Sower Stacia A, Freamat Mihael, Kavanaugh Scott I
Center for Molecular and Comparative Endocrinology and Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA.
Gen Comp Endocrinol. 2009 Mar;161(1):20-9. doi: 10.1016/j.ygcen.2008.11.023. Epub 2008 Dec 3.
The acquisition of a hypothalamic-pituitary axis was a seminal event in vertebrate evolution leading to the neuroendocrine control of many complex functions including growth, reproduction, osmoregulation, stress and metabolism. Lampreys as basal vertebrates are the earliest evolved vertebrates for which there are demonstrated functional roles for two gonadotropin-releasing hormones (GnRHs) that act via the hypothalamic-pituitary-gonadal axis controlling reproductive processes. With the availability of the lamprey genome, we have identified a novel GnRH form (lamprey GnRH-II) and a novel glycoprotein hormone receptor, lGpH-R II (thyroid-stimulating hormone-like receptor). Based on functional studies, in situ hybridization and phylogenetic analysis, we hypothesize that the newly identified lamprey GnRH-II is an ancestral GnRH to the vertebrate GnRHs. This finding opens a new understanding of the GnRH family and can help to delineate the evolution of the complex neuro/endocrine axis of reproduction. A second glycoprotein hormone receptor (lGpH-R II) was also identified in the sea lamprey. The existing data suggest the existence of a primitive, overlapping yet functional HPG and HPT endocrine systems in this organism, involving one possibly two pituitary glycoprotein hormones and two glycoprotein hormone receptors as opposed to three or four glycoprotein hormones interacting specifically with three receptors in gnathostomes. We hypothesize that the glycoprotein hormone/glycoprotein hormone receptor systems emerged as a link between the neuro-hormonal and peripheral control levels during the early stages of gnathostome divergence. The significance of the results obtained by analysis of the HPG/T axes in sea lamprey may transcend the limited scope of the corresponding physiological compartments by providing important clues in respect to the interplay between genome-wide events (duplications), coding sequence (mutation) and expression control level evolutionary mechanisms in definition of the chemical control pathways in vertebrates.
下丘脑 - 垂体轴的形成是脊椎动物进化中的一个重大事件，它导致了对包括生长、繁殖、渗透压调节、应激和新陈代谢等许多复杂功能的神经内分泌控制。七鳃鳗作为基础脊椎动物，是最早进化出的脊椎动物，已证明有两种促性腺激素释放激素（GnRHs）通过下丘脑 - 垂体 - 性腺轴发挥功能，控制生殖过程。随着七鳃鳗基因组的可得性，我们鉴定出一种新型的GnRH形式（七鳃鳗GnRH-II）和一种新型糖蛋白激素受体，即lGpH-R II（促甲状腺激素样受体）。基于功能研究、原位杂交和系统发育分析，我们推测新鉴定出的七鳃鳗GnRH-II是脊椎动物GnRHs的祖先GnRH。这一发现开启了对GnRH家族的新认识，并有助于描绘复杂的生殖神经/内分泌轴的进化。在海七鳃鳗中还鉴定出了第二种糖蛋白激素受体（lGpH-R II）。现有数据表明，在这种生物中存在一个原始的、重叠但有功能的下丘脑 - 垂体 - 性腺（HPG）和下丘脑 - 垂体 - 甲状腺（HPT）内分泌系统，涉及一种可能两种垂体糖蛋白激素和两种糖蛋白激素受体，而在有颌类动物中则是三种或四种糖蛋白激素与三种受体特异性相互作用。我们推测，糖蛋白激素/糖蛋白激素受体系统在有颌类动物分化的早期阶段作为神经激素和外周控制水平之间的联系出现。通过分析海七鳃鳗的HPG/T轴所获得结果的意义，可能超越相应生理区室的有限范围，为脊椎动物化学控制途径定义中全基因组事件（复制）、编码序列（突变）和表达控制水平进化机制之间的相互作用提供重要线索。
