The rat prepro gastrin releasing peptide gene is transcribed from two initiation sites in the brain

The gastrin-releasing peptide (GRP) is a gastrointestinal hormone, a neuropeptide, and a growth factor. To study systematically GRP gene expression in embryonic and in adult mammals, we cloned the rat prepro-GRP gene from brain cDNA libraries. Analysis of these cDNA clones along with organ-specific mRNA studies show that there are prepro-GRP transcripts initiating in the brain, but not in the duodenum, from a novel promoter. The latter is located at least four hundred base pairs upstream from a second promoter that is active in both duodenum and in brain. In contrast to human prepro-GRP, there is no alternative processing of the 3'-region of rat brain and duodenum prepro-GRP transcripts; hence, these mRNAs encode a single 147 amino acid prepro-GRP hormone that is homologous to the third isoform of the human prepro-GRP hormone.