Substrate-mediated collective cell migration incalvarial bone expansion and disease.

Summary Congenital defects affecting the formation of the skull roof, such as craniosynostosis or persistent fontanelles, occur as a result of abnormal calvarial growth and differentiation. We lack a basic understanding of how calvarial bones grow, which in turn impacts the position, patterning, and fusion of sutures, and thus etiology of these

disorders. The Harris and Atit laboratories have uncovered an unexpected and intriguing role for cellular sensing of graded fibronectin matrix in preferentially regulating apical expansion of calvarial progenitors during mouse development. When cellular lamellipodia are inhibited, mouse calvarial osteoblasts fail to appropriately migrate

resembling defects seen when we conditionally delete fibronectin. These findings are bolstered by data that fibronectin is misregulated in patients with craniosynostosis as well as animal models of this disease. We propose that graded fibronectin may act as a substrate for coordinated migration of calvarial osteoblast progenitors over

the skull roof. Our central hypothesis is that calvarial growth and suture patency are dependent on fibronectin-directed calvarial progenitor cell expansion. Through three focused mechanistic and translational aims, we will directly test this model and hypothesis of fibronectin substrate-mediated migration

underlying a diverse number of cranial pathologies. First, we will assess outcomes of altered fibronectin expression in regulation of calvarial growth. Second, using newly established genetic lines in mouse and zebrafish, we will test the dependence on fibronectin adhesion and the role of lamellipodia-dependent cellular

sensing of an extracellular gradient in apical expansion of calvaria. Third, we will capitalize on diverse mouse models of craniosynostosis to assess commonality of fibronectin disruption in clinically relevant dysmorphologies and whether decreasing fibronectin expression rescues craniosynostosis in in vivo. Our unique genetic tools in

both mouse and zebrafish will allow us to define the function of fibronectin-guided, lamellipodia-based, collective cell movement in vivo during calvarial bone expansion and the impact of fibronectin deficiency on suture patency. Results from these studies will help detail substrate-mediated cell migration of osteoblast progenitors and will

lead to new strategies for targeted therapies of calvarial bone defects and craniofacial disorders.