Shotgun encodes Drosophila E-cadherin and is preferentially required during cell rearrangement in the neurectoderm and other morphogenetically active epithelia

Adhesion molecules of the cadherin superfamily have an important role during vertebrate development. The DE-cadherin homolog DE-cadherin is the first classic cadherin isolated from invertebrates. We report here that DE-cadherin is encoded by the shotgun (shg) gene. shg is expressed in most embryonic epithelia and decreases in cells that undergo epithelial-mesenchymal transitions like the mesoderm or neural precursors. Removal of both maternal and zygotic shg function leads to severe defects in all epithelia expressing shg, suggesting that DE-cadherin, similar to vertebrate classic cadherins, has a crucial role for the formation and/or maintenance of epithelial tissues. Interestingly, the analysis of different shg alleles indicates that the requirement for shg in a given epithelium depends on the degree of its morphogenetic activity. Only epithelia involved in extensive morphogenetic movements require zygotic shg function in addition to maternal expression. In support of this view we find that suppression of morphogenetic movements rescues the zygotic shg phenotype. We find that in zygotic shg nulls the level of D alpha-catenin and Armadillo at adherens junctions is dramatically reduced, surprisingly also in epithelia that differentiate normally and possess a zonula adherens.