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Credit: National Museum of Nature and Science

Invisibility is (almost) possible when human cells are merged with squid genes

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Jun 10, 2020, 2:27 PM EDT

Vegas has nothing on the disappearing acts squid and other cephalopods can pull off. These creatures can blend in to their backgrounds so well it appears as if they’ve vanished, and now human cells merged with squid DNA can do the same thing.

Humans have not been able to make themselves seem invisible yet, but our species just got closer — at least in a petri dish. Scientists at UC Irvine have succeeded at genetically engineering human cells to express the light-scattering properties that camouflage squid (like the giant squid above), cuttlefish, and octopi so well that predators mistake them for rocks or seaweed. When proteins called reflectins were taken from a squid and introduced to embryonic human kidney cells, the cells were able to blend into their backgrounds in the same surreal way a squid can.

“Although many animals have evolved intrinsic transparency for the purpose of concealment, the development of dynamic, that is, controllable and reversible, transparency for living human cells and tissues has remained elusive to date,” said Atrouli Chatterjee, who led a study recently published in Nature Communications.

Cephalopods have evolved adaptive transparency that helps them almost instantly change their colors and patterns by manipulating light. Structures called chromatophores, iridophores, and leucophores make it possible for them to get as close to invisibility as anything on this planet can. Chromatophores are pigmented cells just under the skin that are controlled by muscles which expand and contract a sac of pigment to make color more or less visible.

The problem with chromatophores is that they cannot work alone, because their pigments can only be black, brown, orange, red, or yellow. This is where iridophores and leucophores come in. Iridophores are stacked cells that reflect light back at different wavelengths. The colors they reflect also appear different depending on which angle they are observed from. Leucophores are flat cells found deep in the skin that use “magical” proteins known as reflectins to scatter light surrounding the animal. Along with the textural morphing of bumps on the skin called papillae, a squid can visually trick a hungry shark, or anything else that might be craving calamari for dinner.

“These animals can dynamically alter how their skin transmits, absorbs, and reflects light through the functionality of unique natural optical components,” Chatterjee said.

Ironically, squid and their color-changing brethren are color-blind. Previous studies have shown that they do not respond to visual cues. Instead, they rely on the cells in their skin responding to the light around them, so they can automatically hide without even trying. No need for visual cues told the scientists that reflectins could possibly express their light-reflecting properties if transferred to other cells. They cultured human kidney cells and introduced reflectins from an opalescent inshore squid, Doryteuthis opalescens. This squid has a white stripe on its body, full of leucophores containing reflectins, that can go from opaque white to nearly transparent so predators have no idea a potential meal just passed them by.

Reflectins are disordered proteins that assemble into random shapes, which is exactly what they did while floating around in the cytoplasm of human cells. The cells also went beyond expectations to form the protein into nano-globules and distributed those blobs throughout themselves. They behaved almost like a human version of leucophores. Under a microscope and a spectroscope, the cells revealed that it really was the reflectin that had given them an ability so unreal. Adding more sodium to the solution these cells were swimming in made the cells scatter even more light.

So humans may not be able to disappear yet, but UCI scientists have created some next-generation camo material and stickers with tech that works like cephalopod cells to get humans as close as they can to being invisible.