Morfología microestructural dérmica en juveniles de dos especies hermanas de tiburón pala, Sphyrna tiburo y S. vespertina / Dermal microstructural morphology in juveniles of two sister species of bonnethead shark, Sphyrna tiburo and S. vespertina

RESUMEN: Los dentículos dérmicos son estructuras dermales presentes en el grupo de los condrictios, tienen un papel muy importante en su biología y se les ha utilizado como un carácter taxonómico que permiten reconocer grupos o especies. Por lo que en el presente trabajo se compara la morfología dermal de los juveniles de dos especies de tiburones pala, Sphyrna tiburo y S. vespertina, cuyo origen evolutivo está emparentado con el cierre del istmo centroaméricano. Para ello se obtuvieron muestras dermales (1 cm2) de tres regiones corporales y se procesaron para obtener imágenes de alta resolución por medio de Microscopia electrónica de barrido (MEB). Los dentículos de ambas especies tienen un patrón morfológico común, con variaciones en la longitud de las prolongaciones de las crestas, área libre y superposición de los dentículos, y grado de notoriedad de la ornamentación microestructural.

SUMMARY: The dermal denticles are dermal structures present in the group of chondrichthyans, they have a very important role in their biology and they have been used as a taxonomic character that allows to recognize groups or species. Therefore, in the present work, the dermal morphology of the juveniles of two species of shovel sharks, Sphyrna tiburo and S. vespertina, whose evolutionary origin is related to the closure of the Central American isthmus, is compared. For this, dermal samples (1 cm2) from three body regions were obtained and processed to obtain high resolution images by means of scanning electron microscopy (SEM). The denticles of both species have a common morphological pattern, with variations in the length of the ridge extensions, free area and overlapping of the denticles, and the degree of notoriety of the microstructural ornamentation.

The dermal armor of mylodontid sloths (Mammalia, Xenarthra) from Cueva del Milodón (Última Esperanza, Chile).

Dermal ossifications (osteoderms, dermal ossicles, osteoscutes) appear independently in various tetrapod lineages. In mammals, however, dermal ossifications are only present in some members of Xenarthra. This clade includes Cingulata (armadillos and their relatives), and Pilosa, including Vermilingua (anteaters) and Folivora (sloths). In extant xenarthrans, osteoderms are invariably present in cingulates whereas they are absent in pilosans. Among extinct sloths, however, a limited number of taxa possessed dermal ossifications. Records of mummified skins of ground sloths bearing osteoderms found in Cueva del Milodón (Southern Chile), with a late Pleistocene age, allowed us to analyze their micro- and macroscopic morphology. The main goal of this study is to closely examine a portion of a mylodontid skin portion using radiography. The arrangement, morphology and internal structure of the ossicles are analyzed and the results are discussed in the context of previous research. The results we obtained indicate that ossicles vary in shape and size, and the integument has four different patterns of arrangement of the ossicles: that is, areas without ossicles, disorganized ossicles, rows, and mosaic areas. The latter has two variants, with clusters of ossicles forming rosettes or stars. Thin sections of the ossicles allowed us to recognize and describe anatomical features of the bone and its mode of growth. Finally, paleobiological and functional considerations of the dermal armor are discussed along with its phylogenetic and chronological implications.

TatS: a novel in vitro tattooed human skin model for improved pigment toxicology research.

