Bone Abstracts

COMP (Cartilage Oligomeric Matrix Protein) is a member of the thrombospondin family of extracellular matrix proteins and also referred to as thrombospondin-5. Mutations in COMP lead to chondrodysplasias. Here we studied COMP in zebrafish (Danio rerio) which is a powerful vertebrate model organism. In silico analysis revealed that only one COMP coding gene exists in zebrafish and that the domain structure of COMP is fully conserved. Inspection of gene locus and phylogenetic analysis confirmed that zebrafish COMP is indeed the ortholog of mammalian COMP. Zebrafish COMP was recombinantly expressed, used for immunization of rabbits and guinea pigs and the antisera were affinity purified against recombinant COMP. Immunohistochemistry using affinity purified antibodies showed COMP expression already in early stages of development. Starting from 10 hpf COMP is detected in the somites. This was unexpected, as such an early expression is not known for mammalian COMP. However, in situ hybridization confirmed the unexpected early expression. As in mammals at later stages COMP is found in cartilage, tendons and skin. Nevertheless, in comparison with the strongly expressed cartilage-specific protein matn3a, COMP is only moderately expressed in cartilage. Western blot analysis carried out from protein extracts revealed that zebrafish COMP also forms disulfide-liked pentamers. By Crispr/Cas9, we are aiming at producing mutant zebrafish lines that can be used as models to gain further insight into the pathomechanism and treatment of chondrodysplasias.