Adhesion molecules in skin development: morphogenesis of feather and hair

Dynamic transcriptome profiling reveals essential roles of the Receptor Tyrosine Kinases (RTK) family in feather development of duck

1. Chicken primary myoblasts (CPMs) are precursors that form muscle fibres. The proliferation and differentiation of CPMs is an essential stage in muscle development. Previous RNA-seq analysis showed that phosphoglycerate dehydrogenase (PHGDH) is a differentially expressed gene in chicken muscle tissue at different growth stages. Therefore, the following study explored the effect of PHGDH on the proliferation and differentiation of CPMs.2. The effect on the proliferation of CPMs by RT-qPCR, CCK-8, and EdU assays after the overexpression and knockdown of PHGDH was evaluated. RT-qPCR, western blotting, and indirect immunofluorescence were used to detect the effect of PHGDH on the differentiation of the CPMs. The expression was observed at different time points for differentiation induced by the CPMs.3. The results showed that PHGDH significantly promoted proliferation and differentiation in CPMs. The results showed that overexpression of PHGDH significantly upregulated CPM proliferation, while knockdown had the opposite effect. Marker genes showed that overexpression of PHGDH significantly upregulated the expression of P21, MYOG and MYOD genes, significantly downregulated the expression of the MSTN gene and promoted the expression of the MYHC protein. In contrast, PHGDH knockdown had the opposite effect.4. Desmin immunofluorescence analysis of myotube differentiation in primary myoblasts showed that overexpression of PHGDH significantly increased the area of myotube differentiation and promoted the proliferation and differentiation of myoblasts. Knockdown of PHGDH had the opposite effect.5. In summary, PHGDH was shown to play a positive role in regulating myoblast proliferation and differentiation. This provided a theoretical basis for further analysis of the regulatory mechanism of the PHGDH gene in chicken muscle development and for improving poultry production.

Detecting the Mechanism behind the Transition from Fixed Two-Dimensional Patterned Sika Deer (Cervus nippon) Dermal Papilla Cells to Three-Dimensional Pattern

The hair follicle dermal papilla is critical for hair generation and de novo regeneration. When cultured in vitro, dermal papilla cells from different species demonstrate two distinguishable growth patterns under the conventional culture condition: a self-aggregative three dimensional spheroidal (3D) cell pattern and a two dimensional (2D) monolayer cell pattern, correlating with different hair inducing properties. Whether the loss of self-aggregative behavior relates to species-specific differences or the improper culture condition remains unclear. Can the fixed 2D patterned dermal papilla cells recover the self-aggregative behavior and 3D pattern also remains undetected. Here, we successfully constructed the two growth patterns using sika deer (Cervus nippon) dermal papilla cells and proved it was the culture condition that determined the dermal papilla growth pattern. The two growth patterns could transit mutually as the culture condition was exchanged. The fixed 2D patterned sika deer dermal papilla cells could recover the self-aggregative behavior and transit back to 3D pattern, accompanied by the restoration of hair inducing capability when the culture condition was changed. In addition, the global gene expressions during the transition from 2D pattern to 3D pattern were compared to detect the potential regulating genes and pathways involved in the recovery of 3D pattern and hair inducing capability.

Exploration of key regulators driving primary feather follicle induction in goose skin

The primary feather follicles are universal skin appendages widely distributed in the skin of feathered birds. The morphogenesis and development of the primary feather follicles in goose skin remain largely unknown. Here, the induction of primary feather follicles in goose embryonic skin (pre-induction vs induction) was investigated by de novo transcriptome analyses to reveal 409 differentially expressed genes (DEGs). The DEGs were characterized to potentially regulate the de novo formation of feather follicle primordia consisting of placode (4 genes) and dermal condensate (12 genes), and the thickening of epidermis (5 genes) and dermal fibroblasts (17 genes), respectively. Further analyses enriched DEGs into GO terms represented as cell adhesion and KEGG pathways including Wnt and Hedgehog signaling pathways that are highly correlated with cell communication and molecular regulation. Six selected Wnt pathway genes were detected by qPCR with up-regulation in goose skin during the induction of primary feather follicles. The localization of WNT16, SFRP1 and FRZB by in situ hybridization showed weak expression in the primary feather primordia, whereas FZD1, LEF1 and DKK1 were expressed initially in the inter-follicular skin and feather follicle primordia, then mainly restricted in the feather primordia. The spatial-temporal expression patterns indicate that Wnt pathway genes DKK1, FZD1 and LEF1 are the important regulators functioned in the induction of primary feather follicle in goose skin. The dynamic molecular changes and specific gene expression patterns revealed in this report provide the general knowledge of primary feather follicle and skin development in waterfowl, and contribute to further understand the diversity of hair and feather development beyond the mouse and chicken models.

