Vulval differentiation in C. elegans is mediated by an Epidermalgrowth factor (EGF)- EGF receptor (EGFR) signaling pathway. I havecloned unc-101, a negative regulator of vulval differentiation of the nematodeC. elegans. unc-101 encodes a homolog of AP47, the medium chain of thetrans-Golgi clathrin-associated protein complex. This identity wasconfirmed by cloning and comparing sequence of a C. elegans homolog ofAP50, the medium chain of the plasma membrane clathrin-associatedprotein complex. I provided the first genetic evidence that the trans-Golgiclathrin-coated vesicles are involved in regulation of an EGF signalingpathway. Most of the unc-101 alleles are deletions or nonsense mutations,suggesting that these alleles severely reduce the unc-101 activity. A hybridgene that contains parts of unc-101 and mouse AP4 7 rescued at least twophenotypes of unc-101 mutations, the Unc and the suppression of vulvalessphenotype of let-23(sy1) mutation. Therefore, the functions of AP47 areconserved between nematodes and mammals.
unc-101 mutations can cause a greater than wild-type vulvaldifferentiation in combination with certain mutations in sli-1, anothernegative regulator of the vulval induction pathway. A mutation in a newgene, rok-1, causes no defect by itself, but causes a greater than wild-typevulval differentiation in the presence of a sli-1 mutation. The unc-101; rok-1;sli-1 triple mutants display a greater extent of vulval differentiation than anydouble mutant combinations of unc-101, rok-1 and sli-1. Therefore, rok-1locus defines another negative regulator of the vulval induction pathway.
I analyzed a second gene encoding an AP47 homolog in C. elegans.This gene, CEAP47, encodes a protein 72% identical to both unc-101 andmammalian AP47. A hybrid gene containing parts of unc-101 and CEAP47sequences can rescue phenotypes of unc-101 mutants, indicating that UNC-101 and CEAP47 proteins can be redundant if expressed in the same set ofcells.
