Molecular genetic dissection of tube morphogenesis in the Drosophila tracheal system

In the vascular system and the embryonic Drosophila respiratory (tracheal) system, new tubes arise by “sprouting,” in which cells change positions relative to their neighbors and migrate towards a chemoattractant cue. After initiating and guiding outgrowth of the new branch, the tip cell must form a tube (lumenize) in order to make the new branch functional. When tip cells lumenize, they form “seamless” tubes that, in cross-section, resemble doughnuts; they have an internal apical membrane and lack junctional “seams” (adherens junctions and tight/septate junctions). Tip cells frequently remain seamless tubes in the vascular system; but even tip cells that do not form stable seamless tubes nevertheless pass through an intermediate seamless tube stage, before remodeling their junctions to contribute to multicellular tubes. Thus, seamless tubes are predicted to be essential for formation of patent tubular networks in vertebrates and Drosophila. Despite this, very little is known about seamless tubes, and the dearth of known genetic pathways required for seamless tube morphogenesis represents a critical barrier to progress in the field. In the Drosophila tracheal system, all tip cells come to reside in stereotyped positions and form stable seamless tubes; furthermore, tracheal terminal cells add new seamless tube side branches throughout the course of larval life and also undergo dramatic increases in seamless tube length and diameter. These qualities, combined with the power of molecular genetic analysis in Drosophila, have made tracheal terminal cells an exceptionally useful model for dissecting seamless tube morphogenesis. Larger bore tubes, such as the Drosophila dorsal trunk, are multicellular, and an overlapping but distinct set of genes and genetic pathways are likely to play key roles in the making, shaping and maintenance of those tubes. Here we propose to advance three projects. In project 1 we will dissect how signaling pathways (receptor tyrosine kinase and Notch) intersect to regulate tip cell properties, such as cell adhesion, that are critical to the selection of tip and stalk cells. In project 2 we will pursue a detailed mechanistic understanding of seamless tube formation, examining how cytoskeletal factors, extracellular matrix, and vesicle trafficking are specifically engaged in making, shaping, and maintaining seamless tubes. In project 3 we focus on the regulation of multicellular tube formation, bringing mosaic analysis to bear on the question of how tube length and diameter are regulated. We also propose to characterize two mutations (small potatoes and cincher) that we identified with cell autonomous requirements in dorsal trunk tube morphogenesis. Overall, the goal of the lab is to provide deep insight into the genetic pathways and molecular mechanisms at play in tubulogenesis.