Molecular and genetic analysis of meiotic silencing in C. elegans

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The overall goal of this project is to understand the molecular mechanisms that maintain germline integrity and ensure the production of functional gametes. The research specifically focuses on meiotic silencing of unpaired (unsynapsed) DNA in the nematode, Caenorhabditis elegans. During meiosis in animals and fungi, the expression of genes on unpaired chromosomes is repressed. This broadly conserved phenomenon may be important for genome defense, maintenance of genome integrity, and/or segregation of unpaired chromosomes, as well as germline development. In C. elegans (as in more complex animals), unpaired DNA is repressed at the chromatin level. One hallmark of this repression is the accumulation of a histone modification associated with transcriptional silencing, dimethylation of histone H3 on lysine 9 (H3K9me2). Dr. Maine's laboratory has explored the mechanism of H3K9me2 accumulation during meiosis in C. elegans and found that it requires EGO-1, a putative RNA-directed RNA polymerase (RdRP). They have used gene expression profiling and other approaches to identify transcripts that are elevated in the ego-1 mutant germ line, and predict that targets of EGO-1 chromatin regulation are among these genes. The Maine laboratory has also shown that EGO-1 is required for many aspects of germline development and, ultimately, for fertility. Taken together, these results suggest that meiotic silencing may have a developmental function. Based on the data, Dr. Maine and her colleagues proposed two alternative models for the mechanism of H3K9me2 accumulation on unpaired DNA. In this project, specific predictions of these models will be tested. In Objective 1, a candidate gene approach will be used to identify additional components of the meiotic silencing machinery. In Objective 2, genetic screens will be used to recover mutations in meiotic silencing components. This unbiased approach complements Objective 1 and will allow the recovery of mutations in genes that might not be predicted to function in meiotic silencing. In Objective 3, targets of EGO-1-mediated silencing will be identified. This project will provide information that is critical for understanding several areas of biology, including reproductive biology (and ultimately, fertility). In the last 8-10 years, biologists have discovered that RNA molecules participate in processes that regulate protein production in cells. In this project the investigator will study a newly identified mechanism of transcriptional regulation that is used during the formation of gametes (sperm and eggs). Furthermore, the investigator will fully integrate her research into her teaching and mentoring of both graduate and undergraduate students.