Distibution And Signal Transduction Of Melatonin Receptors In Hypothalamus-pituitary-gonadal Axis Of Female Bactrian Camel In Breeding Season

Seasonal breeding is a characteristic for many mammals in temperate and tropical.Melatonin, which secreted by the mammalian pineal gland, is considered to be one ofmain factors affecting and regulating mammalian seasonal reproduction via melatoninreceptors distributing in hypothalamus-pituitary-gonadal axis (HPGA) of the mammalian.Bactrian camel are seasonal breeding animals living in temperate and tropical. However,they are still unclear about the distribution of melatonin receptor in HPGA and regulatingmechanism in Bactrian camel. In order to study these, sample had been taken from femaleBactrian camel in breeding season (November-December), and molecular biology,immunohistochemistry, in situ hybridization, ELISA and cell culture methods had beenused, with the purpose of revealing relationship between melatonin and the seasonalbreeding of the Bactrian camel. This will provide new ideas for exploring the mechanismof animal seasonal breeding with melatonin.The parts of genes of MT1(452bp) and MT2(411bp), which have more than80%similarity with cattle, sheep, human, rat and swine, has been cloned in Bactrian camelreproduction axle tissues with RT-PCR. The similarity of nucleotide is highest87.5%ofMT1with cattle and highest91.3%of MT2with swine in Genbank. Predicting proteinsequences and blasting amino acid of MT1and MT2receptors,the results shou that theyare protein of G protein couple receptors.The in-situ hybridization results show that the mRNA of melatonin receptorsdisperses in tissues of hypothalamus-pituitary-ovary axis of camel and strongly expressesin the cytoplasm and nucleus of granular lutein, oogonia and oocyte.The immunohistochemistry results show that the receptors of MT1and MT2mainlydistributed in membrane, catoplasm and nuclear membrane of neurocytes and cells ofhypothalamus-pituitary-ovary axis and pineal. But they are, not only strongly but alsodifferently, distributing in neurocytes of hypothalamus and pitutary, and the oogonia,oocyte, granular cells, gravid corpus luteum and corpus albicans of ovary. This suggestthat there are synergistic and independent effecting between MT1and MT2receptors onphysiological function of different cells. The western blot results show that melatoninreceptor protein in ovary is highest than other tissues, and suggest that melatonin is vary important for ovary development.Melatonin decreases cAMP and increases cGMP of ovary granular cell in vitro. Theeffect of melatonin decreasing cAMP can be blocked with Pertussis toxin in vitro. Andalso it can weaken Foskolin's affections. This imply that melatonin regulat the ovariangranulosa cells with pertussis toxin-sensitive G-protein couple receptors signaltransduction pathway. However, melatonin also have an impact on the accumulation ofcGMP, and which is differently with cAMP, indicat that there is another melatoninreceptor signal transduction pathway in cells.It is significant that melatonin regulate MT1and MT2mRNA expression withdifferent times and concentrations to ovary granular cells in vitro. High concentrationmelatonin (10nmol/mL) can significantly promote MR mRNA expression(p<0.01).In conclusions, these results may provide valuable information for mechanism ofmelatonin and Bactrain camel reasonal breeding, and also provide new ideas for exploringthe mechanism of animal seasonal breeding with melatonin.