Keratinocyte Clones Research Articles

Epigenetic switch reshapes epithelial progenitor cell signatures and drives inflammatory pathogenesis in hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a complex inflammatory skin disease with undefined mechanistic underpinnings. Here, we investigated HS epithelial cells and demonstrated that HS basal progenitors modulate their lineage restriction and give rise to pathogenic keratinocyte clones, resulting in epidermal hyperproliferation and dysregulated inflammation in HS. When comparing to healthy epithelial stem/progenitor cells, in HS, we identified changes in gene signatures that revolve around the mitotic cell cycle, DNA damage response and repair, as well as cell-cell adhesion and chromatin remodeling. By reconstructing cell differentiation trajectory and CellChat modeling, we identified a keratinocyte population specific to HS. This population is marked by S100A7/8/9 and KRT6 family members, triggering IL1, IL10, and complement inflammatory cascades. These signals, along with HS-specific proinflammatory cytokines and chemokines, contribute to the recruitment of certain immune cells during the disease progression. Furthermore, we revealed a previously uncharacterized role of S100A8 in regulating the local chromatin environment of target loci in HS keratinocytes. Through the integration of genomic and epigenomic datasets, we identified genome-wide chromatin rewiring alongside the switch of transcription factors (TFs), which mediated HS transcriptional profiles. Importantly, we identified numerous clinically relevant inflammatory enhancers and their coordinated TFs in HS basal CD49fhigh cells. The disruption of the S100A enhancer using the CRISPR/Cas9-mediated approach or the pharmacological inhibition of the interferon regulatory transcription factor 3 (IRF3) efficiently reduced the production of HS-associated inflammatory regulators. Our study not only uncovers the plasticity of epidermal progenitor cells in HS but also elucidates the epigenetic mechanisms underlying HS pathogenesis.

291 Identification of high-yield genomic areas for assessing early photocarcinogenesis in sun-exposed skin

Cutaneous squamous cell carcinomas (cSCC) evolve from early mutated clones of keratinocytes. Numerous genomic regions are highly susceptible to UV mutagenesis. Previous studies indicate differences in clonal mutation burden across skin sites of differing UV exposure. Our current work is aimed at identifying mutations in normal skin (NS) that are associated with more advanced photocarcinogenesis (PCG). We have used our computational tool “hotSPOT” to identify regions most likely to be mutated in cSCC, actinic keratoses (AK), and sun-exposed (SE) NS.

