Fig. 2: Macro-, micro-, and nano-structural abnormalities in load-bearing tendons of Fgf7^−/− mice.

A Gross morphological observation of the patellar tendon, flexor digitorum longus tendon and Achilles tendon in Fgf7^−/− and wild-type mice. Tendons under mechanical load exhibited developmental abnormalities, including the patellar tendon (left), flexor digitorum longus tendon (middle), and Achilles tendon (right). Arrows indicate respective tendons. B Hematoxylin and eosin (HE) staining of the patellar tendon at postnatal days 14, 21, and 10 weeks in Fgf7^−/− and wild-type mice. Scale bars, 20 μm. C Statistical analysis of patellar tendon thickness and patellar tendon paratenon thickness in HE-stained sections at postnatal days 14, 21, and 10 weeks in Fgf7^−/− and wildtype mice (n = 6 per time point, independent experiments, bars represent mean ± SD; WT wildtype. NS: not significant, **p < 0.01, ***p < 0.001, two-tailed Student’s t test. Patellar tendon thickness at postnatal days: 14 days: t = 0.4736, df = 10; 21 days: t = 15.31, df = 10; 10 weeks: t = 7.932, df = 10. Patellar tendon paratenon thickness at postnatal days: 14 days: t = 0.4783, df = 10; 21 days: t = 7.496, df = 10; 10 weeks: t = 4.689, df = 10.). D HE staining of the Achilles tendon at postnatal days 14, 21, and 10 weeks in Fgf7^−/− and wildtype mice. Scale bars, 20 μm. E Statistical analysis of Achilles tendon thickness and Achilles tendon paratenon thickness in HE-stained sections at postnatal days 14, 21, and 10 weeks in Fgf7^−/− and wildtype mice (n = 6 per time point, independent experiments, bars represent mean ± SD; WT wildtype. NS: not significant, ***p < 0.001, two-tailed Student’s t test. Achilles tendon thickness at postnatal days: 14 days: t = 0.2470, df = 10; 21 days: t = 4.356, df = 10; 10 weeks: t = 4.443, df = 10. Achilles tendon paratenon thickness at postnatal days: 14 days: t = 0.9618, df = 10; 21 days: t = 7.398, df = 10; 10 weeks: t = 6.257, df = 10.). F Polarized light images of the patellar tendon at postnatal days 14, 21, and 10 weeks in Fgf7^−/− and wildtype mice. Scale bars, 100 μm. Representative polarized light images from three independent experiments with consistent results. G Polarized light images of the Achilles tendon at postnatal days 14, 21, and 10 weeks in Fgf7^−/− and wildtype mice. Scale bars, 100 μm. Representative polarized light images from three independent experiments with consistent results. Transmission electron microscopy (TEM) images (H) showing transverse and longitudinal sections of collagen fibers in the patellar tendon at 10 weeks in Fgf7^−/− and wildtype mice (n = 3), scale bars: 200 nm, and their respective collagen diameter distribution (I). Scale bars, 0.2 μm. TEM images (J) showing transverse and longitudinal sections of collagen fibers in the Achilles tendon at 10 weeks in Fgf7^−/− and wildtype mice (n = 3), scale bars: 200 nm, and their respective collagen diameter distribution (K). Scale bars, 0.2 μm. Source data are provided as a Source Data file.