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Controlling Events in Meiosis Telephone: (919) 966-5576 E-mail: pukkila@unc.edu Office: 202 Fordham Hall Mailing Address:
Professor (Initial Appointment: 1979) |
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The source of specificity for accurate chromosome pairing during meiosis is not understood, even though homologous pairing is essential for the production of viable gametes. My laboratory has pioneered the use of the basidiomycete fungus Coprinus cinereus as a model system for the genetic control of chromosome pairing and synapsis because many features of the C. cinereus life cycle facilitate such studies. Meiosis occurs synchronously in this mushroom, which is easily cultivated on defined medium. Certain features of the mating system greatly facilitate the recovery of recessive mutations that completely block meiosis and/or spore formation, which has enabled us and others to undertake extensive genetic analyses of meiosis. The methods we developed for DNA-mediated transformation have been used both to disrupt genes as well as to complement induced mutations. Perhaps the most novel and surprising finding to date has been our observation that chromosome synapsis does not depend on the completion of pre-meiotic DNA replication in this system. We also demonstrated that simultaneous synapsis with two pairing partners in triploid nuclei does depend on the presence of sister chromatids, revealing the capacity for independent synaptic behavior of sister chromatids. Others have gone on to show that synapsis of unreplicated chromosomes can occur in the absence of genes that are required for the synapsis of replicated chromosomes in this system. Most recently, my lab has turned to genomic analyses in this emerging model organism. C. cinereus was one of 7 “high priority” fungi selected to be sequenced by the Fungal Genomics Initiative at the Broad (formerly Whitehead) Institute because of the insights the comparative analysis is likely to provide on the development of multicellularity and coordinated cell behavior within a single phylum. The draft sequence was released in July, 2003 using DNA prepared in my laboratory. My lab heads a collaborative project to close the genome, annotate it using additional cDNA sequences and new ab initio gene prediction algorithms, and produce a high-resolution genetic map. (Click here to view the C. cinereus genome database.) Additionally, we are involved in a collaborative project to produce a microarray that will enable the extraordinary temporal resolution of meiosis in this organism to be analyzed at the transcriptional level. These studies are essential since sequence conservation of many genes essential for meiosis is poor. The transcriptional profiling in conjunction with "reverse-genetic" techniques will allow an unbiased approach to the analysis of genes essential for meiotic chromosome behavior. The genes of most interest to us (currently defined only by mutations) are those that are involved in efficient epigenetic alterations of duplicated DNA sequences and also for proper meiotic pairing. The epigenetic alterations involve DNA methylation which has an unusual and interesting specificity in C. cinereus distinct from that found in other fungi. The system allows analysis of chromosome pairing at the DNA level. In addition, we intend to use the high resolution genetic map we are constructing as a part of the genome project to identify localized sub-telomeric sites of crossing-over. It is remarkable that the tiny chromosomes of C. cinereus exhibit patterns of cross-over distribution that are identical to those found in genomes with over 1,000 times the amount of DNA. However, in C. cinereus, the cis- and trans- acting factors responsible for this distribution should be amenable to experimental analysis in ways that are not possible in other organisms. | |
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