Gonadotropin-inhibitory hormone in Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii):: cDNA identification, transcript localization and functional effects in laboratory and field experiments
Gonadotropin-inhibitory hormone in Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii):: cDNA identification, transcript localization and functional effects in laboratory and field experiments
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DOI：
10.1677/joe.0.1820033
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发表时间：
2004-07-01
影响因子：
4
通讯作者：
Tsutsui, K
中科院分区：
文献类型：
--
作者：
Osugi, T;Ukena, K;Tsutsui, K
促性腺激素分泌的神经肽控制主要是通过下丘脑十肽GnRH的刺激作用。我们最近在日本鹌鹑（Coturnix japonica）的下丘脑中发现了一种新的十二肽，其C-末端为Leu-Pro-Leu-Arg-Phe-NH 2序列。这种新的肽在体外抑制鹌鹑垂体前叶促性腺激素的释放，因此它被命名为促性腺激素抑制激素（GnIH）。GnIH可能是一个重要的因素，调节生殖活动，不仅在驯养的鸟类，但也在野生，季节性繁殖的鸟类。因此，我们在季节性繁殖的野生鸟类中测试了合成鹌鹑GnIH。在体内实验中，将鸡促性腺激素释放激素-I（cGnRH-1）单独或cGnRH-I/鹌鹑GnIH混合物静脉注射到非繁殖鸣禽麻雀（Melospiza melodia）中。鹌鹑GnIH迅速（2分钟内）衰减GnRH诱导的血浆LH升高。此外，我们测试了鹌鹑GnIH在去势，光刺激的Gambel的白冠麻雀（Zonotrichia leucophrys gambelli）的影响，使用鹌鹑GnIH或生理盐水注射。再次，鹌鹑GnIH迅速降低血浆LH（3分钟内）与对照组相比。为了充分表征GnIH在野生鸟类中的作用，鉴定其内源性GnIH是必不可少的。因此，本研究采用3'和5'端快速扩增技术，克隆了白冠麻雀脑中GnIH基因的cDNA，并与鹌鹑GnIH基因进行了比较。推测的麻雀GnIH前体蛋白由173个氨基酸残基组成，编码1个麻雀GnIH和2个C端含有Leu-Pro-Xaa-Arg-Phe-NH 2（Xaa=Leu或Gln）的麻雀GnIH相关肽（GnIH-RP-1和GnIH-RP-2）。所有这些肽序列均由甘氨酸C-末端酰胺化信号和每个末端上的单个碱性氨基酸作为内切蛋白水解位点连接。尽管麻雀和鹌鹑的GnIH前体的同源性约为66%，但两个物种的GnIH、GnIH-RP-1和GnIH-RP-2的C末端结构均相同。原位杂交显示麻雀GnIH mRNA的细胞定位在下丘脑室旁核（PVN）。免疫组织化学分析还显示，麻雀GnIH样免疫反应阳性细胞体和终末分别位于PVN和正中隆起。因此，只有麻雀PVN表达GnIH，这似乎是一个下丘脑LH释放的抑制因子，从我们的现场注射GnIH到自由生活繁殖的白冠麻雀。在阿拉斯加北方的繁殖地，当注射到自由生活的甘贝尔白冠麻雀时，麻雀GnIH迅速（2分钟内）降低血浆LH。两者合计，我们的研究结果表明，尽管氨基酸序列的差异，鹌鹑GnIH和麻雀GnIH在野生麻雀物种的生殖轴有类似的抑制作用。因此，GnIH似乎是促性腺激素释放的调节剂。
The neuropeptide control of gonadotropin secretion is primarily through the stimulatory action of the hypothalamic decapeptide, GnRH. We recently identified a novel hypothalamic dodecapeptide with a C-terminal Leu-Pro-Leu-Arg-Phe-NH2 sequence in the domestic bird, Japanese quail (Coturnix japonica). This novel peptide inhibited gonadotropin release in vitro from the quail anterior pituitary; thus it was named gonadotropin-inhibitory hormone (GnIH). GnIH may be an important factor regulating reproductive activity not only in domesticated birds but also in wild, seasonally breeding birds. Thus, we tested synthetic quail GnIH in seasonally breeding wild bird species. In an in vivo experiment, chicken gonadotropin-releasing hormone-I (cGnRH-1) alone or a cGnRH-I/quail GnIH cocktail was injected i.v. into non-breeding song sparrows (Melospiza melodia). Quail GnIH rapidly (within 2 min) attenuated the GnRH-induced rise in plasma LH. Furthermore, we tested the effects of quail GnIH in castrated, photostimulated Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelli), using quail GnIH or saline for injection. Again, quail GnIH rapidly reduced plasma LH (within 3 min) compared with controls. To characterize fully the action of GnIH in wild birds, the identification of their endogenous GnIH is essential. Therefore, in the present study a cDNA encoding GnIH in the brain of Gambel's white-crowned sparrow was cloned by a combination of 3' and 5' rapid amplification of cDNA ends and compared with the quail GnIH cDNA previously identified. The deduced sparrow GnIH precursor consisted of 173 amino acid residues, encoding one sparrow GnIH and two sparrow GnIH-related peptides (sparrow GnIH-RP-1 and GnIH-RP-2) that included Leu-Pro-Xaa-Arg-Phe-NH2 (Xaa=Leu or Gln) at their C-termini. All these peptide sequences were fianked by a glycine C-terminal amidation signal and a single basic amino acid on each end as an endoproteolytic site. Although the homology of sparrow and quail GnIH precursors was approximately 66%, the C-terminal structures of GnIH, GnIH-RP-1 and GnIH-RP-2 were all identical in two species. In situ hybridization revealed the cellular localization of sparrow GnIH mRNA in the paraventricular nucleus (PVN) of the hypothalamus. Immunohistochemical analysis also showed that sparrow GnIH-like immunoreactive cell bodies and terminals were localized in the PVN and median eminence respectively. Thus, only the sparrow PVN expresses GnIH, which appears to be a hypothalamic inhibitory factor for LH release, as evident from our field injections of GnIH into free-living breeding white-crowned sparrows. Sparrow GnIH rapidly (within 2 min) reduced plasma LH when injected into free-living Gambel's white-crowned sparrows on their breeding grounds in northern Alaska. Taken together, our results indicate that, despite amino acid sequence differences, quail GnIH and sparrow GnIH have similar inhibitory effects on the reproductive axis in wild sparrow species. Thus, GnIH appears to be a modulator of gonadotropin release.