Targeted somatic mutagenesis in mouse epidermis

Induction of whole-body gene deletion via R26-regulated tamoxifen-inducible Cre recombinase activity

Germline deletion of certain genes causes embryonic lethality, therefore, understanding the effect of deletion of such genes on mammalian pathophysiology remains challenging. Tamoxifen (TAM)-inducible Cre recombinase is widely used for tissue-specific and temporal induction of gene deletion in mice. However, the tamoxifen treatment regimen for the generation of whole-body deletion of a gene is not yet fully standardized for the majority of organs/tissues. Accordingly, we employed GtROSA26 (R26) promoter-regulated Cre and a reporter gene expression strategy. GtROSA26 (R26) is an ubiquitous promoter and mice carrying the R26^Cre-ERT2 transgene express Cre-ERT2 in all the cells. Similarly, mice carrying the R26^mTOM-mEGFP transgene express mTOM (membrane-targeted tdTomato), in the absence of Cre or mEGFP (membrane-targeted enhanced green fluorescent protein), in the presence of Cre, in all the cells. The progeny carrying one allele of both transgenes were subjected to different TAM regimens, i.e., IP injections (4 injections; 1.35 mg/injection), diet (400 mg TAM-citrate/kg food), or diet (400 mg TAM-citrate/kg food) combined with either TAM-oral gavage (4 gavages; 1.35 mg/gavage) or TAM IP injections (4 injections; 1.35 mg/injection) for 2-weeks beginning at postnatal day (PND) 21 and the extent of Cre recombination in different tissues was determined at PND35. Tamoxifen administration resulted in a transient loss of body weight in all the treatment regimens with a relatively slower rate of weight gain in the TAM-diet plus TAM-oral gavage group compared to other groups. While the efficiency of Cre recombination, as determined by the expression of mEGFP protein, was variable among tissues, major tissues such as the liver, heart, lungs, spleen, and thymus-showed almost complete recombination. No recombination was evident in any of the tissues examined from the control mice. In general, the efficiency of Cre recombination was better with a combined regimen of TAM-diet with either TAM-injections or TAM-oral gavage compared to TAM-diet alone or TAM-injections alone. Our results demonstrate that a combination of TAM-diet with either TAM-injections or TAM-oral gavage can be employed for the efficient deletion of a gene in the whole body. Our findings will provide technical expertise to the researchers employing TAM-inducible Cre for the deletion of floxed genes in varied tissues.

Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study

OBJECTIVES

To determine the prevalence and natural history of sporadic inclusion body myositis (sIBM) and to test the hypothesis that patients with sIBM have higher cancer or mortality rates than the general population.

METHODS

We sought patients with sIBM defined by the 2011 European Neuromuscular Centre (ENMC) diagnostic criteria among Olmsted County, Minnesota, residents in 40-year time period.

RESULTS

We identified 20 patients (10 clinicopathologically defined, 9 clinically defined, and 1 probable) according to the ENMC criteria and 1 patient with all features of clinicopathologically defined sIBM except for symptom onset at <45 years of age. The prevalence of sIBM in 2010 was 18.20 per 100,000 people ≥50 years old. Ten patients developed cancers. The incidence of cancers in sIBM did not differ from that observed in the general population (odds ratio 1.89, 95% confidence interval [CI] 0.639-5.613, p = 0.24). Two-thirds of patients developed dysphagia, and half required a feeding tube. Nine patients required a wheelchair. The median time from symptom onset to wheelchair dependence was 10.5 (range 1-29) years. Overall life expectancy was shorter in the sIBM group compared to the general population (84.1 [95% CI 78-88.4] vs 87.5 [95% CI 85.2-89.5] years, p = 0.03). Thirteen patients died; 9 deaths were sIBM related (7 respiratory and 2 unspecified sIBM complications). Female sex (p = 0.03) and dysphagia (p = 0.05) were independent predictors of death.

CONCLUSION

Olmsted County has the highest prevalence of sIBM reported to date. Patients with sIBM have similar risk of cancer, but slightly shorter life expectancy compared to matched patients without sIBM.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that patients with sIBM have similar risks of cancers and slightly shorter life expectancy compared to controls.

Targeted deletion of Ruvbl1 results in severe defects of epidermal development and perinatal mortality

Epidermal development is a complex process of regulated cellular proliferation, differentiation, and tightly controlled cell death involving multiple cellular signaling networks. Here, we report a first description linking the AAA+ (ATPases associated with various cellular activities) superfamily protein Ruvbl1 to mammalian epidermal development. Keratinocyte-specific Ruvbl1 knockout mice (Ruvbl1^fl/flK14:Cre^tg) show a severe phenotype including dramatic structural epidermal defects resulting in the loss of the functional skin barrier and perinatal death. Thus, Ruvbl1 is a newly identified essential player for the development of differentiated epidermis in mice.

CENP-50 is required for papilloma development in the two-stage skin carcinogenesis model

CENP‐50/U is a component of the CENP‐O complex (CENP‐O/P/Q/R/U) and localizes to the centromere throughout the cell cycle. Aberrant expression of CENP‐50/U has been reported in many types of cancers. However, as Cenp‐50/U‐deficient mice die during early embryogenesis, its functions remain poorly understood in vivo. To investigate the role of Cenp‐50/U in skin carcinogenesis, we generated Cenp‐50/U conditional knockout (K14Cre^ER‐Cenp‐50/U^fl/fl) mice and subjected them to the 7,12‐dimethylbenz(a)anthracene (DMBA)/terephthalic acid (TPA) chemical carcinogenesis protocol. As a result, early‐stage papillomas decreased in Cenp‐50/U‐deficient mice. In contrast, Cenp‐50/U‐deficient mice demonstrated almost the same carcinoma incidence as control mice. Furthermore, mRNA expression analysis using DMBA/TPA‐induced papillomas and carcinomas revealed that Cenp‐50/U expression levels in papillomas were significantly higher than in carcinomas. These results suggest that Cenp‐50/U functions mainly in early papilloma development and it has little effect on malignant conversion.

