Molecular Analysis of the Koala Reproductive Hormones and Their Receptors: Gonadotrophin-Releasing Hormone (GnRH), Follicle-Stimulating Hormone b and Luteinising Hormone b with Localisation of GnRH
E. R. Busby*, S. Soeta†, N. M. Sherwood* and S. D. Johnston‡
*Department of Biology, University of Victoria, Victoria, B.C., Canada
†School of Veterinary Medicine, Nippon Veterinary and Life Science University, Tokyo, Japan
‡School of Agriculture and Food Science, The University of Queensland, Gatton, Australia.
During evolution, reproductive hormones and their receptors in the brain-pituitary-gonadal axis have been altered by genetic mechanisms. To understand how the neuroendocrine control of reproduction evolved in mammals, it is important to examine marsupials, the closest group to placental mammals. We hypothesised that at least some of the hormones and receptors found in placental mammals would be present in koala, a marsupial. We examined the expression of koala mRNA for the reproductive molecules. Koala cDNAs were cloned from brain for gonadotrophin-releasing hormones (GnRH1 and GnRH2) or from pituitary for GnRH receptors, types I and II, follicle-stimulating hormone (FSH)b and luteinising hormone (LH)b, and from gonads for FSH and LH receptors. Deduced proteins were compared by sequence alignment and phylogenetic analysis with those of other vertebrates. In conclusion, the koala expressed mRNA for these eight putative reproductive molecules, whereas at least one of these molecules is missing in some species in the amniote lineage, including humans. In addition, GnRH1 and 2 are shown by immunohistochemistry to be expressed as proteins in the brain.
Key words: marsupials, gonadotrophin-releasing hormone, luteinising hormone, folliclestimulating hormone, receptors, neuropeptides.