Abstract

Lymphangiogenesis is of great clinical interest because of its essential role in such pathologic settings as inflammation, vascular malformations, and tumor metastasis. Previous observational hurdles are now overcome by use of the optically clear and genetically modifiable zebrafish embryo, which provides a vertebrate model for understanding lymphangiogenesis and for revealing putative therapeutic targets for metastatic disease and vascular/lymphatic malformations that currently have no cure. We and others have previously demonstrated that an evolutionarily conserved ETS transcription factor Etv2 / Etsrp functions as a master regulator during embryonic vascular development. However, its role in lymphatic development is not defined. Here we performed conditional knockdown of Etv2 function using photoactivatable morpholinos (MO) in a zebrafish model system to test Etv2 requirement during lymphangiogenesis. Our data show that conditional Etv2 inhibition at 1-day-post-fertilization (dpf) resulted in specific defects in lymphatic development, while blood vessel formation was not affected. The major lymphatic vessel, the thoracic duct, was absent or discontinuous in Etv2-depleted embryos (Figure 1) and the lymphatic progenitors failed to migrate (Figure 2) in absence of Etv2 function. Expression of the lymphatic markers lyve1, prox1a and the major VegfC receptor VegfR3 was strongly down regulated in the conditional Etv2 MO knockdown embryos. We further show that Etv2 expression is enriched in the posterior cardinal vein where lymphangioblasts (lymphatic endothelial cell precursors) originate during lymphangiogenesis and that overexpression of Etv2 throughout blood vasculature perturbs lymphangiogenesis. We further show that in the absence of Etv2 function, lymphatic progenitors fail to respond to VegfC signaling. Our results suggest that Etv2 initiates lymphangiogenesis in part by regulating Vegf3 expression. These results argue that Etv2 is a novel critical factor during lymphatic development, and it may represent a new target for chemical modulation in multiple lymphatic disorders.

Disclosures

No relevant conflicts of interest to declare.

Author notes

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Asterisk with author names denotes non-ASH members.