Abstract PR08: Noninvasive epidermal sampling as a means of genomic UV dosimetry

Abstract It is now well accepted that normal-appearing, but chronically UV-exposed skin, can harbor tremendous mutational loads while maintaining homeostatic function. Even so, clones of keratinocytes harboring tumorigenic mutations can be readily observed using targeted and whole-exome sequencing. Therefore, it may be possible to objectively measure chronic, cumulative UV exposure as a means of predicting skin cancer risk and measuring molecular responses to chemoprevention by identifying UV-driven mutations or damage in epidermal keratinocytes. However, such a methodology requires the ability to noninvasively sample normal, nonlesional skin. We have previously optimized a novel surfactant mixture that, when coupled to ultrasound or mechanical abrasion, can noninvasively sample epidermis without scarring. This process can be tuned to selectively remove epidermis only. Within hours of application, a fibrinous exudate appears over the wound and this area heals completely within 2 weeks without scarring. Using a Hairless UV-driven model of squamous cell carcinoma, we have been able to sample and perform both exome and RNA sequencing with recovery rates of about 2.5-3.5 μg /cm2 of DNA and RNA. Using this model, we demonstrated a dose-dependent increase in mutational load in normal UV-exposed skin that reflects what is seen in humans. Mice were sampled and the DNA exome was sequenced (150X) following exposure to UV. Among the 28 most mutated genes across the exome, mice sampled after 1 month of UV exposure harbored variants in an average of 12 genes. After 3 months of UV exposure, followed by 2 months of no exposure, variants were observed in an average of 22 genes (80%) of the 28, suggesting continuing evolution of clones harboring mutations in exposed epidermis. Interestingly, at this relatively low coverage, none of the genes is strongly associated with skin cancer; instead, many are not expressed, reflecting the expansion of mutational burdens without strong selection on these alterations. We then extended our efforts into humans by sampling immunosuppressed solid organ transplant recipients with markedly elevated risk for skin cancer. Sun-exposed areas had an average of 4.5 times the number of variants than sun-protected areas across targeted exome sequencing of 348 cancer-related genes at a depth of ~5000X. Over 24 genes (including TP53, ATM, NOTCH, and KMT2 family members) were identified with nonsense C-T transitions, suggesting the presence of detectable (and potentially selected) mutational patterns in cancer-related genes that correlate with clinically relevant exposure. Our results collectively suggest that noninvasive sampling and genomic interrogation of normal-appearing epidermis is feasible and potentially useful as a risk prediction and chemoprevention assessment tool. This approach is easily extended to other surface epithelia, and we are currently enhancing the sensitivity of this assay based on identification of hotspots and nontranscribed genes as identified in our model. This abstract is also being presented as Poster A32. Citation Format: Kenneth Y. Tsai, Elnara Muradova, Sandy S. Ojeda, Charles H. Adelmann, Kimberly Nguyen, Samir Mitragotri, Nishit Patel. Noninvasive epidermal sampling as a means of genomic UV dosimetry [abstract]. In: Proceedings of the AACR Special Conference on Environmental Carcinogenesis: Potential Pathway to Cancer Prevention; 2019 Jun 22-24; Charlotte, NC. Philadelphia (PA): AACR; Can Prev Res 2020;13(7 Suppl): Abstract nr PR08.

Efficient CRISPR-Cas9-Mediated Gene Ablation in Human Keratinocytes to Recapitulate Genodermatoses: Modeling of Netherton Syndrome

Current efforts to find specific genodermatoses treatments and define precise pathogenesis mechanisms require appropriate surrogate models with human cells. Although transgenic and gene knockout mouse models for several of these disorders exist, they often fail to faithfully replicate the clinical and histopathological features of the human skin condition. We have established a highly efficient method for precise deletion of critical gene sequences in primary human keratinocytes, based on CRISPR-Cas9-mediated gene editing. Using this methodology, in the present study we generated a model of Netherton syndrome by disruption of SPINK5. Gene-edited cells showed absence of LEKTI expression and were able to recapitulate a hyperkeratotic phenotype with most of the molecular hallmarks of Netherton syndrome, after grafting to immunodeficient mice and in organotypic cultures. To validate the model as a platform for therapeutic intervention, we tested an ex vivo gene therapy approach using a lentiviral vector expressing SPINK5. Re-expression of SPINK5 in an immortalized clone of SPINK5-knockout keratinocytes was capable of reverting from Netherton syndrome to a normal skin phenotype in vivo and in vitro. Our results demonstrate the feasibility of modeling genodermatoses, such as Netherton syndrome, by efficiently disrupting the causative gene to better understand its pathogenesis and to develop novel therapeutic approaches.

Second-Hit Somatic Mutations in Mevalonate Pathway Genes Underlie Porokeratosis

Familial and sporadic porokeratosis are associated with germline heterozygous mutations in mevalonate pathway genes. Kubo etal. show that each skin lesion of disseminated superficial actinic porokeratosis originates from a postnatal keratinocyte clone with a different second-hit genetic event in the wild-type allele of the corresponding gene. They also confirm that linear porokeratosis derives from a single prenatal clone of keratinocytes with a second-hit genetic event.

