Canonical insulin-like receptor DAF-2 signaling-independent patterning and role for FoxO/DAF-16 in early embryos

Forkhead box O (FoxO) transcription factors (DAF-16 in Caenorhabditis elegans) regulate aging, metabolism, and development. Canonically, FoxO/DAF-16 activity is regulated by insulin/insulin-like receptor (DAF-2) signaling, which inhibits its nuclear localization. In C. elegans, strong loss-of-function daf-16; daf-2 double mutants are embryonic lethal. However, because daf-2 null mutants are maternally rescued as embryos and then arrest as larvae, the role of DAF-2 signaling in embryogenesis is unknown. We therefore used quantitative imaging and genetics to study DAF-16 and DAF-2 in early C. elegans embryos. DAF-16 was uniformly low in all nuclei at the 2- to 4-cell stage. From the 8- to 64-cell stage, DAF-16 became enriched in 1-2 nuclei of germ lineage cells. This patterning required germ fate determinants and the lipid phosphatase PTEN/DAF-18, but not DAF-2 kinase activity, and was independent of maternal age. We also found that daf-16; daf-2 double mutant embryos failed morphogenesis, with severe mitotic defects as early as the 1-cell stage. This work identifies germ lineage-specific DAF-16 patterning and a role for DAF-16 in early embryogenesis that is independent of canonical DAF-2 signaling.