Cdh-2 and cortical f-actin dynamically cooperate to establish a stiffness gradient which contributes to forebrain roof plate invagination

Abstract

The invagination of the dorsal forebrain roof plate is critical for cerebral hemisphere formation. Although mutations in several genes have been linked to holoprosencephaly (HPE), and studies in chick embryos have implicated key signaling pathways, the mechanisms by which mechanical forces drive roof plate invagination remain poorly understood. To address this gap, we employed atomic force microscopy to map the spatiotemporal changes in tissue stiffness across the dorsal forebrain in the chick embryo during roof plate invagination. Our analysis revealed that neuroepithelium that is uniformly stiff initially, undergoes dramatic remodelling during this period of morphological change. Ultimately a pronounced stiffness gradient emerges, with the roof plate midline becoming markedly more compliant than the dorsolateral regions. Through expression screening, we identified Cdh2 as a candidate molecular regulator, whose spatiotemporal expression pattern closely mirrors the observed stiffness gradient. Mechanistically, we found that the interplay between Cdh2 and F-actin modulates tissue stiffness by regulating Cdh2 expression levels, apical adherens junction stability, and cortical F-actin distribution along the apico-basal axis of neuroepithelial cells. These findings underscore the importance of apico-basal localization of Cdh2 and provide critical insights into the mechanical forces and molecular interactions that govern forebrain roof plate morphogenesis, while also shedding light on the pathogenesis of HPE.