By Michael Le Page
Alamy
Human cells genetically engineered to vary their transparency by producing a squid protein could one day lead to see-through patches of tissue.
In the short-term, the approach might help biologists get better images of living tissues they are studying under the microscope. In the longer term, it might be possible to make patches of tissue more or less transparent at will, or even to genetically engineer organisms that can control their transparency.
“That’s the crazy, far-out idea,” says Alon Gorodetsky at the University of California Irvine. “But when you see squid doing it, then you think it’s not so far-out after all.”
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Many cephalopods can not only change the colour of their skin, but also control their transparency. For instance, opalescent inshore squid (Doryteuthis opalescens) are largely transparent, but the white testis of males is visible inside their bodies. Females deter aggressive males by turning transparent tissue white to create a white stripe that resembles the male testis.
They do this with the help of a layer of cells containing a protein called reflectin. When the reflectin molecules are separated from each other, most light passes through them.
But when the proteins clump together inside a cell, their refractive index – the speed at which light can travel through a material – changes. The proteins scatter more light, making the cell appear white.
His team used human embryonic kidney cells – which are naturally transparent – then genetically engineered and grew them in a dish to produce the same reflectin protein found in opalescent squid.
By altering the salinity of the fluid surrounding the kidney cells, they were able to make the reflectin inside the cells clump together or separate. This changed the proportion of visible light that was either reflected by the cells or passed through them.
The team used salinity to control reflectin clumping as it is the simplest approach, but for future applications there are lots of other ways it could be done, Gorodetsky says.
His group is also working on a similar method to make artificial materials that can change their transparency.
Journal reference: Nature Communications, DOI: 10.1038/s41467-020-16151-6
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