Different forms of microtubule-associated protein 2 are encoded by separate mRNA transcripts

Brain microtubule-associated protein 2 (MAP2) consists of a pair of high molecular mass (280 kD) polypeptides, MAP2a and MAP2b, and a recently identified 70-kD protein, MAP2c, which is antigenically related to these high molecular mass MAP2's. Using cDNA clones we have analyzed the expression of these three proteins at the nucleic acid level. cDNA probes selective for the high molecular mass MAP2's a and b identified only a 9-kb mRNA, whereas a probe for sequence common to all three MAP2 isoforms, a, b, and c, recognized the 9-kb transcript and additionally a 6-kb mRNA. Southern blot analysis with cDNA probes indicated that there is only one MAP2 gene from which these two distinct mRNAs are derived. The 70-kD MAP2c protein is much more abundant in neurons of developing brain than those of adult tissues. Similarly the expression of the 6-kb MAP2c-related mRNA, is much greater in neonatal than adult rat brain, indicating that the developmental expression of MAP2 is determined by transcriptional regulation from a single MAP2 gene.