Commitment of embryonic stem cells to an epidermal cell fate and differentiation in vitro

Skin Development and Disease: A Molecular Perspective

Skin, the largest organ in the human body, is a crucial protective barrier that plays essential roles in thermoregulation, sensation, and immune defence. This complex organ undergoes intricate processes of development. Skin development initiates during the embryonic stage, orchestrated by molecular cues that control epidermal specification, commitment, stratification, terminal differentiation, and appendage growth. Key signalling pathways are integral in coordinating the development of the epidermis, hair follicles, and sweat glands. The complex interplay among these pathways is vital for the appropriate formation and functionality of the skin. Disruptions in multiple molecular pathways can give rise to a spectrum of skin diseases, from congenital skin disorders to cancers. By delving into the molecular mechanisms implicated in developmental processes, as well as in the pathogenesis of diseases, this narrative review aims to present a comprehensive understanding of these aspects. Such knowledge paves the way for developing innovative targeted therapies and personalised treatment approaches for various skin conditions.

GDF11: An emerging therapeutic target for liver diseases and fibrosis

Growth differentiation factor 11 (GDF11), also known as bone morphogenetic protein 11 (BMP11), has been identified as a key player in various biological processes, including embryonic development, aging, metabolic disorders and cancers. GDF11 has also emerged as a critical component in liver development, injury and fibrosis. However, the effects of GDF11 on liver physiology and pathology have been a subject of debate among researchers due to conflicting reported outcomes. While some studies suggest that GDF11 has anti-aging properties, others have documented its senescence-inducing effects. Similarly, while GDF11 has been implicated in exacerbating liver injury, it has also been shown to have the potential to reduce liver fibrosis. In this narrative review, we present a comprehensive report of recent evidence elucidating the diverse roles of GDF11 in liver development, hepatic injury, regeneration and associated diseases such as non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), liver fibrosis and hepatocellular carcinoma. We also explore the therapeutic potential of GDF11 in managing various liver pathologies.

The role of URO17® in diagnosis and follow up of bladder cancer patients

OBJECTIVE

to evaluate the role of urinary URO17® biomarker in the detection of urothelial tumors in haematuria patients and the detection of recurrence in non-muscle invasive bladder urothelial tumors.

MATERIALS AND METHODS

Our study was formed of two cohorts of patients, group I represents patients presenting with haematuria (n = 98), while group II represents patients with known non-muscle invasive bladder cancers on their scheduled follow up cystoscopic investigation (n = 51). For both groups, patients were asked to provide urine samples before cystoscopy, either primary as part of the haematuria investigation or as a scheduled follow-up. Urine samples were sent anonymously for standard urine cytology and URO17® biomarker immunostaining. Results were compared to cystoscopic findings using Chi-square analysis and Fisher's exact test (P < 0.05).

RESULTS

Group I was formed of 98 patients, with an average age of 60 years. URO17® showed 100% sensitivity and 96.15% specificity with a negative predictive value (NPV) of 100 and a positive predictive value (PPV) of 95.83. The results showed statistical significance with P value < 0.001. Group II was formed of 51 patients, with an average age of 75 years. URO17® was shown to have a sensitivity of 85.71% and NPV of 95.45. Eleven patients of group II were on scheduled BacillusCalmette-Guerin (BCG) and another 5 received Mitomycin C (MMC). The overall results of both groups combined (n = 149) showed statistical significance between flexible cystoscopy results and the results of urinary URO17® and urine cytology.

CONCLUSION

URO17® has a potential to be a reliable test for diagnosis and follow up of urothelial cancer patients and a screening tool adjunct to flexible cystoscopy.

TRIAL REGISTRATION

Not applicable as the current study is not a clinical trial, as per according to the National Institutes of Health, "studies that involve a comparison of methods and that do not evaluate the effect of the interventions on the participant do not meet the NIH clinical trial definition."

The Germinal Origin of Salivary and Lacrimal Glands and the Contributions of Neural Crest Cell-Derived Epithelium to Tissue Regeneration

The vertebrate body comprises four distinct cell populations: cells derived from (1) ectoderm, (2) mesoderm, (3) endoderm, and (4) neural crest cells, often referred to as the fourth germ layer. Neural crest cells arise when the neural plate edges fuse to form a neural tube, which eventually develops into the brain and spinal cord. To date, the embryonic origin of exocrine glands located in the head and neck remains under debate. In this study, transgenic TRiCK mice were used to investigate the germinal origin of the salivary and lacrimal glands. TRiCK mice express fluorescent proteins under the regulatory control of Sox1, T/Brachyury, and Sox17 gene expressions. These genes are representative marker genes for neuroectoderm (Sox1), mesoderm (T), and endoderm (Sox17). Using this approach, the cellular lineages of the salivary and lacrimal glands were examined. We demonstrate that the salivary and lacrimal glands contain cells derived from all three germ layers. Notably, a subset of Sox1-driven fluorescent cells differentiated into epithelial cells, implying their neural crest origin. Also, these Sox1-driven fluorescent cells expressed high levels of stem cell markers. These cells were particularly pronounced in duct ligation and wound damage models, suggesting the involvement of neural crest-derived epithelial cells in regenerative processes following tissue injury. This study provides compelling evidence clarifying the germinal origin of exocrine glands and the contribution of neural crest-derived cells within the glandular epithelium to the regenerative response following tissue damage.

USP39 is essential for mammalian epithelial morphogenesis through upregulation of planar cell polarity components

Previously, we have shown that the translocation of Grainyhead-like 3 (GRHL3) transcription factor from the nucleus to the cytoplasm triggers the switch from canonical Wnt signaling for epidermal differentiation to non-canonical Wnt signaling for epithelial morphogenesis. However, the molecular mechanism that underlies the cytoplasmic localization of GRHL3 protein and that activates non-canonical Wnt signaling is not known. Here, we show that ubiquitin-specific protease 39 (USP39), a deubiquitinating enzyme, is involved in the subcellular localization of GRHL3 as a potential GRHL3-interacting protein and is necessary for epithelial morphogenesis to up-regulate expression of planar cell polarity (PCP) components. Notably, mouse Usp39-deficient embryos display early embryonic lethality due to a failure in primitive streak formation and apico-basal polarity in epiblast cells, resembling those of mutant embryos of the Prickle1 gene, a crucial PCP component. Current findings provide unique insights into how differentiation and morphogenesis are coordinated to construct three-dimensional complex structures via USP39.

The ubiquitin specific protease 39 (USP39) interacts with the transcription factor and cytoplasmic regulator of planar cell polarity (PCP), Grainyheadlike 3 (Grhl3). USP39-dependent PCP gene upregulation contributes to epithelial morphogenesis.

Pluripotent Stem Cell Differentiation Toward Functional Basal Stratified Epithelial Cells

In this chapter, an efficient feeder-free protocol of differentiating human pluripotent stem cells (hPSCs) toward the epidermal lineage to generate induced epidermal keratinocytes (iKCs) is described. The iKCs are able to terminally differentiate supra-basally. This hPSC-to-iKC differentiation can serve as a useful model to study epidermal development and disease as well as for therapeutic applications.

