Expression of N-CAM polypeptides in neurons

N-CAM from rat brain consists of three polypeptides: 190,000 Mr (A), 140,000 Mr (B) and 120,000 Mr (C). It has been reported that cultured neurons express only A and B, whereas glial cultures synthesize mainly B and C. During postnatal development the relative biosynthesis of C increases. This could possibly reflect differentiation of neurons or an increased biosynthetic contribution of glial cells. We have investigated neuronal expression of N-CAM with the aim of determining whether neurons were able to synthesize the C-polypeptide. Biosynthetic labelling of explant cultures of peripheral ganglia and of chromaffin cells from adrenal medulla showed that cultured neurons synthesized not only A and B, but also C. However, the biosynthetic capacity for C production was low. Cell-free translation of microsomes from neuronal cell cultures showed that they contained a messenger RNA coding for C. Finally, retinal ganglion neurons expressed C when located in their natural environment as determined by biosynthetic labelling performed in living rats. Thus, both neurons and glial cells may be involved in the developmentally regulated change in C expression that occurs during postnatal life.