Hypervariable and highly divergent intron-exon organizations in the chordate Oikopleura dioica
Hypervariable and highly divergent intron-exon organizations in the chordate Oikopleura dioica
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DOI：
10.1007/s00239-004-2636-5
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发表时间：
2004-10-01
影响因子：
3.9
通讯作者：
Chourrout, D
中科院分区：
文献类型：
--
作者：
Edvardsen, RB;Lerat, E;Chourrout, D
Oikopleura dioica是一种具有非常小的基因组和非常短的生命周期的远洋被囊动物。为了研究Oikopleura中的内含子-外显子组织，我们分离并鉴定了核糖体蛋白EF-1 α、Hox和α-微管蛋白基因。它们的内含子位置与来自各种无脊椎动物和脊椎动物的相同基因的内含子位置进行了比较，其中包括四种完全测序的基因组。Oikopleura基因和小杆线虫基因一样，在大量的非保守位置上具有内含子，这些内含子必须起源于晚期插入或古老插入的内含子滑动。这两个物种在其α-微管蛋白基因家族内表现出高变的内含子-外显子组织。这是由于该基因家族的单个成员中的大多数非保守内含子位置的定位。在Oikopleura和小杆线虫中内含子位置的高变和分歧可能与短内含子的优势有关，与大内含子相比，短内含子的加工不太依赖于外显子环境。此外，这两个物种都有一个甲基化不足的基因组，甲基化诱导的点突变的控制强加了外显子大小的控制，至少在脊椎动物的基因。在Oikopleura和C.从我们目前对内含子功能的了解和假设中，很难推断出秀丽隐杆线虫可能有特定的用途。我们认为，新的内含子保留在物种的生命周期非常短，因为不合法的交流，包括基因转换被压抑。我们还推测，内含子放置在基因特定的位置可能有助于抑制这些交流，从而有利于自己的持久性。
Oikopleura dioica is a pelagic tunicate with a very small genome and a very short life cycle. In order to investigate the intron-exon organizations in Oikopleura, we have isolated and characterized ribosomal protein EF-1alpha, Hox, and alpha-tubulin genes. Their intron positions have been compared with those of the same genes from various invertebrates and vertebrates, including four species with entirely sequenced genomes. Oikopleura genes, like Caenorhabditis genes, have introns at a large number of nonconserved positions, which must originate from late insertions or intron sliding of ancient insertions. Both species exhibit hypervariable intron-exon organization within their a-tubulin gene family. This is due to localization of most nonconserved intron positions in single members of this gene family. The hypervariability and divergence of intron positions in Oikopleura and Caenorhabditis may be related to the predominance of short introns, the processing of which is not very dependent upon the exonic environment compared to large introns. Also, both species have an undermethylated genome, and the control of methylation-induced point mutations imposes a control on exon size, at least in vertebrate genes. That introns placed at such variable positions in Oikopleura or C. elegans may serve a specific purpose is not easy to infer from our current knowledge and hypotheses on intron functions. We propose that new introns are retained in species with very short life cycles, because illegitimate exchanges including gene conversion are repressed. We also speculate that introns placed at gene-specific positions may contribute to suppressing these exchanges and thereby favor their own persistence.