A bald statement - Current approaches to manipulate miniaturisation focus only on promoting hair growth

Hair plays a large part in communication and society with its role changing through time and across cultures. Most people do not leave the house before combing their hair or shaving their beard and for many hair loss or irregular hair growth can have a significant impact on their psychological health. Somewhat unsurprisingly, according to GMR Data, today's global hair care industry is worth an estimated $87 Billion, with hair loss estimated at $2.8 Billion. Considering that no current hair loss-related products can completely reverse hair loss, it is reasonable to believe this market could expand significantly with the discovery of a comprehensive therapy. As such, a great deal of research focuses on overcoming hair loss, and in particular, a common form of hair loss known as androgenetic alopecia (AGA) or male pattern baldness. In AGA, hair follicles miniaturise in a large step change from a terminal to a vellus state. Within this viewpoint article, we discuss how influx and efflux of cells into and out from the dermal papilla (DP) can modulate DP size during the hair cycle. As DP size is positively correlated with the size of the hair fibre produced by a follicle, we argue here that therapies for treating AGA should be developed which can alter DP size, rather than just promote hair growth. We also discuss current therapeutics for AGA and emphasise the importance of using the right model systems to analyse miniaturisation.

Dynamic transcriptome profiling towards understanding the morphogenesis and development of diverse feather in domestic duck

Background

Feathers with complex and fine structure are hallmark avian integument appendages, which have contributed significantly to the survival and breeding for birds. Here, we aimed to explore the differentiation, morphogenesis and development of diverse feathers in the domestic duck.

Results

Transcriptome profiles of skin owing feather follicle from two body parts at three physiological stages were constructed to understand the molecular network and excavate the candidate genes associated with the development of plumulaceous and flight feather structures. The venn analysis of differentially expressed genes (DEGs) between abdomen and wing skin tissues at three developmental stages showed that 38 genes owing identical differentially expression pattern. Together, our data suggest that feather morphological and structural diversity can be possibly related to the homeobox proteins. The key series-clusters, many candidate biological processes and genes were identified for the morphogenesis, growth and development of two feather types. Through comparing the results of developmental transcriptomes from plumulaceous and flight feather, we found that DEGs belonging to the family of WNT, FGF and BMP have certain differences; even the consistent DEGs of skin and feather follicle transcriptomes from abdomen and wing have the different expression patterns.

Conclusions

Overall, this study detected many functional genes and showed differences in the molecular mechanisms of diverse feather developments. The findings in WNT, FGF and BMP, which were consistent with biological experiments, showed more possible complex modulations. A correlative role of HOX genes was also suggested but future biological verification experiments are required. This work provided valuable information for subsequent research on the morphogenesis of feathers.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4778-7) contains supplementary material, which is available to authorized users.

Using scale and feather traits for module construction provides a functional approach to chicken epidermal development

Gene co-expression network analysis has been a research method widely used in systematically exploring gene function and interaction. Using the Weighted Gene Co-expression Network Analysis (WGCNA) approach to construct a gene co-expression network using data from a customized 44K microarray transcriptome of chicken epidermal embryogenesis, we have identified two distinct modules that are highly correlated with scale or feather development traits. Signaling pathways related to feather development were enriched in the traditional KEGG pathway analysis and functional terms relating specifically to embryonic epidermal development were also enriched in the Gene Ontology analysis. Significant enrichment annotations were discovered from customized enrichment tools such as Modular Single-Set Enrichment Test (MSET) and Medical Subject Headings (MeSH). Hub genes in both trait-correlated modules showed strong specific functional enrichment toward epidermal development. Also, regulatory elements, such as transcription factors and miRNAs, were targeted in the significant enrichment result. This work highlights the advantage of this methodology for functional prediction of genes not previously associated with scale- and feather trait-related modules.

Transcriptomic analyses of regenerating adult feathers in chicken

Background

Feathers have diverse forms with hierarchical branching patterns and are an excellent model for studying the development and evolution of morphological traits. The complex structure of feathers allows for various types of morphological changes to occur. The genetic basis of the structural differences between different parts of a feather and between different types of feather is a fundamental question in the study of feather diversity, yet there is only limited relevant information for gene expression during feather development.

Results

We conducted transcriptomic analysis of five zones of feather morphologies from two feather types at different times during their regeneration after plucking. The expression profiles of genes associated with the development of feather structure were examined. We compared the gene expression patterns in different types of feathers and different portions of a feather and identified morphotype-specific gene expression patterns. Many candidate genes were identified for growth control, morphogenesis, or the differentiation of specific structures of different feather types.

Conclusion

This study laid the ground work for studying the evolutionary origin and diversification of feathers as abundant data were produced for the study of feather morphogenesis. It significantly increased our understanding of the complex molecular and cellular events in feather development processes and provided a foundation for future studies on the development of other skin appendages.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1966-6) contains supplementary material, which is available to authorized users.

