Cnidocytes, often known as stinging cells, are found in corals and jellyfish, according to a new Cornell study by the National Academy of Sciences. This makes us fear for our feet as we roam the sea, and is also a fantastic model for better understanding the formation of new cell types.
In a new study published in the Proceedings of the National Academy of Sciences on May 2, Leslie Babonis, assistant professor of ecology and evolutionary biology at the College of Arts and Sciences, showed that these stinging cells evolved by repurposing a neuron inherited from a pre-Cnidarian ancestor.
“These surprising results demonstrate how new genes jellyfish acquire new functions that drive the evolution of biodiversity,” said Babonis. “They suggest that the co-optation of ancestral cell types was an important source of new cellular functions early in animal evolution.” Understanding how specialized cell types, such as stinging cells, emerge is one of the key challenges in evolutionary biology, Babonis says.
It has been known for almost a century that cnidocytes develop from a pool of stem cells that also give rise to neurons (brain cells), but until now no one knew how these stem cells decide to create a neuron or cnidocyte. Understanding this process in living cnidarians could provide clues to how cnidocytes evolved in the first place, Babonis says. Cnidocytes (“Cnidos” is Greek for “stinging nettle”), common to species in the diverse phylum Cnidaria, can launch toxic spikes or droplets, or allow cnidarians to stun prey or deter invaders.
According to Babonis, cnidarians are the only animals that have cnidocytes, but many animals have neurons. So she and her colleagues at the University of Florida’s Whitney Marine Biology Laboratory studied cnidarians, especially sea anemones, to understand how a neuron could be reprogrammed to create a new cell. “One of the unique things about cnidocytes is that they all have an explosive organelle (a small pocket inside the cell) that contains a harpoon that shoots out to sting you,” Babonis said.
“These harpoons are made from a protein that is also only found in cnidaria, so cnidocytes jellyfish seem to be one of the clearest examples of how the origin of a new gene (coding for a unique protein) can drive the evolution of a new cell type. Using the functional genomics of the starfish sea anemone Nematostella vectensis, the researchers showed that cnidocytes develop by turning off the expression of the neuropeptide RFamide in a subset of developing neurons and repurposing these cells into cnidocytes.
Moreover, the researchers showed that one cnidarian-specific regulatory gene is responsible for both turning off the neural function of these cells and turning on cnidocyte-specific traits. Babonis said that neurons and cnidocytes are similar in shape; both are secretory cells capable of throwing something out of the cell. Neurons secrete neuropeptides – proteins that quickly transmit information to other cells. Cnidocytes secrete poison-soaked harpoons. “There is one gene that acts like a light switch: when it’s on, you get a cnidocyte; when it’s off, you get a neuron,” Babonis said. “It’s pretty simple logic to manage cell identities.”
This is the first study to show that this logic is present in cnidarians, Babonis said, so this feature likely regulates how cells became distinct from each other in the earliest metazoans. Babonis and her lab are planning future studies to find out how widespread these genetic switches are when creating new cell types in animals. One project, for example, will investigate whether a similar mechanism drives the generation of new skeleton-secreting cells in corals.
Source: This news is originally published by timetotimes