Risk and Resilience Variants in the Retinoic Acid Metabolic and Developmental Pathways Associated with Risk of FASD Outcomes.

Fetal Alcohol Spectrum Disorder (FASD) is a common neurodevelopmental disorder that affects an estimated 2-5% of North Americans. FASD is induced by prenatal alcohol exposure (PAE) during pregnancy and while there is a clear genetic contribution, few genetic factors are currently identified or understood. In this study, using a candidate gene approach, we performed a genetic variant analysis of retinoic acid (RA) metabolic and developmental signaling pathway genes on whole exome sequencing data of 23 FASD-diagnosed individuals. We found risk and resilience alleles in ADH and ALDH genes known to normally be involved in alcohol detoxification at the expense of RA production, causing RA deficiency, following PAE. Risk and resilience variants were also identified in RA-regulated developmental pathway genes, especially in SHH and WNT pathways. Notably, we also identified significant variants in the causative genes of rare neurodevelopmental disorders sharing comorbidities with FASD, including STRA6 (Matthew-Wood), SOX9 (Campomelic Dysplasia), FDG1 (Aarskog), and 22q11.2 deletion syndrome (TBX1). Although this is a small exploratory study, the findings support PAE-induced RA deficiency as a major etiology underlying FASD and suggest risk and resilience variants may be suitable biomarkers to determine the risk of FASD outcomes following PAE.

Budget Impact Analysis of an Epigenetic Test Used for Diagnosing Fetal Alcohol Spectrum Disorder from the Perspective of a Laboratory Budget Holder in Manitoba, Canada.

BACKGROUND AND AIMS: Fetal alcohol spectrum disorder (FASD) is a condition that results from prenatal alcohol exposure. Though diagnosis is important for individuals with FASD to receive appropriate care, diagnosis can be difficult to obtain. Accurate diagnoses can be impeded because of an inability to confirm prenatal alcohol exposure. This is particularly problematic in instances when family cannot confirm prenatal alcohol exposure. DNA methylation testing represents a novel approach to identifying prenatal alcohol exposure via epigenetic biomarkers. The objective was to assess the impact on laboratory expenditures from adopting DNA methylation additively to the diagnostic workup for patients suspected of having FASD for whom prenatal alcohol exposure cannot be otherwise confirmed. METHODS: A budget impact model was developed that incorporates laboratory cost data, population data for Manitoba Canada, literature, and expert opinion. Probabilistic analysis was conducted for the primary analysis and deterministic sensitivity analyses were conducted to assess the sensitivity of the budget impact to changes in model parameters. The perspective of the present study is that of the laboratory budget holder at a centralized laboratory in Manitoba, Canada. RESULTS: Over a 5-year period, it was estimated that there would be 500 DNA methylation tests and the predicted budget impact to the laboratory budget holder was $207,574 (95% credible interval: 70,208-408,161) in Canadian dollars (CAD). Over a 10-year period, it was estimated that there would be 1017 DNA methylation tests and the predicted budget impact to the laboratory budget holder was CAD$439,470 (95% credible interval: 148,902-867,328). CONCLUSIONS: Findings provide insight into the impact that DNA methylation testing would have on laboratory budgets if used in the diagnostic workup for FASD in individuals for whom prenatal alcohol exposure cannot be confirmed otherwise.

A novel, ataxic mouse model of ataxia telangiectasia caused by a clinically relevant nonsense mutation.

Ataxia Telangiectasia (A-T) and Ataxia with Ocular Apraxia Type 1 (AOA1) are devastating neurological disorders caused by null mutations in the genome stability genes, A-T mutated (ATM) and Aprataxin (APTX), respectively. Our mechanistic understanding and therapeutic repertoire for treating these disorders are severely lacking, in large part due to the failure of prior animal models with similar null mutations to recapitulate the characteristic loss of motor coordination (i.e., ataxia) and associated cerebellar defects. By increasing genotoxic stress through the insertion of null mutations in both the Atm (nonsense) and Aptx (knockout) genes in the same animal, we have generated a novel mouse model that for the first time develops a progressively severe ataxic phenotype associated with atrophy of the cerebellar molecular layer. We find biophysical properties of cerebellar Purkinje neurons (PNs) are significantly perturbed (e.g., reduced membrane capacitance, lower action potential [AP] thresholds, etc.), while properties of synaptic inputs remain largely unchanged. These perturbations significantly alter PN neural activity, including a progressive reduction in spontaneous AP firing frequency that correlates with both cerebellar atrophy and ataxia over the animal's first year of life. Double mutant mice also exhibit a high predisposition to developing cancer (thymomas) and immune abnormalities (impaired early thymocyte development and T-cell maturation), symptoms characteristic of A-T. Finally, by inserting a clinically relevant nonsense-type null mutation in Atm, we demonstrate that Small Molecule Read-Through (SMRT) compounds can restore ATM production, indicating their potential as a future A-T therapeutic.

