Endothelial Cell Dynamics in Vascular Development: Insights From Live-Imaging in Zebrafish

Abstract

The formation of the vertebrate vasculature involves the acquisition of endothelial cell identities, sprouting, migration, remodeling and maturation of functional vessel networks. To understand the cellular and molecular processes that drive vascular development, live-imaging of dynamic cellular events in the zebrafish embryo have proven highly informative. This review focusses on recent advances, new tools and new insights from imaging studies in vascular cell biology using zebrafish as a model system.

Keywords: anastomosis; angiogenesis; endothelial cell; lymphangiogenesis; vasculogenesis; zebrafish.

FIGURE 1

Recent findings from live imaging primary angiogenesis and lumenization in the zebrafish trunk. Recent studies have shown that asymmetric division of intersegmental filopodia have been shown to be dispensable vessel tip cells, hyaluronic acid turnover in extracellular matrix, and Ca²⁺ oscillation in both tip and stalk cells, drive primary angiogenesis. In contrast, filopodia has been shown to be dispensable for endothelial cell migration. Both vacuolar fusion and inverse blebbing have been proposed as mechanisms for lumenization in intersegmental vessels. DA, dorsal aorta; ECM, extracellular matrix; ISV, Intersegmental vessel.

FIGURE 2

Recent findings from live imaging secondary angiogenesis/lymphatic sprouting in the zebrafish trunk. (A) Schematic diagram showing events that occur during secondary angiogenesis and anastomosis in the zebrafish trunk. Yellow arrows indicate direction of blood flow. Red vessels are arteries while blue vessels are veins. Light blue cell is a venous endothelial cell (EC) and the green cell is a fated lymphatic EC. (B) Schematic diagram illustrating the difference in Notch activity, cell polarity, and cell arrangements between future arterial intersegmental vessels and venous intersegmental vessels prior to secondary sprout anastomosis. (C) Schematic diagram showing how a Prox1-low EC (light green cell) in the posterior cardinal vein undergo bipotential cell division to give rise to a lymphatic EC (green cell) and a venous EC (light blue cell). aISV, arterial intersegmental vessel; DA, dorsal aorta; LEC, lymphatic endothelial cell; ISV, intersegmental vessel; PCV, posterior cardinal vein; vISV, venous intersegmental vessel.

FIGURE 3

Recent findings from live imaging vessel remodeling and tip cell anastomosis in the zebrafish trunk. (A) Schematic diagram showing events that occur during vessel remodeling and tip cell anastomosis in the zebrafish trunk. Yellow arrows indicate direction of blood flow. Red vessels are arteries while blue vessels are veins. Green circles are golgi bodies. (B) Schematic diagram illustrating the different steps of tip cell anastomosis. A stable filopodial connection is first established (junctional spot), which elaborates into a junctional ring as the cell-cell junction expands. (C) Schematic diagram illustrating how cell elongation and cell splitting occur in the dorsal longitudinal anastomotic vessel to remodel a unicellular tube into a multicellular tube. (D) Endothelial cells migrate on top of each other via junctional-based lamellipodia (JBLs) which emanate from the front end of junctional rings. VE-cadherin provides support for F-actin based JBLs to protrude, driving the ZO-1-positive cell junction to migrate forward toward the front end of the JBL via a ratchet-like mechanism. DA, dorsal aorta; DLAV, dorsal longitudinal anastomotic vessel; EC, endothelial cell; JBL, junction-based lamellipodia; PCV, posterior cardinal vein; vISV, venous intersegmental vessel.