[论文解读] Increasing biological complexity is positively correlated with the relative genome-wide expansion of non-protein-coding DNA sequences

Ryan J. Taft, John S. Mattick|ArXiv.org|Jan 15, 2004

RNA and protein synthesis mechanisms参考文献 79被引用 9

一句话总结

本研究提出，真核生物生物复杂性的增加与基因组中非蛋白编码DNA（ncDNA）的相对扩展密切相关。分析85个已测序物种后，作者发现ncDNA/tgDNA比值在原核生物中为0.05–0.24，在复杂多细胞生物中上升至0.62–0.985，表明非编码DNA是基因组和功能复杂性的重要驱动力，而非仅仅是进化的‘垃圾’。

ABSTRACT

Background: Prior to the current genomic era it was suggested that the number of protein-coding genes that an organism made use of was a valid measure of its complexity. It is now clear, however, that major incongruities exist and that there is only a weak relationship between biological complexity and the number of protein coding genes. For example, using the protein-coding gene number as a basis for evaluating biological complexity would make urochordates and insects less complex than nematodes, and humans less complex than rice. Results: We analyzed the ratio of noncoding to total genomic DNA (ncDNA/tgDNA) for 85 sequenced species and found that this ratio correlates well with increasing biological complexity. The ncDNA/tgDNA ratio is generally contained within the bandwidth of 0.05-0.24 for prokaryotes, but rises to 0.26-0.52 in unicellular eukaryotes, and to 0.62-0.985 for developmentally complex multicellular organisms. Significantly, prokaryotic species display a non-uniform species distribution approaching the mean of 0.1177 ncDNA/tgDNA (p=1.58 x 10^-13), and a nonlinear ncDNA/tgDNA relationship to genome size (r=0.15). Importantly, the ncDNA/tgDNA ratio corrects for ploidy, and is not substantially affected by variable loads of repetitive sequences. Conclusions: We suggest that the observed noncoding DNA increases and compositional patterns are primarily a function of increased information content. It is therefore possible that introns, intergenic sequences, repeat elements, and genomic DNA previously regarded as genetically inert may be far more important to the evolution and functional repertoire of complex organisms than has been previously appreciated.

研究动机与目标

• 重新评估生物复杂性，超越蛋白质编码基因数量，因为后者与生物复杂性之间的相关性较弱。
• 研究非蛋白编码DNA（ncDNA）含量是否比蛋白质编码基因数量与生物复杂性具有更强的相关性。
• 确定非编码DNA与总基因组DNA之比（ncDNA/tgDNA）是否可作为稳健的、校正倍性的基因组复杂性度量指标。
• 评估重复序列或倍性水平是否扭曲了ncDNA与复杂性之间的关系。
• 挑战非编码DNA功能惰性的假设，提出其作为调控和进化信息的储备库。

提出的方法

• 收集了涵盖原核生物、单细胞真核生物和多细胞真核生物的85个已测序物种的全基因组DNA组成数据。
• 为每个物种计算ncDNA/tgDNA比值（非编码DNA除以总基因组DNA），以量化相对非编码含量。
• 使用统计分析（p值、相关系数）评估ncDNA/tgDNA在分类群中的趋势显著性。
• 通过标准化ncDNA/tgDNA比值对倍性进行校正，确保比较不受基因组拷贝数的影响。
• 研究基因组大小与ncDNA/tgDNA比值之间的关系，发现在原核生物中存在非线性相关性（r = 0.15）。
• 比较ncDNA/tgDNA的物种分布，以检验其非均匀性，并评估模式是否反映功能约束或中性进化。

实验结果

研究问题

• RQ1 在多样化的生物中，非蛋白编码DNA的相对比例（ncDNA/tgDNA）是否随着生物复杂性的增加而上升？
• RQ2 ncDNA/tgDNA比值在原核生物、单细胞真核生物和复杂多细胞真核生物中如何变化？
• RQ3 ncDNA/tgDNA比值是否对倍性或重复序列含量的变化具有鲁棒性？
• RQ4 ncDNA/tgDNA比值是否可作为比蛋白质编码基因数量更好的生物复杂性指标？
• RQ5 物种间ncDNA/tgDNA比值的分布对非编码DNA的功能角色有何启示？

主要发现

• 原核生物中ncDNA/tgDNA比值范围为0.05至0.24，单细胞真核生物中为0.26–0.52，复杂多细胞生物中达到0.62–0.985。
• 原核生物中ncDNA/tgDNA比值分布非均匀，平均值为0.1177，p值极显著（1.58 × 10⁻¹³），表明变异非随机。
• 原核生物中基因组大小与ncDNA/tgDNA比值的关系为非线性，相关系数为r = 0.15。
• ncDNA/tgDNA比值不受倍性或重复序列负载变化的显著影响，使其成为比较基因组学中的稳定度量指标。
• ncDNA/tgDNA比值随生物复杂性增加而显著上升，挑战了非编码DNA功能惰性的观点。
• 研究结果表明，内含子、基因间隔区和重复元件可能共同贡献于复杂生物的信息含量和进化创新。