An Integrated Transcriptome Atlas of Embryonic Hair Follicle Progenitors, Their Niche, and the Developing Skin

Neurological Mechanisms Exploration and Therapeutic Targets in Segmental Vitiligo Accompanied by White Hair

Vitiligo is the most common skin depigmentation disease, affecting 0.1%-2% of people in the world. 3.5%-20.5% of segmental patients account for the total number of vitiligo patients. It has been clinically observed that segmental vitiligo patients are more likely to generate white hair, which may be related to neuroendocrine factors. The color of human skin and hair is affected by the number and functional status of melanocytes. Vitiligo affects patients' physical and mental health due to the shame it causes from the white patches and hair. This article reviews the underlying mechanisms of segmental vitiligo with white hair based on skin and hair follicle melanocytes. The article attempts to propose possible targets for the treatment of this disease.

Mesenchymal Meis2 controls whisker development independently from trigeminal sensory innervation

Hair follicle development is initiated by reciprocal molecular interactions between the placode-forming epithelium and the underlying mesenchyme. Cell fate transformation in dermal fibroblasts generates a cell niche for placode induction by activation of signaling pathways WNT, EDA, and FGF in the epithelium. These successive paracrine epithelial signals initiate dermal condensation in the underlying mesenchyme. Although epithelial signaling from the placode to mesenchyme is better described, little is known about primary mesenchymal signals resulting in placode induction. Using genetic approach in mice, we show that Meis2 expression in cells derived from the neural crest is critical for whisker formation and also for branching of trigeminal nerves. While whisker formation is independent of the trigeminal sensory innervation, MEIS2 in mesenchymal dermal cells orchestrates the initial steps of epithelial placode formation and subsequent dermal condensation. MEIS2 regulates the expression of transcription factor Foxd1, which is typical of pre-dermal condensation. However, deletion of Foxd1 does not affect whisker development. Overall, our data suggest an early role of mesenchymal MEIS2 during whisker formation and provide evidence that whiskers can normally develop in the absence of sensory innervation or Foxd1 expression.

Experimental method for creating skin with acquired appendage dysfunction

Mammalian skin appendages, such as hair follicles and sweat glands, are essential for both esthetic and functional purposes. Conditions such as burns and ulcers can lead to dysfunction or loss of skin appendages and result in hair loss and dry skin, posing challenges in their regeneration. Existing animal models are insufficient for studying acquired dysfunction of skin appendages without underlying genetic causes. This study aimed to develop more clinically relevant mouse models by evaluating two approaches: keratinocyte transplantation and grafting of skin at varying thicknesses. green fluorescent protein (GFP)-expressing keratinocytes were transplanted into ulcers on nude mice, leading to re-epithelialization with minimal skin appendages at 4 weeks after transplantation. However, the re-epithelialized area was largely derived from recipient cells, with the grafted cells contributing to only 1.31% of the area. In the skin-grafting model, donor skin from GFP transgenic mice was grafted onto nude mice at three thicknesses: full thickness, 10/1000 inch, and 5/1000 inch. The grafted area of the 5/1000-inch grafts remained stable at 89.5% of its original size 5 weeks after transplantation, ensuring a sufficiently large skin area. The 5/1000-inch grafts resulted in a significant reduction in skin appendages, with a mean of only 3.73 hair follicles per 5 mm, compared with 69.7 in the control group. The 5/1000-inch skin grafting in orthotopic autologous transplantation also showed the achievement of skin surfaces with a minimal number of skin appendages. Therefore, a mouse model with skin grafting demonstrated stability in producing large areas of skin with minimal appendages. In conclusion, these two models with acquired skin appendage dysfunction and no underlying genetic causes provide valuable tools for researching skin appendage regeneration, offering insights into potential therapeutic strategies for conditions involving skin appendage loss.

N6-Methyladenosine (m6A)-Circular RNA Pappalysin 1 (circPAPPA) from Cashmere Goats: Identification, Regulatory Network and Expression Potentially Regulated by Methylation in Secondary Hair Follicles Within the First Intron of Its Host Gene

N6-methyladenosine (m6A) is one of the most abundant modifications in eukaryotic RNA molecules and mediates the functional exertion of RNA molecules. We characterized the circPAPPA and validated its potential m6A modification sites in secondary hair follicles (SHFs) of cashmere goats. Furthermore, we generated integrated regulatory networks of the circPAPPA along with enrichment analysis of signaling pathways. We also explored the potential relationship of circPAPPA expression with the first intron methylation of the PAPPA gene in SHFs of cashmere goats. Host source analysis revealed that circPAPPA is derived from the complete exon 2 of the PAPPA gene, spliced in reverse orientation, and predominantly localized in the cytoplasm of SHF stem cells in cashmere goats. The circPAPPA was verified to contain at least four m6A modification sites in SHFs of cashmere goats, including m6A-450/456, m6A-852, m6A-900, and m6A-963. The generated regulatory network indicated complex and diverse regulatory relationships of m6A-circPAPPA with its putative regulatory molecules, including miRNAs, mRNAs, and proteins. Enrichment analysis of signaling pathways showed that m6A-circPAPPA might play multiple functional roles in the growth and development of SHF in cashmere goats through the putative regulatory network mediated by its target miRNAs and regulatory proteins. The first intron methylation of the PAPPA gene most likely is significantly involved in the dynamic expression of m6A-circPAPPA in cashmere goat SHFs. Results from this study provided novel information to elucidate the biological roles and functional regulatory pathways of m6A-circPAPPA in SHF development and the growth of cashmere goat fiber.

Combined ADAMTS10 and ADAMTS17 inactivation exacerbates bone shortening and compromises extracellular matrix formation

Weill-Marchesani syndrome (WMS) is characterized by severe short stature, short hands and feet (brachydactyly), joint contractures, tight skin, and heart valve, eye, and skin anomalies. Whereas recessive WMS is caused by mutations in ADAMTS10, ADAMTS17, or LTBP2, dominant WMS is caused by mutations in FBN1 (encoding fibrillin-1). Since bone growth is driven by chondrocyte proliferation and hypertrophy in the growth plates, the genetics of WMS suggests that the affected ECM proteins act within the same pathway to regulate chondrocyte and growth plate function. Here, we investigated the role of the secreted ADAMTS proteases ADAMTS10 and ADAMTS17 in growth plate function and ECM formation. We generated Adamts10;Adamts17 double knockout (DKO) mice, which showed significant postnatal lethality compared to single Adamts10 or Adamts17 KO mice. Importantly, we observed severe bone shortening DKO mice, which correlated with a narrower hypertrophic zone in their growth plates. ADAMTS17 substrates identified by N-terminomics and yeast two-hybrid screening identified the ECM proteins fibronectin and collagen VI (COL6). However, validation experiments did not reveal direct proteolysis of either fibronectin or COL6 by ADAMTS17. We then investigated ECM formation in primary ADAMTS10- and ADAMTS17-deficient skin fibroblasts and observed compromised fibronectin deposition concomitant with aberrant intracellular accumulation of fibrillin-1. These findings support a role for ADAMTS17 in ECM protein secretion and assembly. Collectively, our data suggest that ADAMTS10 and ADAMTS17 regulate bone growth by regulating chondrocyte hypertrophy or hypertrophic chondrocyte turnover. Mechanistically, ADAMTS17 appears to be a critical regulator of ECM protein secretion or pericellular matrix assembly, whereas ADAMTS10 likely modulates ECM formation at later stages, possibly regulating the spatio-temporal deposition of fibrillin isoforms.

Gpr54 deletion accelerates hair cycle and hair regeneration

GPR54, or KiSS-1R (Kisspeptin receptor), is key in puberty initiation and tumor metastasis prevention, but its role on hair follicles remains unclear. Our study shows that Gpr54 knockout (KO) accelerates hair cycle, synchronized hair regeneration and transplanted hair growth in mice. In Gpr54 KO mice, DPC (dermal papilla cell) activity is enhanced, with elevated expression of Wnts, VEGF, and IGF-1, which stimulate HFSCs. Gpr54 deletion also raises the number of CD34+ and Lgr5+ HFSCs. The Gpr54 inhibitor, kisspeptin234, promotes hair shaft growth in cultured mouse hair follicles and boosts synchronized hair regeneration in vivo. Mechanistically, Gpr54 deletion suppresses NFATC3 expression in DPCs and HFSCs, and decreases levels of SFRP1, a Wnt inhibitor. It also activates the Wnt/β-catenin pathway, promoting β-catenin nuclear localization and upregulating target genes such as Lef1 and ALP. Our findings suggest that Gpr54 deletion may accelerate the hair cycle and promote hair regeneration in mice by regulating the NAFTc3-SFRP1-Wnt signaling pathway. These findings suggest that Gpr54 could be a possible target for future hair loss treatments.

