Genetic regulation of salivary gland development in Drosophila melanogaster.

Studies of salivary gland development in the Drosophila embryo have revealed the morphogenic events by which the salivary gland tubes are formed, and identified the genes and genetic networks that regulate these events. Invagination of the salivary gland primordium occurs by an apical constriction mechanism regulated by the tyrosine kinase, Tec29, the transcription factors, Fork head and Huckebein, and Rho GTPase-mediated actomyosin contraction. After invagination is complete, transcriptional control of the apical membrane protein, Crumbs, by the transcription factors, Hairy, Hkb and Ribbon, and downregulation of Moesin-dependent apical stiffness promotes elongation of the salivary gland lumen. Integrin-mediated adhesion between the gland and surrounding mesoderm, coupled with Rho GTPase-mediated contraction of the proximal gland cells and downregulation of E-cadherin-based cell-cell adhesion by the Rac GTPases, allow turning and posterior migration of the salivary gland. Further posterior migration of the salivary gland is dependent on axon guidance cues, such as Robo and Slit, and close association with surrounding tissues. Many of the genes identified as regulators of salivary gland invagination and migration also control invagination of other epithelial tissues and migration of diverse cell types. Thus, studies of Drosophila salivary gland morphogenesis continue to illuminate the conserved mechanisms by which cells give rise to three-dimensional tissues and organs during embryogenesis.