Pax2a regulates angiogenesis to facilitate mmp2-dependent basement membrane remodeling of the optic fissure

Vertebrate retinal development requires timely and precise fusion of the optic fissure (OF). Recent studies have suggested hyaloid vasculature to be involved in optic fissure fusion. In order to examine this link, we analyzed OF fusion and hyaloid vasculogenesis in the zebrafish pax2anoi mutant line. We determined that OF basement membrane (BM) remodeling, normally preceded by F-actin accumulation is mis-regulated in pax2a-/- embryos. Comparing transcriptomic profiles of pax2a-/- and wildtype eyes we discovered a novel connection between regulation of angiogenesis and fusion. Pax2a-/- eyes exhibited a significant reduction of talin1 expression, a regulator of hyaloid vasculature, in addition to increased expression of an anti-angiogenic protease, adamts1. Using 3D and live imaging we observed reduced OF hyaloid vascularization in pax2a-/- embryos. Additionally, pharmacological inhibition of VEGF signaling or adamts1 mRNA overexpression phenocopied the pax2a-/- vasculature, F-actin and BM remodeling phenotypes. Finally, we show that hyaloid vasculature expresses mmp2 which is necessary for remodeling the fissure BM. Taken together we propose a pax2a driven mechanism that restricts anti-angiogenic activity of adamts1 enabling hyaloid vasculature invasion of the OF and delivery of the BM remodeler mmp2.