Epigenetic regulation of mammalian stem cells

Neural stem cell-derived extracellular vesicles: mini players with key roles in neurogenesis, immunomodulation, neuroprotection and aging

Neural stem/progenitor cells (NSPCs) are self-renewing and multipotent cells of the central nervous system where they give rise to neurons, astrocytes and oligodendrocytes both during embryogenesis and throughout adulthood, although only in a few discrete niches. NSPC can integrate and send a plethora of signals not only within the local microenvironment but also at distance, including the systemic macroenvironment. Extracellular vesicles (EVs) are currently envisioned as main players in cell-cell communication in basic and translational neuroscience where they are emerging as an acellular alternative in regenerative medicine. At present NSPC-derived EVs represent a largely unexplored area compared to EVs from other neural sources and EVs from other stem cells, i.e., mesenchymal stem cells. On the other hand, available data suggest that NSPC-derived EVs can play key roles on neurodevelopmental and adult neurogenesis, and they are endowed with neuroprotective and immunomodulatory properties, and even endocrine functions. In this review we specifically highlight major neurogenic and "non-neurogenic" properties of NSPC-EVs, the current knowledge on their peculiar cargos and their potential translational value.

SHANK family on stem cell fate and development

SH3 and multiple ankyrin repeat domains protein (SHANK) 1, SHANK2, and SHANK3 encode a family of postsynaptic scaffolding proteins present at glutamatergic synapses and play a crucial role in synaptogenesis. In the past years, studies have provided a preliminary appreciation and understanding of the influence of the SHANK family in controlling stem cell fate. Here, we review the modulation of SHANK gene expression and their related signaling pathways, allowing for an in-depth understanding of the role of SHANK in stem cells. Besides, their role in governing stem cell self-renewal, proliferation, differentiation, apoptosis, and metabolism are explored in neural stem cells (NSCs), stem cells from apical papilla (SCAPs), and induced pluripotent stem cells (iPSCs). Moreover, iPSCs and embryonic stem cells (ESCs) have been utilized as model systems for analyzing their functions in terms of neuronal development. SHANK-mediated stem cell fate determination is an intricate and multifactorial process. This study aims to achieve a better understanding of the role of SHANK in these processes and their clinical applications, thereby advancing the field of stem cell therapy. This review unravels the regulatory role of the SHANK family in the fate of stem cells.

The KDM5 Inhibitor KDM5-C70 Induces Astrocyte Differentiation in Rat Neural Stem Cells

Members of the lysine-specific histone demethylase 5 (KDM5/JARID1) family are known to play important roles in stem cell fate determination. Here, using the KDM5 inhibitor C70 (KDM5-C70), we demonstrated that the histone demethylase activity of the KDM5 enzyme is essential for the repression of astrocytic differentiation of neural stem cells (NSCs). KDM5-C70 treatment activated the glial fibrillary acidic protein (Gfap) gene by increasing the trimethylation of histone H3 lysine 4 in the promoter regions and subsequently induced astrocytogenesis in NSCs. In addition, treatment of NSCs with KDM5-C70 activated Janus kinase-signal transducer and activator of transcription (JAK-STAT3) signaling and increased the mRNA expression of transforming growth factor-beta 1 (Tgf-β1). Our data provide evidence that KDM5 is a promising target for NSC fate modulation and suggest that epigenetic regulation is important for NSC fate determination.

AlCl3 exposure regulates neuronal development by modulating DNA modification

BACKGROUND

As the third most abundant element, aluminum is widespread in the environment. Previous studies have shown that aluminum has a neurotoxic effect and its exposure can impair neuronal development and cognitive function.

AIM

To study the effects of aluminum on epigenetic modification in neural stem cells and neurons.

METHODS

Neural stem cells were isolated from the forebrain of adult mice. Neurons were isolated from the hippocampi tissues of embryonic day 16-18 mice. AlCl₃ at 100 and 200 μmol/L was applied to stem cells and neurons.

RESULTS

Aluminum altered the differentiation of adult neural stem cells and caused apoptosis of newborn neurons while having no significant effects on the proliferation of neural stem cells. Aluminum application also significantly inhibited the dendritic development of hippocampal neurons. Mechanistically, aluminum exposure significantly affected the levels of DNA 5-hydroxy-methylcytosine, 5-methylcytosine, and N⁶-methyladenine in stem cells and neurons.

CONCLUSION

Our findings indicate that aluminum may regulate neuronal development by modulating DNA modifications.

The Synthetic Cannabinoids THJ-2201 and 5F-PB22 Enhance In Vitro CB1 Receptor-Mediated Neuronal Differentiation at Biologically Relevant Concentrations

Recreational use of synthetic cannabinoids (SCs) before and during pregnancy poses a major public health risk, due to the potential onset of neurodevelopmental disorders in the offspring. Herein, we report the assessment of the neurotoxic potential of two commonly abused SCs, THJ-2201 and 5F-PB22, particularly focusing on how they affect neuronal differentiation in vitro. Differentiation ratios, total neurite length, and neuronal marker expression were assessed in NG108-15 neuroblastoma x glioma cells exposed to the SCs at non-toxic, biologically relevant concentrations (≤1 μM), either in acute or repeated exposure settings. Both SCs enhanced differentiation ratios and total neurite length of NG108-15 cells near two-fold compared to vehicle-treated cells, in a CB₁R activation-dependent way, as the CB₁R blockade with a specific antagonist (SR141718) abrogated SC-induced effects. Interestingly, repeated 5F-PB22 exposure was required to reach effects similar to a single THJ-2201 dose. Cell viability and proliferation, mitochondrial membrane potential, and intracellular ATP levels were also determined. The tested SCs increased mitochondrial tetramethyl rhodamine ethyl ester (TMRE) accumulation after 24 h at biologically relevant concentrations but did not affect any of the other toxicological parameters. Overall, we report firsthand the CB₁R-mediated enhancement of neurodifferentiation by 5F-PB22 and THJ-2201 at biologically relevant concentrations.

Histone acetylation and the role of histone deacetylases in normal cyclic endometrium

Histone acetylation is a critical epigenetic modification that changes chromatin architecture and regulates gene expression by opening or closing the chromatin structure. It plays an essential role in cell cycle progression and differentiation. The human endometrium goes through cycles of regeneration, proliferation, differentiation, and degradation each month; each phase requiring strict epigenetic regulation for the proper functioning of the endometrium. Aberrant histone acetylation and alterations in levels of two acetylation modulators - histone acetylases (HATs) and histone deacetylases (HDACs) - have been associated with endometrial pathologies such as endometrial cancer, implantation failures, and endometriosis. Thus, histone acetylation is likely to have an essential role in the regulation of endometrial remodelling throughout the menstrual cycle.

