祖先的轴向扭转解释了脊椎动物的对侧前脑和视交叉
An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates
AI总结：
针对前脑对侧映射的进化谜题，本文提出脊椎动物共同祖先发生90度轴向扭转假说，通过组织补偿性迁移解释前脑交叉、视交叉腹侧发育及多种解剖不对称现象。
摘要：
关于大脑最广为人知的事实之一是前脑中视觉、听觉、感觉和运动映射的对侧性。这些是如何以及为何进化出来的？针对这一问题为数不多的理论提供了功能性答案，例如用于视觉运动控制的更好网络。然而，正如本文所讨论的，这些理论与数据相矛盾。相反，我们提出在所有脊椎动物的共同祖先中，围绕身体轴进化出了一次90度的左转。发育过程中组织的补偿性迁移恢复了身体对称性。眼睛、鼻孔和前脑朝扭转方向补偿，而更尾侧的结构则朝相反方向迁移。由于这些相反的迁移，前脑相对于神经系统其余部分变得交叉和倒置。我们表明，这些补偿性迁移运动确实可以在斑马鱼和鸡中观察到。通过模型，我们展示了轴向扭转假说如何预测视交叉应在大脑腹侧发育，而嗅束应不交叉。此外，该假说解释了滑车神经的交叉、嗅觉为何不交叉、小脑半球为何代表同侧身体、鲨鱼前脑两半为何各自代表同侧眼睛、心脏和其他内脏为何在体内不对称。由于化石记录贫乏，可能的进化情景仍属推测。分子证据确实支持该假说。这些发现可能为前脑有问题的结构提供新见解。
英文摘要：
Among the best-known facts of the brain are the contralateral visual, auditory, sensational, and motor mappings in the forebrain. How and why did these evolve? The few theories to this question provide functional answers, such as better networks for visuomotor control. However, these theories contradict the data, as discussed here. Instead we propose that a 90-deg left-turn around the body-axis evolved in a common ancestor of all vertebrates. Compensatory migrations of the tissues during development restore body symmetry. Eyes, nostrils and forebrain compensate in the direction of the turn, whereas more caudal structures migrate in the opposite direction. As a result of these opposite migrations the forebrain becomes crossed and inverted with respect to the rest of the nervous system. We show that these compensatory migratory movements can indeed be observed in the zebrafish (Danio rerio) and the chick (Gallus gallus). With a model we show how the axial twist hypothesis predicts that an optic chiasm should develop on the ventral side of the brain, whereas the olfactory tract should be uncrossed. In addition, the hypothesis explains the decussation of the trochlear nerve, why olfaction is non-crossed, why the cerebellar hemispheres represent the ipsilateral bodyside, why in sharks the forebrain halves each represent the ipsilateral eye, why the heart and other inner organs are asymmetric in the body. Due to the poor fossil record, the possible evolutionary scenarios remain speculative. Molecular evidence does support the hypothesis. The findings may throw new insight on the problematic structure of the forebrain.
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