Abnormal neuronal differentiation and mitochondrial dysfunction in hair follicle-derived induced pluripotent stem cells of schizophrenia patients.

One of the prevailing hypotheses suggests schizophrenia as a neurodevelopmental disorder, involving dysfunction of dopaminergic and glutamatergic systems. Accumulating evidence suggests mitochondria as an additional pathological factor in schizophrenia. An attractive model to study processes related to neurodevelopment in schizophrenia is reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) and differentiating them into different neuronal lineages. iPSCs from three schizophrenia patients and from two controls were reprogrammed from hair follicle keratinocytes, because of their accessibility and common ectodermal origin with neurons. iPSCs were differentiated into Pax6(+)/Nestin(+) neural precursors and then further differentiated into ß3-Tubulin(+)/tyrosine hydroxylase(+)/DAT(+) dopaminergic neurons. In addition, iPSCs were differentiated through embryonic bodies into ß3-Tubulin(+)/Tbox brain1(+) glutamatergic neurons. Schizophrenia-derived dopaminergic cells showed severely impaired ability to differentiate, whereas glutamatergic cells were unable to maturate. Mitochondrial respiration and its sensitivity to dopamine-induced inhibition were impaired in schizophrenia-derived keratinocytes and iPSCs. Moreover, we observed dissipation of mitochondrial membrane potential (Δψm) and perturbations in mitochondrial network structure and connectivity in dopaminergic along the differentiation process and in glutamatergic cells. Our data unravel perturbations in neural differentiation and mitochondrial function, which may be interconnected, and of relevance to dysfunctional neurodevelopmental processes in schizophrenia.

Transposable B2 SINE elements can provide mobile RNA polymerase II promoters.

Short interspersed elements (SINEs) are highly abundant components of mammalian genomes that are propagated by retrotransposition. SINEs are recognized as a causal agent of human disease and must also have had a profound influence in shaping eukaryotic genomes. The B2 SINE family constitutes approximately 0.7% of total mouse genomic DNA (ref. 2) and is also found at low abundance in humans. It resembles the Alu family in several respects, such as its mechanism of propagation. B2 SINEs are derived from tRNA and are transcribed by RNA polymerase (pol) III to generate short transcripts that are not translated. We find here, however, that one B2 SINE also carries an active pol II promoter located outside the tRNA region. Indeed, a B2 element is responsible for the production of a mouse Lama3 transcript. The B2 pol II promoters can be bound and stimulated by the transcription factor USF (for upstream stimulatory factor), as shown by transient transfection experiments. Moreover, this pol II activity does not preclude the pol III transcription necessary for retrotransposition. Dispersal of B2 SINEs by retrotransposition may therefore have provided numerous opportunities for creating regulated pol II transcription at novel genomic sites. This mechanism may have allowed the evolution of new transcription units and new genes.

Herlitz's junctional epidermolysis bullosa is linked to mutations in the gene (LAMC2) for the gamma 2 subunit of nicein/kalinin (LAMININ-5).

We have linked Herlitz's junctional epidermolysis bullosa (H-JEB) to the gene (LAMC2) encoding the gamma 2 subunit of nicein/kalinin, an isolaminin (laminin-5) expressed by basal keratinocytes. In four H-JEB kindreds, a maximum two-point lod score of 5.33 at theta = 0 was observed between a microsatellite near LAMC2 at 1q25-31 and the disease. In one family, a homozygous point mutation leading to a premature stop codon (CGA to TGA) was identified in exon 3 of the gene. The segregation of the mutated allele implicates the mutation in the pathology of the disorder and corroborates the linkage results.

Integrin beta 4 mutations associated with junctional epidermolysis bullosa with pyloric atresia.

Pyloric atresia associated with junctional epidermolysis bullosa (PA-JEB), is a rare inherited disorder characterized by pyloric stenosis and blistering of the skin as primary manifestations. We demonstrate that in one PA-JEB patient the disease resulted from two distinct mutations in the beta 4 integrin gene alleles. The paternal mutation consists of a one base pair deletion causing a shift in the open reading frame, and a downstream premature termination codon. The maternal mutation occurs in a donor splice site, and results in in-frame exon skipping involving the cytoplasmic domain of the polypeptide. Our results implicate mutations in the beta 4 integrin gene in some forms of PA-JEB.

Pathophysiology of aniridia-associated keratopathy: Developmental aspects and unanswered questions.

