into the mechanism of transinduction.
Collapse
Affiliation(s)
- H L Ashe
- Sir William Dunn School of Pathology, University of Oxford, UK
| | | | | | | | | |
Collapse
|
165
|
Forné T, Oswald J, Dean W, Saam JR, Bailleul B, Dandolo L, Tilghman SM, Walter J, Reik W. Loss of the maternal H19 gene induces changes in Igf2 methylation in both cis and trans. Proc Natl Acad Sci U S A 1997; 94:10243-8. [PMID: 9294195 PMCID: PMC23347 DOI: 10.1073/pnas.94.19.10243] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Recent investigations have shown that the maintenance of genomic imprinting of the murine insulin-like growth factor 2 (Igf2) gene involves at least two factors: the DNA (cytosine-5-)-methyltransferase activity, which is required to preserve the paternal specific expression of Igf2, and the H19 gene (lying 90 kb downstream of Igf2 gene), which upon inactivation leads to relaxation of the Igf2 imprint. It is not yet clear how these two factors are related to each other in the process of maintenance of Igf2 imprinting and, in particular, whether the latter is acting through cis elements or whether the H19 RNA itself is involved. By using Southern blots and the bisulfite genomic-sequencing technique, we have investigated the allelic methylation patterns (epigenotypes) of the Igf2 gene in two strains of mouse with distinct deletions of the H19 gene. The results show that maternal transmission of H19 gene deletions leads the maternal allele of Igf2 to adopt the epigenotype of the paternal allele and indicate that this phenomenon is influenced directly or indirectly by the H19 gene expression. More importantly, the bisulfite genomic-sequencing allowed us to show that the methylation pattern of the paternal allele of the Igf2 gene is affected in trans by deletions of the active maternal allele of the H19 gene. Selection during development for the appropriate expression of Igf2, dosage-dependent factors that bind to the Igf2 gene, or methylation transfer between the parental alleles could be involved in this trans effect.
Collapse
Affiliation(s)
- T Forné
- Laboratory of Developmental Genetics and Imprinting, Department of Development and Genetics, The Babraham Institute, Cambridge CB2 4AT, United Kingdom
| | | | | | | | | | | | | | | | | |
Collapse
|
166
|
Ainscough JF, Koide T, Tada M, Barton S, Surani MA. Imprinting of Igf2 and H19 from a 130 kb YAC transgene. Development 1997; 124:3621-32. [PMID: 9342054 DOI: 10.1242/dev.124.18.3621] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A stringent test for imprint control elements is to examine their function at ectopic loci in transgenic experiments. Igf2 and H19 are part of a larger imprinting region and as a first step, we examined these reciprocally imprinted genes in transgenic experiments using a 130 kb YAC clone. After paternal inheritance, H19 was appropriately repressed and Igf2 was expressed, irrespective of copy number or genetic background. After maternal inheritance H19 was consistently expressed, albeit with some variability. The levels of H19 expression per copy of the transgene inversely correlated with Igf2 (-lacZ) expression in cis. The consistent imprinting of H19 from this YAC contrasts with the previously described imprinting of mini-H19 transgenes, which only occurs at multi-copy loci, is inconsistent, and is prone to genetic background effects. We propose a novel model in which silencing of the H19 gene is the default state and its activation after maternal inheritance is the key mechanistic event for imprinting in this region. In addition, in situ analysis of the Igf2-lacZ reporter indicates that additional mesoderm-specific enhancers are present within the YAC clone. No obvious phenotype was detected from the excess gene dosage of H19.
Collapse
MESH Headings
- Animals
- Chromosomes, Artificial, Yeast
- DNA Methylation
- Embryo, Mammalian/metabolism
- Enhancer Elements, Genetic
- Female
- Gene Dosage
- Genes, Reporter
- Genomic Imprinting
- Insulin-Like Growth Factor II/genetics
- Male
- Mesoderm/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Inbred CBA
- Mice, Transgenic
- Models, Genetic
- Muscle Proteins/genetics
- Phenotype
- RNA, Long Noncoding
- RNA, Untranslated
- Transgenes
Collapse
Affiliation(s)
- J F Ainscough
- Wellcome/CRC Institute of Cancer and Developmental Biology, University of Cambridge, UK.
