ARPP-21: murine gene structure and promoter identification of a neuronal phosphoprotein enriched in the limbic...

ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis) is a phosphoprotein highly enriched in concentration in the neurons of the limbic striatum. It is likely a third messenger in the intracellular cascade of events following neuronal stimulation by first-messenger activators of the adenylate cyclase system, including dopamine via the D1 receptor. ARPP-21 expression is restricted to telencephalic post-mitotic, post-migrational neurons, and its precise pattern of temporal and spatial expression makes it an attractive candidate for the study of transcriptional regulation of neuronal maturation. To define genomic regions likely to contain functional promoter elements, we isolated the murine ARPP-21 gene. Primer extension and T2 RNase protection analyses identified multiple transcription start sites, but 1.3 kb of 5'-flanking DNA revealed few consensus transcription factor binding sequences. A series of transient transfection assays in clonal cell lines which do not express ARPP-21 identified a basal promoter active in both neuronal and non-neuronal lines. Expression in all lines was decreased by the inclusion of regions further upstream, and extinguished by the inclusion of the first intron. Further analyses are likely to reveal cell specific regulatory sequences.