The Atlantic salmon prepro-gonadotropin releasing hormone gene and mRNA

Screening for the gene encoding salmon gonadotropin releasing hormone (sGnRH) in an Atlantic salmon (Salmo salar) genomic library resulted in isolation of a positive clone designated lambda sGnRH-1. An anchor polymerase chain reaction (PCR) technique was used to amplify GnRH cDNA derived from salmon hypothalamic mRNA. The cDNA sequence was aligned to the 7607 base pair genomic sequence which was shown to encode the entire prepro-GnRH gene. The cDNA proved that the cloned gene is expressed in the hypothalamus of mature salmon. The coding domain of sGnRH differs from the mammalian GnRH by six nucleotide changes which allow the two amino acid differences between the two GnRH variants. Salmon GnRH associated peptide (GAP) differs extensively in sequence and size from the mammalian counterpart. Compared to the GnRH cDNA of a cichlid species the similarity is 69.3% in the protein coding sequence.