Modeling Mammalian Commitment to the Neural Lineage Using Embryos and Embryonic Stem Cells

Early mammalian embryogenesis relies on a large range of cellular and molecular mechanisms to guide cell fate. In this highly complex interacting system, molecular circuitry tightly controls emergent properties, including cell differentiation, proliferation, morphology, migration, and communication. These molecular circuits include those responsible for the control of gene and protein expression, as well as metabolism and epigenetics. Due to the complexity of this circuitry and the relative inaccessibility of the mammalian embryo in utero, mammalian neural commitment remains one of the most challenging and poorly understood areas of developmental biology. In order to generate the nervous system, the embryo first produces two pluripotent populations, the inner cell mass and then the primitive ectoderm. The latter is the cellular substrate for gastrulation from which the three multipotent germ layers form. The germ layer definitive ectoderm, in turn, is the substrate for multipotent neurectoderm (neural plate and neural tube) formation, representing the first morphological signs of nervous system development. Subsequent patterning of the neural tube is then responsible for the formation of most of the central and peripheral nervous systems. While a large number of studies have assessed how a competent neurectoderm produces mature neural cells, less is known about the molecular signatures of definitive ectoderm and neurectoderm and the key molecular mechanisms driving their formation. Using pluripotent stem cells as a model, we will discuss the current understanding of how the pluripotent inner cell mass transitions to pluripotent primitive ectoderm and sequentially to the multipotent definitive ectoderm and neurectoderm. We will focus on the integration of cell signaling, gene activation, and epigenetic control that govern these developmental steps, and provide insight into the novel growth factor-like role that specific amino acids, such as L-proline, play in this process.

Cytoplasmic localization of GRHL3 upon epidermal differentiation triggers cell shape change for epithelial morphogenesis

Epithelial cell shape change is a pivotal driving force for morphogenesis of complex three-dimensional architecture. However, molecular mechanisms triggering shape changes of epithelial cells in the course of growth and differentiation have not been entirely elucidated. Grhl3 plays a crucial role as a downstream transcription factor of Wnt/β-catenin in epidermal differentiation. Here, we show Grhl3 induced large, mature epidermal cells, enriched with actomyosin networks, from embryoid bodies in vitro. Such epidermal cells were apparently formed by the simultaneous activation of canonical and non-canonical Wnt signaling pathways. A nuclear transcription factor, GRHL3 is localized in the cytoplasm and cell membrane during epidermal differentiation. Subsequently, such extranuclear GRHL3 is essential for the membrane-associated expression of VANGL2 and CELSR1. Cytoplasmic GRHL3, thereby, allows epidermal cells to acquire mechanical properties for changes in epithelial cell shape. Thus, we propose that cytoplasmic localization of GRHL3 upon epidermal differentiation directly triggers epithelial morphogenesis.

Knockdown of KRT17 by siRNA induces antitumoral effects on gastric cancer cells

BACKGROUND

Keratin 17 (KRT17) was shown to be an important molecular marker for predicting the carcinogenesis, progression, and prognosis of various cancer types. Our previous studies identified KRT17 as a possible biomarker for gastric cancer by gene microarray, with an elevated expression that occurred early during tumorigenesis and increased during tumor progression. Based on these findings, we aimed to investigate KRT17 biological functions in gastric adenocarcinoma and its possible use as a rational molecular target for anticancer therapy.

METHODS

We used RNA interference-mediated knockdown of KRT17 expression and analyzed the effects on cell proliferation, cell migration, and signal transduction in two gastric cell lines (AGS and NCI-N87) in vitro and on xenograft growth in vivo.

RESULTS

The functional analysis of KRT17 knockdown cell lines showed a decreased cell proliferation (with 42.36% ± 3.2%) and migration ability (with 37.2% ± 6.2%) relative to scrambled siRNA control. The in vivo tumorigenicity on nude mice exhibited a significant decrease in tumor weight with 69.14% in xenografts obtained from AGS cells and 84.43% in xeno-NCI-N87 tumors. The analysis on KRT17 knockdown outcome on intracellular signaling identifies AKT/mTOR as the main affected pathway that sustains proliferation and survival, and also the AMPKα1/CREB pathway that was recently shown to induce organ protection and antiinflammatory response.

CONCLUSIONS

Our results highlight KRT17 as a possible biomarker in gastric cancer promoting tumor growth, motility, and invasion, and suggest that KRT17 can be a valuable molecular target for development of anti-gastric cancer-specific therapies.

Modified methods for efficiently differentiating human embryonic stem cells into chondrocyte-like cells

INTRODUCTION

Human articular cartilage has a poor regenerative capacity. This often results in the serious joint disease- osteoarthritis (OA) that is characterized by cartilage degradation. An inability to self-repair provided extensive studies on AC regeneration. The cell-based cartilage tissue engineering is a promising approach for cartilage regeneration. So far, numerous cell types have been reported to show chondrogenic potential, among others human embryonic stem cells (hESCs).

MATERIALS AND METHODS

However, the currently used methods for directed differentiation of human ESCs into chondrocyte-like cells via embryoid body (EB) formation, micromass culture (MC) and pellet culture (PC) are not highly efficient and require further improvement. In the present study, these three methods for hESCs differentiation into chondrocyte-like cells in the presence of chondrogenic medium supplemented with diverse combination of growth factors (GFs) were evaluated and modified.

RESULTS

The protocols established here allow highly efficient, simple and inexpensive production of a large number of chondrocyte-like cells suitable for transplantation into the sites of cartilage injury. The most crucial issue is the selection of appropriate GFs in defined concentration. The obtained stem-derived cells reveal the presence of chondrogenic markers such as type II collagen, Sox6 and Sox9 as well as the lack or significantly lower level of pluripotency markers including Nanog and Oct3/4.

DISCUSSION

The most efficient method is the differentiation throughout embryoid bodies. In turn, chondrogenic differentiation via pellet culture is the most promising method for implementation on clinical scale. The most useful GFs are TGF-β1, -3 and BMP-2 that possess the most chondrogenic potential. These methods can also be used to obtain chondrocyte-like cells from differentiating induced pluripotent stem cells (iPSCs).

Transcriptome and proteome characterization of surface ectoderm cells differentiated from human iPSCs

Surface ectoderm (SE) cells give rise to structures including the epidermis and ectodermal associated appendages such as hair, eye, and the mammary gland. In this study, we validate a protocol that utilizes BMP4 and the γ-secretase inhibitor DAPT to induce SE differentiation from human induced pluripotent stem cells (hiPSCs). hiPSC-differentiated SE cells expressed markers suggesting their commitment to the SE lineage. Computational analyses using integrated quantitative transcriptomic and proteomic profiling reveal that TGFβ superfamily signaling pathways are preferentially activated in SE cells compared with hiPSCs. SE differentiation can be enhanced by selectively blocking TGFβ-RI signaling. We also show that SE cells and neural ectoderm cells possess distinct gene expression patterns and signaling networks as indicated by functional Ingenuity Pathway Analysis. Our findings advance current understanding of early human SE cell development and pave the way for modeling of SE-derived tissue development, studying disease pathogenesis, and development of regenerative medicine approaches.

