Department of Molecular, Cellular and Biomedical Sciences, Center for Molecular and Comparative Endocrinology, University of New Hampshire Durham, NH, USA.
Front Endocrinol (Lausanne). 2011 Oct 28;2:58. doi: 10.3389/fendo.2011.00058. eCollection 2011.
The hypothalamic-pituitary system is considered to be a vertebrate innovation and seminal event that emerged prior to or during the differentiation of the ancestral agnathans. Lampreys are the earliest evolved vertebrates for which there is a demonstrated neuroendocrine system. Lampreys have three hypothalamic gonadotropin-releasing hormones (GnRHs; lGnRH-I, -II, and -III) and two and possibly three pituitary GnRH receptors involved in mediating reproductive processes. Estradiol is considered to be a major reproductive steroid in both male and female lampreys. The purpose of this study was to investigate estrogen receptor (ER) expression in the lamprey brain in adult sea lampreys. Expression of ER mRNA was confirmed in the adult lamprey brain using RT-PCR. Using digoxigenin (DIG)-labeled probes, ER expression was shown to yield moderate, but distinct reaction products in specific neuronal nuclei of the lamprey brain, including the olfactory lobe, hypothalamus, habenular area, and hindbrain. Expression of ER in the hypothalamic area of the brain provides evidence of potential interaction between estradiol and GnRH(s), and is consistent with previous evidence showing estrogen feedback on GnRH in adult lamprey brain. Earlier studies have reported that there is a close distribution of glutamic acid decarboxylase (GAD; GABA-synthesizing enzyme) and lamprey GnRH in the preoptic region in adult lampreys. The establishment of a direct estradiol-kisspeptin-GABA-GnRH interaction in lamprey has yet to be determined and will require future functional and co-localization studies. The phylogenetic position of lampreys as a basal vertebrate allows lampreys to be a basis for understanding the molecular evolution of the neuroendocrine system that arose in the vertebrates.
下丘脑-垂体系统被认为是一个脊椎动物的创新和重要事件，它出现在有颌类祖先分化之前或期间。七鳃鳗是最早进化的脊椎动物，有证明的神经内分泌系统。七鳃鳗有三种下丘脑促性腺激素释放激素（GnRHs；lGnRH-I、-II 和 -III）和两种，可能是三种参与介导生殖过程的垂体 GnRH 受体。雌二醇被认为是雄性和雌性七鳃鳗的主要生殖类固醇。本研究旨在研究成年海七鳃鳗脑内雌激素受体（ER）的表达。使用 RT-PCR 证实了成年七鳃鳗脑中 ER mRNA 的表达。使用地高辛（DIG）标记探针，显示 ER 表达在七鳃鳗脑的特定神经元核中产生中等但明显的反应产物，包括嗅叶、下丘脑、缰核区和后脑。脑下丘脑区域 ER 的表达提供了雌二醇和 GnRH(s)之间潜在相互作用的证据，与先前在成年七鳃鳗脑中 GnRH 受雌激素反馈的证据一致。早期研究报道，谷氨酸脱羧酶（GAD；GABA 合成酶）和七鳃鳗 GnRH 在成年七鳃鳗的前脑区有密切的分布。在七鳃鳗中建立直接的雌二醇- kisspeptin-GABA-GnRH 相互作用尚待确定，需要进一步进行功能和共定位研究。七鳃鳗作为基底脊椎动物的系统发育位置允许其成为理解在脊椎动物中出现的神经内分泌系统的分子进化的基础。
