The human brain has 100 billion neurons, creating 100,000 billion connections. Understanding the precise circuits of brain cells that orchestrate all of our daily behaviors, such as moving our limbs, reacting to fear and other emotions, etc., is an incredibly complex puzzle for neuroscientists. But now fundamental questions in behavioral neuroscience can be answered with a much simpler new model organism: tiny jellyfish.
Caltech researchers have now developed a sort of genetic toolkit designed to tinker with Clytia hemisphaerica, a type of jellyfish about 1 centimeter in diameter when ripe. Using this toolkit, the tiny creatures have been genetically engineered so that their neurons individually glow with fluorescent light when activated. Because a jellyfish is transparent, researchers can then observe the glow of the animal’s neuronal activity as it behaves naturally. In other words, the team can read a jellyfish’s mind as it feeds, swims, evades predators, and more, to understand how the animal’s relatively simple brain coordinates its behaviors.
An article describing the new study appears in the journal Cell November 24. The research was conducted primarily in the lab of David J. Anderson, Seymour Benzer biology professor, Tianqiao and Chrissy Chen Institute for Neuroscience Leadership Chair, Howard Hughes Medical Institute Investigator and director of the Tianqiao and Chrissy Chen Institute for Neurosciences.
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 each other than to a jellyfish. In fact, worms are evolutionarily closer to humans than to jellyfish.
“Jellyfish are an important point of comparison because they are so far removed from kinship,” says Brady Weissbourd, postdoctoral researcher and first author of the study. “They let us ask questions like: are there shared neuroscience principles in all nervous systems? Or, what might the early nervous systems have looked like? By exploring nature more broadly, we can also discover useful biological innovations. It’s important to note that many jellyfish are small and transparent, making them exciting platforms for systems neuroscience. This is because there are some amazing new tools for imaging and manipulating neural activity using light, and you can put a whole living jellyfish under a microscope and have access to the whole. of the nervous system at the same time.
Rather than being centralized in one part of the body like our own brain, the jellyfish brain is diffused throughout the animal’s body like a net. The different parts of a jellyfish’s body can function apparently autonomously, without centralized control; for example, a surgically removed jellyfish mouth may continue to “eat” even without the rest of the animal’s body.