Large P body-like RNPs form in C. elegans oocytes in response to arrested ovulation, heat shock, osmotic stress, and anoxia and are regulated by the major sperm protein pathway

Abstract

As Caenorhabditis elegans hermaphrodites age, sperm become depleted, ovulation arrests, and oocytes accumulate in the gonad arm. Large ribonucleoprotein (RNP) foci form in these arrested oocytes that contain RNA-binding proteins and translationally masked maternal mRNAs. Within 65 min of mating, the RNP foci dissociate and fertilization proceeds. The majority of arrested oocytes with foci result in viable embryos upon fertilization, suggesting that foci are not deleterious to oocyte function. We have determined that foci formation is not strictly a function of aging, and the somatic, ceh-18, branch of the major sperm protein pathway regulates the formation and dissociation of oocyte foci. Our hypothesis for the function of oocyte RNP foci is similar to the RNA-related functions of processing bodies (P bodies) and stress granules; here, we show three orthologs of P body proteins, DCP-2, CAR-1 and CGH-1, and two markers of stress granules, poly (A) binding protein (PABP) and TIA-1, appear to be present in the oocyte RNP foci. Our results are the first in vivo demonstration linking components of P bodies and stress granules in the germ line of a metazoan. Furthermore, our data demonstrate that formation of oocyte RNP foci is inducible in non-arrested oocytes by heat shock, osmotic stress, or anoxia, similar to the induction of stress granules in mammalian cells and P bodies in yeast. These data suggest commonalities between oocytes undergoing delayed fertilization and cells that are stressed environmentally, as to how they modulate mRNAs and regulate translation.

A Genomewide RNAi Screen for Genes That Affect the Stability, Distribution and Function of P Granules in Caenorhabditis elegans

“…The different locations and morphologies of cytoplasmic RNA accumulations and enlarged P granules in csr-1(RNAi) suggest that P granules are not the sites of excessive RNA accumulation. Previous studies have shown that depletion of sperm and arrested ovulation cause RNA to accumulate in the rachis; this phenotype is regulated by the major sperm protein pathway (Schisa et al 2001;Jud et al 2008). csr-1(RNAi) animals exhibited no obvious defects in fertilization or ovulation, suggesting that RNA accumulation in csr-1(RNAi) animals is not caused by loss of the major sperm protein pathway.…”

Translational Control in the Caenorhabditis elegans Germ Line

“…For example, in response to heat stress, key eIFs are phosphorylated, which correlates with a general reduction in the abundance of translating ribosomes (Nousch and Eckmann, unpublished data). A different and more indirect indication is the presence of large cytoplasmic RNP structures in response to environmental stresses (Jud et al 2008 ) . The protein composition of these structures resemble in their protein components and dynamics stress granules of yeast or mammalian cells, which are thought to contain repressed translation initiation complexes (Buchan et al 2011 ;Kedersha et al 2005 ) .…”

RNA recognition by the embryonic cell fate determinant and germline totipotency factor MEX-3

“…After the four-cell stage, MEX-3 begins to disappear from the embryo. A small amount of MEX-3 remains in the posterior germline lineage, where it localizes to RNA-rich bodies including germ granules in early embryos and CAR-1/CGH-1 granules in late oocytes (3,(5)(6)(7).…”