Prediction model construction of mouse stem cell pluripotency using CpG and non-CpG DNA methylation markers

Background

Genome-wide studies of DNA methylation across the epigenetic landscape provide insights into the heterogeneity of pluripotent embryonic stem cells (ESCs). Differentiating into embryonic somatic and germ cells, ESCs exhibit varying degrees of pluripotency, and epigenetic changes occurring in this process have emerged as important factors explaining stem cell pluripotency.

Results

Here, using paired scBS-seq and scRNA-seq data of mice, we constructed a machine learning model that predicts degrees of pluripotency for mouse ESCs. Since the biological activities of non-CpG markers have yet to be clarified, we tested the predictive power of CpG and non-CpG markers, as well as a combination thereof, in the model. Through rigorous performance evaluation with both internal and external validation, we discovered that a model using both CpG and non-CpG markers predicted the pluripotency of ESCs with the highest prediction performance (0.956 AUC, external test). The prediction model consisted of 16 CpG and 33 non-CpG markers. The CpG and most of the non-CpG markers targeted depletions of methylation and were indicative of cell pluripotency, whereas only a few non-CpG markers reflected accumulations of methylation. Additionally, we confirmed that there exists the differing pluripotency between individual developmental stages, such as E3.5 and E6.5, as well as between induced mouse pluripotent stem cell (iPSC) and somatic cell.

Conclusions

In this study, we investigated CpG and non-CpG methylation in relation to mouse stem cell pluripotency and developed a model thereon that successfully predicts the pluripotency of mouse ESCs.

Understanding pluripotency under folic acid deficiency using embryonic stem cells as an in vitro model

Innumerable studies have been carried out by people to trace out those elements, find out the mechanisms that are vital to the maintenance of stemness. Amongst them, the one which is gaining importance in the recent past is the metabolism of stem cells, especially One carbon metabolism. Being associated directly or indirectly, with DNA and Histone methylation, One carbon metabolism has an important role to play as far as epigenetic regulation of stemness is concerned. Folic acid being a methyl donor, forms an important component of One Carbon metabolism, and thus its availability has a significant effect on the methylation reactions. The present hypothesis says, using embryonic stem cells grown in vitro as a model system, one can study how deficiency of Folate during pre implantation embryonic development influence the self renewal as well as pluripotency of stem cells, from the perspective of One carbon metabolism and epigenetic mechanisms. Findings from such a study can possibly provide an explanation for the observed intra uterine growth retardation seen under maternal micronutrient deficiency.

miR-124 promotes proliferation and differentiation of neuronal stem cells through inactivating Notch pathway

Background

Neural stem cells (NSCs) are able to differentiate into neurons and astroglia. miRNAs have been demonstrated to be involved in NSC self-renewal, proliferation and differentiation. However, the exact role of miR-124 in the development of NSCs and its underlying mechanism remain to be explored.

Methods

Primary NSCs were isolated from embryos of Wistar rats. Immunocytochemistry was used to stain purified NSCs. miR-124, Delta-like 4 (DLL4), ki-67, Nestin, β-tubulin III, glial fibrillary acidic protein (GFAP), HES1, HEY2, and cyclin D1 (CCND1) expressions were detected by qRT-PCR and western blot. The interaction between miR-124 and DLL4 was confirmed by luciferase reporter assay. Cell proliferation was assessed by MTT assay.

Results

NSCs could self-proliferate and differentiate into neurons and astrocyte. miR-124 was up-regulated and DLL4 was down-regulated during NSC differentiation. DLL4 was identified as a target of miR-124 in NSCs. Ectopic expression of miR-124 or knockdown of DLL4 promoted the proliferation and the formation of NSCs to neurospheres. Moreover, miR-124 overexpression or DLL4 down-regulation improved β-tubulin III expression but decreased GFAP expression in NSCs. Furthermore, enforced expression of DLL4 partially reversed the effects of miR-124 on NSCs proliferation and differentiation. Elevated expression of miR-124 suppressed the expressions of HES1, HEY2, and CCND1 in NSCs, while these effects were attenuated following the enhancement of DLL4 expression.

Conclusion

miR-124 promoted proliferation and differentiation of NSCs through inactivating Notch pathway.

Epigenetic Modulation of Stem Cells in Neurodevelopment: The Role of Methylation and Acetylation

The coordinated development of the nervous system requires fidelity in the expression of specific genes determining the different neural cell phenotypes. Stem cell fate decisions during neurodevelopment are strictly correlated with their epigenetic status. The epigenetic regulatory processes, such as DNA methylation and histone modifications discussed in this review article, may impact both neural stem cell (NSC) self-renewal and differentiation and thus play an important role in neurodevelopment. At the same time, stem cell decisions regarding fate commitment and differentiation are highly dependent on the temporospatial expression of specific genes contingent on the developmental stage of the nervous system. An interplay between the above, as well as basic cell processes, such as transcription regulation, DNA replication, cell cycle regulation and DNA repair therefore determine the accuracy and function of neuronal connections. This may significantly impact embryonic health and development as well as cognitive processes such as neuroplasticity and memory formation later in the adult.

Role of Chromatin Modifications in Drosophila Germline Stem Cell Differentiation

During Drosophila oogenesis, germline stem cells (GSCs) self-renew and differentiate to give rise to a mature egg. Self-renewal and differentiation of GSCs are regulated by both intrinsic mechanisms such as regulation of gene expression in the germ line and extrinsic signaling pathways from the surrounding somatic niche. Epigenetic mechanisms, including histone-modifying proteins, nucleosome remodeling complexes, and histone variants, play a critical role in regulating intrinsic gene expression and extrinsic signaling cues from the somatic niche. In the GSCs, intrinsic epigenetic modifiers are required to maintain a stem cell fate by promoting expression of self-renewal factors and repressing the differentiation program. Subsequently, in the GSC daughters, epigenetic regulators activate the differentiation program to promote GSC differentiation. During differentiation, the GSC daughter undergoes meiosis to give rise to the developing egg, containing a compacted chromatin architecture called the karyosome. Epigenetic modifiers control the attachment of chromosomes to the nuclear lamina to aid in meiotic recombination and the release from the lamina for karyosome formation. The germ line is in close contact with the soma for the entirety of this developmental process. This proximity facilitates signaling from the somatic niche to the developing germ line. Epigenetic modifiers play a critical role in the somatic niche, modulating signaling pathways in order to coordinate the transition of GSC to an egg. Together, intrinsic and extrinsic epigenetic mechanisms modulate this exquisitely balanced program.