201 Loss of notch function promotes UV-induced selection of keratinocyte clones to form skin cancer

201 Loss of notch function promotes UV-induced selection of keratinocyte clones to form skin cancer

Deletion of a Pathogenic Mutation-Containing Exon of COL7A1 Allows Clonal Gene Editing Correction of RDEB Patient Epidermal Stem Cells

Recessive dystrophic epidermolysis bullosa is a severe skin fragility disease caused by loss of functional type VII collagen at the dermal-epidermal junction. A frameshift mutation in exon 80 of COL7A1 gene, c.6527insC, is highly prevalent in the Spanish patient population. We have implemented gene-editing strategies for COL7A1 frame restoration by NHEJ-induced indels in epidermal stem cells from patients carrying this mutation. TALEN nucleases designed to cut within the COL7A1 exon 80 sequence were delivered to primary patient keratinocyte cultures by non-integrating viral vectors. After genotyping a large collection of vector-transduced patient keratinocyte clones with high proliferative potential, we identified a significant percentage of clones with COL7A1 reading frame recovery and Collagen VII protein expression. Skin equivalents generated with cells from a clone lacking exon 80 entirely were able to regenerate phenotypically normal human skin upon their grafting onto immunodeficient mice. These patient-derived human skin grafts showed Collagen VII deposition at the basement membrane zone, formation of anchoring fibrils, and structural integrity when analyzed 12 weeks after grafting. Our data provide a proof-of-principle for recessive dystrophic epidermolysis bullosa treatment through ex vivo gene editing based on removal of pathogenic mutation-containing, functionally expendable COL7A1 exons in patient epidermal stem cells.

Traceless Targeting and Isolation of Gene-Edited Immortalized Keratinocytes from Epidermolysis Bullosa Simplex Patients

Epidermolysis bullosa simplex (EBS) is a blistering skin disease caused by dominant-negative mutations in either KRT5 or KRT14, resulting in impairment of keratin filament structure and epidermal fragility. Currently, nearly 200 mutations distributed across the entire length of these genes are known to cause EBS. Genome editing using programmable nucleases enables the development of ex vivo gene therapies for dominant-negative genetic diseases. A clinically feasible strategy involves the disruption of the mutant allele while leaving the wild-type allele unaffected. Our aim was to develop a traceless approach to efficiently disrupt KRT5 alleles using TALENs displaying unbiased monoallelic disruption events and devise a strategy that allows for subsequent screening and isolation of correctly modified keratinocyte clones without the need for selection markers. Here we report on TALENs that efficiently disrupt the KRT5 locus in immortalized patient-derived EBS keratinocytes. Inactivation of the mutant allele using a TALEN working at sub-optimal levels resulted in restoration of intermediate filament architecture. This approach can be used for the functional inactivation of any mutant keratin allele regardless of the position of the mutation within the gene and is furthermore applicable to the treatment of other inherited skin disorders.

Abstract 2575: Concurrent mutation of CDKN2A and TP53 loci in primary keratinocytes

Abstract Concurrent inactivation of the p16Ink4a and p53 tumor suppressors, often through mutation of CDKN2A and TP53, is frequent in early development of head and neck squamous cell carcinoma (HNSCC) and other cancers. The role of this early combined inactivation, and the oncogenic drivers that subsequently lead to tumor development, are poorly defined. To characterize the precancerous role of concurrently mutated CDKN2A and TP53, we combined a number of recent advances to disrupt both loci in primary cells. First, we grew primary keratinocytes in medium conditioned by irradiated J2-3T3 cells and containing an inhibitor of ROCK kinases, conditions that greatly extend their normally limited proliferative potential. Second, we transfected primary keratinocytes with plasmid vectors expressing both Cas9 and sets of guide RNAs targeting specific regions of CDKN2A and TP53. We targeted either or both of the p14Arf and p16Ink4a protein products of CDKN2A for knockout (KO), together with either TP53 KO or a TP53 point mutation (R248Q protein product), two major categories of genetic alterations of p53 in HNSCC. Third, we evaluated use of nutlin-3, an inhibitor of p53-MDM2 interaction, to try to select against cells that still contained wild-type p53. We assessed KO efficiency by PCR of genomic DNA; the TP53 point mutation introduced a SauA3i site into TP53. Two weeks of nutlin-3 treatment led to a 3 fold increase in p53 KO efficiency versus untreated cells (50% versus 14%). p16Ink4a KO efficiencies were enhanced 2 to 14 fold after nutlin-3 treatment, depending on the specific Cas9/guide-RNA constructs used. In cells transfected to produce p53 R248Q, 14% of PCR products amplifying the mutated region after nutlin-3 exposure showed Sau3Ai digestion, whereas no Sau3Ai digestion was detected in untreated cells. This result suggests that up to 14% of nutlin-3 treated keratinocytes had integrated the mutated donor oligo sequence. We similarly enrich for mutated keratinocytes having p14Arf-specific or combined CDKN2A KO along with TP53 KO or mutation. Combined transfection to generate concurrent CDKN2A and TP53 mutations under conditions that allow extended proliferation in culture, followed by selection for successful TP53 mutation with nutlin-3, will facilitate identification of keratinocyte clones with bi-allelic knockout genotypes. This panel of keratinocytes with concurrent CDKN2A and TP53 mutations will help delineate the roles of these genes in early cancer development and will allow screening for the oncogenic drivers required for tumor development and metastasis, with emphasis on discovering more effective and specific druggable targets for improving treatment. Citation Format: Bin Li, Edmund A. Mroz, James W. Rocco. Concurrent mutation of CDKN2A and TP53 loci in primary keratinocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2575. doi:10.1158/1538-7445.AM2017-2575

