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Nature Jun 2020The skin is a multilayered organ, equipped with appendages (that is, follicles and glands), that is critical for regulating body temperature and the retention of bodily...
The skin is a multilayered organ, equipped with appendages (that is, follicles and glands), that is critical for regulating body temperature and the retention of bodily fluids, guarding against external stresses and mediating the sensation of touch and pain. Reconstructing appendage-bearing skin in cultures and in bioengineered grafts is a biomedical challenge that has yet to be met. Here we report an organoid culture system that generates complex skin from human pluripotent stem cells. We use stepwise modulation of the transforming growth factor β (TGFβ) and fibroblast growth factor (FGF) signalling pathways to co-induce cranial epithelial cells and neural crest cells within a spherical cell aggregate. During an incubation period of 4-5 months, we observe the emergence of a cyst-like skin organoid composed of stratified epidermis, fat-rich dermis and pigmented hair follicles that are equipped with sebaceous glands. A network of sensory neurons and Schwann cells form nerve-like bundles that target Merkel cells in organoid hair follicles, mimicking the neural circuitry associated with human touch. Single-cell RNA sequencing and direct comparison to fetal specimens suggest that the skin organoids are equivalent to the facial skin of human fetuses in the second trimester of development. Moreover, we show that skin organoids form planar hair-bearing skin when grafted onto nude mice. Together, our results demonstrate that nearly complete skin can self-assemble in vitro and be used to reconstitute skin in vivo. We anticipate that our skin organoids will provide a foundation for future studies of human skin development, disease modelling and reconstructive surgery.
Topics: Animals; Ectoderm; Female; Hair; Hair Color; Hair Follicle; Head; Heterografts; Humans; Mice; Mice, Nude; Organoids; Pluripotent Stem Cells; RNA-Seq; Single-Cell Analysis; Skin; Skin Transplantation
PubMed: 32494013
DOI: 10.1038/s41586-020-2352-3 -
Nature Protocols May 2022Human skin uses millions of hairs and glands distributed across the body surface to function as an external barrier, thermoregulator and stimuli sensor. The large-scale... (Review)
Review
Human skin uses millions of hairs and glands distributed across the body surface to function as an external barrier, thermoregulator and stimuli sensor. The large-scale generation of human skin with these appendages would be beneficial, but is challenging. Here, we describe a detailed protocol for generating hair-bearing skin tissue entirely from a homogeneous population of human pluripotent stem cells in a three-dimensional in vitro culture system. Defined culture conditions are used over a 2-week period to induce differentiation of pluripotent stem cells to surface ectoderm and cranial neural crest cells, which give rise to the epidermis and dermis, respectively, in each organoid unit. After 60 d of incubation, the skin organoids produce hair follicles. By day ~130, the skin organoids reach full complexity and contain stratified skin layers, pigmented hair follicles, sebaceous glands, Merkel cells and sensory neurons, recapitulating the cell composition and architecture of fetal skin tissue at week 18 of gestation. Skin organoids can be maintained in culture using this protocol for up to 150 d, enabling the organoids to be used to investigate basic skin biology, model disease and, further, reconstruct or regenerate skin tissue.
