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Since their invention, tissue expanders, which are designed to trigger additional skin growth, have revolutionised many reconstructive surgeries. Currently, however, the sole quantitative method to assess skin growth requires skin excision. Thus, in the context of patient outcomes, a machine learning method which uses non-invasive measurements to predict in vivo skin growth and other skin properties, holds significant value. In this study, the finite element method was used to simulate a typical skin expansion protocol and to perform various simulated wave propagation experiments during the first few days of expansion on 1,000 individual virtual subjects. An artificial neural network trained on this dataset was shown to be capable of predicting the future skin growth at 7 days (avg. R 2 = 0.9353 ) as well as the subject-specific shear modulus ( R 2 = 0.9801 ), growth rate ( R 2 = 0.8649 ), and natural pre-stretch ( R 2 = 0.9783 ) with a very high degree of accuracy. The method presented here has implications for the real-time prediction of patient-specific skin expansion outcomes and could facilitate the development of patient-specific protocols., (© 2024. The Author(s).)

Supraphysiological stretches are exploited in skin expanders to induce tissue growth for autologous implants. As pregnancy is associated with large levels of sustained stretch, we investigated whether skin growth occurs in pregnancy. Therefore, we combined a mechanical model of skin and the observations from suction experiments on several body locations of five pregnant women at different gestational ages. The measurements show a continuous increase in stiffness, with the largest change observed during the last trimester. A comparison with numerical simulations indicates that the measured increase in skin stiffness is far below the level expected for the corresponding deformation of abdominal skin. A new set of simulations accounting for growth could rationalize all observations. The predicted amount of tissue growth corresponds to approximately 40% area increase before delivery. The results of the simulations also offered the opportunity to investigate the biophysical cues present in abdominal skin along gestation and to compare them with those arising in skin expanders. Alterations of the skin mechanome were quantified, including tissue stiffness, hydrostatic and osmotic pressure of the interstitial fluid, its flow velocity and electrical potential. The comparison between pregnancy and skin expansion highlights similarities as well as differences possibly influencing growth and remodeling., (© 2024. The Author(s).)

Morphogens induce variations in tissue mechanics to promote feather budding.

Periodic patterns drive the formation of a variety of tissues, including skin appendages such as feathers and scales. Skin appendages serve important and diverse functions across vertebrates, yet the mechanisms that regulate their patterning are not fully understood. Here, we have used live imaging to investigate dynamic signals regulating the ontogeny of zebrafish scales. Scales are bony skin appendages that develop sequentially along the anterior-posterior and dorsal-ventral axes to cover the fish in a hexagonal array. We have found that scale development requires cell-cell communication and is coordinated through an active wave mechanism. Using a live transcriptional reporter, we show that a wave of Eda/NF-κB activity precedes scale initiation and is required for scale formation. Experiments decoupling the propagation of the wave from dermal placode formation and osteoblast differentiation demonstrate that the Eda/NF-κB activity wavefront controls the timing of the sequential patterning of scales. Moreover, this decoupling resulted in defects in scale size and significant deviations in the hexagonal patterning of scales. Thus, our results demonstrate that a biochemical traveling wave coordinates scale initiation and proper hexagonal patterning across the fish body., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Uniquely among mammalian organs, skin is capable of marked size change in adults, yet the mechanisms underlying this notable capacity are unclear. Here, we use a system of controlled tissue expansion in mice to uncover cellular and molecular determinants of skin growth. Through machine learning-guided three-dimensional tissue reconstruction, we capture morphometric changes in growing skin. We find that most growth is driven by the proliferation of the epidermis in response to mechanical tension, with more limited changes in dermal and subdermal compartments. Epidermal growth is achieved through preferential activation and differentiation of Lgr6 + stem cells of the epidermis, driven in part by the Hippo pathway. By single-cell RNA sequencing, we uncover further changes in mechanosensitive and metabolic pathways underlying growth control in the skin. These studies point to therapeutic strategies to enhance skin growth and establish a platform for understanding organ size dynamics in adult mammals.

Palmoplantar skin has several unique characteristics such as increased thickness, high resilience, hypopigmentation, and lack of hair follicles. The establishment of palmoplantar identity occurs through keratinocyte‒fibroblast interactions, with keratin 9 expression and Wnt signaling playing key roles. Understanding how palmoplantar features develop may help efforts to reproduce them at both palmoplantar and nonpalmoplantar body sites., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Although proliferation of keratinocytes, a major type of skin cells, is a key factor in maintaining the function of skin, their ability to proliferate tends to diminish with age. To solve such a problem, researchers in medical and skin cosmetic fields have tried to utilize epidermal growth factor (EGF), but achieved limited success. Therefore, a small natural compound that can mimic the activity of EGF is highly desired in both medical and cosmetic fields. Here, using the modified biosensor system, we observed that natural small-compound isoprocurcumenol, which is a terpenoid molecule derived from turmeric, can activate EGFR signaling. It increased the phosphorylation of ERK and AKT, and upregulated the expression of genes related to cell growth and proliferation, such as c-myc , c-jun , c-fos , and egr-1 . In addition, isoprocurcumenol induced the proliferation of keratinocytes in both physical and UVB-induced cellular damage, indicative of its function in skin regeneration. These findings reveal that EGF-like isoprocurcumenol promotes the proliferation of keratinocytes and further suggest its potential as an ingredient for medical and cosmetics use.

Intricate color patterns are a defining aspect of morphological diversity in the Felidae. We applied morphological and single-cell gene expression analysis to fetal skin of domestic cats to identify when, where, and how, during fetal development, felid color patterns are established. Early in development, we identify stripe-like alterations in epidermal thickness preceded by a gene expression pre-pattern. The secreted Wnt inhibitor encoded by Dickkopf 4 plays a central role in this process, and is mutated in cats with the Ticked pattern type. Our results bring molecular understanding to how the leopard got its spots, suggest that similar mechanisms underlie periodic color pattern and periodic hair follicle spacing, and identify targets for diverse pattern variation in other mammals., (© 2021. The Author(s).)

Thyroid hormone is a key regulator of post-embryonic vertebrate development. Skin is a biomedically important thyroid hormone target organ, but the cellular and molecular mechanisms underlying skin pathologies associated with thyroid dysfunction remain obscure. The transparent skin of zebrafish is an accessible model system for studying vertebrate skin development. During post-embryonic development of the zebrafish, scales emerge in the skin from a hexagonally patterned array of dermal papillae, like other vertebrate skin appendages such as feathers and hair follicles. We show here that thyroid hormone regulates the rate of post-embryonic dermal development through interaction with nuclear hormone receptors. This couples skin development with body growth to generate a well ordered array of correctly proportioned scales. This work extends our knowledge of thyroid hormone actions on skin by providing in-vivo evidence that thyroid hormone regulates multiple aspects of dermal development., (Copyright © 2021. Published by Elsevier Inc.)