Bimodal behaviour of interfollicular epidermal progenitors regulated by hair follicle position and cycling.

Interfollicular epidermal (IFE) homeostasis is a major physiological process allowing maintenance of the skin barrier function. Despite progress in our understanding of stem cell populations in different hair follicle compartments, cellular mechanisms of IFE maintenance, in particular, whether a hierarchy of progenitors exists within this compartment, have remained controversial. We here used multicolour lineage tracing with Brainbow transgenic labels activated in the epidermis to track individual keratinocyte clones. Two modes of clonal progression could be observed in the adult murine dorsal skin. Clones attached to hair follicles showed rapid increase in size during the growth phase of the hair cycle. On the other hand, clones distant from hair follicles were slow cycling, but could be mobilized by a proliferative stimulus. Reinforced by mathematical modelling, these data support a model where progenitor cycling characteristics are differentially regulated in areas surrounding or away from growing hair follicles. Thus, while IFE progenitors follow a non-hierarchical mode of development, spatiotemporal control by their environment can change their potentialities, with far-reaching implications for epidermal homeostasis, wound repair and cancer development.

HPV16 oncogene expression levels during early cervical carcinogenesis are determined by the balance of epigenetic chromatin modifications at the integrated virus genome.

In cervical squamous cell carcinomas, high-risk human papillomavirus (HRHPV) DNA is usually integrated into host chromosomes. Multiple integration events are thought to be present within the cells of a polyclonal premalignant lesion and the features that underpin clonal selection of one particular integrant remain poorly understood. We previously used the W12 model system to generate a panel of cervical keratinocyte clones, derived from cells of a low-grade premalignant lesion naturally infected with the major HRHPV type, HPV16. The cells were isolated regardless of their selective advantage and differed only by the site of HPV16 integration into the host genome. We used this resource to test the hypothesis that levels of HPV16 E6/E7 oncogene expression in premalignant cells are regulated epigenetically. We performed a comprehensive analysis of the epigenetic landscape of the integrated HPV16 DNA in selected clones, in which levels of virus oncogene expression per DNA template varied ~6.6-fold. Across the cells examined, higher levels of virus expression per template were associated with more open chromatin at the HPV16 long control region, together with greater loading of chromatin remodelling enzymes and lower nucleosome occupancy. There were higher levels of histone post-translational modification hallmarks of transcriptionally active chromatin and lower levels of repressive hallmarks. There was greater abundance of the active/elongating form of the RNA polymerase-II enzyme (RNAPII-Ser2P), together with CDK9, the component of positive transcription elongation factor b complex responsible for Ser2 phosphorylation. The changes observed were functionally significant, as cells with higher HPV16 expression per template showed greater sensitivity to depletion and/or inhibition of histone acetyltransferases and CDK9 and less sensitivity to histone deacetylase inhibition. We conclude that virus gene expression per template following HPV16 integration is determined through multiple layers of epigenetic regulation, which are likely to contribute to selection of individual cells during cervical carcinogenesis.

