[
International Worm Meeting,
2007]
In the arrested oocytes of old-aged Caenorhabditis elegans hermaphrodites that are depleted of sperm, giant ribonucleoprotein (RNP) foci form. The RNP foci are composed of putative RNA-binding proteins and translationally repressed maternal mRNAs. Based on their components, we hypothesize that RNP foci function to maintain maternal mRNA stability, protect the integrity of oocytes, and/or regulate translation of maternal mRNAs while a worm waits for sperm. Because hermaphroditism is rare in the animal kingdom, we tested whether arrested ovulation and RNP foci formation occur in gonochoristic nematodes ancestral to C. elegans: C. remanei, C. sp. PS1010, C. sp. CB5161, and Rhabditella axei. We demonstrate that in multiple Caenorhabditis species, ovulation arrests in unmated females and RNP foci form in the arrested oocytes. These data suggest that a mechanism for preserving oocytes has been conserved from an ancestral gonochoristic state. We are currently expanding our studies to include additional nematode species outside the Caenorhabditis clade. Our hypothesis for the function of RNP foci in oocytes is similar to that for mammalian RNPs called stress granules. We are currently investigating whether orthologs of mammalian stress granule proteins co-localize to C. elegans RNP foci. Our results to date indicate that poly(A) binding protein (PABP-1) co-localizes with the RNA-binding protein, MEX-3, in oocyte foci. We also have preliminary data that large foci of MEX-3 form in non-arrested oocytes in response to heat shock, similar to the induction of stress granules in response to heat stress. We are currently characterizing the heat-shock-induced foci to determine how similar they are to the RNP foci that form in oocytes when sperm are absent.