Tcf3 governs stem cell features and represses cell fate determination in skin

Myoepithelial cells are a dynamic barrier to epithelial dissemination

Myoepithelial cells function collectively as a dynamic barrier to the invasion and dissemination of Twist1⁺ luminal epithelial cells and both luminal and basal phenotype breast cancer cells. Barrier function depends on myoepithelial abundance and both smooth muscle contractility and intercellular adhesion within the myoepithelium.

The mammary epithelium is composed of an inner luminal and surrounding myoepithelial cell layer. The presence of cancer cells beyond the myoepithelium defines invasive breast cancer, yet the role of the myoepithelium during invasion remains unclear. We developed a 3D organotypic culture assay to model this process through lineage-specific expression of the prometastatic transcription factor Twist1. We sought to distinguish the functional role of the myoepithelium in regulating invasion and local dissemination. Myoepithelial-specific Twist1 expression induced cell-autonomous myoepithelial cell escape. Remarkably, luminal-specific Twist1 expression was rarely sufficient for escape. Time-lapse microscopy revealed that myoepithelial cells collectively restrain and reinternalize invading Twist1⁺ luminal cells. Barrier function correlated with myoepithelial abundance and required the expression of α-smooth muscle actin and P-cadherin. We next demonstrated that myoepithelial cells can restrain and recapture invasive cancer cells. Our data establish the concept of the myoepithelium as a dynamic barrier to luminal dissemination and implicate both smooth muscle contractility and intercellular adhesion in barrier function.

Early lineage segregation of multipotent embryonic mammary gland progenitors

The mammary gland (MG) is composed of basal cells (BCs) and luminal cells (LCs). While it is generally believed that MG arises from embryonic multipotent progenitors (EMPs), it remains unclear when lineage restriction occurs and what are the mechanisms responsible for the switch from multipotency to unipotency during MG morphogenesis. Here, we performed multicolor lineage tracing and assessed the fate of single progenitors and demonstrated the existence of a developmental switch from multipotency to unipotency during embryonic MG development. Molecular profiling and single cell RNA-seq revealed that EMPs express a unique hybrid basal and luminal signature and the factors associated with the different lineages. Sustained p63 expression in EMPs promotes unipotent BC fate and was sufficient to reprogram adult LCs into BCs by promoting an intermediate hybrid multipotent like state. Altogether, this study identifies the timing and the mechanisms mediating the early lineage segregation of multipotent progenitors during MG development.

Generation of a biotinylatable Sox2 mouse model to identify Sox2 complexes in vivo

Sox2 is a Sry-box containing family member of related transcription factors sharing homology in their DNA binding domain. Sox2 is important during different stages of development, and previously we showed that Sox2 plays an important role in branching morphogenesis and epithelial cell differentiation in lung development. The transcriptional activity of Sox2 depends on its interaction with other proteins, leading to ‘complex-specific’ DNA binding and transcriptional regulation. In this study, we generated a mouse model containing a biotinylatable-tag targeted at the translational start site of the endogenous Sox2 gene (bioSox2). This tag was biotinylated by the bacterial birA protein and the resulting bioSox2 protein was used to identify associating partners of Sox2 at different phases of lung development in vivo (the Sox2 interactome). Homozygous bioSox2 mice are viable and fertile irrespective of the biotinylation of the bio tag, indicating that the bioSox2 gene is normally expressed and the protein is functional in all tissues. This suggests that partners of Sox2 are most likely able to associate with the bioSox2 protein. BioSox2 complexes were isolated with high affinity using streptavidin beads and analysed by MALDI-ToF mass spectrometry analysis. Several of the identified binding partners are already shown to have a respiratory phenotype. Two of these partners, Wdr5 and Tcf3, were validated to confirm their association in Sox2 complexes. This bioSox2 mouse model will be a valuable tool for isolating in vivo Sox2 complexes from different tissues.

Transcriptional profiling of NCI/ADR-RES cells unveils a complex network of signaling pathways and molecular mechanisms of drug resistance

Background

Ovarian cancer has the highest mortality rate among all the gynecological cancers. This is mostly due to the resistance of ovarian cancer to current chemotherapy regimens. Therefore, it is of crucial importance to identify the molecular mechanisms associated with chemoresistance.

Methods

NCI/ADR-RES is a multidrug-resistant cell line that is a model for the study of drug resistance in ovarian cancer. We carried out a microarray-derived transcriptional profiling analysis of NCI/ADR-RES to identify differentially expressed genes relative to its parental OVCAR-8.

Results

Gene-expression profiling has allowed the identification of genes and pathways that may be important for the development of drug resistance in ovarian cancer. The NCI/ADR-RES cell line has differential expression of genes involved in drug extrusion, inactivation, and efficacy, as well as genes involved in the architectural and functional reorganization of the extracellular matrix. These genes are controlled through different signaling pathways, including MAPK–Akt, Wnt, and Notch.

Conclusion

Our findings highlight the importance of using orthogonal therapies that target completely independent pathways to overcome mechanisms of resistance to both classical chemotherapeutic agents and molecularly targeted drugs.

Non-canonical Wnt signaling regulates neural stem cell quiescence during homeostasis and after demyelination

Adult neural stem cells (NSCs) reside in a specialized microenvironment, the subventricular zone (SVZ), which provides them with unique signaling cues to control their basic properties and prevent their exhaustion. While the signaling mechanisms that regulate NSC lineage progression are well characterized, the molecular mechanisms that trigger the activation of quiescent NSCs during homeostasis and tissue repair are still unclear. Here, we uncovered that the NSC quiescent state is maintained by Rho-GTPase Cdc42, a downstream target of non-canonical Wnt signaling. Mechanistically, activation of Cdc42 induces expression of molecules involved in stem cell identity and anchorage to the niche. Strikingly, during a demyelination injury, downregulation of non-canonical Wnt-dependent Cdc42 activity is necessary to promote activation and lineage progression of quiescent NSCs, thereby initiating the process of tissue repair.

Inflammatory memory sensitizes skin epithelial stem cells to tissue damage

The body’s first line of defense against environmental assaults, the skin barrier is maintained by epithelial stem cells (EpSCs). Despite EpSCs’ vulnerability to inflammatory pressures, neither the primary response nor its enduring consequences are understood. Here, we unearth a prolonged memory to acute inflammation that enables EpSCs to hasten barrier restoration following subsequent tissue damage. This functional adaptation does not require skin resident macrophages or T cells. Rather, EpSCs maintain chromosomal accessibility at key stress response genes that are activated by the primary stimulus. Upon a secondary challenge, genes governed by these domains are transcribed rapidly. Fueling this memory is Aim2, encoding an activator of the inflammasome. Absence of AIM2 or its downstream effectors, Caspase-1 and Interleukin-1β, erases EpSCs’ ability to recollect inflammation. While EpSCs benefit from inflammatory tuning by heightening their responsiveness to subsequent stressors, this enhanced sensitivity likely increases their susceptibility to autoimmune and hyperproliferative disorders, including cancer.

A transgenic toolkit for visualizing and perturbing microtubules reveals unexpected functions in the epidermis

The physiological functions of microtubules (MTs) are poorly understood in many differentiated cell types. We developed a genetic toolkit to study MT dynamics and function in diverse cells. Using TRE-EB1-GFP mice, we found that MT dynamics are strongly suppressed in differentiated keratinocytes in two distinct steps due to alterations in both growth rate and lifetime. To understand the functions of these MT populations, we developed TRE-spastin mice to disrupt MTs in specific cell types. MT perturbation in post-mitotic keratinocytes had profound consequences on epidermal morphogenesis. We uncoupled cell-autonomous roles in cell flattening from non-cell-autonomous requirements for MTs in regulating proliferation, differentiation, and tissue architecture. This work uncovers physiological roles for MTs in epidermal development, and the tools described here will be broadly useful to study MT dynamics and functions in mammals.

