Flatworms can sense light without eyes

Researchers report that microscopic flatworms possess a light-sensing system throughout the body that can coordinate movement. Flatworms have two sensitive eyes connected to a cerebral ganglion but can respond to light even after decapitation. Nishan Shettigar and colleagues report that, in addition to eyes, flatworms possess an independent UV-A-light-sensing system throughout their body that can coordinate movement. After confirming that the movement coordinated by this extraocular system is not localized to the cilia, the authors identified two opsin molecules that looked unlike others molecules in this photoreceptor family. Spatial expression analysis revealed two distinct photoreceptor cellular arrays lining the worm, with one array containing both opsins, NC R-opn 1 and NC R-opn 2, and the other array containing only NC R-opn 1. Ablation experiments suggested that the cells expressing both opsins coordinate movement in response to UV-A light, whereas the cells with only one opsin may be involved in pigmentation. The authors examined light-sensing in newly hatched and developing worms and found that the extraocular sensing develops postembryonically in adult-like animals. UV-A light can arouse worms from a resting state in which the eyes become unresponsive, and attenuating opsin expression prevents this low-light arousal. According to the authors, the results may help illuminate the development and evolution of two distinct light-sensing systems in a single organism.

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Article #20-21426: “Discovery of a body-wide photosensory array that matures in an adult-like animal and mediates eye-brain-independent movement and arousal,” by Nishan Shettigar

et al

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