Multimodal sensory inputs and mechanosensory components mediate C. elegans negative gravitaxis

The ability to sense Earth's gravitational pull is essential for orientation, navigation, and proprioception in most organisms. We report here that C. elegans dauer larvae and adults show a pronounced tendency to move upward away from the center of the Earth. This behavior is antagonized by light and alternating electromagnetic fields, suggesting competition with multiple sensory modalities. Manipulating the direction and intensity of static magnetic fields does not reverse or eliminate this behavior, indicating that vertical migration is not a response to Earth's geomagnetic field, but reflects negative gravitaxis. We screened known mechanosensory genes and found that MEC-5 collagen, MEC-7/12 tubulins, and TRPA-1, but not MEC-4/10 DEG/ENaC channels or other proteins involved in gentle touch transduction, are essential for gravitaxis. These findings implicate a mechanism for gravity sensation involving an ion channel that is also required for gravitaxis in flies, suggesting possible homology in gravity sensing across animal phylogeny.