A Unique Expression of Keratin 14 in a Subset of Trophoblast Cells

The placenta, a transient organ in human, is essential for pregnancy maintenance and for fetal growth and development. Trophoblast and stromal cells are the main cell types present in human placenta. Trophoblast cells are present in different subtypes depending on their differentiation state and their temporal and spatial location during pregnancy. The stromal cells are of extraembryonic mesenchymal origin and are important for villous formation and maintenance. Interestingly, many pregnancy–related diseases are associated with defect in trophoblast differentiation and villous integrity. Therefore, it's crucial to specifically identify each type of placental cells using specific markers. Keratins (CK) are widely used as marker of epithelial cells, cancer origin identification and in some cases as marker of stem/progenitor cells. Vimentin is widely used as marker of mesenchymal cells. The aim of this study is to characterize the presence of different keratins in human trophoblast cells and vimentin in stromal cells. Using immunohistochemistry on term placental sections, our results show that vimentin is solely expressed in stromal-mesenchymal cells while keratins 5, 7, 8, 14 and 19 are expressed in trophoblast cells. Interestingly, all keratins tested, except for keratin 14, were evenly expressed in all trophoblast cells. Keratin 14 was expressed in a subset of CK7 positive cells. Moreover, the same results were obtained when using freshly isolated cytotrophoblast cells or BeWo cells. In conclusion, this study is a crucial step in the advancement of our knowledge in placental cell type identification and characterization.

Keratin-17 Promotes p27KIP1 Nuclear Export and Degradation and Offers Potential Prognostic Utility

Keratins that are overexpressed selectively in human carcinomas may offer diagnostic and prognostic utility. In this study, we show that high expression of keratin-17 (K17) predicts poor outcome in patients with cervical cancer, at early or late stages of disease, surpassing in accuracy either tumor staging or loss of p27(KIP1) as a negative prognostic marker in this setting. We investigated the mechanistic basis for the biologic impact of K17 through loss- and gain-of-function experiments in human cervix, breast, and pancreatic cancer cells. Specifically, we determined that K17 functions as an oncoprotein by regulating the subcellular localization and degradation of p27(KIP1). We found that K17 was released from intermediate filaments and translocated into the nucleus via a nuclear localization signal (NLS), specific among keratins, where it bound p27(KIP1) during G1 phase of the cell cycle. p27(KIP1) lacks a nuclear export signal (NES) and requires an adaptor for CRM1 binding for nuclear export. In K17, we defined and validated a leucine-rich NES that mediated CRM1 binding for export. Cervical cancer cells expressing K17 mutations in its NLS or NES signals exhibited an increase in levels of nuclear p27(KIP1), whereas cells expressing wild-type K17 exhibited a depletion in total endogenous p27(KIP1). In clinical specimens of cervical cancer, we confirmed that the expressions of K17 and p27(KIP1) were inversely correlated, both across tumors and within individual tumors. Overall, our findings establish that K17 functions specially among keratins as an oncoprotein by controlling the ability of p27(KIP1) to influence cervical cancer pathogenesis.

Characterization of murine pituitary-derived cell lines Tpit/F1, Tpit/E and TtT/GF

The pituitary is an important endocrine tissue of the vertebrate that produces and secretes many hormones. Accumulating data suggest that several types of cells compose the pituitary, and there is growing interest in elucidating the origin of these cell types and their roles in pituitary organogenesis. Therein, the histogenous cell line is an extremely valuable experimental tool for investigating the function of derived tissue. In this study, we compared gene expression profiles by microarray analysis and real-time PCR for murine pituitary tumor-derived non-hormone-producing cell lines TtT/GF, Tpit/F1 and Tpit/E. Several genes are characteristically expressed in each cell line: Abcg2, Nestin, Prrx1, Prrx2, CD34, Eng, Cspg4 (Ng2), S100β and nNos in TtT/GF; Cxcl12, Raldh1, Msx1 and Twist1 in Tpit/F1; and Cxadr, Sox9, Cdh1, EpCAM and Krt8 in Tpit/E. Ultimately, we came to the following conclusions: TtT/GF cells show the most differentiated state, and may have some properties of the pituitary vascular endothelial cell and/or pericyte. Tpit/F1 cells show the epithelial and mesenchymal phenotypes with stemness still in a transiting state. Tpit/E cells have a phenotype of epithelial cells and are the most immature cells in the progression of differentiation or in the initial endothelial-mesenchymal transition (EMT). Thus, these three cell lines must be useful model cell lines for investigating pituitary stem/progenitor cells as well as organogenesis.

Epidermal development in mammals: key regulators, signals from beneath, and stem cells

Epidermis is one of the best-studied tissues in mammals that contain types of stem cells. Outstanding works in recent years have shed great light on behaviors of different epidermal stem cell populations in the homeostasis and regeneration of the epidermis as well as hair follicles. Also, the molecular mechanisms governing these stem cells are being elucidated, from genetic to epigenetic levels. Compared with the explicit knowledge about adult skin, embryonic development of the epidermis, especially the early period, still needs exploration. Furthermore, stem cells in the embryonic epidermis are largely unstudied or ambiguously depicted. In this review, we will summarize and discuss the process of embryonic epidermal development, with focuses on some key molecular regulators and the role of the sub-epidermal mesenchyme. We will also try to trace adult epidermal stem cell populations back to embryonic development. In addition, we will comment on in vitro derivation of epidermal lineages from ES cells and iPS cells.

Analysis of transferred keratinocyte-like cells derived from mouse embryonic stem cells on experimental surgical skin wounds of mouse

Autologous/allogenic skin grafts constituted from differentiated adult or embryonic stem cells can be used in treatment of skin disorders. In our study we aimed to differentiate keratinocytes from mouse embryonic stem cells and the transfer of viable keratinocyte-like cells to a model of surgical skin wound of mouse. Embryoid bodies, derived from mouse embryonic stem cells, were cultured on basement membrane matrix with added BMP-4 for 10 days. The identification of differentiated keratinocyte-like cells was done by detection of cytokeratin-8 and cytokeratin-14 localization using an indirect immunoperoxidase technique and transmission electron microscopy evaluation. Distribution of BrdU, cytokeratin-8 and cytokeratin-14 were evaluated using an indirect immunoperoxidase technique from the experimental (dressing including BrdU labelled cells applied after the surgical wound was created on mouse), control (only the surgical wound was created on mouse) and sham (only the dressing applied after the surgical wound was created on mouse) in groups after 3, 5 and 7 days. Immunohistochemically and ultrastructurally, cells derived from mouse embryonic stem cells were similar to differentiated keratinocyte-like cells. Differentiated keratinocyte-like cells were demonstrated by positive BrdU, cytokeratin-8 and cytokeratin-14 staining after transfer to the wound area. In the experimental group wound healing was better after transferring differentiated keratinocytes when compared to the sham and control groups. In vivo continuity and usability of derived cells are very important issues. In wound repair mechanisms, keratinocyte-like cells could provide positive effects during the wound healing and could be used in clinical treatments of wound repair process.

