MOLECULAR CHARACTERIZATION OF DENDRITICALLY LOCALIZED TRANSCRIPTS ENCODING MAP2

Transcripts encoding high molecular weight (Hwt) isoforms of microtubu le-associated protein 2 (MAP2) have been localized in the dendritic co mpartment of neurons. In contrast, nearly all other neuronal messages, including transcripts encoding low molecular weight (Lwt) MAP2 isofor ms, are restricted to cell somas. The mechanisms underlying the dendri tic localization of Hwt-MAP2 transcripts are not known. In non-neurona l systems, mRNAs are localized via signal sequences situated in their 3' untranslated regions (3'-UTRs). In this study, we have localized th e putative dendritic targeting element (DTE) in Hwt-MAP2 mRNAs by comp aring the nucleotide sequences of the somatically localized 6 kb Lwt-M AP2 transcripts with the dendritically localized 9 kb messages. Our an alysis shows that both 6 kb and 9 kb transcripts have identical 3'- an d 5'-UTRs, precluding the possibility that the DTE lies in these regio ns. Within the coding region a single segment that is unique to 9 kb H wt MAP2 transcripts was identified. These findings suggest that the DT E lies within the 4 kb RNA segment that encodes the projection domain of Hwt-MAP2.