Annabelle Couthier1, Theresa Grana2, Aileen Flett1, Jeff Hardin2 and Jonathan Pettitt1 Epidermal morphogenesis is responsible for the change in shape of the C. elegans embryo from an ovoid into a worm, and involves two cadherin-dependent events: ventral enclosure and elongation. We have previously shown that animals homozygous for a hypomorphic alpha-catenin mutation (
fe4) provide a sensitive genetic background to identify molecules that contribute to cadherin-catenin complex function (Pettitt et al., 2003). These primary results have provided the rationale for a genome-wide RNAi screen for C. elegans genes whose loss of function enhances the
fe4 phenotype (Cox and Hardin, 2005, personal communication). We have recently completed a screen of Chromosome III, from which we identified 17 genes whose knock-down by RNAi gives a wild-type phenotype in N2, but which enhances the penetrance and severity of the
fe4 mutation. Most of the genes have homologues in other animal phyla: these include molecules predicted to be involved in cell adhesion and actin organisation, and two genes encoding conserved proteins of unknown function. We have focused our attention on five molecules due to their possible involvement in cell adhesion and actin organisation, and their level conservation with molecules from other phyla. These molecules are: FLI-1 (homologue of Drosophila Flightless I), TAG-213 (homologue of one of the Tho complex proteins), Y71H2AM.17 (contains a HMG box domain and is related to SWI/SNF proteins), F26F4.1 and ZK637.2 (both are of unknown function but are highly conserved across species). We are in the process of determining the cellular and molecular basis of the genetic interactions between these genes and
hmp-1. For instance, regulators of gene expression (i.e
tag-213 and Y71H2AM.17) may directly regulate the expression of cadherin-catenin complex components, or may result in partial defects in epidermal differentiation.. FLI-1 localises to the cytoplasm of hypodermal cells in embryos undergoing morphogenesis. As has been found previously (Lu and Lundquist, IWM 2005), it is also expressed throughout postembryonic development in pharyngeal and muscle cells, and in neurons. We believe FLI-1 contributes to the regulation of actin dynamics at cadherin junctions, such that when
fli-1 function is reduced in
hmp-1(
fe4) worms (which already display minor defects in actin filament organisation), elongation is severely compromised. We are currently examining genetic interactions between
fli-1 and genes encoding other proteins thought to modulate actin filaments at cadherin junctions.