Embryos depend on maternally-encoded mRNAs and proteins until the onset of zygotic transcription. In early embryos, many maternal RNAs are rapidly degraded in somatic blastomeres, but maintained in germline blastomeres. To understand how this difference is established, we have investigated the distribution of P-bodies in early embryos. P-bodies are cytoplasmic RNA-protein complexes that have been implicated in mRNA degradation and translational repression in yeast and mammalian cells. To visualize P bodies, we used an antibody against DCAP-2 (Lall et al., 2005) and we generated GFP fusions to several other P-body proteins (DCAP-1, PATR-1, CGH-1, LSM-1, LSM-3). We find that all localize to numerous granules distributed throughout the cytoplasm of early embryos. We refer to these granules as PATR-1 granules. PATR-1 is the C. elegans homolog of yeast Pat1p, an essential component of P-bodies, which functions both as a general translational repressor and as an activator of mRNA decapping (reveiwed in Coller and Parker, 2004). PATR-1 granules are present in both somatic and germline blastomeres, and are distinct from P granules, which are only in germline blastomeres and do not contain PATR-1. Direct visualization of endogenous PATR-1 by antibody staining is currently underway. Using live imaging, we find that PATR-1 granules behave differently in germline versus somatic blastomeres. In germline blastomeres, PATR-1 granules associate with P granules, often forming discontinuous shells around PGL-1-positive cores. In somatic cells, PATR-1 granules loose their PGL-1 cores and eventually recruit other P-body components, including LSM proteins. In yeast, LSM proteins form a complex with Pat1p to promote mRNA decapping and degradation, raising the possibility that PATR-1/LSM granules could regulate maternal RNA degradation. Consistent with this possibility, we find that 1) recruitment of LSM to PATR-1 granules coincides with the onset of maternal RNA degradation and 2) depletion of
let-711, a subunit of the CCR4/POP2/NOT deadenylation complex, blocks recruitment of LSM to PATR-1 granules and also prevents maternal RNA degradation. We conclude that PATR-1 granules likely correspond to yeast and mammalian P-bodies, and that these structures are regulated differently in the soma versus germline, providing a possible explanation for the differential stability of maternal RNAs in the two cell types.