Immunohistochemical Expression of Cyclo-oxygenase 2 and Liver X Receptor-α in Acne Vulgaris

Introduction

Acne Vulgaris (AV) is a common inflammatory disease of pilosebaceous units. Liver X Receptor-α (LXR-α) is a ligand activated transcription factor. It controls transcription of genes involved in lipid and fatty acid synthesis. Cyclo-oxygenase 2 (COX2) is a rate limiting enzyme in prostaglandin synthesis. It plays important role in inflammation.

Aim

To evaluate the immunohistochemical expression of LXR-α and COX2 in acne vulgaris skin biopsies to explore their possible pathogenic role in this disease.

Materials and Methods

Sixty five subjects were included (45 cases with AV and 20 age and gender-matched healthy controls). Skin biopsies were taken from lesional and perilesional skin of cases and from site-matched areas of control subjects. The evaluation of LXR-α and COX2 was done using immunohistochemical technique. Data were collected, tabulated and statistically analysed using a personal computer with "(SPSS) version 11" program. Chi-square test was used to study the association between qualitative variables. Mann-Whitney test was used for comparison between quantitative variables. Student's t-test was used for comparison between two groups having quantitative variables. Spearman's coefficient was used to study the correlation between two different variables. Differences were considered statistically significant with p<0.05.

Results

COX2 was upregulated in lesional skin compared with peilesional and control skin both in epidermis and pilosebaceous units (p<0.001 for all). Higher epidermal COX2% was significantly associated with papulopustular acne (p=0.009) and higher acne score (p=0.018). Higher pilosebaceous units COX2% was significantly associated with papulopustular acne (p=0.04). LXR-α was upregulated in lesional skin compared with peilesional and control skin both in epidermis and pilosebaceous units (p<0.001 for all). Higher LXR-α % in epidermis and pilosebaceous units was significantly associated with papulopustular acne (p=0.01 for both) and higher acne score (p=0.03 for both). Significant positive correlation was detected between COX2% and LXR-α % in epidermis (p=0.001, r=0.87) and pilosebaceous units (p=0.001, r=0.65).

Conclusion

Both LXR-α and COX-2 play a role in the pathogenesis of acne vulgaris through their effects on cellular proliferation, inflammation and lipid synthesis. Research for new therapeutic modalities based on their inhibition is needed. More understanding of the interaction between LXR-α, COX2 and acne lesions may lead to effective interference, possibly directed toward specific cell types or steps within inflammatory pathways.

Lactate dehydrogenase activity drives hair follicle stem cell activation

Although normally dormant, hair follicle stem cells (HFSCs) quickly become activated to divide during a new hair cycle. The quiescence of HFSCs is known to be regulated by a number of intrinsic and extrinsic mechanisms. Here we provide several lines of evidence to demonstrate that HFSCs utilize glycolytic metabolism and produce significantly more lactate than other cells in the epidermis. Furthermore, lactate generation appears to be critical for the activation of HFSCs as deletion of lactate dehydrogenase (Ldha) prevented their activation. Conversely, genetically promoting lactate production in HFSCs through mitochondrial pyruvate carrier 1 (Mpc1) deletion accelerated their activation and the hair cycle. Finally, we identify small molecules that increase lactate production by stimulating Myc levels or inhibiting Mpc1 carrier activity and can topically induce the hair cycle. These data suggest that HFSCs maintain a metabolic state that allows them to remain dormant and yet quickly respond to appropriate proliferative stimuli.

Hyaluronan Rich Microenvironment in the Limbal Stem Cell Niche Regulates Limbal Stem Cell Differentiation

Purpose

Limbal epithelial stem cells (LSCs), located in the basal layer of the corneal epithelium in the corneal limbus, are vital for maintaining the corneal epithelium. LSCs have a high capacity of self-renewal with increased potential for error-free proliferation and poor differentiation. To date, limited research has focused on unveiling the composition of the limbal stem cell niche, and, more important, on the role the specific stem cell niche may have in LSC differentiation and function. Our work investigates the composition of the extracellular matrix in the LSC niche and how it regulates LSC differentiation and function.

Methods

Hyaluronan (HA) is naturally synthesized by hyaluronan synthases (HASs), and vertebrates have the following three types: HAS1, HAS2, and HAS3. Wild-type and HAS and TSG-6 knockout mice-HAS1-/-;HAS3-/-, HAS2Δ/ΔCorEpi, TSG-6-/--were used to determine the importance of the HA niche in LSC differentiation and specification.

Results

Our data demonstrate that the LSC niche is composed of a HA rich extracellular matrix. HAS1-/-;HAS3-/-, HAS2Δ/ΔCorEpi, and TSG-6-/- mice have delayed wound healing and increased inflammation after injury. Interestingly, upon insult the HAS knock-out mice up-regulate HA throughout the cornea through a compensatory mechanism, and in turn this alters LSC and epithelial cell specification.

Conclusions

The LSC niche is composed of a specialized HA matrix that differs from that present in the rest of the corneal epithelium, and the disruption of this specific HA matrix within the LSC niche leads to compromised corneal epithelial regeneration. Finally, our findings suggest that HA has a major role in maintaining the LSC phenotype.

Spatiotemporal antagonism in mesenchymal-epithelial signaling in sweat versus hair fate decision

The gain of eccrine sweat glands in hairy body skin has empowered humans to run marathons and tolerate temperature extremes. Epithelial-mesenchymal cross-talk is integral to the diverse patterning of skin appendages, but the molecular events underlying their specification remain largely unknown. Using genome-wide analyses and functional studies, we show that sweat glands are specified by mesenchymal-derived bone morphogenetic proteins (BMPs) and fibroblast growth factors that signal to epithelial buds and suppress epithelial-derived sonic hedgehog (SHH) production. Conversely, hair follicles are specified when mesenchymal BMP signaling is blocked, permitting SHH production. Fate determination is confined to a critical developmental window and is regionally specified in mice. In contrast, a shift from hair to gland fates is achieved in humans when a spike in BMP silences SHH during the final embryonic wave(s) of bud morphogenesis.

Linking chromatin dynamics, cell fate plasticity, and tissue homeostasis in adult mouse hair follicle stem cells

Cellular plasticity for fate acquisition is associated with distinct chromatin states, which include histone modifications, dynamic association of chromatin factors with the DNA, and global chromatin compaction and nuclear organization. While embryonic stem cell (ESC) plasticity in vitro and its link with chromatin states have been characterized in depth, little is known about tissue stem cell plasticity in vivo, during adult tissue homeostasis. Recently, we reported a distinct globally low level of histone H3 K4/9/27me3 in mouse hair follicle stem cells (HFSCs) during quiescence. This occurred at the stage preceding fate acquisition, when HFSC fate plasticity must be at its highest. This hypomethylated state was required for proper skin homeostasis and timely hair cycle. Here, we show both in the live tissue and in cell culture that at quiescence HFSCs have higher exchange rates for core histone H2B when compared with proliferative or differentiated cells. This denoted a hyperdynamic chromatin state, which was previously associated with high cell fate plasticity in ESCs. Moreover, we find that quiescent HFSCs display a higher propensity for de-differentiation in response to Yamanaka's reprogramming factors in vivo. These results further support our recent model in which HFSCs render their chromatin into a specific state at quiescence, which is attuned to higher cell fate plasticity.

Comprehensive analysis of differential co-expression patterns reveal transcriptional dysregulation mechanism and identify novel prognostic lncRNAs in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies worldwide and occurs at a relatively high frequency in People's Republic of China. However, the molecular mechanism underlying ESCC is still unclear. In this study, the mRNA and long non-coding RNA (lncRNA) expression profiles of ESCC were downloaded from the Gene Expression Omnibus database, and then differential co-expression analysis was used to reveal the altered co-expression relationship of gene pairs in ESCC tumors. A total of 3,709 mRNAs and 923 lncRNAs were differentially co-expressed between normal and tumor tissues, and we found that most of the gene pairs lost associations in the tumor tissues. The differential regulatory networking approach deciphered that transcriptional dysregulation was ubiquitous in ESCC, and most of the differentially regulated links were modulated by 37 TFs. Our study also found that two novel lncRNAs (ADAMTS9-AS1 and AP000696.2) might be essential in the development of ectoderm and epithelial cells, which could significantly stratify ESCC patients into high-risk and low-risk groups, and were much better than traditional clinical tumor markers. Further inspection of two risk groups showed that the changes in TF-target regulation in the high-risk patients were significantly higher than those in the low-risk patients. In addition, four signal transduction-related DCmRNAs (ERBB3, ENSA, KCNK7, MFSD5), which were differentially co-expressed with the two lncRNAs, might also have the predictive capacity. Our findings will enhance the understanding of ESCC transcriptional dysregulation from a view of cross-link of lncRNA and mRNA, and the two-lncRNA combination may serve as a novel prognostic biomarker for clinical applications of ESCC.

