Coordinated control of lumen size and collective migration in the salivary gland.

The Drosophila embryonic salivary gland is a powerful system to analyze the cellular and molecular mechanisms of tubulogenesis in vivo. The secretory portion of the salivary gland (referred to here as the salivary gland), is a pair of elongated epithelial tubes with a single central lumen, that is formed by the invagination and collective migration of gland cells from the ventral surface of the embryo. ( 1) (,) ( 2) As the salivary gland elongates during migration, the central lumen elongates and narrows at the proximal end. ( 3) A number of genes are known to regulate salivary gland migration and/or lumen size (Table 1); however, it is only recently that we have begun to analyze how control of salivary gland migration is coordinated with control of lumen size. To understand coordinated control of salivary gland migration and lumen size, we analyzed the role of the single Drosophila Rho GTPase, Rho1, in salivary gland tubulogenesis. In addition to the requirement of Rho1 in salivary gland invagination and migration (Xu et al., 2008), our recent studies show that Rho1 controls salivary gland lumen width and length during the migration process (Fig. 1). These studies reveal that Rho1-mediated processes at the proximal end of the migrating salivary gland, such as cell shape change, cell rearrangement and apical domain elongation, contribute to collective migration, and narrowing and elongation of the lumen. ( 4).