Localization of mRNA for neural cell adhesion molecule (N-CAM) polypeptides in neural and nonneural tissues by in situ hybridization.

The differential expression of the mRNA for the neural cell adhesion molecule (N-CAM) has been studied by in situ hybridization and compared with protein localization analyzed by immunohistochemical staining. The distribution of mRNA during chicken embryonic development was analyzed in neural and nonneural tissues by using an RNA probe that detects all N-CAM mRNAs and a probe specific for the mRNA of the large cytoplasmic domain (ld) of N-CAM. The results provide a detailed description of the mRNA distribution for N-CAM. The distribution of mRNA for total N-CAM generally corresponded to that of protein but differed at a more detailed level of analysis. For example, the mRNA was localized only within the cell bodies of neurons, whereas the protein was also in neuronal processes; this differential localization was most clearly seen in the alternating layers of cell bodies and fibers in the optic tectum and cerebellum. N-CAM ld mRNA, which arises from alternative RNA splicing, was expressed only in neural tissues, confirming previous biochemical and histological studies. Differential expression of the ld mRNA was detected in specific neural cell types: N-CAM mRNA was present in the ependymal cells of the spinal cord and optic tectum, but mRNA for the ld form was absent. In contrast, the ld mRNA was among the N-CAM mRNAs found in the Purkinje cells and internal granule cells in the cerebellum. The differential expression of mRNAs for the N-CAM forms emphasizes the potential importance of alternative mRNA splicing in modulating adhesive events during embryonic development, particularly in the nervous system.