TAp63 Is Important for Cardiac Differentiation of Embryonic Stem Cells and Heart Development

Correlation of progesterone receptors and P63 to the histological grade of meningiomas: Review and significance in an African population

Objectives

Meningiomas, a common neoplasm of the central nervous system, is a widely studied meningeal tumor. According to the World Health Organization (WHO) 2021 classification of meningiomas, there are 15 subtypes that have been grouped into grades 1, 2, and 3. The WHO grade 1 meningiomas are generally grouped as benign while the WHO grades 2 and 3 tumors are grouped as malignant. Progesterone receptors and P63 are common immunohistochemical markers that have proven useful in the diagnosis, grading, and prognostication of many neoplasms such as breast carcinoma, prostate carcinoma, and gastrointestinal tumors in histopathology practice. The application of these immunohistochemical markers to the grading of meningiomas has been reported and their usefulness documented in reports from Africa, Europe, North America, South America, and Asia. This study, therefore, seeks to determine if these findings are applicable to the meningiomas seen in an African population.

Materials and Methods

A 10-year review of results and histologically diagnosed cases of meningiomas received in the Department of Morbid Anatomy, University of Nigeria, Enugu. Immunostaining for progesterone receptors (PgRs) and P63 were done and results compared with histologic grades.

Results

The three WHO grades of meningioma were assessed in this study. M: F ratio was 1:1.4 and peak age was 41-50 years age range (SD ± 16.54). The majority of the cases were WHO grade 1 (86.1%) while the WHO grades 2 and 3 tumors were 8% and 5.9%, respectively. The fibrous variant was the most common subtype (27.1%). There was no correlation between progesterone receptor and P63 immunopositivity to the WHO grades of meningioma (P = 0.112 and P = 0.138, respectively).

Conclusion

Our study showed that progesterone receptors and P63 immunopositivity did not correlate with the WHO grades of meningiomas. This may be due to the predominant variant of meningioma seen in this study. These findings indicate that PgR antagonist may not be an effective alternative for treatment in patients with inoperable meningiomas. Furthermore, P63 immunopositivity may not be a sufficient grading tool for managing meningiomas in our population.

Overlap between EEC and AEC syndrome and immunodeficiency in a preterm infant with a TP63 variant

Pathogenic variants in the transcription factor TP63 gene cause a variety of clinical phenotypes, such as ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome and ankyloblepharon-ectodermal dysplasia-clefting (AEC) syndrome. Historically, TP63-related phenotypes have been divided into several syndromes based on both the clinical presentation and location of the pathogenic variant on the TP63 gene. This division is complicated by significant overlap between syndromes. Here we describe a patient with clinical characteristics of different TP63-associated syndromes (cleft lip and palate, split feet, ectropion, erosions of the skin and corneas), associated with a de novo heterozygous pathogenic variant c.1681 T>C, p.(Cys561Arg) in exon 13 of the TP63 gene. Our patient also developed enlargement of the left-sided cardiac compartments and secondary mitral insufficiency, which is a novel finding, and immune deficiency, which has only rarely been reported. The clinical course was further complicated by prematurity and very low birth weight. We illustrate the overlapping features of EEC and AEC syndrome and multidisciplinary care needed to address the various clinical challenges.

Structural diversity of p63 and p73 isoforms

Abstract

The p53 protein family is the most studied protein family of all. Sequence analysis and structure determination have revealed a high similarity of crucial domains between p53, p63 and p73. Functional studies, however, have shown a wide variety of different tasks in tumor suppression, quality control and development. Here we review the structure and organization of the individual domains of p63 and p73, the interaction of these domains in the context of full-length proteins and discuss the evolutionary origin of this protein family.

Facts

Open questions

Dexamethasone Induces Apoptosis of Embryonic Palatal Mesenchymal Cells Through the GATA-6/Bone Morphogenetic Protein-2/p38 MAPK Pathway

ABSTRACT

Exposure to dexamethasone (DEX) causes cleft palate at high rates. Our previous studies proved that GATA binding protein 6 (GATA-6)/bone morphogenetic protein-2 (BMP-2) mediated apoptosis is related to DEX-induced cleft palate, but the specific mechanism is still unclear. The goal of this research was to understand the mechanism of apoptosis in cleft palate formation induced by DEX. Palatal mesenchymal cells from mouse embryos on embryonic day 13 were isolated as the experimental group, GATA-6 was silenced by GATA-6 small interfering Ribonucleic Acid (RNA). Cell Counting Kit-8, flow cytometry and Western Blot were applied to detect cell proliferation ability, cell cycle, the proportion of apoptotic cells, and the expression of apoptosis-related proteins of GATA-6 knockdown palatal mesenchymal cells. Further proteins on the BMP-2/Mitogen-activated protein kinase (MAPK) pathways were detected using Western Blot. T results showed that knockdown of GATA-6 by siRNA significantly decreased cell proliferation and increased the expression of apoptosis-related proteins. Bone morphogenetic protein-2/P38 mitogen Activated protein kinase (P38 MARK) pathway proteins decreased significantly among the GATA-6 knockdown group, DEX-cleft palate group and control +DEX groups. The results indicated that the GATA-6/BMP-2/P38 MAPK athway was involved in the apoptosis caused by GATA-6 silencing, which may be the possible mechanism of DEX inducing cleft palate.

