About the Disease / What is a Merkel cell?

What is a Merkel cell?

Merkel cells are found in the skin, where they function mainly as touch receptors.

Overview of Merkel cells

Friedrich Merkel

Merkel cells are found in the  epidermis epidermis The outermost layer of the two main layers that make up the skin (the dermis is the deeper layer). Merkel cells normally exist in the bottom (basal) layer of the epidermis, about 0.1 mm from skin's surface.  (outer layer of the skin). They were originally described in the late 1800s by Friedrich Merkel, a German anatomist. He found these cells at high density in the paws of rats and surmised they may serve as “touch cells”.  Over 100 years later, although not all of the functions of Merkel cells are known, it is quite clear that they do indeed serve as touch cells and relay touch-related information such as texture and pressure to the brain. While they are present in human skin at varying levels according to body site, they are at highest density on the fingertips and lips/face where touch sensation is most acute. In addition, they produce certain hormones and are sometimes referred to as  neuroendocrine neuroendocrine Neuroendocrine refers to the type of cells that make up Merkel cell carcinoma. "Neuro-" means that these cells have some sensory function related to the nervous system, while "endocrine-" refers to hormonal types of cells. Merkel cells have both such features.  cells, although the reasons they produce certain hormones is unknown.

Merkel cell diagram

In the below illustration of a cross-section of skin, normal Merkel cells are shown in red and connect to nerves shown in yellow. The structures drawn include the epidermis (upper third), dermis dermis The deeper layer of the two main tissue layers that make-up the skin. The dermis is below the epidermis. Merkel cells are normally in the epidermis. In MCC, they grow and invade into the dermis and deeper structures and vessels. (middle), and deeper adipose (fatty) layer. Arteries are depicted as red and veins are blue.


Diagram of normal Merkel cells in the skin
Diagram of normal Merkel cells in the skin. Figure Copyright by Paul Nghiem, MD, PhD & Quade Medical Group.


Do normal Merkel cells turn into Merkel cell carcinoma?

The answer to this question is not known with certainty, but multiple lines of evidence suggest that Merkel cell carcinoma does NOT derive directly from normal Merkel cells. This is in part because it has proven impossible to get a normal Merkel cell to divide and grow. It is more likely that the precursor of a normal Merkel cell (a stem cell in the epidermis) gives rise to both the normal Merkel cell and separately, to Merkel cell carcinoma. There are several studies that have determined that normal Merkel cells are derived from epidermal precursor cells.

Clinical publications

The following clinical publications and scientific research provide additional in-depth information about Merkel cells.

Merkel cells are essential for light-touch responses.

Although Friedrich Merkel believed that the direct connection of these cells to nerves suggested they were ‘touch cells’, it took over 120 years for science to prove this. Studies in which normal Merkel cells were deleted in mice showed that those mice lost normal skin sensation.

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Which are the cells of origin in Merkel cell carcinoma?

Merkel cell carcinoma (MCC), a highly aggressive skin tumour with increasing incidence, is associated with the newly discovered Merkel cell polyomavirus (MCPyV). Studies on MCC and MCPyV as well as other risk factors have significantly increased our knowledge of MCC pathogenesis, but the cells of or...

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Epidermal progenitors give rise to Merkel cells during embryonic development and adult homeostasis.

Merkel cells (MCs) are located in the touch-sensitive area of the epidermis and mediate mechanotransduction in the skin. Whether MCs originate from embryonic epidermal or neural crest progenitors has been a matter of intense controversy since their discovery >130 yr ago. In addition, how MCs are mai...

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Mammalian Merkel cells are descended from the epidermal lineage.

Merkel cells are specialized cells in the skin that are important for proper neural encoding of light touch stimuli. Conflicting evidence suggests that these cells are lineally descended from either the skin or the neural crest. To address this question, we used epidermal (Krt14(Cre)) and neural cre...

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