PMC

Shows tenocyte markers expressed throughout the patellar tendon. A–D show type I collagen, F–I show fibromodulin, and K–N show tenomodulin expression using specific antibody staining. Specific staining in each case is red, and blue shows nuclear staining using DAPI. E, J, and O show semi-quantitation of the antibody staining by measurement of pixel intensity. Scale bar=100 μm. Error bar represents standard error, and the asterisk represents statistical significance (p<0.05). DAPI, 4′,6-diamidino-2-phenylindole.

Shows tenocyte markers expressed predominantly in the tibial insertion site. A–D show tenascin-C, F–J show biglycan, and K–N show COMP staining using specific antibodies. In each panel, red is specific stain, and blue shows cell nuclei stained using DAPI. Scale bar=100 μm. E and J show semi-quantitation of the antibody staining by measurement of pixel intensity. Scale bar=100 μm. Error bar represents standard error, and the asterisk represents statistical significance (p<0.05). COMP, cartilage oligomeric protein.

Shows activated cell signaling pathways in the developing patellar tendon. A–D show cells responding to bone morphogenetic protein signaling (brown stain) using an antibody against pSmad1/5/8. Cell nuclei are stained using fast red. E–H show cells responding to transforming growth factor beta signaling using an antibody against pSmad2/3. Cell nuclei are stained with fast red. I–L show cells responding to FGF signaling (brown stain) using an antibody against pFGFr1. Nuclei are stained with DAPI (blue). M–P show cells responding to hedgehog signaling (blue stain), using the Gli1-LacZ reporter line. Cell nuclei are stained with fast red. Q show the summary of intensity levels of pSmad1/5/8, pSmad2/3, pFGFr-1, and Gli1-LacZ. Scale bar=100 μm. FGF, fibroblast growth factor.

Shows hematoxylin and eosin stained mid-sagittal sections of the mouse patellar tendon at E17.5 (A, E, I), P1 (B, F, J), P7 (C, G, K), and P14 (D, H, L). Higher magnification images of the midsubstance are shown in E–H and of the tibial insertion sites in I–L. P, patella; T, tibial. Scale bar=100 μm. E17.5, embryonic day seventeen and half; P1, P7, P14, postnatal days 1, 7, 14.

Shows cells that are still in the cell cycle in the patellar tendon at E17.5 (A), P1 (B), P7 (C), and P14 (D), using an antibody against Ki67 (red stain). Nuclei are stained blue with DAPI, tenocytes are green, using the ScxGFP reporter mouse line. Cycling cells in the connective tissue of the epitenon are GFP-negative (arrowheads), whereas tenocytes in the cell cycle are GFP-positive (arrows). Scale bar=100 μm. (E) shows counts of cycling cells in the patellar tendon at each stage (mean±SEM) gained by counting Ki67-positive cells from 10 random sections from 3 knee joints at each stage. The asterisk represents statistical significance (p=0.3387 at E17.5, p=0.338 at P1, p=0.001 at P7, and p=0.0001 at P14). ScxGFP, scleraxis-green fluorescent protein.