| | | | | | | | | |
Collapse
|
167
|
Moynahan ME, Jasin M. Loss of heterozygosity induced by a chromosomal double-strand break. Proc Natl Acad Sci U S A 1997; 94:8988-93. [PMID: 9256422 PMCID: PMC22995 DOI: 10.1073/pnas.94.17.8988] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The repair of chromosomal double-strand breaks (DSBs) is necessary for genomic integrity in all organisms. Genetic consequences of misrepair include chromosomal loss, deletion, and duplication resulting in loss of heterozygosity (LOH), a common finding in human solid tumors. Although work with radiation-sensitive cell lines suggests that mammalian cells primarily rejoin DSBs by nonhomologous mechanisms, alternative mechanisms that are implicated in chromosomal LOH, such as allelic recombination, may also occur. We have examined chromosomal DSB repair between homologs in a gene targeted mammalian cell line at the retinoblastoma (Rb) locus. We have found that allelic recombinational repair occurs in mammalian cells and is increased at least two orders of magnitude by the induction of a chromosomal DSB. One consequence of allelic recombination is LOH at the Rb locus. Some of the repair events also resulted in other types of genetic instability, including deletions and duplications. We speculate that mammalian cells may have developed efficient nonhomologous DSB repair processes to bypass allelic recombination and the potential for reduction to homozygosity.
Collapse
Affiliation(s)
- M E Moynahan
- Department of Medicine, Memorial Sloan-Kettering Cancer Center and Cornell University Graduate School of Medical Sciences, 1275 York Avenue, New York, NY 10021, USA
| | | |
Collapse
|
168
|
Hu JF, Vu TH, Hoffman AR. Genomic deletion of an imprint maintenance element abolishes imprinting of both insulin-like growth factor II and H19. J Biol Chem 1997; 272:20715-20. [PMID: 9252392 DOI: 10.1074/jbc.272.33.20715] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Insulin-like growth factor II (Igf2) is maternally imprinted in normal tissues with only the paternal copy of the gene being transcribed, whereas the contiguous gene H19 is paternally imprinted. Dysregulation of IGF2 imprinting is commonly observed in Wilms' tumor and other human tumors. Previous work comparing promoter-specific imprinting of human and mouse Igf2 suggested the presence of a cis element upstream of Igf2 that regulates or maintains the imprinting of three downstream promoters. To explore the molecular mechanism of maintenance of genomic imprinting, we targeted the region between insulin 2 and Igf2, where the cis imprint maintenance element (IME) resides in mouse fibroblasts. In those clones in which the targeting vector was randomly integrated into the genome, mouse Igf2 remained imprinted. However, when the targeted region containing the IME was deleted by homologous recombination, whether from the paternal or maternal allele, activation of the imprinted maternal allele of Igf2 was observed. In addition, there was a loss of H19 imprinting when the IME was deleted. The requirement of IME from both parental alleles for the maintenance of genomic imprinting thus suggests the importance of a spatial structure of DNA around Igf2 and H19. Modifications in the IME, like abnormal methylation in Wilms' tumors, may represent a novel mechanism for loss of genomic imprinting.
Collapse
Affiliation(s)
- J F Hu
- Medical Service and GRECC, Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304, USA
| | | | | |
Collapse
|
169
|
Abstract
Paramutation is an allelic interaction that results in meiotically heritable changes in gene expression. Until recently, the few documented cases in higher plants seemed unusual and rare. This perception is rapidly fading because of the discovery of related examples and the growing recognition of epigenetic changes in a wide variety of biological systems.
Collapse
Affiliation(s)
- J B Hollick
- Institute of Molecular Biology, University of Oregon, Eugene 97403-1229, USA.
| | | | | |
Collapse
|
170
|
Schweifer N, Valk PJ, Delwel R, Cox R, Francis F, Meier-Ewert S, Lehrach H, Barlow DP. Characterization of the C3 YAC contig from proximal mouse chromosome 17 and analysis of allelic expression of genes flanking the imprinted Igf2r gene. Genomics 1997; 43:285-97. [PMID: 9268631 DOI: 10.1006/geno.1997.4816] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The imprinted mouse insulin-like growth factor type 2 receptor (Igf2r) maps to the middle of a gene-rich region in band A2 of mouse chromosome 17. The t(Lub2) chromosome 17 variant contains a small deletion that removes at least seven genes including Igf2r. We have constructed a YAC contig spanning the entire t(Lub2) deletion and created a restriction map that covers 700 kb. The position, transcription orientation, and imprinted status of the genes immediately flanking Igf2r have been assessed. We show here that the Mas gene, which lies 65 kb upstream to Igf2r, contains a novel 5' exon and is not imprinted in adult tissues. We further show that the recently identified Lx1 gene lies immediately downstream and is also expressed from both parental alleles in adult tissues. The remaining genes in this region have previously been shown to be biallelically expressed.