Hepatoepigenetic Alterations in Viral and Nonviral-Induced Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major public health concern and one of the leading causes of tumour-related deaths worldwide. Extensive evidence endorses that HCC is a multifactorial disease characterised by hepatic cirrhosis mostly associated with chronic inflammation and hepatitis B/C viral infections. Interaction of viral products with the host cell machinery may lead to increased frequency of genetic and epigenetic aberrations that cause harmful alterations in gene transcription. This may provide a progressive selective advantage for neoplastic transformation of hepatocytes associated with phenotypic heterogeneity of intratumour HCC cells, thus posing even more challenges in HCC treatment development. Epigenetic aberrations involving DNA methylation, histone modifications, and noncoding miRNA dysregulation have been shown to be intimately linked with and play a critical role in tumour initiation, progression, and metastases. The current review focuses on the aberrant hepatoepigenetics events that play important roles in hepatocarcinogenesis and their utilities in the development of HCC therapy.

Phosphodiesterase7 Inhibition Activates Adult Neurogenesis in Hippocampus and Subventricular Zone In Vitro and In Vivo

The phosphodiesterase 7 (PDE7) enzyme is one of the enzymes responsible for controlling intracellular levels of cyclic adenosine 3',5'-monophosphate in the immune and central nervous system. We have previously shown that inhibitors of this enzyme are potent neuroprotective and anti-inflammatory agents. In addition, we also demonstrated that PDE7 inhibition induces endogenous neuroregenerative processes toward a dopaminergic phenotype. Here, we show that PDE7 inhibition controls stem cell expansion in the subgranular zone of the dentate gyrus of the hippocampus (SGZ) and the subventricular zone (SVZ) in the adult rat brain. Neurospheres cultures obtained from SGZ and SVZ of adult rats treated with PDE7 inhibitors presented an increased proliferation and neuronal differentiation compared to control cultures. PDE7 inhibitors treatment of neurospheres cultures also resulted in an increase of the levels of phosphorylated cAMP response element binding protein, suggesting that their effects were indeed mediated through the activation of the cAMP/PKA signaling pathway. In addition, adult rats orally treated with S14, a specific inhibitor of PDE7, presented elevated numbers of proliferating progenitor cells, and migrating precursors in the SGZ and the SVZ. Moreover, long-term treatment with this PDE7 inhibitor shows a significant increase in newly generated neurons in the olfactory bulb and the hippocampus. Also a better performance in memory tests was observed in S14 treated rats, suggesting a functional relevance for the S14-induced increase in SGZ neurogenesis. Taken together, our results indicate for the first time that inhibition of PDE7 directly regulates proliferation, migration and differentiation of neural stem cells, improving spatial learning and memory tasks. Stem Cells 2017;35:458-472.

An epigenetic view of developmental diseases: new targets, new therapies

BACKGROUND

Function of epigenetic modifications is one of the most competitive fields in life science. Over the past several decades, it has been revealed that epigenetic modifications play essential roles in development and diseases including developmental diseases. In the present review, we summarize the recent progress about the function of epigenetic regulation, especially DNA and RNA modifications in developmental diseases.

DATA SOURCES

Original research articles and literature reviews published in PubMed-indexed journals.

RESULTS

DNA modifications including methylation and demethylation can regulate gene expression, and are involved in development and multiple diseases including Rett syndrome, Autism spectrum disorders, congenital heart disease and cancer, etc. RNA methylation and demethylation play important roles in RNA processing, reprogramming, circadian, and neuronal activity, and then modulate development.

CONCLUSIONS

DNA and RNA modifications play important roles in development and diseases through regulating gene expression. Epigenetic components could serve as novel targets for the treatment of developmental diseases.

Preserved neurogenesis in non-demented individuals with AD neuropathology

Rare individuals remain cognitively intact despite the presence of neuropathology usually associated with fully symptomatic Alzheimer’s disease (AD), which we refer to as Non-Demented with Alzheimer’s disease Neuropathology (NDAN). Understanding the involved mechanism(s) of their cognitive resistance may reveal novel strategies to treat AD-related dementia. In the pursuit of this goal, we determined the number of hippocampal neural stem cells (NSCs) and investigated the expression of several miRNAs in NDAN and AD subjects. Laser-capture microdissection of autopsy human hippocampus DG and qRT-PCR miRNA analyses were combined with immunofluorescence in this study. The number of SOX2⁺ NSCs in the DG was significantly increased in NDAN individuals as compared to AD subjects. Further, the prevalence of SOX2⁺ NSCs was found to correlate with cognitive capacity. Neurogenesis-regulating miRNAs were decreased in NDAN individuals as compared to AD patients. An increased number of NSCs and new neurons in NDAN individuals is associated with a unique expression of regulating miRNAs and strongly support a role of neurogenesis in mediating, in part, the ability of these individuals to resist the pathological burden of AD.

Genetics and Epigenetics in Adult Neurogenesis

The cellular basis of adult neurogenesis is neural stem cells residing in restricted areas of the adult brain. These cells self-renew and are multipotent. The maintenance of "stemness" and commitment to differentiation are tightly controlled by intricate molecular networks. Epigenetic mechanisms, including chromatin remodeling, DNA methylation, and noncoding RNAs (ncRNAs), have profound regulatory roles in mammalian gene expression. Significant advances have been made regarding the dynamic roles of epigenetic modulation and function. It has become evident that epigenetic regulators are key players in neural-stem-cell self-renewal, fate specification, and final maturation of new neurons, therefore, adult neurogenesis. Altered epigenetic regulation can result in a number of neurological and neurodevelopmental disorders. Here, we review recent discoveries that advance our knowledge in epigenetic regulation of mammalian neural stem cells and neurogenesis. Insights from studies of epigenetic gene regulation in neurogenesis may lead to new therapies for the treatment of neurodevelopmental disorders.

