TLX: A master regulator for neural stem cell maintenance and neurogenesis

Mutation of CHD7 impairs the output of neuroepithelium transition that is reversed by the inhibition of EZH2

Haploinsufficiency of CHD7 (Chromo-Helicase-DNA binding protein 7) causes a severe congenital disease CHARGE syndrome. Brain anomaly such as microcephaly and olfactory bulb agenesis seen in CHARGE patients have not been mimicked in previous animal models. Here, we uncover an indispensable function of CHD7 in the neuroepithelium (NE) but not in the neural stem cells (NSCs) after NE transition. Loss of Chd7 in mouse NE resulted in CHARGE-like brain anomalies due to reduced proliferation and differentiation of neural stem and progenitor cells, which were recapitulated in CHD7 KO human forebrain organoids. Mechanistically, we find that CHD7 activates neural transcription factors by removing the repressive histone mark H3K27me3 and promoting chromatin accessibility. Importantly, neurodevelopmental defects caused by CHD7 loss in human brain organoids and mice were ameliorated by the inhibition of H3K27me3 methyltransferase EZH2. Altogether, by implementing appropriate experimental models, we uncover the pathogenesis of CHD7-associated neurodevelopmental diseases, and identify a potential therapeutic opportunity for CHARGE syndrome.

Comparative Evaluation and Profiling of Chemical Tools for the Nuclear Hormone Receptor Family 2

Nuclear receptors regulate transcription in response to ligand signals and enable the pharmacological control of gene expression. However, many nuclear receptors are still poorly explored and are not accessible to ligand-based target identification studies. In particular, most members of the NR2 family are among the least studied proteins of the class, and apart from the retinoid X receptors (RXR), validated NR2 ligands are very rare. Here, we gathered the NR2 modulators reported in literature for comparative profiling in uniform test systems. Most candidate compounds displayed insufficient on-target activity or selectivity to be used as chemical tools for NR2 receptors underscoring the urgent need for further NR2 ligand development. Nevertheless, a small NR2 modulator set could be assembled for application in a chemogenomic fashion. There are 48 ligand-activated transcription factors in humans forming the superfamily of nuclear receptors (NRs, Figure 1a),1,2 which translate (endogenous) ligand signals into changes in gene expression patterns.3 The multifaceted roles of NRs span pivotal physiological processes, encompassing metabolism, inflammation, and cellular differentiation.4 Over decades, the NR1 and NR3 receptor families, including (steroid) hormone receptors and lipid sensors, have emerged as well-explored therapeutic targets of essential drugs like, for example, glucocorticoids as anti-inflammatory drugs, estrogen receptor modulators as contraceptives and anticancer agents, and PPAR agonists as oral antidiabetics.5-7 Despite this progress, a significant portion of the NR superfamily remains understudied, particularly within the NR2 family which comprises the hepatocyte nuclear factor-4 receptors (HNF4α/γ; NR2A1/2), the retinoid X receptors (RXRα/β/γ; NR2B1-3), the testicular receptors (TR2/4; NR2C1/2), the tailless-like receptors (TLX and PNR; NR2E1/3), and the COUP-TF-like receptors (COUP-TF1/2, V-erBA-related gene; NR2F1/2/6).8,9 Apart from RXR, all NR2 receptors are considered as orphan, and their ligands remain widely elusive. Therefore, chemical tools for most NR2 receptors are rare and poorly annotated posing an obstacle to target identification and validation studies. To enable chemogenomics on NR2 receptors and improve annotation, of the few available ligands, we gathered a scarce collection of NR2 modulators (agonists, antagonists, inverse agonists) for comparative evaluation and profiling. While the NR2B family (RXR) is well covered with high-quality ligands and a few early tools are available for NR2E1, we found the available ligands of the NR2A and NR2C families of insufficient quality to be used as chemical tools.

Development of Tailless Homologue Receptor (TLX) Agonist Chemical Tools

The human tailless homologue receptor (TLX) is a ligand-activated transcription factor acting as a master regulator of neural stem cell homeostasis. Despite its promising potential in neurodegenerative disease treatment, TLX ligands are rare but required to explore phenotypic effects of TLX modulation and for target validation. We have systematically studied and optimized a TLX agonist scaffold obtained by fragment fusion. Structural modification enabled the development of two TLX agonists endowed with nanomolar potency and binding affinity. Both exhibited favorable chemical tool characteristics including high selectivity and low toxicity. Most notably, the TLX agonists comprise different scaffolds and display high chemical diversity, enabling their use as a set for target identification and validation studies.

Indirect neurogenesis in space and time

During central nervous system (CNS) development, neural progenitor cells (NPCs) generate neurons and glia in two different ways. In direct neurogenesis, daughter cells differentiate directly into neurons or glia, whereas in indirect neurogenesis, neurons or glia are generated after one or more daughter cell divisions. Intriguingly, indirect neurogenesis is not stochastically deployed and plays instructive roles during CNS development: increased generation of cells from specific lineages; increased generation of early or late-born cell types within a lineage; and increased cell diversification. Increased indirect neurogenesis might contribute to the anterior CNS expansion evident throughout the Bilateria and help to modify brain-region size without requiring increased NPC numbers or extended neurogenesis. Increased indirect neurogenesis could be an evolutionary driver of the gyrencephalic (that is, folded) cortex that emerged during mammalian evolution and might even have increased during hominid evolution. Thus, selection of indirect versus direct neurogenesis provides a powerful developmental and evolutionary instrument that drives not only the evolution of CNS complexity but also brain expansion and modulation of brain-region size, and thereby the evolution of increasingly advanced cognitive abilities. This Review describes indirect neurogenesis in several model species and humans, and highlights some of the molecular genetic mechanisms that control this important process.

Cerebellar granular neuron progenitors exit their germinative niche via BarH-like1 activity mediated partly by inhibition of T-cell factor

Cerebellar granule neuron progenitors (GNPs) originate from the upper rhombic lip (URL), a germinative niche in which developmental defects produce human diseases. T-cell factor (TCF) responsiveness and Notch dependence are hallmarks of self-renewal in neural stem cells. TCF activity, together with transcripts encoding proneural gene repressors hairy and enhancer of split (Hes/Hey), are detected in the URL; however, their functions and regulatory modes are undeciphered. Here, we established amphibian as a pertinent model for studying vertebrate URL development. The amphibian long-lived URL is TCF active, whereas the external granular layer (EGL) is non-proliferative and expresses hes4 and hes5 genes. Using functional and transcriptomic approaches, we show that TCF activity is necessary for URL emergence and maintenance. We establish that the transcription factor Barhl1 controls GNP exit from the URL, acting partly through direct TCF inhibition. Identification of Barhl1 target genes suggests that, besides TCF, Barhl1 inhibits transcription of hes5 genes independently of Notch signaling. Observations in amniotes suggest a conserved role for Barhl in maintenance of the URL and/or EGL via co-regulation of TCF, Hes and Hey genes.

iPSC-Derived Astrocytes and Neurons Replicate Brain Gene Expression, Epigenetic, Cell Morphology and Connectivity Alterations Found in Autism

Excessive inflammatory reactions and oxidative stress are well-recognized molecular findings in autism and these processes can affect or be affected by the epigenetic landscape. Nonetheless, adequate therapeutics are unavailable, as patient-specific brain molecular markers for individualized therapies remain challenging.