Targeting the histone demethylase LSD1 prevents cardiomyopathy in a mouse model of laminopathy

LMNA mutations in patients are responsible for a dilated cardiomyopathy. Molecular mechanisms underlying the origin and development of the pathology are unknown. Herein, using mouse pluripotent embryonic stem cells (ESCs) and a mouse model both harboring the p.H222P Lmna mutation, we found early defects in cardiac differentiation of mutated ESCs and dilatation of mutated embryonic hearts at E13.5, pointing to a developmental origin of the disease. Using mouse ESCs, we demonstrated that cardiac differentiation of LmnaH222P/+ was impaired at the mesodermal stage. Expression of Mesp1, a mesodermal cardiogenic gene involved in epithelial-to-mesenchymal transition of epiblast cells, as well as Snai1 and Twist expression, was decreased in LmnaH222P/+ cells compared with WT cells in the course of differentiation. In turn, cardiomyocyte differentiation was impaired. ChIP assay of H3K4me1 in differentiating cells revealed a specific decrease of this histone mark on regulatory regions of Mesp1 and Twist in LmnaH222P/+ cells. Downregulation or inhibition of LSD1 that specifically demethylated H3K4me1 rescued the epigenetic landscape of mesodermal LmnaH222P/+ cells and in turn contraction of cardiomyocytes. Inhibition of LSD1 in pregnant mice or neonatal mice prevented cardiomyopathy in E13.5 LmnaH222P/H222P offspring and adults, respectively. Thus, LSD1 appeared to be a therapeutic target to prevent or cure dilated cardiomyopathy associated with a laminopathy.

Exploiting ubiquitin ligase cereblon as a target for small-molecule compounds in medicine and chemical biology

Cereblon (CRBN), originally identified as a gene associated with intellectual disability, was identified as primary target of thalidomide. Accumulating evidence has shown that CRBN is a substrate receptor of Cullin Ring E3 ubiquitin ligase 4 (CRL4) containing DDB1, CUL4, and RBX1, which recognizes specific neosubstrates in the presence of thalidomide or its analogs and induces their ubiquitination and proteasomal degradation. A set of small-molecule, CRBN-binding drugs are known as molecular glue degraders because these compounds promote the interaction between CRBN and its neosubstrates. Moreover, CRBN-based proteolysis-targeting chimeras, heterobifunctional molecules hijacking CRBN and inducing degradation of proteins of interest, have emerged as a promising modality in drug development and are being actively investigated. Meanwhile, the original functions and regulations of CRBN are still largely elusive. In this review, we describe key findings surrounding CRBN since its discovery and then discuss a few unanswered issues.

The foggy world(s) of p63 isoform regulation in normal cells and cancer

The p53 family member p63 exists as two major protein variants (TAp63 and ΔNp63) with distinct expression patterns and functional properties. Whilst downstream target genes of p63 have been studied intensively, how p63 variants are themselves controlled has been relatively neglected. Here, we review advances in understanding ΔNp63 and TAp63 regulation, highlighting their distinct pathways. TAp63 has roles in senescence and metabolism, and in germ cell genome maintenance, where it is activated post-transcriptionally by phosphorylation cascades after DNA damage. The function and regulation of TAp63 in mesenchymal and haematopoietic cells is less clear but may involve epigenetic control through DNA methylation. ΔNp63 functions to maintain stem/progenitor cells in various epithelia and is overexpressed in squamous and certain other cancers. ΔNp63 is transcriptionally regulated through multiple enhancers in concert with chromatin modifying proteins. Many signalling pathways including growth factors, morphogens, inflammation, and the extracellular matrix influence ΔNp63 levels, with inconsistent results reported. There is also evidence for reciprocal regulation, including ΔNp63 activating its own transcription. ΔNp63 is downregulated during cell differentiation through transcriptional regulation, while post-transcriptional events cause proteasomal degradation. Throughout the review, we identify knowledge gaps and highlight discordances, providing potential explanations including cell-context and cell-matrix interactions. Identifying individual p63 variants has roles in differential diagnosis and prognosis, and understanding their regulation suggests clinically approved agents for targeting p63 that may be useful combination therapies for selected cancer patients. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

TAp63α targeting of Lgr5 mediates colorectal cancer stem cell properties and sulforaphane inhibition

Cancer stem cells (CSCs) have an established role in cancer progression and therapeutic resistance. The p63 proteins are important transcription factors which belong to the p53 family, but their function and mechanism in CSCs remain elusive. Here, we investigated the role of TAp63α in colorectal CSCs and the effects of sulforaphane on TAp63α. We found that TAp63α was upregulated in spheres with stem cell properties compared to the parental cells. Overexpression of TAp63α promoted self-renewal capacity and enhanced CSC markers expression in colorectal sphere-forming cells. Furthermore, we showed that TAp63α directly bound to the promoter region of Lgr5 to enhance its expression and activate its downstream β-catenin pathway. Functional experiments revealed that sulforaphane suppressed the stemness of colorectal CSCs both in vitro and in vivo. Upregulation of TAp63α attenuated the inhibitory effect of sulforaphane on colorectal CSCs, indicating the role of TAp63α in sulforaphane suppression of the stemness in colorectal cancer. The present study elucidated for the first time that TAp63α promoted CSCs through targeting Lgr5/β-catenin axis and participated in sulforaphane inhibition of the stem cell properties in colorectal cancer.

p63-related signaling at a glance

p63 (also known as TP63) is a transcription factor of the p53 family, along with p73. Multiple isoforms of p63 have been discovered and these have diverse functions encompassing a wide array of cell biology. p63 isoforms are implicated in lineage specification, proliferative potential, differentiation, cell death and survival, DNA damage response and metabolism. Furthermore, p63 is linked to human disease states including cancer. p63 is critical to many aspects of cell signaling, and in this Cell science at a glance article and the accompanying poster, we focus on the signaling cascades regulating TAp63 and ΔNp63 isoforms and those that are regulated by TAp63 and ΔNp63, as well the role of p63 in disease.