Gene Editing for the Efficient Correction of a Recurrent COL7A1 Mutation in Recessive Dystrophic Epidermolysis Bullosa Keratinocytes.

Clonal gene therapy protocols based on the precise manipulation of epidermal stem cells require highly efficient gene-editing molecular tools. We have combined adeno-associated virus (AAV)-mediated delivery of donor template DNA with transcription activator-like nucleases (TALE) expressed by adenoviral vectors to address the correction of the c.6527insC mutation in the COL7A1 gene, causing recessive dystrophic epidermolysis bullosa in a high percentage of Spanish patients. After transduction with these viral vectors, high frequencies of homology-directed repair were found in clones of keratinocytes derived from a recessive dystrophic epidermolysis bullosa (RDEB) patient homozygous for the c.6527insC mutation. Gene-edited clones recovered the expression of the COL7A1 transcript and collagen VII protein at physiological levels. In addition, treatment of patient keratinocytes with TALE nucleases in the absence of a donor template DNA resulted in nonhomologous end joining (NHEJ)-mediated indel generation in the vicinity of the c.6527insC mutation site in a large proportion of keratinocyte clones. A subset of these indels restored the reading frame of COL7A1 and resulted in abundant, supraphysiological expression levels of mutant or truncated collagen VII protein. Keratinocyte clones corrected both by homology-directed repair (HDR) or NHEJ were used to regenerate skin displaying collagen VII in the dermo-epidermal junction.

Rotation is the primary motion of paired human epidermal keratinocytes

BackgroundCollective motion of keratinocytes is involved in morphogenesis, homeostasis, and wound healing of the epidermis. Yet how the collective motion of keratinocytes emerges from the behavior of individual cells is still largely unknown. ObjectiveThe aim of this study was to find the cellular behavior that links single and collective motion of keratinocytes. MethodsWe investigated the behavior of two-cell colonies of HaCaT keratinocytes by a combination of time-lapse imaging and image processing. ResultsThe two-cell colonies of HaCaT cells were formed as a contacted pair of keratinocyte clones. Image analysis and cell culture experiments revealed that the rotational speed of two-cell colonies was positively associated with their proliferative capacity. α6 integrin was required for the rotational motion of two-cell keratinocyte colonies. We also confirmed that two-cell colonies of keratinocytes predominantly exhibited the rotational, but not translational, motion, two modes of motion in a contact pair of rotating objects. ConclusionThe rotational motion is the primary motion of two-cell keratinocyte colonies and its speed is positively associated with their proliferative capacity. This study suggests that the assembly of rotating keratinocytes generates the collective motion of proliferative keratinocytes during morphogenesis and wound healing of the epidermis.

Porokeratoses: an update of clinical, aetiopathogenic and therapeutic features.

Porokeratoses represent a group of uncommon, acquired or hereditary dermatoses, due to a keratinization disorder whose origin is still unclear; they could be due to the expansion of a clone of abnormal epidermal keratinocytes. Several clinical forms exist, of which the most common is disseminated superficial actinic porokeratosis; other forms include Mibelli, disseminated superficial, linear, palmoplantaris punctata and palmaris, plantaris et disseminata. These may coexist in the same patient or in different members of the same family. Porokeratoses manifest clinically with annular or linear, well-circumscribed keratotic plaques and share a common histological hallmark, the cornoid lamella, a vertical stack of parakeratotic corneocytes within the horny layer resting on a shallow depression of the underlying epidermis. Porokeratoses may be seen in the setting of various immunodeficiencies, namely in organ-transplant recipients, in whom the course of the disease may parallel the degree of immunosuppression. The overall prognosis of porokeratoses is favourable but is shadowed by the possibility of malignant transformation of the lesions (usually into squamous cell carcinoma); this happens in less than 10% of cases but may prove fatal. Although several surgical or medical (local or systemic) treatments have been tried, none of them has shown consistent and long-term efficacy.