N6-methyladenosine (m6A)-circHECA from secondary hair follicle of cashmere goats: identification, regulatory network and expression regulated potentially by methylation of its host gene promoter

OBJECTIVE

The objective of this study was to identify the N6-methyladenosine (m6A)- circHECA molecule in secondary hair follicles (SHFs) of cashmere goats, and generate its potential regulatory network, as well as explore the potential relationship between transcriptional pattern of m6A-circHECA and promoter methylation of its host gene (HECA).

METHODS

The validation of circHECA m6A sites was performed using methylation immunoprecipitation (Me-RIP) along with reverse transcription-quantitative polymerase chain reaction (RT-qPCR) technique. The nucleus and cytoplasm localizations of m6AcircHECA were performed using SHF stem cells of cashmere goats with RT-qPCR analysis. Based on in-silico analysis, the regulatory networks of m6A-circHECA were generated with related signal pathway enrichment. The methylation level of promoter region of m6A-circHECA host gene (HECA) was assessed by the bisulfite sequencing PCR (BSPPCR) technique.

RESULTS

The m6A-circHECA was confirmed to contain four m6A modification sites including m6A-213, m6A-297, m6A-780, and m6A-927, and it was detected mainly in cytoplasm of the SHF stem cells of cashmere goats. The integrated regulatory network analysis showed directly or indirectly complex regulatory relationships between m6A-circHECA of cashmere goats and its potential target molecules: miRNAs, mRNAs, and proteins. The regulatory network and pathway enrichment indicated that m6A-circHECA might play multiple roles in the SHF physiology process of cashmere goats through directly or indirectly interacting or regulating its potential target molecules. A higher methylation level of promoter region of HECA gene in SHFs of cashmere goats might cause the lower expression of m6A-circHECA.

CONCLUSION

The m6A-circHECA might play multiple roles in SHF physiology process of cashmere goats through miRNA mediated pathways along with directly or indirectly interaction with its target proteins. The promoter methylation of m6A-circHECA host gene (HECA) most likely was implicated in its expression inhibition in SHFs of cashmere goats.

Dermal Papilla Cells: From Basic Research to Translational Applications

As an appendage of the skin, hair protects against ultraviolet radiation and mechanical damage and regulates body temperature. It also reflects an individual's health status and serves as an important method of expressing personality. Hair loss and graying are significant psychosocial burdens for many people. Hair is produced from hair follicles, which are exclusively controlled by the dermal papilla (DP) at their base. The dermal papilla cells (DPCs) comprise a cluster of specialized mesenchymal cells that induce the formation of hair follicles during early embryonic development through interaction with epithelial precursor cells. They continue to regulate the growth cycle, color, size, and type of hair after the hair follicle matures by secreting various factors. DPCs possess stem cell characteristics and can be cultured and expanded in vitro. DPCs express numerous stemness-related factors, enabling them to be reprogrammed into induced pluripotent stem cells (iPSCs) using only two, or even one, Yamanaka factor. DPCs are an important source of skin-derived precursors (SKPs). When combined with epithelial stem cells, they can reconstitute skin and hair follicles, participating in the regeneration of the dermis, including the DP and dermal sheath. When implanted between the epidermis and dermis, DPCs can induce the formation of new hair follicles on hairless skin. Subcutaneous injection of DPCs and their exosomes can promote hair growth. This review summarizes the in vivo functions of the DP; highlights the potential of DPCs in cell therapy, particularly for the treatment of hair loss; and discusses the challenges and recent advances in the field, from basic research to translational applications.

A lineage-specific nascent RNA assay unveils principles of gene regulation in tissue biology

Gene regulatory mechanisms that modulate RNA Polymerase II activity are difficult to access in mammalian tissues composed of multiple cell lineages. Here, we develop a nascent RNA assay (PReCIS-seq) that measures lineage-specific transcriptionally-engaged Pol II on genes and DNA enhancer elements in intact mouse tissue. By employing keratinocytes as a prototype lineage, we unearth Pol II promoter-recruitment versus pause-release mechanisms operating in adult skin homeostasis. Moreover, we relate active enhancer proximity and transcription factor binding motifs on promoters to Pol II activity and promoter-proximal pausing level. Finally, we find Pol II firing rapidly into elongation on lineage identity genes and highly paused on cellular safeguarding genes in a context-dependent manner. Our work provides a basic platform to investigate mechanistic principles of gene regulation in individual lineages of complex mammalian tissues.

Deconvolving organogenesis in space and time via spatial transcriptomics in thick tissues

Organ development is guided by a space-time landscape that constraints cell behavior. This landscape is challenging to characterize for the hair follicle - the most abundant mini organ - due to its complex microscopic structure and asynchronous development. We developed 3DEEP, a tissue clearing and spatial transcriptomic strategy for characterizing tissue blocks up to 400 µm in thickness. We captured 371 hair follicles at different stages of organogenesis in 1 mm3 of skin of a 12-hour-old mouse with 6 million transcripts from 81 genes. From this single time point, we deconvoluted follicles by age based on whole-organ molecular pseudotimes to animate a stop-motion 3D atlas of follicle development along its trajectory. We defined molecular stages for hair follicle organogenesis and characterized the order of emergence for its structures, differential signaling dynamics at its top and bottom, morphogen shifts preceding and accompanying structural changes, and series of structural changes leading to the formation of its canal and opening. We further found that hair follicle stem cells and their niche are established and stratified early in organogenesis, before the formation of the hair bulb. Overall, this work demonstrates the power of increased depth of spatial transcriptomics to provide a four-dimensional analysis of organogenesis.

ARHGEF3 Regulates Hair Follicle Morphogenesis

During embryogenesis, cells arrange into precise patterns that enable tissues and organs to develop specialized functions. Despite its critical importance, the molecular choreography behind these collective cellular behaviors remains elusive, posing a major challenge in developmental biology and limiting advances in regenerative medicine. By using the mouse hair follicle as a mini-organ system to study the formation of bud-like structures during embryonic development, our work uncovers a crucial role for the Rho GTPase regulator ARHGEF3 in hair follicle morphogenesis. We demonstrate that Arhgef3 expression is upregulated at the onset of hair follicle placode formation. In Arhgef3 knockout animals, we observed defects in placode compaction, leading to impaired hair follicle downgrowth. Through cell culture models, we show that ARHGEF3 promotes F-actin accumulation at the cell cortex and P-cadherin enrichment at cell-cell junctions. Collectively, our study identifies ARHGEF3 as a new regulator of cell shape rearrangements during hair placode morphogenesis, warranting further exploration of its role in other epithelial appendages that arise from similar developmental processes.

Mesenchymal Osr1+ cells regulate embryonic lymphatic vessel formation

The lymphatic system is formed during embryonic development by the commitment of specialized lymphatic endothelial cells (LECs) and their subsequent assembly in primary lymphatic vessels. Although lymphatic cells are in continuous contact with mesenchymal cells during development and in adult tissues, the role of mesenchymal cells in lymphatic vasculature development remains poorly characterized. Here, we show that a subpopulation of mesenchymal cells expressing the transcription factor Osr1 are in close association with migrating LECs and established lymphatic vessels in mice. Lineage tracing experiments revealed that Osr1+ cells precede LEC arrival during lymphatic vasculature assembly in the back of the embryo. Using Osr1-deficient embryos and functional in vitro assays, we show that Osr1 acts in a non-cell-autonomous manner controlling proliferation and early migration of LECs to peripheral tissues. Thereby, mesenchymal Osr1+ cells control, in a bimodal manner, the production of extracellular matrix scaffold components and signal ligands crucial for lymphatic vessel formation.

