Neuronal expression of the rat M1 muscarinic acetylcholine receptor gene is regulated by elements in the first exon.

Muscarinic acetylcholine receptor genes are members of the G-protein coupled receptor superfamily. Each member of this family studied to date appears to have a distinct expression profile, however the mechanisms determining these expression patterns remain largely unknown. We have previously isolated a genomic clone containing the M1 muscarinic receptor gene and determined its gene structure [Pepitoni, Wood and Buckley (1997) J. Biol. Chem. 272, 17112-17117]. We have now identified DNA elements responsible for driving cell specific expression in transient transfection assays of immortalized cell lines. A region of the gene spanning 974 nucleotides and containing 602 nucleotides of the first exon is sufficient to drive specific expression in cell lines. Like the M4 and M2 gene promoters, the M1 promoter contains an Sp1 motif which can recruit transcription factor Sp1 and at least one other protein, although this site does not appear to be functionally important for M1 expression in our assay. We have identified a region within the first exon of the M1 gene that regulates expression in cell lines, contains several positive and negative acting elements and is able to drive expression of a heterologous promoter. A polypyrimidine/polypurine tract and a sequence conserved between M1 genes of various species act in concert to enhance M1 transcription and are able to activate a heterologous promoter. We show that DNA binding proteins interact in vitro with single-stranded DNA derived from these regions and suggest that topology of the DNA is important for regulation of M1 expression.