Genomic Analysis of Localized High-Risk Prostate Cancer Circulating Tumor Cells at the Single-Cell Level.

Accurate risk classification of men with localized high-risk prostate cancer directly affects treatment management decisions and patient outcomes. A wide range of risk assessments and classifications are available. However, each one has significant limitations to distinguish between indolent and aggressive prostate cancers. Circulating tumor cells (CTCs) may provide an alternate additional source, beyond tissue biopsies, to enable individual patient-specific clinical assessment, simply because CTCs can reveal both tumor-derived and germline-specific genetic information more precisely than that gained from a single diagnostic biopsy. In this study, we combined a filtration-based CTC isolation technology with prostate cancer CTC immunophenotyping to identify prostate cancer CTCs. Next, we performed 3-D telomere profiling prior to laser microdissection and single-cell whole-exome sequencing (WES) of 21 CTCs and 4 lymphocytes derived from 10 localized high-risk prostate cancer patient samples. Localized high-risk prostate cancer patient CTCs present a high number of telomere signals with lower signal intensities (short telomeres). To capture the genetic diversity/heterogeneity of high-risk prostate cancer CTCs, we carried out whole-exome sequencing. We identified 202,241 single nucleotide variants (SNVs) and 137,407 insertion-deletions (indels), where less than 10% of these genetic variations were within coding regions. The genetic variation (SNVs + indels) and copy number alteration (CNAs) profiles were highly heterogeneous and intra-patient CTC variation was observed. The pathway enrichment analysis showed the presence of genetic variation in nine telomere maintenance pathways (patients 3, 5, 6, and 7), including an important gene for telomere maintenance called telomeric repeat-binding factor 2 (TRF2). Using the PharmGKB database, we identified nine genetic variations associated with response to docetaxel. A total of 48 SNVs can affect drug response for 24 known cancer drugs. Gene Set Enrichment Analysis (GSEA) (patients 1, 3, 6, and 8) identified the presence of CNAs in 11 different pathways, including the DNA damage repair (DDR) pathway. In conclusion, single-cell approaches (WES and 3-D telomere profiling) showed to be useful in unmasking CTC heterogeneity. DDR pathway mutations have been well-established as a target pathway for cancer therapy. However, the frequent CNA amplifications found in localized high-risk patients may play critical roles in the therapeutic resistance in prostate cancer.

The Canadian Rare Diseases Models and Mechanisms (RDMM) Network: Connecting Understudied Genes to Model Organisms.

Advances in genomics have transformed our ability to identify the genetic causes of rare diseases (RDs), yet we have a limited understanding of the mechanistic roles of most genes in health and disease. When a novel RD gene is first discovered, there is minimal insight into its biological function, the pathogenic mechanisms of disease-causing variants, and how therapy might be approached. To address this gap, the Canadian Rare Diseases Models and Mechanisms (RDMM) Network was established to connect clinicians discovering new disease genes with Canadian scientists able to study equivalent genes and pathways in model organisms (MOs). The Network is built around a registry of more than 500 Canadian MO scientists, representing expertise for over 7,500 human genes. RDMM uses a committee process to identify and evaluate clinician-MO scientist collaborations and approve 25,000 Canadian dollars in catalyst funding. To date, we have made 85 clinician-MO scientist connections and funded 105 projects. These collaborations help confirm variant pathogenicity and unravel the molecular mechanisms of RD, and also test novel therapies and lead to long-term collaborations. To expand the impact and reach of this model, we made the RDMM Registry open-source, portable, and customizable, and we freely share our committee structures and processes. We are currently working with emerging networks in Europe, Australia, and Japan to link international RDMM networks and registries and enable matches across borders. We will continue to create meaningful collaborations, generate knowledge, and advance RD research locally and globally for the benefit of patients and families living with RD.

Genome-Wide Transcriptome Landscape of Embryonic Brain-Derived Neural Stem Cells Exposed to Alcohol with Strain-Specific Cross-Examination in BL6 and CD1 Mice.

