REGULATION OF TUBULIN, TAU AND MICROTUBULE ASSOCIATED PROTEIN-2 EXPRESSION DURING MOUSE-BRAIN DEVELOPMENT

The level of three microtubule proteins, tubulin, Tau and MAP2 and of their encoding mRNA was studied in the mouse brain at an early developmental stage (3 days postnatal) and in adulthood. The level of the mRNA encoding both tubulin and Tau decreased by 85% between these two stages whereas the encoded proteins decreased only by 50% during the same period. Thus, the level of these proteins seems to be regulated both negatively and positively by transcriptional and post translational mechanisms. In vitro transcription assays, performed with nuclei isolated at different postnatal stages, showed that the tubulin and Tau transcripts are produced with some variations during mouse brain development. However these fluctuations are much less important than the drops of the steady state levels of tubulin and Tau mRNA seen in vivo. Thus, the decrease in transcripts levels does not seem to result from reduced transcriptional activities, and can be ascribed to changes in mRNA stability occurring during brain development, i.e. to a post transcriptional mechanism. The situation is even more complex for MAP2: its encoding mRNA level remains constant during development whereas the in vitro transcription activity decreases markedly during the same period. Finally, MAP2 protein level increases during development although its encoding mRNA level remains constant suggesting that this protein is stabilized by a post translational mechanism.