The epidermal differentiation complex (EDC) encodes a group of unique proteins expressed in late epidermal differentiation. The EDC gave integuments new physicochemical properties and is critical in evolution. Recently, we showed β-keratins, members of the EDC, undergo gene cluster switching with overexpression of SATB2 (Special AT-rich binding protein-2), considered a chromatin regulator. We wondered whether this unique regulatory mechanism is specific to β-keratins or may be derived from and common to EDC members. Here we explore (1) the systematic expression patterns of non-β-keratin EDC genes and their preferential expression in different skin appendages during development, (2) whether the expression of non-β-keratin EDC sub-clusters are also regulated in clusters by SATB2. We analyzed bulk RNA-seq and ChIP-seq data and also evaluated the disrupted expression patterns caused by overexpressing SATB2. The results show that the expression of whole EDDA and EDQM sub-clusters are possibly mediated by enhancers in E14-feathers. Overexpressing SATB2 down-regulates the enriched EDCRP sub-cluster in feathers and the EDCH sub-cluster in beaks. These results reveal the potential of complex epigenetic regulation activities within the avian EDC, implying transcriptional regulation of EDC members acting at the gene and/or gene cluster level in a temporal and skin regional-specific fashion, which may contribute to the evolution of diverse avian integuments.

Scarless skin regeneration remains a challenge due to the complicated microenvironment involved in wound healing. Here, the hydrophobic drug, asiaticoside (AC), was loaded inside silk nanofiber hydrogels to achieve bioactive and injectable matrices for skin regeneration. AC was dispersed in aqueous silk nanofiber hydrogels with retention of biological functions that regulated inflammatory reactions and vascularization in vitro. After implantation in full-thickness wound defects, these AC-laden hydrogel matrices achieved scarless wound repair. Inflammatory reactions and angiogenesis were regulated during inflammation and remodeling, which was responsible for wound regeneration similar to normal skin. Both in vitro and in vivo studies demonstrated promising applications of these AC-laden silk hydrogels towards scarless tissue regeneration.

Background: Skinboosters represent the latest category of hyaluronan (HA) hydrogels released for aesthetic purposes. Different from originally developed gels, they are intended for more superficial injections, claiming a skin rejuvenation effect through hydration and possibly prompting biochemical effects in place of the conventional volumetric action. Here, three commercial skinboosters were characterized to unravel the scientific basis for such indication and to compare their performances., Methods: Gels were evaluated for water-soluble/insoluble-HA composition, rheology, hydration, cohesivity, stability and effect, in vitro, on human dermal fibroblasts towards the production of extracellular matrix components., Results: Marked differences in the insoluble-hydrogel amount and in the hydrodynamic parameters for water-soluble-HA chains were evidenced among the gels. Hydration, rigidity and cohesivity also varied over a wide range. Sensitivity to hyaluronidases and Reactive Oxygen Species was demonstrated allowing a stability ranking. Slight differences were found in gels' ability to prompt elastin expression and in ColIV/ColI ratio., Conclusions: A wide panel of biophysical and biochemical parameters for skinboosters was provided, supporting clinicians in the conscious tuning of their use. Data revealed great variability in gels' behavior notwithstanding the same clinical indication and unexpected similarities to the volumetric formulations. Data may be useful to improve customization of gel design toward specific uses.

In vitro skin tissue engineering is challenging due to the manifold differences between the in vivo and in vitro conditions. Yet, three-dimensional (3D) human skin equivalents (HSEs) are able to mimic native human skin in many fundamental aspects. However, the epidermal lipid barrier formation, which is essential for the functionality of the skin barrier, remains compromised. Recently, HSEs with an improved lipid barrier formation were generated by (i) incorporating chitosan in the dermal collagen matrix, (ii) reducing the external oxygen level to 3%, and (iii) inhibiting the liver X receptor (LXR). In this study, we aimed to determine the synergic effects in full-thickness models (FTMs) with combinations of these factors as single-, double-, and triple-targeted optimization approaches. The collagen-chitosan FTM supplemented with the LXR inhibitor showed improved epidermal morphogenesis, an enhanced lipid composition, and a better lipid organization. Importantly, barrier functionality was improved in the corresponding approach. In conclusion, our leading optimization approach substantially improved the epidermal morphogenesis, barrier formation, and functionality in the FTM, which therefore better resembled native human skin.

A proper skin barrier function requires constant formation of stratum corneum, i.e. the outermost layer of epidermis composed of terminally differentiated keratinocytes. The complex process of converting proliferative basal keratinocytes into corneocytes relies on programmed changes in the activity of many well-established genes. Much remains however to be investigated about this process, e.g. in conjunction with epidermal barrier defects due to genetic errors as in ichthyosis. To this end, we re-analyzed two sets of microarray-data comparing altered gene expression in differentiated vs. proliferating keratinocytes and in the skin of patients with autosomal recessive congenital ichthyosis (ARCI) vs. healthy controls, respectively. We thus identified 24 genes to be upregulated in both sets of array and not previously associated with keratinocyte differentiation. For 10 of these genes (AKR1B10, BLNK, ENDOU, GCNT4, GLTP, RHCG, SLC15A1, TMEM45B, TMEM86A and VSNL1), qPCR analysis confirmed the array results and subsequent immunostainings of normal epidermis showed superficial expression of several of the proteins. Furthermore, induction of keratinocyte differentiation using phorbol esters (PMA) resulted in increased expression of eight of the genes, whereas siRNA silencing of PPARδ, a transcription factor supporting differentiation, had the opposite effect. In summary, our results identify ten new candidate genes seemingly involved in human epidermal keratinocyte differentiation and possibly important for epidermal repair in a genetic skin disease characterized by barrier failure., (Copyright © 2021 International Society of Differentiation. Published by Elsevier B.V. All rights reserved.)

Transcription factor p63 has critical functions in epidermal, hindgut/anorectal, and limb development. Human mutations in P63 correlate with congenital syndromes affecting the skin, anorectal, and limbs. Nevertheless, less are detected regarding networks and functions controlled by P63 mutations in dermal fibroblasts, which are closely related to skin physiology. To screen for new targets, we employed microarray technology to investigate the R226Q P63 mutation with regards to the resulting circular RNA (circRNA) profiles from P63 point mutations in human dermal fibroblasts (HDFs). In this study, we show that P63-mutant HDFs display reduced proliferation, collagen synthesis, and myofibroblast differentiation; circAMD1 was also downregulated in P63-mutant HDFs compared with wild-type HDFs. Furthermore, overexpressing circAMD1 rescued the functional and phenotypic alterations of p63-mutant HDFs. We as well determined that miR-27a-3p was circAMD1 target involved in effects of circAMD1 in P63-mutant HDFs. Collectively, our data show that circAMD1 functions as a miR-27a-3p sponge that inhibits the functional and phenotypical alteration of P63-mutant HDFs and may be a critical marker in pathogenesis regarding P63-associated traits., (Copyright © 2021. Published by Elsevier B.V.)