Reports of tattoo-associated risks boosted the interest in tattoo pigment toxicity over the last decades. Nonetheless, the influence of tattoo pigments on skin homeostasis remains largely unknown. In vitro systems are not available to investigate the interactions between pigments and skin. Here, we established TatS, a reconstructed human full-thickness skin model with tattoo pigments incorporated into the dermis. We mixed the most frequently used tattoo pigments carbon black (0.02 mg/ml) and titanium dioxide (TiO2, 0.4 mg/ml) as well as the organic diazo compound Pigment Orange 13 (0.2 mg/ml) into the dermis. Tissue viability, morphology as well as cytokine release were used to characterize TatS. Effects of tattoo pigments were compared to monolayer cultures of human fibroblasts. The tissue architecture of TatS was comparable to native human skin. The epidermal layer was fully differentiated and the keratinocytes expressed occludin, filaggrin and e-cadherin. Staining of collagen IV confirmed the formation of the basement membrane. Tenascin C was expressed in the dermal layer of fibroblasts. Although transmission electron microscopy revealed the uptake of the tattoo pigments into fibroblasts, neither viability nor cytokine secretion was altered in TatS. In contrast, TiO2 significantly decreased cell viability and increased interleukin-8 release in fibroblast monolayers. In conclusion, TatS emulates healed tattooed human skin and underlines the advantages of 3D systems over traditional 2D cell culture in tattoo pigment research. TatS is the first skin model that enables to test the effects of pigments in the dermis upon tattooing.

The systemic influence of chronic smoking on skin structure and mechanical function.

One of the major functions of human skin is to provide protection from the environment. Although we cannot entirely avoid, for example, sun exposure, it is likely that exposure to other environmental factors could affect cutaneous function. A number of studies have identified smoking as one such factor that leads to both facial wrinkle formation and a decline in skin function. In addition to the direct physical effects of tobacco smoke on skin, its inhalation has additional profound systemic effects for the smoker. The adverse effects on the respiratory and cardiovascular systems from smoking are well known. Central to the pathological changes associated with smoking is the elastic fibre, a key component of the extracellular matrices of lungs. In this study we examined the systemic effect of chronic smoking (>40 cigarettes/day; >5 years) on the histology of the cutaneous elastic fibre system, the nanostructure and mechanics of one of its key components, the fibrillin-rich microfibril, and the micromechanical stiffness of the dermis and epidermis. We show that photoprotected skin of chronic smokers exhibits significant remodelling of the elastic fibre network (both elastin and fibrillin-rich microfibrils) as compared to the skin of age- and sex-matched non-smokers. This remodelling is not associated with increased gelatinase activity (as identified by in situ zymography). Histological remodelling is accompanied by significant ultrastructural changes to extracted fibrillin-rich microfibrils. Finally, using scanning acoustic microscopy, we demonstrated that chronic smoking significantly increases the stiffness of both the dermis and the epidermis. Taken together, these data suggest an unappreciated systemic effect of chronic inhalation of tobacco smoke on the cutaneous elastic fibre network. Such changes may in part underlie the skin wrinkling and loss of skin elasticity associated with smoking. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Proteomic and Ultrastructural Analysis of Cellulite-New Findings on an Old Topic.

: Background: Cellulite is a condition in which the skin has a dimpled lumpy appearance. The main causes of cellulite development, studied until now, comprehends modified sensitivity to estrogens, the damage of microvasculature present among dermis and hypodermis. The differences of adipose tissue architecture between male and female might make female more susceptible to cellulite. Adipose tissue is seen to be deeply modified during cellulite development. Our study tried to understand the overall features within and surrounding cellulite to apply the best therapeutic approach. METHODS: Samples of gluteal femoral area were collected from cadavers and women who had undergone surgical treatment to remove orange peel characteristics on the skin. Samples from cadavers were employed for an accurate study of cellulite using magnetic resonance imaging at 7 Tesla and for light microscopy. Specimens from patients were employed for the proteomic analysis, which was performed using high resolution mass spectroscopy (MS). Stromal vascular fraction (SVF) was obtained from the samples, which was studied using MS and flow cytometry. RESULTS: light and electron microscopy of the cellulite affected area showed a morphology completely different from the other usual adipose depots. In cellulite affected tissues, sweat glands associated with adipocytes were found. In particular, there were vesicles in the extracellular matrix, indicating a crosstalk between the two different components. Proteomic analysis showed that adipose tissue affected by cellulite is characterized by high degree of oxidative stress and by remodeling phenomena. CONCLUSIONS: The novel aspects of this study are the peculiar morphology of adipose tissue affected by cellulite, which could influence the surgical procedures finalized to the reduction of dimpling, based on the collagen fibers cutting. The second novel aspect is the role played by the mesenchymal stem cells isolated from stromal vascular fraction of adipose tissue affected by cellulite.