Collapse
Affiliation(s)
- N Schweifer
- The Netherlands Cancer Institute (H5), Amsterdam
| | | | | | | | | | | | | | | |
Collapse
|
171
|
Spritz RA, Bailin T, Nicholls RD, Lee ST, Park SK, Mascari MJ, Butler MG. Hypopigmentation in the Prader-Willi syndrome correlates with P gene deletion but not with haplotype of the hemizygous P allele. AMERICAN JOURNAL OF MEDICAL GENETICS 1997; 71:57-62. [PMID: 9215770 PMCID: PMC6067925 DOI: 10.1002/(sici)1096-8628(19970711)71:1<57::aid-ajmg11>3.0.co;2-u] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The Prader-Willi syndrome (PWS) usually results from a paternal deletion of 15q11-q13 or maternal disomy for chromosome 15. Reduced pigmentation of skin, hair, and eyes is common in PWS and was suggested previously to be associated with the 15q11-q13 deletion. The P gene, located in this same region, is associated with OCA2, an autosomal recessive disorder that is the most frequent form of tyrosinase-positive oculocutaneous albinism. We studied 28 individuals with PWS and found that hemizygosity for the P gene was significantly correlated with the occurrence of hypopigmentation among PWS patients. However, we found little or no relationship between the occurrence of hypopigmentation and the polymorphism haplotype of the intact P allele. Thus, our results indicate that hypopigmentation is likely the result of deletion of the P gene in the context of PWS but do not support the linked hypothesis that hypopigmentation results from hemizygosity for variant P alleles with reduced function.
Collapse
Affiliation(s)
- R A Spritz
- Department of Medical Genetics, University of Wisconsin School of Medicine, Madison 53706, USA.
| | | | | | | | | | | | | |
Collapse
|
172
|
Bürger J, Buiting K, Dittrich B, Gross S, Lich C, Sperling K, Horsthemke B, Reis A. Different mechanisms and recurrence risks of imprinting defects in Angelman syndrome. Am J Hum Genet 1997; 61:88-93. [PMID: 9245988 PMCID: PMC1715864 DOI: 10.1086/513900] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Angelman syndrome (AS) is a neurogenetic disorder that appears to be caused by the loss of function of an imprinted gene expressed from maternal chromosome 15 only. Approximately 6% of patients have a paternal imprint on the maternal chromosome. In the few cases, this is due to an inherited microdeletion, in the 15q11-q13 imprinting center (IC), that blocks the paternal-->maternal imprint switch in the maternal germ line. We have determined the segregation of 15q11-q13 haplotypes in nine families with AS and with an imprinting defect. One family, with two affected siblings, has a microdeletion affecting the IC transcript. In the other eight patients, no mutation was found at this locus. In two families, the patient and a healthy sibling share the same maternal alleles. In one of these families and in two others, grandparental DNA samples were available, and the chromosomes with the imprinting defect were found to be of grandmaternal origin. These findings suggest that germ-line mosaicism or de novo mutations account for a significant fraction of imprinting defects, among patients who have an as-yet-undetected mutation in a cis-acting element. Alternatively, these data may indicate that some imprinting defects are caused by a failure to maintain or to reestablish the maternal imprint in the maternal germ line or by a failure to replicate the imprint postzygotically. Depending on the underlying cause of the imprinting defect, different recurrence risks need to be considered.
Collapse
Affiliation(s)
- J Bürger
- Institute of Human Genetics, Virchow-Klinikum, Humboldt University, Berlin, Germany
| | | | | | | | | | | | | | | |
Collapse
|
173
|
Abney JR, Cutler B, Fillbach ML, Axelrod D, Scalettar BA. Chromatin dynamics in interphase nuclei and its implications for nuclear structure. J Cell Biol 1997; 137:1459-68. [PMID: 9199163 PMCID: PMC2137814 DOI: 10.1083/jcb.137.7.1459] [Citation(s) in RCA: 156] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Translational dynamics of chromatin in interphase nuclei of living Swiss 3T3 and HeLa cells was studied using fluorescence microscopy and fluorescence recovery after photobleaching. Chromatin was fluorescently labeled using dihydroethidium, a membrane-permeant derivative of ethidium bromide. After labeling, a laser was used to bleach small (approximately 0.4 microm radius) spots in the heterochromatin and euchromatin of cells of both types. These spots were observed to persist for >1 h, implying that interphase chromatin is immobile over distance scales >/=0.4 microm. Over very short times (<1 s), a partial fluorescence recovery within the spots was observed. This partial recovery is attributed to independent dye motion, based on comparison with results obtained using ethidium homodimer-1, which binds essentially irreversibly to nucleic acids. The immobility observed here is consistent with chromosome confinement to domains in interphase nuclei. This immobility may reflect motion-impeding steric interactions that arise in the highly concentrated nuclear milieu or outright attachment of the chromatin to underlying nuclear substructures, such as nucleoli, the nuclear lamina, or the nuclear matrix.
