Germline apoptosis is essential for oogenesis in organisms as diverse as nematodes and human. However, molecular mechanisms that control the expression of core apoptotic machinery components in the germline have been poorly understood. Here we present evidence that the conserved RNA-binding protein PUF-8 functions redundantly with TOCA-2, a protein involved in endocytosis, to control physiological germline apoptosis. Worms lacking both PUF-8 and TOCA-2 are sterile; their germlines contain considerably less germ cells and show increased apoptosis. An RNAi screen on
puf-8;
toca-2 double mutant background revealed that the depletion of the mitochondrial Rho GTPase MIRO-1, which is involved in mitochondrial biogenesis, or the dynamin-related protein DRP-1, which promotes mitochondrial fission, restores fertility in
puf-8;
toca-2 double mutant worms. In transgenic worms expressing the
drp-1::gfp transgene, depletion of both PUF-8 and TOCA-2 dramatically increases mitochondrial and cytoplasmic levels of DRP-1::GFP. Examination of
drp-1::gfp expression in the
puf-8 and
toca-2 single mutants reveals that PUF-8 negatively regulates DRP-1 expression, whereas TOCA-2 suppresses its mitochondrial localization.
Earlier work has shown that PUF-8 suppresses the translation of
pal-1 mRNA, which encodes a somatic transcription factor, in the distal germline. In somatic cells, PAL-1 activates the transcription of
ced-3, a core component of the apoptotic machinery. Our in situ hybridization and immunostaining results show that CED-3 is misexpressed in the
puf-8 germline in a PAL-1-dependent manner. Further, depletion of PAL-1 reduces the number of apoptotic nuclei in the
puf-8 mutant germline. Together, our results indicate that PUF-8 regulates germline physiological apoptosis by two ways: 1. It suppresses DRP-1 expression, which is known to promote mitochondrial fission and 2. through its effect on
pal-1 mRNA translation, PUF-8 suppresses
ced-3 transcription.