Elucidating the role of YAP in directing mesenchymal stem cell fate

Mesenchymal stem cells (MSCs) are a type of multipotent stem cell capable of differentiating into several cell types, including fat and bone cells. The Hippo pathway effectors TAZ and YAP have been implicated as important regulators of MSC fate, but their roles in this process are poorly understood. The goal of my thesis work was to illuminate the roles of YAP and TAZ in MSC differentiation. I examined how depleting YAP and/or TAZ, or expressing YAP mutants affect the differentiation of C3H10T1/2 cells, which are a multipotent mouse embryo fibroblast cell line capable of forming bone, fat and cartilage. Interestingly, knocking down either YAP or TAZ had different effects on C3H10T1/2 differentiation. YAP knockdown cells that underwent a brown/beige adipogenic protocol showed a significant increase in the amount of lipids produced as compared to control, suggesting that YAP has a role in inhibiting adipogenesis in these cells. YAP knockdown also increased alkaline phosphatase activity in cells subjected to an osteogenic protocol, while simultaneously producing lipid droplets. In contrast, knockdown of TAZ resulted in a decrease in both lipogenesis (in adipogenic differentiation) and alkaline phosphatase activity (in osteogenic differentiation). These observations indicate that depletion of YAP or TAZ leads to defective MSC