Hiraoka S, Suzuki M, Yanagisawa T, Iwata M, Urano A
Division of Biological Sciences, Hokkaido University, Japan.
Gen Comp Endocrinol. 1993 Nov;92(2):292-301. doi: 10.1006/gcen.1993.1165.
Salmonid fish have pairs of genes for various hypothalamic and pituitary hormones including neurohypophysial hormones, vasotocin, and isotocin, probably because they are tetraploid. The problem here is whether two genes for the same hormone are expressed equally or differently. We therefore examined expression patterns of vasotocin and isotocin genes in four salmonid species using Northern blot analysis with chum salmon cDNAs as hybridization probes. The presence of two vasotocin and also two isotocin genes was confirmed by Southern blot analysis in rainbow trout and sockeye salmon which were not examined previously. Prior to Northern blot analysis, isotocin-I cDNA of sockeye salmon was determined and compared to those of chum salmon and masu salmon, since molecular probes are so specific that cross-species hybridization often leads misinterpretation in a quantitative study. The nucleotide sequence of sockeye salmon isotocin-I cDNA showed sufficiently high homology (> 96.0%) to those of chum salmon and masu salmon for cross-species hybridization among salmonids. Northern blot analysis showed that both isotocin-I and isotocin-II genes were well expressed in all species examined. Expression of isotocin-I gene tended to be relatively higher than that of isotocin-II gene in all species. However, expression pattern of vasotocin-I and vasotocin-II genes did not coincide among species. Expression of vasotocin-II genes was very weak or scarce in masu salmon and rainbow trout, while that in sockeye salmon was stronger than vasotocin-I gene expression. The present result may reflect complicated molecular evolution of salmonid vasotocin genes probably both in regulatory and coding regions.
鲑科鱼类拥有多种下丘脑和垂体激素的成对基因，包括神经垂体激素、加压催产素和异催产素，这可能是因为它们是四倍体。这里的问题是同一激素的两个基因表达是否相同。因此，我们以大麻哈鱼cDNA为杂交探针，用Northern印迹分析法检测了四种鲑科鱼类中加压催产素和异催产素基因的表达模式。通过Southern印迹分析法在之前未检测过的虹鳟和红大马哈鱼中证实了两个加压催产素基因和两个异催产素基因的存在。在进行Northern印迹分析之前，测定了红大马哈鱼的异催产素-I cDNA，并与大麻哈鱼和马苏大麻哈鱼的进行了比较，因为分子探针具有高度特异性，在定量研究中跨物种杂交常常导致错误解读。红大马哈鱼异催产素-I cDNA的核苷酸序列与大麻哈鱼和马苏大麻哈鱼的序列具有足够高的同源性（>96.0%），可用于鲑科鱼类之间的跨物种杂交。Northern印迹分析表明，异催产素-I和异催产素-II基因在所有检测物种中均有良好表达。在所有物种中，异催产素-I基因的表达往往相对高于异催产素-II基因。然而，加压催产素-I和加压催产素-II基因的表达模式在不同物种间并不一致。加压催产素-II基因在马苏大麻哈鱼和虹鳟中的表达非常弱或几乎没有，而在红大马哈鱼中比加压催产素-I基因的表达更强。目前的结果可能反映了鲑科鱼类加压催产素基因在调控和编码区域可能存在复杂的分子进化。
