The Role of Sema3E in Optic Fissure Closure of the Eye in Zebrafish

Abstract

Microphthalmia, anophthalmia, and coloboma are significant birth defects causing up to ten percent of childhood blindness that can be identified in two per ten thousand newborns. Up to seventy percent of microphthalmia, anophthalmia, and coloboma are associated with optic fissure (OF) closure defects and fall into a category of developmental eye defects. One of the goals of our laboratory is to determine the genetic mechanism of developmental eye defects. We are investigating the role of SEMA3E, a gene associated with colobomas in two unrelated children. Class three semaphorins (Sema3s) are a family of molecules known to direct cell movement (Callander et al. 2007). We hypothesized that Sema3E is required for cell movement during OF closure. Following morpholino (MO) knockdown of Sema3E expression in zebrafish embryos, a significant and dose dependent reduction in eye size was observed. Additionally, inverted pear shaped pupils, evidence of defective optic fissure closure, were seen in some of the Sema3E-deficient embryos. A reporter transgenic line of zebrafish expressing green fluorescent protein (GFP) expression at the edges of the OF was used to evaluate OF closure. MO injected embryos had greater GFP intensity at the OF closure line in comparison to un-injected zebrafish, suggesting delayed OF closure. These results indicate that Sema3E plays a critical role in OF closure. Currently, retinal layers of the zebrafish eye are being examined by immunohistochemistry and hematoxylin and eosin (H&E) staining to understand the mechanism(s) by which Sema3E is involved in eye development.