When sperm become depleted in C. elegans hermaphrodites, ovulation arrests and oocytes accumulate in the gonad arm. During meiotic arrest, the distribution of RNA and RNA-binding proteins changes dramatically in oocytes. Several of these molecules transition from being uniformally distributed throughout the cytoplasm, to forming large cytoplasmic foci known as ribonucleoprotein (RNP) granules during arrested ovulation or environmental stresses. The function of RNP granules has yet to be elucidated, but they are hypothesized to protect maternal mRNA during periods of arrest or stress. Our lab has been conducting an RNAi screen to identify genes that are required for the assembly of RNP granules in meiotically-arrested oocytes, and we have identified over 50 genes to date that are necessary for the RNA-binding protein MEX-3 to assemble into large granules. We are currently characterizing these genes and exploring the gene families identified in the screen. One interesting finding was the beta-tubulin genes,
ben-1 and
tbb-1. Previous work by the Greenstein lab has shown that microtubules become cortically enriched in meiotically-arrested oocytes1, and this localization is similar to that of RNP granules. Interestingly, in yeast and mammalian cells, disruption of microtubules stimulates the formation of P bodies (processing bodies), while such disruption results in a failure of stress granules to form. Taken together, these findings suggest the possibility that microtubules have a role in regulating the assembly of oocyte RNP granules. We are currently taking a pharmacological approach to complement the RNAi studies and assessing the role of microtubules in the assembly and dissociation of RNP granules in both meiotically-arrested and stressed oocytes. Our overall goal is to better understand the role of the cytoskeleton in the dynamics of RNPs in oocytes. 1Harris, J.E.,et al., 2006. Major sperm protein signaling promotes oocyte microtubule reorganization prior to fertilization in Caenorhabditis elegans. Dev. Biol. 299, 105-121.