Aniridia, a rare congenital disease, is often characterized by a progressive, pronounced limbal insufficiency and ocular surface pathology termed aniridia-associated keratopathy (AAK). Due to the characteristics of AAK and its bilateral nature, clinical management is challenging and complicated by the multiple coexisting ocular and systemic morbidities in aniridia. Although it is primarily assumed that AAK originates from a congenital limbal stem cell deficiency, in recent years AAK and its pathogenesis has been questioned in the light of new evidence and a refined understanding of ocular development and the biology of limbal stem cells (LSCs) and their niche. Here, by consolidating and comparing the latest clinical and preclinical evidence, we discuss key unanswered questions regarding ocular developmental aspects crucial to AAK. We also highlight hypotheses on the potential role of LSCs and the ocular surface microenvironment in AAK. The insights thus gained lead to a greater appreciation for the role of developmental and cellular processes in the emergence of AAK. They also highlight areas for future research to enable a deeper understanding of aniridia, and thereby the potential to develop new treatments for this rare but blinding ocular surface disease.

Hif-2alpha mediates UV-induced apoptosis through a novel ATF3-dependent death pathway.

In this study, we describe a novel activating transcription factor 3 (ATF3)-dependent death pathway triggered by ultraviolet (UV) irradiation. We demonstrate that ATF3 contributes to UV-induced apoptosis through the regulation of hypoxia inducible factor (Hif)-2alpha expression, which in turn induces the expression of proapoptotic genes, such as Caspase7 or TRAIL (tumor necrosis factor (ligand) superfamily, member 10). Gain of function of Hif-2alpha as well as ATF3 is sufficient to trigger cell death, whereas loss of function of both proteins drastically inhibits UV-induced apoptosis. Repression of Hif-2alpha strongly impairs ATF3-mediated death, providing evidences that Hif-2alpha is the major death effector of ATF3. In addition, Hif-1alpha, already known as a proapoptotic gene, upon UV irradiation, is not able to compensate for the lack of Hif-2alpha expression, thereby confirming the major contribution of Hif-2alpha in UV-mediated cell death. We further demonstrate that this cascade of gene activation depends on p38 and c-Jun N-terminal kinase (JNK) activity. Impairment of such a pathway is likely to contribute to oncogenesis by promoting survival of cells that could accumulate severe chromosomal alterations.

miR-203 represses 'stemness' by repressing DeltaNp63.

The epidermis, the outer layer of the skin composed of keratinocytes, is a stratified epithelium that functions as a barrier to protect the organism from dehydration and external insults. The epidermis develops depending on the transcription factor p63, a member of the p53 family of transcription factors. p63 is strongly expressed in the innermost basal layer where epithelial cells with high clonogenic and proliferative capacity reside. Deletion of p63 in mice results in a dramatic loss of all keratinocytes and loss of stratified epithelia, probably due to a premature proliferative rundown of the stem and transient amplifying cells. Here we report that microRNA (miR)-203 is induced in vitro in primary keratinocytes in parallel with differentiation. We found that miR-203 specifically targets human and mouse p63 3'-UTRs and not SOCS-3, despite bioinformatics alignment between miR-203 and SOCS-3 3'-UTR. We also show that miR-203 overexpression in proliferating keratinocytes is not sufficient to induce full epidermal differentiation in vitro. In addition, we demonstrate that miR-203 is downregulated during the epithelial commitment of embryonic stem cells, and that overexpression of miR-203 in rapidly proliferating human primary keratinocytes significantly reduces their clonogenic capacity. The results suggest that miR-203, by regulating the DeltaNp63 expression level, is a key molecule controlling the p63-dependent proliferative potential of epithelial precursor cells both during keratinocyte differentiation and in epithelial development. In addition, we have shown that miR-203 can regulate DeltaNp63 levels upon genotoxic damage in head and neck squamous cell carcinoma cells, thus controlling cell survival.

BMP-4 induces a Smad-dependent apoptotic cell death of mouse embryonic stem cell-derived neural precursors.

