Rho Signaling-Directed YAP/TAZ Regulation Encourages 3D Spheroid Colony Formation and Boosts Plasticity of Parthenogenetic Stem Cells

Cell proliferation, apoptosis and differentiation are essential processes from the early phases of embryogenesis to adult tissue formation and maintenance. These mechanisms also play a key role in embryonic stem cells (ESCs) that are able to proliferate maintaining pluripotency and, at the same time, to give rise to all populations belonging to the three germ layers, in response to specific stimuli. ESCs are, therefore, considered a well-established in vitro model to study the complexity of these processes. In this perspective, we previously generated parthenogenetic embryonic stem cells (ParthESC), that showed many features and regulatory pathways common to bi-parental ESCs. However, we observed that mono-parental cells demonstrate a high ability to form outgrowths and generate 3D spheroid colonies, which are distinctive signs of high-plasticity. Furthermore, preliminary evidence obtained by WTA, revealed the presence of several differentially expressed genes belonging to the Rho and Hippo signaling pathways. In the present study, we compare bi-parental ESCs and ParthESC and analyze by Real-Time PCR the differentially expressed genes. We demonstrate up-regulation of the Rho signaling pathway and an increased expression of YAP and TAZ in ParthESC. We also show that YAP remains in a dephosphorylated form. This allows its nuclear translocation and its direct binding to TEADs and SMADs, that are up-regulated in ParthESC. Altogether, these complex regulatory interactions result in overexpression of pluripotency related genes, in a global DNA hypomethylation and a histone-dependent chromatin high permissive state that may account for ParthESC high potency, possibly related to their exclusive maternal origin.