Genetic Rescue of Chondrodysplasia and the Perinatal Lethal Effect of Cartilage Link Protein Deficiency

Abstract

The targeted disruption of cartilage link protein gene (Crtl1) in homozygous mice resulted in a severe chon- drodysplasia and perinatal lethality. This raised the question of whether the abnormalities seen in Crtl1 null mice are all caused by the absence of link protein in cartilage or whether the deficiency of the protein in other tissues and organs contributed to the phenotype. To address this question we have generated transgenic mice overexpressing cartilage link protein under the control of a cartilage-specific promoter, and then these transgenic mice were used for a genetic rescue of abnor- malities in Crtl1 null mice. While the overexpression of cartilage link protein resulted in no abnormal pheno- type, the cartilage-specific transgene expression of link protein could completely prevent the perinatal mortal- ity of link protein-deficient mice and, depending on the level of the link protein expression, rescue skeletal ab- normalities. Although link protein was originally iso- lated from cartilage, we found and determined Crtl1 transcripts and corresponding proteins in every organ tested from mouse embryos to aging animals. We also identified three additional members of the link protein family, all co-localized with hyaluronic acid-binding proteoglycans in the mouse genome. The ubiquitous presence of link protein suggests a general and systemic function of link protein in the organization of extracel- lular matrix in a number of tissues, possibly interacting with other proteoglycans, such as versican, brevican, and neurocan.