Centre for Computation, Mathematics and Physics in the Life Sciences and Experimental Biology, University College London, London WC1E 6BT, United Kingdom.
Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom.
Proc Natl Acad Sci U S A. 2022 Aug 30;119(35):e2205041119. doi: 10.1073/pnas.2205041119. Epub 2022 Aug 22.
The transition from prokaryotic lateral gene transfer to eukaryotic meiotic sex is poorly understood. Phylogenetic evidence suggests that it was tightly linked to eukaryogenesis, which involved an unprecedented rise in both genome size and the density of genetic repeats. Expansion of genome size raised the severity of Muller's ratchet, while limiting the effectiveness of lateral gene transfer (LGT) at purging deleterious mutations. In principle, an increase in recombination length combined with higher rates of LGT could solve this problem. Here, we show using a computational model that this solution fails in the presence of genetic repeats prevalent in early eukaryotes. The model demonstrates that dispersed repeat sequences allow ectopic recombination, which leads to the loss of genetic information and curtails the capacity of LGT to prevent mutation accumulation. Increasing recombination length in the presence of repeat sequences exacerbates the problem. Mutational decay can only be resisted with homology along extended sequences of DNA. We conclude that the transition to homologous pairing along linear chromosomes was a key innovation in meiotic sex, which was instrumental in the expansion of eukaryotic genomes and morphological complexity.
从原核侧向基因转移到真核减数分裂性的转变过程还不太清楚。系统发育证据表明，它与真核生物的起源密切相关，真核生物的起源涉及到基因组大小和遗传重复密度的空前增加。基因组大小的扩大增加了 Muller 棘轮的严重程度，同时限制了侧向基因转移 (LGT) 消除有害突变的有效性。原则上，增加重组长度和提高 LGT 率可以解决这个问题。在这里，我们使用一个计算模型表明，在早期真核生物中普遍存在的遗传重复的情况下，这个解决方案是失败的。该模型表明，分散的重复序列允许异位重组，从而导致遗传信息的丢失，并限制了 LGT 防止突变积累的能力。在存在重复序列的情况下增加重组长度会使问题更加严重。只有沿着 DNA 的扩展序列具有同源性，才能抵抗突变衰减。我们的结论是，沿着线性染色体的同源配对的转变是减数分裂性的一个关键创新，这对于真核生物基因组的扩张和形态复杂性的发展至关重要。
