Asymmetric localisation of DLc1 defines trunk neural crest polarity for directional delamination and migration

Abstract

Multipotent neural crest cells (NCCs) originate in the dorsal neural tube and implement a transcriptional programme to initiate an epithelial-mesenchymal transition (EMT) that involves alteration of cytoskeletal structure, loss of cell-cell adhesion and apical-basal polarity to convert an epithelial cell into a mesenchymal motile phenotype. After EMT, these unpolarized NCCs acquire front-back polarity that is prerequisite for directional delamination and migration into the periphery where they form neurons and glia of the periphery nervous system. It has been unclear how this polarization is established and regulated. Using fluorescence biosensory in emigrating NCCs, we show that the breaking of cell symmetry is accompanied with distribution of highly active RhoA small GTPase to the cell rear and fluctuating RhoA activity at the protrusive front. This differential localization and level of RhoA activity predicts the future back-front polarity axis and the direction of movement. Strikingly, the RhoGAP, Deleted in liver cancer 1 (Dlc1), is asymmetrically localized to the cell front and its level of activity determines polarized NC morphology and motility by restricting spatial RhoA activation to the cell rear. We also found that the association of Dlc1 with Nedd9 is crucial for its asymmetric localization and polarized RhoA activity. Moreover, Nedd9 and Dlc1 are subject to the transcriptional regulation of NC specifiers, Sox9 and Sox10, respectively. Thus, we reveal a novel SoxE-Dlc1/Nedd9-RhoA regulatory axis to govern NC migratory polarization.