Sensory - Touch Development

Embryology - 16 Apr 2024        Expand to Translate
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Introduction

Touch receptors in mammalian skin.

Skin Pacinian corpuscle

These notes introduce the development of the sense of touch, part of the somatosensory system. Because of the distribution of the sensory structures within the skin, this topic is generally also covered in integumentary development.

Some Recent Findings

A Cascade of Wnt, Eda, and Shh Signaling Is Essential for Touch Dome Merkel Cell Development "In the skin, touch domes develop in tandem with primary hair follicles and contain sensory Merkel cells. We found dermal Wnt signaling and subsequent epidermal Eda/Edar signaling promoted Merkel cell morphogenesis by inducing Shh expression in early follicles. Lineage-specific gene deletions revealed intraepithelial Shh signaling was necessary for Merkel cell specification. Additionally, a Shh signaling agonist was sufficient to rescue Merkel cell differentiation in Edar-deficient skin. ...Although developmentally associated with hair follicles, fate mapping demonstrated Merkel cells primarily originated outside the hair follicle lineage. These findings suggest that touch dome development requires Wnt-dependent mesenchymal signals to establish reciprocal signaling within the developing ectoderm, including Eda signaling to primary hair placodes and ultimately Shh signaling from primary follicles to extrafollicular Merkel cell progenitors." Sonic hedgehog Unipotent, Atoh1+ progenitors maintain the Merkel cell population in embryonic and adult mice "Resident progenitor cells in mammalian skin generate new cells as a part of tissue homeostasis. We sought to identify the progenitors of Merkel cells, a unique skin cell type that plays critical roles in mechanosensation. We found that some Atoh1-expressing cells in the hairy skin and whisker follicles are mitotically active at embryonic and postnatal ages. Genetic fate-mapping revealed that these Atoh1-expressing cells give rise solely to Merkel cells. Furthermore, selective ablation of Atoh1(+) skin cells in adult mice led to a permanent reduction in Merkel cell numbers, demonstrating that other stem cell populations are incapable of producing Merkel cells. These data identify a novel, unipotent progenitor population in the skin that gives rise to Merkel cells both during development and adulthood." Embryonic maturation of epidermal Merkel cells is controlled by a redundant transcription factor network "Merkel cell-neurite complexes are located in touch-sensitive areas of the mammalian skin and are involved in recognition of the texture and shape of objects. Merkel cells are essential for these tactile discriminations, as they generate action potentials in response to touch stimuli and induce the firing of innervating afferent nerves. It has been shown that Merkel cells originate from epidermal stem cells, but the cellular and molecular mechanisms of their development are largely unknown. In this study, we analyzed Merkel cell differentiation during development and found that it is a temporally regulated maturation process characterized by a sequential activation of Merkel cell-specific genes. We uncovered key transcription factors controlling this process and showed that the transcription factor Atoh1 is required for initial Merkel cell specification. The subsequent maturation steps of Merkel cell differentiation are controlled by cooperative function of the transcription factors Sox2 and Isl1, which physically interact and work to sustain Atoh1 expression" Wetness perception across body sites "Human skin is innervated with a variety of receptors serving somatosensation and includes the sensory sub-modalities of touch, temperature, pain and itch. The density and type of receptors differ across the body surface, and there are various body-map representations in the brain. The perceptions of skin sensations outside of the specified sub-modalities, e.g. wetness or greasiness, are described as 'touch blends' and are learned. ...The perception of wetness is generated from the coincident activation of tactile and thermal receptors. The perception of wetness did not, however, differ significantly across body sites and there were no significant interactions between wetness level and body site." A Shift in Sensory Processing that Enables the Developing Human Brain to Discriminate Touch from Pain "When and how infants begin to discriminate noxious from innocuous stimuli is a fundamental question in neuroscience. However, little is known about the development of the necessary cortical somatosensory functional prerequisites in the intact human brain. ... The results suggest that specific neural circuits necessary for discrimination between touch and nociception emerge from 35-37 weeks gestation in the human brain." Identification of epidermal progenitors for the Merkel cell lineage "Epithelial stem cells in adult mammalian skin are known to maintain epidermal, follicular and sebaceous lineages during homeostasis. Recently, Merkel cell mechanoreceptors were identified as a fourth lineage derived from the proliferative layer of murine skin epithelium; however, the location of the stem or progenitor population for Merkel cells remains unknown. Here, we have identified a previously undescribed population of epidermal progenitors that reside in the touch domes of hairy skin, termed touch dome progenitor cells (TDPCs)."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Touch Development <pubmed limit=5>Touch Development</pubmed>

Historic People

Friedrich Sigmund Merkel (1845-1919)

• Georg Meissner - (1829-1905) German histologist, physiologist and anatomist. Beiträge zur Anatomie und Physiologie der Haut. (Contributions to the anatomy and physiology of the skin.) Leipzig, 1853.
• Friedrich Sigmund Merkel- (1845-1919) German anatomist and histologist, the name "Merckel cell" was based upon his first full description of touch cells (Tastzellen) and named by Robert Bonnet (1851–1921). Referred to these cells as Tastzellen or "touch cells" but this proposed function has been controversial as it has been hard to prove.
• Filippo Pacini - (1812-1883) Italian anatomist, published in 1840, and the name "Pacini's corpuscles" was proposed in 1844 by Henle and also by Kölliker.
• Angelo Ruffini (1864-1929) Italian histologist and embryologist, the name "Ruffini corpuscles" was based upon his first description of skin mechanoreceptors.