The mechanism by which reactive oxygen species (ROS) produced by oxidative stress promote cellular senescence has been studied in detail. This study aimed to verify the preventive or therapeutic effects of mesenchymal stem cell-derived exosomes (MSC-Ex) on the production of ROS induced by oxidative stress in human skin fibroblasts and clarify the mechanisms that promote cellular senescence. In a system where H 2 O 2 was applied to skin fibroblasts, we assessed the effects of the application of MSC-Ex before and after oxidative stress and measured the fluctuations in several signaling molecules involved in subsequent intracellular stress responses. Exosomes were isolated from MSCs (MSC-Ex) and normal human dermal fibroblasts (NHDFs, NHDF-Ex) before and after exposure to H 2 O 2 . NHDFs were treated with exosomes before and after exposure to H 2 O 2 . mRNA expression (aquaporin-1 and aquaporin-3) and hyaluronan secretion associated with skin moisturization were reduced by H 2 O 2 treatment, whereas MSC-Ex reversed these effects. The cellular senescence induced by H 2 O 2 was also reproduced in fibroblasts. Specifically, the downregulation of SIRT1 led to increased acetylated p53 expression over time, which induced the expression of p21, a downstream molecule of p53, and arrested the cell cycle, leading to cell senescence. MSC-Ex enhanced these signal transduction systems. MSC-Ex was also effective at blocking the increase of β-galactosidase activity and accumulation of ROS in cells. This effect was stronger than that of NHDF-Ex. MSC-Ex were found to act defensively against epidermal and cellular senescence induced by oxidative stress.

T cells in human skin play an important role in the immune defense against pathogens and tumors. T cells are present already in fetal skin, where little is known about their cellular phenotype and biological function. Using single-cell analyses, we identified a naive T cell population expressing αβ and γδ T cell receptors (TCRs) that was enriched in fetal skin and intestine but not detected in other fetal organs and peripheral blood. TCR sequencing data revealed that double-positive (DP) αβγδ T cells displayed little overlap of CDR3 sequences with single-positive αβ T cells. Gene signatures, cytokine profiles and in silico receptor-ligand interaction studies indicate their contribution to early skin development. DP αβγδ T cells were phosphoantigen responsive, suggesting their participation in the protection of the fetus against pathogens in intrauterine infections. Together, our analyses unveil a unique cutaneous T cell type within the native skin microenvironment and point to fundamental differences in the immune surveillance between fetal and adult human skin., Competing Interests: Disclosures: The authors declare no competing interests exist., (© 2021 Reitermaier et al.)

Background: The immature skin of preterm infants is uniquely vulnerable to pressure and chemical injury. We sought to qualitatively and quantitatively describe the histopathologic patterns of skin development in preterm infants., Methods: Autopsy skin samples were examined for 48 liveborn preterm infants born at 18+ to 36 weeks, and control groups of term neonates and older infants/children. Quantitative variables included thickness of the stratum corneum, epidermis, and dermis. Qualitative features included stratum corneum, rete ridges, and hair follicles., Results: Patterns of maturation were reproducible. Compact keratin appeared beginning at 21-22 weeks. Basketweave keratin appeared first around hair follicles, and then became more generalized from ∼28 weeks corrected gestational age (CGA) onward. Rete ridges began to appear at ∼30 weeks. Epidemal and dermal thickness increased with age. Infants who survived ≤7 days had thicker dermis than those who survived longer, even adjusted for CGA., Conclusions: Skin development in preterm infants has reproducible milestones. Significant structural changes occurring around 28-30 weeks may improve barrier function, with implications for use of topical compounds such as chlorhexidine. The findings also highlight challenges in evaluating pressure injuries in preterm infants, and postnatal changes in skin parameters.

A morphological and morphometric study of the skin development in the eastern quoll (Dasyurus viverrinus) was conducted to follow the transition from cutaneous to pulmonary gas exchange in this extremely immature marsupial species. Additionally, the development of the cardiac and respiratory system was followed, to evaluate the systemic prerequisites allowing for cutaneous respiration. The skin in the newborn D. viverrinus was very thin (36 ± 3 µm) and undifferentiated (no hair follicles, no sebaceous and perspiratory glands). Numerous superficial cutaneous capillaries were encountered, closely associated with the epidermis, allowing for gaseous exchange. The capillary volume density was highest in the neonate (0.33 ± 0.04) and decreased markedly during the first 4 days (0.06 ± 0.01). In the same time period, the skin diffusion barrier increased from 9 ± 1 µm to 44 ± 6 µm. From this age on the skin development was characterized by thickening of the different cutaneous layers, formation of hair follicles (day 55) and the occurrence of subcutaneous fat (day 19). The heart of the neonate D. viverrinus had incomplete interatrial, inter-ventricular, and aortico-pulmonary septa, allowing for the possibility that oxygenated blood from the skin mixes with that of the systemic circulation. The fast-structural changes in the systemic circulations (closing all shunts) in the early postnatal period (3 days) necessitate the transition from cutaneous to pulmonary respiration despite the immaturity of the lungs. At this time, the lung was still at the canalicular stage of lung development, but had to be mature enough to meet the respiratory needs of the growing organism. The morphometric results for the skin development of D. viverrinus suggest that cutaneous respiration is most pronounced in neonates and decreases rapidly during the first 3 days of postnatal life. After this time a functional transition of the skin from cutaneous respiration to insulation and protection of the body takes place., (© 2020 The Authors. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

Pannexin 3 (Panx3), a member of the gap junction pannexin family is required for the development of hard tissues including bone, cartilage and teeth. However, the role of Panx3 in skin development remains unclear. Here, we demonstrate that Panx3 regulates skin development by modulating the transcription factor, Epiprofin (Epfn). Panx3 -/- mice have impaired skin development and delayed hair follicle regeneration. Loss of Panx3 in knockout mice and suppression by shRNA both elicited a reduction of Epfn expression in the epidermis. In cell culture, Panx3 overexpression promoted HaCaT cell differentiation, cell cycle exit and enhanced Epfn expression. Epfn -/- mice and inhibition of Epfn by siRNA showed no obvious differences of Panx3 expression. Furthermore, Panx3 promotes Akt/NFAT signaling pathway in keratinocyte differentiation by both Panx3 ATP releasing channel and ER Ca 2+ channel functions. Our results reveal that Panx3 has a key role factor for the skin development by regulating Epfn.