Embryonic ectoderm is fated to become either neural or epidermal, depending on patterning processes that occur before and during gastrulation. It has been stated that epidermal commitment proceeds from a bone morphogenetic protein-4 (BMP-4)-dependent inhibition of dorsal ectoderm neuralization. We recently demonstrated that murine embryonic stem (ES) cells treated with BMP-4 undergo effective keratinocyte commitment and epidermogenesis. Focusing on the precise role of BMP-4 in the early choice between neural and epidermal commitment, we show here that BMP-4 treatment of ES cells leads to a dramatic apoptotic death of Sox-1+ neural precursors with concomitant epidermal engagement. In addition, neutralization of the Smad pathway prevents both the BMP-4 apoptotic process and the inhibition of neural differentiation. Our results suggest that, in mammals, BMP-4, as an active inducer of epidermal commitment, interferes with the survival of neural precursors through induction of their apoptotic cell death.

The oncogenic potential of an activated Hox-2.4 homeobox gene in mouse fibroblasts.

The homeobox gene Hox-2.4 is transcriptionally activated in cells of the mouse myeloid leukemia WEHI-3B. The constitutive Hox-2.4 expression in WEHI-3B cells is due to insertion of a transposable element belonging to the family of intracisternal A particles. In this study, we demonstrated the oncogenic potential of this activated homeobox gene. NIH 3T3 fibroblast clones bearing the activated Hox-2.4 gene produced fibrosarcomas in nude mice.

Differential expression of laminin-5 subunits during incisor and molar development in the mouse.

Rodent incisors are continuously growing teeth and enamel deposition is restricted to the labial side. In the present study, the expression of laminin-5 subunits (alpha3, beta3 and gamma2) has been analyzed by in situ hybridization in developing mouse lower incisors and compared to that reported in the molar. At the bud stage (E12), mRNAs for all subunits were detected in the whole epithelial thickening. At E14, when histogenesis had started, transcripts for alpha3 and gamma2 subunits were restricted to the outer dental epithelium (ODE), whereas the beta3 subunit was intensely expressed in the inner dental epithelium (IDE). A transient expression for alpha3 subunit was seen in the enamel knot area and disappeared at E15. Subsequently, all laminin-5 subunit genes were re-expressed in differentiating ameloblasts on the labial side. Similar patterns of transcription were observed in incisor and molar, suggesting that the differential expression of laminin-5 subunits in the IDE might be involved in the histogenesis of the IDE and ameloblast differentiation. At E16.5, cells of the IDE at the anterior extremity of the incisor and in the anterior part of the lingual IDE expressed transcripts for alpha3 and beta3 but not for gamma2 subunit. Similar expression patterns were observed in the enamel-free areas of the E18 molar. This specific expression might thus be related to cells that do not differentiate as functional ameloblasts. Throughout incisor development, intense expression for all laminin-5 subunits was restricted to the labial side of the cervical loop. The asymmetrical expression of laminin-5 might be related to incisor morphogenesis and to the differences in histogenesis and cytodifferentiation of the IDE that exist in the labial versus lingual aspect of the cervical loop.

Nicein (BM-600) in junctional epidermolysis bullosa: polyclonal antibodies provide new clues for pathogenic role.

We have raised polyclonal antibodies against each of three subunits of the new basement membrane component nicein (formerly BM-600), the antigen recognized by the monoclonal antibody GB3 (Biochem Biophys Acta 942:45-56, 1988). Preparation of such antibodies was achieved from gel electrophoresis purification of nicein isolated by immuno-affinity chromatography. These antibodies were reactive with each transblotted denatured nicein subunit and recognized the native protein both in cultured keratinocytes and in all normal human basement membranes where the GB3 antigen is located. A reciprocal immuno-cross-reactivity was detected with the antibodies directed against the 100-kD and 150-kD (sometimes resolved as a 146-150-kD doublet) subunits of nicein, showing that they share some identical epitopes. In tissues and keratinocyte cultures from patients with the Herlitz form of junctional epidermolysis bullosa (H-JEB), GB3 is unable to recognize nicein, and the question arises whether this is due to an absence of synthesis or a structural abnormality of the protein. We report here that the polyclonal antibody directed against the 150-kD subunit of nicein binds its antigen in H-JEB patients (although usually less intensely than in control skin), whereas the other two antibodies either do not recognize or recognize only weakly their respective antigen subunits. These data suggest that nicein is present but structurally altered in basement membranes from H-JEB tissues. Furthermore, in non-Herlitz junctional and dystrophic types of epidermolysis bullosa, all three polyclonal antibodies recognize their antigens normally. Consequently, such antibodies should serve as potentially useful molecular tools for studying the expression of nicein in H-JEB.

