Jellyfish's stinging cells hold clues to biodiversity

According to recent Cornell study, cnidocytes, or stinging cells, which are found in sea anemones, hydrae, corals, and jellyfish and make humans cautious while wading in the ocean, are also a great model for understanding the creation of new cell types.

Leslie Babonis, assistant professor of ecology and evolutionary biology in the College of Arts and Sciences, demonstrated that these stinging cells evolved by repurposing a neuron inherited from a pre-cnidarian ancestor in new research published in the Proceedings of the National Academy of Sciences on May 2.

"These surprising results demonstrate how new genes acquire new functions to drive the evolution of biodiversity," Babonis added. "They suggest that co-option of ancestral cell types was an important source for new cell functions during the early evolution of animals."

One of the major issues in evolutionary biology, according to Babonis, is figuring out how specialized cell types, such as stinging cells, emerge. Cnidocytes have been known to grow from a pool of stem cells that also gives rise to neurons (brain cells) for over a century, but no one knew how those stem cells chose to create either a neuron or a cnidocyte until now. Babonis believes that studying this mechanism in current cnidarians might offer information about how cnidocytes developed in the first place.

Cnidocytes (Cnidocytes) are cells that are found in the "cnidos (Greek for "stinging nettle"), a poisonous barb or blob that may be launched by cnidarians to shock prey or discourage invaders, is found in species across the phylum Cnidaria. Only cnidarians have cnidocytes, yet many animals have neurons, according to Babonis. So she and her colleagues at the University of Florida's Whitney Lab for Marine Bioscience looked to cnidarians to figure out how a neuron may be reprogrammed to produce a new cell.

"One of the unique features of cnidocytes is that they all have an explosive organelle (a little pocket inside the cell) that contains the harpoon that shoots out to sting you," Babonis explained. "These harpoons are made of a protein that is also found only in cnidarians, so cnidocytes seem to be one of the clearest examples of how the origin of a new gene (that encodes a unique protein) could drive the evolution of a new cell type."

The researchers used functional genomics to show that cnidocytes arise by shutting off the production of a neuropeptide called RFamide in a subpopulation of developing neurons and repurposing those cells as cnidocytes. Furthermore, the researchers discovered that a single cnidarian-specific regulatory gene controls both the brain function and the cnidocyte-specific features.

Both neurons and cnidocytes are secretory cells that may release something, according to Babonis. Neuropeptides are proteins secreted by neurons that swiftly transfer information to other cells. Cnidocytes produce poisonous harpoons.

"There is a single gene that acts like a light switch - when it's on, you get a cnidocyte, when it's off you get a neuron," Babonis explained. "It's a pretty simple logic for controlling cell identity."

According to Babonis, this is the first research to establish that this logic exists in a cnidarian, implying that this trait regulated how cells differentiated from one another in the first multicellular creatures.

Future research by Babonis and her team will look at how often this genetic off/on switch is in animals when it comes to developing new cell types. One experiment will look at whether the development of new skeleton-secreting cells in corals is driven by a similar process.