The origin and function of tendon progenitors in craniofacial morphogenesis and patterning



 DESCRIPTION (provided by applicant): The development of the craniofacial musculoskeletal system is a complex process involving the coordination of cell type specification, morphogenesis, patterning and growth. Many human craniofacial conditions such as congenital malformations or postnatal disorders often result from disruptions to one or many of these processes. Despite advances understanding the genetic basis of craniofacial diseases, many aspects of craniofacial development remain poorly understood. In particular, it is unknown how the connective tissue cell types, the tendons and ligaments, are specified and function in craniofacial musculoskeletal development and growth. Indeed, the precise placement and coordinated assembly of the musculoskeletal tissues is required for proper movement. Within the cranial skeleton, abnormal assembly or growth of the musculoskeletal system can result in craniofacial dysmorphology or disease. Tendons and ligaments are essential components of the musculoskeletal system by serving to connect the muscle and bone tissues. Surprisingly, given their importance in enabling movement, very little is known about their formation and function in regulating musculoskeletal patterning and growth. Transplantation studies have suggested that the neural crest derived connective tissues pattern the muscle attachment sites, but the specific function of the cranial tendon and ligament progenitors in this process or in the regulation of other events in craniofacial development has not been explored. We aim to address these major questions using the zebrafish model system. In the zebrafish, we have established that the tendons and ligaments in the craniofacial region are analogous to mammalian tendons in gene expression, morphology, developmental regulation, and ultrastructural characteristics. Using our tendon and ligament markers and a photoconvertible transgenic line, we will create a precise fate map of the tendon and ligament progenitors within the early pharyngeal arch domains. These lineage experiments will be the basis for future studies focusing on tendon cell specification and differentiation in different functional contexts. Next, we have engineered transgenic lines to perform tendon and ligament cell ablation experiments, thus determining their paracrine role in craniofacial development and growth. Finally, we have created scx mutant zebrafish lines to study its role in tendon elongation and craniofacial musculoskeletal morphogenesis. Together, these experiments provide an integral step towards elucidating the molecular pathways regulating tendon and ligament cell induction and function in the context of craniofacial musculoskeletal development, and have the potential to impact our understanding of craniofacial disorders.