Inducible knockout of ∆Np63 alters cell polarity and metabolism during pubertal mammary gland development

The ∆Np63 isoform of the p53-family transcription factor Trp63 is a key regulator of mammary epithelial stem cells that is involved in breast cancer development. To investigate the role of ∆Np63 at different stages of normal mammary gland development, we generated a ∆Np63-inducible conditional knockout (cKO) mouse model. We demonstrate that the deletion of ∆Np63 at puberty results in depletion of mammary stem cell-enriched basal cells, reduces expression of E-cadherin and β-catenin, and leads to a closed ductal lumen. RNA-sequencing analysis reveals reduced expression of oxidative phosphorylation (OXPHOS)-associated proteins and desmosomal polarity proteins. Functional assays show reduced numbers of mitochondria in the mammary epithelial cells of ΔNp63 cKO compared to wild-type, supporting the reduced OXPHOS phenotype. These findings identify a novel role for ∆Np63 in cellular metabolism and mammary epithelial cell polarity.

Epidermal development requires ninein for spindle orientation and cortical microtubule organization

In the epidermis, ninein affects spindle orientation of progenitor cells, as well as cortical microtubule organization, desmosome assembly, and lamellar body secretion in differentiating cells.

In mammalian skin, ninein localizes to the centrosomes of progenitor cells and relocates to the cell cortex upon differentiation of keratinocytes, where cortical arrays of microtubules are formed. To examine the function of ninein in skin development, we use epidermis-specific and constitutive ninein-knockout mice to demonstrate that ninein is necessary for maintaining regular protein levels of the differentiation markers filaggrin and involucrin, for the formation of desmosomes, for the secretion of lamellar bodies, and for the formation of the epidermal barrier. Ninein-deficient mice are viable but develop a thinner skin with partly impaired epidermal barrier. We propose two underlying mechanisms: first, ninein contributes to spindle orientation during the division of progenitor cells, whereas its absence leads to misoriented cell divisions, altering the pool of progenitor cells. Second, ninein is required for the cortical organization of microtubules in differentiating keratinocytes, and for the cortical re-localization of microtubule-organizing proteins, and may thus affect any mechanisms that depend on localized microtubule-dependent transport.

ERK5 is a critical mediator of inflammation-driven cancer

Chronic inflammation is a hallmark of many cancers, yet the pathogenic mechanisms that distinguish cancer-associated inflammation from benign persistent inflammation are still mainly unclear. Here, we report that the protein kinase ERK5 controls the expression of a specific subset of inflammatory mediators in the mouse epidermis, which triggers the recruitment of inflammatory cells needed to support skin carcinogenesis. Accordingly, inactivation of ERK5 in keratinocytes prevents inflammation-driven tumorigenesis in this model. In addition, we found that anti-ERK5 therapy cooperates synergistically with existing antimitotic regimens, enabling efficacy of subtherapeutic doses. Collectively, our findings identified ERK5 as a mediator of cancer-associated inflammation in the setting of epidermal carcinogenesis. Considering that ERK5 is expressed in almost all tumor types, our findings suggest that targeting tumor-associated inflammation via anti-ERK5 therapy may have broad implications for the treatment of human tumors.

Meis1 regulates epidermal stem cells and is required for skin tumorigenesis

Previous studies have shown that Meis1 plays an important role in blood development and vascular homeostasis, and can induce blood cancers, such as leukemia. However, its role in epithelia remains largely unknown. Here, we uncover two roles for Meis1 in the epidermis: as a critical regulator of epidermal homeostasis in normal tissues and as a proto-oncogenic factor in neoplastic tissues. In normal epidermis, we show that Meis1 is predominantly expressed in the bulge region of the hair follicles where multipotent adult stem cells reside, and that the number of these stem cells is reduced when Meis1 is deleted in the epidermal tissue of mice. Mice with epidermal deletion of Meis1 developed significantly fewer DMBA/TPA-induced benign and malignant tumors compared with wild-type mice, suggesting that Meis1 plays a role in both tumor development and malignant progression. This is consistent with the observation that Meis1 expression increases as tumors progress from benign papillomas to malignant carcinomas. Interestingly, we found that Meis1 localization was altered to neoplasia development. Instead of being localized to the stem cell region, Meis1 is localized to more differentiated cells in tumor tissues. These findings suggest that, during the transformation from normal to neoplastic tissues, a functional switch occurs in Meis1.

Transcriptional mechanisms link epithelial plasticity to adhesion and differentiation of epidermal progenitor cells

During epithelial tissue morphogenesis, developmental progenitor cells undergo dynamic adhesive and cytoskeletal remodeling to trigger proliferation and migration. Transcriptional mechanisms that restrict such a mild form of epithelial plasticity to maintain lineage-restricted differentiation in committed epithelial tissues are poorly understood. Here, we report that simultaneous ablation of transcriptional repressor-encoding Ovol1 and Ovol2 results in expansion and blocked terminal differentiation of embryonic epidermal progenitor cells. Conversely, mice overexpressing Ovol2 in their skin epithelia exhibit precocious differentiation accompanied by smaller progenitor cell compartments. We show that Ovol1/Ovol2-deficient epidermal cells fail to undertake α-catenin-driven actin cytoskeletal reorganization and adhesive maturation and exhibit changes that resemble epithelial-to-mesenchymal transition (EMT). Remarkably, these alterations and defective terminal differentiation are reversed upon depletion of EMT-promoting transcriptional factor Zeb1. Collectively, our findings reveal Ovol-Zeb1-α-catenin sequential repression and highlight Ovol1 and Ovol2 as gatekeepers of epithelial adhesion and differentiation by inhibiting progenitor-like traits and epithelial plasticity.

