The novel formin FMNL3 is a cytoskeletal regulator of angiogenesis.

Abstract

The process of angiogenesis requires endothelial cells to undergo profound changes in shape and polarity. This must involve remodelling of the endothelial cell cytoskeleton; however, we know little of this process or of the proteins that control it. We used a co-culture assay of angiogenesis to examine the cytoskeleton of endothelial cells actively undergoing angiogenic morphogenesis. We find that elongation of endothelial cells during angiogenesis is accompanied by stabilisation of microtubules and their alignment into parallel arrays directed at the growing tip. In other systems, similar microtubule alignments are mediated by the formin family of cytoskeletal regulators. We screened a library of human formins and indentified the novel formin FMNL3/FRL2 as a critical regulator of endothelial cell elongation during angiogenesis. We show that activated FMNL3 triggers microtubule alignment and that FMNL3 is required for microtubule alignment during angiogenic morphogenesis. FMNL3 is highly-expressed in the endothelial cells of Zebrafish during development and embryos depleted for FMNL3 show profound defects in developmental angiogenesis that are rescued by expression of the human gene. We conclude that FMNL3 is a novel regulator of endothelial microtubules during angiogenesis and is required for the conversion of quiescent endothelial cells into their elongated angiogenic morphology.