METHODS

We used iPSC-derived neurons and astrocytes of patients with autism vs. controls (5/group) to examine whether they replicate the postmortem brain expression/epigenetic alterations of autism. Additionally, DNA methylation of 10 postmortem brain samples (5/group) was analyzed for genes affected in PSC-derived cells.

RESULTS

We found hyperexpression of TGFB1, TGFB2, IL6 and IFI16 and decreased expression of HAP1, SIRT1, NURR1, RELN, GPX1, EN2, SLC1A2 and SLC1A3 in the astrocytes of patients with autism, along with DNA hypomethylation of TGFB2, IL6, TNFA and EN2 gene promoters and a decrease in HAP1 promoter 5-hydroxymethylation in the astrocytes of patients with autism. In neurons, HAP1 and IL6 expression trended alike. While HAP1 promoter was hypermethylated in neurons, IFI16 and SLC1A3 promoters were hypomethylated and TGFB2 exhibited increased promoter 5-hydroxymethlation. We also found a reduction in neuronal arborization, spine size, growth rate, and migration, but increased astrocyte size and a reduced growth rate in autism. In postmortem brain samples, we found DNA hypomethylation of TGFB2 and IFI16 promoter regions, but DNA hypermethylation of HAP1 and SLC1A2 promoters in autism.

CONCLUSION

Autism-associated expression/epigenetic alterations in iPSC-derived cells replicated those reported in the literature, making them appropriate surrogates to study disease pathogenesis or patient-specific therapeutics.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Apically localized PANX1 impacts neuroepithelial expansion in human cerebral organoids

Dysfunctional paracrine signaling through Pannexin 1 (PANX1) channels is linked to several adult neurological pathologies and emerging evidence suggests that PANX1 plays an important role in human brain development. It remains unclear how early PANX1 influences brain development, or how loss of PANX1 alters the developing human brain. Using a cerebral organoid model of early human brain development, we find that PANX1 is expressed at all stages of organoid development from neural induction through to neuroepithelial expansion and maturation. Interestingly, PANX1 cellular distribution and subcellular localization changes dramatically throughout cerebral organoid development. During neural induction, PANX1 becomes concentrated at the apical membrane domain of neural rosettes where it co-localizes with several apical membrane adhesion molecules. During neuroepithelial expansion, PANX1-/- organoids are significantly smaller than control and exhibit significant gene expression changes related to cell adhesion, WNT signaling and non-coding RNAs. As cerebral organoids mature, PANX1 expression is significantly upregulated and is primarily localized to neuronal populations outside of the ventricular-like zones. Ultimately, PANX1 protein can be detected in all layers of a 21-22 post conception week human fetal cerebral cortex. Together, these results show that PANX1 is dynamically expressed by numerous cell types throughout embryonic and early fetal stages of human corticogenesis and loss of PANX1 compromises neuroepithelial expansion due to dysregulation of cell-cell and cell-matrix adhesion, perturbed intracellular signaling, and changes to gene regulation.

The Dialogue Between Neuroinflammation and Adult Neurogenesis: Mechanisms Involved and Alterations in Neurological Diseases

Adult neurogenesis occurs mainly in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles. Evidence supports the critical role of adult neurogenesis in various conditions, including cognitive dysfunction, Alzheimer's disease (AD), and Parkinson's disease (PD). Several factors can alter adult neurogenesis, including genetic, epigenetic, age, physical activity, diet, sleep status, sex hormones, and central nervous system (CNS) disorders, exerting either pro-neurogenic or anti-neurogenic effects. Compelling evidence suggests that any insult or injury to the CNS, such as traumatic brain injury (TBI), infectious diseases, or neurodegenerative disorders, can provoke an inflammatory response in the CNS. This inflammation could either promote or inhibit neurogenesis, depending on various factors, such as chronicity and severity of the inflammation and underlying neurological disorders. Notably, neuroinflammation, driven by different immune components such as activated glia, cytokines, chemokines, and reactive oxygen species, can regulate every step of adult neurogenesis, including cell proliferation, differentiation, migration, survival of newborn neurons, maturation, synaptogenesis, and neuritogenesis. Therefore, this review aims to present recent findings regarding the effects of various components of the immune system on adult neurogenesis and to provide a better understanding of the role of neuroinflammation and neurogenesis in the context of neurological disorders, including AD, PD, ischemic stroke (IS), seizure/epilepsy, TBI, sleep deprivation, cognitive impairment, and anxiety- and depressive-like behaviors. For each disorder, some of the most recent therapeutic candidates, such as curcumin, ginseng, astragaloside, boswellic acids, andrographolide, caffeine, royal jelly, estrogen, metformin, and minocycline, have been discussed based on the available preclinical and clinical evidence.

Stable expression of a truncated TLX variant drives differentiation of induced pluripotent stem cells into self-renewing neural stem cells for production of extracellular vesicles

Background

Neural stem cells (NSCs)-derived extracellular vesicles (EVs) possess great potential in treating severe neurological and cerebrovascular diseases, as they carry the modulatory and regenerative ingredients of NSCs. Induced pluripotent stem cells (iPSCs)-derived NSCs culture represents a sustainable source of therapeutic EVs. However, there exist two major challenges in obtaining a scalable culture of NSCs for high-efficiency EVs production: (1) the heterogeneity of iPSC-derived NSCs culture impairs the production of high-quality EVs and (2) the intrinsic propensity of neuronal or astroglial differentiation of NSCs during prolonged culturing reduces the number of NSCs for preparing EVs. A NSCs strain that is amenable to stable self-renewal and proliferation is thus greatly needed for scalable and long-term culture.

Methods

Various constructs of the genes encoding the orphan nuclear receptor NR2E1 (TLX) were stably transfected in iPSCs, which were subsequently cultured in a variety of differentiation media for generation of iNSCs^TLX. Transcriptomic and biomarker profile of iNSCs^TLX were investigated. In particular, the positivity ratios of Sox2/Nestin and Musashi/Vimentin were used to gauge the homogeneity of the iNSCs^TLX culture. The iNSCs expressing a truncated version of TLX (TLX-TP) was expanded for up to 45 passages, after which its neuronal differentiation potential and EV activity were evaluated.