Intercellular adhesion molecule-1 and hair follicle regression

Although the intercellular adhesion molecule-1 (ICAM-1) is recognized for its pivotal role in inflammation and immune responses, its role in developmental systems, such as the cyclic growth (anagen) and regression (catagen) of the hair follicle, remains to be explored. Here we demonstrate that ICAM-1 expression in murine skin is even more widespread and more developmentally regulated than was previously believed. In addition to endothelial cells, selected epidermal and follicular keratinocyte subpopulations, as well as interfollicular fibroblasts, express ICAM-1. Murine hair follicles express ICAM-1 only late during morphogenesis. Thereafter, morphologically identical follicles markedly differ in their ICAM-1 expression patterns, which become strikingly hair cycle-dependent in both intra- and extrafollicular skin compartments. Minimal ICAM-1 and leukocyte function-associated (LFA-1) protein and mRNA expression is observed during early anagen and maximal expression during late anagen and catagen. Keratinocytes of the distal outer root sheath, fibroblasts of the perifollicular connective tissue sheath, and perifollicular blood vessels exhibit maximal ICAM-1 immunoreactivity during catagen, which corresponds to changes of LFA-1 expression on perifollicular macrophages. Finally, ICAM-1-deficient mice display significant catagen acceleration compared to wild-type controls. Therefore, ICAM-1 upregulation is not limited to pathological situations but is also important for skin and hair follicle remodeling. Collectively, this suggests a new and apparently nonimmunological function for ICAM-1-related signaling in cutaneous biology.

E- and P-cadherin expression during murine hair follicle morphogenesis and cycling

The role of adhesion molecules in the control of hair follicle (HF) morphogenesis, regression and cycling is still rather enigmatic. Since the adhesion molecules E- and P-cadherin (Ecad and Pcad) are functionally important, e.g. during embryonic pattern formation, we have studied their expression patterns during neonatal HF morphogenesis and cycling in C57/BL6 mice by immunohistology and semi-quantitative RT-PCR. The expression of both cadherins was strikingly hair cycle-dependent and restricted to distinct anatomical HF compartments. During HF morphogenesis, hair bud keratinocytes displayed strong Ecad and Pcad immunoreactivity (IR). While neonatal epidermis showed Ecad IR in all epidermal layers, Pcad IR was restricted to the basal layer. During later stages of HF morphogenesis and during anagen IV-VI of the adolescent murine hair cycle, the outer root sheath showed strong E- and Pcad IR. Instead, the outermost portion of the hair matrix and the inner root sheath displayed isolated Ecad IR, while the innermost portion of the hair matrix exhibited isolated Pcad IR. During telogen, all epidermal and follicular keratinocytes showed strong Ecad IR. This is in contrast to Pcad, whose IR was stringently restricted to matrix and secondary hair germ keratinocytes which are in closest proximity to the dermal papilla. These findings suggest that isolated or combined E- and/or Pcad expression is involved in follicular pattern formation by segregating HF keratinocytes into functionally distinct subpopulations; most notably, isolated Pcad expression may segregate those hair matrix keratinocytes into one functional epithelial tissue unit, which is particularly susceptible to growth control by dermal papilla-derived morphogens. The next challenge is to define which secreted agents implicated in hair growth control modulate these follicular cadherin expression patterns, and to define how these basic parameters of HF topobiology are altered during common hair growth disorders.

Multiple mechanisms contribute to the avoidance of avian epidermis by sensory axons

In birds, sensory innervation of skin is restricted to dermis, with few axons penetrating into the epidermis. This pattern of innervation is maintained in vitro, where sensory neurites avoid explants of epidermis but grow readily on dermis. We have used this coculture paradigm to investigate the mechanisms that impede innervation of avian epidermis. The lack of epidermal innervation in birds has been attributed to diffusible chondroitin sulfate proteoglycans (CSPGs) secreted by the epidermis, although direct experimental evidence is weak. We found that elimination of CSPG function with either chondroitinase or neutralizing antibodies did not promote growth of DRG neurites onto epidermis in vitro, indicating that CSPGs alone are not responsible for preventing epidermal innervation. Moreover, the failure of sensory neurites to invade epidermis is not due exclusively to soluble chemorepulsive factors, since sensory neurites also avoid dead epidermis. This inhibition can be overridden, however, by coating epidermis with the growth-promoting molecule laminin, but only if the tissue is killed first. Epidermal innervation of laminin-coated epidermis is even more robust when CSPGs are also eliminated. Thus, the absence of growth-promoting or permissive molecules, such as laminin, may contribute to the failure of sensory neurites to invade avian epidermis. Together these results show that the inhibitory character of avian epidermis is complex. Cell- or matrix-associated CSPGs clearly contribute to the inhibition, but are not solely responsible.

Distinct patterns of NCAM expression are associated with defined stages of murine hair follicle morphogenesis and regression

Hair follicle development, growth (anagen), and regression (catagen) largely result from bidirectional epithelial-mesenchymal interactions whose molecular basis is still unclear. Because adhesion molecules are critically involved in pattern formation and because the fundamental importance of neural cell adhesion molecule (NCAM) for feather development has been demonstrated, we studied the protein expression patterns of NCAM during hair follicle development and regression in the C57BL/6 mouse model. During murine hair follicle development, NCAM immunoreactivity (IR) was first detected on epithelial hair placodes and later on selected keratinocytes in the distal outer root sheath. Mesenchymal NCAM immunoreactivity (IR) was noted on fibroblasts of the future dermal papilla (DP) and the perifollicular connective tissue sheath. Fetal hair follicle elongation coincided with strong, ubiquitous dermal NCAM IR, which remained strong until the follicles entered into their first neonatal catagen. At this time, the strong interfollicular dermal NCAM IR decreased substantially. During consecutive hair cycles, mesenchymal NCAM IR was seen exclusively on DP and perifollicular connective tissue sheath fibroblasts and on the trailing cells of regressing catagen hair follicles. These highly restricted and developmentally controlled expression patterns suggest an important role for NCAM in hair follicle topobiology during morphogenesis and cyclic remodeling of this miniorgan.

