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Imagine being able to taste something simply by touching it. Octopuses can do just that with their unique sense of “touch-taste”, made possible by the sucker-shaped suckers along each of their eight arms. Now, the researchers report Oct. 29 in the journal Cell to have new evidence on how this sensory capacity works. The findings help explain how octopuses, and perhaps other marine organisms, explore the seafloor by sampling underwater objects with a simple touch.
“Aquatic chemosensation has long been associated with remote water signaling via hydrophilic chemicals, while terrestrial sensation uses the detection of airborne volatile molecules that are poorly soluble in water,” says Nicholas Bellono (@NBellono), Molecular and cellular biologist at Harvard University. “However, aquatic organisms produce and respond to a variety of hydrophobic compounds, suggesting a distinct form of aquatic” taste “mediated by contact-dependent chemosensation of insoluble molecules that do not readily diffuse in water. By identifying specific chemotactile receptors as mediators of this octopus sense, our study also provides a molecular basis for the aquatic “taste” of poorly soluble molecules “.
Bellono and his colleagues first showed that the California two-spotted octopus (Octopus bimaculoides) responded differently when its suckers touched a prey object than another object. The discovery confirmed that their suckers have some sort of tactile ability.
To learn more, the researchers took a closer look at the octopus’ suckers to identify the sensory cells involved. They found that the sucker actually included discrete populations of sensory cells.
But how do the chemical signals received through those suckers work together with other physical stimuli to decide if an octopus grasps what it touches? Although there is much more to learn, this study shows that distinct chemotactile receptors form discrete ion channel complexes that detect specific signals and send them to the nervous system. Bellono suggests that this could serve as a suitable signal filtering system for the octopus’s uniquely distributed nervous system.
“We also showed that separate and distinct chemo and mechanosensory cells express specific receptors and exhibit discrete electrical activities to encode chemical and tactile information, respectively,” Bellono said. “Our results demonstrate that the peripherally distributed octopus nervous system exhibits exceptional signal-filtering properties that are mediated by highly specialized sensory receptors.”
Their findings show that chemicals known as terpenoids act on octopus receptors and sensory cells in their suckers to encourage different responses. They note that terpenoids are produced by many marine invertebrates as a defense or warning signal. By sensing these signals with their arms, octopuses could avoid toxic prey. But, the researchers add, many other unknown natural compounds could also stimulate different responses in a similar way.
In future studies, the researchers hope to explore this tactile-gustatory sense in other cephalopods, such as squid, which have two specialized prey-catching tentacles instead of eight long arms.
This raises a number of intriguing questions. Have chemo tactile receptors evolved to support these specific behaviors? Do the receptors detect specific molecules based on context or ecological behavior? What are the structural mechanisms underlying protein adaptations to mediate different sensitivities to ligands and / or biophysical characteristics? How does this contribute to peripheral processing in the unique nervous system of cephalopods? Bellono and his team will continue to explore these and other questions.
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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.
Cell, van Giesen et al.: “Molecular basis of chemotactile sensation in octopus” www.cell.com/cell/fulltext/S0092-8674(20)31149-1
Cell (@CellCellPress), Cell Press’s flagship journal, is a bimonthly journal that publishes results of unusual significance in any area of experimental biology, including but not limited to cell biology, molecular biology, neuroscience, immunology, virology and microbiology, cancer , human genetics, systems biology, signaling and disease mechanisms and therapies. Visit: http: // www.
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