Molecular Mechanisms of the Teratogenic Effects of Thalidomide

Thalidomide was sold worldwide as a sedative over 60 years ago, but it was quickly withdrawn from the market due to its teratogenic effects. Thalidomide was later found to have therapeutic effects in several diseases, although the molecular mechanisms remained unclear. The discovery of cereblon (CRBN), the direct target of thalidomide, a decade ago greatly improved our understanding of its mechanism of action. Accumulating evidence has shown that CRBN functions as a substrate of Cullin RING E3 ligase (CRL4^CRBN), whose specificity is controlled by ligands such as thalidomide. For example, lenalidomide and pomalidomide, well-known thalidomide derivatives, degrade the neosubstrates Ikaros and Aiolos, resulting in anti-proliferative effects in multiple myeloma. Recently, novel CRBN-binding drugs have been developed. However, for the safe handling of thalidomide and its derivatives, a greater understanding of the mechanisms of its adverse effects is required. The teratogenic effects of thalidomide occur in multiple tissues in the developing fetus and vary in phenotype, making it difficult to clarify this issue. Recently, several CRBN neosubstrates (e.g., SALL4 (Spalt Like Transcription Factor 4) and p63 (Tumor Protein P63)) have been identified as candidate mediators of thalidomide teratogenicity. In this review, we describe the current understanding of molecular mechanisms of thalidomide, particularly in the context of its teratogenicity.

TAp63γ influences mouse cartilage development

Depletion of tumor protein p63 results in severe epithelial as well as limb defects in mice, suggesting that p63 is also required for endochondral ossification during long bone development. A key stage in endochondral ossification is chondrocyte hypertrophy, which has been associated with elevated levels of the p63 variant TAp63γ. To investigate the role of TAp63γ in chondrocyte differentiation and maturation, we developed stable TAp63γ expressing ATDC5 cells. Compared to control cells, TAp63γ cells showed significant upregulation of Col10a1 after 4 and 7 days in culture. Moreover, alkaline phosphatase, Alizarin red, and Alcian blue staining were stronger in TAp63γ cells, suggesting that TAp63γ promotes chondrocyte proliferation, hypertrophic differentiation, and possibly matrix mineralization. To investigate the in vivo function of TAp63γ during endochondral bone formation, we established transgenic mice that express flag-tagged TAp63γ driven by Col10a1 regulatory elements. Skeletal staining of transgenic mice at postnatal day 1 showed accelerated ossification in long bone, tail, and digit bones compared to wild-type littermates. Furthermore, Sox9 expression was reduced and Runx2 expression was increased in the proliferative and/or hypertrophic zones of these mice. Altogether, these results suggest that TAp63γ promotes endochondral ossification and skeletal development, at least partially via controlling chondrocyte differentiation and maturation.

Recent advances in the molecular mechanism of thalidomide teratogenicity

Thalidomide was first marketed in 1957 but soon withdrawn because of its notorious teratogenicity. Studies on the mechanism of action of thalidomide revealed the pleiotropic properties of this class of drugs, including their anti-inflammatory, antiangiogenic and immunomodulatory activities. Based on their notable activities, thalidomide and its analogues, lenalidomide and pomalidomide, have been repurposed to treat erythema nodosum leprosum, multiple myeloma and other haematological malignancies. Thalidomide analogues were recently found to hijack CRL4^CRBN ubiquitin ligase to target a number of cellular proteins for ubiquitination and proteasomal degradation. Thalidomide-mediated degradation of SALL4 and p63, transcription factors essential for embryonic development, very likely plays a critical role in thalidomide embryopathy. In this review, we provide a brief retrospective summary of thalidomide-induced teratogenesis, the mechanism of thalidomide activity, and the latest advances in the molecular mechanism of thalidomide-induced birth malformations.

Novel phenotype of syndromic premature ovarian insufficiency associated with TP63 molecular defect

There is growing evidence that TP63 is associated with isolated as well as syndromic premature ovarian insufficiency (POI). We report two adolescent sisters diagnosed with undetectable ovaries, uterine hypoplasia, and mammary gland hypoplasia. A novel paternally inherited nonsense variant in TP63 [NM_003722.4 c.1927C > T,p.(Arg643*)] in exon 14 was identified by exome sequencing. One of the syndromes linked to TP63 is limb mammary syndrome (LMS), an autosomal dominant inherited disorder characterized by ectrodactyly, hypoplasia of mammary-gland and nipple, lacrimal duct stenosis, nail dysplasia, dental anomalies, cleft palate and/or cleft lip and absence of skin and hair defects. The TP63 variant segregated with symptoms of LMS in the family, however, no affected individual had limb defects. The phenotype reported here represents a novel syndromic phenotype associated with TP63. Reported cases with TP63 associated POI are reviewed.

Molecular mechanisms of thalidomide and its derivatives

Thalidomide, originally developed as a sedative drug, causes multiple defects due to severe teratogenicity, but it has been re-purposed for treating multiple myeloma, and derivatives such as lenalidomide and pomalidomide have been developed for treating blood cancers. Although the molecular mechanisms of thalidomide and its derivatives remained poorly understood until recently, we identified cereblon (CRBN), a primary direct target of thalidomide, using ferrite glycidyl methacrylate (FG) beads. CRBN is a ligand-dependent substrate receptor of the E3 ubiquitin ligase complex cullin-RING ligase 4 (CRL4^CRBN). When a ligand such as thalidomide binds to CRBN, it recognizes various 'neosubstrates' depending on the shape of the ligand. CRL4^CRBN binds many neosubstrates in the presence of various ligands. CRBN has been utilized in a novel protein knockdown technology named proteolysis targeting chimeras (PROTACs). Heterobifunctional molecules such as dBET1 are being developed to specifically degrade proteins of interest. Herein, we review recent advances in CRBN research.