Efficient Generation of Skin Organoids from Pluripotent Cells via Defined Extracellular Matrix Cues and Morphogen Gradients in a Spindle-Shaped Microfluidic Device

Pluripotent stem cell-derived skin organoids (PSOs) emerge as a developmental skin model that is self-organized into multiple components, such as hair follicles. Despite their impressive complexity, PSOs are currently generated in the absence of 3D extracellular matrix (ECM) signals and have several major limitations, including an inverted anatomy (e.g., epidermis inside/dermis outside). In this work, a method is established to generate PSOs effectively in a chemically-defined 3D ECM environment. After examining various dermal ECM molecules, it is found that PSOs generated in collagen -type I (COLI) supplemented with laminin 511 (LAM511) exhibit increased growth compared to conventional free-floating conditions, but fail to induce complete skin differentiation due in part to necrosis. This problem is addressed by generating the PSOs in a 3D bioprinted spindle-shaped hydrogel device, which constrains organoid growth longitudinally. This culture system significantly reduces organoid necrosis and leads to a twofold increase in keratinocyte differentiation and an eightfold increase in hair follicle formation. Finally, the system is adapted as a microfluidic device to create asymmetrical gradients of differentiation factors and improves the spatial organization of dermal and epidermal cells. This study highlights the pivotal role of ECM and morphogen gradients in promoting and spatially-controlling skin differentiation in the PSO framework.

Three-dimensional genome architecture persists in a 52,000-year-old woolly mammoth skin sample

Analyses of ancient DNA typically involve sequencing the surviving short oligonucleotides and aligning to genome assemblies from related, modern species. Here, we report that skin from a female woolly mammoth (†Mammuthus primigenius) that died 52,000 years ago retained its ancient genome architecture. We use PaleoHi-C to map chromatin contacts and assemble its genome, yielding 28 chromosome-length scaffolds. Chromosome territories, compartments, loops, Barr bodies, and inactive X chromosome (Xi) superdomains persist. The active and inactive genome compartments in mammoth skin more closely resemble Asian elephant skin than other elephant tissues. Our analyses uncover new biology. Differences in compartmentalization reveal genes whose transcription was potentially altered in mammoths vs. elephants. Mammoth Xi has a tetradic architecture, not bipartite like human and mouse. We hypothesize that, shortly after this mammoth's death, the sample spontaneously freeze-dried in the Siberian cold, leading to a glass transition that preserved subfossils of ancient chromosomes at nanometer scale.

Single-Cell and Spatial Transcriptome Analysis of Dermal Fibroblast Development in Perinatal Mouse Skin: Dynamic Lineage Differentiation and Key Driver Genes

Several single-cell RNA studies of developing mouse skin have elucidated the molecular and cellular processes involved in skin development. However, they have primarily focused on either the fetal or early postnatal period, leaving a gap in our understanding of skin development. In this study, we conducted a comprehensive time-series analysis by combining single-cell RNA-sequencing datasets collected at different stages of development (embryonic days 13.5, 14.5, and 16.5 and postnatal days 0, 2, and 4) and validated our findings through multipanel in situ spatial transcriptomics. Our analysis indicated that embryonic fibroblasts exhibit heterogeneity from a very early stage and that the rapid determination of each lineage occurs within days after birth. The expression of putative key driver genes, including Hey1, Ebf1, Runx3, and Sox11 for the dermal papilla trajectory; Lrrc15 for the dermal sheath trajectory; Zfp536 and Nrn1 for the papillary fibroblast trajectory; and Lrrn4cl and Mfap5 for the fascia fibroblast trajectory, was detected in the corresponding, spatially identified cell types. Finally, cell-to-cell interaction analysis indicated that the dermal papilla lineage is the primary source of the noncanonical Wnt pathway during skin development. Together, our study provides a transcriptomic reference for future research in the field of skin development and regeneration.

Stabilization of Epithelial β-Catenin Compromises Mammary Cell Fate Acquisition and Branching Morphogenesis

The Wnt/β-catenin pathway plays a critical role in cell fate specification, morphogenesis, and stem cell activation across diverse tissues, including the skin. In mammals, the embryonic surface epithelium gives rise to the epidermis as well as the associated appendages including hair follicles and mammary glands, both of which depend on epithelial Wnt/β-catenin activity for initiation of their development. Later on, Wnts are thought to enhance mammary gland growth and branching, whereas in hair follicles, they are essential for hair shaft formation. In this study, we report a strong downregulation of epithelial Wnt/β-catenin activity as the mammary bud progresses to branching. We show that forced activation of epithelial β-catenin severely compromises embryonic mammary gland branching. However, the phenotype of conditional Lef1-deficient embryos implies that a low level of Wnt/β-catenin activity is necessary for mammary cell survival. Transcriptomic profiling suggests that sustained high β-catenin activity leads to maintenance of mammary bud gene signature at the expense of outgrowth/branching gene signature. In addition, it leads to upregulation of epidermal differentiation genes. Strikingly, we find a partial switch to hair follicle fate early on upon stabilization of β-catenin, suggesting that the level of epithelial Wnt/β-catenin signaling activity may contribute to the choice between skin appendage identities.

Emx2 underlies the development and evolution of marsupial gliding membranes

Phenotypic variation among species is a product of evolutionary changes to developmental programs1,2. However, how these changes generate novel morphological traits remains largely unclear. Here we studied the genomic and developmental basis of the mammalian gliding membrane, or patagium-an adaptative trait that has repeatedly evolved in different lineages, including in closely related marsupial species. Through comparative genomic analysis of 15 marsupial genomes, both from gliding and non-gliding species, we find that the Emx2 locus experienced lineage-specific patterns of accelerated cis-regulatory evolution in gliding species. By combining epigenomics, transcriptomics and in-pouch marsupial transgenics, we show that Emx2 is a critical upstream regulator of patagium development. Moreover, we identify different cis-regulatory elements that may be responsible for driving increased Emx2 expression levels in gliding species. Lastly, using mouse functional experiments, we find evidence that Emx2 expression patterns in gliders may have been modified from a pre-existing program found in all mammals. Together, our results suggest that patagia repeatedly originated through a process of convergent genomic evolution, whereby regulation of Emx2 was altered by distinct cis-regulatory elements in independently evolved species. Thus, different regulatory elements targeting the same key developmental gene may constitute an effective strategy by which natural selection has harnessed regulatory evolution in marsupial genomes to generate phenotypic novelty.

Immune niches for hair follicle development and homeostasis

The hair follicle is a dynamic mini-organ that has specialized cycles and architectures with diverse cell types to form hairs. Previous studies for several decades have investigated morphogenesis and signaling pathways during embryonic development and adult hair cycles in both mouse and human skin. In particular, hair follicle stem cells and mesenchymal niches received major attention as key players, and their roles and interactions were heavily revealed. Although resident and circulating immune cells affect cellular function and interactions in the skin, research on immune cells has mainly received attention on diseases rather than development or homeostasis. Recently, many studies have suggested the functional roles of diverse immune cells as a niche for hair follicles. Here, we will review recent findings about immune niches for hair follicles and provide insight into mechanisms of hair growth and diseases.

Nuclear mechanotransduction on skin stem cell fate regulation

Mammalian skin is a highly dynamic and regenerative organ that has long been recognized as a mechanically active composite of tissues withstanding daily compressive and tensile forces that arise from body movement. Importantly, cell- and tissue-scale mechanical signals are critical regulators of skin morphogenesis and homeostasis. These signals are sensed at the cellular periphery and transduced by mechanosensitive proteins within the plasma membrane to the cytoskeletal networks, and eventually into the nucleus to regulate chromatin organization and gene expression. The role of each of these nodes in producing a coherent mechanoresponse at both cell- and tissue-scales is emerging. Here we focus on the key cytoplasmic and nuclear mechanosensitive structures that are critical for the mammalian skin development and homeostatic maintenance. We propose that the mechanical state of the skin, in particular of its nuclear compartment, is a critical rheostat that fine-tunes developmental and homeostatic processes essential for the proper function of the organ.

