Neural recognition molecules, NrCAM and Contactin, during development and aging.

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Various cell adhesion molecules participate in the cell recognition events not only during development, but also in adulthood and during aging. We have been studying the biological roles of contactin, a neural adhesion molecule in the immunoglobulin superfamily, in the aged brain. NrCAM is one of the immunoglobulin superfamily molecules, which is known to interact with contactin and TAG-1 of the contactin subgroup. In this study, we first investigated the expression of NrCAM during development and aging. In the Western blot analysis, we found two bands of 135-kDa and 130-kDa in the adult rat brain. The 130-kDa band was not detected until postnatal day 10, whereas the 135-kDa band was detected from embryo to adulthood. The cDNA that we found encoded a splicing isoform of NrCAM, which has additional 19 amino acid residues in the N-terminal region comparing with the NrCAM reported previously. In order to know whether the two bands on the Western blot analysis were the splicing isoforms or not, we performed RT-PCR. The developmental expression pattern of these two isoform transcripts detected by the RT-PCR conformed to the appearance of the two bands on the Western blot. These results have suggested that the two splicing isoforms play different roles form each other in the brain function. Next, we examined the interaction of NrCAM with the other contactin subgroup molecules. By the immunoprecipitation, it was demonstrated that NrCAM interacted with contactin and TAG-1 in the hippocampus, whereas the interaction with NB-3 of the another contactin subgroup molecule was not detected. Taken together, NrCAM do not interact with all the contactin subgroup molecules. The results obtained here will be of great use for understanding the roles of NrCAM during aging.