We have previously reported the deregulatory impact of ethanol on global DNA methylation of brain-derived neural stem cells (NSC). Here, we conducted a genome-wide RNA-seq analysis in differentiating NSC exposed to different modes of ethanol exposure. RNA-seq results showed distinct gene expression patterns and canonical pathways induced by ethanol exposure and withdrawal. Short-term ethanol exposure caused abnormal up-regulation of synaptic pathways, while continuous ethanol treatment profoundly affected brain cells' morphology. Ethanol withdrawal restored the gene expression profile of differentiating NSC without rescuing impaired expression of epigenetics factors. Ingenuity Pathway Analysis (IPA) analysis predicated that ethanol may impact synaptic functions via GABA receptor signalling pathway and affects neural system and brain morphology. We identified Sptbn2, Dcc, and Scn3a as candidate genes which may link alcohol-induced neuronal morphology to brain structural abnormalities, predicted by IPA analysis. Cross-examination of Scn3a and As3mt in differentiated NSC from two different mouse strains (BL6 and CD1) showed a consistent pattern of induction and reduction, respectively. Collectively, our study identifies genetic networks, which may contribute to alcohol-mediated cellular and brain structural dysmorphology, contributing to our knowledge of alcohol-mediated damage to central nervous system, paving the path for better understanding of FASD pathobiology.

Insights into retinoic acid deficiency and the induction of craniofacial malformations and microcephaly in fetal alcohol spectrum disorder.

Fetal Alcohol Spectrum Disorder (FASD) is a set of neurodevelopmental malformations caused by maternal consumption of alcohol during pregnancy. FASD sentinel facial features are unique to the disorder, and microcephaly is common in severe forms of FASD. Retinoic acid deficiency has been shown to cause craniofacial malformations and microcephaly in animal models reminiscent of those caused by prenatal alcohol exposure. Alcohol exposure affects the migration and survival of cranial neural crest cells, which are required for proper frontonasal prominence and pharyngeal arch development. Defects in craniofacial development are further amplified by the many downstream pathways that are transcriptionally controlled retinoic acid target genes, including Shh signaling. Recent evidence shows that alcohol exposure itself is sufficient to induce retinoic acid deficiency in the embryo. These data suggest that retinoic acid deficiency is an important underlying etiology of FASD. In disorders like Vitamin A Deficiency, FASD, DiGeorge (22q11.2 Deletion Syndrome), CHARGE, Smith-Magenis, Matthew-Wood, and Congenital Zika Syndromes, evidence is accumulating to link reduced retinoic acid signaling with developmental defects like craniofacial malformations and microcephaly. Research focus on characterizing the effects of retinoic acid deficiency during early development and on understanding the downstream signaling pathways involved in aberrant head, and craniofacial development will reveal underlying etiologies of these disorders.

ALS/FTD-Linked Mutation in FUS Suppresses Intra-axonal Protein Synthesis and Drives Disease Without Nuclear Loss-of-Function of FUS.

Through the generation of humanized FUS mice expressing full-length human FUS, we identify that when expressed at near endogenous murine FUS levels, both wild-type and ALS-causing and frontotemporal dementia (FTD)-causing mutations complement the essential function(s) of murine FUS. Replacement of murine FUS with mutant, but not wild-type, human FUS causes stress-mediated induction of chaperones, decreased expression of ion channels and transporters essential for synaptic function, and reduced synaptic activity without loss of nuclear FUS or its cytoplasmic aggregation. Most strikingly, accumulation of mutant human FUS is shown to activate an integrated stress response and to inhibit local, intra-axonal protein synthesis in hippocampal neurons and sciatic nerves. Collectively, our evidence demonstrates that human ALS/FTD-linked mutations in FUS induce a gain of toxicity that includes stress-mediated suppression in intra-axonal translation, synaptic dysfunction, and progressive age-dependent motor and cognitive disease without cytoplasmic aggregation, altered nuclear localization, or aberrant splicing of FUS-bound pre-mRNAs. VIDEO ABSTRACT.

Copy number variation in fetal alcohol spectrum disorder.

