The role of Pth1r in posterior cranium cartilage regulation and craniosynostosis.

Craniosynostosis is a major craniofacial congenital disorder that causes developmental complications. During normal cranial development, intramembranous ossification forms the flat bones and sutures, while cartilage appears transiently in the posterior calvarial region. However, in craniosynostosis, premature suture fusion disturbs normal calvarial morphogenesis. To clarify the role of transient cartilage in this morphogenetic disruption, we investigated its molecular regulation and pathology in mice, focusing on parathyroid hormone 1 receptor (Pth1r) signaling. Conditional deletion of Pth1r in the cranial mesenchyme unexpectedly caused acrocephalic dysmorphology and craniosynostosis, with altered cartilage differentiation. Occipito-interparietal synostosis consistently occurred in Pth1r-ablated Gli1+ and Acan+ lineages, but not after adult Gli1-CreERT2 deletion, indicating a developmental role. Bulk and single-cell RNA-seq analysis revealed nine mesenchymal subsets, with mutant cells showing abnormal chondrocyte differentiation and upregulated Indian hedgehog (Ihh) signaling. These findings indicate that Pth1r maintains proper chondrogenic regulation during calvarial development, and its loss induces craniosynostosis through Ihh overactivation.