The tectum transversum maintains patency of the developing coronal suture.

Craniosynostosis, the premature fusion of calvarial bones, is a common congenital defect often attributed to the loss of fibrous sutures or excessive ossification. Recent studies have reported aberrant cartilage formation near affected sutures, suggesting a previously unrecognized role for cartilage in suture morphogenesis and maintenance. The tectum transversum (TTR), a transient cartilage adjacent to the coronal suture, has been considered absent in humans. By analyzing published human embryonic datasets, we demonstrate that the TTR is in fact a conserved structure in humans. We further investigated the developmental dynamics and function of the TTR in mice. Spatial transcriptomic analyses reveal that the TTR mediates critical tissue-tissue interactions and may serve as a physical and molecular barrier restricting BMP signaling activation within the coronal suture, potentially modulated by the underlying dura mater. These findings identify the TTR as a conserved regulator of coronal suture morphogenesis and provide new mechanistic insight into the etiology of coronal craniosynostosis.