Peel Test to Assess the Adhesion Strength of the Dermal-Epidermal Junction in Tissue-Engineered Skin.

Innovative therapies combining gene-corrected stem cells and the production of bioengineered tissues to treat epidermolysis bullosa are emerging. However, quantitative tests to measure the adhesion forces between two highly viscoelastic substrates such as those found in bilayered bioengineered skin are needed and are still lacking. The objective of this study was to develop a mechanical test to measure the dermal-epidermal adhesion strength of our bilayered tissue-engineered skin substitute (TES) produced with the self-assembly method. We developed a peel test, which allows the displacement of both skin layers in a T configuration, based on the ASTM International standard. A MATLAB program was written to process and analyze raw data. The experimental setup was tested by measuring the dermal-epidermal adhesion strength in TESs produced with normal or collagen VII-deficient cells. Our peel testing method allowed us to detect the impact of the absence of collagen VII in the dermal-epidermal adhesion strength of TESs and also to examine the progression of the dermal-epidermal adhesion strength in relation to culture time in normal TES. Impact statement This study describes a method for assessing the adhesion strength at the dermal-epidermal junction of individual tissue-engineered skin substitute (TES). An ASTM standardized protocol of peel testing was designed to measure this important mechanical property. Our innovative approach will serve as a quality control in the production, improvement, and application of TESs for the treatment of pathologies affecting the dermal-epidermal adhesion such as epidermolysis bullosa. Data presented contribute to research on the interfaces between biological substrates and provide a reference factor for the characterization of products derived from tissue engineering.

The multiscale hierarchical structure of Heloderma suspectum osteoderms and their mechanical properties.

Osteoderms are hard tissues embedded in the dermis of vertebrates and have been suggested to be formed from several different mineralized regions. However, their nano architecture and micro mechanical properties had not been fully characterized. Here, using electron microscopy, µ-CT, atomic force microscopy and finite element simulation, an in-depth characterization of osteoderms from the lizard Heloderma suspectum, is presented. Results show that osteoderms are made of three different mineralized regions: a dense apex, a fibre-enforced region comprising the majority of the osteoderm, and a bone-like region surrounding the vasculature. The dense apex is stiff, the fibre-enforced region is flexible and the mechanical properties of the bone-like region fall somewhere between the other two regions. Our finite element analyses suggest that when combined into the osteoderm structure, the distinct tissue regions are able to shield the body of the animal by bearing the external forces. These findings reveal the structure-function relationship of the Heloderma suspectum osteoderm in unprecedented detail. STATEMENT OF SIGNIFICANCE: The structures of bone and teeth have been thoroughly investigated. They provide a basis not only for understanding the mechanical properties and functions of these hard tissues, but also for the de novo design of composite materials. Osteoderms, however, are hard tissues that must possess mechanical properties distinct from teeth and bone to function as a protective armour. Here we provide a detailed analysis of the nanostructure of vertebrate osteoderms from Heloderma suspectum, and show that their mechanical properties are determined by their multiscale hierarchical tissue. We believe this study contributes to advance the current knowledge of the structure-function relationship of the hierarchical structures in the Heloderma suspectum osteoderm. This knowledge might in turn provide a source of inspiration for the design of bioinspired and biomimetic materials.

Light and electron microscopy of chlorpromazine-induced hyperpigmentation.

