Healing Connections

A new report published in the open-access journal PLoS Biology examines the effect that light has on humans and animals. Most of us are familiar with how light affects the growth and development of plants (phototropism, for example, describes how plants grow towards light), but researcher Nathalie Hoang and colleagues set out to explore light’s impact on humans and mammals.

Plants have photoreceptor proteins called cryptochromes that take in blue light to help the plant grow and develop seedlings. Cryptochromes are also present in mammals, and the researchers studied those found in flies, mice, and humans. In humans, cryptochromes have been shown to have an effect on regulating the circadian clock (the 24 hour cycle of biochemical, physiological or behavioral processes), but we still do not know much about exactly how these cryptochromes operate.

In plants, blue light exposure leads to a reduction in flavin pigments, which activates the cryptochromes and begins growth and seedling development. Hoang and colleagues used this idea to expose flies, animals, and humans to blue light. The researchers measured the number of oxidized flavins after blue light exposure and found that prolonged exposure led to a decrease in the number of flavins.

The similarity in how blue light affects flavin levels in plants and animals, however, should not lead to an assumption that flavins affect circadian rhythms in the same way. For example, mice that lacked the cryptochromes Mcry1 and Mcry2 seemed to completely lose circadian rhythm behaviors (such as wheel-running), but these behavioral changes occurred with or without light exposure.