Wounding induces dedifferentiation of epidermal Gata6+ cells and acquisition of stem cell properties

The epidermis is maintained by multiple stem cell populations whose progeny differentiate along diverse, and spatially distinct, lineages. Here we show that the transcription factor Gata6 controls the identity of the previously uncharacterized sebaceous duct (SD) lineage and identify the Gata6 downstream transcription factor network that specifies a lineage switch between sebocytes and SD cells. During wound healing differentiated Gata6⁺ cells migrate from the SD into the interfollicular epidermis and dedifferentiate, acquiring the ability to undergo long-term self-renewal and differentiate into a much wider range of epidermal lineages than in undamaged tissue. Our data not only demonstrate that the structural and functional complexity of the junctional zone is regulated by Gata6, but also reveal that dedifferentiation is a previously unrecognized property of post-mitotic, terminally differentiated cells that have lost contact with the basement membrane. This resolves the long-standing debate about the contribution of terminally differentiated cells to epidermal wound repair.

Stem Cell Lineage Infidelity Drives Wound Repair and Cancer

Tissue stem cells contribute to tissue regeneration and wound repair through cellular programs that can be hijacked by cancer cells. Here, we investigate such a phenomenon in skin, where during homeostasis, stem cells of the epidermis and hair follicle fuel their respective tissues. We find that breakdown of stem cell lineage confinement-granting privileges associated with both fates-is not only hallmark but also functional in cancer development. We show that lineage plasticity is critical in wound repair, where it operates transiently to redirect fates. Investigating mechanism, we discover that irrespective of cellular origin, lineage infidelity occurs in wounding when stress-responsive enhancers become activated and override homeostatic enhancers that govern lineage specificity. In cancer, stress-responsive transcription factor levels rise, causing lineage commanders to reach excess. When lineage and stress factors collaborate, they activate oncogenic enhancers that distinguish cancers from wounds.

TCF7L1 promotes skin tumorigenesis independently of β-catenin through induction of LCN2

The transcription factor TCF7L1 is an embryonic stem cell signature gene that is upregulated in multiple aggressive cancer types, but its role in skin tumorigenesis has not yet been defined. Here we document TCF7L1 upregulation in skin squamous cell carcinoma (SCC) and demonstrate that TCF7L1 overexpression increases tumor incidence, tumor multiplicity, and malignant progression in the chemically induced mouse model of skin SCC. Additionally, we show that downregulation of TCF7L1 and its paralogue TCF7L2 reduces tumor growth in a xenograft model of human skin SCC. Using separation-of-function mutants, we show that TCF7L1 promotes tumor growth, enhances cell migration, and overrides oncogenic RAS-induced senescence independently of its interaction with β-catenin. Through transcriptome profiling and combined gain- and loss-of-function studies, we identified LCN2 as a major downstream effector of TCF7L1 that drives tumor growth. Our findings establish a tumor-promoting role for TCF7L1 in skin and elucidate the mechanisms underlying its tumorigenic capacity.

Mechanisms of pluripotency maintenance in mouse embryonic stem cells

Mouse embryonic stem cells (mESCs), characterized by their pluripotency and capacity for self-renewal, are driven by a complex gene expression program composed of several regulatory mechanisms. These mechanisms collaborate to maintain the delicate balance of pluripotency gene expression and their disruption leads to loss of pluripotency. In this review, we provide an extensive overview of the key pillars of mESC pluripotency by elaborating on the various essential transcription factor networks and signaling pathways that directly or indirectly support this state. Furthermore, we consider the latest developments in the role of epigenetic regulation, such as noncoding RNA signaling or histone modifications.

The increased expression of TCF3 is correlated with poor prognosis in Chinese patients with nasopharyngeal carcinoma

OBJECTIVES

Regulatory factors controlling stem cell identity and self-renewal are often active in aggressive cancers and are thought to promote cancer growth and progression. B-cell-specific transcription factor 3 (TCF3/E2A) is a member of the T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factor family that is central to regulating epidermal and embryonic stem cell identity. It has been reported that TCF3 was connected with the development and progression of a number of human cancers. In this study, we aimed to identify the expression of TCF3 in human nasopharyngeal carcinoma (NPC) and evaluate its clinical significance.

DESIGN

To investigate the expression of TCF3 in NPC and its relationship to prognosis.

SETTING

An in vitro study.

MAIN OUTCOME MEASURES

We analysed the expression of TCF3 in NPC and in non-tumourous nasopharyngeal tissues by quantitative RT-PCR and Western blotting. The expression patterns of TCF3 in 117 archived paraffin-embedded NPC specimens were characterised by immunohistochemistry, and the correlation between the TCF3 protein expression and the clinicopathological features of NPC was analysed.

RESULTS

We observed that TCF3 had a higher expression in NPC than in non-tumourous nasopharyngeal tissues of 117 archived paraffin-embedded NPC specimens, and 80 (68.4%) biopsy tissues revealed high levels of TCF3 expression. Furthermore, statistical analyses demonstrated that the increased expression of TCF3 was closely related to clinical stage, locoregional recurrence and distant metastasis of NPC. NPC patients with high levels of TCF3 expression had a shorter survival time, whereas patients with lower levels of TCF3 expression survived longer. Moreover, multivariate analysis suggested that the upregulation of TCF3 was a critical prognostic factor for NPC.

CONCLUSIONS

Our observations suggest, for the first time, that TCF3 is significantly associated with the development and progression of NPC, which can be used as an important prognostic marker for patients with NPC and may be an effective target for the treatment of NPC.

Genetically modified laboratory mice with sebaceous glands abnormalities

Sebaceous glands (SG) are exocrine glands that release their product by holocrine secretion, meaning that the whole cell becomes a secretion following disruption of the membrane. SG may be found in association with a hair follicle, forming the pilosebaceous unit, or as modified SG at different body sites such as the eyelids (Meibomian glands) or the preputial glands. Depending on their location, SG fulfill a number of functions, including protection of the skin and fur, thermoregulation, formation of the tear lipid film, and pheromone-based communication. Accordingly, SG abnormalities are associated with several diseases such as acne, cicatricial alopecia, and dry eye disease. An increasing number of genetically modified laboratory mouse lines develop SG abnormalities, and their study may provide important clues regarding the molecular pathways regulating SG development, physiology, and pathology. Here, we summarize in tabulated form the available mouse lines with SG abnormalities and, focusing on selected examples, discuss the insights they provide into SG biology and pathology. We hope this survey will become a helpful information source for researchers with a primary interest in SG but also as for researchers from unrelated fields that are unexpectedly confronted with a SG phenotype in newly generated mouse lines.

Cell-Type-Specific Chromatin States Differentially Prime Squamous Cell Carcinoma Tumor-Initiating Cells for Epithelial to Mesenchymal Transition

Epithelial to mesenchymal transition (EMT) in cancer cells has been associated with metastasis, stemness, and resistance to therapy. Some tumors undergo EMT while others do not, which may reflect intrinsic properties of their cell of origin. However, this possibility is largely unexplored. By targeting the same oncogenic mutations to discrete skin compartments, we show that cell-type-specific chromatin and transcriptional states differentially prime tumors to EMT. Squamous cell carcinomas (SCCs) derived from interfollicular epidermis (IFE) are generally well differentiated, while hair follicle (HF) stem cell-derived SCCs frequently exhibit EMT, efficiently form secondary tumors, and possess increased metastatic potential. Transcriptional and epigenomic profiling revealed that IFE and HF tumor-initiating cells possess distinct chromatin landscapes and gene regulatory networks associated with tumorigenesis and EMT that correlate with accessibility of key epithelial and EMT transcription factor binding sites. These findings highlight the importance of chromatin states and transcriptional priming in dictating tumor phenotypes and EMT.

