Kountikov Evgueni, Wilson Melanie, Quiniou Sylvie, Miller Norman, Clem William, Bengtén Eva
Department of Microbiology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216-4505, USA.
Immunogenetics. 2005 Jun;57(5):374-83. doi: 10.1007/s00251-005-0797-z. Epub 2005 May 3.
CD45 is a transmembrane protein tyrosine phosphatase, which in mammals plays an important role in T and B cell receptor and cytokine signaling. Recently, a catfish cDNA was shown to contain all characteristic CD45 features: an alternatively spliced amino-terminus, a cysteine-rich region, three fibronectin domains, a transmembrane region, and two phosphotyrosine phosphatase domains. However, analyses of CD45 cDNAs from various catfish lymphoid cell lines demonstrated that catfish CD45 is unique in that it contains a large number of alternatively spliced exons. Sequence analyses of cDNAs derived from the catfish clonal B cell line 3B11 indicated that this cell line expresses up to 13 alternatively spliced exons. Furthermore, sequence similarity among the alternatively spliced exons suggested duplication events. To establish the exact number and organization of alternatively spliced exons, a bacterial artificial chromosome library was screened, and the catfish functional CD45 gene plus six CD45 pseudogenes were sequenced. The catfish functional CD45 gene spans 37 kb and contains 49 exons. In comparison, the human and pufferfish CD45 genes consist of 34 and 30 exons, respectively. This difference in the otherwise structurally conserved catfish gene is due to the presence of 18 alternatively spliced exons that were likely derived through several duplication events. In addition, duplication events were also likely involved in generating the six pseudogenes, truncated at the 3' ends. A similarly 3' truncated CD45 pseudogene is also present in the pufferfish genome, suggesting that this specific CD45 gene duplication occurred before catfish and pufferfish diverged (approximately 400 million years ago).
CD45是一种跨膜蛋白酪氨酸磷酸酶，在哺乳动物中，它在T细胞和B细胞受体以及细胞因子信号传导中发挥重要作用。最近，一个鲶鱼cDNA被证明包含所有典型的CD45特征：一个可变剪接的氨基末端、一个富含半胱氨酸的区域、三个纤连蛋白结构域、一个跨膜区域和两个磷酸酪氨酸磷酸酶结构域。然而，对来自各种鲶鱼淋巴细胞系的CD45 cDNA的分析表明，鲶鱼CD45的独特之处在于它包含大量可变剪接的外显子。对鲶鱼克隆B细胞系3B11来源的cDNA进行序列分析表明，该细胞系表达多达13个可变剪接的外显子。此外，可变剪接外显子之间的序列相似性表明发生了重复事件。为了确定可变剪接外显子的确切数量和组织方式，筛选了一个细菌人工染色体文库，并对鲶鱼功能性CD45基因以及六个CD45假基因进行了测序。鲶鱼功能性CD45基因跨度为37 kb，包含49个外显子。相比之下，人类和河豚的CD45基因分别由34个和30个外显子组成。鲶鱼基因在结构上保守，但存在这种差异是由于存在18个可变剪接的外显子，这些外显子可能是通过几次重复事件产生的。此外，重复事件也可能参与了六个假基因的产生，这些假基因在3'端被截断。河豚基因组中也存在一个类似的3'端截断的CD45假基因，这表明这种特定的CD45基因重复事件发生在鲶鱼和河豚分化之前（大约4亿年前）。
