Mayer W E, O'Huigin C, Tichy H, Terzic J, Saraga-Babic M
Max-Planck-Institut für Biologie, Abt. Immungenetik, Corrensstr. 42, 72076 Tübingen, Germany.
Scand J Immunol. 2002 Feb;55(2):162-70. doi: 10.1046/j.1365-3083.2002.01026.x.
The jawless Agnatha (lampreys and hagfishes) represent the phylogenetically oldest order of vertebrates that are believed to lack the adaptive immune system of jawed vertebrates. In order to search for molecular markers specific for cellular components of the adaptive immune system in lampreys, we used the polymerase chain reaction (PCR) to identify genes for transcription factors of the Ikaros family in genomic DNA and cDNA libraries from two species of lampreys, Petromyzon marinus and Lampetra fluviatilis. The mammalian Ikaros-like family of transcription factors consists of five members, Ikaros, Helios, Aiolos, Eos and Pegasus, of which the first three appear to be essential for lymphocyte development. Two different Ikaros-like genes, named IKLF1 and IKLF2, were identified in lamprey. They both have the conserved exon-intron structure of seven exons and show alternative splicing like their counterparts in jawed vertebrates. The genes code for predicted proteins of 589 and 513 amino acid residues, respectively. The proteins contain six highly conserved zinc finger motifs that are 83-91% identical to the mammalian members of the Ikaros-like family. The remaining parts of the sequences are, however, mostly unalignable. Phylogenetic analysis based on the alignable segments of the sequences does not identify the orthologous gene in jawed vertebrates but rather shows equidistance of the lamprey Ikaros-like factors to each other and to Ikaros, Helios, Aiolos and Eos. Expression studies by reverse transcription (RT)-PCR and in situ hybridization (ISH), however, provide evidence for moderate expression in presumed lymphoid tissues like the gut epithelium and for high levels of expression in the gonads, especially in the ovary.
无颌类脊椎动物（七鳃鳗和盲鳗）代表了系统发育上最古老的脊椎动物目，人们认为它们缺乏有颌脊椎动物的适应性免疫系统。为了寻找七鳃鳗中适应性免疫系统细胞成分特有的分子标记，我们利用聚合酶链反应（PCR）从两种七鳃鳗，即海七鳃鳗和河七鳃鳗的基因组DNA和cDNA文库中鉴定伊卡洛斯（Ikaros）家族转录因子的基因。哺乳动物中类似伊卡洛斯的转录因子家族由五个成员组成，即伊卡洛斯、太阳神（Helios）、爱奥洛斯（Aiolos）、曙光女神（Eos）和珀加索斯（Pegasus），其中前三个成员似乎对淋巴细胞发育至关重要。在七鳃鳗中鉴定出了两个不同的类似伊卡洛斯的基因，分别命名为IKLF1和IKLF2。它们都具有由七个外显子组成的保守外显子-内含子结构，并且像有颌脊椎动物中的对应基因一样表现出可变剪接。这两个基因分别编码预测的含有589个和513个氨基酸残基的蛋白质。这些蛋白质含有六个高度保守的锌指基序，与类似伊卡洛斯家族的哺乳动物成员的锌指基序有83 - 91%的同源性。然而，序列的其余部分大多无法比对。基于序列可比对片段的系统发育分析并未在有颌脊椎动物中鉴定出直系同源基因，而是显示七鳃鳗类似伊卡洛斯的因子彼此之间以及与伊卡洛斯、太阳神、爱奥洛斯和曙光女神之间的距离相等。然而，通过逆转录（RT）-PCR和原位杂交（ISH）进行的表达研究提供了证据，表明在假定的淋巴组织如肠道上皮中有适度表达，而在性腺中，尤其是卵巢中有高水平表达。
