Growth plate mature chondrocytes contribute to the osteoblast pool during postnatal growth.

<p>Two-week-old <i>Agc1-CreERT2; ROSA-tdTomato, Agc1-CreERT2; 2.3-GFP;ROSA-tdTomato</i> and control mice were treated with tamoxifen and sacrificed 8 days (A) and 28 days post injection (B). All images in this figure are images of femur sections. A: Panel a: neither Tomato nor EGFP signals were detected in the <i>ROSA-tdTomato</i> control. Panel b (blue and red channels): the fluorescence image revealed that there were more Tomato⁺ cells in the primary spongiosa in the post injection day 8 <i>Agc1-CreERT2; 2.3-GFP;ROSA-tdTomato</i> mouse compared to the post injection day 2 mouse (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004820#pgen-1004820-g007" target="_blank">Fig. 7B</a> right panels), and the Tomato⁺ cells in the day 8 mouse were distributed in an even broader area than in the day 2 mouse. Very few Tomato⁺ cells were found on the endosteum and within the cortex. Panel b′: blue, red and green channels. Lower panels: magnified images of primary spongiosa in b′. Lower left (red rectangle): red and blue channels; Lower middle (green rectangle): green and blue channels; Lower right (yellow rectangle): red, green and blue channels: a few Tomato⁺EGFP⁺ cells (white arrows) were present in the primary spongiosa especially in proximity of the periosteum. B: Panel a: no Tomato or GFP signals were detected in the post tamoxifen day 28 <i>ROSA-tdTomato</i> control. Panel b: in the post tamoxifen day 28 <i>Agc1-CreERT2; ROSA-tdTomato</i> mouse, not only was the number of Tomato⁺ cells in the primary spongiosa increased compared to the post injection day 8 mouse, but some of these Tomato⁺ cells were on the endosteum (red arrows) and embedded within the cortex (green asterisk). Panel c: there were many more Tomato⁺EGFP⁺ cells (white arrows in magnified lower right panel) in the day 28 <i>Agc1-CreERT2; ROSA-tdTomato</i> mouse than in the day 8 mouse (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004820#pgen-1004820-g008" target="_blank">Fig. 8A</a>). Lower left panel: magnified trabecular area of panel c (red and blue channels) showed that there were many Tomato⁺ cells on the trabecular surfaces (white arrows) and embedded within the trabeculae (white arrowheads). Red arrowhead: periosteum; Green arrowhead: endosteum; gp: growth plate (white brackets); ps: primary spongiosa.