Abstract
Purpose:
To determine the role of Sema3A during ocular vasculogenesis and formation of the avascular cornea. Given that angioblasts and ocular blood vessels in the periocular region express Nrp1, a receptor for both Vegf (angiogenic factor) and Sema3A (anti-angiogenic factor), we hypothesized that lens-derived Sema3A prevents angioblast migration and vascularization of the developing cornea.
Methods:
We identified the localization of migratory angioblasts and forming vasculature in the periocular region of Tg(tie1:H2B:eYFP) transgenic quail. We examined the expression of Vegf and Sema3A in the lens by immunohistochemistry and quantified their mRNA by qPCR. We then blocked Sema3A signaling from the region of the presumptive cornea by lens ablation or injection of Sema3A inhibitory peptides. We also investigated whether addition of Sema3A would inhibit Vegf-induced vascularization of the cornea. Furthermore, we analyzed Nrp1(Sema-/-) mutant mice that lack Sema/Nrp1 signaling for defects in corneal avascularity.
Results:
Our results show that angioblasts do not migrate into the region of the forming cornea located between the ectoderm and lens. Both Sema3A and Vegf are present in the lens, but the levels of Sema3A transcripts are significantly higher than Vegf during cornea development. Inhibition of lens Sema3A resulted in ectopic angioblast migration and vascularization of the forming cornea. Addition of Sema3A protein inhibited Vegf-induced vascularization of the cornea. We also observed ectopic angioblasts and vasculature in corneas of Nrp1(Sema-/-) mutant embryos.
Conclusions:
Together, our results clearly indicate that corneal avascularity is established early during ocular development and that, Sema3A signaling from the lens plays a crucial role in this process.
Keywords: 480 cornea: basic science •
497 development •
609 neovascularization