Distinct roles of neural crest cell populations in cranial suture development and disease - PROJECT SUMMARY Cranial sutures are fibrous joints that separate the flat bones of the skull; they coordinate growth of the brain and the overlying calvarium. Premature fusion of sutures, known as craniosynostosis, affects 1:2,250 (148,000) children each year. Synostosis causes facial deformities, skull defects, and brain damage via intracranial pressure. Surgical intervention is the most common treatment, often as a suite of corrective postoperative refusion surgeries, each of which increases patient morbidity and mortality. Thus, patients and their families experience profound physical, cognitive, social, and financial burdens. A biological therapeutic that resolves suture fusions in vivo is not yet identified, perhaps because a long-standing question in the field is why do post- operative fusions occur? One often affected tissue that holds osteogenic potential to induce calvarial ossifications is the underlying meninges, which segregates the brain from the calvarial bone. The meninges, composed of neural crest and mesoderm lineages, plays an instructive role in calvarial healing, suture patency, and closure, but how the meninges regulate the development and maintenance of the overlying sutures remains unknown. Fibroblast growth factor (FGF) signaling makes up 50% (74,000 cases annually) of syndromes that result in premature skull fusion, including Crouzon, Beare-Stevenson, Bent Bone Dysplasia (BBDS), Apert and Pfeiffer. The latter two syndromes are among the most severe. All five syndromes result from gain-of-function mutations in FGF Receptor 2 (FGFR2; 32%). The involvement of FGFR2 in several congenital disorders underscores this gene’s clinical relevance [17-23]. Therefore, a deeper understanding of the diseased state of the receptor is necessitated for breakthroughs in therapeutics that will attenuate skull fusions and reduce the need for multiple surgeries. FGFR2 is highly expressed at the suture bone fronts and throughout the underlying meninges; yet the role of FGFR2 in the meninges is not well understood. Mouse conditional activation of nuclear Fgfr2 (BBDS allele) in neural crest cells result in progressive multi-suture synostosis, with meningeal neural crest contribution to mesoderm-derived bones. But the identity of the populations that cross the neural crest-mesoderm boundary, are unknown. To understand the neural crest/meningeal regulation of the suture, I will employ the mouse conditional allele, Fgfr2IIIcΔ/+, because it mimics more severe forms of synostoses, BBDS, Apert and Pfeiffer’s. Therefore, I will test the hypothesis that distinct neural crest populations expressing Fgfr2IIIcΔ/+ during development induce synostosis by reducing the levels of CCN2, a patency inducer, near cranial sutures. In Aim 1, I will determine the role of neural crest-derivatives in Fgfr2IIIcΔ/+ -mediated synostosis. In Aim 2, I will determine whether overexpression of the Fgfr2 noncanonical inhibitor, CTGF/CCN2, in distinct neural crest populations resolves Fgfr2IIIcΔ/+-mediated synostosis during development and adulthood. Completion of this study will reveal the role of neural crest cell/meninges in suture development, congenital disease, and will identify candidate biological therapeutics for suture regeneration.
