Some cephalopods such as cuttlefish, octopuses, and cuttlefish have the ability to camouflage themselves by making themselves transparent and/or changing color. Scientists would like to know more about the exact mechanisms behind this unique ability, but cuttlefish skin cells cannot be grown in the laboratory. Researchers at the University of California, Irvine, have discovered a viable solution: replicate the properties of cuttlefish skin cells in mammalian (human) cells in the laboratory. they presented their research At this week’s American Chemical Society meeting in Indianapolis.
“Generally speaking, there are two ways you can achieve transparency,” said Alon Gorodetsky, who has been fascinated with squid camouflage for the past decade or so. during a media briefing At the ACS meeting. “One way is by reducing the amount of light that gets absorbed—pigment-based coloring, usually. Another way is by changing how the light is scattered, usually by adjusting for differences in refractive index.” The latter is the focus of his lab’s research.
Cuttlefish skin is transparent and features an outer layer of pigment cells called chromatophores that control the absorption of light. Each chromatophore is attached to muscle fibers that line the surface of the skin, and these fibers, in turn, are connected to nerve fibers. It is a simple matter of stimulating those nerves with electrical impulses, causing the muscles to contract. Because the muscles tighten in different directions, the cell expands with the pigmented areas, which changes color. As the cell shrinks, the pigmented areas shrink.
Under the chromatophores, there is a separate layer of iris mounts. Unlike chromatophores, the iris is not pigment-based but an example of structural color, similar to the crystals in a butterfly’s wings, except that the iris of a cuttlefish is dynamic rather than static. They can be tuned to reflect different wavelengths of light. a Paper 2012 suggested that this dynamically tunable structural color of the iris is related to a neurotransmitter called acetylcholine. The two layers work together to generate the unique optical properties of cuttlefish skin.
Then there are leucophores, similar to irises except they scatter the full spectrum of light, so they appear white. They contain reflective proteins that normally clump together into nanoparticles, so that light is scattered rather than absorbed or transmitted directly. Leucophores are mostly found in cuttlefish and octopuses, but there are some female cuttlefish of the genus sepioteuthis Which contain leucophores that can “tune” them to scatter only certain wavelengths of light. If cells allow light to pass through with little scattering, they will appear more transparent, while cells become opaque and clearer by scattering more light. These are the cells that interest Gorodetsky.
In 2015, the Gorodetsky Laboratory was established Squid inspired masking stickers For a day to help soldiers disguise themselves, even from infrared cameras. The stickers were thin, flexible layers of camouflage Ability To take a pattern to match the infrared reflection of the soldiers with their background. Instead of killing the squid to synthesize the reflective proteins, they can express it H. coli bacterial cultures. Then they covered the equivalent of regular household packing tape with the modified bacteria. Labeling can only be adjusted by changing the thickness of the bacterial film. Thin films appeared blue; Thick films appeared orange.
Having already experimented with truncated versions of the protein to study its refractive index and how it scatters light, Gorodetsky’s team has now expanded that research by introducing squid-derived genes that encode diffraction into human cells. The trick was to get the reflective nanostructures to form stably rather than temporarily. Adding salt to the cell culture medium caused the reflectance to clump together into light-scattering nanoparticles, and by gradually increasing salt concentrations, the nanoparticles became larger so that more light was scattered, essentially ‘tuning’ their dimming. They took detailed time-lapse images of the nanoparticles’ properties using a technique called holotography.
“We were really trying to understand whether the intrinsic properties of these proteins — their high refractive indices, their ability to self-assemble into specific structures — could be replicated in the mammalian cell,” Gorodetsky said. “So we engineered mammalian cells to make large amounts of this protein. And we found that… [resulting] The self-assembling structures were very similar in many ways in terms of their sizes and optical properties. “
When the COVID-19 pandemic hit, and it wasn’t possible to work in the lab, Gorodetsky’s graduate student Georgy Bogdanov used imaging data to create a computational model, enabling them to make predictions and compare the optical properties of squid cells and their engineered mammary cells. “Refractive indices are comparable, which is the main component of this phenomenon,” Bogdanov said. “Although the sizes of these particles are also similar, this gives a perfect comparison of the light scattering that occurs in squid skin and mammalian cells.”
What about potential applications? Earlier this year, we reported that engineers at the University of Toronto were inspired by cuttlefish to create a prototype of “liquid windows” that can change the wavelength, intensity, and distribution of light transmitted through those windows, thus saving energy costs significantly. One potential application of his research, Gorodetsky said, is the use of reflective proteins as high-refractive index subcellular molecular probes, used in conjunction with advanced microscopy techniques. Such genetically encoded markers would not ovulate inside human cells, enabling scientists to trace cell structure to gain a better understanding of cell growth and development.
DOI: ACS Biomaterials Science & Engineering, 2023. 10.1021/acsbiomaterials.2c00088 (about DOIs).
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