Cardioprotective mechanisms of salvianic acid A sodium in rats with myocardial infarction based on proteome and transcriptome analysis

Ischemic heart diseases (IHDs) cause great morbidity and mortality worldwide, necessitating effective treatment. Salvianic acid A sodium (SAAS) is an active compound derived from the well-known herbal medicine Danshen, which has been widely used for clinical treatment of cardiovascular diseases in China. This study aimed to confirm the cardioprotective effects of SAAS in rats with myocardial infarction and to investigate the underlying molecular mechanisms based on proteome and transcriptome profiling of myocardial tissue. The results showed that SAAS effectively protected against myocardial injury and improved cardiac function. The differentially expressed proteins and genes included important structural molecules, receptors, transcription factors, and cofactors. Functional enrichment analysis indicated that SAAS participated in the regulation of actin cytoskeleton, phagosome, focal adhesion, tight junction, apoptosis, MAPK signaling, and Wnt signaling pathways, which are closely related to cardiovascular diseases. SAAS may exert its cardioprotective effect by targeting multiple pathways at both the proteome and transcriptome levels. This study has provided not only new insights into the pathogenesis of myocardial infarction but also a road map of the cardioprotective molecular mechanisms of SAAS, which may provide pharmacological evidence to aid in its clinical application.

Master regulatory role of p63 in epidermal development and disease

The transcription factor p63 is a master regulator of epidermal development. Mutations in p63 give rise to human developmental diseases that often manifest epidermal defects. In this review, we summarize major p63 isoforms identified so far and p63 mutation-associated human diseases that show epidermal defects. We discuss key roles of p63 in epidermal keratinocyte proliferation and differentiation, emphasizing its master regulatory control of the gene expression pattern and epigenetic landscape that define epidermal fate. We subsequently review the essential function of p63 during epidermal commitment and transdifferentiation towards epithelial lineages, highlighting the notion that p63 is the guardian of the epithelial lineage. Finally, we discuss current therapeutic development strategies for p63 mutation-associated diseases. Our review proposes future directions for dissecting p63-controlled mechanisms in normal and diseased epidermal development and for developing therapeutic options.

DNA replication timing alterations identify common markers between distinct progeroid diseases

Progeroid syndromes are rare genetic disorders that phenotypically resemble natural aging. Different causal mutations have been identified, but no molecular alterations have been identified that are in common to these diseases. DNA replication timing (RT) is a robust cell type-specific epigenetic feature highly conserved in the same cell types from different individuals but altered in disease. Here, we characterized DNA RT program alterations in Hutchinson-Gilford progeria syndrome (HGPS) and Rothmund-Thomson syndrome (RTS) patients compared with natural aging and cellular senescence. Our results identified a progeroid-specific RT signature that is common to cells from three HGPS and three RTS patients and distinguishes them from healthy individuals across a wide range of ages. Among the RT abnormalities, we identified the tumor protein p63 gene (TP63) as a gene marker for progeroid syndromes. By using the redifferentiation of four patient-derived induced pluripotent stem cells as a model for the onset of progeroid syndromes, we tracked the progression of RT abnormalities during development, revealing altered RT of the TP63 gene as an early event in disease progression of both HGPS and RTS. Moreover, the RT abnormalities in progeroid patients were associated with altered isoform expression of TP63 Our findings demonstrate the value of RT studies to identify biomarkers not detected by other methods, reveal abnormal TP63 RT as an early event in progeroid disease progression, and suggest TP63 gene regulation as a potential therapeutic target.

Conditional ablation of p63 indicates that it is essential for embryonic development of the central nervous system

p63 is a member of the p53 family that regulates the survival of neural precursors in the adult brain. However, the relative importance of p63 in the developing brain is still unclear, since embryonic p63^−/− mice display no apparent deficits in neural development. Here, we have used a more definitive conditional knockout mouse approach to address this issue, crossing p63^fl/fl mice to mice carrying a nestin-CreERT2 transgene that drives inducible recombination in neural precursors following tamoxifen treatment. Inducible ablation of p63 following tamoxifen treatment of mice on embryonic day 12 resulted in highly perturbed forebrain morphology including a thinner cortex and enlarged lateral ventricles 3 d later. While the normal cortical layers were still present following acute p63 ablation, cortical precursors and neurons were both reduced in number due to widespread cellular apoptosis. This apoptosis was cell-autonomous, since it also occurred when p63 was inducibly ablated in primary cultured cortical precursors. Finally, we demonstrate increased expression of the mRNA encoding another p53 family member, ΔNp73, in cortical precursors of p63^−/− but not tamoxifen-treated p63^fl/fl;R26YFP^fl/fl;nestin-CreERT2^+/Ø embryos. Since ΔNp73 promotes cell survival, then this compensatory increase likely explains the lack of an embryonic brain phenotype in p63^−/− mice. Thus, p63 plays a key prosurvival role in the developing mammalian brain.

Transcriptional activator TAp63 is upregulated in muscular atrophy during ALS and induces the pro-atrophic ubiquitin ligase Trim63

Mechanisms of muscle atrophy are complex and their understanding might help finding therapeutic solutions for pathologies such as amyotrophic lateral sclerosis (ALS). We meta-analyzed transcriptomic experiments of muscles of ALS patients and mouse models, uncovering a p53 deregulation as common denominator. We then characterized the induction of several p53 family members (p53, p63, p73) and a correlation between the levels of p53 family target genes and the severity of muscle atrophy in ALS patients and mice. In particular, we observed increased p63 protein levels in the fibers of atrophic muscles via denervation-dependent and -independent mechanisms. At a functional level, we demonstrated that TAp63 and p53 transactivate the promoter and increased the expression of Trim63 (MuRF1), an effector of muscle atrophy. Altogether, these results suggest a novel function for p63 as a contributor to muscular atrophic processes via the regulation of multiple genes, including the muscle atrophy gene Trim63.

How Does p73 Cause Neuronal Defects?

