Tracheal tube fusion inDrosophilainvolves release of extracellular vesicles from multivesicular bodies

Abstract

Fusion of endothelial or epithelial tubes is essential for the development of organs like the vertebrate vasculature or the insect tracheal system, but the mechanisms underlying the formation of tubular connections (anastomoses) are not well understood. Tracheal tube fusion in Drosophila is mediated by tip cells that transform into lumenized toroids to connect adjacent tubes. This process depends on the Munc13-4 orthologue Staccato (Stac), which localizes to tip-cell-specific lysosome-related organelles (LROs). We show that tracheal LROs display features of multivesicular bodies (MVBs) and that the tracheal lumen contains membranous extracellular vesicles (EVs), a subset of which carries Stac/Munc13-4 and is associated with tracheal anastomosis sites. The presence of LROs and luminal Stac-EVs depends on the tip-cell-specific GTPase Arl3, suggesting that Stac-EVs derive from fusion of MVBs with the luminal membrane in tip cells during anastomosis formation. The GTPases Rab27 and Rab35 cooperate downstream of Arl3 to promote Stac-MVB formation and tube fusion. We propose that Stac-MVBs act as membrane reservoirs that facilitate lumen fusion in tip cells, in a process regulated by Arl3, Rab27, Rab35, and Stac/Munc13-4.

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“…The mechanism of lumen connection in the vertebrate vasculature shares many morphological similarities with the one in the tracheal system of D. melanogaster (Camelo et al, 2022;Caviglia and Luschnig, 2014;Hayashi and Kondo, 2018;Kotini et al, 2019). In the embryonic trachea, the formation of a continuous lumen via apical membrane fusion has been described to be dependent on vesicular trafficking (Caviglia et al, 2016).…”