June 29, 2009

Merkel Cells Give You a Light Touch

Image of skin tissue shows clusters of green cells linked to red nerve fibers In the skin, Merkel cells (green) are connected to nerve fibers (red) that respond to light touch.Baylor College of Medicine

If you can feel the softness of silk or the fuzziness of a peach, you can definitely thank your Merkel cells, scientists say. A new study confirms what researchers have long suspected—that cells in the skin called Merkel cells are essential to the sense of light touch.

Merkel cells form crescent-shaped clusters in the skin that attach to the tip of a sensory nerve cell. Merkel cells are especially concentrated in our fingertips and lips. They’re also abundant around the whiskers of many mammals. In hairy skin, Merkel cell clusters and their associated nerve fibers are organized into specialized structures called touch domes. 

Since Merkel cells were discovered over 100 years ago, researchers have generally believed them to play some role in the sense of light touch—like the ability to read Braille—but studies examining this issue have yielded conflicting results.

In the new study, Drs. Ellen A. Lumpkin and Huda Y. Zoghbi and their colleagues at the Baylor College of Medicine found a way to create genetically engineered mice that lack Merkel cells throughout most of their skin. To do this, they selectively knocked out a regulatory gene called Atoh1 that is needed for the creation of Merkel cells during development. Their research was partly supported by NIH’s National Institute of Neurological Disorders and Stroke (NINDS), the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and other components of NIH.

In the June 19, 2009, issue of Science, the investigators reported that the hairy skin in the genetically engineered mice contained otherwise normal-looking touch domes—with skin cells, hair follicles and sensory nerve cells generally in their proper locations, even though the Merkel cells were missing. But skin preparations from these mice showed that the type of nerve cell that resolves fine shapes and textures no longer responded to light touch. Other nerve cells, like those that detect hair movements or skin stretch, were still able to respond normally. The findings suggest that Merkel cells are essential to stimulating the sensation of light touch in the skin.

The precise role of Merkel cells is still not clear. The cells may themselves be sensitive to the mechanical force of light touch and convert that energy into an electrical signal that travels to the brain. Alternatively, it may be the nerve cells that first respond to mechanical touch, with Merkel cells helping to send proper signals to the brain. The investigators are now working to tease apart the specific functions of the nerve and Merkel cells.

—by Vicki Contie