Cicatricial pemphigoid autoantibodies react with multiple sites on the BP180 extracellular domain.

Cicatricial pemphigoid (CP) is an autoimmune blistering disease that primarily affects mucosal tissues. Autoantibodies to laminin-5 have previously been detected in certain patients with a CP-like disease; however, individuals that exhibit this reactivity profile apparently represent a small subset of CP patients. In the present investigation, 0 of 18 CP sera showed reactivity with laminin-5 by immunoblotting. In contrast, 18 of 23 CP sera (78%) recognized a 180-kDa epidermal antigen that, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, co-migrated with BP180, a hemidesmosomal glycoprotein associated with two other autoimmune blistering diseases, bullous pemphigoid and herpes gestationis. To investigate further the CP autoimmune response, various segments of human BP180 were expressed as bacterial fusion proteins and assayed by immunoblotting for reactivity with CP patients' sera. The results of this investigation demonstrated that the BP180 autoantigen is indeed a major target of CP autoantibodies. Further, two distinct CP-reactive sites were identified on the extracellular domain of the BP180 protein, one located in the non-collagenous (NC) 16A domain (at or near the previously defined autoantibody-reactive site recognized by bullous pemphigoid and herpes gestationis sera) and the other in the carboxy-terminal region of this protein. Sixteen of 23 CP sera (70%) reacted with one or both of these antigenic sites of BP180. Other immunologic data suggested that BP180 may harbor additional CP-reactive sites. In conclusion, there are now three bullous diseases, bullous pemphigoid, herpes gestationis, and cicatricial pemphigoid, that are known to be associated with an autoimmune response against the extracellular domain of the BP180 antigen.

Localization of laminin-5 in the epidermal basement membrane.

Laminin-5 (kalinin/nicein/BM600) is a component of the epidermal basement membrane zone. Previous en bloc pre-embedding immunogold electron microscopy (EM) has shown that the epitope of GB3, a monoclonal antibody against laminin-5, is present in the lamina lucida (LL). However, precise localization of the entire laminin-5 molecule was unclear because of uneven and limited penetration of gold-labeled antibody in pre-embedding immunolabeling. In addition, the location of the GB3 epitope may not directly represent the location of the laminin-5 moelcule itself. To elucidate the precise ultrastructural distribution of the entire laminin-5 molecule, we used polyclonal antibodies against different sites of laminin-5. Dual staining immunofluorescence with anti-laminin-5 and anti-melanocyte antibodies and immunoperoxidase EM showed that laminin-5 was present only beneath keratinocytes and not beneath melanocytes. Both cryoultramicrotomy and postembedding immunogold EM demonstrated that laminin-5 was localized to the lamina densa (LD) and the lower LL, with major labeling beneath the hemidesmosome. Quantitative analysis showed that 67-69% of gold particles were distributed to the LD and 88-90% were distributed beneath the hemidesmosome. Our results indicate that laminin-5 is localized mainly to the LD and partially to the lower LL, and is associated predominantly with hemidesmosomes.

Transcriptional regulation of laminin gene expression.

Laminins are the most abundant structural non-collagenous glycoproteins ubiquitously present in basement membranes. They are multidomain molecules consisting of of alpha, beta, and gamma chains. Although the precise functional differences between the laminin variants are not well understood, the diversity of laminin isoforms may reflect the formation of distinct basement membranes. The laminins display a remarkable restricted expression profile, suggesting a fine regulation of their genes. In this review, we focus on the most recent developments of laminin biology, centering on transcriptional and posttranscriptional controls. We discuss only those laminin chains whose gene organization and promoter elements have been characterized and proved to be functional. When possible, we correlate the effects of growth factors, cytokines, retinoids, and transcription factors on laminin gene expression with the identity of cis-acting elements in their genomic control regions.

Regulation of skin aging and heart development by TAp63.