Genetic lineage tracing in skin reveals predominant expression of HEY2 in dermal papilla during telogen and that HEY2+ cells contribute to the regeneration of dermal cells during wound healing

Dermal papilla (DP) cells are specialized mesenchymal cells that play a crucial role in regulating hair morphology, colour and growth through the secretion of specific factors. It is still unclear what the source of progenitor cells is for dermal cell regeneration during wound healing, and whether DP cells are involved in this process. We analyzed the gene expression profile of various skin cell populations using existing datasets and found that the Hey2 gene was predominantly expressed in DP cells. We introduced Hey2-CreERT2 knockin mice and crossed them with Rosa26-ZsGreen reporter mice. After induction in the double transgenic mice by administration of tamoxifen, the reporter ZsGreen was found to be predominantly expressed in DP cells both at anagen and telogen phases, and broadly expressed in some other dermal cells at anagen. We also created a wound after tamoxifen induction, and found there were abundant ZsGreen+ cells in the regenerated dermis. We conclude that the HEY2+ DP cells and dermal cells exhibit some stemness properties and can contribute to the dermal cell regeneration during wound healing.

A multifunctional Wnt regulator underlies the evolution of rodent stripe patterns

Animal pigment patterns are excellent models to elucidate mechanisms of biological organization. Although theoretical simulations, such as Turing reaction-diffusion systems, recapitulate many animal patterns, they are insufficient to account for those showing a high degree of spatial organization and reproducibility. Here, we study the coat of the African striped mouse (Rhabdomys pumilio) to uncover how periodic stripes form. Combining transcriptomics, mathematical modelling and mouse transgenics, we show that the Wnt modulator Sfrp2 regulates the distribution of hair follicles and establishes an embryonic prepattern that foreshadows pigment stripes. Moreover, by developing in vivo gene editing in striped mice, we find that Sfrp2 knockout is sufficient to alter the stripe pattern. Strikingly, mutants exhibited changes in pigmentation, revealing that Sfrp2 also regulates hair colour. Lastly, through evolutionary analyses, we find that striped mice have evolved lineage-specific changes in regulatory elements surrounding Sfrp2, many of which may be implicated in modulating the expression of this gene. Altogether, our results show that a single factor controls coat pattern formation by acting both as an orienting signalling mechanism and a modulator of pigmentation. More broadly, our work provides insights into how spatial patterns are established in developing embryos and the mechanisms by which phenotypic novelty originates.

Induced differentiation of primordial germ cell like cells from SOX9+ porcine skin derived stem cells

Understanding the mechanisms behind porcine primordial germ cell like cells (pPGCLCs) development, differentiation, and gametogenesis is crucial in the treatment of infertility. In this study, SOX9+ skin derived stem cells (SOX9+ SDSCs) were isolated from fetal porcine skin and a high-purity SOX9+ SDSCs population was obtained. The SOX9+ SDSCs were induced to transdifferentiate into PGCLCs during 8 days of cultured. The results of RNA-seq, western blot and immunofluorescence staining verified SDSCs have the potential to transdifferentiate into PGCLCs from aspects of transcription factor activation, germ layer differentiation, energy metabolism, and epigenetic changes. Both adherent and suspended cells were collected. The adherent cells were found to be very similar to early porcine primordial germ cells (pPGCs). The suspended cells resembled late stage pPGCs and had a potential to enter meiotic process. This SDSCs culture-induced in vitro model is expected to provide suitable donor cells for stem cell transplantation in the future.

Mesenchyme governs hair follicle induction

Tissue interactions are essential for guiding organ development and regeneration. Hair follicle formation relies on inductive signalling between two tissues, the embryonic surface epithelium and the adjacent mesenchyme. Although previous research has highlighted the hair-inducing potential of the mesenchymal component of the hair follicle - the dermal papilla and its precursor, the dermal condensate - the source and nature of the primary inductive signal before dermal condensate formation have remained elusive. Here, we performed epithelial-mesenchymal tissue recombination experiments using hair-forming back skin and glabrous plantar skin from mouse embryos to unveil that the back skin mesenchyme is inductive even before dermal condensate formation. Moreover, the naïve, unpatterned mesenchyme was sufficient to trigger hair follicle formation even in the oral epithelium. Building on previous knowledge, we explored the hair-inductive ability of the Wnt agonist R-spondin 1 and a Bmp receptor inhibitor in embryonic skin explants. Although R-spondin 1 instigated precocious placode-specific transcriptional responses, it was insufficient for hair follicle induction, either alone or in combination with Bmp receptor inhibition. Our findings pave the way for identifying the hair follicle-inducing cue.

Molecular and spatial landmarks of early mouse skin development

A wealth of specialized cell populations within the skin facilitates its hair-producing, protective, sensory, and thermoregulatory functions. How the vast cell-type diversity and tissue architecture develops is largely unexplored. Here, with single-cell transcriptomics, spatial cell-type assignment, and cell-lineage tracing, we deconstruct early embryonic mouse skin during the key transitions from seemingly uniform developmental precursor states to a multilayered, multilineage epithelium, and complex dermal identity. We identify the spatiotemporal emergence of hair-follicle-inducing, muscle-supportive, and fascia-forming fibroblasts. We also demonstrate the formation of the panniculus carnosus muscle (PCM), sprouting blood vessels without pericyte coverage, and the earliest residence of mast and dendritic immune cells in skin. Finally, we identify an unexpected epithelial heterogeneity within the early single-layered epidermis and a signaling-rich periderm layer. Overall, this cellular and molecular blueprint of early skin development-which can be explored at https://kasperlab.org/tools-establishes histological landmarks and highlights unprecedented dynamic interactions among skin cells.

Lineage commitment of dermal fibroblast progenitors is controlled by Kdm6b-mediated chromatin demethylation

Dermal Fibroblast Progenitors (DFPs) differentiate into distinct fibroblast lineages during skin development. However, the epigenetic mechanisms that regulate DFP differentiation are not known. Our objective was to use multimodal single-cell approaches, epigenetic assays, and allografting techniques to define a DFP state and the mechanism that governs its differentiation potential. Our initial results indicated that the overall transcription profile of DFPs is repressed by H3K27me3 and has inaccessible chromatin at lineage-specific genes. Surprisingly, the repressive chromatin profile of DFPs renders them unable to reform the skin in allograft assays despite their multipotent potential. We hypothesized that chromatin derepression was modulated by the H3K27me3 demethylase, Kdm6b/Jmjd3. Dermal fibroblast-specific deletion of Kdm6b/Jmjd3 in mice resulted in adipocyte compartment ablation and inhibition of mature dermal papilla functions, confirmed by additional single-cell RNA-seq, ChIP-seq, and allografting assays. We conclude that DFPs are functionally derepressed during murine skin development by Kdm6b/Jmjd3. Our studies therefore reveal a multimodal understanding of how DFPs differentiate into distinct fibroblast lineages and provide a novel publicly available multiomics search tool.

Identification of genes involved in regulating the development of feathered feet in chicken embryo

The genetic and developmental factors driving the diverse distribution and morphogenesis of feathers and scales on bird feet are yet unclear. Within a single species, Guangxi domestic chickens exhibit dramatic variety in feathered feet, making them an accessible model for research into the molecular basis of variations in skin appendages. In this study, we used H&E staining to observe the morphogenesis of feathered feet, scaled feet and wings skin at different embryonic stages in Longsheng-Feng chickens and Guangxi Partridge chickens. We selected 4 periods (E6, E7, E8, and E12) that play an important role in feather development and performed transcriptome sequencing to screen for candidate genes associated with feathered feet. Through comparison and analysis of transcriptome data, we identified a set of differently expressed genes (DGEs), which were enriched in appendage organ development, hindlimb morphogenesis, activation of transcription factor binding, and binding of sequence-specific DNA in the cis-regulatory region. In addition, we identified some feathered feet-related genes by analyzing the classical signaling pathways that regulate feather development. Finally, we identified candidate genes that regulate feathered feet formation, which include TBX5, PITX1, ZIC1, FGF20, WNT11, WNT7A, WNT16, and SHH. Interestingly, we found that TBX5 was significantly overexpressed in the skin of the feathered feet and had the highest expression at E7 (P < 0.01), whereas PITX1 expression was significantly reduced at E7(P < 0.01). It is hypothesized that TBX5 and PITX1 regulate the development of hair follicles through the Wnt/β-catenin signaling pathway at E7. Our results provide a theoretical basis for investigating the molecular regulatory mechanisms underlying the formation of chicken feathered feet.