Results

Stable expression of TLX-TP could confer the iPSCs with rapid and self-driven differentiation into NSCs through stable passaging up to 225 days. The long-term culture of NSCs maintained the highly homogenous expression of NSC-specific biomarkers and potential of neuronal differentiation. EVs harvested from the TLX-expressing NSCs cultures exhibited anti-inflammatory and neuroprotective activities.

Conclusions

iPSC-derived NSCs stably expressing TLX-TP is a promising cell line for scalable production of EVs, which should be further exploited for therapeutic development in neurological treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03131-4.

The Transcriptional Repressor Orphan Nuclear Receptor TLX Is Responsive to Xanthines

The orphan nuclear receptor tailless homologue (TLX) is expressed almost exclusively in neural stem cells acting as an essential factor for their survival and is hence considered as a promising drug target in neurodegeneration. However, few studies have characterized the roles of TLX due to the lack of ligands and limited functional understanding. Here, we identify xanthines including caffeine and istradefylline as TLX modulators that counteract the receptor's intrinsic repressor activity. Mutagenesis of residues lining a cavity within the TLX ligand binding domain altered the activity of these ligands, suggesting direct interactions with helix 5. Using xanthines as tool compounds, we observed a ligand-sensitive recruitment of the co-repressor silencing mediator for retinoid or thyroid-hormone receptors, TLX homodimerization, and heterodimerization with the retinoid X receptor. These protein-protein interactions evolve as factors that modulate the TLX function and suggest an unprecedented role of TLX in directly repressing other nuclear receptors.

Glial PAMPering and DAMPening of Adult Hippocampal Neurogenesis

Adult neurogenesis represents a mature brain's capacity to integrate newly generated neurons into functional circuits. Impairment of neurogenesis contributes to the pathophysiology of various mood and cognitive disorders such as depression and Alzheimer's Disease. The hippocampal neurogenic niche hosts neural progenitors, glia, and vasculature, which all respond to intrinsic and environmental cues, helping determine their current state and ultimate fate. In this article we focus on the major immune communication pathways and mechanisms through which glial cells sense, interact with, and modulate the neurogenic niche. We pay particular attention to those related to the sensing of and response to innate immune danger signals. Receptors for danger signals were first discovered as a critical component of the innate immune system response to pathogens but are now also recognized to play a crucial role in modulating non-pathogenic sterile inflammation. In the neurogenic niche, viable, stressed, apoptotic, and dying cells can activate danger responses in neuroimmune cells, resulting in neuroprotection or neurotoxicity. Through these mechanisms glial cells can influence hippocampal stem cell fate, survival, neuronal maturation, and integration. Depending on the context, such responses may be appropriate and on-target, as in the case of learning-associated synaptic pruning, or excessive and off-target, as in neurodegenerative disorders.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

The Potential Role of Inflammation in Modulating Endogenous Hippocampal Neurogenesis After Spinal Cord Injury

Currently there are approximately 291,000 people suffering from a spinal cord injury (SCI) in the United States. SCI is associated with traumatic changes in mobility and neuralgia, as well as many other long-term chronic health complications, including metabolic disorders, diabetes mellitus, non-alcoholic steatohepatitis, osteoporosis, and elevated inflammatory markers. Due to medical advances, patients with SCI survive much longer than previously. This increase in life expectancy exposes them to novel neurological complications such as memory loss, cognitive decline, depression, and Alzheimer's disease. In fact, these usually age-associated disorders are more prevalent in people living with SCI. A common factor of these disorders is the reduction in hippocampal neurogenesis. Inflammation, which is elevated after SCI, plays a major role in modulating hippocampal neurogenesis. While there is no clear consensus on the mechanism of the decline in hippocampal neurogenesis and cognition after SCI, we will examine in this review how SCI-induced inflammation could modulate hippocampal neurogenesis and provoke age-associated neurological disorders. Thereafter, we will discuss possible therapeutic options which may mitigate the influence of SCI associated complications on hippocampal neurogenesis.

Retinal Stem Cell 'Retirement Plans': Growth, Regulation and Species Adaptations in the Retinal Ciliary Marginal Zone

The vertebrate retina develops from a specified group of precursor cells that adopt distinct identities and generate lineages of either the neural retina, retinal pigmented epithelium, or ciliary body. In some species, including teleost fish and amphibians, proliferative cells with stem-cell-like properties capable of continuously supplying new retinal cells post-embryonically have been characterized and extensively studied. This region, termed the ciliary or circumferential marginal zone (CMZ), possibly represents a conserved retinal stem cell niche. In this review, we highlight the research characterizing similar CMZ-like regions, or stem-like cells located at the peripheral margin, across multiple different species. We discuss the proliferative parameters, multipotency and growth mechanisms of these cells to understand how they behave in vivo and how different molecular factors and signalling networks converge at the CMZ niche to regulate their activity. The evidence suggests that the mature retina may have a conserved propensity for homeostatic growth and plasticity and that dysfunction in the regulation of CMZ activity may partially account for dystrophic eye growth diseases such as myopia and hyperopia. A better understanding of the properties of CMZ cells will enable important insight into how an endogenous generative tissue compartment can adapt to altered retinal physiology and potentially even restore vision loss caused by retinal degenerative conditions.

Nuclear Receptors and Development of Marine Invertebrates

Nuclear Receptors (NRs) are a superfamily of transcription factors specific to metazoans that have the unique ability to directly translate the message of a signaling molecule into a transcriptional response. In vertebrates, NRs are pivotal players in countless processes of both embryonic and adult physiology, with embryonic development being one of the most dynamic periods of NR activity. Accumulating evidence suggests that NR signaling is also a major regulator of development in marine invertebrates, although ligands and transactivation dynamics are not necessarily conserved with respect to vertebrates. The explosion of genome sequencing projects and the interpretation of the resulting data in a phylogenetic context allowed significant progress toward an understanding of NR superfamily evolution, both in terms of molecular activities and developmental functions. In this context, marine invertebrates have been crucial for characterizing the ancestral states of NR-ligand interactions, further strengthening the importance of these organisms in the field of evolutionary developmental biology.

Genetic analysis of the NR2E1 gene as a candidate gene of schizophrenia

NR2E1 is implicated in the regulation of neurogenesis and considered as a candidate gene for schizophrenia. We resequenced all the exons of NR2E1 in 547 patients with schizophrenia and 567 controls from Taiwan. We identified five common SNPs with no association with patients with schizophrenia. Further haplotype-based association analysis showed that two haplotypes within NR2E1 were correlated with the schizophrenia risk. Four rare mutations located at untranslated regions were identified in patients with schizophrenia but not in our control sample. The present study suggests that NR2E1 is likely to play a significant role in conferring susceptibility to schizophrenia.

