GnRH Gene Cloning And Its Expression Mechanism In Pregrancy In The Yak (Bos Grunniens)

The yak is not only the largest animal in the extreme environment of the cold and hypoxia in the Qinghai-Tibet plateau,but also is a seasonal breeder in bovidae animals. Seasonal reproduction of yak is one of the very important measures, which is adapted to their extreme environment. Gonadotropin-releasing hormone (GnRH) is mostly known in mammals as a key player in the control of the hypothalamus-pituitary-gonadal axis. GnRH is a major gene in the highly complex and sophisticated process of pregnancy. To investigate the regulatory mechanism of pregnancy of yak, the GnRH gene was firstly cloned and compared to the analysis with cattle's. The expression of GnRH of the pregnant and non-pregnancy yak was detailly analysised in the hypothalamus-pituitary-gonadal axis by immunohistochemical SABC and Image-Pro Plus 6.0 software. Results:(1) A segment of 334 bp in length of GnRH gene cDNA of yak was obtained (the sequence number is JF798425), the identities of the nucleotide sequence is 99% for cattle. (2) The differential expression of GnRH GnRH-positive productions was found in the hypothalamus-pituitary-ovarian axis of the pregnant and non-pregnancy yak, and the GnRH immunopositive productions were found in the anterior hypothalamic nucleus (AH), medial mammillary nucleus (MMN), ventromedial nucleus (VMN), arcuate nucleus (ARC) and periventricular nucleus (PVN); the order of sum area (S) and integrated optical density (IOD) of GnRH immunopositive productions in the hypothalamus nucleus were SAH>SMMN>SVMN>SARC>SPVN and IODAH>IODMMN> IODVMN＞IODARC>IODPVN(P<0.01); there was the tangent phenomenon in a part of the round and oval neurons, and even the neurons was distribution of rows in the the anterior hypothalamic nucleus, medial mammillary nucleus, arcuate nucleus and periventricular nucleus of pregnant yak. In the yak pituitary, GnRH-positive productions were distributed in the neurohypophysis, anterior pituitary and pituitary pars intermedia; in the middle part of the neurohypophysis, there were a number of the spindle and ovoid GnRH-positive cell, the other part of the neurohypophysis, there was only lots of GnRH-positive nerve fibers; In anterior pituitary, GnRH immunopositive productions were mainly distributed in the distant part of the pituitary and the majority of sinus-like capillaries surrounding; the S and IOD of GnRH immunopositive productions in the pituitary of pregnant yak were larger than that of the non-pregnancy yak (P<0.01). In the yak ovary, GnRH immunoreactive productions are mainly distributed in the ovarian cortex, and the IOD of GnRH immunoreactive productions of pregnant yak was significantly higher than that of non-pregnancy yak (P<0.01). Conclusion: The yak GnRHl gene has high identity for cattle, and was very conservative. GnRH immunopositive productions was highly expressed in the anterior hypothalamic nucleus, medial mammillary nucleus, ventromedial nucleus, arcuate nucleus and periventricular nucleus, especially in the anterior hypothalamic nucleus, medial mammillary nucleus, ventromedial nucleus nucleus; the three nucleuses may play a major role in the regulation of reproductive behavior, maintain energy homeostasis and hormone balance. In the pituitary and ovarian of yak, GnRH may have important roles in hormone homeostasis and regulation of pregnancy by the way of autocrine and paracrine. In short, GnRH is highly expressed in the hypothalamus-pituitary-ovarian axis of the pregnant yak, which is the important regulative mechanism of normal physiological process during pregnancy.