A developmental study of the biosynthesis of the neural cell adhesion molecule.

The neural cell adhesion molecule (N-CAM) is a glycoprotein found in neurons, glial cells and muscle cells. In this report we describe developmental changes in biosynthesis of N-CAM polypeptides in rat forebrain explant cultures. N-CAM was synthesized as the following polypeptides: HMr (Mr between 250,000 and 350,000), A (200,000 Mr), B (135,000 Mr) and C (115,000 Mr). The biosynthetic pattern of N-CAM polypeptides changed during development: the biosynthesis of HMr and C increased relative to A and B. N-CAM biosynthesis decreased 100-fold from embryonic day 17 to postnatal day 25; N-CAM turnover decreased 350-fold during the same period. N-CAM polysialylation and sulfatation decreased markedly with age, whereas phosphorylation seemed to be constant during development. Only polypeptides A and B were phosphorylated, whereas A, B and C were sulfated. A was more sulfated and phosphorylated than B. It is concluded that the above described modulations of N-CAM may be of importance in the developmental regulation of cell-cell adhesion.