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

INTRODUCTION AND AIMSThe 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.

METHODSWe 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.

RESULTSSingle-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.

CONCLUSIONThis 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 RELEVANCEPreliminary 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.