Concise review: Fragile X proteins in stem cell maintenance and differentiation

Fragile X syndrome (FXS), the most common genetic form of autism spectrum disorder, is caused by deficiency of the fragile X mental retardation protein (FMRP). Despite extensive research and scientific progress, understanding how FMRP regulates brain development and function remains a major challenge. FMRP is a neuronal RNA-binding protein that binds about a third of messenger RNAs in the brain and controls their translation, stability, and cellular localization. The absence of FMRP results in increased protein synthesis, leading to enhanced signaling in a number of intracellular pathways, including the mTOR, mGLuR5, ERK, Gsk3β, PI3K, and insulin pathways. Until recently, FXS was largely considered a deficit of mature neurons; however, a number of new studies have shown that FMRP may also play important roles in stem cells, among them neural stem cells, germline stem cells, and pluripotent stem cells. In this review, we will cover these newly discovered functions of FMRP, as well as the other two fragile X-related proteins, in stem cells. We will also discuss the literature on the use of stem cells, particularly neural stem cells and induced pluripotent stem cells, as model systems for studying the functions of FMRP in neuronal development.

microRNAs: key triggers of neuronal cell fate

Development of the central nervous system (CNS) requires a precisely coordinated series of events. During embryonic development, different intra- and extracellular signals stimulate neural stem cells to become neural progenitors, which eventually irreversibly exit from the cell cycle to begin the first stage of neurogenesis. However, before this event occurs, the self-renewal and proliferative capacities of neural stem cells and neural progenitors must be tightly regulated. Accordingly, the participation of various evolutionary conserved microRNAs is key in distinct central nervous system (CNS) developmental processes of many organisms including human, mouse, chicken, frog, and zebrafish. microRNAs specifically recognize and regulate the expression of target mRNAs by sequence complementarity within the mRNAs 3′ untranslated region and importantly, a single microRNA can have several target mRNAs to regulate a process; likewise, a unique mRNA can be targeted by more than one microRNA. Thus, by regulating different target genes, microRNAs let-7, microRNA-124, and microRNA-9 have been shown to promote the differentiation of neural stem cells and neural progenitors into specific neural cell types while microRNA-134, microRNA-25 and microRNA-137 have been characterized as microRNAs that induce the proliferation of neural stem cells and neural progenitors. Here we review the mechanisms of action of these two sets of microRNAs and their functional implications during the transition from neural stem cells and neural progenitors to fully differentiated neurons. The genetic and epigenetic mechanisms that regulate the expression of these microRNAs as well as the role of the recently described natural RNA circles which act as natural microRNA sponges regulating post-transcriptional microRNA expression and function during the early stages of neurogenesis is also discussed.

5-Hydroxymethylcytosine: A new player in brain disorders?

5-Hydroxymethylcytosine (5 hmC), a novel modified cytosine, is oxidized from 5-methylcytosine (5 mC) by the ten-eleven translocation (Tet) protein family. The specific distribution of 5 hmC in mammalian brain and its roles in gene regulation suggest that 5 hmC is important in brain development. 5 hmC may also contribute to the mechanisms underlying neurological diseases. Here, we summarize the current knowledge of 5 hmC, with an emphasis on its roles in neurodevelopmental and neurodegenerative disorders.

5-hydroxymethylcytosine-mediated DNA demethylation in stem cells and development

The pursuit of DNA demethylation has a colorful history, but it was not until 2009 that the stars of this story, the Ten-eleven-translocation (Tet) family of proteins, were really identified. Tet proteins convert 5-methylcytosine to 5-hydroxymethylcytosine (5hmC), which can be further oxidized to 5-formylcytosine and 5-cyboxycytosine by Tet proteins to achieve DNA demethylation. Recent studies have revealed that 5hmC-mediated DNA demethylation can play essential roles in diverse biological processes, including development and diseases. Here, we review recent discoveries in 5hmC-mediated DNA demethylation in the context of stem cells and development.

Analysis of the transfer of circulating microRNA between cells mediated by gap junction

A significant breakthrough in the field of research was the identification of microRNAs (miRNAs), which are small molecule, single-stranded nucleic acids. MiRNAs have diverse roles in cellular biology with the ability for translation in different areas of medicine. The size of miRNAs provides them for passage through gap junction. Recent studies have demonstrated the passage of miRNAs through gap junctional intercellular communication (GJIC) among cancer cells and between breast cancer cells and bone marrow stroma. The transfer of miRNAs has been implicated in the etiology of breast cancer dormancy. To this end, we have developed a miRNA reporter assay to assess the ability of miRNAs to be transferred between stem and breast cancer cells and target a specific recognition sequence.

Neonatal tumours

Neonatal or perinatal tumours frequently relate to prenatal or developmental events and have a short exposure window which provides an opportunity to study tumours in a selective sensitive period of development. As a result, they display a number of host-specific features which include occasional spontaneous maturational changes with cells still responding to developmental influences. Neonatal tumours (NNT) are studied for a number of important reasons. Firstly, many of the benign tumours arising from soft tissue appear to result from disturbances in growth and development and some are associated with other congenital anomalies. Study of these aspects may open the door for investigation of genetic and epigenetic changes in genes controlling foetal development as well as environmental and drug effects during pregnancy. Secondly, the clinical behaviour of NNT differs from that of similar tumours occurring later in childhood. In addition, certain apparently malignant NNT can 'change course' in infancy leading to the maturation of apparently highly malignant tumours. Thirdly, NNT underline the genetic associations of most tumours but appear to differ in the effects of proto-oncogenes and other oncogenic factors. In this context, there are also connections between the foetal and neonatal period and some "adult" cancers. Fourthly, they appear to arise in a period in which minimal environmental interference has occurred, thus providing a unique potential window of opportunity to study the pathogenesis of tumour behaviour. This study will seek to review what is currently known in each of these areas of study as they apply to NNT. Further study of the provocative differences in tumour behaviour in neonates provides insights into the natural history of cancer in humans and promotes novel cancer therapies.

Epigenetic regulation in adult stem cells and cancers

Adult stem cells maintain tissue homeostasis by their ability to both self-renew and differentiate to distinct cell types. Multiple signaling pathways have been shown to play essential roles as extrinsic cues in maintaining adult stem cell identity and activity. Recent studies also show dynamic regulation by epigenetic mechanisms as intrinsic factors in multiple adult stem cell lineages. Emerging evidence demonstrates intimate crosstalk between these two mechanisms. Misregulation of adult stem cell activity could lead to tumorigenesis, and it has been proposed that cancer stem cells may be responsible for tumor growth and metastasis. However, it is unclear whether cancer stem cells share commonalities with normal adult stem cells. In this review, we will focus on recent discoveries of epigenetic regulation in multiple adult stem cell lineages. We will also discuss how epigenetic mechanisms regulate cancer stem cell activity and probe the common and different features between cancer stem cells and normal adult stem cells.

