Keratan Sulfate Epitopes Exhibit a Conserved Distribution During Joint Development That Remains Undisclosed on the Basis of Glycosaminoglycan Charge DensityEmma Kavanagha, Anne C. Osbornea, Doreen E. Ashhurstb, and Andrew A. Pitsillidesaa Department of Veterinary Basic Sciences, The Royal Veterinary College, London, United Kingdom b Department of Anatomy, St George's Hospital Medical School, London, United Kingdom Correspondence to: Emma Kavanagh, Dept. of Veterinary Basic Sciences, The Royal Veterinary College, University of London, London NW1 0TU, UK. E-mail: e.kavanagh@vcl.ac.uk Changes in glycosaminoglycan (GAG) content and distribution are vital for joint development. However, their precise character has not been established. We have used immunohistochemistry (IHC) and "critical electrolyte" Alcian blue staining to assess such changes in developing chick and rabbit joints. IHC showed chondroitin sulfate labeling in chick epiphyseal cartilage but not in interzones. In contrast, prominent labeling for keratan sulfate (KS) was restricted to chick cartilageinterzone interfaces. In rabbit knees, KS labeling was also prominent at presumptive cavity borders, but weak in interzone and cartilage. Selective pre-digestion produced appropriate loss of label and undersulfated KS was undetectable. Quantification of Alcian blue staining by scanning and integrating microdensitometry showed prominent hyaluronan-like (HA-like) interzone staining, with chondroitin sulfate and weaker KS staining restricted to epiphyseal cartilage. Hyaluronidase decreased HA-like staining in the interzone. Surprisingly, keratanases also reduced HA-like but not sulfated GAG (sGAG-like) staining in the interzone. Chondroitinase ABC had little effect on HA-like staining but decreased sGAG staining in all regions. Rabbit joints also showed HA-like but not KS staining in the interzone and strong chondroitin sulfate-like staining in epiphyseal cartilage. Our findings show restricted KS distribution in the region close to the presumptive joint cavity of developing chick and rabbit joints. Alcian blue staining does not detect this moiety. Therefore, it appears that although histochemistry allows relatively insensitive quantitative assessment of GAGs, IHC increases these detection limits. This is particularly evident for KS, which exhibits immunolabeling patterns in joints from different species that is consistent with a conserved functional role in chondrogenesis. (J Histochem Cytochem 50:10391047, 2002) Key Words: articular cartilage, joint development, hyaluronan, glycosaminoglycans, chondrogenesis, quantitative histochemistry, immunochemistry, embryonic, chick, rabbit
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