Davail B, Pakdel F, Bujo H, Perazzolo L M, Waclawek M, Schneider W J, Le Menn F
Biology of Fish Reproduction, UA INRA, University Bordeaux I, Talence, France.
J Lipid Res. 1998 Oct;39(10):1929-37.
Receptors that transport vitellogenin (VTG) into oocytes are of vital importance to egg-laying species because they mediate a key step in oocyte development. Here we describe the cloning of the first piscine oocyte-specific receptor cDNA, i.e., that encoding the VTG receptor from the rainbow trout (Oncorhynchus mykiss). The receptor, a 826-residue type-I membrane protein, is a member of the low density lipoprotein receptor (LDLR) superfamily. It closely resembles the mammalian so-called very low density lipoprotein receptors, in that its aminoterminal ligand binding domain consists of a cluster of 8 cysteine-rich repeats. The short intracellular portion contains the internalization signal typical for the LDLR superfamily, Phe-Glu-Asn-Pro-Val-Tyr. Notably, the receptor lacks a domain with a high density of potential O-glycosylation sites often found in somatic cell-specific members of the LDLR family. A specific transcript of 3.9 kb is abundant in ovary, but undetectable in muscle and heart, which are the major sites of expression of very low density lipoprotein receptors in mammals. In vitro translation of the full-length cDNA produced a 97-kDa protein, and transient expression in COS-1 cells showed that the cDNA encodes a protein of the same size that binds vitellogenin in ligand blots. As revealed by in situ hybridization, transcripts are present in previtellogenic oocytes, indicating that production of receptor protein precedes the phase of yolk deposition. Our results in fish, together with those in birds (Bujo, H., et al. 1994. EMBO J. 13: 5165-5175) suggest that vitelogenesis provides a prime model for the study of ligand/receptor systems designed to sustain reproduction.
将卵黄蛋白原（VTG）转运至卵母细胞的受体对于产卵物种至关重要，因为它们介导了卵母细胞发育中的关键步骤。在此，我们描述了首个鱼类卵母细胞特异性受体cDNA的克隆，即编码虹鳟（Oncorhynchus mykiss）卵黄蛋白原受体的cDNA。该受体是一种含826个氨基酸残基的I型膜蛋白，属于低密度脂蛋白受体（LDLR）超家族成员。它与哺乳动物所谓的极低密度脂蛋白受体极为相似，其氨基末端配体结合结构域由一簇8个富含半胱氨酸的重复序列组成。较短的细胞内部分含有LDLR超家族典型的内化信号，即苯丙氨酸-谷氨酸-天冬酰胺-脯氨酸-缬氨酸-酪氨酸。值得注意的是，该受体缺乏LDLR家族体细胞特异性成员中常见的高密度潜在O-糖基化位点结构域。一个3.9 kb的特异性转录本在卵巢中大量存在，但在肌肉和心脏中无法检测到，而肌肉和心脏是哺乳动物极低密度脂蛋白受体主要表达部位。全长cDNA的体外翻译产生了一种97 kDa的蛋白质，在COS-1细胞中的瞬时表达表明该cDNA编码了相同大小的能在配体印迹中结合卵黄蛋白原的蛋白质。原位杂交显示，转录本存在于卵黄发生前的卵母细胞中，这表明受体蛋白的产生先于卵黄沉积阶段。我们在鱼类中的研究结果，以及鸟类中的研究结果（Bujo, H., 等人，1994. EMBO J. 13: 5165 - 5175）表明，卵黄发生为研究旨在维持繁殖的配体/受体系统提供了一个主要模型。
