An updated classification of hair follicle morphogenesis

Dynamic duo: Cell-extracellular matrix interactions in hair follicle development and regeneration

Ectodermal organs, such as hair follicles, originate from simple epithelial and mesenchymal sheets through a complex developmental process driven by interactions between these cell types. This process involves dermal condensation, placode formation, bud morphogenesis, and organogenesis, and all of these processes require intricate interactions among various tissues. Recent research has emphasized the crucial role of reciprocal and dynamic interactions between cells and the extracellular matrix (ECM), referred to as the "dynamic duo", in the development of ectodermal organs. These interactions provide spatially and temporally changing biophysical and biochemical cues within tissues. Using the hair follicle as an example, this review highlights two types of cell-ECM adhesion units-focal adhesion-type and hemidesmosome-type adhesion units-that facilitate communication between epithelial and mesenchymal cells. This review further explores how these adhesion units, along with other cell-ECM interactions, evolve during hair follicle development and regeneration, underscoring their importance in guiding both developmental and regenerative processes.

Study on the expression patterns of inner root sheath-specific genes in Tan sheep hair follicle during different developmental stages

By analyzing the expression patterns of inner root sheath (IRS) specific genes during different developmental stages of hair follicle (HF) in Tan sheep embryos and at birth, this study aims to reveal the influence of the IRS on crimped wool. Skin tissues from the scapular region of male Tan sheep were collected at 85 days (E85) and 120 days (E120) of fetal development, and at 0 days (D0), 35 days (D35), and 60 days (D60) after birth, with four samples at each stage. Real-time quantitative polymerase chain reaction (RT-qPCR) was employed to determine the relative expression levels of IRS type I keratin genes (KRT25, KRT26, KRT27, KRT28), type II keratin genes (KRT71, KRT72, KRT73, KRT74), and the trichohyalin gene (TCHH) in the skin of Tan sheep at different stages. Results showed that the expression levels of all IRS-specific genes peaked at D0, with the expression of all genes significantly higher than at E85 (P < 0.01), except for KRT73 and TCHH. The expression levels of KRT25, KRT26, and KRT72 were also significantly higher than at E120 (P < 0.01). Furthermore, the expression levels of KRT27, KRT28, KRT71, and KRT74 were significantly higher than both at E120 and D35 (P < 0.01). The expression levels of other genes at different stages showed no significant difference (P > 0.05). Conclusion: The IRS-specific genes exhibit the highest expression levels in Tan sheep at the neonatal stage. The expression levels of KRT71, KRT72, and TCHH, which are consistent with the pattern of wool crimp, may influence the morphology of the IRS and thereby affect the crimp of Tan sheep wool.

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 prenatal skin atlas reveals immune regulation of human skin morphogenesis

Human prenatal skin is populated by innate immune cells, including macrophages, but whether they act solely in immunity or have additional functions in morphogenesis is unclear. Here we assembled a comprehensive multi-omics reference atlas of prenatal human skin (7-17 post-conception weeks), combining single-cell and spatial transcriptomics data, to characterize the microanatomical tissue niches of the skin. This atlas revealed that crosstalk between non-immune and immune cells underpins the formation of hair follicles, is implicated in scarless wound healing and is crucial for skin angiogenesis. We systematically compared a hair-bearing skin organoid (SkO) model derived from human embryonic stem cells and induced pluripotent stem cells to prenatal and adult skin1. The SkO model closely recapitulated in vivo skin epidermal and dermal cell types during hair follicle development and expression of genes implicated in the pathogenesis of genetic hair and skin disorders. However, the SkO model lacked immune cells and had markedly reduced endothelial cell heterogeneity and quantity. Our in vivo prenatal skin cell atlas indicated that macrophages and macrophage-derived growth factors have a role in driving endothelial development. Indeed, vascular network remodelling was enhanced following transfer of autologous macrophages derived from induced pluripotent stem cells into SkO cultures. Innate immune cells are therefore key players in skin morphogenesis beyond their conventional role in immunity, a function they achieve through crosstalk with non-immune cells.

The molecular anatomy of cashmere goat hair follicle during cytodifferentiation stage

BACKGROUND

Cashmere, named as "soft gold", derives from the secondary hair follicles (SHFs) of cashmere goat which is vital to Northwest China's economy. The cytodifferentiation stage (E120), mirroring the complete hair follicle (HF) structure of adult goats and marking a critical phase in SHF development. Therefore, this study aims to enhance the understanding of SHF development and its impact on fiber quality, informing breeding strategies.

RESULTS

From the scRNA-seq data analysis, the intricate processes and transcriptional dynamics of inner layer cell differentiation of HFs were unveiled in this study. we identified nine cell populations during cytodifferentiation and key structures such as the hair shaft and inner root sheath. And we discovered three main inner layer lineages and seven subpopulations, clarifying their roles in specialization and signaling. Pseudotime mapping analysis showed cell evolution from early stage to mature stages marked by unique gene expressions, and the intermediate stage on the differentiation of each lineage was revealed. The identification and spatial localization of specific transcription factors, such as GATA3, LEF1 and PRDM1, as well as keratin genes highlight regulatory pathways involved in HF development, which was further validated by immunofluorescence. These findings suggested the potential strategies to improve fiber quality, and the discovery of diverse cell types and their developmental molecular mechanisms, particularly in this species-specific context, offered a nuanced view of the regulatory mechanisms driving HF development in cashmere goats.

CONCLUSION

Overall, these findings provide a systematic molecular atlas of skin, defining three major branches and cell states of inner layer cells of HF, and determining how the branch-specific transcription factors, keratins, and signals coordinate HF morphogenesis during cytodifferentiation stage. This research not only advances skin tissue research in goats but also holds broader implications for the understanding of HF regeneration and development across various species.

