Sleeping Without a 'Brain'? Discovery of Hydra Sleep Behavior

UNIST Professor Lim Jeong-hoon's Team Makes Remarkable Discovery in Brainless Cnidarian Research
Unveiling Evolutionary Development Principles of Central Nervous System and Sleep… Published in Science Advances

(A) Appearance of Hydra and (B) Changes in somatic cell proliferation when Hydra's sleep is disturbed.

[Asia Economy Yeongnam Reporting Headquarters Reporter Kim Yong-woo] Do creatures without brains sleep?

It has attracted attention as it was discovered for the first time in the world that brainless Hydra exhibits sleep behaviors similar to humans.

This is a surprising discovery considering that sleep behavior has been regarded as the exclusive domain of animals with a central nervous system, including the brain.

Professor Lim Jeong-hoon’s team from the Department of Life Sciences at Ulsan National Institute of Science and Technology (UNIST) recently revealed that Hydra, a primitive animal without a brain, exhibits sleep behavior similar to that of higher animals such as humans.

Professor Jeonghoon Lim, Department of Life Sciences, Ulsan National Institute of Science and Technology (UNIST).

It was also confirmed that Hydra promotes somatic cell growth through sleep. This is an eye-catching study since sleep behavior has been considered a biological activity of higher animals for brain rest.

According to the research, Hydra distinguishes between day and night to sleep like humans, and when sleep is disturbed by physical stimuli or increased ambient temperature, it also exhibited compensatory sleep behavior similar to humans.

When Hydra’s movements were continuously recorded for 24 hours, its movements slowed down when the lights were turned off. This led to the conclusion that such behavior corresponds to human sleep.

The substances that promote sleep in Hydra differed from those in humans. Dopamine, a neurotransmitter, suppresses sleep in humans but promoted sleep in Hydra.

This suggests that the role of dopamine may have reversed during biological evolution. Melatonin and GABA (gamma-aminobutyric acid), which promote sleep in humans, also showed the same sleep-promoting effect in Hydra.

Professor Lim Jeong-hoon explained, “Dopamine, a representative neurotransmitter, is well known to suppress sleep in humans and Drosophila, but we newly discovered that it actually promotes sleep in Hydra.”

The research team compared Hydra’s sleep phenomena with those of animals possessing a central nervous system such as Drosophila and humans. Hydra is a cnidarian with a primitive form similar to sea anemones. This study provides clues about how the regulatory mechanisms of sleep evolved as the central nervous system gradually developed from primitive life forms like cnidarians (Hydra) to arthropods (Drosophila) and vertebrates (humans).

Professor Lim Jeong-hoon said, “This study provides an important foundation for research tracing the origin of sleep, including when newly emerged animals started sleeping during evolution and how the regulatory mechanisms of sleep have changed with the evolution of the central nervous system.”

Figure of gene expression analysis due to sleep deprivation in Hydra and exploration of novel sleep-regulating genes using a sleep model of transgenic Drosophila.

The research team also found the reason why Hydra, a ‘brainless animal,’ needs to sleep. Sleep contributes to promoting somatic cell growth in Hydra. When Hydra’s sleep is disturbed, somatic cell proliferation is suppressed. In higher animals with brains, sleep activities are known to remove brain waste and adjust the connections of neurons important for memory.

The team identified genes regulating Hydra’s sleep and compared them with those of other organisms. The PRKG1 gene, known as a phosphorylation enzyme that promotes sleep in Drosophila and mice, also promoted sleep in Hydra.

However, ornithine aminotransferase (OAT), an enzyme involved in ornithine metabolism and a type of amino acid, showed the opposite sleep regulatory function compared to evolved organisms like Drosophila. The role of ornithine metabolism and the OAT enzyme in sleep was newly elucidated in this study.

This research, conducted jointly with Professor Taichi Itoh’s team at Kyushu University in Japan, was published on October 7 (local time) in the international journal Science Advances.

The research was supported by the Seokyeongbae Science Foundation, the Korea Research Foundation’s Leading Research Center Support Project, the X-Project, and the Global Ph.D. Training Program.

This content was produced with the assistance of AI translation services.