Molecular cloning of rabbit hyaluronic acid synthases and their expression patterns in synovial membrane and articular cartilage.

cDNAs for hyaluronic acid synthases (HAS2 and HAS3) were cloned from a cDNA library of cultured rabbit synovial membrane cells. The cDNA encoding the open reading frame of rabbit HAS2 and HAS3 was 1659 nucleotides in length with a predicted molecular mass of about 63 kDa. The amino acid sequence showed that the rabbit HAS2 was 98.7 and 98.4%, and HAS3 was 98.2 and 97.5% identical with human and mouse forms of the proteins, respectively. The predicted sequences for hyaluronic acid (HA) binding motifs and the catalytic domains related to beta 1-4 and beta 1-3 linkages, essential for HA synthesis, were almost conserved in both rabbit HAS2 and HAS3, similarly to human and mouse HASs. RT-PCR analysis and in situ hybridization revealed that the mRNA of HAS2 was highly expressed in the synovial membrane and articular cartilage, whereas the expression of HAS3 mRNA was slightest in these tissues. Thus, it is demonstrated that rabbit HASs are highly conserved in sequence content as compared to the human and mouse homologues described previously, and that HAS2 is predominantly expressed in the synovial membrane and articular cartilage, but HAS3 is not.