Maternal vgll4a promotes blastoderm cohesion enabling yap1-mediated mechano-transduction during zebrafish epiboly

Cellular cohesion provides tissue tension, which is then sensed by the cytoskeleton and decoded by the activity of mechano-transducers, such as the transcriptional cofactor Yap1, thereby enabling morphogenetic responses in multi-cellular organisms. How cell cohesion is regulated is nevertheless unclear. Here we show that, zebrafish epiboly progression, a prototypic morphogenetic event that depends on Yap activity, requires the maternal contribution of the proposed yap1 competitor vgll4a. In embryos lacking maternal/zygotic vgll4a (MZvgll4a), spreading epithelial cells are ruffled, blastopore closure is delayed and the expression of the yap1-mediator arhgap18 is decreased, impairing the actomyosin ring at the syncytial layer. Furthermore, rather than competing with Yap1, vgll4a coordinate the levels of the E-Cadherin/{beta}-catenin adhesion complex components at the blastomere plasma membrane and hence their actin cortex distribution. Taking these results together, we propose that maternal vgll4a may act at epiboly initiation to coordinate blastomere adhesion/cohesion, which is a fundamental piece of the self-sustained bio-mechanical regulatory loop underlying morphogenetic rearrangements during gastrulation.