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Developmental Expression of HNK‐1‐Reactive Antigens in Rat Cerebral Cortex and Molecular Heterogeneity of Sulfoglucuronylneolactotetraosylceramide in CNS Versus PNS

Monoclonal antibody HNK‐1 reacts with a carbohydrate epitope present in proteins, proteoglycans, and sulfoglucuronylglycolipids (SGGLs). On high‐performance TLC plates, SGGLs of the CNS from several species migrated consistently slower than those from the PNS, a result indicating possible differences in the structures. The structural characteristics of the major SGGL, sulfoglucuronylneolac‐totetraosylceramide (SGGL‐1), from CNS was compared with those of SGGL‐1 from PNS. Although the composition, sequence, and linkages of the carbohydrate moiety of the SGGL‐1 species were identical, SGGL‐1 from CNS contained mainly short‐chain fatty acids, 16:0, 18:0, and 18:1, amounting to 85% of the total fatty acids, whereas SGGL‐1 from PNS contained large proportions (59%) of long‐chain fatty acids (> 18:0). These differences in the fatty acid composition accounted for the different migration pattern observed. The developmental expression of SGGLs and HNK‐1‐reactive proteins was studied in rat cerebral cortex between embryonic day (ED) 15 to adulthood. SGGLs in the rat cortex were maximally expressed around ED 19 and almost completely disappeared by postnatal day (PD) 20. This expression was contrary to their increasing expression in the cerebellum and sciatic nerve with postnatal development. Six to eight protein bands with a molecular mass of > 160 kDa were HNK‐1 reactive in the rat cerebral cortex at different ages. The major HNK‐1 reactivity to the 160‐kDa protein band seen in ED 19 to PD 10 cortex decreased and completely disappeared from the adult cortex, whereas several other proteins remained HNK‐1 reactive even in the adult. Western blot analyses of the neural cell adhesion molecules (N‐CAMs) during development of the rat cortex with a polyclonal anti‐N‐CAM antibody showed that the major HNK‐1‐reactive protein bands were not N‐CAMs. Between PD 1 and 10, 190–200‐kDa N‐CAM was the major N‐CAM, and between PD 15 to adulthood, 180‐kDa N‐CAM was the only N‐CAM present in the rat cortex.