Mouse cathepsin K: cDNA cloning and predominant expression of the gene in osteoclasts, and in some hypertrophying chondrocytes during mouse development

We have constructed cDNA clones covering the entire coding region of mouse, human and rabbit preprocathepsin K mRNA for studies on bone turnover. The clone pMCatK-1 for mouse cathepsin K shares 87% nucleotide homology with the corresponding human and rabbit sequences. Analysis of a panel of mouse tissues for tissue distribution of cathepsin K mRNA revealed the highest levels in musculoskeletal tissues: bone, cartilage and skeletal muscle. In situ hybridization of developing mouse embryos was performed to identify the cellular source of cathepsin K mRNA. The strongest mRNA signal was detected in osteoclasts of bone, identified in serial sections by positive TRAP staining. Cathepsin K mRNA was also observed in some hypertrophic chondrocytes of growth cartilages. Association of cathepsin K production with degradation of bone and cartilage matrix suggests that this enzyme and its mRNA levels could serve as markers for matrix degradation in diseases affecting these tissues.