Clec14a genetically interacts with Etv2 and Vegf signaling during vasculogenesis and angiogenesis in zebrafish.

BACKGROUND: C-lectin family 14 Member A (Clec14a) is a transmembrane protein specifically expressed in vascular endothelial cells during embryogenesis. Previous in vitro and in vivo studies have provided conflicting data regarding Clec14a role in promoting or inhibiting angiogenesis, therefore its functional role in vascular development remains poorly understood. RESULTS: Here we have generated a novel clec14a mutant allele in zebrafish embryos using TALEN genome editing. clec14a mutant embryos exhibit partial defects and delay in the sprouting of intersegmental vessels. These defects in angiogenesis are greatly increased upon the knockdown of a structurally related C1qr protein. Furthermore, a partial knockdown of an ETS transcription factor Etv2 results in a synergistic effect with the clec14a mutation and inhibits expression of early vascular markers in endothelial progenitor cells, arguing that clec14a is involved in promoting vasculogenesis. In addition, Clec14a genetically interacts with Vegfa signaling. A partial knockdown of Vegfaa function in the clec14a mutant background resulted in a synergistic inhibition of intersegmental vessel sprouting. CONCLUSIONS: These results argue that clec14a is involved in both vasculogenesis and angiogenesis, and suggest that Clec14a genetically interacts with Etv2 and Vegf signaling during vascular development in zebrafish embryos.

ETS transcription factor Etsrp / Etv2 is required for lymphangiogenesis and directly regulates vegfr3 / flt4 expression.

The molecular mechanisms initiating the formation of the lymphatic system, lymphangiogenesis, are still poorly understood. Here we have identified a novel role in lymphangiogenesis for an ETS transcription factor, Etv2/Etsrp, a known regulator of embryonic vascular development. Through the use of fully validated photoactivatable morpholinos we show that inducible Etv2 inhibition in zebrafish embryos at 1 day post-fertilization (dpf) results in significant inhibition of lymphangiogenesis, while development of blood vessels is unaffected. In Etv2-inhibited embryos and larvae, the number of lymphatic progenitors is greatly reduced, the major lymphatic vessel, the thoracic duct, is absent or severely fragmented, and lymphangiogenesis-associated marker expression, including lyve1b, prox1a, and vegfr3/flt4, is strongly downregulated. We also demonstrate that lymphatic progenitors in Etv2 deficient embryos fail to respond to Vegfc signaling. Chromatin immunoprecipitation and sequencing (ChIP-Seq) studies using differentiated mouse embryonic stem (ES) cells as well as luciferase reporter studies in the ES cells and in zebrafish embryos argue that Etv2 directly binds the promoter/enhancer regions of Vegfc receptor Vegfr3/Flt4 and lymphatic marker Lyve1, and promotes their expression. Together these data support a model where Etv2 initiates lymphangiogenesis by directly promoting the expression of flt4 within the posterior cardinal vein.