Histone demethylase dUTX antagonizes JAK-STAT signaling to maintain proper gene expression and architecture of the Drosophila testis niche

Adult stem cells reside in microenvironments called niches, where they are regulated by both extrinsic cues, such as signaling from neighboring cells, and intrinsic factors, such as chromatin structure. Here we report that in the Drosophila testis niche an H3K27me3-specific histone demethylase encoded by Ubiquitously transcribed tetratricopeptide repeat gene on the X chromosome (dUTX) maintains active transcription of the Suppressor of cytokine signaling at 36E (Socs36E) gene by removing the repressive H3K27me3 modification near its transcription start site. Socs36E encodes an inhibitor of the Janus kinase signal transducer and activator of transcription (JAK-STAT) signaling pathway. Whereas much is known about niche-to-stem cell signaling, such as the JAK-STAT signaling that is crucial for stem cell identity and activity, comparatively little is known about signaling from stem cells to the niche. Our results reveal that stem cells send feedback to niche cells to maintain the proper gene expression and architecture of the niche. We found that dUTX acts in cyst stem cells to maintain gene expression in hub cells through activating Socs36E transcription and preventing hyperactivation of JAK-STAT signaling. dUTX also acts in germline stem cells to maintain hub structure through regulating DE-Cadherin levels. Therefore, our findings provide new insights into how an epigenetic factor regulates crosstalk among different cell types within an endogenous stem cell niche, and shed light on the biological functions of a histone demethylase in vivo.

An epigenetic feedback regulatory loop involving microRNA-195 and MBD1 governs neural stem cell differentiation

Background

Epigenetic mechanisms, including DNA methylation, histone modification, and microRNAs, play pivotal roles in stem cell biology. Methyl-CpG binding protein 1 (MBD1), an important epigenetic regulator of adult neurogenesis, controls the proliferation and differentiation of adult neural stem/progenitor cells (aNSCs). We recently demonstrated that MBD1 deficiency in aNSCs leads to altered expression of several noncoding microRNAs (miRNAs).

Methodology/Principal Findings

Here we show that one of these miRNAs, miR-195, and MBD1 form a negative feedback loop. While MBD1 directly represses the expression of miR-195 in aNSCs, high levels of miR-195 in turn repress the expression of MBD1. Both gain-of-function and loss-of-function investigations show that alterations of the MBD1–miR-195 feedback loop tip the balance between aNSC proliferation and differentiation.

Conclusions/Significance

Therefore the regulatory loop formed by MBD1 and miR-195 is an important component of the epigenetic network that controls aNSC fate.

Epigenetic regulation of cancer stem cell gene expression

The concept of cancer as a stem cell disease has slowly gained ground over the last decade. A 'stem-like' state essentially necessitates that some cells in the developing tumor express the properties of remaining quiescent, self-renewing and regenerating tumors through establishment of aberrant cellular hierarchies. Alternatively, such capacities may also be reacquired through a de-differentiation process. The abnormal cellular differentiation patterns involved during either process during carcinogenesis are likely to be driven through a combination of genetic events and epigenetic regulation. The role(s) of the latter is increasingly being appreciated in acquiring the requisite genomic specificity and flexibility required for phenotypic plasticity, specifically in a context wherein genome sequences are not altered for differentiation to ensue. In this chapter, the recent advances in elucidating epigenetic mechanisms that govern the self-renewal, differentiation and regenerative potentials of cancer stem cells will be presented.

Orchestrating transcriptional control of adult neurogenesis

Stem cells have captured our imagination and generated hope, representing a source of replacement cells to treat a host of medical conditions. Tucked away in specialized niches, stem cells maintain tissue function and rejuvenate organs. Balancing the equation between cellular supply and demand is especially important in the adult brain, as neural stem cells (NSCs) in two discrete regions, the subgranular zone (SGZ) of the dentate gyrus and the subventricular zone (SVZ) next to the lateral ventricles, continuously self-renew and differentiate into neurons in a process called adult neurogenesis. Through the interplay of intrinsic and extrinsic factors, adult neurogenic niches ensure neuronal turnover throughout life, contributing to plasticity and homeostatic processes in the brain. This review summarizes recent progress on the molecular control of adult neurogenesis in the SGZ and SVZ, focusing on the role of specific transcription factors that mediate the progression from NSCs to lineage-committed progenitors and, ultimately, the generation of mature neurons and glia.

Crosstalk among Epigenetic Pathways Regulates Neurogenesis

The process of neurogenesis includes neural stem cell proliferation, fate specification, young neuron migration, neuronal maturation, and functional integration into existing circuits. Although neurogenesis occurs largely during embryonic development, low levels but functionally important neurogenesis persists in restricted regions of the postnatal brain, including the subgranular zone of the dentate gyrus in the hippocampus and the subventricular zone of the lateral ventricles. This review will cover both embryonic and adult neurogenesis with an emphasis on the latter. Of the many endogenous mediators of postnatal neurogenesis, epigenetic pathways, such as mediators of DNA methylation, chromatin remodeling systems, and non-coding RNA modulators, appear to play an integral role. Mounting evidence shows that such epigenetic factors form regulatory networks, which govern each step of postnatal neurogenesis. In this review, we explore the emerging roles of epigenetic mechanisms particularly microRNAs, element-1 silencing transcription factor/neuron-restrictive silencing factor (REST/NRSF), polycomb proteins, and methyl-CpG bindings proteins, in regulating the entire process of postnatal and adult neurogenesis. We further summarize recent data regarding how the crosstalk among these different epigenetic proteins forms the critical regulatory network that regulates neuronal development. We finally discuss how crosstalk between these pathways may serve to translate environmental cues into control of the neurogenic process.

Dermatan sulfotransferase Chst14/D4st1, but not chondroitin sulfotransferase Chst11/C4st1, regulates proliferation and neurogenesis of neural progenitor cells

Chondroitin sulfates (CSs) and dermatan sulfates (DSs) are enriched in the microenvironment of neural stem cells (NSCs) during development and in the adult neurogenic niche, and have been implicated in mechanisms governing neural precursor migration, proliferation and differentiation. In contrast to previous studies, in which a chondroitinaseABC-dependent unselective deglycosylation of both CSs and DSs was performed, we used chondroitin 4-O-sulfotransferase-1 (Chst11/C4st1)- and dermatan 4-O-sulfotransferase-1 (Chst14/D4st1)-deficient NSCs specific for CSs and DSs, respectively, to investigate the involvement of specific sulfation profiles of CS and DS chains, and thus the potentially distinct roles of CSs and DSs in NSC biology. In comparison to wild-type controls, deficiency for Chst14 resulted in decreased neurogenesis and diminished proliferation of NSCs accompanied by increased expression of GLAST and decreased expression of Mash-1, and an upregulation of the expression of the receptors for fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF). By contrast, deficiency in Chst11 did not influence NSC proliferation, migration or differentiation. These observations indicate for the first time that CSs and DSs play distinct roles in the self-renewal and differentiation of NSCs.

