In the nematode Caenorhabditis elegans, there exist two μ1 medium chains of the AP-1 clathrin-associated protein complex. Mutations of unc-101, the gene that encodes one of the μ1 chains, cause pleiotropic effects ( Lee et al., 1994 ). In this report, we identified and analyzed the second μ1 chain gene, apm-1. Unlike the mammalian homologs, the two medium chains are expressed ubiquitously throughout development. RNA interference (RNAi) experiments with apm-1 showed thatapm-1 and unc-101 were redundant in embryogenesis and in vulval development. Consistent with this, a hybrid protein containing APM-1, when overexpressed, rescued the phenotype of an unc-101 mutant. However, single disruptions ofapm-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 (ς1, β1, or γ) showed a phenotype identical to that caused by the simultaneous disruption of unc-101 andapm-1, but not that by single disruption of either gene. This suggests that the two medium chains may share large and small chains in the AP-1 complexes. Thus, apm-1 andunc-101 encode two highly related μ1 chains that share redundant and distinct functions within AP-1 clathrin-associated protein complexes of the same tissue.
Functional analysis of the single calmodulin gene in the nematode Caenorhabditis elegans by RNA interference and 4-D microscopy