Radially patterned morphogenesis of murine hair follicle placodes ensures robust epithelial budding

The bending of simple cellular sheets into complex three-dimensional (3D) forms requires developmental patterning cues to specify where deformations occur, but how positional information directs morphological change is poorly understood. Here, we investigate how morphogen signaling and cell fate diversification contribute to the morphogenesis of murine hair placodes, in which collective cell movements transform radially symmetric primordia into bilaterally symmetric tubes. Through live imaging and 3D volumetric reconstructions, we demonstrate that Wnt and Shh establish radial patterns of cell fate, cell morphology, and movement within developing placodes. Cell fate diversity at different radial positions provides unique and essential contributions to placode morphogenesis. Further, we show that downstream of radial patterning, gradients of classical cadherin expression are required for efficient epithelial rearrangements. Given that the transformation of epithelial discs into 3D tubes is a common morphological motif used to shape diverse organ primordia, mechanisms of radially patterned morphogenesis are likely highly conserved across evolution.

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.

The overexpression of R-spondin 3 affects hair morphogenesis and hair development along with the formation and maturation of the hair follicle stem cells

Mice hair follicles (HFs) are a valuable model for studying various aspects of hair biology, including morphogenesis, development, and regeneration due to their easily observable phenotype and genetic manipulability. The initiation and progression of hair follicle morphogenesis, as well as the hair follicle cycle, are regulated by various signaling pathways, of which the main role is played by the Wingless-type MMTV integration site family (Wnt) and the Bone Morphogenic Protein (BMP). During the hair follicle cycle, the BMP pathway maintains hair follicle stem cells (HFSCs) in a dormant state while the Wnt pathway activates them for hair growth. Given the pivotal role of the Wnt pathway in hair biology and HFSCs regulation, we investigated the influence of the Wnt modulator - R-spondin 3 (Rspo3), in these processes. For this purpose, we developed a transgenic mice model with the overexpression of Rspo3 (Rspo3GOF) in the whole ectoderm and its derivatives, starting from early morphogenesis. Rspo3GOF mice exhibited a distinct phenotype with sparse hair and visible bald areas, caused by reduced proliferation and increased apoptosis of hair matrix progenitor cells, which resulted in a premature anagen-to-catagen transition with a shortened growth phase and decreased overall length of all hair types. In addition, Rspo3GOF promoted induction of auchene and awl, canonical Wnt-dependent hair type during morphogenesis, but the overall hair amount remained reduced. We also discovered a delay in the pre-bulge formation during morphogenesis and prolonged immaturity of the HFSC population in the bulge region postnatally, which further impaired proper hair regeneration throughout the mice's lifespan. Our data supported that Rspo3 function observed in our model works in HFSCs' formation of pre-bulge during morphogenesis via enhancing activation of the canonical Wnt pathway, whereas in contrast, in the postnatal immature bulge, activation of canonical Wnt signaling was attenuated. In vitro studies on keratinocytes revealed changes in proliferation, migration, and colony formation, highlighting the inhibitory effect of constitutive overexpression of Rspo3 on these cellular processes. Our research provides novel insights into the role of Rspo3 in the regulation of hair morphogenesis and development, along with the formation and maturation of the HFSCs, which affect hair regeneration.

The development of hair follicles and nail

The hair follicle and nail unit develop and regenerate through epithelial-mesenchymal interactions. Here, we review some of the key signals and molecular interactions that regulate mammalian hair follicle and nail formation during embryonic development and how these interactions are reutilized to promote their regeneration during adult homeostasis and in response to skin wounding. Finally, we highlight the role of some of these signals in mediating human hair follicle and nail conditions.

MicroRNA-181a Targets GNAI2 and Affects the Proliferation and Induction Ability of Dermal Papilla Cells: The Potential Involvement of the Wnt/β-Catenin Signaling Pathway

Wool is generated by hair follicles (HFs), which are crucial in defining the length, diameter, and morphology of wool fibers. However, the regulatory mechanism of HF growth and development remains largely unknown. Dermal papilla cells (DPCs) are a specialized cell type within HFs that play a crucial role in governing the growth and development of HFs. This study aims to investigate the proliferation and induction ability of ovine DPCs to enhance our understanding of the potential regulatory mechanisms underlying ovine HF growth and development. Previous research has demonstrated that microRNA-181a (miR-181a) was differentially expressed in skin tissues with different wool phenotypes, which indicated that miR-181a might play a crucial role in wool morphogenesis. In this study, we revealed that miR-181a inhibited the proliferation and induction ability of ovine DPCs by quantitative Real-time PCR (qRT-PCR), cell counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, and alkaline phosphatase staining. Then, we also confirmed G protein subunit alpha i2 (GNAI2) is a target gene of miR-181a by dual luciferase reporter assay, qRT-PCR, and Western blot, and that it could promote the proliferation and induction ability of ovine DPCs. In addition, GNAI2 could also activate the Wnt/β-Catenin signaling pathway in ovine DPCs. This study showed that miR-181a can inhibit the proliferation and induction ability of ovine DPCs by targeting GNAI2 through the Wnt/β-Catenin signaling pathway.

Shh Gene Regulates the Proliferation and Apoptosis of Dermal Papilla Cells to Affect Its Differential Expression in Secondary Hair Follicle Growth Cycle of Cashmere Goats

Sonic hedgehog (Shh) is a component of the Hedgehog signaling pathway, playing an important role in regulating cell proliferation, differentiation, apoptosis, and the repair of damaged organisms. To further clarify the expression pattern of Shh gene in the secondary hair follicle growth cycle of cashmere goats and its mechanism of action on secondary hair follicle papilla cells, and improve cashmere quality, in this study, we took Inner Mongolia Albas white cashmere goats as the research objects and collected skin samples at different growth stages to obtain secondary hair follicles, detected Shh and its gene expression by RT-qPCR, Western blot, immunohistochemistry, and other techniques, while we also cultured DPCs in vitro. Shh gene overexpression and interference vectors were constructed, and the effects of Shh gene on the proliferation and apoptosis of DPCs were studied through cell transfection technology. The results showed that there are significant differences in Shh and its gene expression in the secondary hair follicle growth cycle skins of cashmere goats, with the highest expression level in anagen, followed by catagen, and the lowest expression level in telogen. Shh was mainly expressed in the inner root sheath, outer root sheath, and secondary hair follicle papilla. After the overexpression of Shh gene, the proliferation and vitality of the hair papilla cells were enhanced compared to the interference group. After Shh gene interference, the apoptosis rate of the cells increased, indicating that Shh gene can regulate downstream Ptch, Smo, and Gli2 gene expression to promote the proliferation of DPCs, and thus form its expression pattern in the secondary hair follicle growth cycle of cashmere goats.