Several types of 3-dimensional (3D) biological matrices are employed for clinical and surgical applications, but few indications are available to guide surgeons in the choice among these materials. Here we compare the in vitro growth of human primary fibroblasts on different biological matrices commonly used for clinical and surgical applications and the activation of specific molecular pathways over 30 days of growth. Morphological analyses by Scanning Electron Microscopy and proliferation curves showed that fibroblasts have different ability to attach and proliferate on the different biological matrices. They activated similar gene expression programs, reducing the expression of collagen genes and myofibroblast differentiation markers compared to fibroblasts grown in 2D. However, differences among 3D matrices were observed in the expression of specific metalloproteinases and interleukin-6. Indeed, cell proliferation and expression of matrix degrading enzymes occur in the initial steps of interaction between fibroblast and the investigated meshes, whereas collagen and interleukin-6 expression appear to start later. The data reported here highlight features of fibroblasts grown on different 3D biological matrices and warrant further studies to understand how these findings may be used to help the clinicians choose the correct material for specific applications.

Primary closure of fetal skin in spina bifida protects the spinal cord and improves clinical outcome, but is also associated with postnatal growth malformations and spinal cord tethering. In this study, we evaluated the postnatal effects of prenatally closed full-thickness skin defects in sheep applying collagen scaffolds with and without heparin/vascular endothelial growth factor/fibroblast growth factor 2, focusing on skin regeneration and growth. At 6 months, collagen scaffold functionalized with heparin, VEGF, and FGF2 (COL-HEP/GF) resulted in a 6.9-fold increase of the surface area of the regenerated skin opposed to 1.7 × for collagen only. Epidermal thickness increased 5.7-fold at 1 month, in line with high gene expression of S100 proteins, and decreased to 2.1 at 6 months. Increased adipose tissue and reduced scaffold degradation and number of myofibroblasts were observed for COL-HEP/GF. Gene ontology terms related to extracellular matrix (ECM) organization were enriched for both scaffold treatments. In COL-HEP/GF, ECM gene expression resembled native skin. Expression of hair follicle-related genes in COL-HEP/GF was comparable to native skin, and de novo hair follicle generation was indicated. In conclusion, in utero closure of skin defects using functionalized collagen scaffolds resulted in long-term skin regeneration and growth. Functionalized collagen scaffolds that grow with the child may be useful for prenatal treatment of closure defects like spina bifida. Impact statement Prenatal closure of fetal skin in case of spina bifida prevents damage to the spinal cord. Closure of the defect is challenging and may result in postnatal growth malformations. In this study, the postnatal effects of a prenatally applied collagen scaffold functionalized with heparin and vascular endothelial growth factor (VEGF)/fibroblast growth factor (FGF) were investigated. An increase of the surface area of regenerated skin ("growing with the child") and generation of hair follicles was observed. Gene expression levels resembled those of native skin with respect to the extracellular matrix and hair follicles. Overall, in utero closure of skin defects using heparin/VEGF/FGF functionalized collagen scaffolds results in long-term skin regeneration.

The blood vascular system is a tree-like hierarchical branching structure and needs to function even before fully established. Abnormal formation of blood vessels results in embryonic lethality and also contributes to the pathogenesis of a number of human diseases, including cancer metastasis. To understand the molecular events associated with blood vessel formation, we established a fluorescence staining-based protocol on mouse embryonic skin. We harvested mouse embryonic skin and performed whole-mount staining. The reconstructed three-dimensional vascular structure provided detailed information on angiogenesis., (© 2021. Springer Science+Business Media, LLC, part of Springer Nature.)

The first differentiation event in mammalian embryos is the formation of the trophectoderm, which is the progenitor of the outer epithelial component of the placenta and supports the fetus during intrauterine life. Our understanding of these events is limited, particularly in human, because of ethical and legal restrictions and availability of adequate in vitro models would be very advantageous. Here we describe a method that converts human fibroblasts into trophoblast-like cells, combining the use of 5-azacytidine-CR (5-aza-CR) to erase the original cell phenotype and a cocktail containing bone morphogenetic protein 4 (BMP4) with inhibitors of the Activin/Nodal/ERK signaling pathways, to drive erased fibroblasts into the trophoblastic differentiation. This innovative method uses very easily accessible cells to derive trophoblast-like cells and it can be useful to study embryo implantation disorders related to aging.

Cutaneous wound healing is an intricate and multifaceted process. Despite these complexities, the distinct phases of wound healing provide a unique opportunity to evaluate the roles of different targets in these coordinated responses. This protocol details an in vivo wound healing assay to study the intersection of cellular, molecular, and systemic effector pathways. The role of certain proteins in the wound healing process can be efficiently explored in vivo through the generation of tissue-specific deficient mice. This approach, although optimized for use with animal models displaying epithelial deficiencies, can be used for other tissue-specific deficiencies, and utilizes simple and cost-effective methods, allowing investigators to precisely devise their experimental design. The coordination of immunological, epithelial, vascular, and microenvironmental factors in wound healing makes this technique a valuable tool for investigators across fields.

Skin integrity and function depends to a large extent on the composition of the extracellular matrix, which regulates tissue organization. Collagen XII is a homotrimer with short collagenous domains that confer binding to the surface of collagen I-containing fibrils and extended flexible arms, which bind to non-collagenous matrix components. Thereby, collagen XII helps to maintain collagen suprastructure and to absorb stress. Mutant or absent collagen XII leads to reduced muscle and bone strength and lax skin, whereas increased collagen XII amounts are observed in tumor stroma, scarring and fibrosis. This study aimed at uncovering in vivo mechanisms by which collagen XII may achieve these contrasting outcomes. We analyzed skin as a model tissue that contains abundant fibrils, composed of collagen I, III and V with collagen XII decorating their surface, and which is subject to mechanical stress. The impact of different collagen XII levels was investigated in collagen XII-deficient (Col12-KO) mice and in mice with collagen XII overexpression in the dermis (Col12-OE). Unchallenged skin of these mice was histologically inconspicuous, but at the ultrastructural level revealed distinct aberrations in collagen network suprastructure. Repair of excisional wounds deviated from controls in both models by delayed healing kinetics, which was, however, caused by completely different mechanisms in the two mouse lines. The disorganized matrix in Col12-KO wounds failed to properly sequester TGFβ, resulting in elevated numbers of myofibroblasts. These are, however, unable to contract and remodel the collagen XII-deficient matrix. Excess of collagen XII, in contrast, promotes persistence of M1-like macrophages in the wound bed, thereby stalling the wounds in an early inflammatory stage of the repair process and delaying healing. Taken together, we demonstrate that collagen XII is a key component that assists in orchestrating proper skin matrix structure, controls growth factor availability and regulates cellular composition and function. Together, these functions are pivotal for re-establishing homeostasis after injury., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to declare., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: Keratin-associated protein (KAP), the structural protein molecule of hair fibers, plays a key role in determining the physical properties of hair. Studies of Krtap11-1 have focused only on its localization. Functional studies of Krtap11-1 in hair follicle development have so far not been reported., Objective: This study aimed to provide evidence for the role of Krtap11-1 in skin and hair development., Methods: Full-length cloning and analysis of Krtap11-1 were conducted to ascertain its function. Overexpression vectors and interference sequences were constructed and transfected into RAB-9 cells. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to investigate the hair follicle developmental stage of Krtap11-1, the expression of different tissues, and the effects on other hair follicle development-related genes., Results: The full length of cloned Krtap11-1 was 947 bp. Krtap11-1 was confirmed to be a hydrophilic protein localized mostly in mitochondria. The greatest mRNA expression was observed in skin. Using a follicle synchronization model, it was found that Krtap11-1 mRNA expression levels first increased then decreased over the passage of time, principally during hair follicle catagen and telogen. Following the overexpression of Krtap11-1, mRNA expression levels of the WNT-2, KRT17, BMP-2, and TGF-β-1 genes increased, and LEF-1 decreased (P < 0.05), the converse after the corresponding use of si-RNA interference., Conclusions: Krtap11-1 exerts a promoting effect. The results provide novel insight into the relationship between hair follicle development and Krtap11-1 gene expression.