Circumscribed Palmar or Plantar Hypokeratosis 10 Years After the First Description: What Is Known and the Issues Under Discussion

This review of the literature on palmoplantar hypokeratosis, a process that was first indentified only 10 years ago, discusses the current state of our understanding, the therapeutic options available, and the debate about etiology. Forty-four publications reporting 69 cases were found. Palmar or plantar hypokeratosis occurs mainly in women (76.8%) and age at the time of a first visit to a physician ranges from 42 to 84 years. Most cases present between the ages of 51 and 70 years. The majority of patients have had solitary lesions usually located on the right palm, particularly in the regions of the thenar (in 44/79 lesions [55.7%]) or hypothenar eminences (in 11/79 lesions [13.9%]). In only 8 cases was there a history of prior trauma at the site. Studies using polymerase chain reaction techniques to identify human papillomavirus involvement were negative in most cases. These hypokeratotic lesions are localized epidermal depressions formed by an abrupt thinning of the stratum corneum, providing a singular histopathologic feature. This condition can currently be considered a localized keratinization disorder affecting zones where there is a thick stratum corneum. The precipitating cause is unknown and a definitive treatment remains to be found. The mechanism would be the localized failure of a clone of keratinocytes during differentiation toward normal palmoplantar hyperkeratinization.

Hipoqueratosis circunscrita palmar o plantar. Conocimientos y controversias tras 10 años de su descripción

This review of the literature on palmoplantar hypokeratosis, a process that was first indentified only 10 years ago, discusses the current state of our understanding, the therapeutic options available, and the debate about etiology. Forty-four publications reporting 69 cases were found. Palmar or plantar hypokeratosis occurs mainly in women (76.8%) and age at the time of a first visit to a physician ranges from 42 to 84 years. Most cases present between the ages of 51 and 70 years. The majority of patients have had solitary lesions usually located on the right palm, particularly in the regions of the thenar (in 44/79 lesions [55.7%]) or hypothenar eminences (in 11/79 lesions [13.9%]). In only 8 cases was there a history of prior trauma at the site. Studies using polymerase chain reaction techniques to identify human papillomavirus involvement were negative in most cases. These hypokeratotic lesions are localized epidermal depressions formed by an abrupt thinning of the stratum corneum, providing a singular histopathologic feature. This condition can currently be considered a localized keratinization disorder affecting zones where there is a thick stratum corneum. The precipitating cause is unknown and a definitive treatment remains to be found. The mechanism would be the localized failure of a clone of keratinocytes during differentiation toward normal palmoplantar hyperkeratinization.

Self-inactivating MLV vectors have a reduced genotoxic profile in human epidermal keratinocytes

Transplantation of epithelia derived from keratinocyte stem cells transduced by retroviral vectors is a potential therapy for epidermolysis bullosa (EB), a family of inherited skin adhesion defects. The biosafety characteristics of retroviral vectors in keratinocytes are, however, poorly defined. We developed self-inactivating (SIN) vectors derived from the Moloney murine leukemia (MLV) and the human immunodeficiency (HIV) viruses expressing therapeutic levels of LAMB3, a transgene defective in junctional EB, and tested their integration profile in human primary keratinocytes. The SIN-HIV vector showed the expected preference for transcribed genes while the SIN-MLV vector integrated preferentially in regulatory elements, but showed a significantly lower tendency to target cell growth-related genes, transcription start sites and epigenetically defined promoters compared with a wild-type MLV vector in an epithelial cell context. A quantitative gene expression assay in individual keratinocyte clones showed that MLV-derived vectors deregulate expression of targeted genes at a lower frequency than in hematopoietic cells, and that the SIN-MLV design has the lowest activity compared to both MLV and SIN-HIV vectors. This study indicates that SIN-MLV vectors may have a better safety profile in keratinocyte than in hematopoietic cells, and be a reasonable alternative to lentiviral vectors for gene therapy of inherited skin disorders.

