Protein found in fingertip ‘capsules’ may be critical to our sense of touch

2020-12-11

Can you tell the difference between high– and low–thread-count sheets just by touching them? Thank usherin, a protein found in a mysterious structure in your fingertips. Usherin also helps us see and hear, suggesting a deep molecular connection among our most important senses.

“The work is surprising,” says Ellen Lumpkin, a neuroscientist at the University of California (UC), Berkeley, who was not involved in the study. The study, she says, points to a single protein being used over and over again in distinct ways to help us monitor the outside world.

Scientists already had some hints that usherin is important for our sense of touch. A mutation in the gene that codes for it, USH2A, causes Usher syndrome—a rare, inherited disease that leads to blindness, deafness, and an inability to feel faint vibrations in the fingertips.

To further explore usherin’s role in touch, researchers recruited 13 patients with a form of Usher syndrome that specifically affects touch. The team—led by Gary Lewin, a neuroscientist at the Max Delbrück Center for Molecular Medicine—measured how well each person sensed pain, temperature changes, and tiny vibrations at 10 and 125 hertz (Hz), mimicking the sensation of moving a fingertip across a rough surface. The scientists then compared the patients’ results against those of 65 healthy volunteers.

People with Usher syndrome did just as well as their counterparts at sensing temperature changes and mild pain, the team found. But they were four times less likely to pick up on the 125-Hz vibrations and 1.5 times less likely to detect the 10-Hz vibrations.

To find out why, the researchers replicated the experiment using mice with or without the USH2A gene. As with their human equivalents, rodents in both groups were fine at detecting temperature changes and pain. But mice with USH2A were better at detecting both degrees of vibrations than those without it, the team reports this week in Nature Neuroscience.

The study also unveiled a surprising source for usherin. The protein is typically present in nerve cells responsible for vision and hearing. But in mice and humans, the scientists found it in the “Meissner corpuscle,” a microscopic, oval-shaped capsule that surrounds nerve cells in fingers.

The find adds to an emerging area of research: exploring how molecules outside neurons, once thought to merely support or protect nerve cells, shape our sense of touch, says Theanne Griffith, a neuroscientist at UC Davis who was not involved with the work. Until about 20 years ago, she says, researchers thought these neurons were operating alone to pass on sensory signals to the brain. “It’s amazing that they were able to show these results.”

Lewin says he and his team plan to determine exactly how USH2A is working to help us detect vibrations, noting that further work with both the gene and protein could lead to a better understanding of how we gauge and control our grip strength. “We now have evidence that something being made in the Meissner corpuscle is necessary,” he says, “but there are likely many more elements at play.”

sciencemag.org, 11 December 2020
; https://www.sciencemag.org