Interplay between orphan nuclear receptors and androgen receptor-dependent or-independent growth signalings in prostate cancer

It is well-established that both the initial and advanced growth of prostate cancer depends critically on androgens and thus on the activated androgen receptor (AR) -mediated signaling pathway. The unique hormone-dependent feature of prostate cancer forms the biological basis of hormone or androgen-deprivation therapy (ADT) that aims to suppress the AR signaling by androgen depletion or AR antagonists. ADT still remains the mainstay treatment option for locally advanced or metastatic prostate cancer. However, most patients upon ADT will inevitably develop therapy-resistance and progress to relapse in the form of castration-resistant disease (castration-resistant prostate cancer or CRPC) or even a more aggressive androgen-independent subtype (therapy-related neuroendocrine prostate cancer or NEPC). Recent advances show that besides AR, some ligand-independent members of nuclear receptor superfamily-designated as orphan nuclear receptors (ONRs), as their endogenous physiological ligands are either absent or not yet identified to date, also play significant roles in the growth regulation of prostate cancer via multiple AR-dependent or -independent (AR-bypass) pathways or mechanisms. In this review, we summarize the recent progress in the newly elucidated roles of ONRs in prostate cancer, with a focus on their interplay in the AR-dependent pathways (intratumoral androgen biosynthesis and suppression of AR signaling) and AR-independent pathways or cellular processes (hypoxia, oncogene- or tumor suppressor-induced senescence, apoptosis and regulation of prostate cancer stem cells). These ONRs with their newly characterized roles not only can serve as novel biomarkers but also as potential therapeutic targets for management of advanced prostate cancer.

Tumorigenic effects of TLX overexpression in HEK 293T cells

BACKGROUND

The human orphan receptor TLX (NR2E1) is a key regulator of neurogenesis, adult stem cell maintenance, and tumorigenesis. However, little is known about the genetic and transcriptomic events that occur following TLX overexpression in human cell lines.

AIMS

Here, we used cytogenetics and RNA sequencing to investigate the effect of TLX overexpression with an inducible vector system in the HEK 293T cell line.

METHODS AND RESULTS

Conventional spectral karyotyping was used to identify chromosomal abnormalities, followed by fluorescence in situ hybridization (FISH) analysis on chromosome spreads to assess TLX DNA copy number. Illumina paired-end whole transcriptome sequencing was then performed to characterize recurrent genetic variants (single nucleotide polymorphisms (SNPs) and indels), expressed gene fusions, and gene expression profiles. Lastly, flow cytometry was used to analyze cell cycle distribution. Intriguingly, we show that upon transfection with a vector containing the human TLX gene (eGFP-hTLX), an isochromosome forms on the long arm of chromosome 6, thereby resulting in DNA gain of the TLX locus (6q21) and upregulation of TLX. Induction of the eGFP-hTLX vector further increased TLX expression levels, leading to G0-G1 cell cycle arrest, genetic aberrations, modulation of gene expression patterns, and crosstalk with other nuclear receptors (AR, ESR1, ESR2, NR1H4, and NR3C2). We identified a 49-gene signature associated with central nervous system (CNS) development and carcinogenesis, in addition to potentially cancer-driving gene fusions (LARP1-CNOT8 and NSL1-ZDBF2) and deleterious genetic variants (frameshift insertions in the CTSH, DBF4, POSTN, and WDR78 genes).

CONCLUSION

Taken together, these findings illustrate that TLX may play a pivotal role in tumorigenesis via genomic instability and perturbation of cancer-related processes.

A role for the orphan nuclear receptor TLX in the interaction between neural precursor cells and microglia

Microglia are an essential component of the neurogenic niche in the adult hippocampus and are involved in the control of neural precursor cell (NPC) proliferation, differentiation and the survival and integration of newborn neurons in hippocampal circuitry. Microglial and neuronal cross-talk is mediated in part by the chemokine fractalkine/chemokine (C-X3-C motif) ligand 1 (CX3CL1) released from neurons, and its receptor CX3C chemokine receptor 1 (CX3CR1) which is expressed on microglia. A disruption in this pathway has been associated with impaired neurogenesis yet the specific molecular mechanisms by which this interaction occurs remain unclear. The orphan nuclear receptor TLX (Nr2e1; homologue of the Drosophila tailless gene) is a key regulator of hippocampal neurogenesis, and we have shown that in its absence microglia exhibit a pro-inflammatory activation phenotype. However, it is unclear whether a disturbance in CX3CL1/CX3CR1 communication mediates an impairment in TLX-related pathways which may have subsequent effects on neurogenesis. To this end, we assessed miRNA expression of up- and down-stream signalling molecules of TLX in the hippocampus of mice lacking CX3CR1. Our results demonstrate that a lack of CX3CR1 is associated with altered expression of TLX and its downstream targets in the hippocampus without significantly affecting upstream regulators of TLX. Thus, TLX may be a potential participant in neural stem cell (NSC)-microglial cross-talk and may be an important target in understanding inflammatory-associated impairments in neurogenesis.

Molecular correlates of hypothalamic development in songbird ontogeny in comparison with the telencephalon

Development of the songbird brain provides an excellent experimental model for understanding the regulation of sex differences in ontogeny. Considering the regulatory role of the hypothalamus in endocrine, in particular reproductive, physiology, we measured the structural (volume) and molecular correlates of hypothalamic development during ontogeny of male and female zebra finches. We quantified by relative quantitative polymerase chain reaction (rqPCR) the expression of 14 genes related to thyroid and steroid hormones actions as well as 12 genes related to brain plasticity at four specific time points during ontogeny and compared these expression patterns with the expression of the same genes as detected by transcriptomics in the telencephalon. These two different methodological approaches detected specific changes with age and demonstrated that in a substantial number of cases changes observed in both brain regions are nearly identical. Other genes however had a tissue-specific developmental pattern. Sex differences or interactions of sex by age were detected in the expression of a subset of genes, more in hypothalamus than telencephalon. These results correlate with multiple known aspects of the developmental and reproductive physiology but also raise a number of new functional questions.

Characterization of LSD1 Expression Within the Murine Eye

Purpose

The purpose of this study was to extend the current understanding of endogenous lysine-specific demethylase 1 (LSD1) expression spatially and temporally in the retina. Toward that end, we determined the localization and levels of LSD1 and its substrates H3K4me1 and H3K4me2 (H3K4me1/2) within the murine eye.

Methods

Immunofluorescent microscopy for LSD1, H3K4me1, and H3K4me2 was conducted on murine formalin-fixed paraffin-embedded eye sections across development in addition to Western immunoblotting to assess localization and protein levels.

Results

Retinal LSD1 protein levels were highest at postnatal day 7 (P7), whereas its substrates H3K4me1 and H3K4me2 had equally high levels at P2 and P14. Concentrations of all three proteins gradually decreased over developmental time until reaching a basement level of ∼60% of maximum at P36. LSD1 and H3K4me1/2 were expressed uniformly in all retinal progenitor cells. By P36, there was variability in LSD1 expression in the ganglion cell layer, uniform expression in the inner nuclear layer, and dichotomous expression between photoreceptors in the outer nuclear layer. This contrasted with H3K4me1/2 expression, which remained uniform. Additionally, LSD1 was widely expressed in the lens, cornea, and retinal pigment epithelium.

