MIMECAN, THE 25-KDA CORNEAL KERATAN SULFATE PROTEOGLYCAN, IS A PRODUCT OF THE GENE PRODUCING OSTEOGLYCIN

Bovine cornea contains three unique keratan sulfate proteoglycans (KSP Gs), of which two (lumican and keratocan) have been characterized usin g molecular cloning, The gene for the third protein (KSPG25) has not b een identified, This study examined the relationship between the KSPG2 5 protein and the gene for osteoglycin, a 12-kDa bone glycoprotein, Th e N-terminal amino acid sequence of KSPG25 occurs in osteoglycin cDNA cloned from bovine cornea, The osteoglycin amino acid sequence makes u p the C-terminal 47% of the deduced sequence of the KSPG25 protein, An tibodies to osteoglycin reacted with intact corneal KSPG, with KSPG25 protein, and with a 36-kDa protein, distinct from lumican and keratoca n, KSPG25-related proteins, not modified with keratan sulfate, were al so detected in several connective tissues, Northern blot analysis show ed mRNA transcripts of 2.4, 2.5, and 2.6 kilobases in numerous tissues with the 2.4-kilobase transcript enriched in ocular tissues, Ribonucl ease protection analysis detected several protected KSPG25 mRNA fragme nts, suggesting alternate splicing of KSPG25 transcripts, We conclude that the full-length translation product of the gene producing osteogl ycin is a corneal keratan sulfate proteoglycan, also present in many n on-corneal tissues without keratan sulfate chains, The multiple size p rotein products of this gene appear to result from ia situ proteolytic processing and/or alternative splicing of mRNA, The name mimecan is p roposed for this gene and its products.