Background: Tissue expansion relies on the ability of skin to grow in response to sustained mechanical strain. This study focuses on correlation of cellular and histologic changes with skin growth and deformation during tissue expansion., Methods: Tissue expanders were placed underneath the skin of five Yucatan minipigs and inflated with one fill of 60 cc of saline 1 hour, 24 hours, 3 days, and 7 days before the animals were killed, or two fills of either 30 cc or 60 cc at 10 and 3 days or 14 and 7 days before the animals were killed. Skin biopsy specimens and three-dimensional photographs were used to calculate skin growth and stretch according to the authors' novel finite element analysis model., Results: The mitotic index of keratinocytes in the basal layer increased 1 hour after stimulus was applied (4 percent) (p = 0.022), peaked at approximately day 3 (26 percent) (p < 0.0001), and tapered by day 7 (12.5 percent) (p = 0.012) after tissue expansion. The authors demonstrated that it is the volume per fill rather than the total volume in the expander that scales the magnitude of response. Lastly, the authors demonstrated that the ratio of deformation attributable to growth versus stretch (Fgrowth/Fstretch) after 60 cc of tissue expansion fill was 1.03 at 1 hour, 0.82 at 1 day, 0.85 at day 3, and 0.95 at 7 days., Conclusions: Peak cell proliferation occurred 3 days after tissue expansion fill and is scaled in response to stimulus magnitude. The growth component of deformation equilibrates to the stretch component at day 7, as cell proliferation has started to translate to skin growth.

Wound healing has been intensely studied to expedite recovery times and reduce scarring. However, current technologies fail to achieve regenerative capabilities, leaving wounds with scarring and lack of skin accessories. The recent emergence of nanotechnology has provided a new clinical modality of zinc nanoparticles in wound care. This present study investigated Zinc Sulfide nanoparticles (ZnS-NP) on wound healing in vitro with 2D and 3D models and in vivo with rat full-thickness wound model. ZnS-NP inhibited fetal bovine serum-stimulated rat skin fibroblast cell proliferation, altered cytoskeletal organization, and reduced collagen synthesis as well as contractile activity. ZnS-NP regulated redox homeostatsis and promoted fibroblast viability in 3D hypoxia conditions. In the rat full-thickness wound model, ZnS-NP reduced wound contraction, enhanced re-epithelization, and promoted skin appendage formation. The biological activities of ZnS-NPs determined in our current study may suggest promising practical applications for topical or systemic treatment for wound repair., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Tissue expansion procedures (TE) utilize mechanical forces to induce skin growth and regeneration. While the impact of quick mechanical stimulation on molecular changes in cells has been studied extensively, there is a clear gap in knowledge about sequential biological processes activated during long-term stimulation of skin in vivo. Here, we present the first genome-wide study of transcriptional changes in skin during TE, starting from 1 h to 7 days of expansion. Our results indicate that mechanical forces from a tissue expander induce broad molecular changes in gene expression, and that these changes are time-dependent. We revealed hierarchical changes in skin cell biology, including activation of an immune response, a switch in cell metabolism and processes related to muscle contraction and cytoskeleton organization. In addition to known mechanoresponsive genes (TNC, MMPs), we have identified novel candidate genes (SFRP2, SPP1, CCR1, C2, MSR1, C4A, PLA2G2F, HBB), which might play crucial roles in stretched-induced skin growth. Understanding which biological processes are affected by mechanical forces in TE is important for the development of skin treatments to maximize the efficacy and minimize the risk of complications during expansion procedures.

Acute and chronic skin wounds due to burns, pressure injuries, and trauma represent a substantial challenge to healthcare delivery with particular impacts on geriatric, paraplegic, and quadriplegic demographics worldwide. Nevertheless, the current standard of care relies extensively on preventive measures to mitigate pressure injury, surgical debridement, skin flap procedures, and negative pressure wound vacuum measures. This article highlights the potential of adipose-, blood-, and cellulose-derived products (cells, decellularized matrices and scaffolds, and exosome and secretome factors) as a means to address this unmet medical need. The current status of this research area is evaluated and discussed in the context of promising avenues for future discovery.

Accurate diet formulations are required to fulfil the nutrient requirements of birds in order to achieve optimal production. Knowing how the skin, nodule and feather production characteristics vary with diets of different nutrient densities will help in least-cost modelling. Feather growth and nodule development are factors that were previously neglected in ostrich diet formulation, both of which are essential for the development of a predictive production model. In this trial, 120 birds were placed in 15 pens. Varying energy regimes (high, medium and low) and accompanying protein and amino acid profile levels (level 1-5) were assigned ad libitum to each pen. A randomly selected bird from each pen was slaughtered at 1, 35, 63, 103, 159, 168 and 244 days of age. During the slaughter, each bird was weighed, stunned, exsanguinated, defeathered and eviscerated. Feathers from four regions of the skin were plucked and weighed. The shaft diameter of the wing feathers was measured. The nodule size of the tanned skin was measured for each slaughter age. The data were transformed to natural logarithms and regressed against the total feather weight and the total featherless empty body protein weight to set up allometric growth equations. A prediction equation to determine nodule size of the live bird was proposed. Feed cost optimisation is paramount, and results from this study will aid in setting up least-cost optimisation (simulation) formulation models.

Expression of cell death regulators RIPK-1 and RIPK-3 in mouse and human hair follicle structures was studied by immunohistochemistry. At anagen and catagen stages of mouse hair follicle, RIPK-1+ cells were located in the inner root sheath, whereas RIPK-3+ cells were found in the inner and outer root sheath, dermal papilla, and interfollicular epidermis. RIPK-1 expression intensity was low in the early anagen and increased as mature anagen and catagen approached. RIPK-1+ and RIPK-3+ cells were also found in human hair follicle. It is assumed that the role of necroptosis markers in hair follicle life activity is independent of programmed cell death and that they may have yet unknown functions and take part in noncanonical signal cascades.