Conclusions

Consistent with its known role in neuronal differentiation, LSD1 is highly and uniformly expressed throughout all retinal progenitor cells. Variability in LSD1 expression, particularly in photoreceptors, may be indicative of their unique transcriptomes and epigenetic patterns of rods and cones. Murine rod nuclei exhibit LSD1 expression in a ring or shell, rather than throughout the nucleus, consistent with their unique inverted chromatin organization. LSD1 has substantial expression throughout adulthood, especially in cone nuclei. By providing insight into endogenous LSD1 expression, our current findings could directly inform future studies to determine the exact role of Lsd1 in the development and maintenance of specific structures and cell types within the eye.

Anterior CNS expansion driven by brain transcription factors

During CNS development, there is prominent expansion of the anterior region, the brain. In Drosophila, anterior CNS expansion emerges from three rostral features: (1) increased progenitor cell generation, (2) extended progenitor cell proliferation, (3) more proliferative daughters. We find that tailless (mouse Nr2E1/Tlx), otp/Rx/hbn (Otp/Arx/Rax) and Doc1/2/3 (Tbx2/3/6) are important for brain progenitor generation. These genes, and earmuff (FezF1/2), are also important for subsequent progenitor and/or daughter cell proliferation in the brain. Brain TF co-misexpression can drive brain-profile proliferation in the nerve cord, and can reprogram developing wing discs into brain neural progenitors. Brain TF expression is promoted by the PRC2 complex, acting to keep the brain free of anti-proliferative and repressive action of Hox homeotic genes. Hence, anterior expansion of the Drosophila CNS is mediated by brain TF driven ‘super-generation’ of progenitors, as well as ‘hyper-proliferation’ of progenitor and daughter cells, promoted by PRC2-mediated repression of Hox activity.

Nuclear receptor TLX regulates islet beta cell proliferation via E2F6

Both type 1 and type 2 diabetes are associated with loss of functional beta cell mass, and strategies to restore beta cells are urgently needed. We reported previously that overexpression of the nuclear receptor TLX induces beta cell proliferation, but the underlying molecular mechanism has not been defined. Here, we identified direct targets of TLX in beta cells at the genome-wide level by ChIP-Seq. These targets include a cadre of regulators that are known to be critical for proliferation. Among these ChIP targets, E2F6 was tightly associated with the cell cycle modules, and thus, we further analyzed E2F6 expression and function in beta cells. We showed that E2F6 is strongly downregulated by TLX, and its expression inhibits beta cell proliferation. Moreover, coexpression of E2F6 with TLX partially abrogated the proliferative effects of TLX. These results strongly suggest that TLX acts through E2F6 to regulate beta cell proliferation. Together, the results of this study reveal a direct interaction between TLX and E2F6 and suggest new targets for the expansion of functional beta cell mass.

Aberrant transcriptomes and DNA methylomes define pathways that drive pathogenesis and loss of brain laterality/asymmetry in schizophrenia and bipolar disorder

Although the loss of brain laterality is one of the most consistent modalities in schizophrenia (SCZ) and bipolar disorder (BD), its molecular basis remains elusive. Our limited previous studies indicated that epigenetic modifications are key to the asymmetric transcriptomes of brain hemispheres. We used whole-genome expression microarrays to profile postmortem brain samples from subjects with SCZ, psychotic BD [BD[+]] or non-psychotic BD [BD(-)], or matched controls (10/group) and performed whole-genome DNA methylation (DNAM) profiling of the same samples (3-4/group) to identify pathways associated with SCZ or BD[+] and genes/sites susceptible to epigenetic regulation. qRT-PCR and quantitative DNAM analysis were employed to validate findings in larger sample sets (35/group). Gene Set Enrichment Analysis (GSEA) demonstrated that BMP signaling and astrocyte and cerebral cortex development are significantly (FDR q < 0.25) coordinately upregulated in both SCZ and BD[+], and glutamate signaling and TGFβ signaling are significantly coordinately upregulated in SCZ. GSEA also indicated that collagens are downregulated in right versus left brain of controls, but not in SCZ or BD[+] patients. Ingenuity Pathway Analysis predicted that TGFB2 is an upstream regulator of these genes (p = .0012). While lateralized expression of TGFB2 in controls (p = .017) is associated with a corresponding change in DNAM (p ≤ .023), lateralized expression and DNAM of TGFB2 are absent in SCZ or BD. Loss of brain laterality in SCZ and BD corresponds to aberrant epigenetic regulation of TGFB2 and changes in TGFβ signaling, indicating potential avenues for disease prevention/treatment.

Altered Nup153 Expression Impairs the Function of Cultured Hippocampal Neural Stem Cells Isolated from a Mouse Model of Alzheimer's Disease

Impairment of adult hippocampal neurogenesis is an early event in Alzheimer's disease (AD), playing a crucial role in cognitive dysfunction associated with this pathology. However, the mechanisms underlying defective neurogenesis in AD are still unclear. Recently, the nucleoporin Nup153 has been described as a new epigenetic determinant of adult neural stem cell (NSC) maintenance and fate. Here we investigated whether Nup153 dysfunction could affect the plasticity of NSCs in AD. Nup153 expression was strongly reduced in AD-NSCs, as well as its interaction with the transcription factor Sox2, a master regulator of NSC stemness and their neuronal differentiation. Similar Nup153 reduction was also observed in WT-NSCs treated with amyloid-β (Aβ) or stimulated with a nitric oxide donor. Accordingly, AD-NSCs treated with either a γ-secretase inhibitor or antioxidant compounds showed higher Nup153 levels suggesting that both nitrosative stress and Aβ accumulation affect Nup153 expression. Of note, restoration of Nup153 levels in AD-NSCs promoted their proliferation, as assessed by BrdU incorporation, neurosphere assay, and stemness gene expression analysis. Nup153 overexpression also recovered AD-NSC response to differentiation, increasing the expression of pro-neuronal genes, the percentage of cells positive for neuronal markers, and the acquisition of a more mature neuronal phenotype. Electrophysiological recordings revealed that neurons differentiated from Nup153-transfected AD-NSCs displayed higher Na⁺ current density, comparable to those deriving from WT-NSCs. Our data uncover a novel role for Nup153 in NSCs from animal model of AD and point to Nup153 as potential target to restore physiological NSC behavior and fate in neurodegenerative diseases.