Fetal alcohol spectrum disorder (FASD) is characterized by a combination of neurological, developmental, and congenital defects that may occur as a consequence of prenatal alcohol exposure. Earlier reports showed that large chromosomal anomalies may link to FASD. Here, we examined the prevalence and types of copy number variations (CNVs) in FASD cases previously diagnosed by a multidisciplinary FASD team in sites across Canada. We genotyped 95 children with FASD and 87 age-matched, typically developing controls on the Illumina Human Omni2.5 SNP (single nucleotide polymorphisms) array platform. We compared their CNVs with those of 10 851 population controls to identify rare CNVs (<0.1% frequency), which may include large unbalanced chromosomal abnormalities, that might be relevant to FASD. In 12/95 (13%) of the FASD cases, rare CNVs were found that impact potentially clinically relevant developmental genes, including the CACNA1H involved in epilepsy and autism, the 3q29 deletion disorder, and others. Our results show that a subset of children diagnosed with FASD have chromosomal deletions and duplications that may co-occur or explain the neurodevelopmental impairments in a diagnosed cohort of FASD individuals. Children suspected to have FASD with or without sentinel facial features of fetal alcohol syndrome and neurodevelopmental delays should potentially be evaluated by a clinical geneticist and possibly have genetic investigations as appropriate to exclude other etiologies.

Translating to the Community (T2C): a protocol paper describing the development of Canada's first social epigenetic FASD biobank.

Translating to the Community (T2C) is a social biorepository designed to advance new diagnostic tools and realign community-clinical processes, with the aim to mitigate the short- and long-term impacts of fetal alcohol spectrum disorder (FASD) as well as prenatal alcohol exposure and its co-morbidities and behaviors. In this paper, we describe the evolution of this repository as a new translational partnership to advance a precision-medicine approach to FASD. Key to its evolution was a partnership between academic researchers, Indigenous communities, families, and a regional diagnostic clinic. We further describe the rationale for social biobanking, the type of banking, ethical engagement of families, communities, and clinics, their roles in repository design, governance, translation, and research activities, types of data collected from families, and how the study data are managed, reported, and accessed. The repository design includes biological samples, social-contextual health-survey data, and clinical data (which are linkable to administrative data) from community and clinical cohorts of diagnosed children, children prenatally exposed but not diagnosed, children suspected to have had a prenatal exposure, and related siblings, biological parents, and unrelated children and their parents. From these cohorts and families, potential studies drawing on this data will shed light on various risk factors, social and biological pathways, and service utilization issues, with the aim to implement primary and secondary prevention and intervention strategies.

Effects of prenatal alcohol exposure (PAE): insights into FASD using mouse models of PAE.

The potential impact of prenatal alcohol exposure (PAE) varies considerably among exposed individuals, with some displaying serious alcohol-related effects and many others showing few or no overt signs of fetal alcohol spectrum disorder (FASD). In animal models, variables such as nutrition, genetic background, health, other drugs, and stress, as well as dosage, duration, and gestational timing of exposure to alcohol can all be controlled in a way that is not possible in a clinical situation. In this review we examine mouse models of PAE and focus on those with demonstrated craniofacial malformations, abnormal brain development, or behavioral phenotypes that may be considered FASD-like outcomes. Analysis of these data should provide a valuable tool for researchers wishing to choose the PAE model best suited to their research questions or to investigate established PAE models for FASD comorbidities. It should also allow recognition of patterns linking gestational timing, dosage, and duration of PAE, such as recognizing that binge alcohol exposure(s) during early gestation can lead to severe FASD outcomes. Identified patterns could be particularly insightful and lead to a better understanding of the molecular mechanisms underlying FASD.

MicroRNA-200b regulates distal airway development by maintaining epithelial integrity.

miR-200b plays a role in epithelial-to-mesenchymal transition (EMT) in cancer. We recently reported abnormal expression of miR-200b in the context of human pulmonary hypoplasia in congenital diaphragmatic hernia (CDH). Smaller lung size, a lower number of airway generations, and a thicker mesenchyme characterize pulmonary hypoplasia in CDH. The aim of this study was to define the role of miR-200b during lung development. Here we show that miR-200b-/- mice have abnormal lung function due to dysfunctional surfactant, increased fibroblast-like cells and thicker mesenchyme in between the alveolar walls. We profiled the lung transcriptome in miR-200b-/- mice, and, using Gene Ontology analysis, we determined that the most affected biological processes include cell cycle, apoptosis and protein transport. Our results demonstrate that miR-200b regulates distal airway development through maintaining an epithelial cell phenotype. The lung abnormalities observed in miR-200b-/- mice recapitulate lung hypoplasia in CDH.

FUS/TLS acts as an aggregation-dependent modifier of polyglutamine disease model mice.