Cutaneous wound healing is associated with the unpleasant sensation of itching. Here we investigated the mechanisms underlying this type of itch, focusing on the contribution of soluble factors released during healing. We found high amounts of interleukin 31 (IL-31) in skin wound tissue during the peak of itch responses. Il31 -/- mice lacked wound-induced itch responses. IL-31 was released by dermal conventional type 2 dendritic cells (cDC2s) recruited to wounds and increased itch sensory neuron sensitivity. Transfer of cDC2s isolated from late-stage wounds into healthy skin was sufficient to induce itching in a manner dependent on IL-31 expression. Addition of the cytokine TGF-β1, which promotes wound healing, to dermal DCs in vitro was sufficient to induce Il31 expression, and Tgfbr1 f/f CD11c-Cre mice exhibited reduced scratching and decreased Il31 expression in wounds in vivo. Thus, cDC2s promote itching during skin would healing via a TGF-β-IL-31 axis with implications for treatment of wound itching., Competing Interests: Declaration of Interests The authors declare no competing interests., (Published by Elsevier Inc.)

The expression of hair features is an evolutionary adaptation resulting from interactions between many organisms and their environment. Elucidation of the mechanisms that underlie the expression of such traits is a topic in evolutionary biology research. Therefore, we assessed the de novo transcriptome of Atelerix albiventris at three developmental stages and compared gene expression profiles between abdomen hair and dorsal spine tissues. We identified 328,576 unigenes in our transcriptome, among which 4,435 were differentially expressed between hair- and spine-type tissues. Dorsal and abdomen skin tissues 5 days after birth were compared and the resulting DEGs were mainly enriched in keratin filament, epithelium cell differentiation, and epidermis development based on GO enrichment analysis, and tight junction, p53, and cell cycle signaling pathways based on KEGG enrichment analysis. MBP8, SFN, Wnt1 and KRT1 gene may involve in the development of hedgehog skin and its appendages. Strikingly, DEGs in hair-type tissues were also significantly enriched in immune-related terms and pathways with hair-type tissues exhibiting more upregulated immune genes than spine-type tissues. Our study provided a list of potential genes involved in skin appendage development and differentiation in A. albiventris, and the candidate genes provided valuable information for further studies of skin appendages.

This review describes the formation, structure, and function of bony compartments in antlers, horns, ossicones, osteoderm and the os penis/os clitoris (collectively referred to herein as AHOOO structures) in extant mammals. AHOOOs are extra-skeletal bones that originate from subcutaneous (dermal) tissues in a wide variety of mammals, and this review elaborates on the co-development of the bone and skin in these structures. During foetal stages, primordial cells for the bony compartments arise in subcutaneous tissues. The epithelial-mesenchymal transition is assumed to play a key role in the differentiation of bone, cartilage, skin and other tissues in AHOOO structures. AHOOO ossification takes place after skeletal bone formation, and may depend on sexual maturity. Skin keratinization occurs in tandem with ossification and may be under the control of androgens. Both endochondral and intramembranous ossification participate in bony compartment formation. There is variation in gradients of density in different AHOOO structures. These gradients, which vary according to function and species, primarily reduce mechanical stress. Anchorage of AHOOOs to their surrounding tissues fortifies these structures and is accomplished by bone-bone fusion and Sharpey fibres. The presence of the integument is essential for the protection and function of the bony compartments. Three major functions can be attributed to AHOOOs: mechanical, visual, and thermoregulatory. This review provides the first extensive comparative description of the skeletal and integumentary systems of AHOOOs in a variety of mammals., (© 2020 Cambridge Philosophical Society.)

The ability of the skin to grow in response to stretching has been exploited in reconstructive surgery 1 . Although the response of epidermal cells to stretching has been studied in vitro 2,3 , it remains unclear how mechanical forces affect their behaviour in vivo. Here we develop a mouse model in which the consequences of stretching on skin epidermis can be studied at single-cell resolution. Using a multidisciplinary approach that combines clonal analysis with quantitative modelling and single-cell RNA sequencing, we show that stretching induces skin expansion by creating a transient bias in the renewal activity of epidermal stem cells, while a second subpopulation of basal progenitors remains committed to differentiation. Transcriptional and chromatin profiling identifies how cell states and gene-regulatory networks are modulated by stretching. Using pharmacological inhibitors and mouse mutants, we define the step-by-step mechanisms that control stretch-mediated tissue expansion at single-cell resolution in vivo.

The development of the epidermis of octopus, Octopus vulgaris, throughout its life cycle was studied by conventional staining and histochemical techniques using lectins. The mantle, the arm and the two parts of the suckers: the infundibulum and the acetabulum were analysed independently. With the exception of the suckers, the general morphology of the epidermis does not vary from the first days post-hatching to adulthood. In general terms, histochemical techniques do not indicate changes in the composition of glycoconjugates of the epidermis main cells, epithelial and secretory cells. The epithelial cells of the mantle and arm show positivity for mannose (ConA+) in their apical portions, indicating the presence of n-glycoproteins that, among other things, provide lubrication to the surface of the body. In the suckers, the apical surface of the infundibulum contains sulphated glycosaminoglycans of the N-acetylglucosamine type that provide adhesive properties. In addition to observing three types of mucocytes, m1 and m2 are characteristic of the mantle and arm, and m3 is found in the suckers. The paralarva epidermis is characterised by the presence of Kölliker's organs whose exact function is unknown. In this study, the absence of staining with alcian blue/periodic acid-Schiff(AB/PAS) prevents the possibility of attributing a secretory function. Nevertheless, the linkage of three lectins (WGA, LEL and GSL-I) in the fascicle of the organ suggests the presence of proteoglycans rich in N-acetylglucosamine that would mainly have a structural role., (© 2020 Blackwell Verlag GmbH.)

