Neural cell adhesion molecule (NCAM) and N-cadherin mRNA during development and aging: selective reduction in the 7.4-kb and 6.7-kb NCAM mRNA levels in the hippocampus of adult and old rats

By examining the time course, from E15 to 720 days of age, for changes in the prevalence of mRNAs coding for neural cell adhesion molecule (NCAM), N-cadherin and alpha-tubulin in rat hippocampus and forebrain, it was concluded that (i) the NCAM 7.4-, 6.7-, 5.2-, 4.3- and 2.9-kb mRNAs are differentially regulated during development and aging; (ii) the 7.4- and 6.7-kb mRNA are drastically reduced starting from day 21 onward; (iii) the E15- and day-1-specific mRNA of 4.3 kb is replaced with the 5.2-kb mRNA starting with 21 days, thereafter the 5.2-kb message remained relatively constant over the entire life-span studied. Likewise, the 2.9-kb mRNA, which was very abundantly expressed at E15 and early postnatal stages, remained relatively constant between 180 days and 720 days; (iv) postnatal rat brains showed both qualitative and quantitative changes in N-cadherin 4.3- and 4.0-kb transcripts. The 4.3-kb mRNA was relatively abundant at 1 and 21 days postnatal stages, thereafter the signal remained very low over the entire life-span studied. The 4.0-kb message, which was specific for the E15 stage, was replaced with the 4.3-kb message; (v) as expected, the 1.8-kb mRNA coding for embryonic alpha-tubulin decreased dramatically after 1 day, but became stabilized at moderate levels during the subsequent developmental stages. At least for the NCAM gene, the regulation seems to occur post-transcriptionally, possibly at the level of RNA processing while the N-cadherin mRNA expression seems to be transcriptionally regulated.