Social Control of Reproduction: Molecular Studies of GnRH in the African Cichlid Haplochromis burtoni

During 500 million years of evolution, the primary structure of GnRH has been remarkably conserved. Recently, peptide sequence analysis of GnRH-like immunoreactive material from lamprey brain has shown that 5 of 10 amino acid residues are identical between agnathan and mammalian GnRH. In addition, the pyro-glu amino terminal structure and amidation of the carboxy terminus of the decapeptide are conserved (1). To date, the amino acid sequence has been determined and bioactivity demonstrated for 5 separate forms of the GnRH decapeptide (2). Two GnRH decapeptide sequences have been found in the chicken (3, 4). Immunologic and chromatographic evidence indicate that there may be 2 decapeptides in other vertebrates, including some species of reptiles and teleost fish. However, amino acid sequences for these putative second GnRH forms have not yet been determined (5).