A third broad lineage of major histocompatibility complex (MHC) class I in teleost fish; MHC class II linkage and processed genes
A third broad lineage of major histocompatibility complex (MHC) class I in teleost fish; MHC class II linkage and processed genes
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DOI：
10.1007/s00251-007-0198-6
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发表时间：
2007-04-01
期刊：
影响因子：
3.2
通讯作者：
Shiina, Takashi
中科院分区：
文献类型：
--
作者：
Dijkstra, Johannes Martinus;Katagiri, Takayuki;Shiina, Takashi
以前研究的大多数硬骨鱼MHC I类分子可以分为两大类：“U”和“Z/ZE”。然而，关于鲤科和鲑科鱼类基因的数据库报告显示，还有第三个主要谱系，到目前为止还缺乏详细的分析。因为一个耐人寻味的连锁特征，我们将这个世系命名为“L”。也就是说，斑马鱼L的一个座位与MHC II类座位紧密连锁，尽管广泛报道硬骨鱼I类与II类不连锁。L谱系由高度可变的非经典MHC I类基因组成，在硬骨鱼之外没有明显的同源基因。L家族不同于大多数其他MHC I类的特征是：(1)在α1区没有两个高度保守的色氨酸残基W51和W60，(2)α1和α2外显子的GC含量很低，(3)在α3区有一个HINLTL基序，包括一个可能的糖基化位点。我们在虹鳟鱼中详细分析了几个完整的L基因，包括它们的基因组结构和转录模式。Onmy-laA基因与onmy-LBA、onmy-LCA、onmy-LDA和onmy-LEA基因有很大的不同，而后四个基因是相似的，被归类为“onmy-LBA-like”。Onmy-LAA基因的结构类似于典型的MHC-I类基因，而onmy-LBA类基因是经过加工的，除内含子1外，缺少所有内含子。onmy-LAA主要在肠道表达，而onmy-LBA-like转录本显示出相当均匀的组织分布。据我们所知，这是第一次描述具有多个加工基因副本的MHC I类谱系，这些基因是完整的和转录的。本研究显著提高了人们对硬骨鱼MHC I类变异的认识。
Most of the previously studied teleost MHC class I molecules can be classified into two broad lineages: "U" and "Z/ZE." However, database reports on genes in cyprinid and salmonid fishes show that there is a third major lineage, which lacks detailed analysis so far. We designated this lineage "L" because of an intriguing linkage characteristic. Namely, one zebrafish L locus is closely linked with MHC class II loci, despite the extensively documented nonlinkage of teleost class I with class II. The L lineage consists of highly variable, nonclassical MHC class I genes, and has no apparent orthologues outside teleost fishes. Characteristics that distinguish the L lineage from most other MHC class I are (1) absence of two otherwise highly conserved tryptophan residues W51 and W60 in the alpha 1 domain, (2) a low GC content of the alpha 1 and alpha 2 exons, and (3) an HINLTL motif including a possible glycosylation site in the alpha 3 domain. In rainbow trout (Oncorhynchus mykiss) we analyzed several intact L genes in detail, including their genomic organization and transcription pattern. The gene Onmy-LAA is quite different from the genes Onmy-LBA, Onmy-LCA, Onmy-LDA, and Onmy-LEA, while the latter four are similar and categorized as "Onmy-LBA-like." Whereas the Onmy-LAA gene is organized like a canonical MHC class I gene, the Onmy-LBA-like genes are processed and lack all introns except intron 1. Onmy-LAA is predominantly expressed in the intestine, while the Onmy-LBA-like transcripts display a rather homogeneous tissue distribution. To our knowledge, this is the first description of an MHC class I lineage with multiple copies of processed genes, which are intact and transcribed. The present study significantly improves the knowledge of MHC class I variation in teleosts.