Fig. 7.

Epb41l5 and DeltaD compete for Mib1 binding. (A) Epb41l5 protein is stabilized in DAPT-treated embryos. mRNA encoding Myc-Epb41l5 and HA-mRFP was co-injected into wild-type embryos. Embryos were treated with DAPT for 4 h. HA-mRFP was used for standardization. (B) Co-expression with DeltaD inhibits Epb41l5-Mib1 interaction in HEK293 cells. When HA-Delta is co-expressed, a smaller amount of myc-Mib1 is co-immunoprecipitated with Flag-Epb41l5 in a dose-dependent manner. No HA-Delta is co-immunoprecipitated by Flag-Epb41l5. The destabilization of Flag-Epb41l5 by Mib1 is rescued by co-expression of HA-DeltaD. (C) Co-expression of Flag-Epb41l5 reduces DeltaD-Mib1 interaction. When Flag-Epb41l5 is co-expressed, a smaller amount of Myc-Mib1 is co-immunoprecipitated with HA-DeltaD. No Flag-Epb415 is co-immunoprecipitated by HA-DeltaD. Mib1 or Epb41l5 does not change the stability of HA-DeltaD. (D) A model for how Epb41l5 might coordinate specification and differentiation of NPCs selected to become neurons. In unspecified NPCs (yellow), with relatively low levels of proneural factors and Delta, more Mib1 is available for ubiquitylation and degradation of Epb41l5. The resulting relatively low level of Epb41l5 might keep AJCs stable. In NPCs specified to become neurons (orange), with high levels of proneural factors and Delta, a greater proportion of Mib1 interacts with Delta and less with Epb41l5. This might reduce Mib1-dependent Epb41l5 degradation, allowing Epb41l5 to accumulate and facilitate disassembly of AJCs and differentiation of NPCs.