Giachello Carlo N G, Scrutton Nigel S, Jones Alex R, Baines Richard A
Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom.
Manchester Institute of Biotechnology, University of Manchester, Manchester M1 7DN, United Kingdom, and.
J Neurosci. 2016 Oct 19;36(42):10742-10749. doi: 10.1523/JNEUROSCI.2140-16.2016.
Many animals are able to sense the Earth's geomagnetic field to enable behaviors such as migration. It is proposed that the magnitude and direction of the geomagnetic field modulates the activity of cryptochrome (CRY) by influencing photochemical radical pair intermediates within the protein. However, this proposal will remain theoretical until a CRY-dependent effect on a receptor neuron is shown to be modified by an external magnetic field (MF). It is established that blue-light (BL) photoactivation of CRY is sufficient to depolarize and activate Drosophila neurons. Here, we show that this CRY-dependent effect is significantly potentiated in the presence of an applied MF (100 mT). We use electrophysiological recordings from larval identified motoneurons, in which CRY is ectopically expressed, to show that BL-dependent depolarization of membrane potential and increased input resistance are markedly potentiated by an MF. Analysis of membrane excitability shows that these effects of MF exposure evoke increased action potential firing. Almost nothing is known about the mechanism by which a magnetically induced change in CRY activity might produce a behavioral response. We further report that specific structural changes to the protein alter the impact of the MF in ways that are strikingly similar to those from recent behavioral studies into the magnetic sense of Drosophila These observations provide the first direct experimental evidence to support the hypothesis that MF modulation of CRY activity is capable of influencing neuron activity to allow animal magnetoreception.
The biophysical mechanism of animal magnetoreception is still unclear. The photoreceptor protein cryptochrome has risen to prominence as a candidate magnetoreceptor molecule based on multiple reports derived from behavioral studies. However, the role of cryptochrome as a magnetoreceptor remains controversial primarily because of a lack of direct experimental evidence linking magnetic field (MF) exposure to a change in neuronal activity. Here, we show that exposure to an MF (100 mT) is sufficient to potentiate the ability of light-activated cryptochrome to increase neuronal action potential firing. Our results provide critical missing evidence to show that the activity of cryptochrome is sensitive to an external MF that is capable of modifying animal behavior.
许多动物能够感知地球的地磁场，以实现诸如迁徙等行为。有人提出，地磁场的大小和方向通过影响蛋白质内的光化学自由基对中间体来调节隐花色素（CRY）的活性。然而，在CRY对受体神经元的依赖性效应被证明可被外部磁场（MF）改变之前，这一观点仍将停留在理论层面。已知CRY的蓝光（BL）光激活足以使果蝇神经元去极化并激活它们。在此，我们表明，在施加的MF（100 mT）存在的情况下，这种依赖于CRY的效应会显著增强。我们使用对异位表达CRY的幼虫特定运动神经元进行的电生理记录，来表明MF能显著增强BL依赖的膜电位去极化和输入电阻增加。对膜兴奋性的分析表明，MF暴露的这些效应会引发动作电位发放增加。关于MF诱导的CRY活性变化可能产生行为反应的机制，人们几乎一无所知。我们进一步报告称，蛋白质的特定结构变化以与最近对果蝇磁感的行为研究惊人相似的方式改变了MF的影响。这些观察结果提供了首个直接实验证据，以支持MF调节CRY活性能够影响神经元活动从而实现动物磁感受这一假说。
动物磁感受的生物物理机制仍不清楚。基于行为研究的多份报告，光感受器蛋白隐花色素作为候选磁受体分子已备受关注。然而，隐花色素作为磁受体的作用仍存在争议，主要是因为缺乏将磁场（MF）暴露与神经元活动变化联系起来的直接实验证据。在此，我们表明暴露于MF（100 mT）足以增强光激活的隐花色素增加神经元动作电位发放的能力。我们的结果提供了关键的缺失证据，表明隐花色素的活性对能够改变动物行为的外部MF敏感。
