BMP-eBM niche formation involves a timely orchestration of cellular differentiation. (A-B) Analysis of BMP-eBM development compared to femoral secondary ossification center (SOC). BMP-eBMs were harvested 3, 5, 7, 10, 14, or 28 days after implantation. Femurs were harvested from C57BL6J mice at postnatal day 3 (P3), P5, P7, P10, P14, or P28. (A) Safranin-O staining images (upper panels). High-middle panels are high-magnification images of the squares in the upper images. Middle-lower panels: green, Cxcl12-GFP; red, Emcn. Lower panels: green, Col1a1(2.3)-GFP; red, Trap-tdTomato. The blue color represents DAPI staining. (B) Semiquantitative analysis of the cellular populations during BMP-eBM and LB-BM development (illustrative). (C) Fluorescence images of BMP-eBM or LB-BM 4 weeks after implantation in LepR-cre; tdTomato mice. Red, LepR-cre; tdTomato; green, Runt-related Transcription Factor 2 (Runx2); blue, DAPI. (D) Frequency of tdTomato⁺ per Runx2⁺ cells (n = 4).