Adult stem cells in small animal wound healing models

This chapter broadly reviews the use of stem cells as a means to accelerate wound healing, focusing first on the properties of stem cells that make them attractive agents to influence repair, both alone and as vehicles for growth factor delivery. Major stem cell reservoirs are described, including adult, embryonic, and induced pluripotent cell sources, outlining the advantages and limitations of each source as wound healing agents, as well as the possible mechanisms responsible for wound healing acceleration. Finally, the chapter includes a materials and methods section that provides an in-depth description of adult tissue harvest techniques.

Treatment of early avascular necrosis of femoral head by small intestinal submucosal matrix with peripheral blood stem cells

BACKGROUND

Avascular necrosis of the femoral head (ANFH) is a highly mutilating disease. There are no effective ways to treat early femoral head ischemia. Peripheral blood stem cell (PBSC) transplantation may be superior to conventional bone marrow transplantation. Small intestinal submucosae matrix (SIS) is composed of highly conserved collagens, glycoproteins, proteoglycans, and glycoaminoglycans in their natural configuration and concentrations. When implanted in a number of microenvironments in vivo, SIS has been used to induce proliferation, remodeling, and regeneration of host tissues. This study was designed to verify the curative effects of PBSC and SIS transplantation-induced vascular regeneration to improve ischemic femoral head necrosis in rabbits.

METHODS

32 New Zealand white rabbits underwent ischemic femoral head necrosis modeling in both hindlimbs by liquid-nitrogen refrigeration. All rabbits were intraperitoneally injected with grannlocytectomy-stimulating factor (250 μg/kg/d), except for normal control subjects injected with equivalent saline solution. After separation of peripheral blood stem cells (PBSCs), 64 femoral heads in 32 rabbits were randomly divided into 4 groups: group A, cancellous bone and peripheral blood stem cells cultured with small intestinal submucosa; group B, cancellous bone and PBSCs; group C, cancellous bone autografts; and group D, no treatment. The specimens were harvested at 4 and 8 weeks after surgery. All specimens were examined to observe angiogenesis and osteogenesis repairing the avascular necrosis of the femoral head by using gross observation, x-ray, histology, and immunohistochemical staining.

RESULTS

In 4 weeks after peripheral stem cell transplantation, the standing ability and activity of the transplanted hindlimbs were improved remarkably, but there were no obvious changes in the control limbs. X-rays showed a greater density of grafts than the host bone in groups A,B, and group C was unchanged at 4 weeks. Histology revealed many osteoprogenitor cells and osteoblasts and no inflammatory cell infiltration at 4 weeks with much new bone formed at 8 weeks in group A and at 4 weeks in group B. The cancellous bone autograft was absorbed completely at 8 weeks in group C. There was little osteoid tissue formed in group D at 8 weeks. The zone of new bone formation in group A was greater than that in group B (P < .05), but there was no significant difference between groups A and C (P > .05). Immunohistochemical staining with CD31 mouse antibody showed greater amounts and zones of new blood vessels in groups A and B at 4 and 8 weeks and little evidence in group D. There was no significant difference between groups A and B (P > .05) and significant differences between groups A and B versus C and D (P < .05).

CONCLUSION

Transplantation of PBSCs cultured with SIS effectively improved ischemic femoral head necrosis.

Wound healing and regenerative strategies

Wound healing is a complex biological process that affects multiple tissue types. Wounds in the oral cavity are particularly challenging given the variety of tissue types that exist in close proximity to one another. The goal of regenerative medicine is to facilitate the rapid replacement of lost or damaged tissue with tissue that is functional, and physiologically similar to what previously existed. This review provides a general overview of wound healing and regenerative medicine, focusing specifically on how recent advances in the fields of stem cell biology, tissue engineering, and oral disease could translate into improved clinical outcomes.

Stem cell therapies for recessive dystrophic epidermolysis bullosa

Human epidermis is composed of a stratified squamous epithelium that provides a mechanical barrier against the external environment and which is renewed every 3-4 weeks by resident stem cells in the epidermis. However, in the inherited skin fragility disorder, recessive dystrophic epidermolysis bullosa (RDEB), there is recurrent trauma-induced subepidermal blistering that disrupts epidermal homeostasis and is likely to deplete the epidermal stem cell pool. This review article discusses the nature of epidermal stem cells and other stem cell populations in the skin, as well as other possible extracutaneous sources of stem cells, that might have physiological or therapeutic relevance to cell therapy approaches for RDEB. Strategies to identify, create and use cells with multipotent or pluripotent properties are explored and current clinical experience of stem cell therapy in RDEB is reviewed. There is currently no single optimal therapy for patients with RDEB, but cell therapy technologies are evolving and hold great potential for modifying disease severity and improving quality of life for people living with RDEB.

Probing stemness and neural commitment in human amniotic fluid cells

Recently, human amniotic fluid (AF) cells have attracted a great deal of attention as an alternative cell source for transplantation and tissue engineering. AF contains a variety of cell types derived from fetal tissues, of which a small percentage is believed to represent stem cell sub-population(s). In contrast to human embryonic stem (ES) cells, AF cells are not subject to extensive legal or ethical considerations; nor are they limited by lineage commitment characteristic of adult stem cells. However, to become therapeutically valuable, better protocols for the isolation of AF stem cell sub-populations need to be developed. This study was designed to examine the molecular components involved in self-renewal, neural commitment and differentiation of AF cells obtained at different gestational ages. Our results showed that, although morphologically heterogeneous, AF cells derived from early gestational periods ubiquitously expressed KERATIN 8 (K8), suggesting that the majority of these cells may have an epithelial origin. In addition, AF cells expressed various components of NOTCH signaling (ligands, receptors and target genes), a pathway involved in stem cell maintenance, determination and differentiation. A sub-population of K8 positive cells (<10%) co-expressed NESTIN, a marker detected in the neuroepithelium, neural stem cells and neural progenitors. Throughout the gestational periods, a much smaller AF cell sub-population (<1%) expressed pluripotency markers, OCT4a, NANOG and SOX2, from which SOX2 positive AF cells could be isolated through single cell cloning. The SOX2 expressing AF clones showed the capacity to give rise to a neuron-like phenotype in culture, expressing neuronal markers such as MAP2, NFL and NSE. Taken together, our findings demonstrated the presence of fetal cells with stem cell characteristics in the amniotic fluid, highlighting the need for further research on their biology and clinical applications.

Embryoid body attachment to reconstituted basement membrane induces a genetic program of epithelial differentiation via jun N-terminal kinase signaling

Embryonic stem (ES) cells are derived from early stage mammalian embryos and have broad developmental potential. These cells can be manipulated experimentally to generate cells of multiple tissue types which could be important in treating human diseases. The ability to produce relevant amounts of these differentiated cell populations creates the basis for clinical interventions in tissue regeneration and repair. Understanding how embryonic stem cells differentiate also can reveal important insights into cell biology. A previously reported mouse embryonic stem cell model demonstrated that differentiated epithelial cells migrated out of embryoid bodies attached to reconstituted basement membrane. We used genomic technology to profile ES cell populations in order to understand the molecular mechanisms leading to epithelial differentiation. Cells with characteristics of cultured epithelium migrated from embryoid bodies attached to reconstituted basement membrane. However, cells that comprised embryoid bodies also rapidly lost ES cell-specific gene expression and expressed proteins characteristic of stratified epithelia within hours of attachment to basement membrane. Gene expression profiling of sorted cell populations revealed upregulation of the BMP/TGFbeta signaling pathway, which was not sufficient for epithelial differentiation in the absence of basement membrane attachment. Activation of c-jun N-terminal kinase 1 (JNK1) and increased expression of Jun family transcription factors was observed during epithelial differentiation of ES cells. Inhibition of JNK signaling completely blocked epithelial differentiation in this model, revealing a key mechanism by which ES cells adopt epithelial characteristics via basement membrane attachment.