The p53-family member, p73, plays a key role in the development of the central nervous system (CNS), in senescence, and in tumor formation. The role of p73 in neuronal differentiation is complex and involves several downstream pathways. Indeed, in the last few years, we have learnt that TAp73 directly or indirectly regulates several genes involved in neural biology. In particular, TAp73 is involved in the maintenance of neural stem/progenitor cell self-renewal and differentiation throughout the regulation of SOX-2, Hey-2, TRIM32 and Notch. In addition, TAp73 is also implicated in the regulation of the differentiation and function of postmitotic neurons by regulating the expression of p75NTR and GLS2 (glutamine metabolism). Further still, the regulation of miR-34a by TAp73 indicates that microRNAs can also participate in this multifunctional role of p73 in adult brain physiology. However, contradictory results still exist in the relationship between p73 and brain disorders, and this remains an important area for further investigation.

Transcriptional control of late differentiation in human keratinocytes by TAp63 and Notch

We previously showed that in cervical carcinoma cells, the TAp63β isoform of the p63 transcription factor is negatively interfering with the carcinogenic pathways promoting anchorage-independent growth. In this study, we have defined the mechanisms underlying the effects of TAp63β through a transcriptome analysis of human keratinocytes overexpressing this protein. TAp63β modulated expression of 1203 genes (944 activated and 259 repressed; P-value <0.05), notably genes involved in epithelial development and keratinocyte differentiation. In comparison, while TAp63γ acts similarly to TAp63β to transactivate a selected panel of target genes, other p63 isoforms, including ΔNp63α, which is highly expressed in keratinocytes, are inactive. Upon induction of differentiation of primary human keratinocytes, we observed endogenous expression of TAp63β and γ isoforms, along with transcriptional activation of selected target genes. Intriguingly, our data also indicated that TAp63β activates transcription of members of the Notch pathway, which is known to promote keratinocyte differentiation. By inhibiting and activating the Notch pathway, we revealed a subset of TAp63β-activated genes that were co-dependent on Notch for their expression. Our work demonstrates that the shorter TAp63 isoforms (TAp63β/γ) are specifically induced in human keratinocytes and cooperate with Notch signalling to activate transcription of late differentiation genes supporting their role as putative tumor suppressors in HPV-associated tumorigenesis.

Gene regulatory mechanisms orchestrated by p63 in epithelial development and related disorders

The transcription factor p63 belongs to the p53 family and is a key regulator in epithelial commitment and development. Mutations in p63 give rise to several epithelial related disorders with defects in skin, limb and orofacial structures. Since the discovery of p63, efforts have been made to identify its target genes using individual gene approaches and to understand p63 function in normal epithelial development and related diseases. Recent genome-wide approaches have identified tens of thousands of potential p63-regulated target genes and regulatory elements, and reshaped the concept of gene regulation orchestrated by p63. These data also provide insights into p63-related disease mechanisms. In this review, we discuss the regulatory role of p63 in normal and diseased epithelial development in light of these novel findings. We also propose future perspectives for dissecting the molecular mechanism of p63-mediated epithelial development and related disorders as well as for potential therapeutic strategies.

iASPP, a previously unidentified regulator of desmosomes, prevents arrhythmogenic right ventricular cardiomyopathy (ARVC)-induced sudden death

Desmosomes are anchoring junctions that exist in cells that endure physical stress such as cardiac myocytes. The importance of desmosomes in maintaining the homeostasis of the myocardium is underscored by frequent mutations of desmosome components found in human patients and animal models. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a phenotype caused by mutations in desmosomal components in ∼ 50% of patients, however, the causes in the remaining 50% of patients still remain unknown. A deficiency of inhibitor of apoptosis-stimulating protein of p53 (iASPP), an evolutionarily conserved inhibitor of p53, caused by spontaneous mutation recently has been associated with a lethal autosomal recessive cardiomyopathy in Poll Hereford calves and Wa3 mice. However, the molecular mechanisms that mediate this putative function of iASPP are completely unknown. Here, we show that iASPP is expressed at intercalated discs in human and mouse postmitotic cardiomyocytes. iASPP interacts with desmoplakin and desmin in cardiomyocytes to maintain the integrity of desmosomes and intermediate filament networks in vitro and in vivo. iASPP deficiency specifically induces right ventricular dilatation in mouse embryos at embryonic day 16.5. iASPP-deficient mice with exon 8 deletion (Ppp1r13l(Δ8/Δ8)) die of sudden cardiac death, displaying features of ARVC. Intercalated discs in cardiomyocytes from four of six human ARVC cases show reduced or loss of iASPP. ARVC-derived desmoplakin mutants DSP-1-V30M and DSP-1-S299R exhibit weaker binding to iASPP. These data demonstrate that by interacting with desmoplakin and desmin, iASPP is an important regulator of desmosomal function both in vitro and in vivo. This newly identified property of iASPP may provide new molecular insight into the pathogenesis of ARVC.

Transcriptional response to cardiac injury in the zebrafish: systematic identification of genes with highly concordant activity across in vivo models

Background

Zebrafish is a clinically-relevant model of heart regeneration. Unlike mammals, it has a remarkable heart repair capacity after injury, and promises novel translational applications. Amputation and cryoinjury models are key research tools for understanding injury response and regeneration in vivo. An understanding of the transcriptional responses following injury is needed to identify key players of heart tissue repair, as well as potential targets for boosting this property in humans.

Results

We investigated amputation and cryoinjury in vivo models of heart damage in the zebrafish through unbiased, integrative analyses of independent molecular datasets. To detect genes with potential biological roles, we derived computational prediction models with microarray data from heart amputation experiments. We focused on a top-ranked set of genes highly activated in the early post-injury stage, whose activity was further verified in independent microarray datasets. Next, we performed independent validations of expression responses with qPCR in a cryoinjury model. Across in vivo models, the top candidates showed highly concordant responses at 1 and 3 days post-injury, which highlights the predictive power of our analysis strategies and the possible biological relevance of these genes. Top candidates are significantly involved in cell fate specification and differentiation, and include heart failure markers such as periostin, as well as potential new targets for heart regeneration. For example, ptgis and ca2 were overexpressed, while usp2a, a regulator of the p53 pathway, was down-regulated in our in vivo models. Interestingly, a high activity of ptgis and ca2 has been previously observed in failing hearts from rats and humans.

