Magnetosensitive neurons mediate geomagnetic orientation in Caenorhabditis elegans.
Magnetosensitive neurons mediate geomagnetic orientation in Caenorhabditis elegans.
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DOI：
10.7554/elife.07493
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发表时间：
2015-06-17
期刊：
影响因子：
7.7
通讯作者：
Pierce-Shimomura J
中科院分区：
文献类型：
--
作者：
Vidal-Gadea A;Ward K;Beron C;Ghorashian N;Gokce S;Russell J;Truong N;Parikh A;Gadea O;Ben-Yakar A;Pierce-Shimomura J
从细菌到哺乳动物的许多生物都以地球磁场为导向。在少数动物中，已经发现了对地球磁场有反应的中枢神经元;然而，磁感觉神经元还没有在任何动物中被发现。我们表明，线虫秀丽隐杆线虫定向地球的磁场在垂直穴居迁移。吃饱了的蠕虫往上爬，饿了的蠕虫往下爬。与世界各地隔离的种群，以与磁矢量成一定角度的方式迁移，这将优化它们在本土土壤中的垂直平移，北方和南半球的蠕虫显示出相反的迁移偏好。磁取向和垂直迁移需要TAX-4环核苷酸门控离子通道的AFD感觉神经元对。钙离子成像显示，即使没有突触输入，这些神经元也会对磁场产生反应。C.秀丽线虫可能已经适应了磁性定向，通过将定向任务从三维减少到一维来简化它们的垂直穴居迁移。http://dx.doi.org/10.7554/eLife.07493.001地球有一个磁场，保护地球免受宇宙射线的有害影响，宇宙射线是由环绕地球固体内核的熔融金属层的运动产生的。磁场相对于地球表面的方向在地球仪周围变化，就像磁铁棒周围的铁屑所采用的模式。许多生物，从细菌到鸟类（如北极燕鸥）和哺乳动物（如狼），都能够利用地球磁场的这种变化来帮助它们导航。在细菌中，这种能力与拥有与地球磁场线对齐的微小磁性颗粒有关。然而，目前还不清楚动物是如何利用磁场来导航的。Vidal-Gadea等人现在已经从一个令人惊讶的来源获得了这一过程的线索，即一种名为秀丽隐杆线虫的土壤线虫。将蠕虫置于充满明胶的圆柱体中，它们更喜欢向下挖掘，但暴露在一个实际上逆转了地球磁场的人工磁场中，它们会向上挖掘。相比之下，吃得饱饱的蠕虫则朝相反的方向打洞。当蠕虫被允许在一个平行磁场的平面上爬行时，地球磁场的地图显示，这些蠕虫最初来自英国，但在美国进行了测试，它们移动的角度对应于-在英国-当它们饥饿时向下挖掘，不饿时向上挖掘。与此相一致的是，澳大利亚的蠕虫与英国蠕虫的爬行方向相反，在澳大利亚，它们的爬行角度也相当于饥饿时向下，吃饱时向上。夏威夷蠕虫也有相同的结果。来自赤道国家的蠕虫对磁场的敏感度低于北方和南方的同类;这表明这种反应是遗传编码的。事实上，一项对不同神经元有缺陷的突变蠕虫的调查发现了一对被称为“AFD神经元”的感觉神经元，它们起到了指南针的作用，并允许动物利用地磁导航。目前还不清楚AFD神经元是如何探测地球磁场的，也不清楚为什么饥饿的蠕虫会向下挖掘，而满足的蠕虫会向上挖掘。一种可能性是饥饿的蠕虫向下移动，以植物根部生长的丰富但营养贫乏的细菌为食，而饱足的蠕虫可以冒险移动到表面，寻找更理想但不太可靠的食物来源。未来的工作可以着手检验这些解释。DOI：http://dx.doi.org/10.7554/eLife.07493.002网站
Many organisms spanning from bacteria to mammals orient to the earth's magnetic field. For a few animals, central neurons responsive to earth-strength magnetic fields have been identified; however, magnetosensory neurons have yet to be identified in any animal. We show that the nematode Caenorhabditis elegans orients to the earth's magnetic field during vertical burrowing migrations. Well-fed worms migrated up, while starved worms migrated down. Populations isolated from around the world, migrated at angles to the magnetic vector that would optimize vertical translation in their native soil, with northern- and southern-hemisphere worms displaying opposite migratory preferences. Magnetic orientation and vertical migrations required the TAX-4 cyclic nucleotide-gated ion channel in the AFD sensory neuron pair. Calcium imaging showed that these neurons respond to magnetic fields even without synaptic input. C. elegans may have adapted magnetic orientation to simplify their vertical burrowing migration by reducing the orientation task from three dimensions to one. DOI: http://dx.doi.org/10.7554/eLife.07493.001 The Earth has a magnetic field that protects the planet from the harmful effects of cosmic rays, which is generated by the movement of the layer of molten metal that surrounds the planet's solid inner core. The orientation of the magnetic field relative to the Earth's surface varies around the globe, and is like the pattern adopted by iron filings around a bar magnet. Many organisms, from bacteria to birds such as the Arctic Tern and mammals such as wolves, are able to exploit this variation in the Earth's magnetic field to help them navigate. In bacteria, this ability has been linked to the possession of tiny magnetic particles that align with the Earth's magnetic field lines. However, it is not clear how animals are able use the magnetic field to navigate. Vidal-Gadea et al. have now obtained clues to this process from a surprising source, namely a soil-dwelling nematode worm called Caenorhabiditis elegans. Worms that were placed inside a gelatin-filled cylinder preferred to burrow downward, but exposure to an artificial magnetic field that in effect reversed the Earth's magnetic field caused them to burrow upward. By contrast, worms that had been well-fed burrowed in the opposite direction. When worms were instead allowed to crawl across a flat surface with a parallel magnetic field, a map of the Earth's magnetic field revealed that the worms, which were originally from England but which were tested in the US, moved at an angle that would correspond—in England—to burrowing downwards when they were hungry and upwards when were not. Consistent with this, worms from Australia crawled in the opposite direction to English worms, setting off at an angle that would also be equivalent—in Australia—to downwards when hungry and upwards when full. Identical results were found for Hawaiian worms. Worms from countries on the Equator were less sensitive to magnetic fields than their northern and southern counterparts; which suggests that the response is genetically encoded. And indeed, a survey of mutant worms with defects in different neurons uncovered a pair of sensory neurons called ‘AFD neurons’ that serve the purpose of a compass, and allow the animals to navigate using geomagnetism. It remains unclear exactly how AFD neurons detect the Earth's magnetic field, and it is also not clear why hungry worms should burrow downwards while satisfied worms burrow upwards. One possibility is that hungry worms move downwards to feed on abundant but nutrient-poor bacteria growing on plant roots, whereas sated worms can afford to risk moving to the surface in search of more desirable, but less reliable, food sources. Future work could set out to test these explanations. DOI: http://dx.doi.org/10.7554/eLife.07493.002