From the shark Scyliorhinus stellaris we cloned and sequenced a cDNA encoding a novel type I keratin, termed SstK10. By MALDI-MS peptide mass fingerprinting of cytoskeletal proteins separated on polyacrylamide gels, we assigned SstK10 to a 46-kDa protein which is the major epidermal type I ("IE") keratin in this fish and is specifically expressed in stratified epithelia. In a phylogenetic tree based on type I keratin sequences and with lamprey keratins applied as outgroup, SstK10 branches off in a rather basal position. This tree strongly supports the concept that teleost keratins and tetrapod keratins resulted from two independent gene radiation processes. The only exception is human K18 because its orthologs have been found in all jawed vertebrates (Gnathostomata) studied; in the tree, they form a common, most early branch, with the shark version, SstK18, in the most basal position. Thus, the sequences of SstK10 and SstK18 also favor the classical view of vertebrate evolution that considers the cartilaginous fishes as the most ancient living Gnathostomata. To determine the overall expression patterns of epidermal ("E") and simple epithelial ("S") keratins in this shark, we furthermore tested a panel of monoclonal anti-keratin antibodies by immunofluorescence microscopy of frozen tissue sections, and in immunoblots of cytoskeletal preparations, demonstrating that immunodetection of specific keratins is a convenient method to characterize epithelial tissues in shark.

中文翻译：

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鲨鱼Scyliorhinus stellaris的表皮I型角蛋白的序列，进化和组织表达模式。

我们从鲨鱼Scyliorhinus stellaris中克隆并测序了一种编码新型I型角蛋白（称为SstK10）的cDNA。通过在聚丙烯酰胺凝胶上分离的细胞骨架蛋白的MALDI-MS肽质谱指纹分析，我们将SstK10分配给46-kDa蛋白，该蛋白是该鱼中主要的表皮I型（“ IE”）角蛋白，并在分层上皮中特异性表达。在基于I型角蛋白序列并以七lamp鳗角蛋白为一组的系统发育树中，SstK10在相当基础的位置分支。这棵树强烈支持硬骨鱼角蛋白和四足角蛋白是由两个独立的基因辐射过程产生的概念。唯一的例外是人类K18，因为其直系同源物已在所有研究的颌骨脊椎动物（Gnathostomata）中发现；在树上，它们形成了一个共同的，最早期的分支，鲨鱼版本SstK18处于最基础的位置。因此，SstK10和SstK18的序列也支持脊椎动物进化的经典观点，即认为软骨鱼类是最古老的活食虫。为了确定该鲨鱼中表皮（“ E”）和简单上皮（“ S”）角蛋白的总体表达模式，我们进一步通过冷冻组织切片和细胞骨架免疫印迹的免疫荧光显微镜检查了一组单克隆抗角蛋白抗体制剂，证明特定角蛋白的免疫检测是表征鲨鱼上皮组织的便捷方法。SstK10和SstK18的序列也有利于脊椎动物进化的经典观点，即认为软骨鱼类是最古老的食角兽。为了确定该鲨鱼中表皮（“ E”）和简单上皮（“ S”）角蛋白的总体表达模式，我们进一步通过冷冻组织切片和细胞骨架免疫印迹的免疫荧光显微镜检查了一组单克隆抗角蛋白抗体制剂，证明特定角蛋白的免疫检测是表征鲨鱼上皮组织的便捷方法。SstK10和SstK18的序列也有利于脊椎动物进化的经典观点，即认为软骨鱼类是最古老的食角兽。为了确定该鲨鱼中表皮（“ E”）和简单上皮（“ S”）角蛋白的总体表达模式，我们进一步通过冷冻组织切片和细胞骨架免疫印迹的免疫荧光显微镜检查了一组单克隆抗角蛋白抗体制剂，证明特定角蛋白的免疫检测是表征鲨鱼上皮组织的便捷方法。