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 express ed in most embryonic epithelia and decreases in cells that undergo epi thelial-mesenchymal transitions like the mesoderm or neural precursors . Removal of both maternal and zygotic shg function leads to severe de fects in all epithelia expressing shg, suggesting that DE-cadherin, si milar to vertebrate classic cadherins, has a crucial role for the form ation and/or maintenance of epithelial tissues. Interestingly, the ana lysis of different shg alleles indicates that the requirement for shg in a given epithelium depends on the degree of its morphogenetic activ ity. Only epithelia involved in extensive morphogenetic movements requ ire zygotic shg function in addition to maternal expression. In suppor t of this view we find that suppression of morphogenetic movements res cues the zygotic shg phenotype. We find that in zygotic shg nulls the level of D alpha-catenin and Armadillo at adherens junctions is dramat ically reduced, surprisingly also in epithelia that differentiate norm ally and possess a zonula adherens.