Economy, speed and size matter: Evolutionary forces driving nuclear genome miniaturization and expansion
Economy, speed and size matter: Evolutionary forces driving nuclear genome miniaturization and expansion
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DOI：
10.1093/aob/mci010
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发表时间：
2005-01-01
期刊：
影响因子：
4.2
通讯作者：
Cavalier-Smith, T
中科院分区：
文献类型：
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作者：
Cavalier-Smith, T
背景 核基因组大小变化 300 000 倍，而转录组大小仅变化 17 倍。在最大的基因组中，几乎所有 DNA 都是非基因二级 DNA，大部分是基因间的，但也在内含子内。现在有令人信服的证据表明次级DNA是有功能的，即通过有机体选择进行积极选择，而不是突变压力的纯粹中性或“自私”的结果。骨骼DNA理论认为，核体积主要由核DNA数量决定，并在一定程度上受到影响DNA包装或解折叠程度的基因的调节：核基因组大小的巨大扩散是核膜起源和DNA组装成核的必然结果，加上适应性显着的300 000倍的细胞体积范围和通过优化核质体积比（基本上不随细胞体积变化）选择平衡生长。根据对异染色质和核纤层性质的新见解，对 C 值悖论的简单解释在此进行了完善。细胞体积的遗传控制。和大规模真核生物系统发育，特别强调核基因组大小进化基本原理的原生生物测试案例。基因组小型化和扩展细胞内寄生虫（例如疟原虫、微孢子虫）通过基因丢失和消除几乎所有次级 DNA 使其基因组变得矮小。基因组减少的主要驱动力是代谢和空间经济以及细胞增殖速度。最极端的核收缩，在隐单胞菌和氯蛛的一些微小的被奴役核（核形态）中产生了小至 0.38 Mb 的基因组（使核基因组大小有效地扩大了 180 万倍！），这些嵌合细胞也保留了单独的正常大核。后者显示出基因组大小和细胞体积之间的典型相关性，但核形体却没有，尽管在同一细胞中共存> 500 My。因此，突变压力不会无情地增加基因组大小；如果需要的话，选择可以消除基本上所有的非编码DNA。核形体和微孢子虫甚至缩小了基因大小。主核和大细胞真核生物中次级 DNA 的扩展必须对其功能进行积极选择。纤毛虫核二态性提供了一个关键的测试，驳斥了自私的DNA，并有力地支持了基因组大小进化的骨骼DNA/核质比率解释。细胞体积的遗传控制是多基因的。基因组大小和细胞大小之间的定量比例相关性不能用纯粹的突变理论来解释，因为真核细胞体积是由细胞周期控制基因而不是DNA数量决定的。 (C) 2005 年植物学公司年鉴。
Background Nuclear genome size varies 300 000-fold, whereas transcriptome size varies merely 17-fold. In the largest genomes nearly all DNA is non-genic secondary DNA, mostly intergenic but also within introns. There is now compelling evidence that secondary DNA is functional, i.e. positively selected by organismal selection, not the purely neutral or 'selfish' outcome of mutation pressure. The skeletal DNA theory argued that nuclear volumes are genetically determined primarily by nuclear DNA amounts, modulated somewhat by genes affecting the degree of DNA packing or unfolding: the huge spread of nuclear genome sizes is the necessary consequence of the, origin of the nuclear envelope and the nucleation of its assembly by DNA, plus the adaptively significant 300 000-fold range of cell volumes and selection for balanced growth by optimizing karyoplasmic volume ratios (essentially invariant with cell volume in growing/multiplying cells).This simple explanation of the C-value paradox is refined here in the light of new insights into the nature of heterochromatin and the nuclear lamina. the genetic control of cell volume. and large-scale eukaryote phylogeny, placing special emphasis on protist test cases of the basic principles of nuclear genome size evolution.Genome Miniaturization and Expansion Intracellular parasites (e.g. Plasmodium, microsporidia) dwarfed their genomes by gene loss and eliminating virtually all secondary DNA . The primary driving, forces for genome reduction are metabolic and spatial economy and cell multiplication speed. Most extreme nuclear shrinkage, yielded genomes as tiny as 0.38 Mb (making the nuclear genome size range effectively 1.8 million-fold!) in some minute enslaved nuclei (nucleomorphs) of cryptomonads and chlorarachneans, chimaeric cells that also retain a separate normal large nucleus. The latter shows typical correlation between genome size and cell volume, but nucleomorphs do not despite co-existing in the same cell for >500 My. Thus mutation pressure does not inexorably increase genome size; selection can eliminate essentially all non-coding DNA if need be. Nucleomorphs and microsporidia even reduced gene size. Expansion of secondary DNA in the main nucleus, and in large-celled eukaryotes generally, must be positively selected for function. Ciliate nuclear dimorphism provides a key test that refutes the selfish DNA and strongly supports the skeletal DNA/karyoplasmic ratio interpretation of genome size evolution.Genetic Control of Cell Volume is Multigenic The quantitatively proportional correlation between genome size and cell size cannot be explained by purely mutational theories, as eukaryote cell volumes are causally determined by cell cycle control genes, not by DNA amounts. (C) 2005 Annals of Botany Company.