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Lead author Brady Weissbourd conducted part of this research as an MBLWhitman Center Fellow in 2016 and 2017.

The human brain has 100 billion neurons, making 100 trillion connections. Understanding the precise circuits of brain cells that orchestrate all of our day-to-day behaviors—such as moving our limbs, responding to fear and other emotions, and so on—is an incredibly complex puzzle for neuroscientists. But now, fundamental questions about the neuroscience of behavior may be answered through a new and much simpler model organism: tiny jellyfish.

Caltech researchers have now developed a kind of genetic toolbox tailored for tinkering with Clytia hemisphaerica, a type of jellyfish about 1 centimeter in diameter when fully grown. Using this toolkit, the tiny creatures have been genetically modified so that their neurons individually glow with fluorescent light when activated. Because a jellyfish is transparent, researchers can then watch the glow of the animal’s neural activity as it behaves naturally. In other words, the team can read a jellyfish’s mind as it feeds, swims, evades predators, and more, in order to understand how the animal’s relatively simple brain coordinates its behaviors.

 appears in the journal Cell on November 24. The research was conducted primarily in the laboratory of , Seymour Benzer Professor of Biology, Tianqiao and Chrissy Chen Institute for Neuroscience Leadership Chair, Howard Hughes Medical Institute Investigator, and director of the .

When it comes to model organisms used in laboratories, jellyfish are an extreme outlier. Worms, flies, fish, and mice—some of the most commonly used laboratory model organisms—are all more closely related, genetically speaking, to one another than any are to a jellyfish. In fact, worms are evolutionarily closer to humans than they are to jellyfish.

“Jellyfish are an important point of comparison because they’re so distantly related,” says Brady Weissbourd, postdoctoral scholar and first author on the study. “They let us ask questions like, are there principles of neuroscience shared across all nervous systems? Or, what might the first nervous systems have looked like? By exploring nature more broadly, we may also discover useful biological innovations. Importantly, many jellyfish are small and transparent, which makes them exciting platforms for systems neuroscience. That is because there are amazing new tools for imaging and manipulating neural activity using light, and you can put an entire living jellyfish under a microscope and have access to the whole nervous system at once.”  

Citation: Weissbourd, Brady et al. (2021). A genetically tractable jellyfish model for systems and evolutionary neuroscience. Cell,