Sameshima Shiro, Nakao Miki, Somamoto Tomonori
Laboratory of Marine Biochemistry, Department of Bioscience and Biotechnology, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan.
Results Immunol. 2012 Feb 1;2:25-34. doi: 10.1016/j.rinim.2012.01.003. eCollection 2012.
CD2 family receptor (CD2f) is evolutionarily conserved and is widely expressed by various types of leukocytes. To elucidate the phylogenetic diversity of the CD2f, we characterized CD2f in teleosts using ginbuna crucian carp and zebrafish. The identified CD2f isoforms of the ginbuna carp (caauCD2f) exhibited high sequence similarity to the mammalian CD2 subsets CD48, CD244, and CD319, but it was difficult to classify them into their respective mammalian CD2f based on sequence similarity, the presence of an immunoreceptor tyrosine-based switch motif (ITSM), and phylogenetic tree analysis. Although the four caauCD2f isoforms share an extracellular domain with quite high identity (83-94% identity at the nucleic acid level), they differ in the number of ITSM motifs in their cytoplasmic tail. RT-PCR and in situ hybridization analyses showed that the caauCD2f isoforms are expressed by different cell populations, suggesting that they, like mammalian CD2f, have diverse roles. Interestingly, immunoglobulin (Ig) domain-like sequences with high identity to caauCD2fs are clustered close together within 0.6 Mbp on zebrafish chromosomes 1 and 2 (at least 8 and 35 sequences, respectively), and many pairs of the Ig domains share more than 90% identity at the amino acid level. Therefore, the teleost CD2fs with considerably high identity have been probably generated from a common ancestral Ig-domain gene by a very recent gene duplication event. These findings suggest that the identified CD2f acquired functional diversification through successive duplications together with the acquisition of ITSM.
CD2家族受体（CD2f）在进化上是保守的，并且在各种类型的白细胞中广泛表达。为了阐明CD2f的系统发育多样性，我们利用金鱼和斑马鱼对硬骨鱼中的CD2f进行了表征。鉴定出的金鱼CD2f亚型（caauCD2f）与哺乳动物CD2亚群CD48、CD244和CD319表现出高度的序列相似性，但基于序列相似性、免疫受体酪氨酸基开关基序（ITSM）的存在以及系统发育树分析，很难将它们归类到各自对应的哺乳动物CD2f中。尽管四个caauCD2f亚型共享一个细胞外结构域，其核酸水平的同一性相当高（83-94%），但它们的细胞质尾巴中的ITSM基序数量不同。逆转录聚合酶链反应（RT-PCR）和原位杂交分析表明，caauCD2f亚型由不同的细胞群体表达，这表明它们与哺乳动物CD2f一样具有多种作用。有趣的是，与caauCD2f具有高度同一性的免疫球蛋白（Ig）结构域样序列在斑马鱼1号和2号染色体上0.6兆碱基对范围内紧密聚集在一起（分别至少有8个和35个序列），并且许多对Ig结构域在氨基酸水平上的同一性超过90%。因此，具有相当高同一性的硬骨鱼CD2f可能是通过最近的基因复制事件从一个共同的祖先Ig结构域基因产生的。这些发现表明，鉴定出的CD2f通过连续复制以及ITSM的获得实现了功能多样化。
