Tissue-specific expression of the rat galanin gene

We have isolated and characterized cDNAs encoding rat galanin from a cDNA library prepared from rat hypothalamic tissue. Analysis of these clones reveals that rat galanin is synthesized initially as part of a 124-amino acid precursor that includes a signal peptide, galanin (29 amino acids), and a 60-amino acid galanin mRNA-associated peptide. In the precursor, galanin includes a C-terminal glycine and is flanked on each side by dibasic tryptic cleavage sites. The deduced amino acid sequence of rat galanin is 90% similar to porcine galanin, with all three amino acid differences in the C-terminal heptapeptide. The predicted galanin mRNA-associated peptide includes a 35-amino acid sequence that is 78% similar to the previously reported porcine analogue. This sequence is set off by a single basic tryptic cleavage site and includes a 17-amino acid region that is nearly identical to the porcine counterpart. The high interspecies conservation suggests a biological role for this putative peptide. Blot hybridization analysis using rat genomic DNA is consistent with a single galanin-encoding gene. RNA blot analysis of total RNA prepared from rat tissues reveals a single band of hybridizing mRNA that is approximately 900 nucleotides long. Rat galanin mRNA is located predominantly in the central nervous system and gastrointestinal tract. Highest central nervous system concentrations are found in the hypothalamus, with lower levels in the cortex and brainstem. Gastrointestinal rat galanin mRNA is most abundant in the duodenum, with progressively lower concentrations in the stomach, small intestine, and colon.