Characterization of the chicken preprogonadotrophin-releasing hormone-I gene

Partial cDNA clones for chicken gonadotrophin-releasing hormone (GnRH)-I were isolated by reverse transcription-polymerase chain reaction using total RNA from the hypothalami of domestic chickens. Primers for amplification were based on the nucleotide sequence of the mammalian GnRH genes. These amplified clones were used to screen a genomic library from which a series of overlapping clones was isolated. A 6.3 kb EcoRI fragment containing all the exons and 3.0 kb of the 5' upstream region was sequenced. The exon-intron structure of the gene was found to be of a similar configuration to those of the mammalian and osteichthyes GnRH genes analysed so far. Individual domains of the predicted prepropeptide are similar to those of mammalian GnRH prepropeptides, comprising a 23 amino acid signal peptide, the decapeptide hormone and a Gly-Lys-Arg cleavage site, followed by a 56 amino acid GnRH-associated peptide. The nucleotide sequence coding for the decapeptide hormone translates into the amino sequence for chicken GnRH-I. The prepropeptide has approximately 50% identity with mammalian prepropeptides and 25% identity with the teleost prepropeptides.