Department of Physiology, Biophysics and Neurosciences, Centre for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav-IPN), Mexico City 07360, Mexico.
Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA.
J Exp Biol. 2023 May 15;226(10). doi: 10.1242/jeb.244692. Epub 2023 May 18.
Scaling between specific organs and overall body size has long fascinated biologists, being a primary mechanism by which organ shapes evolve. Yet, the genetic mechanisms that underlie the evolution of scaling relationships remain elusive. Here, we compared wing and fore tibia lengths (the latter as a proxy of body size) in Drosophila melanogaster, Drosophila simulans, Drosophila ananassae and Drosophila virilis, and show that the first three of these species have roughly a similar wing-to-tibia scaling behavior. In contrast, D. virilis exhibits much smaller wings relative to their body size compared with the other species and this is reflected in the intercept of the wing-to-tibia allometry. We then asked whether the evolution of this relationship could be explained by changes in a specific cis-regulatory region or enhancer that drives expression of the wing selector gene, vestigial (vg), whose function is broadly conserved in insects and contributes to wing size. To test this hypothesis directly, we used CRISPR/Cas9 to replace the DNA sequence of the predicted Quadrant Enhancer (vgQE) from D. virilis for the corresponding vgQE sequence in the genome of D. melanogaster. Strikingly, we discovered that D. melanogaster flies carrying the D. virilis vgQE sequence have wings that are significantly smaller with respect to controls, partially shifting the intercept of the wing-to-tibia scaling relationship towards that observed in D. virilis. We conclude that a single cis-regulatory element in D. virilis contributes to constraining wing size in this species, supporting the hypothesis that scaling could evolve through genetic variations in cis-regulatory elements.
特定器官与整体体型之间的比例一直令生物学家着迷，它是器官形态进化的主要机制。然而，构成比例关系进化的遗传机制仍然难以捉摸。在这里，我们比较了黑腹果蝇、拟暗果蝇、粗糙拟暗果蝇和黄果蝇的翅膀和前胫骨长度（后者作为体型的代表），结果表明，前三种物种的翅膀与胫骨的比例行为大致相似。相比之下，与其他物种相比，黄果蝇的翅膀相对于其体型要小得多，这反映在翅膀与胫骨的异速生长截距上。然后，我们想知道这种关系的进化是否可以用特定的顺式调控区或增强子的变化来解释，这些顺式调控区或增强子驱动着翅膀选择基因 vestigial (vg) 的表达，其功能在昆虫中广泛保守，并有助于翅膀大小。为了直接检验这个假设，我们使用 CRISPR/Cas9 技术将黄果蝇预测的四象限增强子（vgQE）的 DNA 序列替换为黑腹果蝇基因组中的相应 vgQE 序列。令人惊讶的是，我们发现携带黄果蝇 vgQE 序列的黑腹果蝇的翅膀明显较小，相对于对照组，翅膀与胫骨比例关系的截距向黄果蝇的方向移动。我们得出结论，黄果蝇中的一个单一顺式调控元件有助于限制该物种的翅膀大小，这支持了比例关系可以通过顺式调控元件的遗传变异进化的假说。