FUS/TLS is an RNA/DNA-binding protein associated with neurodegenerative diseases including amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Previously, we found that a prion-like domain in the N-terminus of FUS/TLS mediates co-aggregation between FUS/TLS and mutant huntingtin, the gene product of Huntington's disease (HD). Here, we show that heterozygous knockout of FUS/TLS worsened the phenotypes of model mice of (HD, but not spinal and bulbar muscular atrophy (SBMA). This difference was correlated with the degree of pathological association between disease proteins and FUS/TLS. Co-aggregation between FUS/TLS and mutant huntingtin resulted in the depletion of free FUS/TLS protein in HD mice that was detected as a monomer in SDS-PAGE analysis. Recently, we found that FUS/TLS paralogs, TAF15 and EWS, were up-regulated in homozygous FUS/TLS knockout mice. These two proteins were up-regulated in both HD and FUS/TLS heterozygote mice, and were further elevated in HD-TLS+/- double mutant mice, consistent with the functional impairment of FUS/TLS. These results suggest that FUS/TLS sequestration by co-aggregation is a rate-limiting factor of disease phenotypes of HD and that inclusions may have an adverse aspect, rather than being simply benign or protective. In addition, our results highlight inclusions as repositories of potential modifiers of neurodegeneration.

FUS/TLS deficiency causes behavioral and pathological abnormalities distinct from amyotrophic lateral sclerosis.

INTRODUCTION: FUS/TLS is an RNA-binding protein whose genetic mutations or pathological inclusions are associated with neurological diseases including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration, and essential tremor (ET). It is unclear whether their pathogenesis is mediated by gain or loss of function of FUS/TLS. RESULTS: Here, we established outbred FUS/TLS knockout mice to clarify the effects of FUS/TLS dysfunction in vivo. We obtained homozygous knockout mice that grew into adulthood. Importantly, they did not manifest ALS- or ET-like phenotypes until nearly two years. Instead, they showed distinct histological and behavioral alterations including vacuolation in hippocampus, hyperactivity, and reduction in anxiety-like behavior. Knockout mice showed transcriptome alterations including upregulation of Taf15 and Hnrnpa1, while they have normal morphology of RNA-related granules such as Gems. CONCLUSIONS: Collectively, FUS/TLS depletion causes phenotypes possibly related to neuropsychiatric and neurodegenerative conditions, but distinct from ALS and ET, together with specific alterations in RNA metabolisms.

FUS-regulated RNA metabolism and DNA damage repair: Implications for amyotrophic lateral sclerosis and frontotemporal dementia pathogenesis.

Cytoplasmic inclusion of RNA binding protein FUS/TLS in neurons and glial cells is a characteristic pathology of a subgroup of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Dysregulation of RNA metabolism caused by FUS cytoplasmic inclusion emerges to be a key event in FUS-associated ALS/FTD pathogenesis. Our recent discovery of a FUS autoregulatory mechanism and its dysregulation in ALS-FUS mutants demonstrated that dysregulated alternative splicing can directly exacerbate the pathological FUS accumulation. We show here that FUS targets RNA for pre-mRNA alternative splicing and for the processing of long intron-containing transcripts, and that these targets are enriched for genes in neurogenesis and gene expression regulation. We also identify that FUS RNA targets are enriched for genes in the DNA damage response pathway. Together, the data support a model in which dysregulated RNA metabolism and DNA damage repair together may render neurons more vulnerable and accelerate neurodegeneration in ALS and FTD.

ALS-associated FUS mutations result in compromised FUS alternative splicing and autoregulation.