Meis1 is required for the maintenance of postnatal thymic epithelial cells

Most epithelial tissues retain stem/progenitor cells to maintain homeostasis of the adult tissues; however, the existence of a thymic epithelial cell (TEC) progenitor capable of maintaining homeostasis of the postnatal thymus remains unclear. Here, we show that a cell population expressing high levels of Meis1, a homeodomain transcription factor, is enriched in TECs with an immature cellular phenotype. These TECs selectively express genes involved in embryonic thymic organogenesis and epithelial stem cell maintenance, and also have the potential to proliferate and differentiate into mature TEC populations. Furthermore, postnatal inactivation of Meis1 in TECs caused disorganization of the thymic architecture, which ultimately leads to premature disappearance of the thymus. There was an age-associated reduction in the proportion of the TEC population expressing high levels of Meis1, which may also be related to thymic involution. These findings indicate that Meis1 is potentially involved in the maintenance of postnatal TECs with progenitor activity that is required for homeostasis of the postnatal thymus.

Mutant laboratory mice with abnormalities in hair follicle morphogenesis, cycling, and/or structure: an update

Human hair disorders comprise a number of different types of alopecia, atrichia, hypotrichosis, distinct hair shaft disorders as well as hirsutism and hypertrichosis. Their causes vary from genodermatoses (e.g. hypotrichoses) via immunological disorders (e.g. alopecia areata, autoimmune cicatrical alopecias) to hormone-dependent abnormalities (e.g. androgenetic alopecia). A large number of spontaneous mouse mutants and genetically engineered mice develop abnormalities in hair follicle morphogenesis, cycling, and/or hair shaft formation, whose analysis has proven invaluable to define the molecular regulation of hair growth, ranging from hair follicle development, and cycling to hair shaft formation and stem cell biology. Also, the accumulating reports on hair phenotypes of mouse strains provide important pointers to better understand the molecular mechanisms underlying human hair growth disorders. Since numerous new mouse mutants with a hair phenotype have been reported since the publication of our earlier review on this matter a decade ago, we present here an updated, tabulated mini-review. The updated annotated tables list a wide selection of mouse mutants with hair growth abnormalities, classified into four categories: Mutations that affect hair follicle (1) morphogenesis, (2) cycling, (3) structure, and (4) mutations that induce extrafollicular events (for example immune system defects) resulting in secondary hair growth abnormalities. This synthesis is intended to provide a useful source of reference when studying the molecular controls of hair follicle growth and differentiation, and whenever the hair phenotypes of a newly generated mouse mutant need to be compared with existing ones.

Cardiac-specific inducible and conditional gene targeting in mice

Mouse genetic engineering has revolutionized our understanding of the molecular and genetic basis of heart development and disease. This technology involves conditional tissue-specific and temporal transgenic and gene targeting approaches, as well as introduction of polymorphisms into the mouse genome. These approaches are increasingly used to elucidate the genetic pathways underlying tissue homeostasis, physiology, and pathophysiology of adult heart. They have also led to the development of clinically relevant models of human cardiac diseases. Here, we review the technologies and their limitations in general and the cardiovascular research community in particular.

Genetic mouse models for skin research: strategies and resources

A number of features contributed to establishing the mouse as the favorite model organism for skin research: the genetic and pathophysiological similarities to humans, the small size and relatively short reproductive period, meaning low maintenance costs, and the availability of sophisticated tools for manipulating the genome, gametes, and embryos. While initial studies depended on strains displaying skin abnormalities due to spontaneous genetic mutations, the availability of the transgenic and knockout technologies and their astonishing perfection during the last decades allowed the development of mouse lines permitting any imaginable genetic modification including gene inactivation, substitution, modification, or overexpression. While these technologies have already contributed to the functional analysis of several genes and processes related to skin research, continued progress requires understanding, awareness, and access to these mouse resources. This review will identify the strategies currently employed for the genetic manipulation of mice in skin research, and outline current resources and their limitations.

Long-term observational study of sporadic inclusion body myositis

We describe a long-term observational study of a large cohort of patients with sporadic inclusion body myositis and propose a sporadic inclusion body myositis weakness composite index that is easy to perform during a clinic. Data collection from two groups of patients (Paris and Oxford) was completed either during a clinic visit (52%), or by extraction from previous medical records (48%). One hundred and thirty-six patients [57% males, 61 (interquartile range 55-69) years at onset] were included. At the last visit all patients had muscle weakness (proximal British Medical Research Council scale <3/5 in 48%, distal British Medical Research Council scale <3/5 in 40%, swallowing problems in 46%). During their follow-up, 75% of patients had significant walking difficulties and 37% used a wheelchair (after a median duration from onset of 14 years). The sporadic inclusion body myositis weakness composite index, which correlated with grip strength (correlation coefficient: 0.47; P < 0.001) and Rivermead Mobility Index (correlation coefficient: 0.85; P < 0.001), decreased significantly with disease duration (correlation coefficient: -0.47; P < 0.001). The risk of death was only influenced by older age at onset of first symptoms. Seventy-one (52%) patients received immunosuppressive treatments [prednisone in 91.5%, associated (in 64.8%) with other immunomodulatory drugs (intravenous immunoglobulins, methotrexate or azathioprine) for a median duration of 40.8 months]. At the last assessment, patients who had been treated were more severely affected on disability scales (Walton P = 0.007, Rivermead Mobility Index P = 0.004) and on the sporadic inclusion body myositis weakness composite index (P = 0.04). The first stage of disease progression towards handicap for walking was more rapid among patients receiving immunosuppressive treatments (hazard ratio = 2.0, P = 0.002). This study confirms that sporadic inclusion body myositis is slowly progressive but not lethal and that immunosuppressive treatments do not ameliorate its natural course, thus confirming findings from smaller studies. Furthermore, our findings suggest that immunosuppressant drug therapy could have modestly exacerbated progression of disability. The sporadic inclusion body myositis weakness composite index might be a valuable outcome measure for future clinical trials, but requires further assessment and validation.

