Fig. 2.

Skeletal contribution of Ddr2-expressing cells. a Protocol. b–d, Lineage tracing in Ddr2^mer-iCre-mer; R26R^tdTomato mice at the postnatal day 5 (P5), P14 and 2 months (n = 2 mice). Red: Ddr2-positive cells; gray: cell nuclei; gp Growth plate; bm Bone marrow; SOC Secondary ossification center; ms Muscle; R Resting zone; P Proliferative zone; H Hypertrophic zone. b Fluorescent tdTomato (red) distribution in the proximal tibia at P5 showing initial labeling in perichondrium, periosteum, primary spongiosa, and sporadic cells in the growth plate. Scale bar: 200 μm. The boxed region is shown in higher magnification (right). Arrowheads indicate expression in perichondrium. Scale bar: 100 μm. c Fluorescent tdTomato distribution at P14 showing label in the resting and proliferative zones of growth plate and in primary spongiosa, but not in the hypertrophic zone. Scale bar: 200 μm. Boxed region is shown in higher magnification (right) Scale bar: 100 μm. Dotted Line denotes chondro-osseous junction. d Fluorescent tdTomato distribution at 2 months showing persistence of tdTomato labeling and contribution to (1) growth plate columns, (2) bone cells in primary spongiosa, and (3) periosteum and osteocytes in cortical bone (arrowheads). Scale bar: 200 μm. Images at a higher magnification for different areas of tibia are shown on the right side. Scale bar: 20 μm. e High power image of 2-month growth plate and trabecular regions showing co-staining of tdTomato⁺ cells with an anti-OSX antibody (green) in osteoblasts on the trabecular surface. Scale bar: 100 μm