TLX knockdown in the dorsal dentate gyrus of juvenile rats differentially affects adolescent and adult behaviour

The orphan nuclear receptor TLX is predominantly expressed in the central nervous system and is an important factor regulating the maintenance and self-renewal of neural stem cells from embryonic development through adulthood. In adolescence and adulthood, TLX expression is restricted to the neurogenic niches of the brain: the dentate gyrus of the hippocampus and the subventricular zone. The adolescent period is critical for maturation of the hippocampus with heightened levels of neurogenesis observed in rodents. Therefore, we investigated whether lentiviral silencing of TLX expression (TLX knockdown) in the dorsal dentate gyrus of juvenile rats incurred differential impairments in behaviour during late adolescence and adulthood. Our results showed that knockdown of TLX in the dorsal dentate gyrus led to a decrease in cell proliferation in the dorsal but not ventral dentate gyrus. At a behavioural level we observed differential effects in adolescence and adulthood across a number of parameters. A hyperactive phenotype was present in adolescent but not adult TLX knockdown rats, and an increase in immobility during adolescence and in swimming frequency during adulthood was observed in the forced swim test. There was an increased defecation frequency in the open field during adulthood but not adolescence. There were no changes in cognitive performance on hippocampus-dependent tasks or in anxiety-related behaviours. In conclusion, silencing of TLX in the dorsal dentate gyrus led to impairments in hippocampal-independent behaviours which either did not persist or were reversed during adulthood. The current data highlight the temporal importance and function of the nuclear receptor TLX during development.

MicroRNAs Engage in Complex Circuits Regulating Adult Neurogenesis

The finding that the adult mammalian brain is still capable of producing neurons has ignited a new field of research aiming to identify the molecular mechanisms regulating adult neurogenesis. An improved understanding of these mechanisms could lead to the development of novel approaches to delay cognitive decline and facilitate neuroregeneration in the adult human brain. Accumulating evidence suggest microRNAs (miRNAs), which represent a class of post-transcriptional gene expression regulators, as crucial part of the gene regulatory networks governing adult neurogenesis. This review attempts to illustrate how miRNAs modulate key processes in the adult neurogenic niche by interacting with each other and with transcriptional regulators. We discuss the function of miRNAs in adult neurogenesis following the life-journey of an adult-born neuron from the adult neural stem cell (NSCs) compartment to its final target site. We first survey how miRNAs control the initial step of adult neurogenesis, that is the transition of quiescent to activated proliferative adult NSCs, and then go on to discuss the role of miRNAs to regulate neuronal differentiation, survival, and functional integration of the newborn neurons. In this context, we highlight miRNAs that converge on functionally related targets or act within cross talking gene regulatory networks. The cooperative manner of miRNA action and the broad target repertoire of each individual miRNA could make the miRNA system a promising tool to gain control on adult NSCs in the context of therapeutic approaches.

Regulation of Age-related Decline by Transcription Factors and Their Crosstalk with the Epigenome

Aging is a complex phenomenon, where damage accumulation, increasing deregulation of biological pathways, and loss of cellular homeostasis lead to the decline of organismal functions over time. Interestingly, aging is not entirely a stochastic process and progressing at a constant rate, but it is subject to extensive regulation, in the hands of an elaborate and highly interconnected signaling network. This network can integrate a variety of aging-regulatory stimuli, i.e. fertility, nutrient availability, or diverse stresses, and relay them via signaling cascades into gene regulatory events - mostly of genes that confer stress resistance and thus help protect from damage accumulation and homeostasis loss. Transcription factors have long been perceived as the pivotal nodes in this network. Yet, it is well known that the epigenome substantially influences eukaryotic gene regulation, too. A growing body of work has recently underscored the importance of the epigenome also during aging, where it not only undergoes drastic age-dependent changes but also actively influences the aging process. In this review, we introduce the major signaling pathways that regulate age-related decline and discuss the synergy between transcriptional regulation and the epigenetic landscape.

FOXP1 Promotes Embryonic Neural Stem Cell Differentiation by Repressing Jagged1 Expression

Mutations in FOXP1 have been linked to neurodevelopmental disorders including intellectual disability and autism; however, the underlying molecular mechanisms remain ill-defined. Here, we demonstrate with RNA and chromatin immunoprecipitation sequencing that FOXP1 directly regulates genes controlling neurogenesis. We show that FOXP1 is expressed in embryonic neural stem cells (NSCs), and modulation of FOXP1 expression affects both neuron and astrocyte differentiation. Using a murine model of cortical development, FOXP1-knockdown in utero was found to reduce NSC differentiation and migration during corticogenesis. Furthermore, transplantation of FOXP1-knockdown NSCs in neonatal mice after hypoxia-ischemia challenge demonstrated that FOXP1 is also required for neuronal differentiation and functionality in vivo. FOXP1 was found to repress the expression of Notch pathway genes including the Notch-ligand Jagged1, resulting in inhibition of Notch signaling. Finally, blockade of Jagged1 in FOXP1-knockdown NSCs rescued neuronal differentiation in vitro. Together, these data support a role for FOXP1 in regulating embryonic NSC differentiation by modulating Notch signaling.

•

FOXP1 promotes astrocyte and neuronal differentiation of NSCs in vitro

•

FOXP1 promotes neuronal differentiation of NSCs in vivo

•

FOXP1 transcriptionally regulates pro-neural genes and represses Notch pathway genes

•

FOXP1 promotes neuronal differentiation by limiting Jagged1 expression

Cell Signaling in Neuronal Stem Cells

The defining characteristic of neural stem cells (NSCs) is their ability to multiply through symmetric divisions and proliferation, and differentiation by asymmetric divisions, thus giving rise to different types of cells of the central nervous system (CNS). A strict temporal space control of the NSC differentiation is necessary, because its alterations are associated with neurological dysfunctions and, in some cases, death. This work reviews the current state of the molecular mechanisms that regulate the transcription in NSCs, organized according to whether the origin of the stimulus that triggers the molecular cascade in the CNS is internal (intrinsic factors) or whether it is the result of the microenvironment that surrounds the CNS (extrinsic factors).

KDM1A microenvironment, its oncogenic potential, and therapeutic significance

The lysine-specific histone demethylase 1A (KDM1A) was the first demethylase to challenge the concept of the irreversible nature of methylation marks. KDM1A, containing a flavin adenine dinucleotide (FAD)-dependent amine oxidase domain, demethylates histone 3 lysine 4 and histone 3 lysine 9 (H3K4me1/2 and H3K9me1/2). It has emerged as an epigenetic developmental regulator and was shown to be involved in carcinogenesis. The functional diversity of KDM1A originates from its complex structure and interactions with transcription factors, promoters, enhancers, oncoproteins, and tumor-associated genes (tumor suppressors and activators). In this review, we discuss the microenvironment of KDM1A in cancer progression that enables this protein to activate or repress target gene expression, thus making it an important epigenetic modifier that regulates the growth and differentiation potential of cells. A detailed analysis of the mechanisms underlying the interactions between KDM1A and the associated complexes will help to improve our understanding of epigenetic regulation, which may enable the discovery of more effective anticancer drugs.