Genetic methods to identify and manipulate newly born neurons in the adult brain

Although mammalian neurogenesis is mostly completed by the perinatal period, new neurons are continuously generated in the subventricular zone of the lateral ventricle and the subgranular zone of the hippocampal dentate gyrus. Since the discovery of adult neurogenesis, many extensive studies have been performed on various aspects of adult neurogenesis, including proliferation and fate-specification of adult neural stem cells, and the migration, maturation and synaptic integration of newly born neurons. Furthermore, recent research has shed light on the intensive contribution of adult neurogenesis to olfactory-related and hippocampus-mediated brain functions. The field of adult neurogenesis progressed tremendously thanks to technical advances that facilitate the identification and selective manipulation of newly born neurons among billions of pre-existing neurons in the adult central nervous system. In this review, we introduce recent advances in the methodologies for visualizing newly generated neurons and manipulating neurogenesis in the adult brain. Particularly, the application of site-specific recombinases and Tet inducible system in combination with transgenic or gene targeting strategy is discussed in further detail.

Generation of Spatio-Temporally Controlled Targeted Somatic Mutations in the Mouse

The generation of ligand-activated site-specific Cre recombinases has led to the development of cell type-specific temporally controlled targeted somatic mutagenesis in the mouse. We illustrate this technique using K14-Cre-ER(T2) transgenic mice that express the tamoxifen (tam)-activatable Cre-ER(T2) recombinase in epidermal basal keratinocytes to induce mutations in epidermal keratinocytes of adult mice. Our highly reproducible technique, based on induction of Cre-ER(T2) recombinase activity by tamoxifen administration at low doses (once daily 100-µg intraperitoneal injection for 5 days), has allowed the generation of site-directed somatic mutations of numerous genes in mouse epidermal keratinocytes, and several mouse models of human diseases. The present step-by-step protocol describes how to introduce temporally controlled targeted mutations in epidermal keratinocytes of adult mice. Curr. Protoc. Mouse Biol. 1:55-70. © 2011 by John Wiley & Sons, Inc.

The ATM-Chk2 and ATR-Chk1 pathways in DNA damage signaling and cancer

DNA damage is a key factor both in the evolution and treatment of cancer. Genomic instability is a common feature of cancer cells, fuelling accumulation of oncogenic mutations, while radiation and diverse genotoxic agents remain important, if imperfect, therapeutic modalities. Cellular responses to DNA damage are coordinated primarily by two distinct kinase signaling cascades, the ATM-Chk2 and ATR-Chk1 pathways, which are activated by DNA double-strand breaks (DSBs) and single-stranded DNA respectively. Historically, these pathways were thought to act in parallel with overlapping functions; however, more recently it has become apparent that their relationship is more complex. In response to DSBs, ATM is required both for ATR-Chk1 activation and to initiate DNA repair via homologous recombination (HRR) by promoting formation of single-stranded DNA at sites of damage through nucleolytic resection. Interestingly, cells and organisms survive with mutations in ATM or other components required for HRR, such as BRCA1 and BRCA2, but at the cost of genomic instability and cancer predisposition. By contrast, the ATR-Chk1 pathway is the principal direct effector of the DNA damage and replication checkpoints and, as such, is essential for the survival of many, although not all, cell types. Remarkably, deficiency for HRR in BRCA1- and BRCA2-deficient tumors confers sensitivity to cisplatin and inhibitors of poly(ADP-ribose) polymerase (PARP), an enzyme required for repair of endogenous DNA damage. In addition, suppressing DNA damage and replication checkpoint responses by inhibiting Chk1 can enhance tumor cell killing by diverse genotoxic agents. Here, we review current understanding of the organization and functions of the ATM-Chk2 and ATR-Chk1 pathways and the prospects for targeting DNA damage signaling processes for therapeutic purposes.

Basal cell carcinomas arise from hair follicle stem cells in Ptch1(+/-) mice

Basal cell carcinomas (BCCs) are hedgehog-driven tumors that resemble follicular and interfollicular epidermal basal keratinocytes and hence long have been thought to arise from these cells. However, the actual cell of origin is unknown. Using cell fate tracking of X-ray induced BCCs in Ptch1(+/-) mice, we found their essentially exclusive origin to be keratin 15-expressing stem cells of the follicular bulge. However, conditional loss of p53 not only enhanced BCC carcinogenesis from the bulge but also produced BCCs from the interfollicular epidermis, at least in part by enhancing Smo expression. This latter finding is consistent with the lack of visible tumors on ears and tail, sites lacking Smo expression, in Ptch1(+/-) mice.

Generating conditional knockout mice

Gene targeting in ES cells is extensively used to generate designed mouse mutants and to study gene function in vivo. Knockout mice that harbor a null allele in their germline provide appropriate genetic models of inherited diseases and often exhibit embryonic or early postnatal lethality. To study gene function in adult mice and in selected cell types, a refined strategy for conditional gene inactivation has been developed that relies on the DNA recombinase Cre and its recognition (loxP) sites. For conditional mutagenesis, a target gene is modified by the insertion of two loxP sites that enable to excise the flanked (floxed) gene segment through Cre-mediated recombination. Conditional mutant mice are obtained by crossing the floxed strain with a Cre transgenic line such that the target gene becomes inactivated in vivo within the expression domain of Cre. A large collection of Cre transgenic lines has been generated over time and can be used in a combinatorial manner to achieve gene inactivation in many different cell types. A growing number of CreER(T2) transgenic mice further allows for inducible inactivation of floxed alleles in adult mice upon administration of tamoxifen. This chapter covers the design and construction of loxP flanked alleles and refers to the vectors, ES cells, and mice generated by the European conditional mouse mutagenesis (EUCOMM) project. We further describe the design and use of Cre and CreER(T2) transgenic mice and a convenient breeding strategy to raise conditional mutants and controls for phenotype analysis.