Topics: Cell Differentiation; Hair; Hair Follicle; Humans; Organoids; Pluripotent Stem Cells; Skin
PubMed: 35322210
DOI: 10.1038/s41596-022-00681-y -
Medecine Sciences : M/S Feb 2006The skin consists of an outer epidermis, the dermis, and the hypodermis. It includes nerves, blood vessels, glands and hair follicles. Epidermis is a continually... (Review)
Review
The skin consists of an outer epidermis, the dermis, and the hypodermis. It includes nerves, blood vessels, glands and hair follicles. Epidermis is a continually renewing, stratified squamous epithelium. It is populated by keratinocytes (80 %) and dendritic cells (20 %) : melanocytes, Langerhans and Merkel cells. In standard histology, keratinocytes are arranged in layers that represent different stages of their differentiation while melanocytes and Langerhans cells appear as clear cells respectively between the basal and the supra-basal cells of epidermis. The Merkel cells cannot be clearly identified. Dendritic processes of the dendritic cells can only be recognized by immunocytochemistry. At the dermal-epidermal junction, a PAS reactive basement membrane follows the contour of the basal cells. Dermis consists of collagenous and elastic fibers embedded into an amorphous ground substance. Fibroblasts, macrophages, mast cells and lymphocytes are its resident cells. Hypodermis is composed of adipocyte lobules defined by fibrous connective tissue septa. Hair follicle consists of 3 parts : the lower portion, from the base of the follicle including hair bulb to the insertion of the arrector pili muscle or buldge ; the isthmus, from the insertion of the arrector pili to the entrance of the sebaceous duct, and the infundibulum, from the entrance of the sebaceous duct to the follicular orifice. The lower portion is composed of the dermal hair papilla, the hair matrix, the hair, and the inner and the outer root sheaths. The hair matrix cells within hair bulb give rise to the hair and to the inner root sheath. With the electron microscope, one can obtain a more detailed view of the characteristic skin structures. Much of them can now be explained in terms of function and in many instances, in correlation with its biochemical composition. An attempt has been made in this paper to precisely give the location of molecules that are relevant in basic skin functions and understanding of auto-immune and genetic diseases.
Topics: Adipocytes; Animals; Connective Tissue; Dermis; Epidermis; Hair Follicle; Humans; Keratinocytes; Langerhans Cells; Melanocytes; Merkel Cells; Sebaceous Glands; Skin
PubMed: 16457751
DOI: 10.1051/medsci/2006222131 -
Nature May 2014How we sense touch remains fundamentally unknown. The Merkel cell-neurite complex is a gentle touch receptor in the skin that mediates slowly adapting responses of Aβ...
How we sense touch remains fundamentally unknown. The Merkel cell-neurite complex is a gentle touch receptor in the skin that mediates slowly adapting responses of Aβ sensory fibres to encode fine details of objects. This mechanoreceptor complex was recognized to have an essential role in sensing gentle touch nearly 50 years ago. However, whether Merkel cells or afferent fibres themselves sense mechanical force is still debated, and the molecular mechanism of mechanotransduction is unknown. Synapse-like junctions are observed between Merkel cells and associated afferents, and yet it is unclear whether Merkel cells are inherently mechanosensitive or whether they can rapidly transmit such information to the neighbouring nerve. Here we show that Merkel cells produce touch-sensitive currents in vitro. Piezo2, a mechanically activated cation channel, is expressed in Merkel cells. We engineered mice deficient in Piezo2 in the skin, but not in sensory neurons, and show that Merkel-cell mechanosensitivity completely depends on Piezo2. In these mice, slowly adapting responses in vivo mediated by the Merkel cell-neurite complex show reduced static firing rates, and moreover, the mice display moderately decreased behavioural responses to gentle touch. Our results indicate that Piezo2 is the Merkel-cell mechanotransduction channel and provide the first line of evidence that Piezo channels have a physiological role in mechanosensation in mammals. Furthermore, our data present evidence for a two-receptor-site model, in which both Merkel cells and innervating afferents act together as mechanosensors. The two-receptor system could provide this mechanoreceptor complex with a tuning mechanism to achieve highly sophisticated responses to a given mechanical stimulus.
Topics: Action Potentials; Animals; Electric Conductivity; Female; In Vitro Techniques; Ion Channels; Male; Mechanotransduction, Cellular; Merkel Cells; Mice; Mice, Knockout; Neurites; Neurons, Afferent; Skin; Touch
PubMed: 24717433
DOI: 10.1038/nature13251 -
Nature Dec 2014The sense of touch provides critical information about our physical environment by transforming mechanical energy into electrical signals. It is postulated that...