Peripheral transient receptor potential vanilloid type 4 hypersensitivity contributes to chronic sickle cell disease pain

ABSTRACT

Debilitating pain affects the lives of patients with sickle cell disease (SCD). Current pain treatment for patients with SCD fail to completely resolve acute or chronic SCD pain. Previous research indicates that the cation channel transient receptor potential vanilloid type 4 (TRPV4) mediates peripheral hypersensitivity in various inflammatory and neuropathic pain conditions that may share similar pathophysiology with SCD, but this channel's role in chronic SCD pain remains unknown. Thus, the current experiments examined whether TRPV4 regulates hyperalgesia in transgenic mouse models of SCD. Acute blockade of TRPV4 alleviated evoked behavioral hypersensitivity to punctate, but not dynamic, mechanical stimuli in mice with SCD. TRPV4 blockade also reduced the mechanical sensitivity of small, but not large, dorsal root ganglia neurons from mice with SCD. Furthermore, keratinocytes from mice with SCD showed sensitized TRPV4-dependent calcium responses. These results shed new light on the role of TRPV4 in SCD chronic pain and are the first to suggest a role for epidermal keratinocytes in the heightened sensitivity observed in SCD.

Transcriptomic landscape of early hair follicle and epidermal development

Morphogenesis of ectodermal organs, such as hair, tooth, and mammary gland, starts with the formation of local epithelial thickenings, or placodes, but it remains to be determined how distinct cell types and differentiation programs are established during ontogeny. Here, we use bulk and single-cell transcriptomics and pseudotime modeling to address these questions in developing hair follicles and epidermis and produce a comprehensive transcriptomic profile of cellular populations in the hair placode and interplacodal epithelium. We report previously unknown cell populations and marker genes, including early suprabasal and genuine interfollicular basal markers, and propose the identity of suprabasal progenitors. By uncovering four different hair placode cell populations organized in three spatially distinct areas, with fine gene expression gradients between them, we posit early biases in cell fate establishment. This work is accompanied by a readily accessible online tool to stimulate further research on skin appendages and their progenitors.

Automatic landmarking identifies new loci associated with face morphology and implicates Neanderthal introgression in human nasal shape

We report a genome-wide association study of facial features in >6000 Latin Americans based on automatic landmarking of 2D portraits and testing for association with inter-landmark distances. We detected significant associations (P-value <5 × 10-8) at 42 genome regions, nine of which have been previously reported. In follow-up analyses, 26 of the 33 novel regions replicate in East Asians, Europeans, or Africans, and one mouse homologous region influences craniofacial morphology in mice. The novel region in 1q32.3 shows introgression from Neanderthals and we find that the introgressed tract increases nasal height (consistent with the differentiation between Neanderthals and modern humans). Novel regions include candidate genes and genome regulatory elements previously implicated in craniofacial development, and show preferential transcription in cranial neural crest cells. The automated approach used here should simplify the collection of large study samples from across the world, facilitating a cosmopolitan characterization of the genetics of facial features.

The effects of GPR40 agonists on hair growth are mediated by ANGPTL4

GPR40 is found primarily in pancreatic β cells, and is well known to regulate insulin secretion. Despite numerous studies on GPR40, the role and functions of GPR40 related to hair growth are not yet known. The current study investigated hair growth promoting effect of the GPR40 agonists and its mechanism of action using various bio-informatics tools, in vitro and animal experiments. GPR40 may affect the hair cycle, according to clustering and Gene Set Enrichment Analysis (GSEA). Hair growth effect of GPR40 was validated by telogen-to-anagen transition and vibrissae organ culture in the mouse. GPR40 was predominantly expressed in the outer root sheath (ORS) in anagen stage, suggesting that ORS cell is the target of GPR40 agonists. To investigate the mechanism of action for GPR40 agonists' hair growth effect, Gene Ontology (GO) enrichment analysis was performed and it revealed that GPR40 agonists were associated with angiogenesis. ANGPTL4, known for promoting angiogenesis, was highly up-regulated after GPR40 agonists treatment in the hORS cells, and also increased the proliferation and migration. Furthermore, GPR40 agonists promoted hair growth by inducing angiogenesis via ANGPTL4 in the animal experiment. GPR40 agonists activated MAPK and peroxisome proliferator-activated receptors (PPARγ) pathway in hORS cells, while the inhibition of MAPK pathway attenuated ANGPTL4 expression. Finally, GPR40 agonists increased hair growth via autocrine effects in the ORS cells, and induced angiogenesis through paracrine effects by upregulating ANGPTL4 via p38 and PPARγ pathways. As a result, GPR40 agonists have potential as a therapeutic drug for hair loss treatment.

The Fraser Complex Proteins (Frem1, Frem2, and Fras1) Can Form Anchoring Cords in the Absence of AMACO at the Dermal–Epidermal Junction of Mouse Skin

AMACO (VWA2 protein), secreted by epithelial cells, is strongly expressed at basement membranes when budding or invagination occurs in embryos. In skin, AMACO associates with proteins of the Fraser complex, which form anchoring cords. These, during development, temporally stabilize the dermal–epidermal junction, pending the formation of collagen VII-containing anchoring fibrils. Fraser syndrome in humans results if any of the core members of the Fraser complex (Fras1, Frem1, Frem2) are mutated. Fraser syndrome is characterized by subepidermal blistering, cryptophthalmos, and syndactyly. In an attempt to determine AMACO function, we generated and characterized AMACO-deficient mice. In contrast to Fraser complex mutant mice, AMACO-deficient animals lack an obvious phenotype. The mutually interdependent basement membrane deposition of the Fraser complex proteins, and the formation of anchoring cords, are not affected. Furthermore, hair follicle development in newborn AMACO-deficient mice showed no gross aberration. Surprisingly, it appears that, while AMACO is a component of the anchoring cords, it is not essential for their formation or function.

A Cre knockin mouse reveals specific expression of Agouti gene in mesenchymal lineage cells in multiple organs and provides a unique tool for conditional gene targeting

The mouse Agouti gene encodes a paracrine signaling factor which promotes melanocytes to produce yellow instead of black pigment. It has been reported that Agouti mRNA is confined to the dermal papilla after birth in various mammalian species. In this study, we created and characterized a knockin mouse strain in which Cre recombinase was expressed in-frame with endogenous Agouti coding sequence. The Agouti-Cre mice were bred with reporter mice (Rosa26-tdTomato or Rosa26-ZsGreen) to trace the lineage of Agouti-expressing cells during development. In skin, the reporter was detected in some dermal fibroblasts at the embryonic stage and in all dermal fibroblasts postnatally. It was also expressed in all mesenchymal lineage cells in other organs/tissues, including eyes, tongue, muscle, intestine, adipose, prostate and testis. Interestingly, the reporter expression was excluded from epithelial cells in the above organs/tissues. In brain, the reporter was observed in the outermost meningeal fibroblasts. Our work helps to illustrate the Agouti expression pattern during development and provides a valuable mouse strain for conditional gene targeting in mesenchymal lineage cells in multiple organs.

Lineage Commitment of Dermal Fibroblast Progenitors is Mediated by Chromatin De-repression

Dermal Fibroblast Progenitors (DFPs) differentiate into distinct fibroblast lineages during skin development. However, the mechanisms that regulate lineage commitment of naive dermal progenitors to form niches around the hair follicle, dermis, and hypodermis, are unknown. In our study, we used multimodal single-cell approaches, epigenetic assays, and allografting techniques to define a DFP state and the mechanisms that govern its differentiation potential. Our results indicate that the overall chromatin profile of DFPs is repressed by H3K27me3 and has inaccessible chromatin at lineage specific genes. Surprisingly, the repressed chromatin profile of DFPs renders them unable to reform skin in allograft assays despite their multipotent potential. Distinct fibroblast lineages, such as the dermal papilla and adipocytes contained specific chromatin profiles that were de-repressed during late embryogenesis by the H3K27-me3 demethylase, Kdm6b/Jmjd3. Tissue-specific deletion of Kdm6b/Jmjd3 resulted in ablating the adipocyte compartment and inhibiting mature dermal papilla functions in single-cell-RNA-seq, ChIPseq, and allografting assays. Altogether our studies reveal a mechanistic multimodal understanding of how DFPs differentiate into distinct fibroblast lineages, and we provide a novel multiomic search-tool within skinregeneration.org.