Chlorpromazine may induce abnormal skin hyperpigmentation in exposed areas, described as slate-gray, purple, or blue-grayish discoloration. A 58-year-old man with schizophrenia, had been taking chlorpromazine for 5 years, and his sun-exposed skin areas exhibited a blue-grayish color. Large deposits of brown pigment and granular basophilic material were seen in the dermis with light microscopy. HMB-45 and anti-Melan-A antibody immunostaining labeled some pigment in the dermis. Transmission electron microscopy identified deposits among dermal collagen bundles collagen in both transverse and longitudinal sections. In the latter, an arboriform aspect of deposits was quite clear, and some melanophages were also seen. The three-dimensional examination of the dermis with scanning electron microscopy also identified deposits, which at higher magnification demonstrated an appearance in the shape of leaves, grass-like, interspersed with normal collagen. These results suggest a complex pathogenic mechanism, including deposition of dermal melanin together with drug itself and potentially additional unknown metabolites.

Commentaries on the publication entitled: "Structure and distribution of an unrecognized interstitium in human tissues" by Benias et al. (2018)

The claim made in this publication of the existence of a hitherto unknown interstitial space is based on studies with sample-based confocal laser endo-microscopy (pCLM). Due to postings on various web portals (New Cellvizio, EurekAlert, Google Scholar,...) the alleged discovery has found great resonance. Nevertheless, there are several critical issues in this publication, the most important being that this is not the discovery of an "unrecognized" interstitium as it has, in fact, been known for a long time

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Reply to "Commentaries on the publication entitled: 'Structure and distribution of an unrecognized interstitium in human tissues' by Benias et al. (2018)

We appreciate the time and attention paid to our paper by Prof. Mestres-Ventura and similarly appreciate the opportunity to respond to his concerns. We would like to address what we believe are several fundamental misunderstandings in his commentary.1. Scale: The most significant misunderstanding is one of scale. The schematic (Fig. 1) provided by Prof. Mestres-Ventura is (per personal communication) at the nano scale, while in vivo microscopy of extrahepatic bile duct and dermis shows that the collagen bundles we report are at the micron scale, each containing many individual fibrils at the nanometer scale. Indeed, examining the tissues described in our paper - submucosae, dermis and subcutaneous fascia - fresh in resected specimens or intraoperatively, we find that the structures we describe are visible at the macroscopic level (if one leans in closely enough). In other words, they are macroscopic, not microscopic. Prof. Mestres-Ventura, in summarizing the prior pCLE work of Wallace and Fockens, which he notes is similar to ours, states "the 'holes' shown under intravital microscopy and in cryofixed samples are huge (over 20 µm)" This is exactly our point - we were surprised as well at the scale of these structures, as this has not been well appreciated in the past

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Absence of Collagen Flowers on Electron Microscopy and Identification of (Likely) Pathogenic COL5A1 Variants in Two Patients.

Two probands are reported with pathogenic and likely pathogenic COL5A1 variants (frameshift and splice site) in whom no collagen flowers have been identified with transmission electron microscopy (TEM). One proband fulfils the clinical criteria for classical Ehlers-Danlos syndrome (cEDS) while the other does not and presents with a vascular complication. This case report highlights the significant intrafamilial variability within the cEDS phenotype and demonstrates that patients with pathogenic COL5A1 variants can have an absence of collagen flowers on TEM skin biopsy analysis. This has not been previously reported in the literature and is important when evaluating the significance of a TEM result in patients with clinically suspected cEDS and underscores the relevance of molecular analysis.

Granulomatous slack skin: case report with electron microscopic features.

Granulomatous slack skin (GSS) is a rare subtype of mycosis fungoides. It usually presents as slowly evolving, erythematous, slack plaques that usually involve folds of lax skin. Herein, we report a case of GSS and we show electron microscopy examination. Atypical T cells with convoluted and cerebriform nuclei, lymphophagocytosis, and elastophagocytosis are key features of GSS under electron microscopy.

Exploring the collagen nanostructure of dermal tissues after injury.

