Cellular mechanisms during vascular development

The vascular system is an essential organ in vertebrate animals and provides the organism with enough oxygen and nutrients. It is composed of an interconnected network of blood vessels, which form using a number of different morphogenetic mechanisms. Angiogenesis describes the formation of new blood vessels from preexisting vessels. A number of molecular pathways have been shown to be essential during angiogenesis. However, cellular architecture of blood vessels as well as cellular mechanisms involved during vessel formation and anasotmosis have remained largely unknown.
The intersegmental vessels (ISVs) of the developing zebrafish embryo have served as a paradigm to study angiogenesis in vivo. ISVs sprout bilaterally from the dorsal aorta (DA) in the zebrafish trunk, grow dorsally and ultimately connect with adjacent ISVs on the dorsal side of the trunk forming the dorsal longitudinal anastomotic vessel (DLAV).
We used antibody labeling of endothelial cell-cell junctions, single cell labeling and live-imaging of junctions to investigate cellular architecture and mechanisms during ISV formation and anastonosis. In contrast to previous studies, we found that a large part of ISVs consist of multicellular tubes where the lumen is surrounded by several cells. Seamless tubes with an intracellular lumen are predominantly found in the DLAV. In addition, we found distinct cellular mechanisms to be involved in ISV anastomosis, forming seamless or multicellular tubes respectively. These results show that endothelial cells a rather plastic and can use different mechanisms to form functional blood vessels.