Molecular and functional aspects of the hairless (hr) gene in laboratory rodents and humans

For many years, hairless and rhino mouse mutants have provided a useful and extensively exploited model for studying different aspects of skin physiology, including skin aging, pharmacokinetic evaluation of drug activity and cutaneous absorption, skin carcinogenesis, and skin toxicology. Interestingly, however, hairless and rhino mice have rarely been studied for their primary cellular defect - hairlessness - and thus, the hairless gene itself and its physiological functions have been largely overlooked for decades. The recent identification of the human homolog of the hairless gene on human Chromosome 8p12 confirmed the clinical significance of the phenomenon of "hairlessness" in humans, which was predicted on the basis of similarities between hairless mice and a congenital hair disorder characterized by atrichia with papules. Mutations in the hairless gene of mice provide instructive models for further studies of hr gene function, and may facilitate insights into the pathophysiology of different human disorders associated with the disruption of hr gene activity. We provide an overview of current data on the structure and expression patterns of the hr gene, and of mutations at the hairless locus in mice and humans, including the genetic basis of different alleles, the pathology of hairlessness, reproductive and immunological defects, and susceptibility to dioxin toxicity. On the basis of our current understanding of hairlessness, we speculate on the putative functions of the hr gene product in skin physiology, and particularly, in hair follicle biology.

Towards defining the pathogenesis of the hairless phenotype

Mutation of the hairless (hr) gene in mice causes severe abnormalities during the first hair follicle regression (catagen), resulting in complete baldness. Here, we further characterize how hairlessness develops in HRS/J hairless mouse skin (hr) by histology, histochemistry, immunohistology, and in situ hybridization. We show that, in hr skin, only two defined epithelial cell populations in the distal outer root sheath (ORS) retain their integrity, whereas the rest of the ORS disintegrates. The surviving distal ORS forms the characteristic utriculi, whereas the remnants of the bulge get isolated from other epithelial compartments, but retain the capacity to proliferate and to produce either columnar epithelial outgrowths or selected dermal cysts. Normal dermal papilla structures get lost during the development of hairlessness. Based on the patterns of keratin 17 mRNA and neural cell adhesion molecule antigen expression, and on the distribution of alkaline phosphatase activity, we propose that dermal cysts in hr skin arise from (i) the central ORS, (ii) bulge-derived cells, or (iii) the disintegrating proximal ORS under the influence of dermal papilla remnants. The hr mutation seems to disrupt the integrity of key functional tissue units in the hair follicle, possibly due to a dysregulation of normal, catagen-associated apoptosis and/or an impairment of cell adhesion, whereas the distal follicle epithelium (including its stem cell region) seems to be largely protected from this. Thus, hairless mice offer a unique model for dissecting the as yet obscure functional properties of the hr gene product in maintaining follicle integrity during normal catagen.

Changing pattern of desmocollin 3 expression accompanies epidermal organisation during skin development

The adhesive core of the desmosome is composed of cadherin-like glycoproteins of 2 families, desmocollins and desmogleins. The desmosomal cadherins show distinct patterns of expression in adult epidermis, and we have suggested that the desmocollins have a functional role in regulating the differentiation and/or morphogenesis of that epithelium (North et al. [1996] Proc. Natl. Acad. Sci. USA 93:7701-7705.). To examine this hypothesis, we cloned murine desmocollins and examined the induction patterns of desmocollins 1 and 3 during skin and skin appendage development. Desmocollins 3 and 1 were first expressed in epidermis in highly regional patterns at embryonic days 13.0 and 13.5, respectively, and both were up-regulated in general body epidermis at day 14.5. At this stage, epidermis is undifferentiated and the desmocollins showed an unexpected expression pattern. However, by day 18.5 when skin had undergone terminal differentiation, desmocollin 1 and 3 expression resembled that found in the adult. Thus, the establishment of the adult pattern of desmocollin expression corresponds to the adult pattern of epidermal stratification. We suggest that it is the ratio of desmocollin 1 to desmocollin 3 expression at different levels in the epidermis that is fundamental in establishing this pattern of differentiation.

Expression of two Ig family adhesion molecules in the murine hair cycle: DCC in the bulge epithelia and NCAM in the follicular papilla

The hair cycle involves remodeling of cells and of cell groups into a complex follicular structure. During skin appendage development, adhesion molecules such as neural cell adhesion molecule (NCAM) and deleted in colon carcinoma (DC) participate in the formation of cell groups. NCAM has been found to be expressed in the mesenchyme during mouse hair follicle induction. DCC expression has been observed in the epithelial cells of the developing feather. We postulate that these two molecules may also define cell groups in the cycling hair follicle. Here we report their spatio-temporal expression patterns during the depilation-induced murine hair cycle. NCAM expression was also examined in positive and negative hair-inductive follicular papilla cell lines. Throughout the hair cycle, DCC expression was confined to the basal keratinocytes of the epidermis and the epithelial portion of the hair follicle. During mid-anagen, two types of deleted in colon carcinoma staining were observed. One was a cell surface pattern seen in the epithelial cells in the bulge region where the follicular stem cells reside. The other was a diffuse cytoplasmic staining pattern in the transient hair follicle epithelia located below the bulge region. Prominent NCAM staining was observed in the follicular papilla throughout the hair cycle and was accompanied by weak staining of the matrix epithelia. NCAM expression correlated with hair induction by a follicular papilla cell line. The results suggest that DCC and NCAM define the permanent cell groups of the hair follicle and that NCAM is important for hair induction.