New mimetic peptides of the kinase-inhibitory region (KIR) of SOCS1 through focused peptide libraries

SOCS (suppressor of cytokine signalling) proteins are negative-feedback regulators of the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway. Their expression levels are low under physiological conditions, but they are up-regulated in response to cytokine stimulation in many immune and inflammatory processes. Overexpression of SOCS1 in keratinocyte clones abrogates the IFNγ (interferon γ)-induced expression of many pro-inflammatory genes and the release of related chemokines by blocking the JAK/STAT pathway. SOCS1 inhibits JAK2 kinase activity by binding the catalytic site of JAK2, with its KIR (kinase-inhibitory region) acting as a pseudo-substrate of the enzyme. In the present study, we screened a focused combinatorial peptide library of KIR to identify new peptides able to mimic its function with an improved affinity towards the JAK2 catalytic site. Using an alanine-scanning method, KIR residues that are crucial for the interaction with JAK2 were unveiled. In this way, the KIR sequence was restricted to a shorter segment and ‘non-essential’ residues were replaced by different amino acids following a simplified combinatorial approach. We selected a new unnatural sequence able to bind to JAK2 with Kd values in the nanomolar range. This peptide was tested in human keratinocyte cultures and reduced the phosphorylation of STAT1 and the expression levels of IRF-1 (interferon regulatory factor-1).

TCF/Lef1 activity controls establishment of diverse stem and progenitor cell compartments in mouse epidermis

Mammalian epidermis consists of the interfollicular epidermis, hair follicles (HFs) and associated sebaceous glands (SGs). It is constantly renewed by stem and progenitor cell populations that have been identified and each compartment features a distinct mechanism of cellular turnover during renewal. The functional relationship between the diverse stem cell (SC) pools is not known and molecular signals regulating the establishment and maintenance of SC compartments are not well understood. Here, we performed lineage tracing experiments to demonstrate that progeny of HF bulge SCs transit through other SC compartments, suggesting a hierarchy of competent multipotent keratinocytes contributing to tissue renewal. The bulge was identified as a bipotent SC compartment that drives both cyclic regeneration of HFs and continuous renewal of SGs. Our data demonstrate that aberrant signalling by TCF/Lef1, transcription factors crucial for bulge SC activation and hair differentiation, results in development of ectopic SGs originating from bulge cells. This process of de novo SG formation is accompanied by the establishment of new progenitor niches. Detailed molecular analysis suggests the recapitulation of steps of tissue morphogenesis.

A Sleeping Beauty DNA transposon-based genetic sensor for functional screening of vitamin D3 analogues

BackgroundAnalogues of vitamin D3 are extensively used in the treatment of various illnesses, such as osteoporosis, inflammatory skin diseases, and cancer. Functional testing of new vitamin D3 analogues and formulations for improved systemic and topical administration is supported by sensitive screening methods that allow a comparative evaluation of drug properties. As a new tool in functional screening of vitamin D3 analogues, we describe a genomically integratable sensor for sensitive drug detection. This system facilitates assessment of the pharmacokinetic and pharmadynamic properties of vitamin D3 analogues. The tri-cistronic genetic sensor encodes a drug-sensoring protein, a reporter protein expressed from an activated sensor-responsive promoter, and a resistance marker.ResultsThe three expression cassettes, inserted in a head-to-tail orientation in a Sleeping Beauty DNA transposon vector, are efficiently inserted as a single genetic entity into the genome of cells of interest in a reaction catalyzed by the hyperactive SB100X transposase. The applicability of the sensor for screening purposes is demonstrated by the functional comparison of potent synthetic analogues of vitamin D3 designed for the treatment of psoriasis and cancer. In clones of human keratinocytes carrying from a single to numerous insertions of the vitamin D3 sensor, a sensitive sensor read-out is detected upon exposure to even low concentrations of vitamin D3 analogues. In comparative studies, the sensor unveils superior potency of new candidate drugs in comparison with analogues that are currently in clinical use.ConclusionsOur findings demonstrate the use of the genetic sensor as a tool in first-line evaluation of new vitamin D3 analogues and pave the way for new types of drug delivery studies in sensor-transgenic animals.