Aging and chronic sun exposure cause distinct epigenetic changes in human skin

Epigenetic changes are widely considered to play an important role in aging, but experimental evidence to support this hypothesis has been scarce. We have used array-based analysis to determine genome-scale DNA methylation patterns from human skin samples and to investigate the effects of aging, chronic sun exposure, and tissue variation. Our results reveal a high degree of tissue specificity in the methylation patterns and also showed very little interindividual variation within tissues. Data stratification by age revealed that DNA from older individuals was characterized by a specific hypermethylation pattern affecting less than 1% of the markers analyzed. Interestingly, stratification by sun exposure produced a fundamentally different pattern with a significant trend towards hypomethylation. Our results thus identify defined age-related DNA methylation changes and suggest that these alterations might contribute to the phenotypic changes associated with skin aging.

Although a role of epigenetic mechanisms in aging and in the adaptation to environmental exposures has been widely assumed, research in this area has been hampered by major methodological challenges. We have now used a novel platform for genome-scale methylation analysis to determine the methylation patterns of human skin samples. Skin represents a particularly suitable model for this study because of its well-known phenotype changes associated with aging and sun exposure, and because skin samples are characterized by a very high degree of cellular homogeneity. By examining 50 samples, and analyzing 50 million data points, we show that aging and sun exposure are associated with comparably small, but significant changes in the DNA methylation patterns of human epidermis and dermis samples. Interestingly, aging was not associated with a general variation in DNA methylation patterns, but rather with a directed DNA hypermethylation shift. Importantly, our results also suggest that epigenetic mechanisms may be functionally important for the phenotypic changes associated with aging and chronic sun exposure.

Response to BMP4 signalling during ES cell differentiation defines intermediates of the ectoderm lineage

The formation and differentiation of multipotent precursors underlies the generation of cell diversity during mammalian development. Recognition and analysis of these transient cell populations has been hampered by technical difficulties in accessing them in vivo. In vitro model systems, based on the differentiation of embryonic stem (ES) cells, provide an alternative means of identifying and characterizing these populations. Using a previously established mouse ES-cell-based system that recapitulates the development of the ectoderm lineage we have identified a transient population that is consistent with definitive ectoderm. This previously unidentified progenitor occurs as a temporally discrete population during ES cell differentiation, and differs from the preceding and succeeding populations in gene expression and differentiation potential, with the unique ability to form surface ectoderm in response to BMP4 signalling.

Structure and functions of keratin proteins in simple, stratified, keratinized and cornified epithelia

Historically, the term 'keratin' stood for all of the proteins extracted from skin modifications, such as horns, claws and hooves. Subsequently, it was realized that this keratin is actually a mixture of keratins, keratin filament-associated proteins and other proteins, such as enzymes. Keratins were then defined as certain filament-forming proteins with specific physicochemical properties and extracted from the cornified layer of the epidermis, whereas those filament-forming proteins that were extracted from the living layers of the epidermis were grouped as 'prekeratins' or 'cytokeratins'. Currently, the term 'keratin' covers all intermediate filament-forming proteins with specific physicochemical properties and produced in any vertebrate epithelia. Similarly, the nomenclature of epithelia as cornified, keratinized or non-keratinized is based historically on the notion that only the epidermis of skin modifications such as horns, claws and hooves is cornified, that the non-modified epidermis is a keratinized stratified epithelium, and that all other stratified and non-stratified epithelia are non-keratinized epithelia. At this point in time, the concepts of keratins and of keratinized or cornified epithelia need clarification and revision concerning the structure and function of keratin and keratin filaments in various epithelia of different species, as well as of keratin genes and their modifications, in view of recent research, such as the sequencing of keratin proteins and their genes, cell culture, transfection of epithelial cells, immunohistochemistry and immunoblotting. Recently, new functions of keratins and keratin filaments in cell signaling and intracellular vesicle transport have been discovered. It is currently understood that all stratified epithelia are keratinized and that some of these keratinized stratified epithelia cornify by forming a Stratum corneum. The processes of keratinization and cornification in skin modifications are different especially with respect to the keratins that are produced. Future research in keratins will provide a better understanding of the processes of keratinization and cornification of stratified epithelia, including those of skin modifications, of the adaptability of epithelia in general, of skin diseases, and of the changes in structure and function of epithelia in the course of evolution. This review focuses on keratins and keratin filaments in mammalian tissue but keratins in the tissues of some other vertebrates are also considered.

A revaluation of trichofolliculoma: the histopathological and immunohistochemical features

Few investigations on the histopathology of trichofolliculoma (TF) have so far included an immunohistochemical study. To seek new insight into TF with a revaluation of the histopathological features and an investigation of the immunohistochemical profile, 14 TFs were revaluated for the histopathology and the immunohistochemical profile of various cytokeratins (CKs), hair follicle stem cell markers, and others. The CK15 expression was upregulated in the basal cells from the primary cystic structures beyond to secondary follicles without expression of CK19. CK16 and CK17 were positive in the suprabasal cells of the primary cystic structures and the immature secondary hair follicles. No exact isthmus/bulge region was seen in the anagen secondary hair follicles, and newly developed (tertiary) hair follicles arose randomly from the involuting secondary follicles. Ber EP4 expression was generally weakened in the secondary or tertiary hair germ-like structures. The size of secondary hair follicles varied from vellus hair follicles to terminal hair follicles, even though no lesions located on the regions where the terminal hairs develop were included in this study. S-100 protein-positive wavy spindle cells were accidentally found in the surrounding connective tissue of the secondary follicles in 2 TF lesions. TFs were characterized by the proliferation of abnormal CK15-positive hair follicle stem cells, which basically differentiated toward the outer root sheath and attempting to make hair but losing the proper differentiation. The control of the size of the anagen hair follicles and the regular hair cycle were also disordered.

A novel role for gamma-secretase in the formation of primitive streak-like intermediates from ES cells in culture

gamma-Secretase is a membrane-associated protease with multiple intracellular targets, a number of which have been shown to influence embryonic development and embryonic stem (ES) cell differentiation. This paper describes the use of the gamma-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) to evaluate the role of gamma-secretase in the differentiation of pluripotent stem cells to the germ lineages. The addition of DAPT did not prevent the formation of primitive ectoderm-like cells from ES cells in culture. In contrast, the addition of DAPT during primitive ectoderm-like cell differentiation interfered with the ability of both serum and BMP4 to induce a primitive streak-like intermediate and resulted in the preferential formation of neurectoderm. Similarly, DAPT reduced the formation of primitive streak-like intermediates from differentiating human ES cells; the culture conditions used resulted in a population enriched in human surface ectoderm. These data suggest that gamma-secretase may form part of the general pathway by which mesoderm is specified within the primitive streak. The addition of an E-cadherin neutralizing antibody was able to partially reverse the effect of DAPT, suggesting that DAPT may be preventing the formation of primitive streak-like intermediates and promoting neurectoderm differentiation by stabilizing E-cadherin and preventing its proteolysis.