Molecular histology in skin appendage morphogenesis

Classical histological studies have demonstrated the cellular organization of skin appendages and helped us appreciate the intricate structures and function of skin appendages. At this juncture, questions can be directed to determine how these cellular organizations are achieved. How do cells rearrange themselves to form the complex cyto-architecture of skin appendages? What are the molecular bases of the morphogenesis and histogenesis of skin appendages? Recently, many new molecules expressed in a spatial and temporal specific manner during the formation of skin appendages were identified by molecular biological approaches. In this review, novel molecular techniques that are useful in skin appendage research are discussed. The distribution of exemplary molecules from different categories including growth factors, intracellular signaling molecules, homeobox genes, adhesion molecules, and extracellular matrix molecules are summarized in a diagram using feather and hair as models. We hope that these results will serve as the ground work for completing the molecular mapping of skin appendages which will refine and re-define our understanding of the developmental process beyond relying on morphological criteria. We also hope that the listed protocols will help those who are interested in this venture. This new molecular histology of skin appendages is the foundation for forming new hypotheses on how molecules are mechanistically involved in skin appendage development and for designing experiments to test them. This may also lead to the modulation of healing and regeneration processes in future treatment modalities.

The regulatory biology of the human pilosebaceous unit

The last few years have witnessed an acceleration in our understanding of the regulation of the human pilosebaceous unit. Recombination and histochemical experiments are beginning to elucidate the role of homeotic genes, transcription factors, growth factors and adhesion molecules in pilosebaceous embryology. Histochemical studies, experiments in gene-modified animals, and in vitro studies on growing human hairs, have identified a number of growth factors that are central to normal hair growth. Thus epidermal growth factor and transforming growth factor-alpha appear to be involved in the triggering of both anagen and catagen. Insulin-like growth factor-I appears to sustain normal anagen growth, transforming growth factor-beta will inhibit anagen growth, while interleukin-1-alpha and tumour necrosis factor-alpha will induce matrix cell death. These complex growth factor effects are beginning to be moulded into an integrated model of pilosebaceous regulation. The role of steroid hormones in modulating these growth factor effects is also beginning to be understood.

Human epidermal keratinocytes are a source of tenascin-C during wound healing

Tenascin-C is a large hexameric extracellular matrix glycoprotein that is expressed in a temporally and spatially restricted pattern associated with stromal-epithelial interactions. In adult human skin, the expression level of tenascin-C is low, but tenascin-C is abundantly present in the dermal compartment during embryogenesis and wound healing and in skin tumors. Herein we have investigated the cellular source of tenascin-C production in human skin, both in vivo and in vitro, by using immunohistochemistry, mRNA in situ hybridization, western blotting, and an enzyme-linked immunosorbent assay. In addition we studied the cell-matrix interaction between epidermal keratinocytes and purified tenascin-C. By using in vitro culture models, we found that keratinocytes not only synthesize and secrete tenascin-C but can also deposit tenascin-C in de-epidermized dermis in a pattern that is very similar to that in vivo. In vivo, during wound healing of normal human skin, we found tenascin-C extracellularly in the wound bed and also in a granular pattern within the neo-epidermis. By mRNA in situ hybridization, we could identify the basal migrated keratinocytes as the main source of tenascin-C in the early phase of wound healing. In the granulation phase, tenascin-C expression by the keratinocytes is downregulated. Cultured keratinocytes were found to adhere poorly to tenascin-C, and those that did adhere retained a rounded morphology. We conclude that human keratinocytes are a major source of tenascin-C during the early phase of wound healing, and we hypothesize that tenascin-C is unlikely to be an adhesive substrate for migrating keratinocytes.

Histochemistry of the human hair follicle

Immunohistochemistry of the human hair follicle is of increasing interest in hair research. The data on antigen distribution in the different epithelial and mesenchymal structures of this unique skin appendage are superfluous now. In the present chapter, I will concentrate on selected aspects related to hair follicle differentiation, epithelial-mesenchymal interactions, proliferation and metabolic activity. Hair diseases are common. Not unusually, hair growth and structure reflect systemic disturbances. Basic knowledge of hair anatomy and histochemistry is required for their rational evaluation. Immunohistochemistry is a valuable tool for microanatomy of the hair apparatus. It offers a link between the biochemical data and structural components of hair follicles, which may help to better understand physiology of hair growth and hair diseases.

Hair follicle growth controls

Research in hair biology has embarked in the pursuit for molecules that control hair growth. Many molecules already have been associated with the controls of hair patterning, hair maturation, and hair cycling and differentiation. Knowing how these molecules work gives us the tools for understanding and treating patients with hair disorders.

