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Octopuses have captured the human imagination for centuries, inspiring sea monster sagas from Scandinavian Kraken legends to the television series “Voyage to the Bottom of the Sea” and, more recently, the less threatening Netflix “My Octopus Teacher.” With its eight suction cup-covered tentacles, their appearance is unique, and their ability to use those appendages to touch and taste while foraging sets them apart even more.
In fact, scientists have wondered for decades how those arms, or more specifically the suction cups on them, do their job, prompting a series of biomechanical experiments. But very few have studied what is happening at the molecular level. In a new report, Harvard researchers were able to glimpse how the nervous system in the octopus’s arms (which operates largely independently of its centralized brain) handles this feat.
The work published Thursday in Cell.
The scientists identified a new family of sensors in the first layer of cells within the suction cups that have adapted to react and detect molecules that do not dissolve well in water. Research suggests that these sensors, called chemotactile receptors, use these molecules to help the animal figure out what it is touching and whether that object is prey.
“We think that because the molecules do not solubilize well, they could, for example, be found on the surface of octopus prey and [whatever the animals touch]”said Nicholas Bellono, assistant professor of molecular and cell biology and lead author of the study.” So when the octopus touches a rock instead of a crab, now his arm knows: ‘Okay, I’m touching a crab [because] I know there is not only touch, but also this kind of taste. ‘”
In addition, the scientists found diversity in what receptors responded and the signals that they then transmitted to cells and the nervous system.
“We think this is important because it could facilitate the complexity of what the octopus perceives and also how it can process a variety of signals using its semiautonomous arm nervous system to produce complex behaviors,” said Bellono.
Scientists believe this research may help uncover similar receptor systems in other cephalopods, the invertebrate family that also includes squid and cuttlefish. The hope is to determine how these systems work at the molecular level and answer some relatively unexplored questions about how these creatures’ abilities evolved to adapt to their environment.
“Not much is known about marine chemotactile behavior and with this family of receptors as a model system, we can now study what signals are important to the animal and how they can be encoded,” said Lena van Giesen, a postdoctoral fellow in the Bellono laboratory. and main author of the article. “This understanding of protein evolution and signal coding goes well beyond cephalopods.”
Along with Giesen, other co-authors from the lab include Peter B. Kilian, an animal technician, and Corey AH Allard, a postdoctoral fellow.
“The strategies they have developed to solve problems in their environment are unique to them, and that inspires great interest from scientists and non-scientists alike,” Kilian said. “People are attracted to octopuses and other cephalopods because they are tremendously different from most other animals.”
The team set out to discover how receptors can detect chemicals and pick up signals in what they touch, like a tentacle around a snail, to help them make decisions.
Octopus arms are distinct and complex. About two-thirds of an octopus’s neurons are found in its arms. Because the arms operate partially independently of the brain, if you cut yourself, you can still reach, identify, and grasp items.
The team began by identifying which cells in the suction cups actually perform the detection. After isolating and cloning the chemical and tactile receptors, they inserted them into frog eggs and human cell lines to study their function in isolation. There is no such thing as these receptors in frog or human cells, so the cells essentially act as closed vessels for the study of these receptors.
The researchers then exposed those cells to molecules like octopus prey extracts and other elements that these receptors are known to react to. Some test subjects were soluble in water, such as salts, sugars, amino acids; others do not dissolve well and are generally not of interest to aquatic animals. Surprisingly, only poorly soluble molecules activated the receptors.
The researchers then went back to the octopuses in their lab to see if they, too, responded to those molecules by putting those same extracts on the floor of their tanks. They found that the only odors that octopus receptors responded to were a class of naturally occurring chemicals known as terpenoid molecules that don’t dissolve.
“[The octopus] it responded very well only to the part of the soil that had the infused molecule, “said Bellono. This led the researchers to believe that the receptors they identified pick up these types of molecules and help the octopus distinguish what it is touching.” semi-autonomous nervous system, you can quickly make this decision: ‘Do I contract and grab this crab or do I keep looking?’ “
While the study provides a molecular explanation for this aquatic touch-taste sensation in octopuses through their chemotactile receptors, the researchers suggest that further study is needed, as a large number of unknown natural compounds could also stimulate these receptors to mediate complex behaviors.
“Now we are trying to look for other natural molecules that these animals can detect,” said Bellono.
This research was supported by the New York Stem Cell Foundation, the Searle Scholars Program, the Sloan Foundation, the Klingenstein-Simons Fellowship, the National Institutes of Health, and the Swiss National Science Foundation.
Reference:
Lena van Giesen. Corey AH Allard Nicholas W. et al. Molecular basis of chemotactile sensation in octopus. Cell, 2020 DOI: 10.1016 / j.cell.2020.09.008
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