Scar often occurred during wound repair. It was known that there were differences in collagen structure in dermal tissues at millimeter scale and micron scale, however, it was not known whether there were differences in collagen structure in dermal tissues at nanoscale during wound repair. In order to compare the difference at nanoscale, skin samples from patients were selected, the control groups were the normal skin from the same patients. These samples were tested by the small angle X-ray scattering techniques (SAXS) and wide angle X-ray scattering (WAXS) techniques. The transmission electron microscopy (TEM) was used as a comparison. The results showed that there were not only significantly differences between the normal tissue and scar tissue, but also between the center and the margin of the scar tissue at nanoscale by SAXS and WAXS, which was not demonstrated by other studies. These findings demonstrated that the SAXS and WAXS were excellent tools to detect the collagen structure at nanoscale and the orientation of the collagen alignment, which was beneficial for skin tissue engineering and skin regenerative medicine.

The structure of the skin, types and distribution of mucous cell of yangtze sturgeon ( Acipenser dabryanus ) / La estructura de la piel, los tipos y distribución de las células mucosas del esturión yangtze ( Acipenser dabryanus )

The structural characteristics of the skin, types and distribution of mucous cells of Yangtze sturgeon (Acipenser dabryanus) were studied at the light microscope level, stained with Haematoxylin-eosin (HE) and Alcian blue-periodie acid Schiff (ABPAS). The skin of both was composed of epidermis and dermis. The dermis was divided into stratum spongiosum and stratum compactum. The stained color of stratum compactum was stained more deeply than that of stratum spongiosum. The skin thickness displayed differences in the fish at different body positions. The thickest of epidermis layer was on the dorsal region for Yangtze sturgeon, reversely, the thinnest was the mandibular region; Stratum spongiosum on the mandibular region was the thickest, the stratum spongiosum of the maxillary region was not obvious. In summary, keratinized spines, a kind of keratin derivative, are widely distributed in the mandibular, ventral, dorsal, and caudal peduncle skin surface for Yangtze sturgeon, and some pit organs mainly present in the skin surface of the maxillary and ventral regions. In short, the small amount of mucous cells in the skin of Yangtze sturgeon and the type of mucous cell were main Type IV, nevertheless there was a distribution of a few Type III.

Se estudiaron las características estructurales de la piel, los tipos y la distribución de las células mucosas del esturión Yangtze (Acipenser dabryanus) con microscopio de luz, teñidas con hematoxilina-eosina (HE) y azul alcián-ácido de Schiff (AB-PAS). La piel estaba compuesta por epidermis y dermis. La dermis se dividía en estrato esponjoso y estrato compacto. El grosor de la piel mostró diferencias en los peces en diferentes posiciones del cuerpo. La capa más gruesa de la epidermis se observó en la región dorsal del esturión Yangtze; a la inversa, la más delgada en la región mandibular. El estrato esponjoso en la región mandibular era el más grueso, el estrato esponjoso de la región maxilar no era visualizado. En resumen, las espinas queratinizadas, un tipo derivado de la queratina, estaban ampliamente distribuidas en la superficie de la piel del pedúnculo mandibular, ventral, dorsal y caudal en el esturión Yangtze, y algunos órganos en fosas, presentes principalmente en la superficie de la piel de las regiones mandibular y ventral. En resumen, la pequeña cantidad de células mucosas en la piel del esturión Yangtze y el tipo de célula mucosa eran células principales tipo IV, sin embargo, se observaron algunas células tipo III.

Cellular retinoic acid binding protein-II expression and its potential role in skin aging.