Immunohistochemical studies of the adult human ovary: possible contribution of immune and epithelial factors to folliculogenesis

PROBLEM

Formation of primordial follicles in adult ovaries could be a cryptic process limited to relatively small areas of the ovarian cortex and occurring during a certain stage of the menstrual cycle. Such an event may require a specific milieu provided by factors involved in developmental processes, i.e., morphoregulatory molecules and macrophages.

METHOD

Adult human ovaries were investigated by immunohistochemistry for surface epithelium and granulosa cell markers (cytokeratin 18 and MHC class I), immune system-related morphoregulatory molecules (Thy-1 glycoprotein and N-CAM), and macrophage phenotypes (CD14, CD68, and MHC class II).

RESULTS

In some ovaries 300-500 microns areas of surface epithelium were overgrown by tunica albuginea, descended into the stroma, and apparently fragmented into individual small (20-40 microns) follicle-like cell nests. Differentiation of the surface epithelium was accompanied by macrophages and Thy-1 glycoprotein. Small segments of surface epithelium showed N-CAM and a lacked MHC class I expression. In such segments, clear spherical germ-like cells migrated into the deeper stroma, associated with the microvasculature, and eventually aggregated with follicle-like cell nests.

CONCLUSIONS

Our data suggest that surface epithelium may be involved in the formation of some primordial follicles in adult ovaries. This process, and further follicular fate, may require a precise interplay of immune system related morphoregulatory molecules and macrophages.

Follicular origin of epidermal papillomas in v-Ha-ras transgenic TG.AC mouse skin

A follicular origin for some skin tumors has been hypothesized in both humans and animal models. Because of its rapid and sensitive response to tumor promoter treatment, a v-Ha-ras transgenic (TG.AC) mouse line was used to determine the origins of epidermal papillomas. Using histological studies and transgene expression as a marker for papilloma development, we determined that pedunculated papillomas arose from focal hyperplasias of the permanent portion of the follicular epithelium in phorbol 12-myristate 13-acetate-treated TG.AC mouse skin. Damage to the hair follicle by depilation was also sufficient to induce papillomas that were histologically indistinguishable from those produced by chemical exposure. Identification of the cellular origins of papillomas in this transgenic mouse model will allow for an analysis of the role of the hair follicle and hair cycle-associated signaling in tumor development.

Molecules of the cycling hair follicle--a tabulated review

In this review we tabulated molecules which have been experimentally identified to be associated with, or play a role in, hair follicle growth. While compiling these data we were impressed by the fact that this field is only now beginning to be developed in terms of molecular analysis. Ironically, hair was used in some of the earliest molecular approaches to biologic structure (e.g. Astbury and Street, 1931), but the field did not develop from there. From our review we have come to the following conclusions. (1) As indicated by the growing number of reports dealing with follicle-associated molecules in the past 3 years, the field of hair biology has entered a new molecular era. (2) In many reported hair biology studies not enough emphasis has been placed on the fact that the follicle is a dynamic structure. All too often a study is limited to follicles of one particular phase of the cycle or one phase of development. Students in the field have to be more sensitive to the remarkable changes that this deceptively simple structure can undergo during its cycle. (3) Although we have not been able to find any molecules unique to the follicle, some of the structural molecules come close to an ideal tool. It is our impression that even more specific molecule tags will be found. Whether this requires a subtraction library approach or gene mapping of specific mutants is not yet clear. It would appear that the large, diverse family of intermediate filament-associated proteins will prove to be an excellent source of unique follicle-labeling molecules. (4) There is an acute need for molecules which distinguish the phases of the cycle, e.g. telogen from early anagen. Telogen is by far the most difficult phase to identify morphologically since the earliest phase of anagen and the latest phase of catagen may appear structurally like telogen. That these phases are functionally distinguishable must imply a molecular difference. As the number of recognized hair follicle-associated molecules and their interactions increase, it will be essential to assemble libraries of highly specific RNA and antibody probes for localization and mapping studies. We recognize that this review, as written, is imperfect. It is particularly deficient in making any effort towards identifying unifying principles of structure and function. We look forward to returning to this subject within 3 years.(ABSTRACT TRUNCATED AT 400 WORDS)

Dynamic expression patterns of tenascin, proteoglycans, and cell adhesion molecules during human hair follicle morphogenesis

