EVIDENCE FOR INSERTION OF A NEW INTRON INTO AN MHC GENE OF PERCH-LIKE FISH
EVIDENCE FOR INSERTION OF A NEW INTRON INTO AN MHC GENE OF PERCH-LIKE FISH
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DOI：
10.1098/rspb.1995.0048
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发表时间：
1995-03-22
影响因子：
4.7
通讯作者：
KLEIN, J
中科院分区：
文献类型：
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作者：
FIGUEROA, F;ONO, H;KLEIN, J
主要组织相容性复合体(MHC)的进化已经被研究，以了解免疫系统的起源，它是免疫系统的重要组成部分。在本研究中，MHC被用来阐明关于鱼类内含子的起源和系统发育的问题：主要组织相容性复合体(MHC)I类和II类基因的编码(外显子)和非编码(内含子)区域的组织在所有脊椎动物类别中都高度保守；到目前为止观察到的唯一变化是编码膜锚定部分的外显子的数量。此外，DNA水平上的外显子-内含子组织与蛋白质水平上的结构和功能定义结构域的划分之间的对应关系。在这里，我们描述了这种一致性的第一个主要例外。与迄今研究的所有其他脊椎动物不同，鲈鱼(Percomforma)中II类β链的免疫球蛋白样域不是编码在一个外显子中，而是编码在两个外显子中。额外内含子的长度因基因和物种的不同而不同，但通常小于200个碱基对(b.p.)。只有一个测序的内含子约为500b.p。长。在一些基因中，内含子包含一个六聚体重复。该重复出现在转录本中，位于基因组DNA中内含子中断外显子3的位置。因此，内含子可能是通过重复串联复制该序列而产生的。该内含子存在于Percomforma和AtherinMora(银边状鱼类)的代表中，而在迄今测试的非棘翅目鱼类(和其他脊椎动物)中不存在。内含子的分布支持棘鳍鱼类的单系性。在类似鲈鱼的鱼类中，内含子存在于不同的II类B基因座上，支持这些基因座起源于单个祖先基因的重复复制的观点。
The evolution of the major histocompatibility complex (Mhc) has been studied to understand the origin of the immune system, of which it constitutes an essential part. In the present study, the Mhc is used to shed light on questions regarding the origin of introns and the phylogeny of fishes: The organization of the coding (exon) and non-coding (intron) regions of both class I and class II major histocompatibility complex (Mhc) genes is highly conserved in all vertebrate classes; the only variation observed until now is in the number of exons encoding the membrane-anchoring part. Moreover, correspondence between the exon-intron organization at the DNA level and the division into structurally and functionally defined domains at the protein level. Here we describe the first major exception to this uniformity. The immunoglobulin-like domain of the class II beta-chains in perch-like fishes (Percomorpha) is not encoded in one exon, as it is in all other vertebrates studied thus far, but in two exons. The length of the extra intron varies from gene to gene and from species to species, but is generally less than 200 base pairs (b.p.). Only one of the sequenced introns is about 500 b.p. long. In some of the genes, the intron contains a hexamer repeat. The repeat is present in the transcript at the site at which the intron interrupts exon 3 in the genomic DNA. The intron may therefore have arisen by repeated tandem duplication of this sequence. The intron is present in representatives of the Percomorpha and Atherinomorpha (silverside-like fishes) and absent in non-acanthopterygian fishes (and other vertebrates) tested thus far. The intron's distribution supports the monophyly of the Acanthopterigii (ray-finned fishes). In the perch-like fishes, the intron is present in different class II B loci, supporting the notion that these loci originated by repeated duplications from a single ancestral gene.