TCF/LEF Transcription Factors: An Update from the Internet Resources

T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) proteins (TCFs) from the High Mobility Group (HMG) box family act as the main downstream effectors of the Wnt signaling pathway. The mammalian TCF/LEF family comprises four nuclear factors designated TCF7, LEF1, TCF7L1, and TCF7L2 (also known as TCF1, LEF1, TCF3, and TCF4, respectively). The proteins display common structural features and are often expressed in overlapping patterns implying their redundancy. Such redundancy was indeed observed in gene targeting studies; however, individual family members also exhibit unique features that are not recapitulated by the related proteins. In the present viewpoint, we summarized our current knowledge about the specific features of individual TCFs, namely structural-functional studies, posttranslational modifications, interacting partners, and phenotypes obtained upon gene targeting in the mouse. In addition, we employed several publicly available databases and web tools to evaluate the expression patterns and production of gene-specific isoforms of the TCF/LEF family members in human cells and tissues.

Divergent regulation of functionally distinct γ-tubulin complexes during differentiation

Differentiation induces the formation of noncentrosomal microtubule arrays in diverse tissues. The formation of these arrays requires loss of microtubule-organizing activity (MTOC) at the centrosome, but the mechanisms regulating this transition remain largely unexplored. Here, we use the robust loss of centrosomal MTOC activity in the epidermis to identify two pools of γ-tubulin that are biochemically and functionally distinct and differentially regulated. Nucleation-competent CDK5RAP2-γ-tubulin complexes were maintained at centrosomes upon initial epidermal differentiation. In contrast, Nedd1-γ-tubulin complexes did not promote nucleation but were required for anchoring of microtubules, a previously uncharacterized activity for this complex. Cell cycle exit specifically triggered loss of Nedd1-γ-tubulin complexes, providing a mechanistic link connecting MTOC activity and differentiation. Collectively, our studies demonstrate that distinct γ-tubulin complexes regulate different microtubule behaviors at the centrosome and show that differential regulation of these complexes drives loss of centrosomal MTOC activity.

Quantitative lineage tracing strategies to resolve multipotency in tissue-specific stem cells

Here, Wuidart et al. present a rigorous new method for assessing the lineage relationship and stem cell fate in different organs and tissues. The authors developed two novel methods for determining lineage relationships: the first one based on statistical analysis of multicolor lineage tracing, and the second one based on lineage tracing at saturation to assess the fate of all stem cells within a given lineage and the “flux” of cells between different lineages.

Lineage tracing has become the method of choice to study the fate and dynamics of stem cells (SCs) during development, homeostasis, and regeneration. However, transgenic and knock-in Cre drivers used to perform lineage tracing experiments are often dynamically, temporally, and heterogeneously expressed, leading to the initial labeling of different cell types and thereby complicating their interpretation. Here, we developed two methods: the first one based on statistical analysis of multicolor lineage tracing, allowing the definition of multipotency potential to be achieved with high confidence, and the second one based on lineage tracing at saturation to assess the fate of all SCs within a given lineage and the “flux” of cells between different lineages. Our analysis clearly shows that, whereas the prostate develops from multipotent SCs, only unipotent SCs mediate mammary gland (MG) development and adult tissue remodeling. These methods offer a rigorous framework to assess the lineage relationship and SC fate in different organs and tissues.

EdnrB Governs Regenerative Response of Melanocyte Stem Cells by Crosstalk with Wnt Signaling

Delineating the crosstalk between distinct signaling pathways is key to understanding the diverse and dynamic responses of adult stem cells during tissue regeneration. Here, we demonstrate that the Edn/EdnrB signaling pathway can interact with other signaling pathways to elicit distinct stem cell functions during tissue regeneration. EdnrB signaling promotes proliferation and differentiation of melanocyte stem cells (McSCs), dramatically enhancing the regeneration of hair and epidermal melanocytes. This effect is dependent upon active Wnt signaling that is initiated by Wnt ligand secretion from the hair follicle epithelial niche. Further, this Wnt-dependent EdnrB signaling can rescue the defects in melanocyte regeneration caused by Mc1R loss. This suggests that targeting Edn/EdnrB signaling in McSCs can be a therapeutic approach to promote photoprotective-melanocyte regeneration, which may be useful for those with increased risk of skin cancers due to Mc1R variants.

Transcription factor 7-like 1 dysregulates keratinocyte differentiation through upregulating lipocalin 2

Recent studies strongly suggested that transcription factor 7-like 1 (Tcf7l1, also known as Tcf3) is involved in the differentiation of several types of cells, and demonstrated that Tcf7l1 modulates keratinocytes physiologically through regulating lipocalin 2 (LCN2), a key regulator of cell differentiation. To reveal the potential role of Tcf7l1 in the dysregulation of keratinocyte differentiation, both Tcf7l1 and LCN2 were determined in a variety of skin disorders. The in vitro effect of Tcf7l1 on keratinocyte differentiation was studied by culturing SCC-13 cells, and the human foreskin keratinocytes (HFKs) that were transfected with vectors for overexpressing human papillomavirus E6/E7 or Tcf7l1 genes. We found that both Tcf7l1 and LCN2 were highly expressed in those diseases characterized by defective keratinocyte differentiation (especially psoriasis vulgaris, condyloma acuminatum, squamous cell carcinoma, etc). Moreover, compared with control HFKs, SCC-13 cells and E6/E7-harboring HFKs expressed more Tcf7l1 and LCN2. Tcf7l1 siRNA transfection decreased LCN2 but increased involucrin and loricrin in HFKs under calcium stimuli. Conversely, Tcf7l1 overexpression in SCC-13 cells or vector-transfected HFKs induced lower involucrin and loricrin expression and less keratinocyte apoptosis, both of which, however, were partially abrogated by LCN2 siRNA or neutralizing anti-LCN2 antibody. Interestingly, the Tcf7l1 expression in HFKs correlated positively with the MMP-2 level, and the inhibition of MMP-2 decreased the LCN2 level and even attenuated the effect of Tcf7l1 on LCN2 expression. Therefore, Tcf7l1 dysregulates keratinocyte differentiation, possibly through upregulating the LCN2 pathway in an MMP-2 mediated manner. Elucidating the interaction between Tcf7l1 and LCN2 may help understand disordered cell differentiation in some skin diseases.

The role of PPARγ-mediated signalling in skin biology and pathology: new targets and opportunities for clinical dermatology

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that modulate the expression of multiple different genes involved in the regulation of lipid, glucose and amino acid metabolism. PPARs and cognate ligands also regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. This includes a role in mediating skin and pilosebaceous unit homoeostasis: PPARs appear to be essential for maintaining skin barrier permeability, inhibit keratinocyte cell growth, promote keratinocyte terminal differentiation and regulate skin inflammation. They also may have protective effects on human hair follicle (HFs) epithelial stem cells, while defects in PPARγ-mediated signalling may promote the death of these stem cells and thus facilitate the development of cicatricial alopecia (lichen planopilaris). Overall, however, selected PPARγ modulators appear to act as hair growth inhibitors that reduce the proliferation and promote apoptosis of hair matrix keratinocytes. The fact that commonly prescribed PPARγ-modulatory drugs of the thiazolidine-2,4-dione class can exhibit a battery of adverse cutaneous effects underscores the importance of distinguishing beneficial from clinically undesired cutaneous activities of PPARγ ligands and to better understand on the molecular level how PPARγ-regulated cutaneous lipid metabolism and PPARγ-mediated signalling impact on human skin physiology and pathology. Surely, the therapeutic potential that endogenous and exogenous PPARγ modulators may possess in selected skin diseases, ranging from chronic inflammatory hyperproliferative dermatoses like psoriasis and atopic dermatitis, via scarring alopecia and acne can only be harnessed if the complexities of PPARγ signalling in human skin and its appendages are systematically dissected.

