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Keratocytes of the corneal stroma secrete a unique population of proteoglycan molecules considered essential for corneal transparency. In healing corneal wounds, keratocytes exhibit a myofibroblastic phenotype in response to transforming growth factor ␤ (TGF-

Left ventricular mass (LVM) and cardiac gene expression are complex traits regulated by factors both intrinsic and extrinsic to the heart. To dissect the major determinants of LVM, we combined expression quantitative trait locus1 and quantitative trait transcript2 (QTT) analyses of the cardiac transcriptome in the rat. Using these methods and in vitro functional assays, we identified osteoglycin (Ogn) as a major candidate regulator of rat LVM, with increased Ogn protein expression associated with elevated LVM. We also applied genome-wide QTT analysis to the human heart and observed that, out of ~22,000 transcripts, OGN transcript abundance had the © 2008 Nature Publishing Group Correspondence should be addressed to T.J.A. (t.aitman@csc.mrc.ac.uk) or S.A.C. (stuart.cook@imperial.ac.uk).. 11 These authors contributed equally to this work. AUTHOR CONTRIBUTIONS The study was designed by S.A.C., E.P. and T.J.A.; S.A.C. obtained funding, supervised the study and coordinated the collaborations; R.S. performed PCR-based experiments and genotyping; H.L. and M.K.K. generated rat microarray data; B.S. and Y.M.P. generated human microarray data; M.B. generated immunofluorescence confocal micrographs; R.S. and H.L. performed cell culture and cloning experiments; R.S., B.S. and M.B. performed immunoblotting; P.J.M. and R.S. performed in vivo analyses in Ogn knockout mice; E.S.T., L.M.C., M.D.W. and G.W.C. provided and genotyped the Ogn knockout mice; N.H. and J.F. carried out sequence analysis of Ogn; T.W.K., V.K. and M.P. provided telemetric blood pressure data; P.P.P. provided human tissues for protein studies; S.K.P., D.J.P. and C.K. provided the human cardiac MRI data; E.P. designed, interpreted and supervised all statistical analyses; E.P., I.G. and R.S. performed statistical and bioinformatic analyses and were aided by J.M.; and E.P. and S.A.C. wrote the manuscript.Note: Supplementary information is available on the Nature Genetics website.Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions Europe PMC Funders GroupAuthor Manuscript Nat Genet. Author manuscript; available in PMC 2009 September 11. Elevated indexed LVM is a major cause of morbidity and mortality and is regulated, in part, by hemodynamic indices3. However, only a small proportion of LVM variation is determined by hemodynamic effects4, and it has been proposed that genetic influences may also be important5,6. Many studies have shown that gene expression is heritable and that the genetic control of transcription affects physiological traits and disease phenotypes1,7. We have shown that gene transcription is highly heritable in the rat heart8, which led us to hypothesize that the genetic control of cardiac gene expression may be important in regulating LVM. Here, we used an integrated approach combining correlation of expression quantitative trait loci (eQTL)1 and genome-wide expression profiles with physiological traits, previously designated as quantitative trait transcript (QTT) analysis2, to ide...

