Developmental Study of the Cell Adhesion Molecule L1

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Abstract
Cell adhesion molecules are involved in several morphogenetic events during development. A spatiotemporal regulation of the expression of the neural cell adhesion molecule NCAM has previously been demonstrated. In this study, we describe developmental changes in the rat brain in the expression of another neural cell adhesion molecule, L1. The amount of L1 varies with age showing a peak value in early post-natal life. L1 is synthesized as a polypeptide with a relative molecular weight (Mr) of 200,000 in explant cultures of rat forebrain from embryonic day 17 to post-natal day 15, but L1 synthesis decreases relative to total protein synthesis during the same period. L1 sulphation does not appear to change developmentally whereas the degree of phosphorylation seems to decrease. At the plasma membrane L1 is present as three polypeptides with Mr 200,000, 140,000 and 80,000. The latter is phosphorylated like the 200,000 Mr polypeptide. Furthermore, L1 exists in a soluble form which consists of 170,000, 140,000 and 80,000 Mr polypeptides. During development a slight decrease in Mr of the 200,000 and 140,000 Mr polypeptides is observed, possibly due to changes in glycosylation. To conclude, L1 expression is temporally regulated and its function may thus, like NCAM, be developmentally modified by some of these changes.