Foxi3 Deficiency Compromises Hair Follicle Stem Cell Specification and Activation

The hair follicle is an ideal system to study stem cell specification and homeostasis due to its well characterized morphogenesis and stereotypic cycles of stem cell activation upon each hair cycle to produce a new hair shaft. The adult hair follicle stem cell niche consists of two distinct populations, the bulge and the more activation-prone secondary hair germ (HG). Hair follicle stem cells are set aside during early stages of morphogenesis. This process is known to depend on the Sox9 transcription factor, but otherwise the establishment of the hair follicle stem cell niche is poorly understood. Here, we show that that mutation of Foxi3, a Forkhead family transcription factor mutated in several hairless dog breeds, compromises stem cell specification. Further, loss of Foxi3 impedes hair follicle downgrowth and progression of the hair cycle. Genome-wide profiling revealed a number of downstream effectors of Foxi3 including transcription factors with a recognized function in hair follicle stem cells such as Lhx2, Runx1, and Nfatc1, suggesting that the Foxi3 mutant phenotype results from simultaneous downregulation of several stem cell signature genes. We show that Foxi3 displays a highly dynamic expression pattern during hair morphogenesis and cycling, and identify Foxi3 as a novel secondary HG marker. Absence of Foxi3 results in poor hair regeneration upon hair plucking, and a sparse fur phenotype in unperturbed mice that exacerbates with age, caused by impaired secondary HG activation leading to progressive depletion of stem cells. Thus, Foxi3 regulates multiple aspects of hair follicle development and homeostasis. Stem Cells 2016;34:1896-1908.

Wakayama symposium: role of canonical Notch signaling in conjucntival goblet cell differentiation and dry eye syndrome

This review summarizes a recent finding regarding the intrinsic canonical Notch signaling pathway in regulating normal ocular surface morphogenesis and its role in the pathogenesis of goblet cell deficiency-associated keratoconjunctivitis sicca (KCS, or dry eye). Specifically, we used novel transgenic mice to investigate the mechanism of how the Notch1 activation may serve as the upstream control of expression of transcription factors Krüppel-like factors 4 or 5 (Klf4 or Klf5) which in turn controls goblet cell differentiation and activates mucin 5/ac synthesis during ocular surface morphogenesis.

Embryonic attenuated Wnt/β-catenin signaling defines niche location and long-term stem cell fate in hair follicle

Long-term adult stem cells sustain tissue regeneration throughout the lifetime of an organism. They were hypothesized to originate from embryonic progenitor cells that acquire long-term self-renewal ability and multipotency at the end of organogenesis. The process through which this is achieved often remains unclear. Here, we discovered that long-term hair follicle stem cells arise from embryonic progenitor cells occupying a niche location that is defined by attenuated Wnt/β-catenin signaling. Hair follicle initiation is marked by placode formation, which depends on the activation of Wnt/β-catenin signaling. Soon afterwards, a region with attenuated Wnt/β-catenin signaling emerges in the upper follicle. Embryonic progenitor cells residing in this region gain expression of adult stem cell markers and become definitive long-term hair follicle stem cells at the end of organogenesis. Attenuation of Wnt/β-catenin signaling is a prerequisite for hair follicle stem cell specification because it suppresses Sox9, which is required for stem cell formation.

DOI:http://dx.doi.org/10.7554/eLife.10567.001

Many tissues and organs in an adult’s body – including bone marrow, skin and intestines – contain a small number of cells called adult stem cells. These cells usually stay dormant within these tissues (at a site called a ‘niche’) until they are required to repair damaged or lost cells. At this point, adult stem cells can specialize, or ‘differentiate’, into the many different cell types that make up the tissue or organ where they reside.

The cells that produce hairs are an example of adult stem cells. In mammals, hairs grow from structures called hair follicles that are found in the skin, and over the life of an animal, old hairs are shed and replaced. Previous research had suggested that certain embryonic cells are set to become hair follicle stem cells before the hair follicles emerge in the adult tissue. However it remained unclear how this decision is made, and which genes and molecules are involved in this process.

Xu et al. have now found that, in mice, the fate of hair follicle stem cells is decided at an early stage in development, when the hair follicle is a simpler structure called a ‘hair peg’. Cells near the upper part of the hair peg tend to become dormant and adopt an adult stem cell fate, while the ones in the lower part are more likely to differentiate straight away. This shows that the position, hence the niche environment, plays a key role in determining these different cells’ fates.

Xu et al. went on to discover that the decision for a cell to become a hair follicle stem cell relies on reduced signaling through the so-called Wnt signal pathway. Understanding how adult stem cells become established during development may help future efforts to grow tissues and organs in the laboratory for research purposes or organ transplantation.

DOI:http://dx.doi.org/10.7554/eLife.10567.002

ETS family transcriptional regulators drive chromatin dynamics and malignancy in squamous cell carcinomas

Tumor-initiating stem cells (SCs) exhibit distinct patterns of transcription factors and gene expression compared to healthy counterparts. Here, we show that dramatic shifts in large open-chromatin domain (super-enhancer) landscapes underlie these differences and reflect tumor microenvironment. By in vivo super-enhancer and transcriptional profiling, we uncover a dynamic cancer-specific epigenetic network selectively enriched for binding motifs of a transcription factor cohort expressed in squamous cell carcinoma SCs (SCC-SCs). Many of their genes, including Ets2 and Elk3, are themselves regulated by SCC-SC super-enhancers suggesting a cooperative feed-forward loop. Malignant progression requires these genes, whose knockdown severely impairs tumor growth and prohibits progression from benign papillomas to SCCs. ETS2-deficiency disrupts the SCC-SC super-enhancer landscape and downstream cancer genes while ETS2-overactivation in epidermal-SCs induces hyperproliferation and SCC super-enhancer-associated genes Fos, Junb and Klf5. Together, our findings unearth an essential regulatory network required for the SCC-SC chromatin landscape and unveil its importance in malignant progression.

DOI:http://dx.doi.org/10.7554/eLife.10870.001

Many cancers contain a mixture of different types of cells. Of these, cells known as cancer stem cells can form new tumours and drive the growth and spread of the cancer around the body. A central question is how cancer stem cells differ from healthy adult stem cells. Recent evidence suggests that, in addition to having genetic mutations, cancer stem cells live in a very different environment to other cells within the tumour. This 'microenvironment'also has a major impact on how these cells behave compared to normal stem cells. Together, the genetic and environmental differences profoundly change the way genes are expressed in the cancer cells.

In 2013, a group of researchers identified regions of DNA called super-enhancers. These regions are long stretches of DNA that proteins called transcription factors can interact with to coordinate the expression of nearby genes to alter the production of certain proteins. Super-enhancers contain several transcription factor-binding sites that are close to each other with the different sites being associated with transcription factors that are only active in specific types of cells. Furthermore, super-enhancers are often self-regulatory, meaning that the binding of transcription factors to a super-enhancer can lead to an increase in the expression of the genes that encode the same transcription factors.

Yang, Schramek et al. have now identified the super-enhancers in a skin cancer called squamous cell carcinoma and showed that they differ dramatically from the super-enhancers of normal skin stem cells. Their experiments show that the active super-enhancers in cancer stem cells are associated with a very different set of genes that are highly and often specifically expressed in cancer stem cells. In the cancer stem cells, a transcription factor called ETS2 binds to the super-enhancers and reprograms the expression of genes to promote the development of cancer. Yang, Schramek et al. also show that over-active ETS2 is a major driver of squamous cell carcinoma. Furthermore, ETS2 also increases the expression of genes that cause inflammation and promote the growth of cancers.

Yang, Schramek et al.’s findings reveal a new regulatory network that governs the expression of genes involved in cancer. Furthermore, the experiments show that high levels of ETS2 are linked with poor outcomes for patients with head and neck squamous cell carcinoma, which is one of the most life-threatening cancers world-wide. In the future, these findings might lead to the development of new therapies to treat these cancers.