Conclusions

We identified genes with potential critical roles in the response to cardiac damage in the zebrafish. Their transcriptional activities are reproducible in different in vivo models of cardiac injury.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-852) contains supplementary material, which is available to authorized users.

All-trans-retinoid acid (ATRA) suppresses chondrogenesis of rat primary hind limb bud mesenchymal cells by downregulating p63 and cartilage-specific molecules

P63 null mice have no or truncated limbs and mutations in human p63 cause several skeletal syndromes that also show limb and digit abnormalities, suggesting its essential role in bone development. In the current study, we investigated the effect of ATRA on chondrogenesis using mesenchymal cells from rat hind limb bud and further examined the mRNA and protein expression of Sox9 and Col2a1 and p63 in rat hind limb bud cells. Limb buds were isolated from embryos from euthanized female rats. Growth of hind limb bud mesenchymal cells was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assays. Formation of cartilage nodules was examined by Alcian blue-nuclear fast red staining. The expression of Sox9, Col2al and p63 was determined by Real-time RT-PCR and immunoblotting assays, respectively. Our MTT assays revealed that ATRA at 1 and 10μM significantly suppressed the growth of mesenchymal cells from rat hind limb bud at 24 and 48h (P<0.01 vs. controls). Alcian blue staining further showed that ATRA caused a significant dose-dependent reduction in the area of cartilage nodules (P<0.05 in all vs. controls). At 1μM ATRA, the area of cartilage nodules from hind limb bud cells was reduced to 0.05±0.03mm from 0.15±0.01mm in controls. Real-time RT-PCR assays further indicated that 1 and 10μM ATRA markedly reduced the mRNA expression of Sox9, Col2al and p63 in hind limb bud cells (P<0.05 in all vs. controls). In addition, ATRA time-dependently inhibits the mRNA expression of p63, Sox9 and Col2al. Western blotting assays additionally showed that ATRA dose-dependently reduced the expression of Sox9, Col2al and p63 (P<0.05 in all vs. controls). Together, our results suggest that ATRA suppresses chondrogenesis by modulating the expression of Sox9, Col2al and p63 in primary hind limb bud mesenchymal cells.

Tissue microarray technology and findings for diagnostic immunohistochemistry

AIMS

This study was undertaken to determine the validity and viability of tissue microarray (TMA) technology in assessing diagnostic immunohistochemistry (IHC) at a single laboratory site.

METHODS

IHC using 57 primary antibodies was performed on a TMA paraffin block containing 89 cores of duplicate previously identified 1 mm diameter tissue specimens. IHC was interpreted by a histology scientist with IHC experience, with pathologist assistance if required. Review of the literature was performed to investigate cases of unexpected immunoreactivity.

RESULTS

55 of 57 antibodies had expected positive staining against the TMA tissue panel that correlated with the original paraffin blocks. Immunostaining of duplicate 1 mm cores correlated with the originally sourced paraffin block in 42 of 43 (98%) tissue types. Some antibodies had unexpected positive immunoreactivity.

DISCUSSION

TMA technology can be utilised effectively in the diagnostic IHC laboratory as a universal positive multiple tissue control block for routine IHC, and can provide valuable information for the benefit of histology scientists and pathologists with respect to interpretation of IHC staining.

Transcriptional networks regulating the costamere, sarcomere, and other cytoskeletal structures in striated muscle

Structural abnormalities in striated muscle have been observed in numerous transcription factor gain- and loss-of-function phenotypes in animal and cell culture model systems, indicating that transcription is important in regulating the cytoarchitecture. While most characterized cytoarchitectural defects are largely indistinguishable by histological and ultrastructural criteria, analysis of dysregulated gene expression in each mutant phenotype has yielded valuable information regarding specific structural gene programs that may be uniquely controlled by each of these transcription factors. Linking the formation and maintenance of each subcellular structure or subset of proteins within a cytoskeletal compartment to an overlapping but distinct transcription factor cohort may enable striated muscle to control cytoarchitectural function in an efficient and specific manner. Here we summarize the available evidence that connects transcription factors, those with established roles in striated muscle such as MEF2 and SRF, as well as other non-muscle transcription factors, to the regulation of a defined cytoskeletal structure. The notion that genes encoding proteins localized to the same subcellular compartment are coordinately transcriptionally regulated may prompt rationally designed approaches that target specific transcription factor pathways to correct structural defects in muscle disease.

Angiomodulin is required for cardiogenesis of embryonic stem cells and is maintained by a feedback loop network of p63 and Activin-A

The transcription factor p63, member of the p53 gene family, encodes for two main isoforms, TAp63 and ΔNp63 with distinct functions on epithelial homeostasis and cancer. Recently, we discovered that TAp63 is essential for in vitro cardiogenesis and heart development in vivo. TAp63 is expressed by embryonic endoderm and acts on cardiac progenitors by a cell-non-autonomous manner. In the present study, we search for cardiogenic secreted factors that could be regulated by TAp63 and, by ChIP-seq analysis, identified Angiomodulin (AGM), also named IGFBP7 or IGFBP-rP1. We demonstrate that AGM is necessary for cardiac commitment of embryonic stem cells (ESCs) and its regulation depends on TAp63 isoform. TAp63 directly activates both AGM and Activin-A during ESC cardiogenesis while these secreted factors modulate TAp63 gene expression by a feedback loop mechanism. The molecular circuitry controlled by TAp63 on AGM/Activin-A signaling pathway and thus on cardiogenesis emphasizes the importance of p63 during early cardiac development.

