The cadherins are a major class of membrane proteins with prominent roles in cell adhesion, and the regulation of tissue organisation and morphogenesis. The C. elegans genome encodes 13 cadherins, including representatives of the major cadherin sub-types that are conserved between insects and vertebrates: the so-called classic, Fat-like, Flamingo and calsyntenin classes. The function of most of these in C. elegans is still unknown, or poorly understood, mainly because clear loss-of-function mutations have been isolated for only a few. As is true for the cadherin families of other organisms, most is known about classic cadherin function. C. elegans has a single classic cadherin gene, which encodes two isoforms: one predominantly expressed in the nervous system, and the other more broadly expressed in all epithelial cells. The epithelial cadherin-catenin complex appears to be functionally equivalent to that found in Drosophila and vertebrates, and is critically required for embryonic morphogenesis. Mutant phenotypes have also been described for cdh-3
, which encode a Fat-like cadherin, and the C. elegans Flamingo homologue, respectively. cdh-3
mutants display incompletely penetrant defects in the morphogenesis of hyp10
, the cell which forms the tip of the tail, and the excretory duct cell; though the mechanistic role of CDH-3 in these processes is not known. FMI-1 is required during neuronal development consistent with the known role of the Drosophila homologue in controlling tissue polarity. Five of the cadherins have no obvious homologues beyond the nematodes, and thus may be phyla-specific.