Zinovieva R D, Tomarev S I, Piatigorsky J
Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1993 May 25;268(15):11449-55.
omega-Crystallin of the octopus lens is related to aldehyde dehydrogenases (ALDH) of vertebrates (Tomarev, S. I., Zinovieva, R. D., and Piatigorsky, J. (1991) J. Biol. Chem. 266, 24226-24231) and ALDH1/eta-crystallin of elephant shrews (Wistow, G., and Kim, H. (1991) J. Mol. Evol. 32, 262-269). Only very low amounts of omega-crystallin are present in the squid lens. Here, we have cloned omega-crystallin cDNAs of the octopus (Octopus dofleini) and squid (Ommastrephes sloani pacificus) lenses. The deduced amino acid sequences of omega-crystallin from these species are 78% identical to each other, 56-58% identical to cytoplasmic ALDH1 and mitochondrial ALDH2 of vertebrates (which are 66-68% identical to each other), and 40% identical to Escherichia coli and spinach ALDHs. These data are consistent with the idea that the ALDH1/ALDH2 gene duplication in vertebrates occurred after divergence of cephalopods from the line giving rise to vertebrates, but before the separation of squid and octopus. Southern blot hybridization indicated that omega-crystallin is encoded by few genes (possibly just one) in octopus and squid. Northern blot hybridization revealed two bands (2.7 and 9.0 kilobases) of omega-crystallin RNA in the octopus lens and one band (4.2 kilobases) in the squid lens; omega-crystallin RNAs were undetectable in numerous non-lens tissues of octopus and squid, suggesting lens-specific expression of this gene(s). Finally, extracts of the octopus lens had no detectable ALDH activity using different substrates, consistent with omega-crystallin having no enzymatic activity. Taken together, our results suggest that omega-crystallin evolved by duplication of an ancestral gene encoding ALDH and subsequently specialized for refraction in the transparent lens while losing ALDH activity and expression in other tissues.
章鱼晶状体的ω-晶状体蛋白与脊椎动物的醛脱氢酶（ALDH）相关（托马列夫，S. I.，齐诺维耶娃，R. D.，以及皮亚蒂戈尔斯基，J.（1991年）《生物化学杂志》266卷，24226 - 24231页），也与象鼩的ALDH1/η-晶状体蛋白相关（威斯托，G.，以及金，H.（1991年）《分子进化杂志》32卷，262 - 269页）。在鱿鱼晶状体中仅存在极少量的ω-晶状体蛋白。在此，我们克隆了章鱼（杜氏章鱼）和鱿鱼（太平洋斯氏柔鱼）晶状体的ω-晶状体蛋白cDNA。这些物种的ω-晶状体蛋白推导氨基酸序列彼此间有78%的同一性，与脊椎动物的细胞质ALDH1和线粒体ALDH2有56 - 58%的同一性（它们彼此间有66 - 68%的同一性），与大肠杆菌和菠菜的ALDH有40%的同一性。这些数据与以下观点一致，即脊椎动物中ALDH1/ALDH2基因复制发生在头足类动物从产生脊椎动物的谱系中分化之后，但在鱿鱼和章鱼分离之前。Southern印迹杂交表明ω-晶状体蛋白在章鱼和鱿鱼中由少数基因（可能只有一个）编码。Northern印迹杂交揭示章鱼晶状体中有两条ω-晶状体蛋白RNA条带（2.7和9.0千碱基），鱿鱼晶状体中有一条条带（4.2千碱基）；在章鱼和鱿鱼的众多非晶状体组织中未检测到ω-晶状体蛋白RNA，表明该基因（们）在晶状体中特异性表达。最后，使用不同底物时章鱼晶状体提取物没有可检测到的ALDH活性，这与ω-晶状体蛋白没有酶活性一致。综上所述，我们的结果表明ω-晶状体蛋白是通过复制一个编码ALDH的祖先基因进化而来，随后专门用于透明晶状体中的折射，同时失去了在其他组织中的ALDH活性和表达。