Collapse
Affiliation(s)
- J R Abney
- Department of Physics, Lewis & Clark College, Portland, Oregon 97219, USA
| | | | | | | | | |
Collapse
|
174
|
Henikoff S. Nuclear organization and gene expression: homologous pairing and long-range interactions. Curr Opin Cell Biol 1997; 9:388-95. [PMID: 9159074 DOI: 10.1016/s0955-0674(97)80012-9] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Genetic studies have demonstrated that pairing interactions between homologous chromosomes and long-range associations between nonhomologous sites can influence gene expression. Recent work has revealed that such influences are widespread in eukaryotes and that chromosome architecture is likely to be of fundamental importance for nuclear structure and function.
Collapse
Affiliation(s)
- S Henikoff
- Howard Hughes Medical Institute, Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98104, USA.
| |
Collapse
|
175
|
Marshall WF, Fung JC, Sedat JW. Deconstructing the nucleus: global architecture from local interactions. Curr Opin Genet Dev 1997; 7:259-63. [PMID: 9115425 DOI: 10.1016/s0959-437x(97)80136-0] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Recent advances in fluorescence in situ hybridization and three-dimensional microscopy have revealed a high degree of large-scale order in the nucleus, indicating that the position of each gene within the nucleus is not random. As with any other biological phenomenon, this large-scale organization must ultimately be specified by molecular interactions. Biochemical and molecular investigations have revealed a small set of local molecular-scale interactions that can be used together in a combinatorial fashion to establish a global large-scale nuclear architecture.
Collapse
Affiliation(s)
- W F Marshall
- Department of Biochemistry and Biophysics, University of California, San Francisco, California, 94143, USA
| | | | | |
Collapse
|
176
|
Wooten GF, Currie LJ, Bennett JP, Harrison MB, Trugman JM, Parker WD. Maternal inheritance in Parkinson's disease. Ann Neurol 1997; 41:265-8. [PMID: 9029076 DOI: 10.1002/ana.410410218] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
To evaluate possible matrilineal factors in the inheritance of Parkinson's disease, we prospectively identified families in which a parent and multiple siblings had Parkinson's disease. In each of the 5 families identified, the affected parent was the mother (p < 0.03). The age at onset in the offspring generation in these 5 families was younger than the age at onset in the parental generation (p < 0.001). In addition, the age at onset in all patients with an affected mother (n = 18) was younger than the age at onset in the affected mothers (p < 0.001). No difference was found between the age at onset in patients with an affected father (n = 14) and the age at onset in the affected fathers. These results are consistent with a role for inherited abnormalities of mitochondrial DNA in the pathogenesis of at least some cases of Parkinson's disease.
Collapse
Affiliation(s)
- G F Wooten
- Department of Neurology, University of Virginia Health Sciences Center, Charlottesville 22908, USA
| | | | | | | | | | | |
Collapse
|
177
|
Abstract
Parental imprinting is a process that results in allele-specific differences in transcription, DNA methylation, and DNA replication timing. Imprinting plays an important role in development, and its deregulation can cause certain defined disease states. Absence of a paternal contribution to chromosome 15q11-q13, due to hemizygous deletion or uniparental disomy, results in the Prader-Willi syndrome. The absence of a normal maternal copy of the same region causes Angelman syndrome. The Beckwith-Wiedemann syndrome is associated with the failure of normal biparental inheritance of chromosome 11p15, and loss of imprinting is observed in several cancers including Wilms' tumor. The study of the molecular basis of abnormal imprinting in these disorders will facilitate the identification and characterization of other imprinted human disease loci.
Collapse
Affiliation(s)
- M Lalande
- Howard Hughes Medical Institute, Genetics Division, Children's Hospital, Boston, Massachusetts, USA.
