Karabinos Anton, Zimek Alexander, Weber Klaus
Department of Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Goettingen, Germany.
Gene. 2004 Feb 4;326:123-9. doi: 10.1016/j.gene.2003.10.019.
We screened the recently established draft genome of the early chordate Ciona intestinalis for genes encoding cytoplasmic intermediate filament (IF) proteins. The draft of the tunicate/urochordate genome contains only the five genes (IF-A, IF-B, IF-C, IF-D and IF-F) previously established by cDNA cloning. Three of these IF proteins (IF-D, IF-C, IF-A) were shown to be orthologs of vertebrate IF subfamilies I to III while two proteins (IF-B, IF-F) seemed tunicate specific. This is now firmly established for protein IF-F since the genomic data show that it arises as a fusion protein with a C-terminal annexin domain, a feature not found before in the very large collection of metazoan IF proteins. The results also confirm the previous proposal that urochordates lack orthologs of vertebrate type IV IF proteins. We discuss the striking increase of IF complexity from 5 tunicate to 65 human genes during chordate evolution. Thus the tunicate has a single keratin pair, which is expressed in the epidermis, while the human genome has at least 25 genes each for keratins I and keratins II. Finally there are four normal Ciona annexin genes in addition to the gene encoding the IF-annexin fusion proteins (IF-F).
我们在最近构建的早期脊索动物海鞘的基因组草图中筛选编码细胞质中间丝（IF）蛋白的基因。被囊动物/尾索动物基因组草图中仅包含先前通过cDNA克隆确定的五个基因（IF - A、IF - B、IF - C、IF - D和IF - F）。其中三种IF蛋白（IF - D、IF - C、IF - A）被证明是脊椎动物IF亚家族I至III的直系同源物，而另外两种蛋白（IF - B、IF - F）似乎是被囊动物特有的。现在对于蛋白IF - F这一点已经确定无疑，因为基因组数据显示它是一种带有C末端膜联蛋白结构域的融合蛋白，这一特征在大量后生动物IF蛋白中从未发现过。研究结果也证实了之前的推测，即尾索动物缺乏脊椎动物IV型IF蛋白的直系同源物。我们讨论了在脊索动物进化过程中IF复杂性从5个被囊动物基因显著增加到65个人类基因的情况。因此，被囊动物有一对角蛋白，在表皮中表达，而人类基因组中角蛋白I和角蛋白II各自至少有25个基因。最后，除了编码IF - 膜联蛋白融合蛋白（IF - F）的基因外，还有四个正常的海鞘膜联蛋白基因存在。