Loss of the p53/p63 regulated desmosomal protein Perp promotes tumorigenesis

Dysregulated cell–cell adhesion plays a critical role in epithelial cancer development. Studies of human and mouse cancers have indicated that loss of adhesion complexes known as adherens junctions contributes to tumor progression and metastasis. In contrast, little is known regarding the role of the related cell–cell adhesion junction, the desmosome, during cancer development. Studies analyzing expression of desmosome components during human cancer progression have yielded conflicting results, and therefore genetic studies using knockout mice to examine the functional consequence of desmosome inactivation for tumorigenesis are essential for elucidating the role of desmosomes in cancer development. Here, we investigate the consequences of desmosome loss for carcinogenesis by analyzing conditional knockout mice lacking Perp, a p53/p63 regulated gene that encodes an important component of desmosomes. Analysis of Perp-deficient mice in a UVB-induced squamous cell skin carcinoma model reveals that Perp ablation promotes both tumor initiation and progression. Tumor development is associated with inactivation of both of Perp's known functions, in apoptosis and cell–cell adhesion. Interestingly, Perp-deficient tumors exhibit widespread downregulation of desmosomal constituents while adherens junctions remain intact, suggesting that desmosome loss is a specific event important for tumorigenesis rather than a reflection of a general change in differentiation status. Similarly, human squamous cell carcinomas display loss of PERP expression with retention of adherens junctions components, indicating that this is a relevant stage of human cancer development. Using gene expression profiling, we show further that Perp loss induces a set of inflammation-related genes that could stimulate tumorigenesis. Together, these studies suggest that Perp-deficiency promotes cancer by enhancing cell survival, desmosome loss, and inflammation, and they highlight a fundamental role for Perp and desmosomes in tumor suppression. An understanding of the factors affecting cancer progression is important for ultimately improving the diagnosis, prognostication, and treatment of cancer.

Changes in tissue architecture, such as loss of adhesion between cells, have been shown to facilitate cancer development, especially metastasis where cells can detach from a tumor and spread throughout the body. While various studies have demonstrated that inactivation of an adhesion complex known as the adherens junction promotes cancer development and metastasis, little is known about the role of the desmosome—a related cell–cell adhesion complex—in tumorigenesis. Here we examine the consequence of desmosome-deficiency for tumor development by studying mice lacking a key component of desmosomes in the skin, a protein known as Perp. Using a mouse model for human skin cancer, in which ultraviolet light promotes skin cancer development, we demonstrate that Perp-deficiency indeed leads to accelerated skin tumorigenesis. We similarly observe that PERP is lost during human skin cancer development, suggesting that PERP is also important as a tumor suppressor in humans. These findings demonstrate that desmosome-deficiency achieved by Perp inactivation can promote cancer and suggest the potential utility of monitoring PERP status for staging, prognostication, or treatment of human cancers.

The mitogen-activated protein kinase kinase 4 has a pro-oncogenic role in skin cancer

The mitogen-activated protein kinase (MAPK) kinase 4 (MKK4) is a nonredundant component of stress-activated MAPK signaling modules. Its function in tumorigenesis remains highly controversial with some studies indicating that MKK4 is a tumor suppressor, whereas others have reported a pro-oncogenic role. To clarify the role of MKK4 in cancer, we have created a novel mouse model to test the effect of the specific loss of MKK4 in the epidermis on the formation of papillomas caused by activated ras mutation. We have discovered that skin-specific MKK4-deficient mice are resistant to carcinogen-induced tumorigenesis. One mechanism by which MKK4 promotes cell proliferation and the formation of tumors is by increasing epidermal growth factor receptor expression through the c-Jun NH(2)-terminal protein kinase/c-Jun signaling pathway. Together, our results provide the first genetic demonstration that MKK4 is essential to mediate the oncogenic effect of Ras in vivo, thereby validating MKK4 as a potential drug target for cancer therapy.

Epithelial-specific requirement of FGFR2 signaling during tooth and palate development

Reciprocal interactions between epithelium and mesenchyme are crucial for embryonic development. Fibroblast growth factors (FGFs) are a growth factor family that play an important role in epithelial-mesenchymal tissue interaction. We have generated epithelial-specific conditional knockout mice targeting Fibroblast growth factor receptor 2 (Fgfr2) to investigate the function of FGF signaling during craniofacial development. K14-Cre;Fgfr2(fl/fl) mice have skin defects, retarded tooth formation, and cleft palate. During the formation of the tooth primordium and palatal processes, cell proliferation in the epithelial cells of K14-Cre;Fgfr2(fl/fl) mice is reduced. Thus, FGF signaling via FGFR2 in the epithelium is crucial for cell proliferation activity during tooth and palate development.

Transgenic mice exhibiting inducible and spontaneous Cre activities driven by a bovine keratin 5 promoter that can be used for the conditional analysis of basal epithelial cells in multiple organs

Background

Cre/loxP-mediated genetic modification is the most widely used conditional genetic approach used in the mouse. Engineered Cre and the mutated ligand-binding domain of estrogen receptor fusion recombinase (CreER^T) allow temporal control of Cre activity.

Results

In this study, we have generated two distinct transgenic mouse lines expressing CreER^T, which show 4-hydroxytamoxifen (4-OHT)-inducible and spontaneous (4-OHT-independent) Cre activities, referred to Tg(BK5-CreER^T)I and Tg(BK5-CreER^T)S, respectively. The transgenic construct is driven by the bovine Keratin 5 promoter, which is active in the basal epithelial lineage of stratified and pseudo-stratified epithelium across multiple organs. Despite the difference in 4-OHT dependency, the Tg(BK5-CreER^T)I and Tg(BK5-CreER^T)S mouse lines shared similar Cre-mediated recombination among various organs, except for unique mammary epithelial Cre activity in Tg(BK5-CreER^T)S females.

