Identification of FMNL3 as a novel regulator of the cytoskeleton in angiogenesis

Abstract

Sprouting angiogenesis is the formation of new blood vessels from the pre-existing vasculature. Endothelial cells in quiescent blood vessels form a highly organised array with tight cell-cell junctions and uniform polarity. When pro-angiogenic signals initiate angiogenesis, endothelial, cells must become invasive and migrate into the extracellular matrix that surrounds the blood vessels. Sprouting endothelial cells become highly elongated, and this involves dramatic changes in cell shape and polarity. The mechanisms controlling angiogenic morphogenesis are poorly characterised. Cell shape and polarity are orchestrated by the cytoskeleton. The aim of this study was to characterise the cytoskeleton as endothelial cells convert to an angiogenic morphology, and identify novel regulators of this process. An in vitro model of angiogenesis was used to study endothelial cell elongation, in which endothelial cells form capillary-like tubes. It was found that this process was accompanied by the reorganisation of the microtubule network to form a parallel array along the length of the endothelial cells. These microtubules accumulated a modified form of the tubulin monomer, which indicates microtubule stabilisation. Stabilised microtubules were not found in quiescent endothelial cells, and so were associated with the initiation or maintenance of endothelial cell elongation. The formin family of cytoskeletal regulators have been shown to cause similar stabilisation of the microtubule network, in addition to modulating actin dynamics. A screen of the form in family of proteins in the in vitro model demonstrated that the novel formin FMNL3 is critical for endothelial cell elongation. Loss of FMNL3 caused a dramatic decrease in endothelial cell tube formation and resulted in disorganisation of the microtubule cytoskeleton. This study describes the identification of FMNL3 as a novel cytoskeletal regulator and its characterisation in endothelial cells.EThOS - Electronic Theses Online ServiceGBUnited Kingdo