Merkel cell

Merkel cell
Merkel cells (shown in blue) are located in the basal epidermal layer of the skin.
Details
LocationSkin of vertebrates
FunctionLight touch sensation
Identifiers
MeSHD018862
NeuroLex IDnifext_87
Anatomical terms of neuroanatomy

Merkel cells, also known as Merkel–Ranvier cells or tactile epithelial cells, are oval-shaped mechanoreceptors essential for light touch sensation and found in the skin of vertebrates. They are abundant in highly sensitive skin like that of the fingertips in humans, and make synaptic contacts with somatosensory afferent nerve fibers. It has been reported that Merkel cells are derived from neural crest cells, though more recent experiments in mammals have indicated that they are epithelial in origin.

Merkel cells functionally resemble the enterochromaffin cell, the mechanosensory cell of the gastrointestinal epithelium.[1]

Structure

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Merkel cell.

Merkel cells are found in the skin and some parts of the mucosa of all vertebrates. In mammalian skin, they are clear cells found in the stratum basale[2][3] (at the bottom of sweat duct ridges) of the epidermis approximately 10 μm in diameter. They are oval-shaped mechanoreceptors essential for light touch sensation and found in the skin of vertebrates. They are abundant in highly sensitive skin like that of the fingertips in humans, and make synaptic contacts with somatosensory afferent nerve fibers.[4] They also occur in epidermal invaginations of the plantar foot surface called rete ridges.[5]

Most often, they are associated with sensory nerve endings, when they are known as Merkel nerve endings (also called a Merkel cell-neurite complex). They are associated with slowly adapting (SA1) somatosensory nerve fibers. They react to low vibrations (5–15 Hz) and deep static touch such as shapes and edges. Due to a small receptive field (extremely detailed info) they are densely present in areas like fingertips; they are not covered (shelled) and thus respond to pressures over long periods.

Developmental

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The origin of Merkel cells has been debated for over 20 years. Evidence from skin graft experiments in birds implies that they are neural crest derived,[6] but experiments in mammals now demonstrate an epidermal origin.[7][8]

Function

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The German anatomist Friedrich Sigmund Merkel referred to Merkel cells as Tastzellen or "touch cells". Until recently this proposed function was controversial and hard to prove, due to the close physical association of Merkel cells with sensory nerve endings. However, recent work in mice and other model organisms demonstrates that Merkel cells intrinsically transform touch into electrical signals that are transmitted to the nervous system.[9] Merkel cells express PIEZO2, a mechanosensitive ion channel that responds to mechanical forces. Mice in which Piezo2 is knocked-out specifically in skin cells, but not sensory neurons, show decreased behavioral responses to gentle touch.[10]

Merkel cells are sometimes considered APUD cells (an older definition, more commonly classified as a part of dispersed neuroendocrine system) because they contain dense core granules, and thus may also have a neuroendocrine function.[11]

Susceptibility to malignancy

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Although uncommon, these cells may become malignant and form a Merkel cell carcinoma—an aggressive and difficult to treat skin cancer.[12][13]

See also

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References

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  1. ^ Chang W, Kanda H, Ikeda R, Ling J, DeBerry JJ, Gu JG. Merkel disc is a serotonergic synapse in the epidermis for transmitting tactile signals in mammals. Proc Natl Acad Sci U S A. 2016 Sep 13;113(37): E5491-500. doi: 10.1073/pnas.1610176113.
  2. ^ Halata Z, Baumann KI, Grim M (January 2008). "6.02 - Merkel Cells". In Masland RH, Albright TD, Albright TD, Masland RH (eds.). The Senses: A Comprehensive Reference. New York: Academic Press. pp. 33–38. doi:10.1016/b978-012370880-9.00341-8. ISBN 978-0-12-370880-9.
  3. ^ Fenner J, Clark RA (January 2016). "Anatomy, Physiology, Histology, and Immunohistochemistry of Human Skin". Skin Tissue Engineering and Regenerative Medicine. Academic Press. pp. 1–17. doi:10.1016/b978-0-12-801654-1.00001-2. ISBN 978-0-12-801654-1.
  4. ^ Mescher, Anthony L (2016). Junqueira's Basic Histology. McGraw-Hill Education. ISBN 978-0-07-184270-9.
  5. ^ Halata Z, Grim M, Bauman KI (March 2003). "Friedrich Sigmund Merkel and his "Merkel cell", morphology, development, and physiology: review and new results". The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology. 271 (1): 225–239. doi:10.1002/ar.a.10029. PMID 12552639.[dead link]
  6. ^ Baumann KI, Halata Z, Moll I (2003). The Merkel cell: structure-development-function- cancerogenesis. Springer. pp. 99–. ISBN 978-3-540-00374-8. Retrieved 2 May 2010.
  7. ^ Morrison KM, Miesegaes GR, Lumpkin EA, Maricich SM (December 2009). "Mammalian Merkel cells are descended from the epidermal lineage". Developmental Biology. 336 (1): 76–83. doi:10.1016/j.ydbio.2009.09.032. PMC 2783667. PMID 19782676.
  8. ^ Van Keymeulen A, Mascre G, Youseff KK, Harel I, Michaux C, De Geest N, et al. (October 2009). "Epidermal progenitors give rise to Merkel cells during embryonic development and adult homeostasis". The Journal of Cell Biology. 187 (1): 91–100. doi:10.1083/jcb.200907080. PMC 2762088. PMID 19786578.
  9. ^ Maksimovic S, Nakatani M, Baba Y, Nelson AM, Marshall KL, Wellnitz SA, et al. (May 2014). "Epidermal Merkel cells are mechanosensory cells that tune mammalian touch receptors". Nature. 509 (7502): 617–621. Bibcode:2014Natur.509..617M. doi:10.1038/nature13250. PMC 4097312. PMID 24717432.
  10. ^ Woo SH, Ranade S, Weyer AD, Dubin AE, Baba Y, Qiu Z, et al. (May 2014). "Piezo2 is required for Merkel-cell mechanotransduction". Nature. 509 (7502): 622–626. Bibcode:2014Natur.509..622W. doi:10.1038/nature13251. PMC 4039622. PMID 24717433.
  11. ^ Barbieri JS, Wanat K, Seykora J (January 2014). "Skin: Basic Structure and Function". In McManus LM, Mitchell RN (eds.). Pathobiology of Human Disease. San Diego: Academic Press. pp. 1134–1144. doi:10.1016/b978-0-12-386456-7.03501-2. ISBN 978-0-12-386457-4.
  12. ^ Rotondo JC, Bononi I, Puozzo A, Govoni M, Foschi V, Lanza G, et al. (July 2017). "Merkel Cell Carcinomas Arising in Autoimmune Disease Affected Patients Treated with Biologic Drugs, Including Anti-TNF". Clinical Cancer Research. 23 (14): 3929–3934. doi:10.1158/1078-0432.CCR-16-2899. hdl:11392/2378829. PMID 28174236.
  13. ^ Munde PB, Khandekar SP, Dive AM, Sharma A (September 2013). "Pathophysiology of merkel cell". Journal of Oral and Maxillofacial Pathology. 17 (3): 408–412. doi:10.4103/0973-029x.125208. PMC 3927344. PMID 24574661.
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