CHONDROITIN SULFATE AND CHONDROITIN KERATAN SULFATE PROTEOGLYCANS OF NERVOUS-TISSUE - DEVELOPMENTAL-CHANGES OF NEUROCAN AND PHOSPHACAN/

We have studied developmental changes in the structure and concentrati on of the hyaluronic acid-binding proteoglycan, neurocan, and of phosp hacan, another major chondroitin sulfate proteoglycan of nervous tissu e that represents the extracellular domain of a receptor-type protein tyrosine phosphatase. A new monoclonal antibody (designated 1F6), whic h recognizes an epitope in the N-terminal portion of neurocan, has bee n used for the isolation of proteolytic processing fragments that occu r together with link protein in a complex with hyaluronic acid, Both l ink protein and two of the neurocan fragments were identified by amino acid sequencing. The N-terminal fragments of neurocan are also recogn ized by monoclonal antibodies (5C4, 8A4, and 3B1) to epitopes in the G 1 and G2 domains of aggrecan and/or in the hyaluronic acid-binding dom ain of link protein. The presence in brain of these N-terminal fragmen ts is consistent with the developmentally regulated appearance of the C-terminal half of neurocan, which we described previously. We have al so used a slot-blot radioimmunoassay to determine the concentrations o f neurocan and phosphacan in developing brain, The levels of both prot eoglycans increased rapidly during early brain development, but wherea s neurocan reached a peak at approximately postnatal day 4 and then de clined to below embryonic levels in adult brain, the concentration of phosphacan remained essentially unchanged after postnatal day 12, Kera tan sulfate on phosphacan-KS (a glycoform that contains both chondroit in sulfate and keratan sulfate chains) was not detectable until just b efore birth, and its peak concentration (at 3 weeks postnatal) was rea ched similar to 1 week later than that of the phosphacan core protein, Immunocytochemical studies using monoclonal antibodies to keratan sul fate (3H1 and 5D4) together with specific glycosidases (endo-beta-gala ctosidase, keratanase, and keratanase II) also showed that with the ex ception of some very localized areas, keratan sulfate is generally not present in the embryonic rat CNS.