Murine skin-derived multipotent papillary dermal fibroblast progenitors show germline potential in vitro

BACKGROUND

Many laboratories have described the in vitro isolation of multipotent cells with stem cell properties from the skin of various species termed skin-derived stem cells (SDSCs). However, the cellular origin of these cells and their capability to give rise, among various cell types, to male germ cells, remain largely unexplored.

METHODS

SDSCs were isolated from newborn mice skin, and then differentiated into primordial germ cell-like cells (PGCLCs) in vitro. Single-cell RNA sequencing (scRNA-seq) was then applied to dissect the cellular origin of SDSCs using cells isolated from newborn mouse skin and SDSC colonies. Based on an optimized culture strategy, we successfully generated spermatogonial stem cell-like cells (SSCLCs) in vitro.

RESULTS

Here, using scRNA-seq and analyzing the profile of 7543 single-cell transcriptomes from newborn mouse skin and SDSCs, we discovered that they mainly consist of multipotent papillary dermal fibroblast progenitors (pDFPs) residing in the dermal layer. Moreover, we found that epidermal growth factor (EGF) signaling is pivotal for the capability of these progenitors to proliferate and form large colonies in vitro. Finally, we optimized the protocol to efficiently generate PGCLCs from SDSCs. Furthermore, PGCLCs were induced into SSCLCs and these SSCLCs showed meiotic potential when cultured with testicular organoids.

CONCLUSIONS

Our findings here identify pDFPs as SDSCs derived from newborn skin and show for the first time that such precursors can be induced to generate cells of the male germline.

Progenitor-derived endothelin controls dermal sheath contraction for hair follicle regression

Substantial follicle remodelling during the regression phase of the hair growth cycle is coordinated by the contraction of the dermal sheath smooth muscle, but how dermal-sheath-generated forces are regulated is unclear. Here, we identify spatiotemporally controlled endothelin signalling-a potent vasoconstriction-regulating pathway-as the key activating mechanism of dermal sheath contraction. Pharmacological blocking or genetic ablation of both endothelin receptors, ET_A and ET_B, impedes dermal sheath contraction and halts follicle regression. Epithelial progenitors at the club hair-epithelial strand bottleneck produce the endothelin ligand ET-1, which is required for follicle regression. ET signalling in dermal sheath cells and downstream contraction is dynamically regulated by cytoplasmic Ca²⁺ levels through cell membrane and sarcoplasmic reticulum calcium channels. Together, these findings illuminate an epithelial-mesenchymal interaction paradigm in which progenitors-destined to undergo programmed cell death-control the contraction of the surrounding sheath smooth muscle to orchestrate homeostatic tissue regression and reorganization for the next stem cell activation and regeneration cycle.

DNA dioxygenases Tet2/3 regulate gene promoter accessibility and chromatin topology in lineage-specific loci to control epithelial differentiation

Execution of lineage-specific differentiation programs requires tight coordination between many regulators including Ten-eleven translocation (TET) family enzymes, catalyzing 5-methylcytosine oxidation in DNA. Here, by using Keratin 14-Cre-driven ablation of Tet genes in skin epithelial cells, we demonstrate that ablation of Tet2/Tet3 results in marked alterations of hair shape and length followed by hair loss. We show that, through DNA demethylation, Tet2/Tet3 control chromatin accessibility and Dlx3 binding and promoter activity of the Krt25 and Krt28 genes regulating hair shape, as well as regulate interactions between the Krt28 gene promoter and distal enhancer. Moreover, Tet2/Tet3 also control three-dimensional chromatin topology in Keratin type I/II gene loci via DNA methylation-independent mechanisms. These data demonstrate the essential roles for Tet2/3 in establishment of lineage-specific gene expression program and control of Dlx3/Krt25/Krt28 axis in hair follicle epithelial cells and implicate modulation of DNA methylation as a novel approach for hair growth control.

Celsr1 and Celsr2 exhibit distinct adhesive interactions and contributions to planar cell polarity

Cadherin EGF LAG seven-pass G-type receptor (Celsr) proteins 1-3 comprise a subgroup of adhesion GPCRs whose functions range from planar cell polarity (PCP) signaling to axon pathfinding and ciliogenesis. Like its Drosophila ortholog, Flamingo, mammalian Celsr1 is a core component of the PCP pathway, which, among other roles, is responsible for the coordinated alignment of hair follicles across the skin surface. Although the role of Celsr1 in epidermal planar polarity is well established, the contribution of the other major epidermally expressed Celsr protein, Celsr2, has not been investigated. Here, using two new CRISPR/Cas9-targeted Celsr1 and Celsr2 knockout mouse lines, we define the relative contributions of Celsr1 and Celsr2 to PCP establishment in the skin. We find that Celsr1 is the major Celsr family member involved in epidermal PCP. Removal of Celsr1 function alone abolishes PCP protein asymmetry and hair follicle polarization, whereas epidermal PCP is unaffected by loss of Celsr2. Further, elimination of both Celsr proteins only minimally enhances the Celsr1 ^-/- phenotype. Using FRAP and junctional enrichment assays to measure differences in Celsr1 and Celsr2 adhesive interactions, we find that compared to Celsr1, which stably enriches at junctional interfaces, Celsr2 is much less efficiently recruited to and immobilized at junctions. As the two proteins seem equivalent in their ability to interact with core PCP proteins Vangl2 and Fz6, we suggest that perhaps differences in homophilic adhesion contribute to the differential involvement of Celsr1 and Celsr2 in epidermal PCP.

Generation of Pmel-dependent conditional and inducible Cre-driver mouse line for melanocytic-targeted gene manipulation

Conditional and inducible gene targeting using Cre/loxP-mediated recombination is a powerful reverse genetics approach used to study spatiotemporal gene functions in specified cell types. To enable temporal gene manipulation in the melanocyte lineage, we established a novel inducible Cre-driver mouse line by targeting an all-in-one tetracycline/doxycycline (Dox)-inducible Cre expression cassette into the Pmel locus (Pmel^{P2A-TetON3G-TRE3G-iCre} ), a gene locus preferentially expressed in pigment cells. By crossing these Cre-driver mice with a strong Cre-reporter mouse line, Gt(ROSA)26Sor^{tm9(CAG-tdTomato)Hze} , we show the effectiveness of the Pmel^{P2A-TetON3G-TRE3G-iCre} mouse line in facilitating Dox-inducible Cre/loxP recombination in a wide variety of pigment cell lineages including hair follicle melanocytes and their stem cells. Furthermore, to demonstrate proof of concept, we ablated Notch signaling postnatally in the Pmel^{P2A-TetON3G-TRE3G-iCre} mice. In agreement with the previously reported phenotype, induced ablation of Notch signaling in the melanocyte lineage resulted in premature hair graying, demonstrating the utility of the Pmel^{P2A-TetON3G-TRE3G-iCre} allele. Therefore, the Pmel^{P2A-TetON3G-TRE3G-iCre} mouse line is suitable for assessing gene functions in melanocytes using an in vivo inducible reverse genetics approach. Furthermore, we unexpectedly identified previously unrecognized PMEL-expressing cells in non-pigmentary organs in the mice, suggesting unanticipated functions of PMEL other than melanosome formation.

Defining ovine dermal papilla cell markers and identifying key signaling pathways regulating its intrinsic properties

Dermal papilla cell (DPC), one of the key cell types during hair follicle development and regeneration, specifies hair size, shape and cycling. It is also an important in vitro screening model for hair growth. Although some characteristics of DPCs, such as agglutinative growth and marker genes, have been studied in mice and humans, the intrinsic properties of ovine DPCs and the regulatory mechanism of the intrinsic properties during continued culture in vitro remained unknown. In this study, based on our previous single-cell transcriptome sequencing on sheep lambskin, we verified SOX18 and PDGFRA as the novel marker genes of ovine DPCs through immunofluorescence staining on skin sections and cultured DPCs. Using continued cell culture and alkaline phosphatase staining, we found that different from mice and humans, ovine DPCs exhibit particularly robust and stable aggregation with unbated alkaline phosphatase activity till 30 passages during continued culture in vitro. Also, we found that the expression of some marker genes and the activity of Wnt/β-catenin signaling differ between early passaged DPCs and multiple passaged DPCs. Further, using Wnt/β-catenin agonist and antagonist, we demonstrated that Wnt/β-catenin signaling could regulate cell aggregation and alkaline phosphatase activity of ovine DPCs through regulating FGF and IGF signaling. This study provides the basis for isolating ovine DPCs and defines their intrinsic properties, which contribute to improving wool performance and medicine of hair regeneration.