Pilose antler extracts promotes hair growth in androgenetic alopecia mice by activating hair follicle stem cells via the AKT and Wnt pathways

Background: Angrogenetic alopecia (AGA) is one of the most prevalent hair loss disorders worldwide. The hair follicle stem cell (HFSC) is closely related to the formation of hair follicle (HF) structure and HF self-renewal. The activation of HFSC in AGA is critical for hair growth. Pilose antler has been reported to have hair growth-promoting activity, but the mechanism of action on AGA and HFSC has not been reported. Methods: We previously extracted an active component from the pilose antler known as PAEs. In this study, we conducted experiments using AGA mice and HFSC. The effects of PAEs on hair growth in AGA mice were firstly detected, and then the mechanisms of PAEs for AGA were predicted by integrating network pharmacology and de novo transcriptomics data of pilose antler. Finally, biological experiments were used to validate the molecular mechanism of PAEs in treating AGA both in vivo and in vitro. Results: It was found that PAEs promoted hair regrowth by accelerating the activation of anagen, delaying the anagen-catagen transition. It also alleviated the morphological changes, such as hair shortening, thinning, miniaturization, and HF number reduction, and regulated the hair regeneration process of four subtypes of hair. We further found that PAEs could promote the proliferation of HFSC, outer root sheath (ORS) cells, and hair bulb cells in AGA mice. We then integrated network pharmacology and pilose antler transcriptomics data to predict that the mechanism of PAEs treatment in AGA mice is closely related to the PI3K-AKT/Wnt-β-Catenin pathways. Subsequently, it was also verified that PAEs could activate both pathways in the skin of AGA mice. In addition, we found that PAEs perhaps increased the number of blood vessels around dermal papilla (DP) in experiments in vivo. Meanwhile, the PAEs stimulated the HFSC proliferation in vitro and activated the AKT and Wnt pathways. However, the proliferative activity of HFSC was inhibited after blocking the Wnt pathway and AKT activity. Conclusion: This study suggests that the hair growth-promoting effect of PAEs in AGA mice may be closely related to the stimulation of the AKT and Wnt pathways, which in turn activates the proliferation of HFSC.

The Role of BMP7 in the Proliferation of Hu Sheep Dermal Papilla Cells Is Influenced by DNA Methylation

Previous studies have shown that the BMP7 gene is differentially expressed in Hu sheep lamb skin of different pattern types, and its expression level is significantly correlated with hair follicle indices of different pattern types, but the molecular mechanism of the differential expression of the BMP7 gene remains unclear. This study investigated the effect of DNA methylation on the transcriptional expression of BMP7. Firstly, we found that the mRNA expression of the BMP7 gene and the activity of the core promoter of the BMP7 gene were upregulated after 5-Aza-Deoxycytidine-induced demethylation treatment using qRT-PCR and double luciferase reporter assay. Then, we found that the proliferation of Hu sheep DPCs in vitro was promoted after 5-Aza-Deoxycytidine-induced demethylation treatment through qRT-PCR, CCK-8, and EdU assay, and that the overexpression of DNMT1 in DPCs induced the opposite effect. In addition, the results of the cell cycle assay reveal that the percentage of cells in the S phase was increased after 5-Aza-Deoxycytidine-induced demethylation treatment, and that the percentage of cells in the S phase was decreased after overexpression of DNMT1 in DPCs. This study indicated that the differential expression of the BMP7 gene in different patterns of Hu sheep lamb skin may be regulated by DNA methylation modification. In addition, DNA methylation can regulate the proliferation and cell cycle of DPCs in Hu sheep.

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.

Dermal β-Catenin Is Required for Hedgehog-Driven Hair Follicle Neogenesis

Hair follicle neogenesis (HFN) occurs after large skin excisions in mice, serving as a rare regenerative model in mammalian wound healing. Wound healing typically results in fibrosis in mice and humans. We previously showed that small skin excisions in mice result in scarring devoid of HFN, displaying features of nonregenerative healing, and hedgehog (Hh) activation in the dermis of such wounds can induce HFN. In this study, we sought to verify the role of dermal Wnt/β-catenin signaling in HFN because this pathway is essential for hair follicle development but is also paradoxically well-characterized in fibrosis of adult wounds. By deletion of β-catenin in large wound myofibroblasts, we show that Wnt/β-catenin signaling is required for endogenous mechanisms of HFN. By utilizing a combined mouse model that simultaneously induces deletion of β-catenin and constitutive activation of Smoothened in myofibroblasts, we also found that β-catenin is required for Hh-driven dermal papilla formation. Transcriptome analysis confirms that Wnt/β-catenin and Hh pathways are activated in dermal papilla cells. Our results indicate that Wnt-active fibrotic status may also create a permissive state for the regenerative function of Hh, suggesting that activation of both Wnt and Hh pathways in skin wound fibroblasts must be ensured in future strategies to promote HFN.

Integrating Single-Cell and Spatial Transcriptomics Reveals Heterogeneity of Early Pig Skin Development and a Subpopulation with Hair Placode Formation

The dermis and epidermis, crucial structural layers of the skin, encompass appendages, hair follicles (HFs), and intricate cellular heterogeneity. However, an integrated spatiotemporal transcriptomic atlas of embryonic skin has not yet been described and would be invaluable for studying skin-related diseases in humans. Here, single-cell and spatial transcriptomic analyses are performed on skin samples of normal and hairless fetal pigs across four developmental periods. The cross-species comparison of skin cells illustrated that the pig epidermis is more representative of the human epidermis than mice epidermis. Moreover, Phenome-wide association study analysis revealed that the conserved genes between pigs and humans are strongly associated with human skin-related diseases. In the epidermis, two lineage differentiation trajectories describe hair follicle (HF) morphogenesis and epidermal development. By comparing normal and hairless fetal pigs, it is found that the hair placode (Pc), the most characteristic initial structure in HFs, arises from progenitor-like OGN+/UCHL1+ cells. These progenitors appear earlier in development than the previously described early Pc cells and exhibit abnormal proliferation and migration during differentiation in hairless pigs. The study provides a valuable resource for in-depth insights into HF development, which may serve as a key reference atlas for studying human skin disease etiology using porcine models.