Fragile X mental retardation protein and stem cells

Stem cells, which can self-renew and produce different cell types, are regulated by both extrinsic signals and intrinsic factors. Fragile X syndrome, one of the most common forms of inherited mental retardation, is caused by the functional loss of fragile X mental retardation protein (FMRP). FMRP is a selective RNA-binding protein that forms a messenger ribonucleoprotein (mRNP) complex that associates with polyribosomes. Recently, the role of Fmrp in stem cell biology has been explored in both Drosophila and the mouse. In this chapter, we discuss the role of FMRP in regulating the proliferation and differentiation of stem cells.

Functional aspects of cytidine-guanosine dinucleotides and their locations in genes

Originally, the finding of a particular distribution of cytidine-guanosine dinucleotides (CpGs) in genomic DNA was considered to be an interesting structural feature of eukaryotic genome organization. Despite a global depletion of CpGs, genes are frequently associated with CpG clusters called CpG islands (CGIs). CGIs are prevalently unmethylated but often found methylated in pathologic situations. On the other hand, CpGs outside of CGIs are generally methylated and are found mainly in the heterochromatic fraction of the genome. Hypomethylation of those CpGs is associated with genomic instability in malignancy. Additionally, CpG-rich and CpG-poor regions, as well as CpG-shores, are defined. Usually, the methylation status inversely correlates with gene expression. Methylation of CpGs, as well as demethylation and generation of hydroxmethyl-cytosines, is strictly regulated during development and differentiation. This review deals with the relevance of the organizational features of CpGs and their relation to each other.

RNA-binding protein FXR2 regulates adult hippocampal neurogenesis by reducing Noggin expression

In adult mammalian brains, neurogenesis persists in the subventricular zone of the lateral ventricles (SVZ) and the dentate gyrus (DG) of the hippocampus. Although evidence suggest that adult neurogenesis in these two regions is subjected to differential regulation, the underlying mechanism is unclear. Here, we show that the RNA-binding protein FXR2 specifically regulates DG neurogenesis by reducing the stability of Noggin mRNA. FXR2 deficiency leads to increased Noggin expression and subsequently reduced BMP signaling, which results in increased proliferation and altered fate specification of neural stem/progenitor cells in DG. In contrast, Noggin is not regulated by FXR2 in the SVZ, because Noggin expression is restricted to the ependymal cells of the lateral ventricles, where FXR2 is not expressed. Differential regulation of SVZ and DG stem cells by FXR2 may be a key component of the mechanism that governs the different neurogenic processes in these two adult germinal zones.

Regulation of the stem cell marker CD133 is independent of promoter hypermethylation in human epithelial differentiation and cancer

Background

Epigenetic control is essential for maintenance of tissue hierarchy and correct differentiation. In cancer, this hierarchical structure is altered and epigenetic control deregulated, but the relationship between these two phenomena is still unclear. CD133 is a marker for adult stem cells in various tissues and tumour types. Stem cell specificity is maintained by tight regulation of CD133 expression at both transcriptional and post-translational levels. In this study we investigated the role of epigenetic regulation of CD133 in epithelial differentiation and cancer.

Methods

DNA methylation analysis of the CD133 promoter was done by pyrosequencing and methylation specific PCR; qRT-PCR was used to measure CD133 expression and chromatin structure was determined by ChIP. Cells were treated with DNA demethylating agents and HDAC inhibitors. All the experiments were carried out in both cell lines and primary samples.

Results

We found that CD133 expression is repressed by DNA methylation in the majority of prostate epithelial cell lines examined, where the promoter is heavily CpG hypermethylated, whereas in primary prostate cancer and benign prostatic hyperplasia, low levels of DNA methylation, accompanied by low levels of mRNA, were found. Moreover, differential methylation of CD133 was absent from both benign or malignant CD133⁺/α₂β₁integrin^hi prostate (stem) cells, when compared to CD133^-/α₂β₁integrin^hi (transit amplifying) cells or CD133^-/α₂β₁integrin^low (basal committed) cells, selected from primary epithelial cultures. Condensed chromatin was associated with CD133 downregulation in all of the cell lines, and treatment with HDAC inhibitors resulted in CD133 re-expression in both cell lines and primary samples.

Conclusions

CD133 is tightly regulated by DNA methylation only in cell lines, where promoter methylation and gene expression inversely correlate. This highlights the crucial choice of cell model systems when studying epigenetic control in cancer biology and stem cell biology. Significantly, in both benign and malignant prostate primary tissues, regulation of CD133 is independent of DNA methylation, but is under the dynamic control of chromatin condensation. This indicates that CD133 expression is not altered in prostate cancer and it is consistent with an important role for CD133 in the maintenance of the hierarchical cell differentiation patterns in cancer.

Loss of the chromatin regulator MRG15 limits neural stem/progenitor cell proliferation via increased expression of the p21 Cdk inhibitor

Chromatin regulation is crucial for many biological processes such as transcriptional regulation, DNA replication, and DNA damage repair. We have found that it is also important for neural stem/progenitor cell (NSC) function and neurogenesis. Here, we demonstrate that expression of the cyclin-dependent kinase inhibitor p21 is specifically up-regulated in Mrg15 deficient NSCs. Knockdown of p21 expression by p21 shRNA results in restoration of cell proliferation. This indicates that p21 is directly involved in the growth defects observed in Mrg15 deficient NSCs. Activated p53 accumulates in Mrg15 deficient NSCs and this most likely accounts for the up-regulation of p21 expression in the cells. We observed decreased p53 and p21 levels and a concomitant increase in the percentage of BrdU positive cells in Mrg15 null cultures following expression of p53 shRNA. DNA damage foci, as indicated by immunostaining for γH2AX and 53BP1, are detectable in a sub-population of Mrg15 deficient NSC cultures under normal growing conditions and the majority of p21-positive cells are also positive for 53BP1 foci. Furthermore, Mrg15 deficient NSCs exhibit severe defects in DNA damage response following ionizing radiation. Our observations highlight the importance of chromatin regulation and DNA damage response in NSC function and maintenance.