The development of skin appendages such as hair, feathers, and teeth is brought about by reciprocal interactions between epidermal and mesenchymal tissues and is thought to be influenced in part by cell adhesion molecules and components of the extracellular matrix. The developmental distributions of tenascin, neural cell adhesion molecule (NCAM), E-cadherin, intercellular adhesion molecule 1 (ICAM-1), chondroitin sulfate proteoglycan (CSPG), and the heparan sulfate proteoglycan perlecan were studied in relation to hair follicle morphogenesis in fetal human skin. Tenascin first appeared in developing skin in focal concentrations at the epidermal-mesenchymal interface, just prior to, and presumably correlated with, hair follicle initiation. Tenascin immunostaining remained prominent in the basement membrane zone and extracellular matrix of the follicle sheath during subsequent morphogenetic stages. Two forms of tenascin (M(r) 250 x 10(3) and 280-300 x 10(3)), were revealed by Western blots of skin extracts. NCAM immunolabeling was initially present throughout the dermis, and became progressively restricted to the dermal condensation and the follicle sheath. Western blot analysis revealed an isoform of NCAM (M(r) 160 x 10(3)) which lacked polysialic acid. At all stages, E-cadherin staining was diminished on follicle cells situated adjacent to the basement membrane, relative to cells in the follicle interior. Follicle-specific immunostaining for ICAM-1 was transient, appearing only at the pre-germ and hair germ stages of development. Antibodies to three distinct CSPG determinants revealed unique immunolabeling patterns following follicle initiation: One CSPG epitope co-distributed with tenascin in the follicle basement membrane and follicle sheath extracellular matrix; one CSPG epitope was similarly expressed, and was also found on follicle epithelial cells; and the third CSPG determinant was noticeably absent from the follicle sheath during elongation of the developing appendage. Perlecan was concentrated in the dermal papilla, in addition to its distribution in all skin basement membranes. A model for how these diverse molecules may interact to influence human hair follicle morphogenesis is presented.

Asymmetric patterns of gap junctional communication in developing chicken skin

To study the pattern of gap junctional communication in chicken skin and feather development, we injected Lucifer Yellow into single cells and monitored the transfer of the fluorescent dye through gap junctions. Dye coupling is present between cells of the epithelium as well as between cells of the mesoderm. However, dye transfer did not occur equally in all directions and showed several consistent patterns and asymmetries, including: (1) no dye coupling between mesoderm and epithelium, (2) partial restriction of dye coupling at the feather bud/interbud boundary during early feather bud development, (3) preferential distribution of Lucifer Yellow along the anteroposterior axis of the feather placode and (4) absence of dye coupling in some epithelial cells. These results suggest the presence of preferential pathways of communication that may play a role in the patterning of chicken skin.

The making of a feather: homeoproteins, retinoids and adhesion molecules

We have been using feather development as a model for understanding the molecular basis of pattern formation and to explore the roles of homeoproteins, retinoids and adhesion molecules in this process. Two kinds of homeobox (Hox) protein gradients in the skin have been identified: a 'microgradient' within a single feather bud and a 'macrogradient' across the feather tract. The asynchronous alignment of different Hox macrogradients establishes a unique repertoire of Hox expression patterns in skin appendages within the integument, designated here as the 'Hox codes of skin appendages'. It is hypothesized that these Hox codes contribute to the phenotypic determination of skin appendages. High doses of retinoic acid cause a morphological transformation between feather and scale, while low doses of retinoic acid cause an alteration of the axial orientation of skin appendages. We have tested the ability of molecules directly involved in the feather formation process to mediate the action of the Hox codes, and surmise that adhesion molecules are potential candidates. Using specific Fabs to suppress the activity of adhesion molecules, we have found that L-CAM is involved in the formation of the hexagonal pattern, N-CAM is involved in mediating dermal condensations, tenascin is involved in feather bud growth and elongation, and integrin beta-1 is essential for epithelial-mesenchymal interactions. More work is in progress to fully understand the molecular pathways regulating the feather formation process.

Adhesion molecules and homeoproteins in the phenotypic determination of skin appendages

We examined the roles of adhesion molecules and homeoproteins in the morphogenesis of skin appendages using feather as a model. The expression pattern of these molecules in different stages of feather development were very dynamic. For example, neural cell adhesion molecules are present first in the dermal condensations, then in distal bud epithelium, then in the dermal papilla, and finally in the marginal and axial plates. Tenascin is present first in the placode, then in the anterior bud epithelium and mesoderm, and then in the dermal papilla. The expression patterns suggest that the adhesion molecules are involved in forming the boundary of cell groups that interact to form skin appendages. Antibody perturbation of embryonic skin-explant cultures showed that liver cell adhesion molecules are involved in establishing the hexagonal pattern, neural cell adhesion molecules are involved in the formation of dermal condensations, tenascin appears to be involved in the growth of feather buds, and integrin is essential for epithelial-mesenchymal interactions. Using antibodies to XlHbox 1 (similar to Hox 3.3 or C6) and Hox 4.2 (or D4), we showed that there is a homeoprotein gradient within the feather buds, and that the expression pattern is position-specific. It is hypothesized that Hox codes, derived from the combined expression pattern of homeoproteins, determine the phenotypes and orientation of skin appendages. Experiments using retinoids in the media or retinoid-soaked beads to create a local retinoid gradient are consistent with this hypothesis. As demonstrated here, feather development provides an excellent opportunity to analyze the molecular cascade of skin-appendage morphogenesis.