The orphan nuclear receptor TLX regulates hippocampal transcriptome changes induced by IL-1β

TLX is an orphan nuclear receptor highly expressed within neural progenitor cells (NPCs) in the hippocampus where is regulates proliferation. Inflammation has been shown to have negative effects on hippocampal function as well as on NPC proliferation. Specifically, the pro-inflammatory cytokine IL-1β suppresses NPC proliferation as well as TLX expression in the hippocampus. However, it is unknown whether TLX itself is involved in regulating the inflammatory response in the hippocampus. To explore the role of TLX in inflammation, we assessed changes in the transcriptional landscape of the hippocampus of TLX knockout mice (TLX^-/-) compared to wildtype (WT) littermate controls with and without intrahippocampal injection of IL-1β using a whole transcriptome RNA sequencing approach. We demonstrated that there is an increase in the transcription of genes involved in the promotion of inflammation and regulation of cell chemotaxis (Tnf, Il1b, Cxcr1, Cxcr2, Tlr4) and a decrease in the expression of genes relating to synaptic signalling (Lypd1, Syt4, Cplx2) in cannulated TLX^-/- mice compared to WT controls. We demonstrate that mice lacking in TLX share a similar increase in 176 genes involved in regulating inflammation (e.g. Cxcl1, Tnf, Il1b) as WT mice injected with IL-1β into the hippocampus. Moreover, TLX^-/- mice injected with IL-1β displayed a blunted transcriptional profile compared to WT mice injected with IL-1β. Thus, TLX^-/- mice, which already have an exaggerated inflammatory profile after cannulation surgery, are primed to respond differently to an inflammatory stimulus such as IL-1β. Together, these results demonstrate that TLX regulates hippocampal inflammatory transcriptome response to brain injury (in this case cannulation surgery) and cytokine stimulation.

The Vast Complexity of the Epigenetic Landscape during Neurodevelopment: An Open Frame to Understanding Brain Function

Development is a well-defined stage-to-stage process that allows the coordination and maintenance of the structure and function of cells and their progenitors, in a complete organism embedded in an environment that, in turn, will shape cellular responses to external stimuli. Epigenetic mechanisms comprise a group of process that regulate genetic expression without changing the DNA sequence, and they contribute to the necessary plasticity of individuals to face a constantly changing medium. These mechanisms act in conjunction with genetic pools and their correct interactions will be crucial to zygote formation, embryo development, and brain tissue organization. In this work, we will summarize the main findings related to DNA methylation and histone modifications in embryonic stem cells and throughout early development phases. Furthermore, we will critically outline some key observations on how epigenetic mechanisms influence the rest of the developmental process and how long its footprint is extended from fecundation to adulthood.

Orphan nuclear receptor TLX contributes to androgen insensitivity in castration-resistant prostate cancer via its repression of androgen receptor transcription

The metastatic castration-resistant prostate cancer (CRPC) is a lethal form of prostate cancer, in which the expression of androgen receptor (AR) is highly heterogeneous. Indeed, lower AR expression and attenuated AR signature activity is shown in CRPC tissues, especially in the subset of neuroendocrine prostate cancer (NEPC) and prostate cancer stem-like cells (PCSCs). However, the significance of AR downregulation in androgen insensitivity and de-differentiation of tumor cells in CRPC is poorly understood and much neglected. Our previous study shows that the orphan nuclear receptor TLX (NR2E1), which is upregulated in prostate cancer, plays an oncogenic role in prostate carcinogenesis by suppressing oncogene-induced senescence. In the present study, we further established that TLX exhibited an increased expression in metastatic CRPC. Further analyses showed that overexpression of TLX could confer resistance to androgen deprivation and anti-androgen in androgen-dependent prostate cancer cells in vitro and in vivo, whereas knockdown of endogenous TLX could potentiate the sensitivity to androgen deprivation and anti-androgen in prostate cancer cells. Our study revealed that the TLX-induced resistance to androgen deprivation and anti-androgen was mediated through its direct suppression of AR gene transcription and signaling in both androgen-stimulated and -unstimulated prostate cancer cells. We also characterized that TLX could bind directly to AR promoter and repress AR transcription by recruitment of histone modifiers, including HDAC1, HDAC3, and LSD1. Together, our present study shows, for the first time, that TLX can contribute to androgen insensitivity in CRPC via repression of AR gene transcription and signaling, and also implicates that targeting the druggable TLX may have a potential therapeutic significance in CRPC management, particularly in NEPC and PCSCs.

Brain-derived neurotrophic factor: a mediator of inflammation-associated neurogenesis in Alzheimer's disease

In early- or late-onset Alzheimer's disease (AD), inflammation, which is triggered by pathologic conditions, influences the progression of neurodegeneration. Brain-derived neurotrophic factor (BDNF) has emerged as a crucial mediator of neurogenesis, because it exhibits a remarkable activity-dependent regulation of expression, which suggests that it may link inflammation to neurogenesis. Emerging evidence suggests that acute and chronic inflammation in AD differentially modulates neurotrophin functions, which are related to the roles of inflammation in neuroprotection and neurodegeneration. Recent studies also indicate novel mechanisms of BDNF-mediated neuroprotection, including the modulation of autophagy. Numerous research studies have demonstrated reverse parallel alterations between proinflammatory cytokines and BDNF during neurodegeneration; thus, we hypothesize that one mechanism that underlies the negative impact of chronic inflammation on neurogenesis is the reduction of BDNF production and function by proinflammatory cytokines.

Brain plasticity, cognitive functions and neural stem cells: a pivotal role for the brain-specific neural master gene |-SRGAP2-FAM72-|

Due to an aging society with an increased dementia-induced threat to higher cognitive functions, it has become imperative to understand the molecular and cellular events controlling the memory and learning processes in the brain. Here, we suggest that the novel master gene pair |-SRGAP2-FAM72-| (SLIT-ROBO Rho GTPase activating the protein 2, family with sequence similarity to 72) reveals a new dogma for the regulation of neural stem cell (NSC) gene expression and is a distinctive player in the control of human brain plasticity. Insight into the specific regulation of the brain-specific neural master gene |-SRGAP2-FAM72-| may essentially contribute to novel therapeutic approaches to restore or improve higher cognitive functions.

