The integrity of the vascular system is established during development. During vertebrate embryogenesis, the first endothelial precursors arise in the lateral plate mesoderm (LPM) as early as 12hpf. At mid-somitogenesis stages, angioblasts migrate towards the midline, merge and organize into nascent cords giving rise to the major blood vessels (vasculogenesis). Subsequently, primary sprouting events occur from the pre-existing vessels (angiogenesis). We use the zebrafish model to investigate how the endothelial program initiates.
We are interested in dlc1, a gene encoding a RhoGTPase activating protein and tumor suppressor gene, which plays a role in the regulation of RhoA, B and C activity, hence influencing several cell processes such as migration or adhesion. dlc1 is first expressed in the primordial angioblasts of the LPM, consistent with the high motility of these cells. Several gain-of-function approaches led to similar phenotypes: although arterio-venous specification was not impaired, angiogenic sprouting is greatly affected, resulting in poorly lumenized or hypersprouting intersegmental vessels (ISV) in the trunk of the embryo. As a result, blood circulation is disturbed leading to cardiac edemas and brain hemorrhages.
To further elucidate dlc1’s role in vascular development, we generated a mutant line with the CRISPR/Cas9 technology. Whereas dlc1 knock-out mice die in utero preventing the study of any vascular phenotype, the dlc1 null zebrafish survives until 5 days, allowing a better insight into its role in angiogenesis. The mutant fish has severe vascular defects that manifest in impaired primary blood circulation in aorta and vein, which is resulting in massive cardiac edemas. We will now use this new tool to investigate the angiogenic processes. Altogether, we will understand the physiological role of dlc1 during development and reveal new mechanisms controlling angiogenesis in vertebrates.