Can jellyfish eyes provide clues to the genetic evolution of this organ? And the stinging cells, how is it possible that they are “specialized” neurons?
For those who like the sea as a holiday destination and to escape the high temperatures —like this first heat wave in which we are immersed—, alert you to the presence of jellyfish (jellyfish) is a nuisance and even motivates visceral fears. But despite the rejection that swimmers arouse, these aquatic creatures, belonging to the phylum Cnidaria, arouse the interest of scientists, as shown by two recent studies; one on the genetic evolution of the eye and the other on how stinging cells are created from neural cells.
One eye, two eyes… or no eyes
Some jellyfish have simple eyes; others complex; and there are even those who have no eyes. According to recent research, jellyfish eyes have evolved separately and independently in different species for millennia, making them a model for studying how the trait is expressed genetically.
That’s what a team of American researchers formed by Paulyn Cartwright, professor of ecology and evolutionary biology at the University of Kansas, and his team of scientists from other universities are trying to discover: to study how the evolution of the eye in jellyfish works at the genetic level. , cellular and morphological.
“Eyes evolved independently several times within the jellyfish,” explains Cartwright. “We’ve known for a long time that there is no single origin of eyes in all animals, but we were surprised at how many times they evolved independently in jellyfish.”
Cartwright and his collaborators plan a scientific “deep dive” into evolutionary patterns to find out whether jellyfish used the same or different aspects of their genetic toolkit to build eyes each time they evolved.
“Some jellyfish have very complex, camera-like eyes that form images and have a lens, cornea and retina”
“Jellyfish are well suited for this because they have a diversity of eyes that range from simple groups of light-sensitive cells to very complex, camera-like, image-forming eyes that have a lens, a cornea and a retina.” says Cartwright.
The researcher plans to analyze many species of jellyfish in her laboratory at the University of Kansas to determine all the genes expressed in individual cells of different jellyfish eyes, and thus find out what is shared between different jellyfish instances and what has changed. components.
“Cells themselves have their own characteristics,” says Cartwright, “and they are really the result of the expression of many, many different genes, so sometimes we can miss an overall pattern when looking at individual genes. But if we look at all the genes that are expressed in the cell and what that specific outcome is, that can give us a different level of information.”
“That’s why it’s great to look at all these different levels and see what’s similar and what’s changed to really help us understand this very complicated issue. Jellyfish are a great system to do this because they are very prone to these types of experiments. We can look at individual genes and how they are expressed; we can look wholesale at all the genes that are expressed in these cells.”
Specimen collection in the genomic era
The three researchers will travel to Panama, a jellyfish biodiversity hotspot, to collect specimens and build a more detailed phylogenetic tree (or evolutionary history) of jellyfish.
“Jellyfish are very diverse, there are thousands of species. Figuring out their exact evolutionary history is a challenge, in part because so much of this diversification took place over half a billion years ago,” says Cartwright. small and hard to find. […] We’re very excited about the age of genomics, because we can get more data, sequence more genes, and produce more DNA sequences. We look forward to very promising information to resolve some of these cnidarian relationships.”
From neurons to stinging cells
On the other hand, at Cornell University (in Ithaca, New York and Doha) they are interested in the stinging cells of jellyfish, responsible for their “sting” and which bathers have to avoid because their contact is painful and in in some cases it can cause anaphylactic shock. These cells, called cnidocytes or cnidoblastsare also an excellent model for understanding the emergence of new types of cells, according to research carried out by this university and published in Proceedings of the National Academy of Sciences last May.
New genes take on new roles to drive the evolution of biodiversity
Leslie Babonis, an assistant professor of ecology and evolutionary biology in the College of Arts and Sciences who led the study, says these stinging cells evolved from neurons in their cnidarian ancestors. “The results demonstrate how new genes take on new roles to drive the evolution of biodiversity,” he says.
Understanding how specialized cell types such as stinging cells arise is one of the main challenges in evolutionary biology, says Babonis. It has been known for nearly a century that cnidocytes developed 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 form a neuron or a cnidocyte. . Understanding this process in living cnidarians could reveal clues about the current evolution of cnidocytes, says Babonis.
reprogrammed neurons
“Cnidarians are the only animals that have cnidocytes, but many animals have neurons”, says the professor. So she and her colleagues at the University of Florida’s Whitney Laboratory of Marine Biosciences studied cnidarians, specifically sea anemones, to understand how a neuron can be reprogrammed to create a new cell.
“One of the unique features of cnidocytes is that they all have an explosive organelle (a small pouch inside the cell) that contains the harpoon that fires to sting. [a su presa]Babonis says. “These harpoons are made from a protein that is also found only in cnidarians, so cnidocytes appear to be one of the clearest examples of how the origin of a new gene (which encodes a unique protein) can drive the evolution of a new type of species. cell .
Using functional genomics in the star sea anemone, Nematostella vectensis, the researchers showed that cnidocytes develop by turning off the expression of a neuropeptide, RFamide, in a subset of developing neurons and redirecting those cells as cnidocytes. Furthermore, the researchers showed that a single cnidarian-specific regulatory gene is responsible for turning off neural function in these cells and activating cnidocyte-specific features.
Neurons and cnidocytes are similar in shape, according to Babonis; both are secretory cells capable of expelling something out of the cell. Neurons secrete neuropeptides, proteins that quickly communicate information to other cells. Cnidocytes secrete poisoned harpoons.
Cnidocyte or Neuron?
“There’s 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,” says Babonis. “It’s a pretty simple logic to control the cell’s identity.”
This is the first study to show that this logic exists in a cnidarian, so it’s likely that this feature governs how cells differentiated from one another in early multicellular animals.
Now, Babonis and his lab plan future studies to investigate how pervasive this genetic on/off switch is in creating new cell types in animals.
REFERENCES
Jellyfish stinging cells hold clues to biodiversity
MEDUSA’S EYES WILL ALLOW RESEARCHERS TO PURSUE THE INTERNAL FUNCTIONING OF EVOLUTION
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