Expression of the apoptosis inducer gene head involution defective in primordial germ cells of the Drosophila embryo requires eiger, p53, and loki function.

Nanos (Nos) is an evolutionarily conserved protein essential for the maintenance of primordial germ cells (PGCs). In Drosophila, the PGCs or pole cells express head involution defective (hid), which is required for caspase activation, but its translation is repressed by maternal Nos. In the absence of Nos activity, translation of hid mRNA into protein induces apoptosis in pole cells. However, it remains unclear how hid mRNA is regulated in pole cells. Here, we report that hid expression requires eiger (egr), a tumor necrosis factor ligand (TNF) homologue, which is induced in pole cells by decapentaplegic (dpp). In addition, we demonstrate that p53 and loki (lok), a damage-activated kinase known to be required for p53 phosphorylation, are both required for hid expression in pole cells. Since maternal lok mRNA is enriched in pole cells, it is possible that ubiquitously distributed p53 is activated in pole cells by maternal Lok. We propose that hid expression is activated in a pole cell-specific manner by loki/p53 and dpp/egr during embryogenesis.