DOI:http://dx.doi.org/10.7554/eLife.10870.002

Loss of corneal epithelial heparan sulfate leads to corneal degeneration and impaired wound healing

PURPOSE

Heparan sulfate (HS) is a highly modified glycosaminoglycan (GAG) bound to a core protein to form heparan sulfate proteoglycans (HSPGs) that are vital in many cellular processes ranging from development to adult physiology, as well as in disease, through interactions with various protein ligands. This study aimed to elucidate the role of HS in corneal epithelial homeostasis and wound healing.

METHODS

An inducible quadruple transgenic mouse model was generated to excise Ext1 and Ndst1, which encode the critical HS chain elongation enzyme and N-deacetylase/N-sulfotransferase, respectively, in keratin 14-positive cells upon doxycycline induction.

RESULTS

EXT(Δ/ΔCEpi) mice (deletion of Ext1 in corneal epithelium) induced at P20 presented progressive thinning of the corneal epithelium with a significant loss in the number of epithelial layers by P55. EXT(Δ/ΔCEpi) mice presented tight junction disruption, loss of cell-basement membrane adhesion complexes, and impaired wound healing. Interestingly, EXT(Δ/ΔCEpi) and NDST(Δ/ΔCEpi) mice presented an increase in cell proliferation, which was assayed by both Ki67 staining and 5-ethynyl-2'-deoxyuridine (EdU) incorporation. Moreover, EXT(Δ/ΔCEpi) mice presented compromised epithelial stratification 7 days after a debridement wound. The conditional knockout of HS from keratocytes using the keratocan promoter led to no corneal abnormalities or any disruption in wound healing.

CONCLUSIONS

Corneal epithelial cells require HS for maintaining corneal homeostasis, and the loss of epithelial HS leads to both impaired wound healing and impaired corneal stratification.

Integrin-linked kinase regulates the niche of quiescent epidermal stem cells

Stem cells reside in specialized niches that are critical for their function. Quiescent hair follicle stem cells (HFSCs) are confined within the bulge niche, but how the molecular composition of the niche regulates stem cell behaviour is poorly understood. Here we show that integrin-linked kinase (ILK) is a key regulator of the bulge extracellular matrix microenvironment, thereby governing the activation and maintenance of HFSCs. ILK mediates deposition of inverse laminin (LN)-332 and LN-511 gradients within the basement membrane (BM) wrapping the hair follicles. The precise BM composition tunes activities of Wnt and transforming growth factor-β pathways and subsequently regulates HFSC activation. Notably, reconstituting an optimal LN microenvironment restores the altered signalling in ILK-deficient cells. Aberrant stem cell activation in ILK-deficient epidermis leads to increased replicative stress, predisposing the tissue to carcinogenesis. Overall, our findings uncover a critical role for the BM niche in regulating stem cell activation and thereby skin homeostasis.

Esophageal Cancer: Insights From Mouse Models

Esophageal cancer is the eighth leading cause of cancer and the sixth most common cause of cancer-related death worldwide. Despite recent advances in the development of surgical techniques in combination with the use of radiotherapy and chemotherapy, the prognosis for esophageal cancer remains poor. The cellular and molecular mechanisms that drive the pathogenesis of esophageal cancer are still poorly understood. Hence, understanding these mechanisms is crucial to improving outcomes for patients with esophageal cancer. Mouse models constitute valuable tools for modeling human cancers and for the preclinical testing of therapeutic strategies in a manner not possible in human subjects. Mice are excellent models for studying human cancers because they are similar to humans at the physiological and molecular levels and because they have a shorter gestation time and life cycle. Moreover, a wide range of well-developed technologies for introducing genetic modifications into mice are currently available. In this review, we describe how different mouse models are used to study esophageal cancer.

Reactivation of multipotency by oncogenic PIK3CA induces breast tumour heterogeneity

Breast cancer is the most frequent cancer in women and consists of heterogeneous types of tumours that are classified into different histological and molecular subtypes. PIK3CA and P53 (also known as TP53) are the two most frequently mutated genes and are associated with different types of human breast cancers. The cellular origin and the mechanisms leading to PIK3CA-induced tumour heterogeneity remain unknown. Here we used a genetic approach in mice to define the cellular origin of Pik3ca-derived tumours and the impact of mutations in this gene on tumour heterogeneity. Surprisingly, oncogenic Pik3ca(H1047R) mutant expression at physiological levels in basal cells using keratin (K)5-CreER(T2) mice induced the formation of luminal oestrogen receptor (ER)-positive/progesterone receptor (PR)-positive tumours, while its expression in luminal cells using K8-CReER(T2) mice gave rise to luminal ER(+)PR(+) tumours or basal-like ER(-)PR(-) tumours. Concomitant deletion of p53 and expression of Pik3ca(H1047R) accelerated tumour development and induced more aggressive mammary tumours. Interestingly, expression of Pik3ca(H1047R) in unipotent basal cells gave rise to luminal-like cells, while its expression in unipotent luminal cells gave rise to basal-like cells before progressing into invasive tumours. Transcriptional profiling of cells that underwent cell fate transition upon Pik3ca(H1047R) expression in unipotent progenitors demonstrated a profound oncogene-induced reprogramming of these newly formed cells and identified gene signatures characteristic of the different cell fate switches that occur upon Pik3ca(H1047R) expression in basal and luminal cells, which correlated with the cell of origin, tumour type and different clinical outcomes. Altogether our study identifies the cellular origin of Pik3ca-induced tumours and reveals that oncogenic Pik3ca(H1047R) activates a multipotent genetic program in normally lineage-restricted populations at the early stage of tumour initiation, setting the stage for future intratumoural heterogeneity. These results have important implications for our understanding of the mechanisms controlling tumour heterogeneity and the development of new strategies to block PIK3CA breast cancer initiation.

Gene Signature of Human Oral Mucosa Fibroblasts: Comparison with Dermal Fibroblasts and Induced Pluripotent Stem Cells

Oral mucosa is a useful material for regeneration therapy with the advantages of its accessibility and versatility regardless of age and gender. However, little is known about the molecular characteristics of oral mucosa. Here we report the first comparative profiles of the gene signatures of human oral mucosa fibroblasts (hOFs), human dermal fibroblasts (hDFs), and hOF-derived induced pluripotent stem cells (hOF-iPSCs), linking these with biological roles by functional annotation and pathway analyses. As a common feature of fibroblasts, both hOFs and hDFs expressed glycolipid metabolism-related genes at higher levels compared with hOF-iPSCs. Distinct characteristics of hOFs compared with hDFs included a high expression of glycoprotein genes, involved in signaling, extracellular matrix, membrane, and receptor proteins, besides a low expression of HOX genes, the hDFs-markers. The results of the pathway analyses indicated that tissue-reconstructive, proliferative, and signaling pathways are active, whereas senescence-related genes in p53 pathway are inactive in hOFs. Furthermore, more than half of hOF-specific genes were similarly expressed to those of hOF-iPSC genes and might be controlled by WNT signaling. Our findings demonstrated that hOFs have unique cellular characteristics in specificity and plasticity. These data may provide useful insight into application of oral fibroblasts for direct reprograming.

Transcription Factor CTIP2 Maintains Hair Follicle Stem Cell Pool and Contributes to Altered Expression of LHX2 and NFATC1

Transcription factor CTIP2 (COUP-TF-interacting protein 2), also known as BCL11B, is expressed in hair follicles of embryonic and adult skin. Ctip2-null mice exhibit reduced hair follicle density during embryonic development. In contrast, conditional inactivation of Ctip2 in epidermis (Ctip2^ep−/− mice) leads to a shorter telogen and premature entry into anagen during the second phase of hair cycling without a detectable change in the number of hair follicles. Keratinocytes of the bulge stem cells niche of Ctip2^ep−/− mice proliferate more and undergo reduced apoptosis than the corresponding cells of wild-type mice. However, premature activation of follicular stem cells in mice lacking CTIP2 leads to the exhaustion of this stem cell compartment in comparison to Ctip2^L2/L2 mice, which retained quiescent follicle stem cells. CTIP2 modulates expression of genes encoding EGFR and NOTCH1 during formation of hair follicles, and those encoding NFATC1 and LHX2 during normal hair cycling in adult skin. The expression of most of these genes is disrupted in mice lacking CTIP2 and these alterations may underlie the phenotype of Ctip2-null and Ctip2^ep−/− mice. CTIP2 appears to serve as a transcriptional organizer that integrates input from multiple signaling cues during hair follicle morphogenesis and hair cycling.

