Molecular cloning, sequencing, and tissue and developmental expression of mouse cartilage oligomeric matrix protein (COMP)

Mouse cartilage oligomeric matrix protein cDNA was cloned and sequenced by a reverse transcription-polymerase chain reaction. The open reading frame encoded a product of 755 amino acids that shares a high degree of identity to and possesses all the characteristic molecular features of both rat and human cartilage oligomeric matrix protein. This suggests that cartilage oligomeric matrix protein is highly conserved during evolution. The clone was 83, 84, and 95% identical to human, bovine, and rat cartilage oligomeric matrix protein cDNA, respectively. In tissues from the adult mouse, cartilage oligomeric matrix protein was expressed not only in cartilage and tendon but in trachea, bone, skeletal muscle, eye, heart, and placenta as well, and no expression was found in other tissues. Immunohistology revealed that cartilage oligomeric matrix was deposited as early as 10 days post coitus in predifferentiated mouse embryo mesenchyme. It was detected in all cartilaginous tissues and in the skeletal muscles of the embryo at day 13. As development progressed, accumulation of cartilage oligomeric matrix protein was marked in the growth plate. At 19 days post coitus, it was prominently deposited in the hypertrophic zone of the growth plate, perichondrium, and periosteum and in the superficial layer of the articular cartilage surface but was absent in the more central areas of the epiphyseal cartilage. The restricted tissue distribution and expression of cartilage oligomeric matrix protein in developing as well as adult mouse tissues suggest the regulation of this protein at the transcriptional level. The findings reported herein are the first detailed characterization of the distribution of cartilage oligomeric matrix protein during early skeletal development of the mouse.