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

各种细胞粘附分子不仅在发育过程中参与细胞识别事件，而且在成年期和衰老过程中也参与细胞识别事件。我们一直在研究接触蛋白在老年大脑中的生物学作用，接触蛋白是免疫球蛋白超家族中的一种神经粘附分子。NrCAM是免疫球蛋白超家族分子之一，已知与接触蛋白亚群中的接触蛋白和TAG-1相互作用。在本研究中，我们首先研究了NrCAM在发育和衰老过程中的表达。在Western blot分析中，我们在成年大鼠脑中发现了135-kDa和130-kDa两条条带。130-kDa条带直到出生后第10天才被检测到，而135-kDa条带从胚胎到成年都被检测到。该cDNA编码了NrCAM的一个剪接异构体，与之前报道的NrCAM相比，在n端区域增加了19个氨基酸残基。为了确定Western blot分析上的两条条带是否为剪接异构体，我们进行了RT-PCR。RT-PCR检测到的这两种异构体转录本的发育表达模式与Western blot上的两条条带相符。这些结果表明，这两种剪接异构体在大脑功能中起着不同的作用。接下来，我们研究了NrCAM与其他接触蛋白亚群分子的相互作用。免疫沉淀结果表明，NrCAM在海马中与contactin和TAG-1相互作用，而与另一个contactin亚群分子NB-3没有相互作用。总的来说，NrCAM并不与所有的接触蛋白亚群分子相互作用。本研究结果对了解NrCAM在衰老过程中的作用具有重要意义。

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.