Venkatesh B, Brenner S
Institute of Molecular and Cell Biology, National University of Singapore, Singapore.
Adv Exp Med Biol. 1995;395:629-38.
Oxytocin and vasopressin are structurally related mammalian neurohypophysial hormones with distinct physiological activities. Homologues of these two hormones are found in all vertebrate groups except the primitive cyclostomes in which only a vasopressin-like hormone has been reported so far. Genes encoding the mammalian oxytocin and vasopressin hormone precursors exhibit a similar genomic organisation, and are closely linked (3.5 kb to 12 kb apart) in a tail-to-tail manner suggesting a common evolutionary origin. However, no linkage among genes of the vasopressin/oxytocin family has been demonstrated in any of the lower vertebrates. The Japanese pufferfish, Fugu rubripes, has been shown to have a very compact genome of about 400 Mb with very few repetitive sequences. We used this model vertebrate genome to analyse the genomic organisation of vasotocin and isotocin genes, the teleost homologues of vasopressin and oxytocin. We have cloned and mapped the vasotocin/isotocin locus in Fugu and obtained complete nucleotide sequences of the vasotocin and isotocin genes. The coding sequences of the Fugu vasotocin and isotocin genes are interrupted by two introns at identical positions, similar to their homologues in higher vertebrates. The deduced amino acid sequences as well as the coding sequences of the two genes show high homology in the neurophysin region. Furthermore, the two genes are linked in a tandem manner with an intergenic region of about 20 kb. Random sequencing has shown that there are at least two known vertebrate genes in the intergenic region. Genomic organisation of the Fugu vasotocin/isotocin locus suggests that the teleost vasotocin and isotocin genes have evolved from a common ancestor through tandem duplication and that this locus seems to have undergone a localised reorganisation during vertebrate evolution.
催产素和加压素是结构相关的哺乳动物神经垂体激素，具有不同的生理活性。除了原始的圆口纲动物（目前仅报道了一种类似加压素的激素）外，在所有脊椎动物类群中都发现了这两种激素的同源物。编码哺乳动物催产素和加压素激素前体的基因表现出相似的基因组组织方式，并以尾对尾的方式紧密连锁（相距3.5 kb至12 kb），这表明它们有共同的进化起源。然而，在任何低等脊椎动物中都未证明加压素/催产素家族基因之间存在连锁关系。日本河豚，红鳍东方鲀，已被证明具有约400 Mb的非常紧凑的基因组，重复序列很少。我们利用这个模式脊椎动物基因组来分析加压催产素和异催产素基因的基因组组织方式，它们分别是加压素和催产素在硬骨鱼中的同源物。我们已经克隆并定位了河豚中的加压催产素/异催产素基因座，并获得了加压催产素和异催产素基因的完整核苷酸序列。河豚加压催产素和异催产素基因的编码序列在相同位置被两个内含子打断，这与它们在高等脊椎动物中的同源物相似。这两个基因推导的氨基酸序列以及编码序列在神经垂体激素区域显示出高度同源性。此外，这两个基因以串联方式连锁，基因间区域约为20 kb。随机测序表明，基因间区域至少有两个已知的脊椎动物基因。河豚加压催产素/异催产素基因座的基因组组织方式表明，硬骨鱼的加压催产素和异催产素基因是通过串联重复从共同祖先进化而来的，并且这个基因座似乎在脊椎动物进化过程中经历了局部重组。