Conclusion

These two new transgenic mouse lines for the analysis of basal epithelial function and for the genetic modification have been created allowing the identification of these cell lineages and analysis of their differentiation during embryogenesis, during perinatal development and in adult mice.

Dual role of COUP-TF-interacting protein 2 in epidermal homeostasis and permeability barrier formation

COUP-TF-interacting protein 2 (CTIP2; also known as Bcl11b) is a transcription factor that plays key roles in the development of the central nervous and immune systems. CTIP2 is also highly expressed in the developing epidermis, and at lower levels in the dermis and in adult skin. Analyses of mice harboring a germline deletion of CTIP2 revealed that the protein plays critical roles in skin during development, particularly in keratinocyte proliferation and late differentiation events, as well as in the development of the epidermal permeability barrier. At the core of all of these actions is a relatively large network of genes, described herein, that is regulated directly or indirectly by CTIP2. The analysis of conditionally null mice, in which expression of CTIP2 was ablated specifically in epidermal keratinocytes, suggests that CTIP2 functions in both cell and non-cell autonomous contexts to exert regulatory influence over multiple phases of skin development, including barrier establishment. Considered together, our results suggest that CTIP2 functions as a top-level regulator of skin morphogenesis.

LKB1 deficiency sensitizes mice to carcinogen-induced tumorigenesis

Lkb1 is a central regulator of cell polarity and energy metabolism through its capacity to activate the AMP-activated protein kinase (AMPK)-related family of protein kinases. Germ line-inactivating mutation of Lkb1 leads to Peutz-Jeghers syndrome, which is characterized by benign hamartomas and a susceptibility to malignant epithelial tumors. Mutations in Lkb1 are also found in sporadic carcinomas, most frequently in lung cancers associated with tobacco carcinogen exposure. The basis for Lkb1-dependent tumor suppression is not defined. Here, we uncover a marked sensitivity of Lkb1 mutant mice to the chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA). Lkb1(+/-) mice are highly prone to DMBA-induced squamous cell carcinoma (SCC) of the skin and lung. Confirming a cell autonomous tumor suppressor role of Lkb1, mice with epidermal-specific Lkb1 deletion are also susceptible to DMBA-induced SCC and develop spontaneous SCC with long latency. Restoration of wild-type Lkb1 causes senescence in tumor-derived cell lines, a process that can be partially bypassed by inactivation of the Rb pathway, but not by inactivation of p53 or AMPK. Our data indicate that Lkb1 is a potent suppressor of carcinogen-induced skin and lung cancers and that downstream targets beyond the AMPK-mTOR pathway are likely mediators of Lkb1-dependent tumor suppression.

Corneal Epithelial Cell Fate Is Maintained during Repair by Notch1 Signaling via the Regulation of Vitamin A Metabolism

Integrity and preservation of a transparent cornea are essential for good vision. The corneal epithelium is stratified and nonkeratinized and is maintained and repaired by corneal stem cells. Here we demonstrate that Notch1 signaling is essential for cell fate maintenance of corneal epithelium during repair. Inducible ablation of Notch1 in the cornea combined with mechanical wounding show that Notch1-deficient corneal progenitor cells differentiate into a hyperplastic, keratinized, skin-like epithelium. This cell fate switch leads to corneal blindness and involves cell nonautonomous processes, characterized by secretion of fibroblast growth factor-2 (FGF-2) through Notch1(-/-) epithelium followed by vascularization and remodeling of the underlying stroma. Vitamin A deficiency is known to induce a similar corneal defect in humans (severe xerophthalmia). Accordingly, we found that Notch1 signaling is linked to vitamin A metabolism by regulating the expression of cellular retinol binding protein 1 (CRBP1), required to generate a pool of intracellular retinol.

Macrophages and neutrophils are the targets for immune suppression by glucocorticoids in contact allergy

Glucocorticoids (GCs) are widely used in the treatment of allergic skin conditions despite having numerous side effects. Here we use Cre/loxP-engineered tissue- and cell-specific and function-selective GC receptor (GR) mutant mice to identify responsive cell types and molecular mechanisms underlying the antiinflammatory activity of GCs in contact hypersensitivity (CHS). CHS was repressed by GCs only at the challenge phase, i.e., during reexposure to the hapten. Inactivation of the GR gene in keratinocytes or T cells of mutant mice did not attenuate the effects of GCs, but its ablation in macrophages and neutrophils abolished downregulation of the inflammatory response. Moreover, mice expressing a DNA binding-defective GR were also resistant to GC treatment. The persistent infiltration of macrophages and neutrophils in these mice is explained by an impaired repression of inflammatory cytokines and chemokines such as IL-1beta, monocyte chemoattractant protein-1, macrophage inflammatory protein-2, and IFN-gamma-inducible protein 10. In contrast TNF-alpha repression remained intact. Consequently, injection of recombinant proteins of these cytokines and chemokines partially reversed suppression of CHS by GCs. These studies provide evidence that in contact allergy, therapeutic action of corticosteroids is in macrophages and neutrophils and that dimerization GR is required.

Analysis of mouse development with conditional mutagenesis

Explorations into the molecular embryology of the mouse have played a vital role in our understanding of the basic mechanisms of gene regulation that govern development and disease. In the last 15 years, these mechanisms have been analyzed with vastly greater precision and clarity with the advent of systems that allow the conditional control of gene expression. Typically, this control is achieved by silencing or activating the gene of interest with site-specific DNA recombination or transcriptional transactivation. In this review, I discuss the application of these technologies to mouse development, focusing on recent innovations and experimental designs that specifically aid the study of the mouse embryo.