| |
Collapse
|
178
|
Shelby RD, Hahn KM, Sullivan KF. Dynamic elastic behavior of alpha-satellite DNA domains visualized in situ in living human cells. J Biophys Biochem Cytol 1996; 135:545-57. [PMID: 8909532 PMCID: PMC2121065 DOI: 10.1083/jcb.135.3.545] [Citation(s) in RCA: 166] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have constructed a fluorescent alpha-satellite DNA-binding protein to explore the motile and mechanical properties of human centromeres. A fusion protein consisting of human CENP-B coupled to the green fluorescent protein (GFP) of A. victoria specifically targets to centromeres when expressed in human cells. Morphometric analysis revealed that the alpha-satellite DNA domain bound by CENPB-GFP becomes elongated in mitosis in a microtubule-dependent fashion. Time lapse confocal microscopy in live mitotic cells revealed apparent elastic deformations of the central domain of the centromere that occurred during metaphase chromosome oscillations. These observations demonstrate that the interior region of the centromere behaves as an elastic element that could play a role in the mechanoregulatory mechanisms recently identified at centromeres. Fluorescent labeling of centromeres revealed that they disperse throughout the nucleus in a nearly isometric expansion during chromosome decondensation in telophase and early G1. During interphase, centromeres were primarily stationary, although motility of individual or small groups of centromeres was occasionally observed at very slow rates of 7-10 microns/h.
Collapse
Affiliation(s)
- R D Shelby
- Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037, USA
| | | | | |
Collapse
|
179
|
Issa JP, Vertino PM, Boehm CD, Newsham IF, Baylin SB. Switch from monoallelic to biallelic human IGF2 promoter methylation during aging and carcinogenesis. Proc Natl Acad Sci U S A 1996; 93:11757-62. [PMID: 8876210 PMCID: PMC38131 DOI: 10.1073/pnas.93.21.11757] [Citation(s) in RCA: 199] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We have previously linked aging, carcinogenesis, and de novo methylation within the promoter of the estrogen receptor (ER) gene in human colon. We now examine the dynamics of this process for the imprinted gene for insulin-like growth factor II (IGF2). In young individuals, the P2-4 promoters of IGF2 are methylated exclusively on the silenced maternal allele. During aging, this promoter methylation becomes more extensive and involves the originally unmethylated allele. Most adult human tumors, including colon, breast, lung, and leukemias, exhibit increased methylation at the P2-4 IGF2 promoters, suggesting further spreading during the neoplastic process. In tumors, this methylation is associated with diminished or absent IGF2 expression from the methylated P3 promoter but maintained expression from P1, an upstream promoter that is not contained within the IGF2 CpG island. Our results demonstrate a remarkable evolution of methylation patterns in the imprinted promoter of the IGF2 gene during aging and carcinogenesis, and provide further evidence for a potential link between aberrant methylation and diseases of aging.
Collapse
Affiliation(s)
- J P Issa
- Oncology Center, Johns Hopkins University Medical Institutions, Baltimore, MD 21231, USA
| | | | | | | | | |
Collapse
|
180
|
Colot V, Maloisel L, Rossignol JL. Interchromosomal transfer of epigenetic states in Ascobolus: transfer of DNA methylation is mechanistically related to homologous recombination. Cell 1996; 86:855-64. [PMID: 8808621 DOI: 10.1016/s0092-8674(00)80161-0] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The transfer of methylation between alleles represents a plausible epigenetic mutational mechanism to explain loss of imprinting in mammals and paramutation in plants. Here, we have exploited advantages unique to the fungus Ascobolus immersus to obtain direct experimental evidence that methylation transfer can occur between homologous chromosomes. A methylated allele and an unmethylated allele of the Ascobolus b2 spore color gene were brought together in individual meiotic cells. Frequent transfer of methylation to the unmethylated allele was observed. This transfer was polarized 5' to 3' along the b2 gene, as is gene conversion, and always accompanied the latter process when tested in the same cross. These and other observations strongly suggest that methylation transfer and recombination are mechanistically related.
Collapse
Affiliation(s)
- V Colot
- Institut de Génétique et Microbiologie, Université Paris-Sud, Orsay,France
| | | | | |
Collapse
|
181
|
Abstract
The Neurospora crassa Asm-1+ (ascospore maturation 1) gene encodes an abundant nucleus-localized protein required for formation of female structures and for ascospore maturation. Deletion mutants of Asm-1+ are "ascus-dominant," i.e., when crossed to wild type, neither Asm-1+ nor Asm-1 delta spores mature. To explain this behavior, we considered three models: an effect of reduced dosage of the gene product, failure of internuclear communication, and failure of transvection (regulation dependent on pairing of alleles). We found that for proper regulation of subsequent sexual sporulation, Asm-1+ must be in proximity, probably paired, to its allelic counterpart in the zygote: i.e., transvection must occur. Disruption of pairing causes failure of ascospore progeny to mature. Transvection in Neurospora, unlike in Drosophila, occurs immediately before meiosis, and can be demonstrated between wild-type alleles.
Collapse
Affiliation(s)
- R Aramayo
- Department of Biomolecular Chemistry, University of Wisconsin, Madison 53706, USA
| | | |
Collapse
|