Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, USA.
Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA, USA.
Science. 2019 Jan 4;363(6422):81-84. doi: 10.1126/science.aan1425. Epub 2019 Jan 3.
Evolution generates a remarkable breadth of living forms, but many traits evolve repeatedly, by mechanisms that are still poorly understood. A classic example of repeated evolution is the loss of pelvic hindfins in stickleback fish (). Repeated pelvic loss maps to recurrent deletions of a pelvic enhancer of the gene. Here, we identify molecular features contributing to these recurrent deletions. enhancer sequences form alternative DNA structures in vitro and increase double-strand breaks and deletions in vivo. Enhancer mutability depends on DNA replication direction and is caused by TG-dinucleotide repeats. Modeling shows that elevated mutation rates can influence evolution under demographic conditions relevant for sticklebacks and humans. DNA fragility may thus help explain why the same loci are often used repeatedly during parallel adaptive evolution.
进化产生了惊人的多样化的生物形式，但许多特征通过仍未被很好理解的机制重复进化。棘鱼（）中后半身鱼鳍退化的现象就是一个经典的重复进化的例子。重复的后半身鱼鳍退化与基因的鱼鳍增强子的重复缺失有关。在这里，我们确定了导致这些重复缺失的分子特征。体外实验表明，鱼鳍增强子序列形成了替代的 DNA 结构，并增加了体内的双链断裂和缺失。增强子的可变性取决于 DNA 复制的方向，并由 TG-二核苷酸重复引起。模型表明，在与棘鱼和人类相关的人口条件下，升高的突变率可能会影响进化。因此，DNA 脆性可能有助于解释为什么在平行适应进化中，相同的基因座经常被重复使用。