Foxp1 Regulates the Proliferation of Hair Follicle Stem Cells in Response to Oxidative Stress during Hair Cycling

Hair follicle stem cells (HFSCs) in the bugle circularly generate outer root sheath (ORS) through linear proliferation within limited cycles during anagen phases. However, the mechanisms controlling the pace of HFSC proliferation remain unclear. Here we revealed that Foxp1, a transcriptional factor, was dynamically relocated from the nucleus to the cytoplasm of HFSCs in phase transitions from anagen to catagen, coupled with the rise of oxidative stress. Mass spectrum analyses revealed that the S468 phosphorylation of Foxp1 protein was responsive to oxidative stress and affected its nucleocytoplasmic translocation. Foxp1 deficiency in hair follicles led to compromised ROS accrual and increased HFSC proliferation. And more, NAC treatment profoundly elongated the anagen duration and HFSC proliferation in Foxp1-deficient background. Molecularly, Foxp1 augmented ROS levels through suppression of Trx1-mediated reductive function, thereafter imposing the cell cycle arrest by modulating the activity of p19/p53 pathway. Our findings identify a novel role for Foxp1 in controlling HFSC proliferation with cellular dynamic location in response to oxidative stress during hair cycling.

JmjC Domain-containing Protein 6 (Jmjd6) Derepresses the Transcriptional Repressor Transcription Factor 7-like 1 (Tcf7l1) and Is Required for Body Axis Patterning during Xenopus Embryogenesis

Tcf7l1 (also known as Tcf3) is a bimodal transcription factor that plays essential roles in embryogenesis and embryonic and adult stem cells. On one hand, Tcf7l1 works as transcriptional repressor via the recruitment of Groucho-related transcriptional corepressors to repress the transcription of Wnt target genes, and, on the other hand, it activates Wnt target genes when Wnt-activated β-catenin interacts with it. However, how its activity is modulated is not well understood. Here we demonstrate that a JmjC-domain containing protein, Jmjd6, interacts with Tcf7l and derepresses Tcf7l. We show that Jmjd6 binds to a region of Tcf7l1 that is also responsible for Groucho interaction, therefore making it possible that Jmjd6 binding displaces the Groucho transcriptional corepressor from Tcf7l1. Moreover, we show that Jmjd6 antagonizes the repression effect of Tcf7l1 on target gene transcription and is able to enhance β-catenin-induced gene activation and that, vice versa, inhibition of Jmjd6 activity compromises gene activation in both cells and Xenopus early embryos. We also show that jmjd6 is both maternally and zygotically transcribed during Xenopus embryogenesis. Loss of Jmjd6 function causes defects in anterioposterior body axis formation and down-regulation of genes that are involved in anterioposterior axis patterning. The results elucidate a novel mechanism underlying the regulation of Tcf7l1 activity and the regulation of embryonic body axis formation.

Transcriptomic profiling comparison of YAP over-expression and conditional knockout mouse tooth germs

To identify the downstream target genes of YAP, we used RNA-Seq technology to compare the transcriptomic profilings of Yap conditional knockout (Yap CKO) and YAP over-expression mouse tooth germs. Our results showed that some Hox, Wnt and Laminin family genes had concurrent changes with YAP transcripts, indicating that the expression of these genes may be regulated by YAP. Here, we provide the detailed experimental procedure for the transcriptomic profiling results (NCBI GEO accession number GSE65524). The associated study on the regulation of Hoxa1 and Hoxc13 genes by YAP was published in Molecular Cellular Biology in 2015 [Liu et al., 2015].

Embryonic stem cell-derived osteocytes are capable of responding to mechanical oscillatory hydrostatic pressure

Osteoblasts can be derived from embryonic stem cells (ESCs) by a 30 day differentiation process, whereupon cells spontaneously differentiate upon removal of LIF and respond to exogenously added 1,25α(OH)2 vitamin D3 with enhanced matrix mineralization. However, bone is a load-bearing tissue that has to perform under dynamic pressure changes during daily movement, a capacity that is executed by osteocytes. At present, it is unclear whether ESC-derived osteogenic cultures contain osteocytes and whether these are capable of responding to a relevant cyclic hydrostatic compression stimulus. Here, we show that ESC-osteoblastogenesis is followed by the generation of osteocytes and then mechanically load ESC-derived osteogenic cultures in a compression chamber using a cyclic loading protocol. Following mechanical loading of the cells, iNOS mRNA was upregulated 31-fold, which was consistent with a role for iNOS as an immediate early mechanoresponsive gene. Further analysis of matrix and bone-specific genes suggested a cellular response in favor of matrix remodeling. Immediate iNOS upregulation also correlated with a concomitant increase in Ctnnb1 and Tcf7l2 mRNAs along with increased nuclear TCF transcriptional activity, while the mRNA for the repressive Tcf7l1 was downregulated, providing a possible mechanistic explanation for the noted matrix remodeling. We conclude that ESC-derived osteocytes are capable of responding to relevant mechanical cues, at least such that mimic oscillatory compression stress, which not only provides new basic understanding, but also information that likely will be important for their use in cell-based regenerative therapies.

Study of Wnt2 secreted by A-549 cells in paracrine activation of β-catenin in co-cultured mesenchymal stem cells

The canonical Wnt signal pathway is a key regulator of self-renewal and cell fate determination in various types of stem cells. The total pool of β-catenin consists of two different forms: the signaling form of the protein transmits the Wnt signals from the cell membrane to the target genes, whereas the membrane β-catenin is involved in formation of cell-to-cell contact at cadherin junctions. Earlier we developed an in vitro model of epithelial differentiation of mesenchymal stem cells (MSCs) co-cultured with epithelial A-549 cells. The purpose of the present work was to study the role of Wnt2 secreted by the A-549 cells in paracrine induction of β-catenin in co-cultured MSCs. Using the somatic gene knockdown technique, we obtained A-549 cell cultures with down-regulated WNT2. The MSCs co-cultured with the control A-549 cells displayed an increase in the levels of total cellular and signaling β-catenin and transactivation of a reporter construction containing the Lef/Tcf protein family binding sites. In contrast, β-catenin was not induced in the MSCs co-cultured with the A-549 cells with down-regulated WNT2 expression, but the total protein level was increased. We suggest that Wnt2 secreted by A-549 cells induces in co-cultured MSCs the Wnt/β-catenin signaling pathway, whereas the associated increase in total β-catenin level should be due to another mechanism.

YAP regulates the expression of Hoxa1 and Hoxc13 in mouse and human oral and skin epithelial tissues

Yes-associated protein (YAP) is a Hippo signaling transcriptional coactivator that plays pivotal roles in stem cell proliferation, organ size control, and tumor development. The downstream targets of YAP have been shown to be highly context dependent. In this study, we used the embryonic mouse tooth germ as a tool to search for the downstream targets of YAP in ectoderm-derived tissues. Yap deficiency in the dental epithelium resulted in a small tooth germ with reduced epithelial cell proliferation. We compared the gene expression profiles of embryonic day 14.5 (E14.5) Yap conditional knockout and YAP transgenic mouse tooth germs using transcriptome sequencing (RNA-Seq) and further confirmed the differentially expressed genes using real-time PCR and in situ hybridization. We found that YAP regulates the expression of Hoxa1 and Hoxc13 in oral and dental epithelial tissues as well as in the epidermis of skin during embryonic and adult stages. Sphere formation assay suggested that Hoxa1 and Hoxc13 are functionally involved in YAP-regulated epithelial progenitor cell proliferation, and chromatin immunoprecipitation (ChIP) assay implies that YAP may regulate Hoxa1 and Hoxc13 expression through TEAD transcription factors. These results provide mechanistic insights into abnormal YAP activities in mice and humans.

