Erα Induced Refaly Phase Separation Drives Condylar Hypertrophic Chondrocyte Transdifferentiation

This study investigates whether estrogen deficiency impairs mandibular development by disrupting hypertrophic chondrocyte (HCC) transdifferentiation into osteoblasts. Col10-creERT2;R26RtdTomato;Col1a1-GFP gene-traced mice and Col10-creERT2-ZSGreen-DTA mice were used. Single-cell transcriptomics, ChIP-seq, fluorescence recovery after photobleaching (FRAP), tissue clearing technology, and in vitro assays (ATDC5 cells) assessed ERα-mediated Irx3 regulation through phase separation (IACUC: 2308037). Local estrogen and Irx3-overexpressing adenovirus in vivo therapy were tested in OVX gene-traced mice. (1) Estrogen-deficient mice exhibited impaired condylar subchondral bone formation and reduced HCC transdifferentiation. (2) ERα recruited coactivator REF/Aly to induce phase separation, enhancing Irx3 transcription and osteogenic differentiation. (3) Local estrogen or Irx3 therapy rescued mandibular underdevelopment in OVX mice. Estrogen-ERα promotes Irx3 expression via phase separation, driving HCC transdifferentiation and mandibular growth. Targeting ERα-Irx3 axis could treat estrogen-related mandibular micrognathia.