Normal skeletal development of mice lacking matrilin 1: Redundant functionof matrilins in cartilage?

Matrilin 1, or cartilage matrix protein, is a member of a novel family of e xtracellular matrix proteins. To date, four members of the family have been identified, but their biological role is unknown. Matrilin 1 and matrilin 3 are expressed in cartilage, while matrilin 2 and matrilin 4 are present i n many tissues. Here we describe the generation and analysis of mice carryi ng a null mutation in the Crtm gene encoding matrilin 1. Anatomical and his tological studies demonstrated normal development of homozygous mutant mice . Northern blot and biochemical analyses show no compensatory up-regulation of matrilin 2 or 3 in the cartilage of knockout mice. Although matrilin 1 interacts with the collagen II and aggrecan networks of cartilage, suggesti ng that it may play a role in cartilage tissue organization, studies of col lagen extractability indicated that collagen fibril maturation and covalent cross-linking were unaffected by the absence of matrilin 1. Ultrastructura l analysis did not reveal any abnormalities of matrix organization. These d ata suggest that matrilin 1 is not critically required for cartilage struct ure and function and that matrilin 1 and matrilin 3 may have functionally r edundant roles.