Yap and Taz promote osteogenesis in neural crest cells by preventing chondrogenesis.

The neural crest (NC) is a unique migratory stem cell population only existed during vertebrate embryogenesis. It has remarkable multipotency to give rise to various cell types including osteoblasts and chondrocytes, which contribute to majority of the cranial skeleton development. Defects in NC development led to many congenital diseases, including cleft palate and craniofacial abnormities. Recently, the Hippo-Yap pathway, a conserved fundamental pathway has been indicated to play a key role in NCCs. Yet, the roles of Yap and Taz, function as Hippo signaling effectors, in NCC cells are still poorly understood. To understand the roles of Yap and Taz, we performed both in vitro, ex vivo and in vivo studies using O9-1 NC cells and Yap/Taz conditionally knockout (CKO) mice driven by Wnt1creSOR. We found that Yap/Taz are required for the osteogenic versus chondrogenic cell fate decision of NC cells. Yap/Taz prevent O9-1 NC cells from differentiating into chondrocytes to favor osteogenesis, and Yap/Taz deficiency in NC cells resulted in chondrogenesis instead of osteogenesis. Notably, in vivo, we observed NC-derived cranial bone defects accompanied by ectopic cartilage formation. From RNA-seq and CUT/RUN datasets we found that Yap/Taz directly regulate key genes that govern osteogenesis (Dlx5, Runx2,…) and chondrogenesis (Sox9/5/6,…). Interestingly, many of those genes are known Wnt target genes. Moreover, our data from ATAC-seq, PLA and Co-IP demonstrated that Yap/Taz directly interact with β-catenin to coordinately regulate related genes expression in NCCs to orchestrate the osteogenic or chondrogenic cell fate, such as the key chondrogenesis gene Sox9. In summary, our data indicated that Yap/Taz play pivotal roles in determining osteogenesis or chondrogenesis of NC, partly through interactions with the Wnt-β-catenin pathway, which reveal potential novel diagnostic and therapeutic targets for the NC-derived diseases.