ᅟ: Animals are known to have higher rates of exon skipping than other eukaryotes. In a recent study, Grau-Bové et al. (Genome Biology 19:135, 2018) have used RNA-seq data across 65 eukaryotic species to investigate when and how this high prevalence of exon skipping evolved. They have found that bilaterian Metazoa have significantly increased exon skipping frequencies compared to all other eukaryotic groups and that exon skipping in nearly all animals, including non-bilaterians, is strongly enriched for frame-preserving events. The authors have hypothesized that "the increase of exon skipping rates in animals followed a two-step process. First, exon skipping in early animals became enriched for frame-preserving events. Second, bilaterian ancestors dramatically increased their exon skipping frequencies, likely driven by the interplay between a shift in their genome architectures towards more exon definition and recruitment of frame-preserving exon skipping events to functionally diversify their cell-specific proteomes." Here we offer a different explanation for the higher frequency of frame-preserving exon skipping in Metzoa than in all other eukaryotes. In our view these observations reflect the fact that the majority of multidomain proteins unique to metazoa and indispensable for metazoan type multicellularity were assembled by exon-shuffling from 'symmetrical' modules (i.e. modules flanked by introns of the same phase), whereas this type of protein evolution played a minor role in other groups of eukaryotes, including plants. The higher frequency of 'symmetrical' exons in Metazoan genomes provides an explanation for the enrichment for frame-preserving events since skipping or inclusion of 'symmetrical' modules during alternative splicing does not result in a reading-frame shift. REVIEWERS: This article was reviewed by Manuel Irimia, Ashish Lal and Erez Levanon. The reviewers were nominated by the Editorial Board.

中文翻译：

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动物的外显子跳跃丰富的转录组反映了外显子改组在后生动物蛋白质组进化中的重要性。

ᅟ：已知动物的外显子跳跃率高于其他真核生物。在最近的一项研究中，Grau-Bové等人。Genome Biology 19：135，2018）使用了65种真核物种的RNA-seq数据来研究这种外显子跳跃的高流行何时以及如何演变。他们发现，与所有其他真核生物组相比，双侧后足动物的外显子跳跃频率显着提高，并且几乎所有动物（包括非双脚动物）中的外显子跳跃都非常丰富，可以保存框架。作者假设“动物中外显子跳跃率的增加遵循两个步骤。首先，早期动物中的外显子跳跃变得更加富于框架保存事件。其次，双边祖先大大增加了其外显子跳跃频率，后生动物基因组中的外显子提供了丰富的保存框架事件的解释，因为在选择性剪接过程中跳过或包含“对称”模块不会导致阅读框架移位。审阅者：本文由Manuel Irimia，Ashish Lal和Erez Levanon审阅。审稿人由编辑委员会提名。