The gene encoding a DNA/RNA binding protein FUS/TLS is frequently mutated in amyotrophic lateral sclerosis (ALS). Mutations commonly affect its carboxy-terminal nuclear localization signal, resulting in varying deficiencies of FUS nuclear localization and abnormal cytoplasmic accumulation. Increasing evidence suggests deficiencies in FUS nuclear function may contribute to neuron degeneration. Here we report a novel FUS autoregulatory mechanism and its deficiency in ALS-associated mutants. Using FUS CLIP-seq, we identified significant FUS binding to a highly conserved region of exon 7 and the flanking introns of its own pre-mRNAs. We demonstrated that FUS is a repressor of exon 7 splicing and that the exon 7-skipped splice variant is subject to nonsense-mediated decay (NMD). Overexpression of FUS led to the repression of exon 7 splicing and a reduction of endogenous FUS protein. Conversely, the repression of exon 7 was reduced by knockdown of FUS protein, and moreover, it was rescued by expression of EGFP-FUS. This dynamic regulation of alternative splicing describes a novel mechanism of FUS autoregulation. Given that ALS-associated FUS mutants are deficient in nuclear localization, we examined whether cells expressing these mutants would be deficient in repressing exon 7 splicing. We showed that FUS harbouring R521G, R522G or ΔExon15 mutation (minor, moderate or severe cytoplasmic localization, respectively) directly correlated with respectively increasing deficiencies in both exon 7 repression and autoregulation of its own protein levels. These data suggest that compromised FUS autoregulation can directly exacerbate the pathogenic accumulation of cytoplasmic FUS protein in ALS. We showed that exon 7 skipping can be induced by antisense oligonucleotides targeting its flanking splice sites, indicating the potential to alleviate abnormal cytoplasmic FUS accumulation in ALS. Taken together, FUS autoregulation by alternative splicing provides insight into a molecular mechanism by which FUS-regulated pre-mRNA processing can impact a significant number of targets important to neurodegeneration.

Divergent roles of ALS-linked proteins FUS/TLS and TDP-43 intersect in processing long pre-mRNAs.

FUS/TLS (fused in sarcoma/translocated in liposarcoma) and TDP-43 are integrally involved in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. We found that FUS/TLS binds to RNAs from >5,500 genes in mouse and human brain, primarily through a GUGGU-binding motif. We identified a sawtooth-like binding pattern, consistent with co-transcriptional deposition of FUS/TLS. Depletion of FUS/TLS from the adult nervous system altered the levels or splicing of >950 mRNAs, most of which are distinct from RNAs dependent on TDP-43. Abundance of only 45 RNAs was reduced after depletion of either TDP-43 or FUS/TLS from mouse brain, but among these were mRNAs that were transcribed from genes with exceptionally long introns and that encode proteins that are essential for neuronal integrity. Expression levels of a subset of these were lowered after TDP-43 or FUS/TLS depletion in stem cell-derived human neurons and in TDP-43 aggregate-containing motor neurons in sporadic ALS, supporting a common loss-of-function pathway as one component underlying motor neuron death from misregulation of TDP-43 or FUS/TLS.

A generalizable pre-clinical research approach for orphan disease therapy.

With the advent of next-generation DNA sequencing, the pace of inherited orphan disease gene identification has increased dramatically, a situation that will continue for at least the next several years. At present, the numbers of such identified disease genes significantly outstrips the number of laboratories available to investigate a given disorder, an asymmetry that will only increase over time. The hope for any genetic disorder is, where possible and in addition to accurate diagnostic test formulation, the development of therapeutic approaches. To this end, we propose here the development of a strategic toolbox and preclinical research pathway for inherited orphan disease. Taking much of what has been learned from rare genetic disease research over the past two decades, we propose generalizable methods utilizing transcriptomic, system-wide chemical biology datasets combined with chemical informatics and, where possible, repurposing of FDA approved drugs for pre-clinical orphan disease therapies. It is hoped that this approach may be of utility for the broader orphan disease research community and provide funding organizations and patient advocacy groups with suggestions for the optimal path forward. In addition to enabling academic pre-clinical research, strategies such as this may also aid in seeding startup companies, as well as further engaging the pharmaceutical industry in the treatment of rare genetic disease.

The emerging functions of the p53-miRNA network in stem cell biology.

The p53 pathway plays an essential role in tumor suppression, regulating multiple cellular processes coordinately to maintain genome integrity in both somatic cells and stem cells. Despite decades of research dedicated to p53 function in differentiated somatic cells, we are just starting to understand the complexity of the p53 pathway in the biology of pluripotent stem cells and tissue stem cells. Recent studies have demonstrated that p53 suppresses proliferation, promotes differentiation of embryonic stem (ES) cells and constitutes an important barrier to somatic reprogramming. In addition, emerging evidence reveals the role of the p53 network in the self-renewal, proliferation and genomic integrity of adult stem cells. Interestingly, non-coding RNAs, and microRNAs in particular, are integral components of the p53 network, regulating multiple p53-controlled biological processes to modulate the self-renewal and differentiation potential of a variety of stem cells. Thus, elucidation of the p53-miRNA axis in stem cell biology may generate profound insights into the mechanistic overlap between malignant transformation and stem cell biology.