A single-cell transcriptomic atlas identifies hierarchical skeletal progenitors and zonal patterning in mouse mandibular cartilage.

Skeletal and synovial joint development involves distinct skeletal stem/progenitor populations. However, in neural crest-derived temporomandibular joint (TMJ), skeletal stem/progenitor lineage dynamics and ossification programs remain poorly defined. Here, we performed single-cell RNA sequencing (scRNA-seq) on mouse mandibular cartilage at embryonic day 16.5 (E16.5), postnatal day 0 (P0), and 13 weeks to construct a high-resolution atlas of skeletal stem/progenitor populations. At embryonic and postnatal stages, the outer perichondrium contained Lgr5+Pthlh+ cells expressing Dlx5, consistent with an intramembranous ossification-associated program. In contrast, a previously uncharacterized Crabp1+ subpopulation within the inner perichondrium expressed Nrg1, Lsamp, Tac1, and Igfbp5, consistent with an early chondrogenic-associated transcriptional state. These results suggest spatially distinct ossification-associated programs and reveal the transcriptional regulation underlying TMJ development. Our findings provide a model for understanding neural crest-derived TMJ skeletal stem/progenitor cell regulation and may inform future studies of TMJ cartilage biology and regeneration strategies within this specialized tissue.