Cytoplasmic regulation of mRNA/protein complexes (mRNPs) is important to numerous events in animal development but is poorly understood. In C. elegans, mRNP control is critical for germline and embryonic development. We found that several different RNA-binding proteins tightly repress Notch/glp-1 and other mRNAs at different stages of oocyte and embryonic development. These RNA-binding regulators function through distinct 3 UTR elements in
glp-1 mRNA. Interestingly, repressed
glp-1 mRNA and two of these proteins (GLD-1 and PUF-5) were found to co-localize with regulated granules during oogenesis. Other repressed mRNAs were also targeted to these granules, but translationally active mRNAs were not. Large mRNP particles have recently been found in multiple organisms and include processing bodies (P bodies), stress granules, germ granules and neuronal granules. These various mRNP granules share homologous components and may be sites of translational repression and degradation of mRNAs. Indeed we found that the P body/Stress granule factors CGH-1 (RCK/Dhh1), CAR-1 (RAP55/Trailerhitch), and AIN-1 (GW protein) co-localized with
glp-1 mRNA and its regulators in large granules upon oocyte arrest. These observations suggest the hypothesis that during oogenesis specific RNA binding proteins bind to 3UTR elements and target mRNAs to P body or stress granule-like mRNP granules, and that these granules participate in mRNA repression. In support of this idea, the
glp-1 3 UTR was sufficient to target injected reporter mRNA to these granules. Furthermore, RNAi of CAR-1 and CGH-1 disrupted granule morphology and caused ectopic GLP-1 expression in oocytes. However several observations suggest complexity of mRNP granules and their control. (i) Germline mRNPs had different compositions and morphologies at different stages of oogenesis. (ii) CAR-1 RNAi disrupted GLP-1 repression only during late stages of oogenesis, when PUF-5 functions. (iii) CAR-1 and CGH-1 loss altered oocyte mRNP granule morphology in different ways. (iv) mRNP granules changed in size and composition upon oocyte arrest and following fertilization. (v) At least two kinds of granules were detected within arrested oocytes; one enriched for the decapping enzyme DCP-2 (a P body marker), and larger granules enriched for other P body/stress granule factors and repressed mRNAs. Collectively, these findings suggest that mRNP granules are diverse and are dynamically controlled during development. Notch/glp-1 mRNA may be controlled by different mechanisms at different developmental stages.