Pgc suppresses the zygotically acting RNA decay pathway to protect germ plasm RNAs in the embryo.

Specification of germ cells is pivotal to ensure continuation of animal species. In many animal embryos, germ cell specification depends on maternally supplied determinants in the germ plasm. () mRNA is a component of the germ plasm. encodes a small protein that is transiently expressed in newly formed pole cells, the germline progenitors, where it globally represses mRNA transcription. is also required for pole cell survival, but the mechanism linking transcriptional repression to pole cell survival remains elusive. We report that pole cells lacking show premature loss of germ plasm mRNAs, including the germ cell survival factor , and undergo apoptosis. We found that pole cells misexpress multiple miRNA genes. Reduction of miRNA pathway activity in embryos partially suppressed germ plasm mRNA degradation and pole cell death, suggesting that Pgc represses zygotic miRNA transcription in pole cells to protect germ plasm mRNAs. Interestingly, germ plasm mRNAs are protected from miRNA-mediated degradation in vertebrates, albeit by a different mechanism. Thus, independently evolved mechanisms are used to silence miRNAs during germ cell specification.