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.

Two mutations at KRT74 and EDAR synergistically drive the fine-wool production in Chinese sheep

INTRODUCTION

Fine-wool sheep are the most common breed used by the wool industry worldwide. Fine-wool sheep have over a three-fold higher follicle density and a 50% smaller fiber diameter than coarse-wool sheep.

OBJECTIVES

This study aims to clarify the underlying genetic basis for the denser and finer wool phenotype in fine-wool breeds.

METHOD

Whole-genome sequences of 140 samples, Ovine HD630K SNP array data of 385 samples, including fine, semi-fine, and coarse wool sheep, as well as skin transcriptomes of nine samples were integrated for genomic selection signature analysis.

RESULTS

Two loci at keratin 74 (KRT74) and ectodysplasin receptor (EDAR) were revealed. Fine-scale analysis in 250 fine/semi-fine and 198 coarse wool sheep narrowed this association to one C/A missense variant of KRT74 (OAR3:133,486,008, P = 1.02E-67) and one T/C SNP in the regulatory region upstream of EDAR (OAR3:61,927,840, P = 2.50E-43). Cellular over-expression and ovine skin section staining assays confirmed that C-KRT74 activated the KRT74 protein and specifically enlarged cell size at the Huxley's layer of the inner root sheath (P < 0.01). This structure enhancement shapes the growing hair shaft into the finer wool than the wild type. Luciferase assays validated that the C-to-T mutation upregulated EDAR mRNA expression via a newly created SOX2 binding site and potentially led to the formation of more hair placodes.

CONCLUSIONS

Two functional mutations driving finer and denser wool production were characterized and offered new targets for genetic breeding during wool sheep selection. This study not only provides a theoretical basis for future selection of fine wool sheep breeds but also contributes to improving the value of wool commodities.

Spatiotemporal Expression and Haplotypes Identification of KRT84 Gene and Their Association with Wool Traits in Gansu Alpine Fine-Wool Sheep

Keratin (K) is a major protein component of hair and is involved in hair growth and development. In this study, we analysed the expression, localization, and polymorphism of the K84 gene (KRT84) in Gansu Alpine Fine-wool sheep using immunofluorescence, RT-qPCR, and PARMS (penta-primer amplification refractory mutation system). Haplotypes of KRT84 were also constructed and their relationship with wool traits analysed. It was revealed that KRT84 was highly expressed in hair follicles, including the inner root sheath, outer root sheath, and hair medulla and at all six lamb ages investigated from 1 to 270 days of age. Three SNPs were detected in KRT84 exon 1, and they formed three haplotypes (named H1, H2, and H3) and six genotypes. Analyses revealed an association between haplotype combinations (diplotypes) and the mean fibre curvature, mean staple length, mean staple strength, mean fibre diameter, the coefficient of variation of fibre diameter, and comfort factor for these sheep. These results suggest that KRT84 is of importance in determining several key traits in Gansu Alpine Fine-wool sheep and that the gene could possibly be used as a genetic marker for wool trait selection in these sheep.

Local and systemic mechanisms that control the hair follicle stem cell niche

Hair follicles are essential appendages of the mammalian skin, as hair performs vital functions of protection, thermoregulation and sensation. Hair follicles harbour exceptional regenerative abilities as they contain multiple somatic stem cell populations such as hair follicle stem cells (HFSCs) and melanocyte stem cells. Surrounding the stem cells and their progeny, diverse groups of cells and extracellular matrix proteins are organized to form a microenvironment (called 'niche') that serves to promote and maintain the optimal functioning of these stem cell populations. Recent studies have shed light on the intricate nature of the HFSC niche and its crucial role in regulating hair follicle regeneration. In this Review, we describe how the niche serves as a signalling hub, communicating, deciphering and integrating both local signals within the skin and systemic inputs from the body and environment to modulate HFSC activity. We delve into the recent advancements in identifying the cellular and molecular nature of the niche, providing a holistic perspective on its essential functions in hair follicle morphogenesis, regeneration and ageing.

Preliminary study of melatonin in the proliferation and apoptosis of Hu sheep dermal papilla cells in vitro

Previous studies have shown that melatonin has a certain regulatory effect on the growth of sheep wool. However, the mechanism of melatonin action remains unknown. In the present study, we aimed to understand the role of exogenous melatonin in the dermal papilla cells of Hu sheep. To confirm the optimal melatonin treatment regimen for Hu sheep dermal papilla cells, we detected the cell viability by exposing them to different concentrations of melatonin and different treatment times. The results showed that cell viability was best when dermal papilla cells were treated with 1000 pg/ml of melatonin for 48 h. According to the results of qPCR, CCK-8, EDU, Western blot, and Flow cytometry analysis, we found that 1000 pg/ml melatonin promoted the proliferation and inhibited the apoptosis of dermal papilla cells compared with the exogenous melatonin blank group (control group). Furthermore, we also found that 1000 pg/ml of melatonin promoted the cell cycle progress of dermal papilla cells according to the results of qPCR and Flow cytometry analysis. Overall, our findings showed that melatonin plays an important role in the dermal papilla cells of Hu sheep.

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.

Morphogens enable interacting supracellular phases that generate organ architecture

During vertebrate organogenesis, increases in morphological complexity are tightly coupled to morphogen expression. In this work, we studied how morphogens influence self-organizing processes at the collective or "supra"-cellular scale in avian skin. We made physical measurements across length scales, which revealed morphogen-enabled material property differences that were amplified at supracellular scales in comparison to cellular scales. At the supracellular scale, we found that fibroblast growth factor (FGF) promoted "solidification" of tissues, whereas bone morphogenetic protein (BMP) promoted fluidity and enhanced mechanical activity. Together, these effects created basement membrane-less compartments within mesenchymal tissue that were mechanically primed to drive avian skin tissue budding. Understanding this multiscale process requires the ability to distinguish between proximal effects of morphogens that occur at the cellular scale and their functional effects, which emerge at the supracellular scale.

