Zebrafish enhancer trap line recapitulates embryonic aquaporin 1a expression pattern in vascular endothelial cells

Aquaporin 1 (Aqp1) is a water channel protein, expressed widely in microvascular endothelial cells and implicated in mammalian tumor angiogenesis. However, its developmental expression has not yet been characterized in great detail. An enhancer trap screen was performed using a Tol2-derived GFP reporter in zebrafish embryos. An insertional Et(GBT-B1)tpl1 line was identified that has reporter insertion in the vicinity of the aqp1a gene. We further characterized the embryonic expression pattern of this GFP reporter line, as well as that of endogenous aqp1a. Both endogenous aqp1a and reporter GFP expression were restricted to the vascular endothelial cells within the dorsal aorta, cranial, intersegmental and other secondary vessels, but were absent in the axial venous vasculature. In addition, endogenous aqp1a expression was observed in both primitive and definitive hematopoietic erythroid progenitors, as well as in the otic vesicle, swim bladder, pneumatic duct, intestine and a subset of neurons within the retina and the midbrain-hindbrain region. We further show that gata1 and etsrp/etv2 function is required for hematopoietic and endothelial aqp1a expression, respectively. Aqp1a expression is restricted to endothelial and erythroid cells during early embryogenesis. The transgenic Et(GBT-B1)tpl1 line recapitulates endogenous endothelial aqp1a expression. Because currently very few reporter lines can differentiate between arterial and venous endothelial cells, the Et(GBT-B1)tpl1 transgenic line and characterization of the aqp1a expression pattern will be useful for future studies of endothelial and arterial-venous differentiation.