Construction of transcriptome atlas of white yak hair follicle during anagen and catagen using single-cell RNA sequencing

BACKGROUND

As the direct organ of villus, hair follicles have obvious seasonal cycles. The hair follicle cycle is orchestrated by multiple cell types that together direct cell renewal and differentiation. But the regulation property of hair follicle cells from anagen to catagen in yak is still unknown.

RESULTS

In this study, single-cell RNA sequencing was performed on 24,124 single cells of the scapular skin from white yak. Based on tSNE cluster analysis, the cell types of IFE-DC, epidermal cell lines, fibroblasts, keratinocytes, IRS, DS, INFU, and other cells in yak hair follicles during anagen and catagen were successfully identified, and the gene expression profiles were described. The GO enrichment analysis indicated the different cells characteristic genes to be mainly enriched in the epidermal development, epithelial cell differentiation and wound healing pathways. The pseudotime trajectory analysis described the differentiation trajectory of the epidermal lineage and dermal lineage of the hair follicle during anagen and catagen. Moreover, the dynamic changes of the genes like LHX2, KRT25, and KRT71 were found to be highly expressed in HS and IRS, but not in the IFE-DC, INFU, and keratinocyte during differentiation.

CONCLUSIONS

Our results analyzed the time-varying process of gene expression in the dermal cell lineage and epidermal cell lineage of hair follicles during anagen and catagen during fate differentiation was expounded at the single cell level, revealing the law of fate specialization of different types of cells. In addition, based on the enrichment analysis, the transcriptional regulatory factors involved in the different cell fates were also revealed. These results will help to enhance our understanding of yak hair follicle cycle and promote the development and utilization of yak villus.

Fibroblast inflammatory priming determines regenerative versus fibrotic skin repair in reindeer

Adult mammalian skin wounds heal by forming fibrotic scars. We report that full-thickness injuries of reindeer antler skin (velvet) regenerate, whereas back skin forms fibrotic scar. Single-cell multi-omics reveal that uninjured velvet fibroblasts resemble human fetal fibroblasts, whereas back skin fibroblasts express inflammatory mediators mimicking pro-fibrotic adult human and rodent fibroblasts. Consequently, injury elicits site-specific immune responses: back skin fibroblasts amplify myeloid infiltration and maturation during repair, whereas velvet fibroblasts adopt an immunosuppressive phenotype that restricts leukocyte recruitment and hastens immune resolution. Ectopic transplantation of velvet to scar-forming back skin is initially regenerative, but progressively transitions to a fibrotic phenotype akin to the scarless fetal-to-scar-forming transition reported in humans. Skin regeneration is diminished by intensifying, or enhanced by neutralizing, these pathologic fibroblast-immune interactions. Reindeer represent a powerful comparative model for interrogating divergent wound healing outcomes, and our results nominate decoupling of fibroblast-immune interactions as a promising approach to mitigate scar.

FLG Deficiency in Mice Alters the Early-Life CD4+ T-Cell Response to Skin Commensal Bacteria

FLG variants underlie ichthyosis vulgaris and increased risk of atopic dermatitis, conditions typified by disruption of the skin microbiome and cutaneous immune response. Yet, it remains unclear whether neonatal skin barrier compromise because of FLG deficiency alters the quality of commensal-specific T cells and the functional impact of such responses. To address these questions, we profiled changes in the skin barrier and early cutaneous immune response of neonatal C57BL/6 Flg^‒/‒ and wild-type mice using single-cell RNA sequencing, flow cytometry, and other modalities. Flg^‒/‒ neonates showed little alteration in transepidermal water loss or lipid- or corneocyte-related gene expression. However, they showed increases in barrier disruption genes, epidermal dye penetration, and numbers of skin CD4⁺ T cells. Using an engineered strain of Staphylococcus epidermidis (S. epidermidis 2W) to study the response to neonatal skin colonization, we found that commensal-specific CD4⁺ T cells were skewed in Flg^‒/‒ pups toward effector rather than regulatory T cells. This altered response persisted into adulthood, where it was typified by T helper 17 (Th17) cells and associated with increased susceptibility to imiquimod-induced skin inflammation. Thus, subtle but impactful differences in neonatal barrier function in Flg^‒/‒ mice are accompanied by a skewed commensal-specific CD4⁺ response, with enduring consequences for skin immune homeostasis.

Single-cell chromatin landscapes of mouse skin development

The coat of mammals is produced by hair follicles, and hair follicle is an important and complex accessory organ of skin. As a complex physiological regulation process, hair follicle morphogenesis is regulated by a series of signal pathway factors, involves the interaction of multiple cell types and begins in the early embryonic stage. However, its transcriptional regulatory mechanism is unclear. We have therefore utilized single-cell ATAC sequencing to obtain the chromatin accessibility landscapes of 6,928, 6,961 and 7,374 high-quality cells from the dorsal skins of E13.5, E16.5 and P0 mice (Mus musculus), respectively. Based on marker gene activity clustering, we defined 6, 8 and 5 distinct cell types in E13.5, E16.5 and P0 stages, respectively. Furtherly, we integrated the fibroblasts and keratinocytes clusters, performed further analysis and re-clustered. The single cell map of the chromatin open area was drawn from each cell type and the mechanism of cell transcription regulation was explored. Collectively, our data provide a reference for deeply exploring the epigenetic regulation mechanism of mouse hair follicles development.

ID1 and CEBPA coordinate epidermal progenitor cell differentiation

The regulatory circuits that coordinate epidermal differentiation during development are still not fully understood. Here, we report that the transcriptional regulator ID1 is enriched in mouse basal epidermal progenitor cells and find ID1 expression to be diminished upon differentiation. In utero silencing of Id1 impairs progenitor cell proliferation, leads to precocious delamination of targeted progenitor cells and enables differentiated keratinocytes to retain progenitor markers and characteristics. Transcriptional profiling suggests that ID1 acts by mediating adhesion to the basement membrane while inhibiting spinous layer differentiation. Co-immunoprecipitation reveals ID1 binding to transcriptional regulators of the class I bHLH family. We localize bHLH Tcf3, Tcf4 and Tcf12 to epidermal progenitor cells during epidermal stratification and establish TCF3 as a downstream effector of ID1-mediated epidermal proliferation. Finally, we identify crosstalk between CEBPA, a known mediator of epidermal differentiation, and Id1, and demonstrate that CEBPA antagonizes BMP-induced activation of Id1. Our work establishes ID1 as a key coordinator of epidermal development, acting to balance progenitor proliferation with differentiation and unveils how functional crosstalk between CEBPA and Id1 orchestrates epidermal lineage progression.

Activation of Nrf2 in fibroblasts promotes a skin aging phenotype via an Nrf2-miRNA-collagen axis

Aging is associated with progressive skin fragility and a tendency to tear, which can lead to severe clinical complications. The transcription factor NRF2 is a key regulator of the cellular antioxidant response, and pharmacological NRF2 activation is a promising strategy for the prevention of age-related diseases. Using a combination of molecular and cellular biology, histology, imaging and biomechanical studies we show, however, that constitutive genetic activation of Nrf2 in fibroblasts of mice suppresses collagen and elastin expression, resulting in reduced skin strength as seen in aged mice. Mechanistically, the "aging matrisome" results in part from direct Nrf2-mediated overexpression of a network of microRNAs that target mRNAs of major skin collagens and other matrix components. Bioinformatics and functional studies revealed high NRF2 activity in aged human fibroblasts in 3D skin equivalents and human skin biopsies, highlighting the translational relevance of the functional mouse data. Together, these results identify activated NRF2 as a promoter of age-related molecular and biomechanical skin features.