Touch Receptors

Dermatomes the surface map of segmental spinal nerve innervation of the skin surface.

Touch receptors in mammalian skin and the neural encoding of reception.

Pacinian Corpuscle

These receptors are lamellar vibration receptors that produce rapidly adapting responses. They are located in the subcutaneous tissue, deeper in interosseous membranes, and also mesenteries of the gut. The inner core cells form from Schwann cells extending from the nerve terminal.

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  Pacinian corpuscle (labeled)

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  Pacinian corpuscle (unlabeled)

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  Pacinian corpuscle (detail)

Meissner's Corpuscle

Located in glabrous skin the mechanoreceptor lies between the dermal papillae for sensitivity to light touch. They are rapidly adaptive elongated receptors formed by a connective tissue capsule that formed by several lamellae of Schwann cells enclosing one or more afferent nerve fibres. The sensory corpuscle is a stack of discoid components of flattened axon terminals sandwiched between Schwann cell lamellae covered with a connective tissue capsule linked to the basal aspect of the epidermis by dermal collagen fibers.

Meissner's corpuscle

Meissner's corpuscles are located throughout the skin and are seen concentrated in regions of high touch (finger tips, lips, genital regions).

Merkel Cell

Merkel cells occur in many species including reptiles, fish, and mammals. Merkel cell complexes mediate slowly adapting type I (SAI) responses, which are characterized by an irregular firing pattern during sustained pressure. Merkel cells arise in the embryo and in the adult from an epidermal progenitor cell population. These cells express the transcription factor Atoh1 and when differentiated are post-mitotic. Merkel cells can be organised into specialised clustered structure known as a "touch dome" associated with primary hair follicles.

A molecular signalling cascade from Wnt, Eda, and Shh is required for touch dome Merkel cell development. Keratin 8 (K8) and Keratin 18 (K18) are Merkel cell markers identified in late fetal and adult skin.

Isolated Merkel cell (em)

Merkel cell (Merkel-Ranvier cell) integumentary (skin) receptor cell connected with somatosensory afferents. Cell characteristics a polylobulated nucleus and numerous typical dense-core granules in a clear cytoplasm. The name "Merckel cell" was based upon Friedrich Sigmund Merkel (1845 – 1919) a German anatomist and histologist, first description of these touch cells (Tastzellen) and named in his honour by Robert Bonnet (1851–1921). Scale bar 5 µm (Stain - Osmium)

Integumentary touch dome suggested functions

The Merkel cell is also a part of the touch dome (TD) apparatus, an innervated structure composed of specialised keratinocytes, and may have additional neuroendocrine and immune roles, as they associate with Langerhans cells (dendritic antigen presenting cells) in the epidermis.

In the adult, abnormalities in Merkel cell development can lead to the rare disease of Merkel cell carcinoma (MCC) associated with sun (UV) exposure.

Sensory Modalities

Thermoreceptors

• Receptors for heat (warmth) and cold (chill) detection.
  • heat - C-fibres
  • cold - Aδ fibres

Nociceptors

• Receptors for encoding and processing noxious stimuli.
  • A-δ nociceptors
  • Polymodal C-nociceptors
  • C- mechano-insensitive nociceptors

Abnormalities

• Merkel cell carcinoma (MCC) PMID 12007193

References

Reviews

Lai HC, Seal RP & Johnson JE. (2016). Making sense out of spinal cord somatosensory development. Development , 143, 3434-3448. PMID: 27702783 DOI.

Woo SH, Lumpkin EA & Patapoutian A. (2015). Merkel cells and neurons keep in touch. Trends Cell Biol. , 25, 74-81. PMID: 25480024 DOI.

Zimmerman A, Bai L & Ginty DD. (2014). The gentle touch receptors of mammalian skin. Science , 346, 950-4. PMID: 25414303 DOI.

Jeffry J, Kim S & Chen ZF. (2011). Itch signaling in the nervous system. Physiology (Bethesda) , 26, 286-92. PMID: 21841076 DOI.

Lumpkin EA, Marshall KL & Nelson AM. (2010). The cell biology of touch. J. Cell Biol. , 191, 237-48. PMID: 20956378 DOI.

Articles

Ranade SS, Woo SH, Dubin AE, Moshourab RA, Wetzel C, Petrus M, Mathur J, Bégay V, Coste B, Mainquist J, Wilson AJ, Francisco AG, Reddy K, Qiu Z, Wood JN, Lewin GR & Patapoutian A. (2014). Piezo2 is the major transducer of mechanical forces for touch sensation in mice. Nature , 516, 121-5. PMID: 25471886 DOI.

Books

Neurobiology of Sensation and Reward. Gottfried JA, editor. Boca Raton (FL): CRC Press; 2011. Chapter 7 - Touch PMID 22593916

Search PubMed

Search Pubmed: Touch Development | touch receptors |

External Links

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• Merkel cell carcinoma - http://www.merkelcell.org

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Cite this page: Hill, M.A. (2024, April 16) Embryology Sensory - Touch Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Sensory_-_Touch_Development

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G