Echinoid Regulates Tracheal Morphology and Fusion Cell Fate in Drosophila

Morphogenesis of the Drosophila embryonic trachea involves a stereotyped pattern of epithelial tube branching and fusion. Here, we report unexpected phenotypes resulting from maternal and zygotic (M/Z) loss of the homophilic cell adhesion molecule Echinoid (Ed), as well as the subcellular localization of Ed in the trachea. ed(M/Z) embryos have convoluted trachea reminiscent of septate junction (SJ) and luminal matrix mutants. However, Ed does not localize to SJs, and ece embryos have intact SJs and show normal luminal arxumulation of the matrix-modifying protein Vermiform. Surprisingly, tracheal length is not increased in edmm mutants, but a previously undescribed combination of reduced intersegmental spacing and deep epidermal grooves produces a convoluted tracheal phenotype. In addition, edmm mutants have unique fu ion defects involving supernumerary fusion cells, ectopic fusion events and atypical branch breaks. Tracheal-specific expression of Ed rescues these fusion defects, indicating that Ed acts in trachea to control fusion cell fate. Developmental Dynamics 239:2509-2519, 2010. (C) 2010 Wiley-Liss, Inc.