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

Abstract

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.

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“…During vertebrate eye development, the process of optic fissure closure to create the optic cup involves basement membrane breakdown (Chan et al, 2020). Ocular coloboma, the failure to fuse the retinal epithelium at the optic fissure, is a significant source of human childhood visual impairment, and a zebrafish model of ocular coloboma showed that matrix metalloprotease secretion from the nearby vasculature is required for fusion (Weaver et al, 2020). During Xenopus mouth formation, Hedgehog signaling and Wnt antagonists induce basement membrane breakdown between the ectoderm and endoderm (Dickinson and Sive, 2009;Chen et al, 2017).…”

Eyes on CHARGE syndrome: Roles of CHD7 in ocular development

“…Additionally, periocular mesenchyme cells are required for fissure closure. Specifically, a subset of neural crest cells and endothelial cells seem to be necessary for basement membrane rearrangement (James et al, 2016;Cao et al, 2018;Gestri et al, 2018;Weaver et al, 2020). When optic fissure formation or closure is disrupted, the birth defect known as coloboma results (Chang et al, 2006).…”