Matrilin-1 (cartilage matrix protein; Matn1) is a homotrimeric protein that forms collagen-dependent and collagen-independent fibrils in the extracelluar matrix of cartilage.
These targeted mutant mice carry a knockout allele of the Matn1 gene. Ultrastructural studies of the cartilage of long bone growth plates from homozygotes reveals an abnormal type II collagen fibrillogenesis and fibril organization in the matrix of the zone of maturation. In contrast to the meshwork-like organization of collagen fibrils in wildtype cartilage, the fibrils of matrilin null animals are unidirectional. Fibrils in the mutant cartilage also become significantly larger in diameter than those of controls. The cartilage matrix is stiffer in knockout mice, and the knee joint is prone to injury-induced osteoarthritis.
Reduced matrilin content in the pericellular matrix surrounding chondrocytes decreases their proliferative/gene expression responses to mechanical stimulation. Chondrocytes from the knockout mice cultured under mechanical pressure show only a 0.5-fold increase in mRNA levels of collagen type X, in comparison to the more than 2.5-fold increase seen in wildtype chondrocytes.
Mice heterozygous or homozygous for the targeted allele grow normally and display no major phenotypic differences from the wild-type littermates during skeletal development. Homozygous null mice are fully viable with normal fecundity.