mTOR signaling promotes stem cell activation via counterbalancing BMP-mediated suppression during hair regeneration

Hair follicles (HFs) undergo cycles of degeneration (catagen), rest (telogen), and regeneration (anagen) phases. Anagen begins when the hair follicle stem cells (HFSCs) obtain sufficient activation cues to overcome suppressive signals, mainly the BMP pathway, from their niche cells. Here, we unveil that mTOR complex 1 (mTORC1) signaling is activated in HFSCs, which coincides with the HFSC activation at the telogen-to-anagen transition. By using both an inducible conditional gene targeting strategy and a pharmacological inhibition method to ablate or inhibit mTOR signaling in adult skin epithelium before anagen initiation, we demonstrate that HFs that cannot respond to mTOR signaling display significantly delayed HFSC activation and extended telogen. Unexpectedly, BMP signaling activity is dramatically prolonged in mTOR signaling-deficient HFs. Through both gain- and loss-of-function studies in vitro, we show that mTORC1 signaling negatively affects BMP signaling, which serves as a main mechanism whereby mTORC1 signaling facilitates HFSC activation. Indeed, in vivo suppression of BMP by its antagonist Noggin rescues the HFSC activation defect in mTORC1-null skin. Our findings reveal a critical role for mTOR signaling in regulating stem cell activation through counterbalancing BMP-mediated repression during hair regeneration.

Analysis of histone H2BGFP retention in mouse submandibular gland reveals actively dividing stem cell populations

The purpose of this study was to use histone 2B-green fluorescent protein (H2BGFP) pulse-chase experiments to provide a broad view of population dynamics in salivary gland and to identify the quiescent stem cells that had previously been suggested to reside in the gland. Two transgenic mouse models in which inducible H2BGFP expression was regulated either by keratin (K)14 promoter or by a ubiquitous promoter were generated. The level of fluorescent label in the submandibular gland induced by a pulse of H2BGFP expression was monitored over a period of 18 weeks of chase. Efficient targeting of H2BGFP label to the relatively undifferentiated ductal cells by K14 promoter did not identify a quiescent population of stem cells. Ubiquitous targeting of all ductal cells identified label-retaining cells but these cells were mapped to the more differentiating ductal compartments. Furthermore, they did not display the major characteristics of quiescent stem cells including the undifferentiated phenotype, mobilization in response to injury, and the clonogenicity in culture. Quantitative assessment of H2BGFP loss in various ductal compartments and short-term lineage tracing of K14(+) ductal cells were consistent with the presence of actively dividing pools of stem/progenitor cells in the intercalated ducts and the basal layer of excretory ducts functioning independently during homeostasis.

TGFβ signaling inhibits goblet cell differentiation via SPDEF in conjunctival epithelium

The ocular surface epithelia, including the stratified but non-keratinized corneal, limbal and conjunctival epithelium, in concert with the epidermal keratinized eyelid epithelium, function together to maintain eye health and vision. Abnormalities in cellular proliferation or differentiation in any of these surface epithelia are central in the pathogenesis of many ocular surface disorders. Goblet cells are important secretory cell components of various epithelia, including the conjunctiva; however, mechanisms that regulate goblet cell differentiation in the conjunctiva are not well understood. Herein, we report that conditional deletion of transforming growth factor β receptor II (Tgfbr2) in keratin 14-positive stratified epithelia causes ocular surface epithelial hyperplasia and conjunctival goblet cell expansion that invaginates into the subconjunctival stroma in the mouse eye. We found that, in the absence of an external phenotype, the ocular surface epithelium develops properly, but young mice displayed conjunctival goblet cell expansion, demonstrating that TGFβ signaling is required for normal restriction of goblet cells within the conjunctiva. We observed increased expression of SAM-pointed domain containing ETS transcription factor (SPDEF) in stratified conjunctival epithelial cells in Tgfbr2 cKO mice, suggesting that TGFβ restricted goblet cell differentiation directly by repressing Spdef transcription. Gain of function of Spdef in keratin 14-positive epithelia resulted in the ectopic formation of goblet cells in the eyelid and peripheral cornea in adult mice. We found that Smad3 bound two distinct sites on the Spdef promoter and that treatment of keratin 14-positive cells with TGFβ inhibited SPDEF activation, thereby identifying a novel mechanistic role for TGFβ in regulating goblet cell differentiation.

Tanshinone IIA pretreatment renders free flaps against hypoxic injury through activating Wnt signaling and upregulating stem cell-related biomarkers

Partial or total flap necrosis after flap transplantation is sometimes clinically encountered in reconstructive surgery, often as a result of a period of hypoxia that exceeds the tolerance of the flap tissue. In this study, we determine whether tanshinone IIA (TSA) pretreatment can protect flap tissue against hypoxic injury and improve its viability. Primary epithelial cells isolated from the dorsal skin of mice were pretreated with TSA for two weeks. Cell counting kit-8 and Trypan Blue assays were carried out to examine the proliferation of TSA-pretreated cells after exposure to cobalt chloride. Then, Polymerase chain reaction and Western blot analysis were used to determine the expression of β-catenin, GSK-3β, SOX2, and OCT4 in TSA-treated cells. In vivo, after mice were pretreated with TSA for two weeks, a reproducible ischemic flap model was implemented, and the area of surviving tissue in the transplanted flaps was measured. Immunohistochemistry was also conducted to examine the related biomarkers mentioned above. Results show that epidermal cells, pretreated with TSA, showed enhanced resistance to hypoxia. Activation of the Wnt signaling pathway in TSA-pretreated cells was characterized by the upregulation of β-catenin and the downregulation of GSK-3β. The expression of SOX2 and OCT4 controlled by Wnt signaling were also found higher in TSA pretreated epithelial cells. In the reproducible ischaemic flap model, pretreatment with TSA enhanced resistance to hypoxia and increased the area of surviving tissue in transplanted flaps. The expression of Wnt signaling pathway components, stem-cell related biomarkers, and CD34, which are involved in the regeneration of blood vessels, was also upregulated in TSA-pretreated flap tissue. The results show that TSA pretreatment protects free flaps against hypoxic injury and increases the area of surviving tissue by activating Wnt signaling and upregulating stem cell-related biomarkers.

Smad1 and 5 but not Smad8 establish stem cell quiescence which is critical to transform the premature hair follicle during morphogenesis toward the postnatal state

Hair follicles (HFs) are regenerative miniorgans that offer a highly informative model system to study the regulatory mechanisms of hair follicle stem cells (hfSCs) homeostasis and differentiation. Bone morphogenetic protein (BMP) signaling is key in both of these processes, governing hfSCs quiescence in the bulge and differentiation of matrix progenitors. However, whether canonical or noncanonical pathways of BMP signaling are responsible for these processes remains unresolved. Here, we conditionally ablated two canonical effectors of BMP signaling, Smad1 and Smad5 during hair morphogenesis and postnatal cycling in mouse skin. Deletion of Smad1 and Smad5 (dKO) in the epidermis during morphogenesis resulted in neonatal lethality with lack of visible whiskers. Interestingly, distinct patterns of phospho-Smads (pSmads) activation were detected with pSmad8 restricted to epidermis and pSmad1 and pSmad5 exclusively activated in HFs. Engraftment of dKO skin revealed retarded hair morphogenesis and failure to differentiate into visible hair. The formation of the prebulge and bulge reservoir for quiescent hfSCs was precluded in dKO HFs which remained in prolonged anagen. Surprisingly, in postnatal telogen HFs, pSmad8 expression was no longer limited to epidermis and was also present in dKO bulge hfSCs and matrix progenitors. Although pSmad8 activity alone could not prevent dKO hfSCs precocious anagen activation, it sustained efficient postnatal differentiation and regeneration of visible hairs. Together, our data suggest a pivotal role for canonical BMP signaling demonstrating distinguished nonoverlapping function of pSmad8 with pSmad1 and pSmad5 in hfSCs regulation and hair morphogenesis but a redundant role in adult hair progenitors differentiation.