Bovine cornea contains three unique keratan sulfate proteoglycans (KSPGs), of which two (lumican and keratocan) have been characterized using molecular cloning. The gene for the third protein (KSPG25) has not been identified. This study examined the relationship between the KSPG25 protein and the gene for osteoglycin, a 12-kDa bone glycoprotein. The N-terminal amino acid sequence of KSPG25 occurs in osteoglycin cDNA cloned from bovine cornea. The osteoglycin amino acid sequence makes up the C-terminal 47% of the deduced sequence of the KSPG25 protein. Antibodies to osteoglycin reacted with intact corneal KSPG, with KSPG25 protein, and with a 36-kDa protein, distinct from lumican and keratocan. KSPG25-related proteins, not modified with keratan sulfate, were also detected in several connective tissues. Northern blot analysis showed mRNA transcripts of 2.4, 2.5, and 2.6 kilobases in numerous tissues with the 2.4-kilobase transcript enriched in ocular tissues. Ribonuclease protection analysis detected several protected KSPG25 mRNA fragments, suggesting alternate splicing of KSPG25 transcripts. We conclude that the full-length translation product of the gene producing osteoglycin is a corneal keratan sulfate proteoglycan, also present in many non-corneal tissues without keratan sulfate chains. The multiple size protein products of this gene appear to result from in situ proteolytic processing and/or alternative splicing of mRNA. The name mimecan is proposed for this gene and its products.The corneal stroma of vertebrate organisms contains a unique class of molecules, corneal keratan sulfate proteoglycans (KSPGs), 1 consisting of several related proteins each bearing keratan sulfate. The specialized nature of corneal proteoglycans was recognized almost 60 years ago with the initial description of keratan sulfate, the most abundant glycosaminoglycan in cornea (1). Corneal keratan sulfate is a highly sulfated, linear polymer of N-acetyllactosamine, linked to asparagine residues in the KSPG core proteins (2). The unusual abundance of keratan sulfate in the cornea and studies of heritable metabolic diseases suggest that the KSPG molecules are essential in maintenance of corneal transparency (3, 4). Understanding the role of the KSPGs in corneal transparency, their interactions with cells and other matrix molecules, and the tissue-specific nature of their biosynthesis requires complete knowledge of their structure. Although we have excellent information regarding the carbohydrate components of the KSPGs, the core proteins as representatives of the primary KSPG gene products are still not fully understood.Research from our laboratory has shown that keratan sulfate is attached to three unique proteins in bovine cornea (5, 6). The cDNAs for two of these proteins, keratocan and lumican (originally designated 37A and 37B), have been cloned and sequenced (7,8). A third 25-kDa KSPG core protein, KSPG25, was recognized as unique from lumican and keratocan, but its primary sequence is not yet known. The deduced amino acid sequence...

Previous studies showed that the keratan sulfate-containing proteoglycans of bovine corneal stroma contain three unique core proteins designated 37A, 37B, and 25 (Funderburgh, J. L., Funderburgh, M. L., Mann, M. M., and Conrad, G. W. (1991) J. Biol. Chem. 266, 14226 -14231). Degenerate oligonucleotides designed from amino acid sequences of the 37A protein were used to screen a cDNA expression library from cultured bovine keratocytes. A cDNA clone coding for keratocan, a 37A protein, was isolated and sequenced. The deduced keratocan amino acid sequence is unique but related to two other keratan sulfate-containing proteins, lumican (the 37B core protein) and fibromodulin. These three proteins share approximately 35% amino acid identity and a number of conserved structural features. Northern hybridization and immunoblotting of tissue extracts found keratocan distribution to be more limited than that of lumican or fibromodulin. Keratocan is abundant in cornea and sclera and detected in much lesser amounts in skin, ligament, cartilage, artery, and striated muscles. Only in cornea was keratocan found to contain large, sulfated keratan sulfate chains. Keratocan, like lumican, is a core protein of a major corneal proteoglycan but is present in non-corneal tissues primarily as a nonsulfated glycoprotein.Proteoglycans of the corneal stroma are important in maintaining the transparency of the cornea. These complex molecules are responsible for the hydrophilic character of the tissue, providing tissue hydration that is essential for transparency (1). It is not surprising, therefore, that the corneal stroma has a markedly different proteoglycan composition than that of other fibrous connective tissues such as skin and sclera. The unique character of corneal proteoglycans was recognized almost 60 years ago with the initial description of keratan sulfate, the most abundant glycosaminoglycan in the cornea (2). Corneal keratan sulfate is a highly sulfated, linear polymer of N-acetyllactosamine, linked to asparagine residues in the KSPG 1 core proteins via a mannose-containing oligosaccharide (3, 4). Because the keratan sulfate glycosaminoglycans are posttranslational modifications of the KSPG proteins, determination of the structure and tissue-specific expression of these core proteins are essential to understanding the biological roles of KSPG. Research from our laboratory has demonstrated the existence of three KSPG proteins in bovine cornea. These proteins (designated 37A, 37B, and 25) have unique primary structures and differ in glycosylation, with protein 37A containing three keratan sulfate chains and the other two proteins containing one keratan sulfate chain each (5). Complementary DNA coding for protein 37B (lumican) has been cloned, and the deduced amino acid sequence revealed homology to three other proteoglycan proteins, fibromodulin, decorin, and biglycan (6, 7). Lumican is present in several tissues other than cornea in a non-sulfated form (6, 7).In this paper, we report the sequence of cDNA encoding a KSPG 37A pro...