Project Grant F31DE036514

DEFINING THE MOLECULAR AND SPATIOTEMPORAL ROLES OF TWIST1 AND TCF12 IN REGULATING CRANIAL SUTURE - PROJECT SUMMARY CRANIOSYNOSTOSIS IS A CONGENITAL ANOMALY THAT AFFECTS ~1 IN 2,500 LIVE BIRTHS AND IS CHARACTERIZED BY THE LOSS OF THE CRANIAL SUTURES THAT SEPARATE NEIGHBORING CALVARIAL BONES. THE RESULTING BONE FUSIONS CAUSE INCREASED INTRACRANIAL PRESSURE, CRANIOFACIAL DYSMORPHIA, AND NEURODEVELOPMENTAL COMPLICATIONS AND REQUIRE INVASIVE AND OFTEN REPEATED SURGERIES. ALTHOUGH THE GENETIC CAUSES OF SYNDROMIC CRANIOSYNOSTOSIS HAVE BEEN EXTENSIVELY CATALOGED, THE MECHANISMS BY WHICH THESE MUTATIONS DISRUPT SUTURE BIOLOGY REMAIN POORLY UNDERSTOOD. THIS GAP IS EXEMPLIFIED BY SAETHRE-CHOTZEN SYNDROME, A CONDITION DEFINED BY SELECTIVE CORONAL SUTURE FUSION AND HETEROZYGOUS MUTATIONS IN THE BHLH TRANSCRIPTION FACTORS TWIST1 OR TCF12. DESPITE DISCOVERING THIS RELATIONSHIP OVER A DECADE AGO, THE DEVELOPMENTAL ORIGINS OF SUTURE LOSS IN SAETHRE-CHOTZEN SYNDROME REMAIN UNCLEAR. A LONG-TERM GOAL OF THIS PROPOSAL IS TO DEFINE THE MOLECULAR AND CELLULAR BASIS OF SYNDROMIC CRANIOSYNOSTOSIS TO BUILD FOUNDATIONAL PRINCIPLES OF SUTURE BIOLOGY AND ULTIMATELY INFORM NEW STRATEGIES-INCLUDING FUTURE CELL-BASED APPROACHES-TO RESTORE OR ENGINEER FUNCTIONAL SUTURES. RECENT SINGLE-CELL STUDIES HAVE REDEFINED CRANIAL SUTURES AS COMPLEX BUT CONSERVED STRUCTURES COMPOSED OF OSTEOGENIC AND MESENCHYMAL SUBTYPES, HIGHLIGHTING THE NEED TO UNDERSTAND HOW THESE POPULATIONS FUNCTION DURING NORMAL DEVELOPMENT. MOUSE MODELS OF TWIST1 OR TCF12 DEFICIENCY REVEAL EARLY PHENOTYPES, INCLUDING ACCELERATED OSTEOBLAST DIFFERENTIATION AND IMPAIRED BOUNDARY FORMATION, BUT THE PRECISE SPATIAL AND TEMPORAL REQUIREMENTS OF TWIST1/TCF12, AND THE GENE NETWORKS THEY REGULATE IN VIVO, REMAIN UNKNOWN. I HYPOTHESIZE THAT TWIST1 AND TCF12 ACT COOPERATIVELY TO MAINTAIN CORONAL SUTURE IDENTITY BY RESTRICTING OSTEOGENIC GENE NETWORKS AND PRESERVING A NON-OSTEOGENIC SUTURE MESENCHYME. TO TEST THIS, I WILL DEFINE THE CELLULAR ORIGINS OF BONE GROWTH AT THE EMBRYONIC CORONAL SUTURE, RESOLVE WHEN AND WHERE TWIST1/TCF12 ACTIVITY IS REQUIRED, AND IDENTIFY THE TRANSCRIPTIONAL PROGRAMS THAT TWIST1 AND TCF12 CONTROL. THESE STUDIES WILL UNCOVER FUNDAMENTAL MECHANISMS OF CALVARIAL GROWTH AND LAY ESSENTIAL GROUNDWORK FOR STRATEGIES TO PREVENT SECONDARY SYNOSTOSIS OR RESTORE FUNCTIONAL SUTURES.