Single-Cell Atlas of Human Temporomandibular Joint Condyle Identifies MXD4 as a Regulator of Chondrogenesis

INTRODUCTION AND AIMS: The temporomandibular joint condyle (TMJC) is essential for mandibular and temporomandibular joint (TMJ) development. However, its cellular and molecular dynamics during human embryogenesis remain poorly understood. METHODS: We constructed a single-cell transcriptomic atlas of the human TMJC spanning five embryonic stages from 12 to 25 gestational weeks (GW12-25). Single-cell RNA sequencing was performed to identify cell types, and Monocle 3 and SCENIC analyses were used to infer developmental trajectories and identify key transcriptional regulators. Candidate regulators were functionally validated using zebrafish models. RESULTS: Single-cell RNA sequencing identified 20 major cell types within the TMJC. Immune cells were sparse at GW19 but expanded markedly by GW22. Trajectory analysis revealed a differentiation pathway from mesenchymal stem cells to chondrocytes. SCENIC analysis highlighted multiple transcription factors regulating distinct cell populations, among which MXD4 was identified for the first time as a candidate transcriptional regulator of cartilage development. Functional studies showed that mxd4 knockout in zebrafish led to craniofacial developmental abnormalities. CONCLUSION: This single-cell atlas provides a comprehensive resource for understanding the cellular and molecular mechanisms underlying TMJC development. MXD4 is identified as a candidate regulator in condylar morphogenesis. CLINICAL RELEVANCE: Preliminary investigation of the potential regulatory role of MXD4 in condylar cartilage formation may provide a theoretical basis for diagnostic, therapeutic, and translational studies of craniofacial malformations associated with condylar hypoplasia.