Maternal Nanos represseshid/skl-dependent apoptosis to maintain the germ line inDrosophilaembryos

Abstract

Nanos (Nos) is an evolutionarily conserved protein essential for the survival of primordial germ cells. InDrosophila, maternal Nos partitions into pole cells and suppresses apoptosis to permit proper germ-line development. However, how this critical event is regulated by Nos has remained elusive. Here, we report that Nos represses apoptosis of pole cells by suppressing translation ofhead involution defective(hid), a member of the RHG gene family that is required for Caspase activation. In addition, we demonstrate thathidacts in concert with another RHG gene,sickle(skl), to induce apoptosis. Expression ofsklis induced in pole cells by maternaltao-1, aste20-like serine/threonine kinase. Tao-1-dependentsklexpression is required to potentiatehidactivity. However,sklexpression is largely suppressed in normal pole cells. Once the pole cells lack maternal Nos, Tao-1-dependentsklexpression is fully activated, suggesting thatsklexpression is also restricted by Nos. These findings provide the first evidence that the germ line is maintained through the regulated expression of RHG genes.