Molecular marks for epigenetic identification of developmental and cancer stem cells

Epigenetic regulations of genes by reversible methylation of DNA (at the carbon-5 of cytosine) and numerous reversible modifications of histones play important roles in normal physiology and development, and epigenetic deregulations are associated with developmental disorders and various disease states, including cancer. Stem cells have the capacity to self-renew indefinitely. Similar to stem cells, some malignant cells have the capacity to divide indefinitely and are referred to as cancer stem cells. In recent times, direct correlation between epigenetic modifications and reprogramming of stem cell and cancer stem cell is emerging. Major discoveries were made with investigations on reprogramming gene products, also known as master regulators of totipotency and inducer of pluoripotency, namely, OCT4, NANOG, cMYC, SOX2, Klf4, and LIN28. The challenge to induce pluripotency is the insertion of four reprogramming genes (Oct4, Sox2, Klf4, and c-Myc) into the genome. There are always risks of silencing of these genes by epigenetic modifications in the host cells, particularly, when introduced through retroviral techniques. In this contribution, we will discuss some of the major discoveries on epigenetic modifications within the chromatin of various genes associated with cancer progression and cancer stem cells in comparison to normal development of stem cell. These modifications may be considered as molecular signatures for predicting disorders of development and for identifying disease states.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s13148-010-0016-0) contains supplementary material, which is available to authorized users.

MicroRNA regulation of neural stem cells and neurogenesis

MicroRNAs are a class of small RNA regulators that are involved in numerous cellular processes, including development, proliferation, differentiation, and plasticity. The emerging concept is that microRNAs play a central role in controlling the balance between stem cell self-renewal and fate determination by regulating the expression of stem cell regulators. This review will highlight recent advances in the regulation of neural stem cell self-renewal and neurogenesis by microRNAs. It will cover microRNA functions during the entire process of neurogenesis, from neural stem cell self-renewal and fate determination to neuronal maturation, synaptic formation, and plasticity. The interplay between microRNAs and both cell-intrinsic and -extrinsic stem cell players, including transcription factors, epigenetic regulators, and extrinsic signaling molecules will be discussed. This is a summary of the topics covered in the mini-symposium on microRNA regulation of neural stem cells and neurogenesis in SFN 2010 and is not meant to be a comprehensive review of the subject.

The novel metastasis promoter Merm1/Wbscr22 enhances tumor cell survival in the vasculature by suppressing Zac1/p53-dependent apoptosis

Understanding metastasis is integral to curative cancer treatments. Using a mouse genetic screening model, we identified Merm1/Wbscr22 as a novel metastasis promoter that includes a methyltransferase fold in its structure. Merm1 showed high levels of expression in invasive breast cancer. Ectopic expression of Merm1 in nonmetastatic cells enhanced metastasis formation without affecting cell growth and motility. The intact methyltransferase fold of Merm1 was required for metastasis formation. Interestingly, Merm1 expression promoted cell survival after entrapment in the lung microvasculature. Consistent with these results, knockdown of endogenous Merm1 in tumor cells reduced lung retention and metastasis formation. On the basis of comparative transcriptome analysis, Merm1 expression was negatively correlated with the expression of tumor suppressor Zac1. We confirmed that Merm1 suppressed Zac1 expression with histone H3 methylation at Lys(9) in the Zac1 promoter region. Zac1 can induce apoptosis through its ability to transcriptionally coactivate p53, which regulates apoptosis in the vasculature and is often downregulated in metastasis. We found that Zac1 knockdown reduced the p53-dependent apoptosis that was enhanced by Merm1 knockdown, thereby increasing lung retention of metastatic cells. Our findings show that Merm1 enhances cancer cell survival in the vasculature by suppressing Zac1/p53-dependent apoptosis, thereby enhancing metastasis.

Epigenetic regulation of miR-184 by MBD1 governs neural stem cell proliferation and differentiation

Methyl-CpG binding protein 1 (MBD1) regulates gene expression via a DNA methylation-mediated epigenetic mechanism. We have previously demonstrated that MBD1 deficiency impairs adult neural stem/progenitor cell (aNSC) differentiation and neurogenesis, but the underlying mechanism was unclear. Here, we show that MBD1 regulates the expression of several microRNAs in aNSCs and, specifically, that miR-184 is directly repressed by MBD1. High levels of miR-184 promoted proliferation but inhibited differentiation of aNSCs, whereas inhibition of miR-184 rescued the phenotypes associated with MBD1 deficiency. We further found that miR-184 regulates the expression of Numblike (Numbl), a known regulator of brain development, by binding to the 3'-UTR of Numbl mRNA and affecting its translation. Expression of exogenous Numbl could rescue the aNSC defects that result from either miR-184 overexpression or MBD1 deficiency. Therefore, MBD1, miR-184, and Numbl form a regulatory network that helps control the balance between proliferation and differentiation of aNSCs.

The epigenetic mechanism of mechanically induced osteogenic differentiation

Epigenetic regulation of gene expression occurs due to alterations in chromatin proteins that do not change DNA sequence, but alter the chromatin architecture and the accessibility of genes, resulting in changes to gene expression that are preserved during cell division. Through this process genes are switched on or off in a more durable fashion than other transient mechanisms of gene regulation, such as transcription factors. Thus, epigenetics is central to cellular differentiation and stem cell linage commitment. One such mechanism is DNA methylation, which is associated with gene silencing and is involved in a cell's progression towards a specific fate. Mechanical signals are a crucial regulator of stem cell behavior and important in tissue differentiation; however, there has been no demonstration of a mechanism whereby mechanics can affect gene regulation at the epigenetic level. In this study, we identified candidate DNA methylation sites in the promoter regions of three osteogenic genes from bone marrow derived mesenchymal stem cells (MSCs). We demonstrate that mechanical stimulation alters their epigenetic state by reducing DNA methylation and show an associated increase in expression. We contrast these results with biochemically induced differentiation and distinguish expression changes associated with durable epigenetic regulation from those likely to be due to transient changes in regulation. This is an important advance in stem cell mechanobiology as it is the first demonstration of a mechanism by which the mechanical micro-environment is able to induce epigenetic changes that control osteogenic cell fate, and that can be passed to daughter cells. This is a first step to understanding that will be vital to successful bone tissue engineering and regenerative medicine, where continued expression of a desired long-term phenotype is crucial.

Epigenetic regulation of neuronal dendrite and dendritic spine development

Dendrites and the dendritic spines of neurons play key roles in the connectivity of the brain and have been recognized as the locus of long-term synaptic plasticity, which is correlated with learning and memory. The development of dendrites and spines in the mammalian central nervous system is a complex process that requires specific molecular events over a period of time. It has been shown that specific molecules are needed not only at the spine's point of contact, but also at a distance, providing signals that initiate a cascade of events leading to synapse formation. The specific molecules that act to signal neuronal differentiation, dendritic morphology, and synaptogenesis are tightly regulated by genetic and epigenetic programs. It has been shown that the dendritic spine structure and distribution are altered in many diseases, including many forms of mental retardation (MR), and can also be potentiated by neuronal activities and an enriched environment. Because dendritic spine pathologies are found in many types of MR, it has been proposed that an inability to form normal spines leads to the cognitive and motor deficits that are characteristic of MR. Epigenetic mechanisms, including DNA methylation, chromatin remodeling, and the noncoding RNA-mediated process, have profound regulatory roles in mammalian gene expression. The study of epigenetics focuses on cellular effects that result in a heritable pattern of gene expression without changes to genomic encoding. Despite extensive efforts to understand the molecular regulation of dendrite and spine development, epigenetic mechanisms have only recently been considered. In this review, we will focus on epigenetic mechanisms that regulate the development and maturation of dendrites and spines. We will discuss how epigenetic alterations could result in spine abnormalities that lead to MR, such as is seen in fragile X and Rett syndromes. We will also discuss both general methodology and recent technological advances in the study of neuronal dendrites and spines.

