ZYGOTIC DROSOPHILA E-CADHERIN EXPRESSION IS REQUIRED FOR PROCESSES OFDYNAMIC EPITHELIAL-CELL REARRANGEMENT IN THE DROSOPHILA EMBRYO

Dynamic epithelial reorganization is essential for morphogenesis of va rious organs. In Drosophila embryos, for example, the Malpighian tubul e is generated by cellular rearrangement of a preexisting epithelium a nd the tracheal network is formed by outgrowth, branching, and fusion of epithelial vesicles. Here we report that the previously identified locus shotgun (shg) encodes DE-cadherin, an epithelial cell-cell adhes ion molecule of the classic cadherin type and that zygotic shg mutatio ns rather specifically impair processes of the dynamic epithelial morp hogenesis. In the mutants, the Malpighian tubule disintegrated into sm all spherical structures, and the tracheal network formation was block ed in selected steps. The malformation of these organs could be rescue d by overexpression of DE-cadherin cDNA under a heat shock promoter. U nexpectedly, the zygotic null condition did not severely affect genera l epithelial organization; most epithelial tissues maintained not only their cell-cell associations but also their apicobasal polarity in th e mutants. The zygotic null mutant retained a certain level of materna lly derived DE-cadherin molecules until the end of embryogenesis. Thes e results suggest that zygotic DE-cadherin expression is critical for the rearrangement processes of epithelial cells, whereas the maternall y derived DE-cadherin may serve only for the maintenance of the static architecture of the epithelia.