Role of p63 and the Notch pathway in cochlea development and sensorineural deafness

The ectodermal dysplasias are a group of inherited autosomal dominant syndromes associated with heterozygous mutations in the Tumor Protein p63 (TRP63) gene. Here we show that, in addition to their epidermal pathology, a proportion of these patients have distinct levels of deafness. Accordingly, p63 null mouse embryos show marked cochlea abnormalities, and the transactivating isoform of p63 (TAp63) protein is normally found in the organ of Corti. TAp63 transactivates hairy and enhancer of split 5 (Hes5) and atonal homolog 1 (Atoh1), components of the Notch pathway, known to be involved in cochlear neuroepithelial development. Strikingly, p63 null mice show morphological defects of the organ of Corti, with supernumerary hair cells, as also reported for Hes5 null mice. This phenotype is related to loss of a differentiation property of TAp63 and not to loss of its proapoptotic function, because cochleas in mice lacking the critical Bcl-2 homology domain (BH-3) inducers of p53- and p63-mediated apoptosis--Puma, Noxa, or both--are normal. Collectively, these data demonstrate that TAp63, acting via the Notch pathway, is crucial for the development of the organ of Corti, providing a molecular explanation for the sensorineural deafness in ectodermal dysplasia patients with TRP63 mutations.

A step closer toward therapies for p63-related disorders

Small molecules with low molecular weight are of interest for drug development, as they are more likely to be absorbed. In cancer research, p53 is often mutated in many tumors, and many small molecules targeting mutant p53 have been tested. One of such low molecular weight compounds is APR246/PRIMA-1^MET that was identified as a compound targeting and reactivating p53 mutants based on a cell-based screening for rescuing the apoptotic activity of p53. Recently, we have reported two different model systems, (1) corneal epithelial cells differentiated from induced pluripotent stem cells (iPSCs) derived from reprogramming of patient fibroblasts and (2) skin organotypic reconstitution of patient-derived keratinocytes. We have shown that APR246/PRIMA-1^MET can rescue epithelial differentiation defects caused by mutations in p63 that is a family member of p53 and shares high sequence and structural similarity with the p53 protein.^1,2 The rationale of the two cellular models for drug screening and the potential of APR246/PRIMA-1^MET to restore visual impairment of patients are discussed (Fig. 1).

Distinct function of P63 isoforms during embryonic skeletal development

P63 belongs to the P53 family of transcription factors. There are multiple P63 isoforms that play important functions both in cancer and development. The obvious limb defect in p63 null mice and in human skeletal syndromes with P63 mutations suggest its essential role in long bone development. However, how the different P63 isoforms function during long bone development is largely unknown. We have previously shown that TAP63α, the longest P63 isoform, plays a positive role in embryonic skeletal development, since targeting TAP63α expression in hypertrophic chondrocytes accelerates endochondral ossification at both E17.5 and P1 stages. Here, we report transgenic studies of ΔNP63α, another P63 isoform which lacks the N-terminal transactivation domain compared to TAP63α, using the same hypertrophic chondrocyte-specific Col10a1 control element. No skeletal abnormalities were detected in these Col10a1-ΔNP63α transgenic mice at both E17.5 and P1 stages, suggesting less importance of ΔNP63α during late embryonic skeletal development. To further investigate the function of P63 isoforms during early skeletal development, we have generated ΔNP63α and TAP63α transgenic mice using a chondrocyte-specific Col2a1 control element. Surprisingly, while no skeletal defect was shown in the Col2a1-ΔNP63α transgenic mice, reduced ossification was observed in the digit and tail bones of Col2a1-TAP63α transgenic mice at both E17.5 and P1 stages compared to their wild-type littermates. Expression profiling and immunohistochemical analysis detected upregulated expression of Sox9, a major negative regulator of endochondral ossification, in Col2a1-TAP63α transgenic mice. Taken together, our results suggest a distinct function of P63 isoforms, herein, ΔNP63α and TAP63α, during endochondral ossification.

Early cardiac development: a view from stem cells to embryos

From the 1920s, early cardiac development has been studied in chick and, later, in mouse embryos in order to understand the first cell fate decisions that drive specification and determination of the endocardium, myocardium, and epicardium. More recently, mouse and human embryonic stem cells (ESCs) have demonstrated faithful recapitulation of early cardiogenesis and have contributed significantly to this research over the past few decades. Derived almost 15 years ago, human ESCs have provided a unique developmental model for understanding the genetic and epigenetic regulation of early human cardiogenesis. Here, we review the biological concepts underlying cell fate decisions during early cardiogenesis in model organisms and ESCs. We draw upon both pioneering and recent studies and highlight the continued role for in vitro stem cells in cardiac developmental biology.

APPRIS: annotation of principal and alternative splice isoforms

Here, we present APPRIS (http://appris.bioinfo.cnio.es), a database that houses annotations of human splice isoforms. APPRIS has been designed to provide value to manual annotations of the human genome by adding reliable protein structural and functional data and information from cross-species conservation. The visual representation of the annotations provided by APPRIS for each gene allows annotators and researchers alike to easily identify functional changes brought about by splicing events. In addition to collecting, integrating and analyzing reliable predictions of the effect of splicing events, APPRIS also selects a single reference sequence for each gene, here termed the principal isoform, based on the annotations of structure, function and conservation for each transcript. APPRIS identifies a principal isoform for 85% of the protein-coding genes in the GENCODE 7 release for ENSEMBL. Analysis of the APPRIS data shows that at least 70% of the alternative (non-principal) variants would lose important functional or structural information relative to the principal isoform.

CEL-Seq: single-cell RNA-Seq by multiplexed linear amplification

High-throughput sequencing has allowed for unprecedented detail in gene expression analyses, yet its efficient application to single cells is challenged by the small starting amounts of RNA. We have developed CEL-Seq, a method for overcoming this limitation by barcoding and pooling samples before linearly amplifying mRNA with the use of one round of in vitro transcription. We show that CEL-Seq gives more reproducible, linear, and sensitive results than a PCR-based amplification method. We demonstrate the power of this method by studying early C. elegans embryonic development at single-cell resolution. Differential distribution of transcripts between sister cells is seen as early as the two-cell stage embryo, and zygotic expression in the somatic cell lineages is enriched for transcription factors. The robust transcriptome quantifications enabled by CEL-Seq will be useful for transcriptomic analyses of complex tissues containing populations of diverse cell types.