Nestin is a marker of unipotent embryonic and adult progenitors differentiating into an epithelial cell lineage of the hair follicles

Nestin is an intermediate filament protein transiently expressed in neural stem/progenitor cells. We previously demonstrated that outer root sheath (ORS) keratinocytes of adult hair follicles (HFs) in mice descend from nestin-expressing cells, despite being an epithelial cell lineage. This study determined the exact stage when nestin-expressing ORS stem/precursor cells or their descendants appear during HF morphogenesis, and whether they are present in adult HFs. Using Nes-Cre/CAG-CAT-EGFP mice, in which enhanced green fluorescent protein (EGFP) is expressed following Cre-based recombination driven by the nestin promoter, we found that EGFP⁺ cells appeared in the epithelial layer of embryonic HFs as early as the peg stage. EGFP⁺ cells in hair pegs were positive for keratin 14 (K14) and K5, but not vimentin, SOX2, SOX10, or S100 alpha 6. Tracing of tamoxifen-induced EGFP⁺ cells in postnatal Nes-CreERT2/CAG-CAT-EGFP mice revealed labeling of some isthmus HF epithelial cells in the first anagen stage. EGFP⁺ cells in adult HFs were not immunolabeled for K15, an HF multipotent stem cell marker. However, when hairs were depilated in Nes-CreERT2/CAG-CAT-EGFP mice to induce the anagen stage after tamoxifen injection, the majority of ORS keratinocytes in depilation-induced anagen HFs were labeled for EGFP. Our findings indicate that nestin-expressing unipotent progenitor cells capable of differentiating into ORS keratinocytes are present in HF primordia and adult HFs.

Generation and integration of hair follicle-primed spheroids in bioengineered skin constructs

Skin is a complex organ made up of different cell layers, appendages, connective tissues, and immune repertoires. These different components interact extensively to maintain the overall functions of the integumentary system. In particular, appendages such as hair follicles critically contribute to the skin's function in thermoregulation, sensory perception, and homeostatic regeneration. Despite a strong need for better skin regenerative therapeutics, efforts to bio-engineer highly functional appendage-containing human reconstituted skinin vitrohave not yielded much success. Here, we report methods in generating and incorporating hair follicle-primed heterotypic spheroids into epidermal-dermal skin constructs that induced invaginating outgrowths with follicle-like organization and lineage gene expression. By co-culturing epithelial keratinocytes (KCs) with dermal papilla (DP) cells in low attachment plates, we established the media and culture conditions that best supported the viability, signalling and remodelling of the cell aggregates to form 3D KC-DP spheroids with the expression of both DP inductiveness and hair follicle lineage genes. We show that long-term growth and maturation of KC cells in these spheroids was supported by incorporation into epidermal-dermal constructs but not in scaffold-less media. When cultured, the bio-fabricated constructs developed invaginations from the integrated spheroids with follicle-forming potential. The generation of these constructs is a step towards the development of functional hair-bearing skin mimetics.

Understanding Mammalian Hair Follicle Ecosystems by Single-Cell RNA Sequencing

Simple Summary

Single-cell sequencing technology can reflect cell population heterogeneity at the single-cell level, leading to a better understanding of the role of individual cells in the microenvironment. Over the past few years, single-cell sequencing technology has not only made more new discoveries in the study of cellular heterogeneity of other rare cells such as stem cells, but has also become the most powerful research method for embryonic development, organ differentiation, cancer occurrence, and cell mapping. In this review, we outline the use of scRNA-seq in hair follicles. In particular, by focusing on landmark studies and the recent discovery of novel subpopulations of hair follicles, we summarize the phenotypic diversity of hair follicle cells and their links to hair follicle morphogenesis. Enhancing our understanding of the progress of hair follicle research will help to elucidate the regulatory mechanisms that determine the fate of different types of cells in the hair follicle, thereby guiding hair loss treatment and hair-producing economic animal breeding research.

Abstract

Single-cell sequencing technology can fully reflect the heterogeneity of cell populations at the single cell level, making it possible for us to re-recognize various tissues and organs. At present, the sequencing study of hair follicles is transiting from the traditional ordinary transcriptome level to the single cell level, which will provide diverse insights into the function of hair follicle cells. This review focuses on research advances in the hair follicle microenvironment obtained from scRNA-seq studies of major cell types in hair follicle development, with a special emphasis on the discovery of new subpopulations of hair follicles by single-cell techniques. We also discuss the problems and current solutions in scRNA-seq observation and look forward to its prospects.

Transcriptional Characteristics Showed That miR-144-y/FOXO3 Participates in Embryonic Skin and Feather Follicle Development in Zhedong White Goose

Simple Summary

Feather is one of the most valuable and economical products in goose farming and plays a crucial physiological role in birds. For avian biology and the poultry industry, it is essential to comprehend and regulate how skin and feather follicles develop during embryogenesis. This study showed that several key regulatory genes (FOXO3, CTGF, and PTCH1, among others) and miRNAs (miR-144-y) participated in the developmental process of the skin and feather follicles in Zhedong white goose. Our findings are particularly important because they will serve as a valuable resource for upcoming studies on down feathers in agricultural economic growth regarding complex molecular mechanisms and breeding techniques.

Abstract

Skin and feather follicle development are essential processes for goose embryonic growth. Transcriptome and next-generation sequencing (NGS) network analyses were performed to improve the genome of Zhedong White goose and discover the critical genes, miRNAs, and pathways involved in goose skin and feather follicle morphogenesis. Sequencing output generated 6,002,591,668 to 8,675,720,319 clean reads from fifteen libraries. There were 1234, 3024, 4416, and 5326 different genes showing differential expression in four stages, E10 vs. E13, E10 vs. E18, E10 vs. E23, and E10 vs. E28, respectively. The differentially expressed genes (DEGs) were found to be implicated in multiple biological processes and pathways associated with feather growth and development, such as the Wnt signaling pathway, cell adhesion molecules, ECM–receptor interaction signaling pathways, and cell cycle and DNA replication pathways, according to functional analysis. In total, 8276 DEGs were assembled into twenty gene profiles with diverse expression patterns. The reliability of transcriptome results was verified by real-time quantitative PCR by selecting seven DEGs and five miRNAs. The localization of forkhead box O3 (FOXO3), connective tissue growth factor (CTGF), protein parched homolog1 (PTCH1), and miR-144-y by in situ hybridization showed spatial-temporal expression patterns and that FOXO3 and miR-144-y have an antagonistic targeting relationship. The correlation coefficient of FOXO3 and miR-144-y was -0.948, showing a strong negative correlation. Dual-luciferase reporter assay results demonstrated that miR-144-y could bind to the expected location to suppress the expression of FOXO3, which supports that there is a targeting relationship between them. The detections in this report will provide critical insight into the complex molecular mechanisms and breeding practices underlying the developmental characteristics of skin and feather follicles in Zhedong white geese.

Aging in the sebaceous gland

Sebaceous glands (SGs) originate from hair follicular stem cells and secrete lipids to lubricate the skin. The coordinated effects of intrinsic and extrinsic aging factors generate degradation of SGs at a late age. Senescence of SGs could be a mirror of the late aging of both the human body and skin. The procedure of SG aging goes over an initial SG hyperplasia at light-exposed skin areas to end with SG atrophy, decreased sebum secretion, and altered sebum composition, which is related to skin dryness, lack of brightness, xerosis, roughness, desquamation, and pruritus. During differentiation and aging of SGs, many signaling pathways, such as Wnt/β-catenin, c-Myc, aryl hydrocarbon receptor (AhR), and p53 pathways, are involved. Random processes lead to random cell and DNA damage due to the production of free radicals during the lifespan and neuroendocrine system alterations. Extrinsic factors include sunlight exposure (photoaging), environmental pollution, and cigarette smoking, which can directly activate signaling pathways, such as Wnt/β-catenin, Notch, AhR, and p53 pathways, and are probably associated with the de-differentiation and hyperplasia of SGs, or indirectly activate the abovementioned signaling pathways by elevating the inflammation level. The production of ROS during intrinsic SG aging is less, the signaling pathways are activated slowly and mildly, and sebocytes are still differentiated, yet terminal differentiation is not completed. With extrinsic factors, relevant signaling pathways are activated rapidly and fiercely, thus inhibiting the differentiation of progenitor sebocytes and even inducing the differentiation of progenitor sebocytes into keratinocytes. The management of SG aging is also mentioned.