Skin aging is an intricate biological process consisting of intrinsic and extrinsic alterations of epidermal and dermal structures. Retinoids play an important role in epidermal cell growth and differentiation and are beneficial to counteract skin aging. Cellular retinoic acid binding protein-II (CRABP-II) selectively binds all trans-retinoic acid, the most active retinoid metabolite, contributing to regulate intracytoplasmic retinoid trafficking and keratinocyte differentiation. Immunohistochemistry revealed a reduced epidermal and dermal CRABP-II expression in aged human and mouse skin. To better clarify the role of CRABP-II, we investigated age-related skin changes in CRABP-II knock-out mice. We documented an early reduction of keratinocyte layers, proliferation and differentiation rate, dermal and hypodermal thickness, pilosebaceous units and dermal vascularity in CRABP-II knock-out compared with wild-type mice. Ultrastructural investigation documented reduced number and secretion of epidermal lamellar bodies in CRABP-II knock-out compared with wild-type mice. Cultured CRABP-II knock-out-derived dermal fibroblasts proliferated less and showed reduced levels of TGF-ß signal-related genes, Col1A1, Col1A2, and increased MMP2 transcripts compared with those from wild-type. Our data strongly support the hypothesis that a reduction of CRABP-II expression accelerates and promotes skin aging, and suggest CRABP-II as a novel target to improve the efficacy of retinoid-mediated anti-aging therapies.

Bioengineering the microanatomy of human skin.

Recreating the structure of human tissues in the laboratory is valuable for fundamental research, testing interventions, and reducing the use of animals. Critical to the use of such technology is the ability to produce tissue models that accurately reproduce the microanatomy of the native tissue. Current artificial cell-based skin systems lack thorough characterisation, are not representative of human skin, and can show variation. In this study, we have developed a novel full thickness model of human skin comprised of epidermal and dermal compartments. Using an inert porous scaffold, we created a dermal construct using human fibroblasts that secrete their own extracellular matrix proteins, which avoids the use of animal-derived materials. The dermal construct acts as a foundation upon which epidermal keratinocytes were seeded and differentiated into a stratified keratinised epithelium. In-depth morphological analyses of the model demonstrated very close similarities with native human skin. Extensive immunostaining and electron microscopy analysis revealed ultrastructural details such as keratohyalin granules and lamellar bodies within the stratum granulosum, specialised junctional complexes, and the presence of a basal lamina. These features reflect the functional characteristics and barrier properties of the skin equivalent. Robustness and reproducibility of in vitro models are important attributes in experimental practice, and we demonstrate the consistency of the skin construct between different users. In summary, a new model of full thickness human skin has been developed that possesses microanatomical features reminiscent of native tissue. This skin model platform will be of significant interest to scientists researching the structure and function of human skin.

Histological and functional comparisons of four anatomical regions of porcine skin with human abdominal skin.

Because of the shortage of human skin for research purposes, porcine skin has been used as a model of human skin. The aim of this study was to identify the region of German Landrace pig skin that could be used as the best possible substitute for human abdominal skin. Porcine samples were collected from the ear, flank, back and caudal abdomen; human abdominal skin samples were excised during plastic surgery. Histological and ultrastructural assessments were carried out on the epidermis and dermis, with emphasis on the dermo-epidermal interface length, dermo-epidermal thickness ratio as well as densities of; hair follicles, arrector pili muscles, blood vessels and sweat glands. In the pig, the barrier function of the four anatomical regions was assessed. Results showed that both histologically and ultrastructurally, all four regions of porcine skin were similar to human skin. These include the shapes of keratinocytes, structure of cell contacts and presence of Weibel Palade bodies in endothelial cells. Other parameters such as the thickness of epidermis, the thickness of stratum basale, spinosum and granulosum and the number of cell layers in the stratum corneum were similar in human abdominal and in all four regions of porcine skin. However, there were also significant differences especially in the thickness of the stratum corneum, the dermo-epidermal interface length and the blood vessel density.

Tensile behavior and structural characterization of pig dermis.

