BACKGROUND Vertebrate epithelial cells typically express a specific set of keratins. In teleosts, keratins are also present in a variety of mesenchymal cells, which usually express vimentin. Significantly, our previous studies revealed that virtually all known teleost keratins evolved independently from those present in terrestrial vertebrates. To further elucidate the evolutionary scenario that led to the large variety of keratins and their complex expression patterns in present day teleosts, we have investigated their presence in bichir, sturgeon and gar. RESULTS We have discovered a novel group of type I keratins with members in all three of these ancient ray-finned fish, but apparently no counterparts are present in any other vertebrate class so far investigated, including the modern teleost fish. From sturgeon and gar we sequenced one and from bichir two members of this novel keratin group. By complementary keratin blot-binding assays and peptide mass fingerprinting using MALDI-TOF mass spectrometry, in sturgeon we were able to assign the sequence to a prominent protein spot, present exclusively in a two-dimensionally separated cytoskeletal preparation of skin, thus identifying it as an epidermally expressed type I keratin. In contrast to the other keratins we have so far sequenced from bichir, sturgeon and gar, these new sequences occupy a rather basal position within the phylogenetic tree of type I keratins, in a close vicinity to the keratins we previously cloned from river lamprey. CONCLUSION Thus, this new K14 group seem to belong to a very ancient keratin branch, whose functional role has still to be further elucidated. Furthermore, the exclusive presence of this keratin group in bichir, sturgeon and gar points to the close phylogenetic relationship of these ray- finned fish, an issue still under debate among taxonomists.

中文翻译：

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一种新颖而古老的I型角蛋白，其成员为比希尔，st鱼和尔。

背景技术脊椎动物上皮细胞通常表达一组特定的角蛋白。在硬骨鱼中，通常在表达波形蛋白的各种间充质细胞中也存在角蛋白。重要的是，我们先前的研究表明，几乎所有已知的硬骨蛋白角蛋白均独立于陆生脊椎动物中的蛋白而演化。为了进一步阐明导致当今硬骨鱼中角蛋白种类繁多及其复杂表达方式的进化情况，我们研究了其在比希尔，st鱼和中的存在。结果我们发现了一组新型的I型角蛋白，它们在所有这三种古老的有鳍鱼类中均具有成员，但到目前为止，在包括现代硬骨鱼类在内的任何其他脊椎动物类别中，显然没有对应的成员。我们从st鱼和中测序出了这个新颖的角蛋白组中的一个，从比希尔中测序了两个。通过互补的角蛋白印迹结合测定和使用MALDI-TOF质谱的肽质谱指纹分析，在st鱼中，我们能够将该序列分配给一个显着的蛋白质斑点，该斑点仅存在于二维分离的皮肤细胞骨架制剂中，因此被鉴定为表皮表达的I型角蛋白。与到目前为止我们从比希尔，st鱼和测序的其他角蛋白相反，这些新序列在I型角蛋白的系统树中占据了相当基础的位置，与我们先前从七色河中克隆的角蛋白非常接近。结论因此，这个新的K14基团似乎属于一个非常古老的角蛋白分支，其功能作用有待进一步阐明。此外，