Troskie B, Illing N, Rumbak E, Sun Y M, Hapgood J, Sealfon S, Conklin D, Millar R
MRC Research Unit for Molecular Reproductive Endocrinology, University of Cape Town Medical School, Observatory 7925, Cape Town, South Africa.
Gen Comp Endocrinol. 1998 Dec;112(3):296-302. doi: 10.1006/gcen.1998.7156.
The majority of vertebrates have two or three forms of gonadotropin-releasing hormone (GnRH), which appear to have arisen by successive gene duplication events. This suggests the possibility of concordant gene duplications of the GnRH receptor to produce two or more cognate receptors. Since the extracellular loop 3 (EC3) domain of mammalian GnRH receptors plays a role in distinguishing the different forms of GnRH, we have contemplated that the sequence of this domain will differ significantly in the putative cognate receptors. Degenerate oliognucleotides encoding the sequences of the transmembrane domains preceding and following EC3 were used for PCR amplification of genomic DNA from zebrafish (Brachydanio rerio), goldfish (Carassius auratus), African clawed frog (Xenopus laevis), chicken (Gallus domesticus), and lizard (Agama atra). Isolation and sequencing of specific clones revealed that they fell into three groups. Two of these were most similar to the mammalian pituitary GnRH receptor and were therefore designated Type IA and Type IB. The third form (designated Type II) was most different from the others and was identified in Xenopus, lizard, and human DNA. These findings support the concept of the existence of three distinct GnRH receptors, which have evolved in conjunction with three distinct GnRH ligand classes present in many vertebrates.
大多数脊椎动物有两种或三种促性腺激素释放激素（GnRH）形式，它们似乎是通过连续的基因复制事件产生的。这表明GnRH受体可能存在协同基因复制，从而产生两种或更多种同源受体。由于哺乳动物GnRH受体的细胞外环3（EC3）结构域在区分不同形式的GnRH中起作用，我们推测该结构域的序列在假定的同源受体中会有显著差异。使用编码EC3前后跨膜结构域序列的简并寡核苷酸对斑马鱼（Brachydanio rerio）、金鱼（Carassius auratus）、非洲爪蟾（Xenopus laevis）、鸡（Gallus domesticus）和蜥蜴（Agama atra）的基因组DNA进行PCR扩增。对特定克隆的分离和测序表明它们分为三组。其中两组与哺乳动物垂体GnRH受体最相似，因此被命名为IA型和IB型。第三种形式（命名为II型）与其他形式差异最大，在爪蟾、蜥蜴和人类DNA中被鉴定出来。这些发现支持了三种不同的GnRH受体存在的概念，它们是与许多脊椎动物中存在的三种不同的GnRH配体类别共同进化而来的。