SOX18 Promotes the Proliferation of Dermal Papilla Cells via the Wnt/β-Catenin Signaling Pathway

SRY-box transcription factor 18 (SOX18) is known to play a crucial role in the growth and development of hair follicles (HF) in both humans and mice. However, the specific effect of SOX18 on sheep hair follicles remains largely unknown. In our previous study, we observed that SOX18 was specifically expressed within dermal papilla cells (DPCs) in ovine hair follicles, leading us to investigate its potential role in the growth of hair follicles in sheep. In the present study, we aimed to examine the effect of SOX18 in DPCs and preliminarily study its regulatory mechanism through RNA-seq. We initially found that the overexpression of SOX18 promoted the proliferation of DPCs compared to the negative control group, while the interference of SOX18 had the opposite effect. To gain further insight into the regulatory mechanism of SOX18, we conducted RNA-seq analysis after knocking down SOX18 in Hu sheep DPCs. The result showed that the Wnt/β-Catenin signaling pathway was involved in the growth process of DPC after SOX18 knockdown. Subsequently, we investigated the effect of SOX18 on the Wnt/β-Catenin signaling pathway in DPCs using TOP/FOP-flash, qRT-PCR, and Western blot (WB) analysis. Our data demonstrated that SOX18 could activate the Wnt/β-Catenin signaling pathway in DPCs. Additionally, we observed that SOX18 could rescue the proliferation of DPCs after inhibiting the Wnt/β-Catenin signaling pathway. These findings underscore the essential role of SOX18 as a functional molecule governing the proliferation of DPCs. Additionally, these findings also greatly enhance our understanding of the role of SOX18 in the proliferation of DPCs and the growth of wool in Hu sheep.

Spatial transcriptomics of a giant pilomatricoma

Pilomatricomas (PMs) are common benign adnexal tumors that show a predilection for the head and neck region and are characterized at the molecular level by activating mutations in the beta-catenin (CTNNB1) gene. Giant PMs are a rare histopathological variant, according to the World Health Organization, which are defined by a size greater than 4 cm and are reported to show upregulation of yes-associated protein compared to PMs of typical 1-3 cm size. We describe the case of a 67-year-old man with an 8 cm giant PM involving his temporal scalp, whose PM we characterized by 10X spatial gene expression analysis. This revealed five total transcriptomic clusters, including four distinct clusters within the giant PM, each with a unique transcriptional pattern of hair follicle-related factors, keratin gene expression, and beta-catenin pathway activity.

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.

Rapid mechanosensitive migration and dispersal of newly divided mesenchymal cells aid their recruitment into dermal condensates

Embryonic mesenchymal cells are dispersed within an extracellular matrix but can coalesce to form condensates with key developmental roles. Cells within condensates undergo fate and morphological changes and induce cell fate changes in nearby epithelia to produce structures including hair follicles, feathers, or intestinal villi. Here, by imaging mouse and chicken embryonic skin, we find that mesenchymal cells undergo much of their dispersal in early interphase, in a stereotyped process of displacement driven by 3 hours of rapid and persistent migration followed by a long period of low motility. The cell division plane and the elevated migration speed and persistence of newly born mesenchymal cells are mechanosensitive, aligning with tissue tension, and are reliant on active WNT secretion. This behaviour disperses mesenchymal cells and allows daughters of recent divisions to travel long distances to enter dermal condensates, demonstrating an unanticipated effect of cell cycle subphase on core mesenchymal behaviour.

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

BFNB Enhances Hair Growth in C57BL/6 Mice through the Induction of EGF and FGF7 Factors and the PI3K-AKT-β-Catenin Pathway

The objective of this study was to investigate the potential effects of a formulation derived from the bioactive fraction of nanostructured Bacopa procumbens (BFNB) on the promotion of hair growth in C57BL/6 mice. The characterization of the follicular phases and histomorphological analysis showed that the topical application of the formulation for 15 days significantly increased pigmentation and hair growth on the dorsum and head of the mice. Additionally, an acceleration of the follicular cycle phases was observed, along with an increase in the number of follicles, hair length, and diameter, compared to mice treated with minoxidil. In silico analysis and molecular characterization demonstrated that BFNB enhances the expression of epidermal growth factor (EGF) and fibroblast growth factor 7 (FGF7), activating the PI3K-AKT-β-catenin signaling pathway, as well as the expression of PCNA, KI-67, Cyclin D1, and Cyclin E, regulating the cell cycle and cell proliferation, crucial events for hair regeneration. Our results strongly suggest the utility of BFNB as a therapeutic alternative to stimulate hair growth and promote hair health.

Transcriptomic landscape reveals germline potential of porcine skin-derived multipotent dermal fibroblast progenitors

According to estimations, approximately about 15% of couples worldwide suffer from infertility, in which individuals with azoospermia or oocyte abnormalities cannot be treated with assisted reproductive technology. The skin-derived stem cells (SDSCs) differentiation into primordial germ cell-like cells (PGCLCs) is one of the major breakthroughs in the field of stem cells intervention for infertility treatment in recent years. However, the cellular origin of SDSCs and their dynamic changes in transcription profile during differentiation into PGCLCs in vitro remain largely undissected. Here, the results of single-cell RNA sequencing indicated that porcine SDSCs are mainly derived from multipotent dermal fibroblast progenitors (MDFPs), which are regulated by growth factors (EGF/bFGF). Importantly, porcine SDSCs exhibit pluripotency for differentiating into three germ layers and can effectively differentiate into PGCLCs through complex transcriptional regulation involving histone modification. Moreover, this study also highlights that porcine SDSC-derived PGCLCs specification exhibit conservation with the human primordial germ cells lineage and that its proliferation is mediated by the MAPK signaling pathway. Our findings provide substantial novel insights into the field of regenerative medicine in which stem cells differentiate into germ cells in vitro, as well as potential therapeutic effects in individuals with azoospermia and/or defective oocytes.