The sense of touch provides critical information about our physical environment by transforming mechanical energy into electrical signals. It is postulated that mechanically activated cation channels initiate touch sensation, but the identity of these molecules in mammals has been elusive. Piezo2 is a rapidly adapting, mechanically activated ion channel expressed in a subset of sensory neurons of the dorsal root ganglion and in cutaneous mechanoreceptors known as Merkel-cell-neurite complexes. It has been demonstrated that Merkel cells have a role in vertebrate mechanosensation using Piezo2, particularly in shaping the type of current sent by the innervating sensory neuron; however, major aspects of touch sensation remain intact without Merkel cell activity. Here we show that mice lacking Piezo2 in both adult sensory neurons and Merkel cells exhibit a profound loss of touch sensation. We precisely localize Piezo2 to the peripheral endings of a broad range of low-threshold mechanoreceptors that innervate both hairy and glabrous skin. Most rapidly adapting, mechanically activated currents in dorsal root ganglion neuronal cultures are absent in Piezo2 conditional knockout mice, and ex vivo skin nerve preparation studies show that the mechanosensitivity of low-threshold mechanoreceptors strongly depends on Piezo2. This cellular phenotype correlates with an unprecedented behavioural phenotype: an almost complete deficit in light-touch sensation in multiple behavioural assays, without affecting other somatosensory functions. Our results highlight that a single ion channel that displays rapidly adapting, mechanically activated currents in vitro is responsible for the mechanosensitivity of most low-threshold mechanoreceptor subtypes involved in innocuous touch sensation. Notably, we find that touch and pain sensation are separable, suggesting that as-yet-unknown mechanically activated ion channel(s) must account for noxious (painful) mechanosensation.
Topics: Animals; Ion Channels; Mechanoreceptors; Mechanotransduction, Cellular; Merkel Cells; Mice; Mice, Knockout; Sensory Receptor Cells; Skin; Touch
PubMed: 25471886
DOI: 10.1038/nature13980 -
Oncogene Jul 2022Merkel cell carcinoma (MCC) is an aggressive malignancy with neuroendocrine (NE) features, limited treatment options, and a lack of druggable targets. There is no...
Merkel cell carcinoma (MCC) is an aggressive malignancy with neuroendocrine (NE) features, limited treatment options, and a lack of druggable targets. There is no reported involvement of the MUC1-C oncogenic protein in MCC progression. We show here that MUC1-C is broadly expressed in MCCs and at higher levels in Merkel cell polyomavirus (MCPyV)-positive (MCCP) relative to MCPyV-negative (MCCN) tumors. Our results further demonstrate that MUC1-C is expressed in MCCP, as well as MCCN, cell lines and regulates common sets of signaling pathways related to RNA synthesis, processing, and transport in both subtypes. Mechanistically, MUC1-C (i) interacts with MYCL, which drives MCC progression, (ii) is necessary for expression of the OCT4, SOX2, KLF4, MYC, and NANOG pluripotency factors, and (iii) induces the NEUROD1, BRN2 and ATOH1 NE lineage dictating transcription factors. We show that MUC1-C is also necessary for MCCP and MCCN cell survival by suppressing DNA replication stress, the p53 pathway, and apoptosis. In concert with these results, targeting MUC1-C genetically and pharmacologically inhibits MCC self-renewal capacity and tumorigenicity. These findings demonstrate that MCCP and MCCN cells are addicted to MUC1-C and identify MUC1-C as a potential target for MCC treatment.
Topics: Carcinoma, Merkel Cell; Humans; Merkel cell polyomavirus; Mucin-1; Signal Transduction; Skin Neoplasms
PubMed: 35688945
DOI: 10.1038/s41388-022-02361-3 -
Cancers Jul 2020Viruses are the cause of approximately 15% of all human cancers. Both RNA and DNA human tumor viruses have been identified, with Merkel cell polyomavirus being the most... (Review)
Review
Viruses are the cause of approximately 15% of all human cancers. Both RNA and DNA human tumor viruses have been identified, with Merkel cell polyomavirus being the most recent one to be linked to cancer. This virus is associated with about 80% of Merkel cell carcinomas, a rare, but aggressive cutaneous malignancy. Despite its name, the cells of origin of this tumor may not be Merkel cells. This review provides an update on the structure and life cycle, cell tropism and epidemiology of the virus and its oncogenic properties. Putative strategies to prevent viral infection or treat virus-positive Merkel cell carcinoma patients are discussed.
PubMed: 32635198
DOI: 10.3390/cancers12071774