Differentiation‐Dependent Sialylation of Individual Neural Cell Adhesion Molecule Polypeptides During Postnatal Development

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Abstract
The postnatal sialylation of individual neural cell adhesion molecule (N-CAM) polypeptides by a develop-mentally regulated sialyltransferase in Golgi-enriched fractions isolated from rat brain is described. The 120-kilodal-ton polypeptide of N-CAM was found to be sialylated at each developmental age examined. This was in contrast to the 140- and 180-kilodalton N-CAM polypeptides which were only sialylated until postnatal day 10 and from postnatal day 12, respectively. Immunoblotting procedures demonstrated that all N-CAM polypeptides were expressed in the Golgi fractions at each developmental stage examined. The heavily sialylated “embryonic” form of N-CAM was found to be reexpressed at postnatal days 10 and 12, a time coincident with extensive fibre outgrowth. The “embryonic” form of N-CAM incorporated similar amounts of [14C]sialic acid into its constituent polypeptides reflecting the difference in sialic acid to protein ratio, as this form of N-CAM was virtually undetectable in the immunoblots of postnatal material.