Burning jellyfish cells reveal the secrets of biodiversity: research
Washington [US]May 22: According to a new Cornell study at the National Academy of Sciences, knidocytes, often known as stinging cells, are found in corals and jellyfish. This makes us wary of our feet while passing out to sea, and it’s also a fantastic model for a better understanding of 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, an associate professor in ecology and evolutionary biology at the College of Arts and Sciences, found that these sting cells evolved by reshaping a neuron inherited from a previous cnidarian progenitor.
“These amazing results demonstrate how new genes are gaining new functions to drive the evolution of biodiversity,” Babonis said. “They suggest that the co-optation of ancestral cell types was an important source for new cell functions during the early evolution of animals.”
Understanding how specialized cell types, such as sting cells, are, is a key challenge in evolutionary biology, Babonis said. World Jellyfish Day: jelly species found in the marine world and their characteristics (Watch video)
For almost a century, it has been known that knidocytes evolved from a pool of stem cells that also generate neurons (brain cells), but so far no one knew how these stem cells decided to make a neuron or knidocyte. Understanding this process in living bookworms can reveal clues as to how bookworms evolved, Babonis said.
Cnidocytes (Cnidos in Greek means “stinging nettle”), common to species of different types of Cnidaria, can trigger toxic thorns or droplets or allow cnidarians to stun prey or deter invaders.
Cnidarians are the only animals that have knidocytes, but many animals have neurons, Babonis said. Thus, she and her colleagues from the Whitney Laboratory at the University of Florida in Marine Biology studied cnidaria – particularly actinium – to understand how a neuron can be reprogrammed to create a new cell.
“One of the unique features of knidocytes is that they all have an explosive organelle (a small pocket inside the cage) that contains a harpoon that shoots out to sting you,” Babonis said.
“These harpoons are made from a protein that is also found only in cnidarians, so knidocytes seem to be one of the most striking examples of how the origin of a new gene (encoding a unique protein) can stimulate the evolution of a new cell type.”
Using functional genomics in sea anemones, Nematostella vectensis, the researchers showed that knidocytes develop by disabling the expression of the neuropeptide, RFamide, in a subset of developing neurons, and reprofiling these cells into knidocytes.
Moreover, the researchers showed that one regulatory gene, specific for cnidaria, is responsible for both disabling the neural function of these cells and for the inclusion of book-specific traits.
Neurons and knidocytes are similar in shape, Babonis said; both are secretory cells capable of ejecting something out of the cell. Neurons secrete neuropeptides – proteins that quickly transmit information to other cells. Cnidocytes secrete harpoons with poison. “There’s one gene that acts as a light switch – when it’s turned on, you get a knidocyte, when it’s turned off, you get a neuron,” Babonis said. “It’s pretty simple logic to control cell identity.”
This is the first study to show that this logic works in cnidarians, Babonis said, so this feature probably regulated how cells began to differ from each other in the earliest multicellular animals.
Babonis and her lab are planning future research to investigate how widespread this genetic switch is in creating new cell types in animals. One project, for example, would investigate whether a similar mechanism drives the origin of new skeletal-secreting cells in corals. (ANI)