YAP1 is essential for self-organized differentiation of pluripotent stem cells

The Yes-associated protein 1 (YAP1) is a downstream effector of the Hippo pathway and essential mechanotransducer. It has been suggested to play a crucial role for early embryo development, but the relevance for early germ layer commitment of human induced pluripotent stem cells (iPSCs) remains largely unclear. To gain better insight into the function of YAP1 in these early cell-fate decisions, we generated iPSC lines with YAP1 knockout (YAP-/-) with CRISPR/Cas9 technology and analyzed transcriptomic and epigenetic modifications. In YAP-/- iPSCs the expression of several YAP1 targets changed and NODAL, which is an important regulator of cell differentiation, was upregulated. Furthermore, YAP1 deficiency evoked global DNA methylation changes. Directed differentiation of adherent iPSC colonies toward endoderm, mesoderm, and ectoderm could be induced, albeit endodermal and ectodermal differentiation showed transcriptomic and epigenetic changes in YAP-/- lines. Notably, in self-organized embryoid bodies (EBs) germ layer specification was clearly impaired. This phenotype was rescued via lentiviral overexpression of YAP1 and in tendency also by NODAL inhibitors. Our results demonstrate that YAP1 plays an important role during early germ layer specification of iPSCs, particularly for the non-directed self-organization of EBs, and this is at least partly attributed to activation of the NODAL pathway.