Novel recombinant R-spondin1 promotes hair regeneration by targeting the Wnt/β-catenin signaling pathway

Roof plate-specific spondin 1 (R-spondin1, RSPO1) is a Wnt/β-catenin signaling pathway activator that binds with Wnt ligands to stimulate the Wnt/β-catenin signaling pathway, which is key to hair regeneration. However, it is not clear whether recombinant RSPO1 (rRSPO1) affects hair regeneration. Here, we treat C57BL/6 male mice with rRSPO1 and investigate the expression of the Wnt/β-catenin signaling pathway and the activation of hair follicle stem cells in the dorsal skin. The mouse skin color score and hair-covered area are determined to describe hair growth, and the skin samples are subjected to H&E staining, western blot analysis and immunofluorescence staining to evaluate hair follicle development and the expressions of Wnt/β-catenin signaling pathway-related proteins. We find that rRSPO1 activates mouse hair follicle stem cells (mHFSCs) and accelerates hair regeneration. rRSPO1 increases the hair-covered area, the number of hair follicles, and the hair follicle diameter and length. Moreover, rRSPO1 enhances the activity of Wnt/β-catenin signaling pathway-related proteins and the expressions of HFSC markers, as well as mHFSC viability. These results indicate that subcutaneous injection of rRSPO1 can improve hair follicle development by activating the Wnt/β-catenin signaling pathway, thereby promoting hair regeneration. This study demonstrates that rRSPO1 has the potential to treat hair loss by activating the Wnt/β-catenin signaling pathway.

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.

An optimized force-triggered density gradient sedimentation method for isolation of pelage follicle dermal papilla cells from neonatal mouse skin

BACKGROUND

The dermal papilla cells are a specialized population of mesenchymal cells located at the base of the hair follicle (HF), which possess the capacity to regulate HF morphogenesis and regeneration. However, lack of cell-type specific surface markers restricts the isolation of DP cells and application for tissue engineering purposes.

METHODS

We describe a novel force-triggered density gradient sedimentation (FDGS) method to efficiently obtain purified follicular DP-spheres cells from neonatal mouse back skin, utilizing only centrifugation and optimized density gradients.

RESULTS

Expression of characteristic DP cell markers, alkaline phosphatase, β-catenin, versican, and neural cell adhesion molecules, were confirmed by immunofluorescence. Further, the patch assays demonstrated that DP cells maintained their hair regenerative capacity in vivo. Compared with current methods, including microdissection and fluorescence-activated cell sorting, the FDGS technique is simpler and more efficient for isolating DP cells from neonatal mouse skin.

CONCLUSIONS

The FDGS method will improve the research potential of neonatal mouse pelage-derived DP cells for tissue engineering purposes.

Melatonin promotes the development of the secondary hair follicles by regulating circMPP5

BACKGROUND

The quality and yield of cashmere fibre are closely related to the differentiation and development of secondary hair follicles in the skin of cashmere goats. The higher the density of secondary hair follicles, the higher the quality and yield of cashmere from the fleece. Development of secondary hair follicles commences in the embryonic stage of life and is completed 6 months after birth. Preliminary experimental results from our laboratory showed that melatonin (MT) treatment of goat kids after their birth could increase the density of secondary hair follicles and, thus, improve the subsequent yield and quality of cashmere. These changes in the secondary hair follicles resulted from increases in levels of antioxidant and expression of anti-apoptotic protein, and from a reduction in apoptosis. The present study was conducted to explore the molecular mechanism of MT-induced secondary hair follicle differentiation and development by using whole-genome analysis.

RESULTS

MT had no adverse effect on the growth performance of cashmere kids but significantly improved the character of the secondary hair follicles and the quality of cashmere, and this dominant effect continued to the second year. Melatonin promotes the proliferation of secondary hair follicle cells at an early age. The formation of secondary hair follicles in the MT group was earlier than that in the control group in the second year. The genome-wide data results involved KEGG analysis of 1044 DEmRNAs, 91 DElncRNAs, 1054 DEcircRNAs, and 61 DEmiRNAs which revealed that the mitogen-activated protein kinase (MAPK) signaling pathway is involved in the development of secondary hair follicles, with key genes (FGF2, FGF21, FGFR3, MAPK3 (ERK1)) being up-regulated and expressed. We also found that the circMPP5 could sponged miR-211 and regulate the expression of MAPK3.

CONCLUSIONS

We conclude that MT achieves its effects by regulating the MAPK pathway through the circMPP5 sponged the miR-211, regulating the expression of MAPK3, to induce the differentiation and proliferation of secondary hair follicle cells. In addition there is up-regulation of expression of the anti-apoptotic protein causing reduced apoptosis of hair follicle cells. Collectively, these events increase the numbers of secondary hair follicles, thus improving the production of cashmere from these goats.

The developmental basis of fingerprint pattern formation and variation

Fingerprints are complex and individually unique patterns in the skin. Established prenatally, the molecular and cellular mechanisms that guide fingerprint ridge formation and their intricate arrangements are unknown. Here we show that fingerprint ridges are epithelial structures that undergo a truncated hair follicle developmental program and fail to recruit a mesenchymal condensate. Their spatial pattern is established by a Turing reaction-diffusion system, based on signaling between EDAR, WNT, and antagonistic BMP pathways. These signals resolve epithelial growth into bands of focalized proliferation under a precociously differentiated suprabasal layer. Ridge formation occurs as a set of waves spreading from variable initiation sites defined by the local signaling environments and anatomical intricacies of the digit, with the propagation and meeting of these waves determining the type of pattern that forms. Relying on a dynamic patterning system triggered at spatially distinct sites generates the characteristic types and unending variation of human fingerprint patterns.

One-step generation of core-shell biomimetic microspheres encapsulating double-layer cells using microfluidics for hair regeneration

Tissue engineering of hair follicles (HFs) has enormous potential in the treatment of hair loss. HF morphogenesis is triggered by reciprocal interactions between HF germ epithelial and mesenchymal layers. Here, a microfluidic-assisted technology is developed for the preparation of double aqueous microdroplets that entrap double-layer cells and growth factors to ultimately be used for hair regeneration. Mouse mesenchymal cells (MSCs) and epidermal cells (EPCs) are encapsulated in gelatin methacrylate (GelMA) cores and photo-curable catechol-grafted hyaluronic acid (HAD) shells to fabricate GelMA-MSC/HAD-EPC (G/HAD) microspheres. The findings show that the G/HAD microspheres exhibit ultrafast gelation, aqueous phase separation, superior biocompatibility, and favorable wet adhesion properties. G/HAD microspheres can also support cell proliferation and sustain growth factor release. These composite cell microspheres are capable of efficient HF generation upon transplantation into the dorsal dermis of nude mice. This finding facilitates the large-scale preparation of approximately 80 double-layer cell spheres per min. This simple double-layer cell sphere preparation approach is a promising strategy for improving current hair-regenerative medicine techniques and can potentially be applied along with other organoid techniques for extended applications.

