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

Forkhead box O transcription factors (FoxO/DAF-16 in C. elegans) play a conserved role in metabolism, aging, and development. Canonically, FoxO/DAF-16 is inhibited by insulin receptor signaling (DAF-2 in C. elegans) but also can be regulated by other pathways. Indeed, severe loss-of-function daf-2; daf-16 double mutants have high embryonic lethality despite low lethality in either single mutant; the cause of this synthetic lethality is not known. We used genetics and quantitative imaging to study DAF-16 in early C. elegans embryos. Before the 8-cell stage, DAF-16 localized uniformly at low levels in all nuclei. In 8-cell to 64-cell embryos, DAF-16 became enriched in only 1-2 cell nuclei, which lineage tracing revealed to be germ lineage cells. This DAF-16 patterning required germ fate determinants, the phospholipid phosphatase PTEN/DAF-18, but was DAF-2 activity- and maternal age-independent. We found that severe loss-of-function daf-16; daf-2 double mutant embryos failed to undergo morphogenesis with major mitotic chromosome segregation defects as early as the 1-cell stage. Together, our results identify a novel germ lineage-specific patterning of DAF-16 and a canonical DAF-2 signaling-independent role for DAF-16 during early embryogenesis.