Genetic and Molecular Dissection of Meiotic Silencing by Unpaired DNA

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The overall goal of this project is to delineate the mechanism of Meiotic Silencing by Unpaired DNA (MSUD), a novel gene silencing system in Neurospora crassa. MSUD operates during the brief period of diploidy and the subsequent meiotic divisions in the sexual phase of the life cycle. The diploid cell examines the entire genome and compares the pairing of any DNA segment with its homologue during the homologous pairing stage. Any gene-sized or larger segments of DNA not paired with a homologous sequence generates a sequence-specific signal, which subsequently silences the expression of this unpaired DNA, as well as any sequences homologous to it, whether they are paired or not. Since an RNA-directed RNA polymerase (and presumably a double-stranded RNA species) is required for this process, MSUD is likely to depend on the specific destruction of mRNA transcripts, a mechanism shared by RNA interference (RNAi) and other post-transcriptional gene silencing systems. Owing to its ability to compare the genomes of two mating partners, MSUD represents a defense system for the maintenance of genome integrity as well as a possible isolation mechanism for speciation. N. crassa is an excellent model organism to assess the process of meiotic silencing because of its superior genetics and mutant selection, the ease of molecular techniques, and the availability of full genome sequence information. Genetics, cell biology, and other approaches will be used to identify the machinery and the mechanistic steps required for the meiotic silencing system. The study of MSUD in N. crassa will provide an excellent model for the delineation of the mechanism targeting unpaired DNA for silencing during meiosis, a process that could be important for imprinted X-chromosome inactivation and numerous other phenomena. Since RNAi has tremendous potential as an experimental tool to reveal gene functions, the understanding of MSUD and other RNA-based silencing systems could have a broad impact on research in all areas of biology. Furthermore, the P.I. is involved in a number of teaching and mentoring activities and is registered as a mentor for the Ronald McNair Scholars Program, which aims to promote graduate enrollment for underprivileged first-generation college students and members of underrepresented groups.