Fig. 5.

Sox9 lineage cells of the embryonic enthesis do not contribute to postnatal migrating entheses. (A) Pulse-chase cell lineage experiment using Sox9-CreER^T2;R26R-td Tomato mice demonstrates that Sox9 lineage contributes differently to migrating and to stationary entheses. Sox9⁺ cells were marked at E12.5 by a single tamoxifen administration. At P0, tdTomato⁺ cells were identified in migrating DT and TM entheses (Aa,Ab) as well as in stationary Achilles entheses (Ac). At P14, only a few tdTomato⁺ cells were identified in migrating entheses (Aa′,Ab′,Ad), whereas extensive staining was still seen in stationary entheses (Ac′) and in other areas of the bone, as seen in a section through the humerus in Ad. (B) The contribution of Sox9 lineage to the DT and TM entheses was evaluated by crossing Sox9-Cre or Sox9-CreER^T2 mice with R26R-tdTomato reporter mice. (Ba,Bh) The total contribution of the lineage was evaluated by examination of Sox9-Cre;R26R-tdTomato mice at P14. (Bb-Bg,Bi-Bn) The relative contribution of Sox9 lineage cells specified at different time points was evaluated by pulse-chase experiments on Sox9-CreER^T2;R26R-tdTomato mice, in which a single dose of tamoxifen was administered at various stages from E11.5 through E17.5. Dashed line demarcates the enthesis. Scale bars: 50 µm.