P granules and control of germ cell development

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Abstract Germ cells carry out the reproductive function of multicellular organisms, and normal germ cell development ensures survival of the species. Germ granules are conserved cytoplasmic organelles of germ cells, essential for survival, differentiation, and function of these cells. Mutations in germ granule components or loss of their expression lead to infertility in model organisms and are associated with infertility in humans. By contrast, inappropriate expression of germ granule components in somatic cells is linked to carcinogenesis in humans. Many RNA-binding proteins and developmentally regulated mRNAs are found enriched in germ granules, leading to a hypothesis that these organelles function in regulation of mRNA stability or translational activity; yet, the molecular function of these organelles is still undefined. The nematode C. elegans has been instrumental for analysis of mRNA translational control in germline development. Through focusing on cofactors that promote localization of RNA-binding regulatory protein FBF-2 to germ granules (called P granules in this species) in germline stem cells we have generated a set of innovative tools that will address key mechanisms through which P granules regulate FBF-2 activity. By integrating genetic, molecular, biochemical and imaging-based approaches, we will: 1) Determine how FBF-2 interaction with a cofactor protein DLC-1 important for P granule localization impacts translational repression exerted by FBF-2; 2) Define the mechanisms of P granule remodeling that specifically degrade FBF-2 at the onset of meiosis when stem cells transition from proliferation to differentiation; 3) Determine the role of DLC-1 binding to core P granule components in regulation of stability of embryonic P granules and in recruitment of transient P granule components such as FBF-2 to adult germline P granules. Our experimental system is poised to reveal specific molecular mechanisms mediating the interplay between germ granules and translational regulation. Since germ granules are conserved organelles and our research focuses on conserved regulatory proteins, studies in this model system will provide critical insight into the causes of infertility in humans.