Involucrin–claudin-6 tail deletion mutant (CΔ206) transgenic mice: a model of delayed epidermal permeability barrier formation and repair

Preterm birth is a major global health problem that results in a large number of infant deaths, many of which are attributable to the complications of an immature epidermal permeability barrier (EPB), for which there is currently no effective therapeutic option. The mammalian EPB is formed during development and is essential for survival as it maintains thermoregulation and hydration, and provides a defense against infection. Using transgenic mouse technology, we have demonstrated the importance of claudin (Cldn)-containing tight junctions (TJs) in epidermal differentiation and, in particular, that epidermal suprabasal overexpression of Cldn6 results in an EPB-deficient phenotype that phenocopies the dysfunctional EPB of premature human infants. In this study, we used the same approach to target a Cldn6 tail deletion mutant to the epidermis of mice [involucrin (Inv)-Cldn6-CΔ206 transgenic mice]. The Inv-Cldn6-CΔ206 transgenic mice displayed a developmental delay in EPB formation, as shown by the expression of keratins and Cldns, and by X-Gal penetration assays. Trans-epidermal water loss measurements and immunolocalization studies indicated that the epidermal differentiation program was also perturbed in postnatal Inv-Cldn6-CΔ206 transgenic mice resulting in a delayed maturation. Notably, however, expression/localization of epidermal differentiation and maturation markers, including Cldns, indicated that the transgenic epidermis matured and normalized by postnatal day 10, which is 3 days after the wild-type epidermis. Our results suggest that activation of the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway and Cldn1 phosphorylation are associated with the repair and maturation of the skin barrier processes. These studies provide additional support for the crucial role of Cldns in epidermal differentiation, maturation and the formation of the EPB, and describe a novel animal model for evaluating postnatal epidermal maturation and therapies that may accelerate the process.

Head and neck squamous cancer stromal fibroblasts produce growth factors influencing phenotype of normal human keratinocytes

Epithelial-mesenchymal interaction between stromal fibroblasts and cancer cells influences the functional properties of tumor epithelium, including the tumor progression and spread. We compared fibroblasts prepared from stroma of squamous cell carcinoma and normal dermal fibroblasts concerning their biological activity toward normal keratinocytes assessed by immunocytochemistry and profiling of gene activation for growth factors/cytokines by microarray chip technology. IGF-2 and BMP-4 were determined as candidate factors responsible for tumor-associated fibroblast activity that influences normal epithelia. This effect was confirmed by addition of recombinant IGF-2 and BMP4, respectively, to the culture medium. This hypothesis was also verified by inhibition experiments where blocking antibodies were employed in the medium conditioned by cancer-associated fibroblast. Presence of these growth factors was also detected in tumor samples.

Dermatitis and aging-related barrier dysfunction in transgenic mice overexpressing an epidermal-targeted claudin 6 tail deletion mutant

The barrier function of the skin protects the mammalian body against infection, dehydration, UV irradiation and temperature fluctuation. Barrier function is reduced with the skin's intrinsic aging process, however the molecular mechanisms involved are unknown. We previously demonstrated that Claudin (Cldn)-containing tight junctions (TJs) are essential in the development of the epidermis and that transgenic mice overexpressing Cldn6 in the suprabasal layers of the epidermis undergo a perturbed terminal differentiation program characterized in part by reduced barrier function. To dissect further the mechanisms by which Cldn6 acts during epithelial differentiation, we overexpressed a Cldn6 cytoplasmic tail deletion mutant in the suprabasal compartment of the transgenic mouse epidermis. Although there were no gross phenotypic abnormalities at birth, subtle epidermal anomalies were present that disappeared by one month of age, indicative of a robust injury response. However, with aging, epidermal changes with eventual chronic dermatitis appeared with a concomitant barrier dysfunction manifested in increased trans-epidermal water loss. Immunohistochemical analysis revealed aberrant suprabasal Cldn localization with marked down-regulation of Cldn1. Both the proliferative and terminal differentiation compartments were perturbed as evidenced by mislocalization of multiple epidermal markers. These results suggest that the normally robust injury response mechanism of the epidermis is lost in the aging Involucrin-Cldn6-CΔ196 transgenic epidermis, and provide a model for evaluation of aging-related skin changes.

Mouse embryonic stem cells lacking p38alpha and p38delta can differentiate to endothelial cells, smooth muscle cells, and epithelial cells

The p38 mitogen-activated protein (MAP) kinases (p38) are important signaling molecules that regulate various cellular processes. Four isoforms of p38 family, p38alpha, p38beta, p38gamma, and p38delta, have been identified in mammalian cells. Previous studies have shown that p38alpha knockout is embryonic lethal in mice. At the cellular level, p38alpha is abundantly expressed in mouse embryonic stem cells (ESCs), but p38alpha knockout (p38alpha-/-) ESCs can differentiate to endothelial cells (ECs), smooth muscle cells (SMCs), and neurons. We speculate that the lost function of p38alpha in p38alpha-/- ESCs may be compensated for by the redundant function of other isoforms. To test this hypothesis, we used siRNA approach to knock down the expression of p38delta, the second abundant isoform in ESCs. ESCs stably expressing p38delta siRNA were established from p38alpha-/- ESCs, resulting in 80% reduction of p38delta mRNA expression. However, these ESCs, deficient of both p38alpha and p38delta, could still differentiate into ECs and SMCs. We extended our investigation to test if these cells can differentiate into epithelial cells in which p38delta has been shown to regulate epidermis differentiation. Our results demonstrate again that ESC differentiation to epithelial cells is independent of p38alpha and p38delta. We conclude that p38alpha and p38delta are not essential for ESC differentiating into ECs, SMCs, or epithelial cells although numerous studies have shown that the two kinases regulate various cellular activities in aforementioned cells. Our results highlight the possibility that p38 MAP kinases may play less significant roles in ESC differentiation than in the regulation of cellular activities of fully differentiated somatic cells.

Human embryonic stem cell differentiation on tissue engineering scaffolds: effects of NGF and retinoic acid induction

The indefinite proliferative capacity and ability to differentiate into all somatic cell types can make human embryonic stem cells (hESCs) useful in experimental and applied studies in embryonic development, tissue engineering, genetic engineering, pharmacokinetics, and the like. Cellular differentiation dynamics can be studied in monolayer cell cultures; however, it proceeds in three-dimensional (3D) organization in vivo. The aim of this study was to assess the effects of retinoic acid (RA) and nerve growth factor (NGF) on the differentiation patterns of hESCs in 3D culture environment and to compare it with the monolayer culture. Expanded hESCs (HUES-9) were differentiated in two experimental groups for 21 days: (i) two-dimensional (2D) monolayer cultures of hESC colonies, and (ii) 3D culture of hES single cells in poly(DL-lactic-co-glycolic acid) scaffolds. The media used were embryonic stem cell expansion medium (ES-EM), embryonic stem cell differentiation medium containing fetal calf serum (ES-DM), ES-EM containing either 10 ng/mL NGF or 10(-6) M RA, and their combination. Fixed specimens were analyzed with scanning electron microscopy, and expression of nestin, pan-cytokeratin, troponin, and alpha-fetoprotein at days 7, 14, and 21 was evaluated by immunohistomorphometry and reverse transcriptase--polymerase chain reaction. Results indicate different patterns of ectodermal, mesodermal, and endodermal marker expressions between groups, where NGF and RA preferentially favors the differentiation toward ectodermal and mesodermal lineages. While troponin and nestin expression is significantly elevated in 3D culture environment, pan-cytokeratin expression is favored by 2D culture instead. The effects of 3D scaffold culture imply the usefulness of testing in vitro differentiation properties of hESCs in various culture settings designed as models in prospective tissue engineering applications.

