Regulation of posterior body and ectodermal morphogenesis in zebrafish by localized Yap1 and Wwtr1

The vertebrate embryo undergoes a series of dramatic morphological changes as the body extends to form the complete anterior-posterior axis during the somite-forming stages. The molecular mechanisms regulating these complex processes are still largely unknown. We show that the Hippo pathway transcriptional coactivators Yap1 and Wwtr1 are specifically localized to the ectoderm and notochord, and play a critical and unexpected role in posterior body extension by regulating the assembly of Fibronectin underneath the ectoderm and surrounding the notochord. We also find that Yap1/Wwtr1, also acting through Fibronectin, have an essential role in the ectodermal morphogenesis necessary to form the initial dorsal and ventral fins, a process that had been thought to involve bending of an epithelial sheet, but which we now show involves active cell migration. Our results reveal how the Hippo pathway transcriptional program, localized to two specific tissues, acts to control essential morphological events in the vertebrate embryo. two biological replicates of tails of yap1/wwtr1 double homozygous mutants and siblings (24 each at 16-18 somite stage) were collected for RNAseq. Tails are tissues of the posterior end until the third newest somite (S-III).