Skin, the outermost layer of the body, fulfills a broad range of functions, protecting internal organs from damage and infection, while regulating the body's temperature and water content via the exchange of heat and fluids. It must be able to withstand and recover from extensive deformation and damage that can occur during growth, movement, and potential injuries. A detailed investigation of the evolution of the collagen architecture of the dermis as a function of deformation is conducted, which reveals new aspects that help us to understand the mechanical response of skin. Juvenile pig is used as a model material because of its similarity to human skin. The dermis is found to have a tridimensional woven structure of collagen fibers, which evolves with deformation. After failure, we observe that the fibers have straightened and aligned in the direction of tension. The effects of strain-rate change, cyclic loading, stress relaxation, and orientation are quantitatively established. Digital image correlation techniques are implemented to quantify skin's anisotropy; measurements of the Poisson ratio are reported. This is coupled with transmission electron microscopy which enables obtaining quantitative strain parameters evaluated through the orientation and curvature of the collagen fibers and their changes, for the first time in all three dimensions of the tissue. A model experiment using braided human hair in tension exhibits a similar J-curve response to skin, and we propose that this fiber configuration is at least partially responsible for the monotonic increase of the tangent modulus of skin with strain. The obtained results are intended to serve as a basis for structurally-based models of skin. STATEMENT OF SIGNIFICANCE: Our study reveals a new aspect of the dermis: it is comprised of a tridimensional woven structure of collagen fibers, which evolves with deformation. This is enabled by primarily two techniques, transmission electron microscopy on three perpendicular planes and confocal images with second harmonic generation fluorescence of collagen, captured at different intervals of depth. After failure, the fibers have straightened and aligned in the direction of tension. Digital image correlation techniques are implemented to quantify skin's anisotropy; measurements of the Poisson ratio are reported. A model experiment using braided human hair in tension exhibits a similar J-curve response to skin, and we propose that this fiber configuration is at least partially responsible for the monotonic increase of the tangent modulus of skin with strain.

Histological and immunohistochemical characterization of the integument and parotoids glands Rhinella bergi (Anura: Bufsonidae): Development and differentiation.

A detailed description of the tegument and parotoid glands of pre-metamorphic, post-metamorphic, juvenile and adult individuals of Rhinella bergi is presented to provide an exhaustive analysis of the integumentary characteristics of this species. Fragments of the tegument were fixed in Bouin solution and preserved in buffered Formol 10%. Subsequently, scanning electron microscopy (SEM) was performed to characterize the macroscopic structure of these regions. Microscopic observations were made from histological sections stained with Hematoxylin and Eosin, Alcian Blue (pH 2,5), PAS-H, Coomassie Blue, Oil Red, and Bielschowsky Impregnation.. There were three types of protuberance: warts, tubers, and thorns. These structures became evident from post-metamorphic stages. The ventral surface shows elevations similar to flat warts; however, tubers and spines are absent. Histologically, each structure consists of a spongy dermis of lax connective tissue and dense and compact dermis, associated with granular glands and a keratinized epidermis. The latter, in the dorsal region, forms projections called thorns. The granular glands accumulate, and their alveoli increase in size progressively. This work provides a morphological and histological description of the integument and the parotoid glands during the larval and post-metamorphic stage of the genus Rhinella, with aspects described for the first time in the genus.

Regional Control of Hairless versus Hair-Bearing Skin by Dkk2.

Haired skin is a defining characteristic of mammals. However, some specialized skin regions, such as human palms, soles and ventral wrist, and mouse plantar foot, are entirely hairless. Using mouse plantar skin as a model system, we show that the endogenous secreted Wnt inhibitor DKK2 suppresses plantar hair follicle development and permits the formation of hairless skin. Plantar skin retains all of the mechanistic components needed for hair follicle development, as genetic deletion of Dkk2 permits formation of fully functional plantar hair follicles that give rise to external hair, contain sebaceous glands and a stem cell compartment, and undergo regenerative growth. In the absence of Dkk2, Wnt/ß-catenin signaling activity is initially broadly elevated in embryonic plantar skin and gradually becomes patterned, mimicking follicular development in normally haired areas. These data provide a paradigm in which regionally restricted expression of a Wnt inhibitor underlies specification of hairless versus hairy skin.