Role of Notch Signaling in the Physiological Patterning of Posterofrontal and Sagittal Cranial Sutures.

Background: The mutations in a Notch signaling ligand, jagged 1, are associated with unilateral coronal craniosynostosis in humans. However, the underlying mechanisms of Notch signaling in cranial suture biology still remain unclear. Methods: The temporal and spatial patterns of Notch signaling expression were examined in the posterofrontal and sagittal sutures of Sprague-Dawley rats by real-time quantitative reverse-transcription polymerase chain reaction at postnatal ages of 2, 15, and 25 days. The role of Notch signaling in the proliferation and differentiation of osteoblasts isolated from calvarial was examined in vitro by EdU incorporation assays and real-time quantitative reverse-transcription polymerase chain reaction after activating and inhibiting Notch signaling. Results: The mRNA levels of Notch family members (including Jagged 1, Delta 1, 3, 4, Notch 1-4, Hes 1, and Hes 5) decreased during the posterofrontal cranial suture fusion in rat. However, in the patent sagittal sutures, the mRNA levels of Notch family members (Jagged 2, Delta 1, Notch 1, Notch 3, Hes 5, and Hey 1) increased during suture development. The EdU incorporation assays revealed that the induction of Notch signaling in calvaria osteobalsts using Jagged 1 promoted the proliferation rates in those cells in vitro. Further studies showed that activation of Notch signaling calvaria osteobalsts using Jagged 1 led to the suppression of late osteogenetic markers such as type I collagen and osteocalcin. Conclusions: The regulation of Notch signaling is of crucial importance during the physiological patterning of posterofrontal and sagittal cranial sutures. Thus, targeting this pathway may prove significant for the development of future therapeutic applications in craniosynostosis. (C) 2017 by Mutaz B. Habal, MD.

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