Filopodia are dispensable for endothelial tip cell guidance

Abstract

SUMMARYActin filaments are instrumental in driving processes such as migration, cytokinesis and endocytosis and provide cells with mechanical support. During angiogenesis, actin-rich filopodia protrusions have been proposed to drive endothelial tip cell functions by translating guidance cues into directional migration and mediating new contacts during anastomosis. To investigate the structural organisation, dynamics and functional importance of F-actin in endothelial cells (ECs) during angiogenesis in vivo, we generated a transgenic zebrafish line expressing Lifeact-EGFP in ECs. Live imaging identifies dynamic and transient F-actin-based structures, such as filopodia, contractile ring and cell cortex, and more persistent F-actin-based structures, such as cell junctions. For functional analysis, we used low concentrations of Latrunculin B that preferentially inhibited F-actin polymerisation in filopodia. In the absence of filopodia, ECs continued to migrate, albeit at reduced velocity. Detailed morphological analysis reveals that ECs generate lamellipodia that are sufficient to drive EC migration when filopodia formation is inhibited. Vessel guidance continues unperturbed during intersegmental vessel development in the absence of filopodia. Additionally, hypersprouting induced by loss of Dll4 and attraction of aberrant vessels towards ectopic sources of Vegfa165 can occur in the absence of endothelial filopodia protrusion. These results reveal that the induction of tip cells and the integration of endothelial guidance cues do not require filopodia. Anastomosis, however, shows regional variations in filopodia requirement, suggesting that ECs might rely on different protrusive structures depending on the nature of the environment or of angiogenic cues.

Influence of PECAM-1 ligand interactions on PECAM-1-dependent cell motility and filopodia extension

“…2003; Phng et al. 2013). Although VEGF activation has been implicated in the formation endothelial tip cell filopodia, our understanding of the elaboration of filopodia in ECs remains incomplete (De Smet et al.…”

“…2000) and/or PECAM‐1‐PECAM‐1 interactions between molecules on the filopodia of adjacent tip cells might facilitate the anastomosis of angiogenic sprouts (Phng et al. 2013). …”

Fzd7 (Frizzled-7) Expressed by Endothelial Cells Controls Blood Vessel Formation Through Wnt/β-Catenin Canonical Signaling

“…Filopodia mediate endothelial tip cell migration to guide vascular sprout formation and anastomosis. 22,23 High-resolution analysis of tip cells identified an increase in filopodia protrusions. Moreover, the majority of filopodia (80%) showed an angle profile between 0 and 45° in controls, whereas in retina from fzd7 iECKO mice, filopodia were randomly positioned with a wider angle profile ( Figure 3A).…”

Regulation of signaling interactions and receptor endocytosis in growing blood vessels

“…1B). [7][8][9] More proliferative stalk cells follow the invasive tip cells and form the base of endothelial sprouts, but ECs can also actively compete for the leading position. 8,10 Such cell shuffling events during sprouting angiogenesis are promoted by heterogeneous adhesion interactions between endothelial cells.…”