Since the discovery of the TP63 gene in 1998, many studies have demonstrated that ΔNp63, a p63 isoform of the p53 gene family, is involved in multiple functions during skin development and in adult stem/progenitor cell regulation. In contrast, TAp63 studies have been mostly restricted to its apoptotic function and more recently as the guardian of oocyte integrity. TAp63 endogenous expression is barely detectable in embryos and adult (except in oocytes), presumably because of its rapid degradation and the lack of antibodies able to detect weak expression. Nevertheless, two recent independent studies have demonstrated novel functions for TAp63 that could have potential implications to human pathologies. The first discovery is related to the protective role of TAp63 on premature aging. TAp63 controls skin homeostasis by maintaining dermal and epidermal progenitor/stem cell pool and protecting them from senescence, DNA damage and genomic instability. The second study is related to the role of TAp63, expressed by the primitive endoderm, on heart development. This unexpected role for TAp63 has been discovered by manipulation of embryonic stem cells in vitro and confirmed by the severe cardiomyopathy observed in brdm2 p63-null embryonic hearts. Interestingly, in both cases, TAp63 acts in a cell-nonautonomous manner on adjacent cells. Here, we discuss these findings and their potential connection during development.

Induced pluripotent stem cells from hair follicles as a cellular model for neurodevelopmental disorders.

Disease-specific induced pluripotent stem cells (iPSC) allow unprecedented experimental platforms for basic research as well as high-throughput screening. This may be particularly relevant for neuropsychiatric disorders, in which the affected neuronal cells are not accessible. Keratinocytes isolated from hair follicles are an ideal source of patients' cells for reprogramming, due to their non-invasive accessibility and their common neuroectodermal origin with neurons, which can be important for potential epigenetic memory. From a small number of plucked human hair follicles obtained from two healthy donors we reprogrammed keratinocytes to pluripotent iPSC. We further differentiated these hair follicle-derived iPSC to neural progenitors, forebrain neurons and functional dopaminergic neurons. This study shows that human hair follicle-derived iPSC can be differentiated into various neural lineages, suggesting this experimental system as a promising in vitro model to study normal and pathological neural developments, avoiding the invasiveness of commonly used skin biopsies.

Diverse p63 and p73 isoforms regulate Δ133p53 expression through modulation of the internal TP53 promoter activity.

In response to stress, p53 binds and transactivates the internal TP53 promoter, thus regulating the expression of its own isoform, Δ133p53α. Here, we report that, in addition to p53, at least four p63/p73 isoforms regulate Δ133p53 expression at transcriptional level: p63ß, ΔNp63α, ΔNp63ß and ΔNp73γ. This regulation occurs through direct DNA-binding to the internal TP53 promoter as demonstrated by chromatin immunoprecipitation and the use of DNA-binding mutant p63. The promoter regions involved in the p63/p73-mediated transactivation were identified using deleted, mutant and polymorphic luciferase reporter constructs. In addition, we observed that transient expression of p53 family members modulates endogenous Δ133p53α expression at both mRNA and protein levels. We also report concomitant variation of p63 and Δ133p53 expression during keratinocyte differentiation of HaCat cells and induced pluripotent stem cells derived from mutated p63 ectodermal dysplasia patients. Finally, proliferation assays indicated that Δ133p53α isoform regulates the anti-proliferative activities of p63ß, ΔNp63α, ΔNp63ß and ΔNp73γ. Overall, this study shows a strong interplay between p53, p63 and p73 isoforms to orchestrate cell fate outcome.

ΔNp63 is an ectodermal gatekeeper of epidermal morphogenesis.

p63, a member of p53 family, has a significant role in the development and maintenance of stratified epithelia. However, a persistent dispute remained over the last decade concerning the interpretation of the severe failure of p63-null embryos to develop stratified epithelia. In this study, by investigating both p63-deficient strains, we demonstrated that p63-deficient epithelia failed to develop beyond ectodermal stage as they remained a monolayer of non-proliferating cells expressing K8/K18. Importantly, in the absence of p63, corneal-epithelial commitment (which occurs at embryonic day 12.5 of mouse embryogenesis) was hampered 3 weeks before corneal stem cell renewal (that begins at P14). Taken together, these data illustrate the significant role of p63 in epithelial embryogenesis, before and independently of other functions of p63 in adult stem cells regulation. Transcriptome analysis of laser captured-embryonic tissues confirmed the latter hypothesis, demonstrating that a battery of epidermal genes that were activated in wild-type epidermis remained silent in p63-null tissues. Furthermore, we defined a subset of novel bona fide p63-induced genes orchestrating first epidermal stratification and a subset of p63-repressed mesodermal-specific genes. These data highlight the earliest recognized action of ΔNp63 in the induction epidermal morphogenesis at E11.5. In the absence of p63, a mesodermal program is activated while epidermal morphogenesis does not initiate.