Pluripotent stem cell model reveals essential roles for miR-450b-5p and miR-184 in embryonic corneal lineage specification

Approximately 6 million people worldwide are suffering from severe visual impairments or blindness due to corneal diseases. Corneal allogeneic transplantation is often required to restore vision; however, shortage in corneal grafts and immunorejections remain major challenges. The molecular basis of corneal diseases is poorly understood largely due to lack of appropriate cellular models. Here, we described a robust differentiation of human-induced pluripotent stem cells (hiPSCs) derived from hair follicles or skin fibroblasts into corneal epithelial-like cells. We found that BMP4, coupled with corneal fibroblast-derived conditioned medium and collagen IV allowed efficient corneal epithelial commitment of hiPSCs in a manner that recapitulated corneal epithelial lineage development with high purity. Organotypic reconstitution assays suggested the ability of these cells to stratify into a corneal-like epithelium. This model allowed us identifying miR-450b-5p as a molecular switch of Pax6, a major regulator of eye development. miR-450b-5p and Pax6 were reciprocally distributed at the presumptive epidermis and ocular surface, respectively. miR-450b-5p inhibited Pax6 expression and corneal epithelial fate in vitro, altogether, suggesting that by repressing Pax6, miR-450b-5p triggers epidermal specification of the ectoderm, while its absence allows ocular epithelial development. Additionally, miR-184 was detectable in early eye development and corneal epithelial differentiation of hiPSCs. The knockdown of miR-184 resulted in a decrease in Pax6 and K3, in line with recent findings showing that a point mutation in miR-184 leads to corneal dystrophy. Altogether, these data indicate that hiPSCs are valuable for modeling corneal development and may pave the way for future cell-based therapy.

Ghrelin induces cardiac lineage differentiation of human embryonic stem cells through ERK1/2 pathway

BACKGROUND

Ghrelin, an endogenous ligand for growth hormone secretagogue receptor (GHS-R), shows cardioprotective activity and regulates the differentiation of several mesoderm-derived cells, including myocytes, adipocytes and osteoblasts. The effect of ghrelin on cardiogenesis and its underlying mechanism, however, have not been studied in detail.

METHODS

The effects of ghrelin on cardiomyocyte differentiation were tested both in human embryonic stem cells (hESCs) cultured in embryoid body (EB)-based differentiation protocol, and in hESCs transplanted into rat hearts. The signaling mechanisms of ghrelin were further investigated under the EB-based culture condition.

RESULTS

The generation of beating EBs and the expression of cardiac-specific markers including cardiac troponin I (cTnI) and α-myosin heavy chain (α-MHC) were 2 to 3-fold upregulated by ghrelin. Although GHS-R1α protein was expressed in differentiated EBs, the effects of exogenous ghrelin were unchanged by D-[lys(3)]-GHRP-6, a specific GHS-R1α antagonist. Moreover, des-acyl ghrelin, which does not bind to GHS-R1α, displayed similar effects with ghrelin. Importantly, activation of ERK1/2, but not Akt, was induced by ghrelin in the newly-formed EBs, and the ghrelin-induced effects of cardiomyocyte differentiation were abolished by adding specific ERK1/2 inhibitor PD98059, but not specific PI3K inhibitor Wortmannin. In addition, ghrelin promoted the differentiation of grafted hESCs into Sox9- and Flk1-positive mesodermal/cardiac progenitor cells in rat hearts.

CONCLUSIONS

These results suggest that ghrelin induces cardiomyocyte differentiation from hESCs via the activation of the ERK1/2 signaling pathway. Our study, therefore, indicates that using ghrelin may be an effective strategy to promote the differentiation of hESCs into cardiomyocytes.

[The two faces of p63, Janus of the p53 gene family]

The TP53 family member TP63 encodes two main isoforms TAp63 and ΔNp63 with distinct, often opposite functions during development and in the adult. ΔNp63 is crucial for the formation of the ectodermal derivatives and epidermis, while TAp63 is essential for heart development. In the adult, ΔNp63 behaves as a cell survival factor, controlling cell proliferation, adhesion and cell differentiation. In contrast, TAp63 is a proapoptotic factor that protects oocytes from genotoxic insults and prevents premature aging of dermal stem cells. In agreement with these activities, TAp63 is often lost and ΔNp63 overexpressed in cancer cells. Because of their opposite and competitive effects, p63 isoforms could be viewed as Janus two faces. The review focuses on the accumulating data on the p63 functions and regulation in the last decade.

Notch signaling and cardiac repair

Notch signaling is critical for proper heart development and recently has been reported to participate in adult cardiac repair. Notch resides at the cell surface as a single pass transmembrane receptor, transits through the cytoplasm following activation, and acts as a transcription factor upon entering the nucleus. This dynamic and widespread cellular distribution allows for potential interactions with many signaling and binding partners. Notch displays temporal as well as spatial versatility, acting as a strong developmental signal, controlling cell fate determination and lineage commitment, and playing a pivotal role in embryonic and adult stem cell proliferation and differentiation. This review serves as an update of recent literature addressing Notch signaling in the heart, with attention to findings from noncardiac research that provide clues for further interpretation of how the Notch pathway influences cardiac biology. Specific areas of focus include Notch signaling in adult myocardium following pathologic injury, the role of Notch in cardiac progenitor cells with respect to differentiation and cardiac repair, crosstalk between Notch and other cardiac signaling pathways, and emerging aspects of noncanonical Notch signaling in heart.

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.