Regulation of hair follicle development: an in vitro model for hair follicle invasion of dermis and associated connective tissue remodeling

During embryonic development presumptive hair follicle cells of epithelial and mesenchymal origin are determined in defined body locations. This is followed by rapid proliferation of epithelial cells and associated penetration into the dermis in response to as yet undetermined signals. A collagen matrix culture system, which maintains the three-dimensional relationships of hair follicle cells to each other, was developed to study the regulation of the enlargement of immature hair follicles and the accompanying remodeling of the dermis. In studies with a heterogeneous dermis-derived preparation of murine hair follicles, ranging in size from the earliest down-growing budding cell mass to hair-forming follicles, we had previously shown that cell proliferation was stimulated by cholera toxin and epidermal growth factor, but only the epidermal growth factor-stimulated proliferation was accompanied by digestion of the collagen matrix due to release of collagenolytic enzymes. Further studies revealed that transforming growth factor-alpha also stimulated hair follicle cell proliferation and collagenase release. However, although transforming growth factor-beta inhibited the transforming growth factor-alpha-stimulated proliferation, it enhanced the release and activation of collagenases and other gelatin-degrading enzymes detectable by gelatin zymography. Stimulation of collagenolytic activity depended on the three-dimensional hair follicle structure and did not occur in monolayer cultures of hair follicle cells. Comparison of hair follicle buds with more developed dermis-derived hair follicles, plated at the same cell density (based on DNA content), suggested that a greater fraction of cells in the bud-stage follicle responded to the growth factors by release of collagenases. Possibly only the cells in the advancing portion of growing hair follicles that are closest to the dermal papilla cell cluster produce the collagenases in response to growth factors. To examine the participation of dermal papilla cells in collagenase release and activation, several immortalized rat whisker dermal papilla cell lines were co-cultured with mouse hair follicle buds. Co-culture resulted in a marked enlargement of follicles as well as activation of the 92-kDa type IV collagenase, produced by hair follicle buds, that correlated with ability of the dermal papilla cells to stimulate hair formation in grafts of hair follicle buds on nude mice. Dermal papilla cells cultured alone produced the 72-kDa type IV collagenase, which was also activated during co-culture with hair follicle buds. Thus, two activities, both relevant for hair follicle development, namely, cell proliferation and release and activation of collagenases, have been stimulated in immature hair follicle buds by either growth-factor supplementation or interaction with dermal papilla cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Dermal-epidermal interactions--follicle-derived cell populations in the study of hair-growth mechanisms

All skin appendage development is initiated by a series of dermal-epidermal interactions. These continue to underpin adult hair follicle activities through the specialized follicular cell populations--indeed the inductive properties of isolated dermal papillae from adult vibrissa follicles are well established. Far less is known about the influence of adult follicle epidermis on dermal cells, or inductive properties of papilla cells from other follicle types. Cultured papilla cells, unusually, are able to support the proliferation of skin epidermal cells during simple association in culture, but do not produce more elaborate organization or differentiation. However, germinative epidermal cells from the follicle base are morphologically and behaviorally distinct from other epidermal populations, and in simple association with papilla cells interact to form complex structures with a distinct basal lamina. That hair follicle germinative cells have an important influence on dermal cells is further demonstrated by in vivo recombinations, where germinative cells interact with otherwise non-inductive follicle dermal sheath cells to initiate follicle formation and hair growth. In vitro, several follicle cell populations assembled within the capsule of a vibrissa follicle and grown in a three-dimensional culture system produce hair-type fibers. When cultured pelage follicle dermal papilla cells are implanted alone into footpad skin under controlled conditions, new pelage-type follicles and fibers are induced. This emphasizes the power and universal nature of inductive influences from papilla cells, and underlines the dermatologic potential of cell manipulations. The transdifferentiation of the footpad epidermis is a powerful biologic phenomenon normally only seen in embryonic-type association experiments.

Mechanism of skin morphogenesis. II. Retinoic acid modulates axis orientation and phenotypes of skin appendages

The factors that determine the axial orientation and phenotypes of skin appendages were analyzed by studying the effect of retinoic acid (RA) on embryonic chicken skin explant cultures. With RA uniformly distributed in the culture media, the feather buds became smaller, were disoriented or were transformed into scale-like structures in a concentration-dependent manner (from 0.05-2.5 microM). With RA distributed as a gradient created by a RA-soaked anion exchange bead, a radial zone of inhibition with a rim of disoriented buds was observed. The new axis of the disoriented buds appeared to be determined by a combination of the original feather axis determining force and a new axial force pointing centrifugally away from the RA source. This observed result can be simulated with a computer model using a vectorial sum of different feather axial determination forces. The size of the inhibited zone is linearly correlated to the RA concentration and may be used to quantify the morphogenetic activity of retinoids. These effects are specific to developmental stages (Hamburg and Hamilton stage 31–34). Both all-trans and 13-cis RA have morphogenetic activity. Retinol has no effect and retinal has a small inhibitory effect but neither phenotypic transformation nor axial disorientation were observed. The antero-posterior gradient of homeoprotein XlHbox 1 in feather buds became diffusive after RA treatment. RA dissolves dermal condensations and the distribution of N-CAM is altered from an anterior localized pattern to a diffusive presence in the bud cores. Endogenous retinoids in developing skins show developmental stage-dependent changes both quantitatively and qualitatively. The results suggest that RA either is or can modulate the endogenous morphogen(s) that determine the orientation and phenotype of skin appendages, and that this morphogenetic pathway involves Hox genes and adhesion molecules.