The role of the Rho GTPases in lens placode invagination

Abstract

Epithelial invagination is a central feature of embryonic morphogenesis in animals. Here, we show that RhoA mutant lens placode cells are both longer and less apically constricted than control cells, causing reduced epithelial curvature and reduced invagination. By contrast, Rac1 mutant lens placode cells are shorter and more apically restricted than controls, resulting in increased epithelial curvature and precocious closure of the lens vesicle. Quantification of RhoA and Rac1‐dependent pathway markers over the apical‐basal axis of lens pit cells showed that in RhoA mutant epithelial cells, there was a Rac1 pathway gain‐of‐function and vice versa. These findings suggest that mutual antagonism produces balanced activities of RhoA‐generated apical constriction and Rac1‐dependent cell elongation that controls cell shape and thus the curvature of invaginating epithelium. Previous studies have shown that contractile lens‐specific filopodia, under Cdc42 control, tether to the optic cup during lens placode invagination. Here, we examine the efficacy of lens filopodia in transmitting forces to co‐ordinate lens and retinal shape. Our observations suggest contractile and protrusive forces exerted by lens filopodia aid in shaping the underlying retina, and therefore bring us closer to understanding the important process of tissue co‐ordination for organ functionality.