Failure to prolyl hydroxylate hypoxia-inducible factor alpha phenocopies VHL inactivation in vivo

Many functions have been assigned to the von Hippel-Lindau tumor suppressor gene product (pVHL), including targeting the alpha subunits of the heterodimeric transcription factor HIF (hypoxia-inducible factor) for destruction. The binding of pVHL to HIFalpha requires that HIFalpha be hydroxylated on one of two prolyl residues. We introduced HIF1alpha and HIF2alpha variants that cannot be hydroxylated on these sites into the ubiquitously expressed ROSA26 locus along with a Lox-stop-Lox cassette that renders their expression Cre-dependent. Expression of the HIF2alpha variant in the skin and liver induced changes that were highly similar to those seen when pVHL is lost in these organs. Dual expression of the HIF1alpha and HIF2alpha variants in liver, however, more closely phenocopied the changes seen after pVHL inactivation than did the HIF2alpha variant alone. Moreover, gene expression profiling confirmed that the genes regulated by HIF1alpha and HIF2alpha in the liver are overlapping but non-identical. Therefore, the pathological changes caused by pVHL inactivation in skin and liver are due largely to dysregulation of HIF target genes.

Cell autonomous requirement for Tgfbr2 in the disappearance of medial edge epithelium during palatal fusion

Palatal fusion is a complex, multi-step developmental process; the consequence of failure in this process is cleft palate, one of the most common birth defects in humans. Previous studies have shown that regression of the medial edge epithelium (MEE) upon palatal fusion is required for this process, and TGF-beta signaling plays an important role in regulating palatal fusion. However, the fate of the MEE and the mechanisms underlying its disappearance are still unclear. By using the Cre/lox system, we are able to label the MEE genetically and to ablate Tgfbr2 specifically in the palatal epithelial cells. Our results indicate that epithelial-mesenchymal transformation does not occur in the regression of MEE cells. Ablation of Tgfbr2 in the palatal epithelial cells causes soft palate cleft, submucosal cleft and failure of the primary palate to fuse with the secondary palate. Whereas wild-type MEE cells disappear, the mutant MEE cells continue to proliferate and form cysts and epithelial bridges in the midline of the palate. Our study provides for the first time an animal model for soft palate cleft and submucous cleft. At the molecular level, Tgfb3 and Irf6 have similar expression patterns in the MEE. Mutations in IRF6 disrupt orofacial development and cause cleft palate in humans. We show here that Irf6 expression is downregulated in the MEE of the Tgfbr2 mutant. As a recent study shows that heterozygous mutations in TGFBR1 or TGFBR2 cause multiple human congenital malformations, including soft palate cleft, we propose that TGF-beta mediated Irf6 expression plays an important, cell-autonomous role in regulating the fate of MEE cells during palatogenesis in both mice and humans.

Localized inflammatory skin disease following inducible ablation of I kappa B kinase 2 in murine epidermis

Skin inflammation is a complex process that involves interactions between various cell types residing in different skin compartments. Using mice with conditionally targeted I kappa B kinase 2 (IKK2) alleles, we have previously shown that epidermal keratinocytes can play a dominant role in the initiation of an inflammatory reaction. In order to investigate long-term consequences of IKK2 deletion in adult skin, we have generated mice with floxed IKK2 alleles in which expression of a Tamoxifen-inducible Cre recombinase construct is targeted to epidermal keratinocytes (K14-Cre-ER(T2)IKK2(fl/fl) mice). K14-Cre-ER(T2)IKK2(fl/fl) mice are born normally and do not show signs of a skin disease until the age of 6 months. Deletion of IKK2 can be observed after Tamoxifen application to the back skin or spontaneously, without Tamoxifen application, in mice older than 6 months. This deletion is accompanied by dramatic, localized skin changes that are characterized by invasion of inflammatory cells, hair follicle disruption, and pseudoepitheliomatous hyperplasia of the epidermis, but not by tumor formation. The hyperplastic epithelium shows increased phosphorylation of signal transducer and activator of transcription 3 and extracellular signal-regulated protein kinase 1/2, typical features of psoriatic epidermis. Our results identify a primary role for IKK2 in the development of skin inflammation and confirm its requirement for the maintenance of skin homeostasis.

Notch1 is essential for postnatal hair follicle development and homeostasis

Notch genes encode evolutionarily conserved large, single transmembrane receptors, which regulate many cell fate decisions and differentiation processes during fetal and postnatal life. Multiple Notch receptors and ligands are expressed in both developing and adult epidermis and hair follicles. Proliferation and differentiation of these two ectodermal-derived structures have been proposed to be controlled in part by the Notch pathway. Whether Notch signaling is involved in postnatal hair homeostasis is currently unknown. Here, we investigate and compare the role of the Notch1 receptor during embryonic hair follicle development and postnatal hair homeostasis using Cre-loxP based tissue specific and inducible loss-of-function approaches. During embryonic development, tissue-specific ablation of Notch1 does not perturb formation and patterning of hair follicle placodes. However, Notch1 deficient hair follicles invaginate prematurely into the dermis. Embryonic as well as postnatal inactivation of Notch1 shortly after birth or in adult mice results in almost complete hair loss followed by cyst formation. The first hair cycle of Notch1 deficient mice is characterized by shortened anagen and a premature entry into catagen. These data show that Notch1 is essential for late stages of hair follicle development during embryogenesis as well as for post-natal hair follicle development and hair homeostasis.

