Umar, M.; Bartoletti, G. M.; Sokolowskei, D.; Janser, N.; Tower, R.; He, F.

Craniosynostosis is a congenital defect characterized by the premature fusion of calvarial bones, often attributed to the loss of fibrous sutures or deregulated bone formation. Recent studies have reported abnormal cartilage formation in multiple synostosis models, suggesting a potential role for cartilage in suture formation and maintenance. The tectum transversum (TTR) is a transient cartilage located between the coronal suture and dura, adjacent to the frontal and parietal bones. Abnormal TTR formation has been observed in several models; however, its role in coronal suture development remains unclear. In this study, we investigated the developmental process of TTR in a mouse model and characterized its formation in relation to adjacent tissues, including the calvarial bones and the coronal suture. Through genetic ablation of TTR, we demonstrated its essential role in maintaining coronal suture patency. Furthermore, spatial transcriptomics data suggest that TTR may function as a barrier to BMP signaling activation in the coronal suture, a process potentially influenced by the dura. These findings provide new insights into the mechanisms regulating coronal suture development and the etiology of coronal synostosis.