Elucidating the phenomenon of HESC-derived RPE: anatomy of cell genesis, expansion and retinal transplantation

Healthy Retinal Pigment Epithelium (RPE) cells are required for proper visual function and the phenomenon of RPE derivation from Human Embryonic Stem Cells (HESC) holds great potential for the treatment of retinal diseases. However, little is known about formation, expansion and expression profile of RPE-like cells derived from HESC (HESC-RPE). By studying the genesis of pigmented foci we identified OTX1/2-positive cell types as potential HESC-RPE precursors. When pigmented foci were excised from culture, HESC-RPE expanded to form extensive monolayers, with pigmented cells at the leading edge assuming a precursor role: de-pigmenting, proliferating, expressing keratin 8 and subsequently re-differentiating. As they expanded and differentiated in vitro, HESC-RPE expressed markers of both developing and mature RPE cells which included OTX1/2, Pax6, PMEL17 and at low levels, RPE65. In vitro, without signals from a developing retinal environment, HESC-RPE could produce regular, polarised monolayers with developmentally important apical and basal features. Following transplantation of HESC-RPE into the degenerating retinal environment of Royal College of Surgeons (RCS) dystrophic rats, the cells survived in the subretinal space, where they maintained low levels of RPE65 expression and remained out of the cell cycle. The HESC-RPE cells responded to the in vivo environment by downregulating Pax6, while maintaining expression of other markers. The presence of rhodopsin-positive material within grafted HESC-RPE indicates that in the future, homogenous transplants of this cell type may be capable of supporting visual function following retinal dystrophy.

Immunophenotyping of the human bulge region: the quest to define useful in situ markers for human epithelial hair follicle stem cells and their niche

Since the discovery of epithelial hair follicle stem cells (eHFSCs) in the bulge of human hair follicles (HFs) an important quest has started: to define useful markers. In the current study, we contribute to this by critically evaluating corresponding published immunoreactivity (IR) patterns, and by attempting to identify markers for the in situ identification of human eHFSCs and their niche. For this, human scalp skin cryosections of at least five different individuals were examined, employing standard immunohistology as well as increased sensitivity methods. Defined reference areas were compared by quantitative immunohistochemistry for the relative intensity of their specific IR. According to our experience, the most useful positive markers for human bulge cells turned out to be cytokeratin 15, cytokeratin 19 and CD200, but were not exclusive, while beta1 integrin and Lhx2 IR were not upregulated by human bulge keratinocytes. Absent IR for CD34, connexin43 and nestin on human bulge cells may be exploited as negative markers. alpha6 integrin, fibronectin, nidogen, fibrillin-1 and latent transforming growth factor (TGF)-beta-binding protein-1 were expressed throughout the connective tissue sheath of human HFs. On the other hand, tenascin-C was upregulated in the bulge and may thus constitute a component of the bulge stem cell niche of human HFs. These immunophenotyping results shed further light on the in situ expression patterns of claimed follicular 'stem cell markers' and suggest that not a single marker alone but only the use of a limited corresponding panel of positive and negative markers may offer a reasonable and pragmatic compromise for identifying human bulge stem cells in situ.

Therapeutic potential of stem cells in skin repair and regeneration

Stem cells are defined by their capacity of self-renewal and multilineage differentiation, which make them uniquely situated to treat a broad spectrum of human diseases. Based on a series of remarkable studies in several fields of regenerative medicine, their application is not too far from the clinical practice. Full-thickness burns and severe traumas can injure skin and its appendages, which protect animals from water loss, temperature change, radiation, trauma and infection. In adults, the normal outcome of repair of massive full-thickness burns is fibrosis and scarring without any appendages, such as hair follicles, sweat and sebaceous glands. Perfect skin regeneration has been considered impossible due to the limited regenerative capacity of epidermal keratinocytes, which are generally thought to be the key source of the epidermis and skin appendages. Currently, researches on stem cells, such as epidermal stem cells, dermal stem cells, mesenchymal stem cells from bone marrow, and embryonic stem cells, bring promise to functional repair of skin after severe burn injury, namely, complete regeneration of skin and its appendages. In this study, we present an overview of the most recent advances in skin repair and regeneration by using stem cells.

Marker profiling of normal keratinocytes identifies the stroma from squamous cell carcinoma of the oral cavity as a modulatory microenvironment in co-culture

PURPOSE

The microenvironment established by stromal cells may or may not influence phenotypic aspects of epithelial cells and may be relevant for tumor and stem cell biology. We address this issue for keratinocytes using tumor-derived stromal cells in a co-culture system.

MATERIALS AND METHODS

We isolated stromal cells from human squamous cell carcinoma tissue and studied their effect on phenotypic characteristics of normal human interfollicular keratinocytes in vitro.

RESULTS

Stromal fibroblasts significantly influence immuno- and lectin cytochemical properties of co-cultured normal keratinocytes. Expression of keratins 8 and 19, the nucleolar protein nucleostemin, parameters related to adhesion/growth-regulatory galectins and the epithelial-mesenchymal transition were altered. This biological activity of tumor-derived stromal cells, which did not require cell contact, appeared to be stable, because it was maintained during passaging of keratinocytes in the absence of cancer cells.

CONCLUSIONS

Tumor-derived stromal fibroblasts acquire distinct properties to shape a microenvironment conducive to altering the phenotypic characteristics of normal epithelial cells in vitro.

A pure population of ectodermal cells derived from human embryonic stem cells

Embryonic stem (ES) cells represent a unique cellular model to recapitulate in vitro early steps of embryonic development and an unlimited cellular source in therapy for many diseases, as well as targets for drug discovery and toxicology screens. Although previous studies have reported epidermal differentiation of mouse and human embryonic stem (huES) cells, the heterogeneity of the resulting cell culture impairs the evaluation of differentiated cells for cell therapy. We report here the reproducible isolation of a homogenous ectodermal cell population, IT1, from human ES cells. Like primary cells, IT1 cells remain homogenous over 15 passages, expand up to 60 population doublings, and then die through senescence. Accordingly, IT1 cells display a normal karyotype and a somatic cell cycle kinetics and do not produce teratoma in nude mice. The production of K14-expressing epithelial cells driven by p63 expression strengthens the ectodermal nature of IT1 cells. Since IT1 can be isolated from different huES cell lines, it may provide a ready source of ectodermal progenitors for the development of a toxicology cell model, new-drug-screening strategies, and cell therapy transplantation.

