TY - JOUR T1 - Myosin II activity is not required for <em>Drosophila</em> tracheal branching morphogenesis JF - bioRxiv DO - 10.1101/098814 SP - 098814 AU - Amanda Ochoa-Espinosa AU - Stefan Harmansa AU - Emmanuel Caussinus AU - Markus Affolter Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/01/06/098814.abstract N2 - The Drosophila tracheal system consists of an interconnected network of monolayered epithelial tubes that ensures oxygen transport in the larval and adult body. During tracheal dorsal branch (DB) development, individual DBs elongate as a cluster of cells, led by tip cells at the front and trailing cells in the rear. Branch elongation is accompanied by extensive cell intercalation and cell lengthening of the trailing stalk cells. While cell intercalation is governed by Myosin II (MyoII)-dependent forces during tissue elongation in the Drosophila embryo leading to germ-band extension, it remained unclear whether MyoII plays a similar active role during tracheal branch elongation and intercalation. Here, we use a nanobody-based approach to selectively knock-down MyoII in tracheal cells. Our data shows that despite the depletion of MyoII function, tip cells migration and stalk cell intercalation (SCI) proceeds at a normal rate. Therefore, our data confirms a model in which DB elongation and SCI in the trachea occurs as a consequence of tip cell migration, which produces the necessary forces for the branching process.Summary statement Branch elongation during Drosophila tracheal development mechanistically resembles MyoII-independent collective cell migration; tensile forces resulting from tip cell migration are reduced by cell elongation and passive stalk cell intercalation.DBDorsal branchDCDorsal closureE-CadE-CadherinGBEGerm-band extensionMRLCMyosin regulatory light chainMyoIIMyosin IISCIstalk cell intercalationSqhSpaghetti squashSxllSex lethalTCTip cellTrTracheomere ER -