Two salmon gonadotropin-releasing hormone genes and their differential expressions in the goldfish Carassius auratus

Abstract

A complementary DNA (cDNA) encoding salmon type gonadotropin-releasing hormone (sGnRH) has already been isolated and characterized in the goldfish Carassius auratus. In the present study, we isolated and characterized a second sGnRH cDNA which was different from the reported sGnRH cDNA from the brain of goldfish by rapid amplification of cDNA ends. This cDNA included an open reading frame of 282 bp encoding the 94 amino acid residues of sGnRH precursor. Amino acids identity between the second sGnRH precursor and the previously reported sGnRH precursor was 86.2%. Genomic Southern blot analysis showed that the goldfish harbors these two distinct sGnRH genes in its genome. Expressions of the two sGnRH genes were observed in the brain, pituitary, and gonad of goldfish by reverse transcription-polymerase chain reaction analysis. Moreover, the levels of two sGnRH mRNA in these tissues were different depending on sex and maturity of the fish. The differential expressions of two sGnRH genes suggest the existence of the differential regulatory mechanism of the two sGnRH genes and the multiple physiological functions of sGnRH.