A Yap-dependent transcriptional program directs cell migration for embryo axis assembly

The assembly of the embryo’s primary axis is a fundamental landmark to establish the vertebrate body plan. Although the morphogenetic movements directing cell convergence towards the midline have been described extensively, little is known on how gastrulating cells interpret mechanical cues. Yap proteins are well-known transcriptional mechanotransducers, yet their role in gastrulation remains elusive. Here we show that the double knockout of yap and its paralog yap1b in medaka results in an axis assembly failure, due to reduced displacement and migratory persistence in mutant cells. We identified genes involved in cytoskeletal organization and cell-ECM adhesion, rather than in germ layers specification, as direct Yap targets. Dynamic analysis of live sensors and downstream targets reveal that Yap is acting in migratory cells, in which promotes cortical actin and focal adhesions recruitment. Our results indicate that Yap coordinates a mechano-regulatory loop essential to maintain the directed cell migration sustaining embryo axis development. RNA-seq profile of wild type, yap-/- and yap-/- yap1b-/- mutant embryos at stage 16.