Temporally controlled targeted somatic mutagenesis in embryonic surface ectoderm and fetal epidermal keratinocytes unveils two distinct developmental functions of BRG1 in limb morphogenesis and skin barrier formation

Animal SWI2/SNF2 protein complexes containing either the brahma (BRM) or brahma-related gene 1 (BRG1) ATPase are involved in nucleosome remodelling and may control the accessibility of sequence-specific transcription factors to DNA. In vitro studies have indicated that BRM and BRG1 could regulate the expression of distinct sets of genes. However, as mice lacking BRM are viable and fertile, BRG1 might efficiently compensate for BRM loss. By contrast, as Brg1-null fibroblasts are viable but Brg1-null embryos die during the peri-implantation stage, BRG1 might exert cell-specific functions. To further investigate the in vivo role of BRG1, we selectively ablated Brg1 in keratinocytes of the forming mouse epidermis. We show that BRG1 is selectively required for epithelial-mesenchymal interactions in limb patterning, and during keratinocyte terminal differentiation, in which BRM can partially substitute for BRG1. By contrast, neither BRM nor BRG1 are essential for the proliferation and early differentiation of keratinocytes, which may require other ATP-dependent nucleosome-remodelling complexes. Finally, we demonstrate that cell-specific targeted somatic mutations can be created at various times during the development of mouse embryos cell-specifically expressing the tamoxifen-activatable Cre-ER(T2) recombinase.

Peroxisome proliferator-activated receptor-beta as a target for wound healing drugs

Healing of cutaneous wounds, which is crucial for survival after an injury, proceeds via a well-tuned pattern of events including inflammation, re-epithelialisation, and matrix and tissue remodelling. These events are regulated spatio-temporally by a variety of growth factors and cytokines. The inflammation that immediately follows injury increases the expression of peroxisome proliferator-activated receptor (PPAR)-beta in the wound edge keratinocytes and triggers the production of endogenous PPARbeta ligands that activate the newly produced receptor. This elevated PPARbeta activity results in increased resistance of the keratinocytes to the apoptotic signals released during wounding, allowing faster re-epithelialisation. The authors speculate that, in parallel, ligand activation of PPARbeta in infiltrated macrophages attenuates the inflammatory response, which also promotes repair. Thus, current understanding of the roles of PPARbeta in different cell types implicated in tissue repair has revealed an intriguing intercellular cross-talk that coordinates, spatially and temporally, inflammation, keratinocyte survival, proliferation and migration, which are all essential for efficient wound repair. These novel insights into the orchestrating roles of PPARbeta during wound healing may be helpful in the development of drugs for acute and chronic wound disorders.

TAF10 is required for the establishment of skin barrier function in foetal, but not in adult mouse epidermis

TFIID, composed of the TATA box binding protein (TBP) and 13 TBP-associated factors (TAFs), plays a role in nucleating the assembly of the RNA polymerase II preinitiation complexes on protein coding genes. TAF10 (formerly TAF(II)30) is shared between TFIID and other transcription regulatory complexes (i.e. SAGA, TFTC, STAGA and PCAF/GCN5). TAF10 is an essential transcription factor during very early stages of mouse embryo development. To study the in vivo function of TAF10 in cellular differentiation and proliferation at later stages, the role of TAF10 was analysed in keratinocytes during skin development and adult epidermal homeostasis. We demonstrate that ablation of TAF10 in keratinocytes of the forming epidermis affects the expression of some, but not all genes, impairs keratinocyte terminal differentiation and alters skin permeability barrier functions. In contrast, loss of TAF10 in keratinocytes of adult epidermis did not (i) modify the expression of tested genes, (ii) affect epidermal homeostasis and (iii) impair acute response to UV irradiation or skin regeneration after wounding. Thus, this study demonstrates for the first time a differential in vivo requirement for a mammalian TAF for the regulation of gene expression depending on the cellular environment and developmental stage of the cell.

Keratin 14 Cre transgenic mice authenticate keratin 14 as an oocyte-expressed protein

Three mouse lines expressing Cre recombinase under the control of the human K14 promoter induced specific deletion of loxP flanked target sequences in the epidermis, in tongue, and thymic epithelium of the offspring where the Cre allele was inherited from the father. Where the mother carried the Cre allele, loxP flanked sequences were completely deleted in all tissues of the offspring, even in littermates that did not inherit the Cre allele. This maternally inherited phenotype indicates that the human K14 promoter is transcriptionally active in murine oocytes and that the enzyme remains active until after fertilization, even when the Cre allele becomes transmitted to the polar bodies during meiosis. Detection of K14 mRNA by RT-PCR in murine ovaries and immunohistochemical identification of the K14 protein in oocytes demonstrates that the human K14 promoter behaves like its murine homolog, thus identifying K14 as an authentic oocytic protein.

Epithelial Bmpr1a regulates differentiation and proliferation in postnatal hair follicles and is essential for tooth development

Bone morphogenetic protein (BMP) signaling is thought to perform multiple functions in the regulation of skin appendage morphogenesis and the postnatal growth of hair follicles. However, definitive genetic evidence for these roles has been lacking. Here, we show that Cre-mediated mutation of the gene encoding BMP receptor 1A in the surface epithelium and its derivatives causes arrest of tooth morphogenesis and lack of external hair. The hair shaft and hair follicle inner root sheath (IRS) fail to differentiate, and expression of the known transcriptional regulators of follicular differentiation Msx1, Msx2, Foxn1 and Gata3 is markedly downregulated or absent in mutant follicles. Lef1 expression is maintained, but nuclear beta-catenin is absent from the epithelium of severely affected mutant follicles, indicating that activation of the WNT pathway lies downstream of BMPR1A signaling in postnatal follicles. Mutant hair follicles fail to undergo programmed regression, and instead continue to proliferate, producing follicular cysts and matricomas. These results provide definitive genetic evidence that epithelial Bmpr1a is required for completion of tooth morphogenesis, and regulates terminal differentiation and proliferation in postnatal hair follicles.

A prospective natural history study of inclusion body myositis: implications for clinical trials

Eleven patients with untreated inclusion body myositis (IBM) were prospectively studied during a 6-month period that included muscle strength, lean body mass, and muscle mass measurements. There was an overall quantifiable mean decline in percent of predicted normal muscle strength of 4% from baseline in a 6-month period, but one third of patients showed no change or slight improvements in strength. Short-term treatment trials in IBM will require large numbers of patients to detect slowing, arrest, or even slight improvement in muscle strength.