Skin-on-a-chip strategies for human hair follicle regeneration

The number of hair loss patients increases every year, and hair loss treatment has several limitations, so research on hair is attracting attention recently. However, most current hair follicle research models are limited by their inability to replicate several key functions of the hair follicle microenvironment. To complement this, an in vitro culture system similar to the in vivo environment must be constructed. It is necessary to develop a hair-on-a-chip that implements a fully functional hair follicle model by reproducing the main characteristics of hair follicle morphogenesis and cycle. In this review, we summarize the gradation of hair follicle morphogenesis and the roles and mechanisms of molecular signals involved in the hair follicle cycle. In addition, we discuss research results of various in vitro organoid products and organ-on-a-chip-based hair follicle tissue chips for the treatment of alopecia and present future research and development directions.

Distinct bulge stem cell populations maintain the pilosebaceous unit in a β-catenin-dependent manner

The pilosebaceous unit (PSU) is composed of multiple compartments and the self-renewal of PSU depends on distinct hair follicle stem cell (HFSC) populations. However, the differential roles of the HFSCs in sebaceous gland (SG) renewal have not been completely understood. Here, we performed multiple lineage tracing analysis to unveil the contribution of different HFSC populations to PSU regeneration during the hair cycle and wound healing. Our results indicated that the upper bulge stem cells contributed extensively to the SG replenishment during hair cycling, while HFSCs in the lower bugle did not. During skin wound healing, all HFSC populations participated in the SG replenishment. Moreover, β-catenin activation promoted the contribution of HFSCs to SG replenishment, whereas β-catenin deletion substantially repressed the event. Thus, our findings indicated that HFSCs contributed to SG replenishment in a β-catenin-dependent manner.

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.

The origins of skin diversity: lessons from dermal fibroblasts

Skin is largely composed of an epidermis that overlies a supporting dermis. Recent advancements in our understanding of how diverse groups of dermal fibroblasts regulate epidermal and hair follicle growth and differentiation have been fueled by tools capable of resolving molecular heterogeneity at a single-cell level. Fibroblast heterogeneity can be traced back to their developmental origin before their segregation into spatially distinct fibroblast subtypes. The mechanisms that drive this lineage diversification during development are being unraveled, with studies showing that both large- and small-scale positional signals play important roles during dermal development. Here, we first delineate what is known about the origins of the dermis and the central role of Wnt/β-catenin signaling in its specification across anatomical locations. We then discuss how one of the first morphologically recognizable fibroblast subtypes, the hair follicle dermal condensate lineage, emerges. Leveraging the natural variation of skin and its appendages between species and between different anatomical locations, these collective studies have identified shared and divergent factors that contribute to the extraordinary diversity of skin.

Tracing the developmental origin of tissue stem cells

Tissue stem cells are vital for organ homeostasis and regeneration owing to their ability to self-renew and differentiate into the various cell types that constitute organ tissue. These stem cells are formed during complex and dynamic organ development, necessitating spatial-temporal coordination of morphogenetic events and cell fate specification during this process. In recent years, technological advances have enabled the tracing of the cellular dynamics, states, and lineages of individual cells over time in relation to tissue morphological changes. These dynamic data have not only revealed the origin of tissue stem cells in various organs but have also led to an understanding of the molecular, cellular, and biophysical bases of tissue stem cell formation. Herein, we summarize recent findings on the developmental origin of tissue stem cells in the hair follicles, intestines, brain, skeletal muscles, and hematopoietic system, and further discuss how stem cell fate specification is coordinated with tissue topology.

Sebaceous immunobiology - skin homeostasis, pathophysiology, coordination of innate immunity and inflammatory response and disease associations

This review presents several aspects of the innovative concept of sebaceous immunobiology, which summarizes the numerous activities of the sebaceous gland including its classical physiological and pathophysiological tasks, namely sebum production and the development of seborrhea and acne. Sebaceous lipids, which represent 90% of the skin surface lipids in adolescents and adults, are markedly involved in the skin barrier function and perifollicular and dermal innate immune processes, leading to inflammatory skin diseases. Innovative experimental techniques using stem cell and sebocyte models have clarified the roles of distinct stem cells in sebaceous gland physiology and sebocyte function control mechanisms. The sebaceous gland represents an integral part of the pilosebaceous unit and its status is connected to hair follicle morphogenesis. Interestingly, professional inflammatory cells contribute to sebocyte differentiation and homeostasis, whereas the regulation of sebaceous gland function by immune cells is antigen-independent. Inflammation is involved in the very earliest differentiation changes of the pilosebaceous unit in acne. Sebocytes behave as potent immune regulators, integrating into the innate immune responses of the skin. Expressing inflammatory mediators, sebocytes also contribute to the polarization of cutaneous T cells towards the Th17 phenotype. In addition, the immune response of the perifollicular infiltrate depends on factors produced by the sebaceous glands, mostly sebaceous lipids. Human sebocytes in vitro express functional pattern recognition receptors, which are likely to interact with bacteria in acne pathogenesis. Sex steroids, peroxisome proliferator-activated receptor ligands, neuropeptides, endocannabinoids and a selective apoptotic process contribute to a complex regulation of sebocyte-induced immunological reaction in numerous acquired and congenital skin diseases, including hair diseases and atopic dermatitis.

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.