Skeletal myogenic potential of mouse skin-derived precursors

Cell transplantation-based therapy could be an effective way for the treatment of many diseases. Among numerous somatic stem cells isolated and purified, skin-derived precursors (SKPs) are abundant autologous cells, providing a large reservoir of cells for therapeutic transplantation. Previous studies showed that SKPs could be differentiated into neural and mesodermal progeny in vitro. In the present study, we attempted to differentiate SKPs to muscle progenitors in vitro. After treatment with a combination of growth factors, SKPs were differentiated into cells expressing markers of muscle progenitors, including Pax7. Furthermore, some of these cells expressed desmin, TnT, Mstn, and Myog, suggesting their differentiation into the muscular lineage. After single point injection, the differentiation of SKPs from green fluorescent protein positive donors into muscle precursors was also demonstrated in vivo. Additionally, donor SKPs migrated to the niche of muscle progenitors, participated in the regeneration of recipient muscles, and expressed markers of muscle progenitors, including Pax7, M-cadherin, and MyoD. After recovery of donor cells from recipient muscles at 3 weeks postinjection, some of the injected SKPs were converted to myogenic precursors, based on the expression of specific markers (Pax7 and MyoD). Some of these donor cells also expressed muscle makers (desmin, TnT, and Myog). At 20 weeks postinjection, the injected SKPs were localized to recipient muscles without decreases in their population size. In summary, these findings indicated that SKPs could develop into muscle progenitors and differentiated muscle cells in vitro and in vivo, thus providing valuable autologous cells for the treatment of muscle diseases.

miRNA 34a, 100, and 137 modulate differentiation of mouse embryonic stem cells

MicroRNAs (miRNAs) play an important role in proper function and differentiation of mouse embryonic stem cells (ESCs). We performed a systematic comparison of miRNA expression in undifferentiated vs. differentiating ESCs. We report that 138 miRNAs are increased on the induction of differentiation. We compared the entire list of candidate mRNA targets of up-regulated miRNAs with that of mRNA down-regulated in ESCs on induction of differentiation. Among the candidate targets emerging from this analysis, we found three genes, Smarca5, Jarid1b, and Sirt1, previously demonstrated to be involved in sustaining the undifferentiated phenotype in ESCs. On this basis, we first demonstrated that Smarca5 is a direct target of miR-100, Jarid1b of miR-137, and we also confirmed previously published data demonstrating that Sirt1 is a direct target of miR-34a in a different context. The suppression of these three miRNAs by anti-miRs caused the block of ESC differentiation induced by LIF withdrawal. On the other hand, the overexpression of the three miRNAs resulted in an altered expression of differentiation markers. These results demonstrate that miR-34a, miR-100, and miR-137 are required for proper differentiation of mouse ESCs, and that they function in part by targeting Sirt1, Smarca5, and Jarid1b mRNAs.

Fragile x mental retardation protein regulates proliferation and differentiation of adult neural stem/progenitor cells

Fragile X syndrome (FXS), the most common form of inherited mental retardation, is caused by the loss of functional fragile X mental retardation protein (FMRP). FMRP is an RNA–binding protein that can regulate the translation of specific mRNAs. Adult neurogenesis, a process considered important for neuroplasticity and memory, is regulated at multiple molecular levels. In this study, we investigated whether Fmrp deficiency affects adult neurogenesis. We show that in a mouse model of fragile X syndrome, adult neurogenesis is indeed altered. The loss of Fmrp increases the proliferation and alters the fate specification of adult neural progenitor/stem cells (aNPCs). We demonstrate that Fmrp regulates the protein expression of several components critical for aNPC function, including CDK4 and GSK3β. Dysregulation of GSK3β led to reduced Wnt signaling pathway activity, which altered the expression of neurogenin1 and the fate specification of aNPCs. These data unveil a novel regulatory role for Fmrp and translational regulation in adult neurogenesis.

Fragile X syndrome, the most common cause of inherited mental retardation, results from the loss of functional Fragile X mental retardation protein (FMRP). FMRP is an RNA–binding protein and is known to bind to specific mRNAs and to regulate their translation both in vitro and in vivo. Adult neurogenesis, a process considered important for neuroplasticity and memory, is regulated at multiple molecular levels. Here we show that Fmrp could regulate the proliferation and fate specification of adult neural progenitor/stem cells (aNPCs). These data unveil a novel regulatory role for Fmrp in adult neurogenesis.

Roles of small regulatory RNAs in determining neuronal identity

Neurogenesis, the process of generating functional neurons from neural stem cells, is tightly controlled by many intrinsic and extrinsic mechanisms. Uncovering these regulatory mechanisms is crucial for understanding the functions and plasticity of the human brain. Recent studies in both invertebrates and vertebrates point to the importance of small regulatory RNAs in regulating lineage-specific gene expression and determining neuronal identity during neurogenesis. These new observations suggest that small regulatory RNAs could function at many levels to regulate self-renewal of neural stem cells and neuronal fate specification, implicating small regulatory RNAs in the complexity of neurogenesis.

Cancer stem cell epigenetics and chemoresistance

Cancer stem cells (CSCs) are thought to sustain cancer progression, metastasis and recurrence after therapy. There is in vitro and in vivo evidence supporting the idea that CSCs are highly chemoresistant. Epigenetic gene regulation is crucial for both stem cell biology and chemoresistance. In this review, we summarize current data on epigenetic mechanisms of chemoresistance in cancer stem cells. We propose a model integrating classical CSC pathways (Wnt, Hedgehog and Notch), epigenetic effectors (Polycomb) and drug resistance genes (ABCG2, CD44). Moreover, we analyze the potential of epigenetic drugs to reverse CSC chemoresistance. In the future, CSC epigenomic profiling could help to dissect specific chemoresistance pathways, and have a significant clinical impact for patient stratification and rational design of therapeutic regimens.