UNIVERSITY OF MISSOURI SYSTEM

PROJECT SUMMARY Genetic and Molecular Dissection of Meiotic Silencing by Unpaired DNA The overall goal of this project is to delineate the mechanism of Meiotic Silencing by Unpaired DNA (MSUD; Shiu et al., 2001, Cell 107: 905-916), a novel gene silencing system first described in Neurospora crassa. Meiotic silencing operates in the sexual phase of a life cycle. During the chromosome pairing stage, the zygotic cell examines the entire genome and compares the pairing of any DNA segment with its pairing partner. Any gene-sized or larger segments of DNA not paired with a similar sequence generates a silencing signal, which subsequently suppresses the gene expression of this unpaired DNA, as well as any sequences homologous to it, whether they are paired or not. Meiotic silencing utilizes the specific destruction of mRNA transcripts, a mechanism known as RNA interference (RNAi). Neurospora is an excellent model organism to assess the process of meiotic silencing because of its superior genetics and mutant selection, the ease of its molecular techniques, and the availability of its full genome sequence information. Previous work in Neurospora has led to the discovery that DNA lacking a pairing partner in worms, mice, and humans are also targeted for silencing. The study of meiotic silencing will provide an excellent model for the delineation of the mechanism targeting unpaired DNA for silencing during meiosis, a process that is important for imprinted X-chromosome inactivation and programmed cell death during human gametogenesis. Genetics, cell biology, and other approaches will be used to identify the machinery and the mechanistic steps required for the meiotic silencing system. The objectives of this project are: 1. To characterize additional mutants that suppress MSUD. 2. To examine the properties of and interactions among components of the MSUD pathway. 3. To determine what makes the mating-type locus immune to MSUD. 4. To characterize the MSUD-suppressing Spore killer loci. Intellectual merit: RNAi has tremendous potential as a therapeutic approach to silence disease-causing genes and also as an experimental tool to unlock human gene functions. Since the study of meiotic silencing will likely uncover genes that are common to other RNAi pathways, the proposed activity should expand our understanding of silencing mechanisms in other organisms. Broader impact: To broaden the participation of underrepresented groups, the investigators of this project will recruit and train undergraduate students from non-Ph.D.-granting and minority-serving institutions. A postdoctoral training plan with an emphasis on scholar preparation and mentoring/teaching skills will also be implemented.

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