IFAPA Centro El Toruño, 11500 El Puerto de Santa María, Cádiz, Spain.
Comp Biochem Physiol B Biochem Mol Biol. 2012 Mar;161(3):208-18. doi: 10.1016/j.cbpb.2011.11.010. Epub 2011 Nov 30.
Vitamin C (ascorbic acid, AA) is an antioxidant that acts as a free radical scavenger and cofactor for several important enzymatic reactions, thus being important for normal cellular functions, growth and development. Accumulation of AA in cells depends on two types of sodium-dependent vitamin C transporters (SVCTs), designed as SVCT1 and SVCT2. In human, they are the products of SLC23A1 and SLC23A2 genes, respectively. In the present work, the molecular cloning of the cDNAs corresponding to slc23a1 and slc23a2 in a teleost fish, the Senegalese sole (Solea senegalensis Kaup, 1858) is first described. Sequence analysis of the predicted polypeptides revealed a conserved topology with those of mammals with important motifs involved in structure and function, being also present in svct1 and svct2. Phylogenetic analyses including a range of vertebrate SVCTs suggest that both transporters are the result of an ancient gene duplication event that occurred prior to the divergence of tetrapods and teleosts, which took place 450 million years ago. Expression profiles in juvenile tissues and during larval development were analyzed using a real-time PCR approach. In juvenile fish, slc23a1 was strongly expressed in intestine, whereas slc23a2 exhibited a widespread distribution in tissues. Transcripts of both genes were detected at early developmental stages, probably representing mRNAs of maternal origin. A possible regulation by their own substrate was detected after first uptakes of AA from diet in both genes. During metamorphosis, both slc23a1 and slc23a2 were down-regulated, the former in a thyroid hormone (TH) dependent way. This pattern coincided with a significant reduction in the AA content of larvae during metamorphosis. These results are interpreted in a physiological context of general reduction in the metabolism of metamorphic larvae. Data presented here provide the first step toward a better understanding of the physiological role of SVCTs in teleost fish.
维生素 C（抗坏血酸，AA）是一种抗氧化剂，可作为自由基清除剂和几种重要酶促反应的辅助因子，因此对正常细胞功能、生长和发育很重要。细胞中 AA 的积累取决于两种类型的钠离子依赖性维生素 C 转运体（SVCTs），分别设计为 SVCT1 和 SVCT2。在人类中，它们分别是 SLC23A1 和 SLC23A2 基因的产物。在本工作中，首次描述了一种鱼类，塞内加尔比目鱼（Solea senegalensis Kaup，1858）中 slc23a1 和 slc23a2 的 cDNA 的分子克隆。预测多肽的序列分析显示出与哺乳动物的保守拓扑结构，其中包含与结构和功能相关的重要基序，并且在 svct1 和 svct2 中也存在。包括一系列脊椎动物 SVCTs 的系统发育分析表明，这两种转运体都是发生在四足动物和鱼类分化之前的古老基因复制事件的结果，该事件发生在 4.5 亿年前。使用实时 PCR 方法分析了幼鱼组织和幼虫发育过程中的表达谱。在幼鱼中，slc23a1 在肠中强烈表达，而 slc23a2 在组织中广泛分布。在早期发育阶段检测到这两个基因的转录物，可能代表母体来源的 mRNA。在从饮食中首次摄取 AA 后，在这两个基因中检测到了可能的自身底物的调节作用。在变态期间，slc23a1 和 slc23a2 都被下调，前者以甲状腺激素（TH）依赖的方式。这种模式与变态幼虫在变态期间 AA 含量的显著减少相吻合。这些结果在代谢幼虫的新陈代谢普遍降低的生理背景下进行了解释。本文提供了对鱼类 SVCTs 生理作用的更好理解的第一步。
