The germline in C. elegans: origins, proliferation, and silencing.

Germ cells are essential for reproduction, yet the molecular mechanisms that underlie their unique development are only beginning to be understood. Here we review important events that lead to the establishment of the germline and the initiation of meiotic development in C. elegans. Formation of the germline begins in the pregastrulation embryo, where it depends on polarization along the anterior/posterior axis and on the asymmetric segregation of P granules and associated factors. During postembryonic development, the germline expands using the GLP-1/Notch signaling pathway to promote proliferation and regulate entry into meiosis. Throughout their development, germ cells also employ unique "silencing" mechanisms to regulate their genome and protect themselves against unwanted expression from repetitive sequences including transposable elements. Together these mechanisms preserve the health and reproductive potential of the germline.