Distinct and redundant functions of mu 1 medium chains of the AP-1 clathrin-associated protein complex in the nematode Caenorhabditis elegans

In the nematode Eaenorhabditis elegans, there exist two mu 1 medium chains of the AP-1 clathrin-associated protein complex. Mutations of unc-101, the gene that encodes one of the mu 1 chains, cause pleiotropic effects (Lee et nl., 1994). In this report, we identified and analyzed the second mu 1 cha in gene, apm-1. Unlike the mammalian homologs, the two medium chains are ex pressed ubiquitously throughout development. RNA interference (RNAi) experi ments with apm-1 showed that apm-1 and unc-101 were redundant in embryogene sis and in vulval development. Consistent with this, a hybrid protein conta ining APM-1, when overexpressed, rescued the phenotype of an unc-101 mutant . However, single disruptions of apm-1 or unc-101 have distinct phenotypes, indicating that the two medium chains may have distinct functions. RNAi of any one of the small or large chains of AP-1 complex (sigma 1, beta 1, or gamma) showed a phenotype identical to that caused by the simultaneous disr uption of unc-101 and apm-1, but not that by single disruption of either ge ne. This suggests that the two medium chains may share large and small chai ns in the AP-1 complexes. Thus, apm-1 and unc-101 encode two highly related mu 1 chains that share redundant and distinct functions within AP-1 clathr in-associated protein complexes of the same tissue.