4 research outputs found
Stable vascular connections and remodeling require full expression of VE-cadherin in zebrafish embryos.
No full textBackgroundVE-cadherin is an endothelial specific, transmembrane protein, that clusters at adherens junctions where it promotes homotypic cell-cell adhesion. VE-cadherin null mutation in the mouse results in early fetal lethality due to altered vascular development. However, the mechanism of action of VE-cadherin is complex and, in the mouse embryo, it is difficult to define the specific steps of vascular development in which this protein is involved.Methodology and principal findingsIn order to study the role VE-cadherin in the development of the vascular system in a more suitable model, we knocked down the expression of the coding gene in zebrafish. The novel findings reported here are: 1) partial reduction of VE-cadherin expression using low doses of morpholinos causes vascular fragility, head hemorrhages and increase in permeability; this has not been described before and suggests that the total amount of the protein expressed is an important determinant of vascular stability; 2) concentrations of morpholinos which abrogate VE-cadherin expression prevent vessels to establish successful reciprocal contacts and, as a consequence, vascular sprouting activity is not inhibited. This likely explains the observed vascular hyper-sprouting and the presence of several small, collapsing vessels; 3) the common cardinal vein lacks a correct connection with the endocardium leaving the heart separated from the rest of the circulatory system. The lack of closure of the circulatory loop has never been described before and may explain some downstream defects of the phenotype such as the lack of a correct vascular remodeling.Conclusions and significanceOur observations identify several steps of vascular development in which VE-cadherin plays an essential role. While it does not appear to regulate vascular patterning it is implicated in vascular connection and inhibition of sprouting activity. These processes require stable cell-cell junctions which are defective in absence of VE-cadherin. Notably, also partial modifications in VE-cadherin expression prevent the formation of a stable vasculature. This suggests that partial internalization or change of function of this protein may strongly affect vascular stability and organization
VE-cadherin is a critical endothelial regulator of TGF-beta signalling
No full textVE-cadherin is an endothelial-specific transmembrane protein concentrated at cell-to-cell adherens junctions. Besides promoting cell adhesion and controlling vascular permeability, VE-cadherin transfers intracellular signals that contribute to vascular stabilization. However, the molecular mechanism by which VE-cadherin regulates vascular homoeostasis is still poorly understood. Here, we report that VE-cadherin expression and junctional clustering are required for optimal transforming growth factor-β (TGF-β) signalling in endothelial cells (ECs). TGF-β antiproliferative and antimigratory responses are increased in the presence of VE-cadherin. ECs lacking VE-cadherin are less responsive to TGF-β/ALK1- and TGF-β/ALK5-induced Smad phosphorylation and target gene transcription. VE-cadherin coimmunoprecipitates with all the components of the TGF-β receptor complex, TβRII, ALK1, ALK5 and endoglin. Clustered VE-cadherin recruits TβRII and may promote TGF-β signalling by enhancing TβRII/TβRI assembly into an active receptor complex. Taken together, our data indicate that VE-cadherin is a positive and EC-specific regulator of TGF-β signalling. This suggests that reduction or inactivation of VE-cadherin may contribute to progression of diseases where TGF-β signalling is impaired
Cellular mechanisms during vascular development
No full textThe 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
Dynamic cell rearrangements shape the cranial vascular network of developing Zebrafish embryos
No full textTo form the complex network of endothelial tubes making up the vasculature, a number of vessels have to interact and connect to each other during development. This involves the transformation of blunt-ended angiogenic sprouts into interconnected functional tubes, a process called vessel fusion or anastomosis. While much is known about vessel sprouting, little is known about vessel fusion at the cellular and molecular levels. Most of the vessels in the developing vertebrate embryo form in the presence of stable blood flow in adjacent tubes, suggesting the importance of flow and/or blood pressure for angiogenic sprouting and anastomosis. For this reason, my analyses focused on the head vasculature where many vessels form in the presence of stable blood flow in the zebrafish embryo.
In this study I performed detailed analyses of different fusion events in cranial vessels of the developing zebrafish embryo. Using novel transgenic tools and high resolution live imaging I defined a multistep model of vessel fusion and showed that it is conserved in various vascular beds, regardless of vessel shape and the age of the embryo. I also showed that in all the cranial vessels I studied, the initial fusion steps are the same and involve de novo deposition of junctional proteins, ZO-1 and VE-cadherin, in a form of a junctional spot, which subsequently elaborates into a ring, followed by de novo apical membrane insertion. Lumen formation in the newly formed vessel takes place through blood pressure-dependent luminal/apical cell membrane invagination and fusion of apical membranes, leading to a continuous lumen. During this process, the tip cells become unicellular/seamless tubes with transcellular lumen. I found that such newly connected vessels subsequently undergo dynamic cellular rearrangements that lead to the transformation of the unicellular tubes into multicellular ones. This transformation involves cell splitting, a novel cellular mechanism that, to our knowledge, has not been described before in branching morphogenesis of any organ. Additionally, I analyzed the fusion process in VE-cadherin deficient embryos and showed that this adhesion molecule is necessary for formation of a single contact surface between the fusing vessel sprouts and thus, has an important role in coordinating anastomosis.
I have also analyzed vessel regression during vascular pruning and I showed that it follows a multistep process involving dynamic cell rearrangements that resemble “reversed” vessel fusion. These analyses represent the first studies of vessel remodeling at the cellular level in an in vivo system
