By Alan Emanuel

Our sense of touch is mediated by multiple types of specialized neuron endings in the skin. One such ending, the Meissner corpuscle, looks like a tiny, messy onion. Measuring about 30 microns in length, this corpuscle consists of accessory lamellar cells that wrap around axonal endings. Numerous Meissner corpuscles are found within the skin of our fingertips, palms, soles of our feet, and lips. Classically, it has been assumed that the neurons with axonal endings in Meissner corpuscles generate sensitive responses to touch and readily adapt to sustained pressure. It has also been assumed that the type of skin ending dictates this response. However, the role of the Meissner corpuscle in touch has not been tested. In our study, we used mouse genetic tools to gain insights into the anatomy and function of this structure.

Cross section of a Meissner corpuscle traced from an image taken with electron microscopy. Lamellar cells (cyan) wrap around sensory neuron axons (magenta). Image courtesy of Qiyu Zhang.

The first insight was that signaling through a specific molecule (TrkB) expressed within a subset of sensory neurons is required for Meissner corpuscles to develop. Using this insight, we prevented Meissner corpuscles from forming by selectively eliminating TrkB from sensory neurons. We tested sensitivity to gentle touch in these mice and found that they profoundly yet selectively lost the ability to detect low-intensity tactile stimuli. Further, unlike mice with intact corpuscles, they were unable to deftly expose sunflower seeds from their shells, demonstrating that Meissner corpuscles are essential for detection of gentle touch and fine sensorimotor control.

The second insight was that TrkB-expressing neurons were not the only neurons to send axons to the Meissner corpuscle. A second neuron, which can be identified by its expression of another molecule called Ret, does so as well. Using genetic strategies to label these cell types, we recorded their responses to skin stimulation and, to our surprise, found that the sensitivity and response properties of these two neuron types differed dramatically. The Ret-expressing neuron was both less sensitive and less readily adapting than the TrkB-expressing neuron. Computational modeling indicated that touch sensitivity and acuity could be greatly improved by having two cell types rather than only one. By combining genetic labeling and electron microscopy, we took a close look at these endings within the corpuscle. This revealed that lamellar cells wrap around the TrkB⁺ axons more than the Ret⁺ axons, which may underlie the differences in functional properties of these two neurons.

Overall, our experiments have updated our model of the anatomy and function of the Meissner corpuscle. We now know that Meissner corpuscles are innervated by two neurons with different response properties and are essential for gentle touch and fine sensorimotor control.

Alan Emanuel is a postdoc, in the labs of David Ginty and Chris Harvey at Harvard Medical School.

This story will also appear in the HMS Neurobiology Department newsletter, The Action Potential.

Learn more in the original research article:

Meissner Corpuscles and Their Spatially Intermingled Afferents Underlie Gentle Touch Perception. Nicole L Neubarth, Alan J Emanuel, Yin Liu, Mark W Springel, Annie Handler, Qiyu Zhang, Brendan P Lehnert, Chong Guo, Lauren L Orefice, Amira Abdelaziz, Michelle M DeLisle, Michael Iskols, Julia Rhyins, Soo J Kim, Stuart J Cattel, Wade Regehr, Christopher D Harvey, Jan Drugowitsch, David D Ginty. Science, 2020 June 19.