Vertebrate extracellular matrix protein hemicentin-1 interacts physically and genetically with basement membrane protein nidogen-2

Hemicentins are large proteins of the extracellular matrix that belong to the fibulin family and play pivotal roles during development and homeostasis of a variety of invertebrate and vertebrate tissues. However, bona fide interaction partners of hemicentins have not been described as yet. Here, applying surface plasmon resonance spectroscopy and co-immunoprecipitation, we identify the basement membrane protein nidogen-2 (NID2) as a binding partner of mouse and zebrafish hemicentin-1 (HMCN1), in line with the formerly described essential role of mouse HMCN1 in basement membrane integrity. We show that HMCN1 binds to the same protein domain of NID2 (G2) as formerly shown for laminins, but with an approximately 3.5-fold lower affinity and in a competitive manner. Furthermore, immunofluorescence and immunogold labeling revealed that HMCN1/Hmcn1 is localized close to basement membranes and in partial overlap with NID2/Nid2a in different tissues of mouse and zebrafish. Genetic knockout and antisense-mediated knockdown studies in zebrafish further show that loss of Nid2a leads to similar defects in fin fold morphogenesis as the loss of Laminin-α5 (Lama5) or Hmcn1. Finally, combined partial loss-of-function studies indicated that nid2a genetically interacts with both hmcn1 and lama5. Together, these findings suggest that despite their mutually exclusive physical binding, hemicentins, nidogens, and laminins tightly cooperate and support each other during formation, maintenance, and function of basement membranes to confer tissue linkage.

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.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Self-assembled complete hair follicle organoids by coculture of neonatal mouse epidermal cells and dermal cells in Matrigel

BACKGROUND

3D organoid cultures of hair follicles (HFs) are powerful models that mimic native HF for both in-depth study of HF disease and precision therapy. However, few studies have investigated the complete structure and properties of HF organoids. To investigate and characterize the complete HF organoids self-assembled by coculture of neonatal mouse epidermal cells (MECs) and dermal cells in Matrigel.

METHODS

Fresh epidermal and dermal cells from newborn mice (n=4) were isolated, and cocultured (1:1 ratio) in Matrigel using DMEM/F12 medium for 1 week. During the culture, an inverted microscope was used to observe the morphology of the 3D constructs. After 1 week, hematoxylin-eosin (HE) and immunofluorescence (IF) staining of HF-related markers (K5, K73, AE13, and K10), HF stem cell markers (K15, CD34, CD49f), skin-derived precursor-related marker (Nestin), and dermal papillae (DP)-specific markers (SOX2 and ALP) was performed in the harvested constructs to identify the HF organoids.

RESULTS

Epidermal and dermal cells self-assembled into HF organoids comprising an infundibular cyst-like structure, a lower segment-like structure, and a bulb-like structure from tail to root. The HF organoid had multiple, well-defined compartments similar to native anagen HF. Of the three segments, K73 was expressed in the inner root sheath-like layer, AE13 was localized in the hair shaft-like structure, K5, K15, CD34, and CD49f were present in the outer root sheath-like layer, Nestin labeled the connective tissue sheath-like layer, and SOX2 and ALP were expressed in the DP-like structure. Furthermore, K10 and K73 were expressed in the infundibular cyst-like structure. The expression of these molecular proteins was consistent with native anagen HF.

CONCLUSIONS

The complete HF organoid regenerated in Matrigel has specific compartments and is an excellent model to study HF disease and precision therapy.

Reawakening GDNF's regenerative past in mice and humans

The ability of an animal to regenerate lost tissue and body parts has obviously life-saving implications. Understanding how this ability became restricted or active in specific animal lineages will help us understand our own regeneration. According to phylogenic analysis, the glial cell line-derived neurotrophic factor (GDNF) signaling pathway, but not other family members, is conserved in axolotls, a salamander with remarkable regenerative capacity. Furthermore, comparing the pro-regenerative Spiny mouse to its less regenerative descendant, the House mouse, revealed that the GDNF signaling pathway, but not other family members, was induced in regenerating Spiny mice. According to GDNF receptor expression analysis, GDNF may promote hair follicle neogenesis – an important feature of skin regeneration – by determining the fate of dermal fibroblasts as part of new hair follicles. These findings support the idea that GDNF treatment will promote skin regeneration in humans by demonstrating the GDNF signaling pathway's ancestral and cellular nature.

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In pro-regenerative axolotls, the GDNF-GFR□1 signaling system is conserved.

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In pro-regenerative Spiny mice, the GDNF-GFR□1 signaling system is activated.

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In mice, GDNF targets upper-regeneration-competent dermal fibroblasts.

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GDNF-GFR□1 activation may promote skin regeneration in mice and humans.

miR-29a-5p Inhibits Prenatal Hair Placode Formation Through Targeting EDAR by ceRNA Regulatory Network

Hair placode formation is an important stage of hair follicle morphogenesis and it is a complex process facilitated by non-coding RNAs. In this study, we conducted whole transcriptome sequencing analysis of skin, heart, liver, lung, and kidney tissues of day 41 (E41) normal and hairless pig embryos, and respectively detected 15, 8, and 515 skin-specific differentially expressed (DE) lncRNAs, miRNAs, and mRNAs. Furthermore, 18 competing endogenous RNA (ceRNA) networks were constructed. Following weighted gene co-expression network analysis (WGCNA) of stages E39, E41, E45, E52, and E60, between normal and hairless pig embryos, only two ceRNAs (lncRNA2162.1/miR-29a-5p/BMPR1b and lncRNA627.1/miR-29a-5p/EDAR) that showed period-specific differential expression in E41 skin were retained. Dual-luciferase reporter assays further indicated that EDAR was a direct, functioning target of miR-29a-5p and that no binding site was found in BMPR1b. Moreover, miR-29a-5p overexpression inhibited the mRNA and protein expression of EDAR while no significant differential expression of BMPR1b was detected. In addition, over-expressed lncRNA627.1 reduces the expression of miR-29a-5p and increase EDAR expression while inhibits lncRNA627.1 resulted in a opposite expression trend. Cell proliferation result demonstrated that lower expression of EDAR and lncRNA627.1 inhibited hair placode precursor cells (HPPCs) proliferation in a manner similar to that shown by over-expressed miR-29a-5p. This study identified that miR-29a-5p inhibited HPPCs proliferation via the suppression of EDAR expression in the EDA/EDAR signaling pathway, while lncRNA627.1 rescues EDAR expression. Our study provides a basis for a better understanding of the mechanisms underlying the ceRNA complex, miR29a-5p/EDAR/lncRNA627.1, that could regulate hair placode formation, which may help decipher diseases affecting human hair.