An important problem for researchers working in the field of dermatology is the preparation of the human skin equivalent (HSE). Here, we describe a simple and reliable protocol for preparing a skin model from the commercially available cell lines: keratinocytes, fibroblasts, and melanocytes. Importantly, in our 3D model, the keratinocytes are diverse that brings this model closer to the natural skin. For the production of HSE, we used available primary PCS-200-010, PCS-201-010, PCS-200-013, and immortalized CRL-4048 and CRL-4001 cell lines. We used genipin, which is necessary for collagen cross-linking and studied its cytotoxicity for keratinocytes and fibroblasts. The addition of 20 μM genipin reduced the shrinkage of the collagen in the constructs from 59% to 24% on day 12 of the culture of the construct. A higher concentration (80-200 µM) of genipin reduced shrinkage by 14% on average. Genipin in concentration 10 μM and below was not cytotoxic to the keratinocytes, and 150 μM and below to the fibroblasts. Hematoxylin and eosin staining showed that the morphology of HSEs was identical to that of native human skin. The immunohistochemical staining of the constructs showed the presence of vimentin-positive fibroblasts in the skin layer, while the melanocytes were in the epidermis and in the basal layer. We observed that the longer differentiation of constructs led to the higher secretion of GM-CSF, IL-10, IL-15, IL-1α, IL-6, IL-7, IL-8, and MCP-1. We also observed that the longer time of differentiation led to a more stable secretion of all analytes, which was reflected in the coefficient of variation. We described here a simple, reliable, and cost-effective production of the full-thickness human skin equivalents that can be used in the research and industry. With the global trend to decrease animal use for the research and testing, our HSE could be a useful testing tool and an alternative research model.

Vascular endothelial growth factor-A (VEGF-A) is a principal regulator of hematopoiesis as well as angiogenesis. However, the functions of VEGF-A and its receptors (VEGFRs) in the differentiation of mast cells (MCs) in the skin remain unclear. The aim of this study was to determine the expression patterns of two VEGFRs (Flk1 and Flt1) in the skin MCs during development and maturation in rats. From the 17th days of embryonic development (E17) to 1 day after birth (Day 1), most of skin MCs were immature cells containing predominant alcian blue (AB) + rather than safranin O (SO) + granules (AB>SO MCs). AB>SO MC proportions gradually decreased, while mature AB+ MC proportions increased from E20 and reached to approximately 90% from Day 1 to 21, thereafter decreased to about 10% at Day 60 and 90. Flk1 + MC proportions changed almost in parallel with the numbers of MCs and Ki67 + MC proportions from E17 to Day 90. The proportions of MCs with both nuclear and cytoplasmic Flt1-immunoreactivity were markedly increased at Day 28, when the proportions of nuclear Flk1 + , Ki67 + , and AB>SO MCs had significantly decreased, and AB

Background and Objective: Impaired dermal wound healing represents a major medical issue in today's aging populations. Granulation tissue formation in the dermis and reepithelization of the epidermis are both important and necessary for proper wound healing. Although a number of artificial dermal grafts have been used to treat full-thickness dermal loss in humans, they do not induce reepithelization of the wound, requiring subsequent epithelial transplantation. In the present study, we sought a novel biomaterial that accelerates the wound healing process. Approach: We prepared a composite biomaterial made of jellyfish and porcine collagens and developed a hybrid-type dermal graft that composed of the upper layer film and the lower layer sponge made of this composite biomaterial. Its effect on dermal wound healing was examined using a full-thickness excisional wound model. Structural properties of the dermal graft and histological features of the regenerating skin tissue were characterized by electron microscopic observation and immunohistological examination, respectively. Results: The composite biomaterial film stimulated migration of keratinocytes, leading to prompt reepithelization. The regenerating epithelium consisted of two distinct cell populations: keratin 5-positive basal keratinocytes and more differentiated cells expressing tight junction proteins such as claudin-1 and occludin. At the same time, the sponge made of the composite biomaterial possessed a significantly enlarged intrinsic space and enhanced infiltration of inflammatory cells and fibroblasts, accelerating granulation tissue formation. Innovation: This newly developed composite biomaterial may serve as a dermal graft that accelerates wound healing in various pathological conditions. Conclusion: We have developed a novel dermal graft composed of jellyfish and porcine collagens that remarkably accelerates the wound healing process.

The skin is a multilayered organ, equipped with appendages (that is, follicles and glands), that is critical for regulating body temperature and the retention of bodily fluids, guarding against external stresses and mediating the sensation of touch and pain 1,2 . Reconstructing appendage-bearing skin in cultures and in bioengineered grafts is a biomedical challenge that has yet to be met 3-9 . Here we report an organoid culture system that generates complex skin from human pluripotent stem cells. We use stepwise modulation of the transforming growth factor β (TGFβ) and fibroblast growth factor (FGF) signalling pathways to co-induce cranial epithelial cells and neural crest cells within a spherical cell aggregate. During an incubation period of 4-5 months, we observe the emergence of a cyst-like skin organoid composed of stratified epidermis, fat-rich dermis and pigmented hair follicles that are equipped with sebaceous glands. A network of sensory neurons and Schwann cells form nerve-like bundles that target Merkel cells in organoid hair follicles, mimicking the neural circuitry associated with human touch. Single-cell RNA sequencing and direct comparison to fetal specimens suggest that the skin organoids are equivalent to the facial skin of human fetuses in the second trimester of development. Moreover, we show that skin organoids form planar hair-bearing skin when grafted onto nude mice. Together, our results demonstrate that nearly complete skin can self-assemble in vitro and be used to reconstitute skin in vivo. We anticipate that our skin organoids will provide a foundation for future studies of human skin development, disease modelling and reconstructive surgery.

The dietary requirement for cysteine is not determined in poultry since it is not an essential amino acid. The cysteine need is expected to be met through the transsulfuration pathway where homocysteine, a precursor of methionine, is converted to cysteine. Cysteine is a major component of plumage, and the degree to which cysteine is involved in plumage and other keratized proteins are unknown. We randomly assigned chicks to control and treatment (deficient in cysteine) diets for 49 d. The thickness of the skin layers, feather follicle length, and thickness were measured at days 10, 24, 34, and 49. We also measured the hepatic mRNA expressions of cystathionine beta synthase ( CBS ), cystathionine γ-lyase ( CTL ), cysteine dioxygenase ( CDO ), and glutathione synthetase ( GSS) . Chickens fed the treatment diet had reduced epidermis thickness and shorter feather follicles compared with the controls. The chicken fed the treatment diet also had increased mRNA expression of CBS and CTL indicating a disruption of the transsulfuration pathway. The treatment chickens also had a decreased hepatic CDO and increased GSS mRNA expressions which are in concordance with the homeostatic regulation of cysteine. Compromised cysteine metabolism could affect thermoregulation and subsequently affect feed efficiency and welfare of the birds.

The naturally colorful fur of the Rex rabbit is becoming increasingly popular in the modern textile market. Our previous study found that POU class 2 homeobox 1 gene ( POU2F1 ) potentially affects the expression of genes involved in fur color formation in the Rex rabbit, but the function and regulation of POU2F1 has not been reported. In this study, the expression patterns of POU2F1 in Rex rabbits of various colors, as well as in different organs, were analyzed by RT-qPCR. Interference and overexpression of POU2F1 were used to identify the potential effects of POU2F1 on other genes related to fur color formation. The results show that the levels of POU2F1 expression were significantly higher in the dorsal skin of the brown and protein yellow Rex rabbits, compared with that of the black one. POU2F1 mRNAs were widespread in the tissues examined in this study and showed the highest level in the lungs. By transfecting rabbit melanocytes with an POU2F1 -overexpression plasmid, we found that the POU2F1 protein was located at the nucleus, and the protein showed the classic characteristics of a transcription factor. In addition, abnormal expression of POU2F1 significantly affected the expression of pigmentation-related genes, including SLC7A11 , MITF , SLC24A5 , MC1R , and ASIP , revealing the regulatory roles of POU2F1 on pigmentation. The results provide the basis for further exploration of the role of POU2F1 in fur color formation of the Rex rabbit.

