In both vertebrates and Drosophila a single protein, beta-catenin/Armadillo, is a key component of both Wnt signalling and cadherin-mediated cell adhesion. In C. elegans the signalling and adhesion functions of beta-catenin appear to have been distributed between separate proteins. HMP-2 appears to function exclusively in cadherin adhesion complexes, while BAR-1 and WRM-1 act in Wnt signalling pathways. We have identified three genes whose products interact with both BAR-1 and HMP-2 in yeast two hybrid screens. These genes have been designated
bin-1 , -2 and -3 ( b eta-catenin in teracting). The three genes encode related gene products that do not show any significant similarities to other non-worm proteins in the publicly available sequence databases. In order to determine the role of these genes we have examined the effect of depleting their function using RNA interference.
bin-1(RNAi) resulted in variable defects in hypodermal cell positioning, particularly in the seam and ventral hypodermis, often resulting in ventral enclosure, or elongation defects. Neither
bin-2(RNAi) nor
bin-3(RNAi) resulted in an obvious mutant phenotype, and neither did the double RNAi of both
bin-2 and
bin-3 . However, double RNAi of both
bin-1 and
bin-2 resulted in an enhancement in the penetrance and severity of the defects observed with
bin-1(RNAi) alone. RNAi of
bin-1 and
bin-3 resulted in a synthetic phenotype not seen in
bin-1(RNAi) animals. These embryos all arrested with very pronounced defects in the pattern of hypodermal cell junctions, and never initiated ventral enclosure. These results demonstrate that
bin-1 shares functions in regulating hypodermal patterning and morphogenesis with
bin-2 and
bin-3 . We do not know how these gene products act to regulate hypodermal development. They do not appear to regulate the activities of HMP-2 or BAR-1, since the mutant phenotypes of these genes do not cause the same phenotypes. We are currently attempting to determine whether the products of the bin genes can interact with other Armadillo repeat containing proteins, such as WRM-1, APR-1 and the C. elegans homologue of
p120 catenin, as well as examining where they are expressed.