The hindsight gene is required for epithelial maintenance and differentiation of the tracheal system in Drosophila

During animal development, morphogenesis of tissues and organs requires dyn amic cell shape changes and movements that are accomplished without loss of epithelial integrity. Data from vertebrate and invertebrate systems have i mplicated several cell surface and cytoskeleton-associated molecules in the establishment and maintenance of epithelial architecture, but there has be en little analysis of the genetic regulatory hierarchies that control epith elial morphogenesis in specific tissues. Here we show that the Drosophila H indsight nuclear zinc-finger protein is required during tracheal morphogene sis for the maintenance of epithelial integrity and assembly of apical extr acellular structures known as taenidia. In hindsight (hnt) mutants tracheal placodes form, invaginate, and undergo primary branching as well as early fusion events. Starting at midembryogenesis, however, the tracheal epitheli um collapses or expands to give rise to sacs of tissue. While a subset of h ut mutant tracheal cells enters the apoptotic pathway, genetic suppression of apoptosis indicates that this is not the cause of the epithelial defects . Surviving hnt mutant tracheal cells retain cell-cell junctions and a norm al subcellular distribution of apical markers such as Crumbs and DE-Cadheri n. However, taenidia do not form on the lumenal surface of tracheal cells. While loss of epithelial integrity is a common feature of crumbs, stardust, and hut mutants, defective assembly of taenidia is unique to hut mutants. These data suggest that HNT is a tissue-specific factor that regulates main tenance of the tracheal epithelium as well as differentiation of taenidia. (C) 2000 Academic Press.