During embryonic and postnatal development, organs and tissues grow steadily to achieve their final size at the end of puberty. However, little is known about the cellular dynamics that mediate postnatal growth. By combining in vivo clonal lineage tracing, proliferation kinetics, single-cell transcriptomics, and in vitro micro-pattern experiments, we resolved the cellular dynamics taking place during postnatal skin epidermis expansion. Our data revealed that harmonious growth is engineered by a single population of developmental progenitors presenting a fixed fate imbalance of self-renewing divisions with an ever-decreasing proliferation rate. Single-cell RNA sequencing revealed that epidermal developmental progenitors form a more uniform population compared with adult stem and progenitor cells. Finally, we found that the spatial pattern of cell division orientation is dictated locally by the underlying collagen fiber orientation. Our results uncover a simple design principle of organ growth where progenitors and differentiated cells expand in harmony with their surrounding tissues., Competing Interests: Declaration of Interests The authors declare no competing interests., (Crown Copyright © 2020. Published by Elsevier Inc. All rights reserved.)

Background: Seven in absentia homolog 1 (SIAH1) is an E3 ubiquitin ligase containing a RING-finger domain and a key regulator of normal development. Skin and hair follicle development is a complex and special process of morphogenesis involving multiple signaling pathways. SIAH1 is enriched in the Wnt signaling pathway and potentially related to hair follicle cycle and skin development. This study aims to provide evidence for the role of SIAH1 in skin and hair development., Results: Full-length cloning and analysis of SIAH1 was conducted to better understand its function. Phylogenetically, the sequence of SIAH1 in the rabbit shares the greatest homology with Home sapiens, Pongo abelii and Mus mulatta. Based on the rabbit hair follicle synchronization model, we found that the expression level of SIAH1 in the regressive period of the rabbit hair cycle is significantly lower than in the active growth and rest periods. In addition, the mRNA expression levels of skin and hair follicle development-related genes changed significantly when SIAH1 was overexpressed and silenced. After SIAH1 overexpression, the expression levels of WNT2, LEF1 and FGF2 decreased, and those of SFRP2 and DKK1 increased (P < 0.05). After interference of SIAH1, the expression levels of WNT2, LEF1 and FGF2 increased (P < 0.05), and SFRP2 and DKK1 decreased., Conclusions: SIAH1 can affect skin and hair follicle development and exert an inhibitory effect. These results could provide foundamental insights into the role of SIAH1 as a target gene in rabbit skin and hair follicle development.

The aim of the present study was to examine subcutaneous adipose tissue distribution in female volleyball players with regards to (a) variation by anatomical site, (b) differences among age groups and playing positions, and (c) physiological characteristics associated with performance. Participants were adolescent ( n = 89, age 15.6 ± 0.9 years, mean ± standard deviation) and adult female volleyball players ( n = 78, 24.8 ± 5.3 years), who performed a series of anthropometric and performance tests including skinfold thickness in 10 sites, Abalakov jump (AJ) and handgrip test (HG). Chin had the smallest thickness, and iliac crest and abdomen the largest. The largest correlations of skinfold thickness were shown with regards to AJ ad HG. Coefficient of variations in skinfold thickness correlated with performance indices with small magnitude. Triceps and chin were the most frequent predictors of performance indices. The anatomical site of skinfold was near the active muscle groups related to performance in HG. In conclusion, performance indices such AJ and HG were related with thickness of specific skinfolds and with the variation of thickness by anatomical site (i.e., the less the variation, the better the performance). Considering the relevance of specific skinfolds (e.g., triceps and chin) for performance, their further use would be recommended for purposes of training monitoring, volleyball players' selection and talent identification.

Wound-induced hair follicle neogenesis (WIHN) is a phenomenon that occurs in adult mammalian skin, where fully functional hair follicles are regenerated in the center of large full-thickness excisional wounds. Although originally discovered over 50 years ago in mice and rabbits, within the last decade it has received renewed interest, as the molecular mechanism has begun to be defined. This de novo regeneration of hair follicles largely recapitulates embryonic hair development, requiring canonical Wnt signaling in the epidermis, however, important differences between the two are beginning to come to light. TLR3 mediated double stranded RNA sensing is critical for the regeneration, activating retinoic acid signaling following wounding. Inflammatory cells, including Fgf9-producing γ-δ T cells and macrophages, are also emerging as important mediators of WIHN. Additionally, while dispensable in embryonic hair follicle development, Shh signaling plays a major role in WIHN and may be able to redirect cells fated to scarring wounds into a regenerative phenotype. The cellular basis of WIHN is also becoming clearer, with increasing evidence suggesting an incredible level of cellular plasticity. Multiple stem cell populations, along with lineage switching of differentiated cells all contribute towards the regeneration present in WIHN. Further study of WIHN will uncover key steps in mammalian development and regeneration, potentially leading to new clinical treatments for hair-related disorders or fibrotic scarring., (Copyright © 2019. Published by Elsevier Ltd.)

Self-organized pattern behavior is ubiquitous throughout nature, from fish schooling to collective cell dynamics during organism development. Qualitatively these patterns display impressive consistency, yet variability inevitably exists within pattern-forming systems on both microscopic and macroscopic scales. Quantifying variability and measuring pattern features can inform the underlying agent interactions and allow for predictive analyses. Nevertheless, current methods for analyzing patterns that arise from collective behavior capture only macroscopic features or rely on either manual inspection or smoothing algorithms that lose the underlying agent-based nature of the data. Here we introduce methods based on topological data analysis and interpretable machine learning for quantifying both agent-level features and global pattern attributes on a large scale. Because the zebrafish is a model organism for skin pattern formation, we focus specifically on analyzing its skin patterns as a means of illustrating our approach. Using a recent agent-based model, we simulate thousands of wild-type and mutant zebrafish patterns and apply our methodology to better understand pattern variability in zebrafish. Our methodology is able to quantify the differential impact of stochasticity in cell interactions on wild-type and mutant patterns, and we use our methods to predict stripe and spot statistics as a function of varying cellular communication. Our work provides an approach to automatically quantifying biological patterns and analyzing agent-based dynamics so that we can now answer critical questions in pattern formation at a much larger scale., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)