Genetic Regulatory Network in Craniofacial Development

Abstract This competitive renewal continues our efforts to decipher the skeletogenic signaling network underlying craniofacial development and disease. The craniofacial skeleton consists of the viscerocranium and neurocranium, which are subdivided into the calvarium and chondrocranium. During calvarial development, cranial sutures serve as the growth center for skeletogenesis. Defects in suture morphogenesis resulting in premature closure cause craniosynostosis, a devastating childhood disease affecting 1 in ~2,000 individuals. Although human genetic analyses have identified genes associated with the pathogenesis, little is known about the regulation of suture closure essential for the development of a healthy skull. In the previous funding periods, we identified and isolated skeletal stem cells residing in the suture mesenchyme. These suture stem cells (SuSCs) are essential for calvarial development in infants, homeostatic maintenance in adults, and injury- induced bone repair in a cell-autonomous fashion. The in vivo clonal analysis further demonstrates calvarial bone regeneration at a single-cell level. Implantation of SuSCs to an injured site shows not only long-term survival but also facilitation of bone healing via direct engraftments in which the implanted stem cells give rise to osteogenic cell types in the replacement of the damaged tissue. These discoveries also have led to the identification of BMP type I receptor BMPR1A as a stem cell regulator whose ablation in SuSCs disrupts their stemness; the finding of stem cell exhaustion as a new mechanism of craniosynostosis; the purification of human SuSCs-based on cell surface expression of BMPR1A. SuSC characterizations have had tremendous impacts on our understanding of disease etiology and craniofacial reconstruction. In this proposal, we continue our in-depth evaluations of SuSCs by examining their regulation by the crosstalk of skeletogenic signaling essential for healthy development and homeostasis of the calvarium. We will concentrate on the elucidation of molecular and cellular mechanisms underlying craniosynostosis caused by the dysregulation of SuSCs.