Biochemical compensation among matrilins. (A) Whole-mount skeletal staining at postnatal day 2 (P2) shows no obvious skeletal defects in mice lacking matrilin-1, -2 and -3 (Matn1-3−/−) compared to wild type. (B) HE staining of the proximal tibia (original magnification × 10) of the knee joint indicates normal growth plate and articular cartilage structures in Matn1-3−/− mice at 4 weeks of age. (C) Western blot analyses of sequential cartilage extracts (I-neutral salt; II-high salt/EDTA; III-GuHCl) from newborn mice indicates upregulation of matrilin-4 in mice lacking matrilin-1 (m1), matrilin-2 and -3 (m23), matrilin-1 and -3 (m13), and matrilin-1, -2, and -3 (m123). (D) HE staining of the proximal tibia (original magnification × 10) of the knee joint at 4 weeks of age demonstrates that mice lacking matrilin-4 (Matn4−/−) have a normal structure of long bones. (E) Immunohistochemistry (IHC, original magnification × 10) indicates the increased deposition of matrilin-2 in the growth plate of the humerus (rectangle, original magnification × 20) of Matn4−/− mice. (F) Western blot analyses show increased amounts of matrilin-2 in cartilage extracts of Matn4−/− mice (m4), while the levels of matrilin-1 and matrilin-3 are unchanged. Abbreviation: MW-molecular weight marker.