Pluripotency of embryonic stem cells

Embryonic stem (ES) cells derived from pre-implantation embryos have the potential to differentiate into any cell type derived from the three germ layers of ectoderm (epidermal tissues and nerves), mesoderm (muscle, bone, blood), and endoderm (liver, pancreas, gastrointestinal tract, lungs), including fetal and adult cells. Alone, these cells do not develop into a viable fetus or adult animal because they do not retain the potential to contribute to extraembryonic tissue, and in vitro, they lack spatial and temporal signaling cues essential to normal in vivo development. The basis of pluripotentiality resides in conserved regulatory networks composed of numerous transcription factors and multiple signaling cascades. Together, these regulatory networks maintain ES cells in a pluripotent and undifferentiated form; however, alterations in the stoichiometry of these signals promote differentiation. By taking advantage of this differentiation capacity in vitro, ES cells have clearly been shown to possess the potential to generate multipotent stem and progenitor cells capable of differentiating into a limited number of cell fates. These latter types of cells may prove to be therapeutically viable, but perhaps more importantly, the studies of these cells have led to a greater understanding of mammalian development.

Neural induction and neural stem cell development

Embryonic stem (ES) cells are a pluripotent and renewable cellular resource with tremendous potential for broad applications in regenerative medicine. Arguably the most important consideration for stem cell-based therapies is the ability to precisely direct the differentiation of stem cells along a preferred cellular lineage. During development, lineage commitment is a multistep process requiring the activation and repression of sets of genes at various stages, from an ES cell identity to a tissue-specific stem cell identity and beyond. Thus, the challenge is to ensure that the pattern of genomic regulation is recapitulated during the in vitro differentiation of ES cells into stem/progenitor cells of the appropriate tissue in a robust, predictable and stable manner. To address this issue, we must understand the ontogeny of tissue-specific stem cells during normal embryogenesis and compare the ontogeny of tissue-specific stem cells in ES cell models. Here, we discuss the issue of directed differentiation of pluripotent ES cells into neural stem cells, which is fundamentally linked to two early events in the development of the mammalian nervous system: the 'decision' of the ectoderm to acquire a neural identity (neural determination) and the origin of neural stem cells within this neural-committed population of cells. A clearer understanding of the molecular and cellular mechanisms that govern mammalian neural cell fate determination will lead to improved ES technology applications in neural regeneration.

Isolation of a mesenchymal cell population from murine dermis that contains progenitors of multiple cell lineages

The skin contains two known subpopulations of stem cells/epidermal progenitors: a basal keratinocyte population found in the interfollicular epithelium and cells residing in the bulge region of the hair follicle. The major role of the interfollicular basal keratinocyte population may be epidermal renewal, whereas the bulge population may only be activated and recruited to form a cutaneous epithelium in case of trauma. Using 3-dimensional cultures of murine skin under stress conditions in which only reserve epithelial cells would be expected to survive and expand, we demonstrate that a mesenchymal population resident in neonatal murine dermis has the unique potential to develop an epidermis in vitro. In monolayer culture, this dermal subpopulation has long-term survival capabilities in restricted serum and an inducible capacity to evolve into multiple cell lineages, both epithelial and mesenchymal, depending on culture conditions. When grafted subcutaneously, this dermal subpopulation gave rise to fusiform structures, reminiscent of disorganized muscle, that stained positive for smooth muscle actin and desmin; on typical epidermal grafts, abundant melanocytes appeared throughout the dermis that were not associated with hair follicles. The multipotential cells can be repeatedly isolated from neonatal murine dermis by a sequence of differential centrifugation and selective culture conditions. These results suggest that progenitors capable of epidermal differentiation exist in the mesenchymal compartment of an abundant tissue source and may have a function in mesenchymal-epithelial transition upon insult. Moreover, these cells could be available in sufficient quantities for lineage determination or tissue engineering applications.

Nuclear presence of adhesion-/growth-regulatory galectins in normal/malignant cells of squamous epithelial origin

Cellular activities in the regulation of growth or adhesion/migration involve protein (lectin)-carbohydrate recognition at the cell surface. Members of the galectin family of endogenous lectins additionally bind distinct intracellular ligands. These interactions with protein targets explain the relevance of their nuclear and cytoplasmic presence. Expression profiling for galectins and accessible binding sites is a histochemical approach to link localization with cellular growth properties. Non-cross-reactive antibodies for the homodimeric (proto-type) galectins-1, -2 and -7 and the chimera-type galectin-3 (Gal-3) as well as the biotinylated lectins were tested. This analysis was performed with the FaDu squamous carcinoma cell line and long-term cultured human and porcine epidermal cells as models for malignant and normal cells of squamous cell epithelial origin. A set of antibodies was added for phenotypic cell characterization. Strong nuclear and cytoplasmic signals of galectins and the differential reactivity of labeled galectins support the notion of their individual properties. The length of the period of culture was effective in modulating marker expression. Cytochemical expression profiling is a prerequisite for the selection of distinct proteins for targeted modulation of gene expression as a step toward functional analysis.

Delayed epidermal permeability barrier formation and hair follicle aberrations in Inv-Cldn6 mice

Homozygous mice overexpressing Claudin-6 (Cldn6) exhibit a perturbation in the epidermal differentiation program leading to a defective epidermal permeability barrier (EPB) and dehydration induced death ensuing within 48 h of birth [Turksen, K., Troy, T.C., 2002. Permeability barrier dysfunction in transgenic mice overexpressing claudin 6. Development 129, 1775-1784]. Their heterozygous counterparts are also born with an incomplete EPB; however, barrier formation continues after birth and normal hydration levels are achieved by postnatal day 12 allowing survival into adulthood. Heterozygous Inv-Cldn6 mice exhibit a distinct coat phenotype and histological analysis shows mild epidermal hyperkeratosis. Expression of K5 and K14 is aberrant, extending beyond the basal layer into the suprabasal layer where they are not co-localized suggesting that their expression is uncoupled. There is also atypical K17 and patchy K15 expression in the basal layer with no K6 expression in the interfollicular epidermis; together with marked changes in late differentiation markers (e.g. profilaggrin/filaggrin, loricrin, transglutaminase 3) indicating that the normal epidermal differentiation program is modified. The expression compartment of various Cldns is also perturbed although overall protein levels remained comparable. Most notably induction of Cldn5 and Cldn8 was observed in the Inv-Cldn6 epidermis. Heterozygous Inv-Cldn6 animals also exhibit subtle alterations in the differentiation program of the hair follicle including a shorter anagen phase, and altered hair type distribution and length compared to the wild type; the approximately 20% increase in zig-zag hair fibers at the expense of guard hairs and the approximately 30% shorter guard hairs contribute to coat abnormalities in the heterozygous mice. In addition, the transgenic hair follicles exhibit a decreased expression of K15 as well as some hair-specific keratins and express Cldn5 and Cldn18, which are not detectable in the wild type. These data indicate that Cldn6 plays a role in the differentiation processes of the epidermis and hair follicle and supports the notion of a link between Cldn regulation and EPB assembly/maintenance as well as the hair cycle.