Nuclear deterrents: Intrinsic regulators of IL-1β-induced effects on hippocampal neurogenesis

Hippocampal neurogenesis, the process by which new neurons are born and develop into the host circuitry, begins during embryonic development and persists throughout adulthood. Over the last decade considerable insights have been made into the role of hippocampal neurogenesis in cognitive function and the cellular mechanisms behind this process. Additionally, an increasing amount of evidence exists on the impact of environmental factors, such as stress and neuroinflammation on hippocampal neurogenesis and subsequent impairments in cognition. Elevated expression of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus is established as a significant contributor to the neuronal demise evident in many neurological and psychiatric disorders and is now known to negatively regulate hippocampal neurogenesis. In order to prevent the deleterious effects of IL-1β on neurogenesis it is necessary to identify signalling pathways and regulators of neurogenesis within neural progenitor cells that can interact with IL-1β. Nuclear receptors are ligand regulated transcription factors that are involved in modulating a large number of cellular processes including neurogenesis. In this review we focus on the signalling mechanisms of specific nuclear receptors involved in regulating neurogenesis (glucocorticoid receptors, peroxisome proliferator activated receptors, estrogen receptors, and nuclear receptor subfamily 2 group E member 1 (NR2E1 or TLX)). We propose that these nuclear receptors could be targeted to inhibit neuroinflammatory signalling pathways associated with IL-1β. We discuss their potential to be therapeutic targets for neuroinflammatory disorders affecting hippocampal neurogenesis and associated cognitive function.

Developmental pathway genes and neural plasticity underlying emotional learning and stress-related disorders

The manipulation of neural plasticity as a means of intervening in the onset and progression of stress-related disorders retains its appeal for many researchers, despite our limited success in translating such interventions from the laboratory to the clinic. Given the challenges of identifying individual genetic variants that confer increased risk for illnesses like depression and post-traumatic stress disorder, some have turned their attention instead to focusing on so-called "master regulators" of plasticity that may provide a means of controlling these potentially impaired processes in psychiatric illnesses. The mammalian homolog of Tailless (TLX), Wnt, and the homeoprotein Otx2 have all been proposed to constitute master regulators of different forms of plasticity which have, in turn, each been implicated in learning and stress-related disorders. In the present review, we provide an overview of the changing distribution of these genes and their roles both during development and in the adult brain. We further discuss how their distinct expression profiles provide clues as to their function, and may inform their suitability as candidate drug targets in the treatment of psychiatric disorders.

Absence of the neurogenesis-dependent nuclear receptor TLX induces inflammation in the hippocampus

The orphan nuclear receptor TLX (Nr2e1) is a key regulator of hippocampal neurogenesis. Impaired adult hippocampal neurogenesis has been reported in neurodegenerative and psychiatric conditions including dementia and stress-related depression. Neuroinflammation is also implicated in the neuropathology of these disorders, and has been shown to negatively affect hippocampal neurogenesis. To investigate a role for TLX in hippocampal neuroinflammation, we assessed microglial activation in the hippocampus of mice with a spontaneous deletion of TLX. Results from our study suggest that a lack of TLX is implicated in deregulation of microglial phenotype and that consequently, the survival and function of newborn cells in the hippocampus is impaired. TLX may be an important target in understanding inflammatory-associated impairments in neurogenesis.

Vesicular glutamate transporters play a role in neuronal differentiation of cultured SVZ-derived neural precursor cells

The role of glutamate in the regulation of neurogenesis is well-established, but the role of vesicular glutamate transporters (VGLUTs) and excitatory amino acid transporters (EAATs) in controlling adult neurogenesis is unknown. Here we investigated the implication of VGLUTs in the differentiation of subventricular zone (SVZ)-derived neural precursor cells (NPCs). Our results show that NPCs express VGLUT1-3 and EAAT1-3 both at the mRNA and protein level. Their expression increases during differentiation closely associated with the expression of marker genes. In expression analyses we show that VGLUT1 and VGLUT2 are preferentially expressed by cultured SVZ-derived doublecortin+ neuroblasts, while VGLUT3 is found on GFAP+ glial cells. In cultured NPCs, inhibition of VGLUT by Evans Blue increased the mRNA level of neuronal markers doublecortin, B3T and MAP2, elevated the number of NPCs expressing doublecortin protein and promoted the number of cells with morphological appearance of branched neurons, suggesting that VGLUT function prevents neuronal differentiation of NPCs. This survival- and differentiation-promoting effect of Evans blue was corroborated by increased AKT phosphorylation and reduced MAPK phosphorylation. Thus, under physiological conditions, VGLUT1-3 inhibition, and thus decreased glutamate exocytosis, may promote neuronal differentiation of NPCs.

The role of the SWI/SNF chromatin remodeling complex in maintaining the stemness of glioma initiating cells

Glioma initiating cells (GICs) are thought to contribute to therapeutic resistance and tumor recurrence in glioblastoma, a lethal primary brain tumor in adults. Although the stem-like properties of GICs, such as self-renewal and tumorigenicity, are epigenetically regulated, the role of a major chromatin remodeling complex in human, the SWI/SNF complex, remains unknown in these cells. We here demonstrate that the SWI/SNF core complex, that is associated with a unique corepressor complex through the d4-family proteins, DPF1 or DPF3a, plays essential roles in stemness maintenance in GICs. The serum-induced differentiation of GICs downregulated the endogenous expression of DPF1 and DPF3a, and the shRNA-mediated knockdown of each gene reduced both sphere-forming ability and tumor-forming activity in a mouse xenograft model. Rescue experiments revealed that DPF1 has dominant effects over DPF3a. Notably, whereas we have previously reported that d4-family members can function as adaptor proteins between the SWI/SNF complex and NF-κB dimers, this does not significantly contribute to maintaining the stemness properties of GICs. Instead, these proteins were found to link a corepressor complex containing the nuclear receptor, TLX, and LSD1/RCOR2 with the SWI/SNF core complex. Collectively, our results indicate that DPF1 and DPF3a are potential therapeutic targets for glioblastoma.

Steroid Hormones and the Physiological Regulation of Tissue-Resident Stem Cells: Lessons from the Drosophila Ovary

PURPOSE OF REVIEW

Stem cells respond to local paracrine signals; more recently, however, systemic hormones have also emerged as key regulators of stem cells. This review explores the role of steroid hormones in stem cells, using the Drosophila germline stem cell as a centerpiece for discussion.

RECENT FINDINGS

Stem cells sense and respond directly and indirectly to steroid hormones, which regulate diverse sets of target genes via interactions with nuclear hormone receptors. Hormone-regulated networks likely integrate the actions of multiple systemic signals to adjust the activity of stem cell lineages in response to changes in physiological status.

SUMMARY

Hormones are inextricably linked to animal physiology, and can control stem cells and their local niches. Elucidating the molecular mechanisms of hormone signaling in stem cells is essential for our understanding of the fundamental underpinnings of stem cell biology, and for informing new therapeutic interventions against cancers or for regenerative medicine.

CONSERVED AND EXAPTED FUNCTIONS OF NUCLEAR RECEPTORS IN ANIMAL DEVELOPMENT

The nuclear receptor gene family includes 18 members that are broadly conserved among multiple disparate animal phyla, indicating that they trace their evolutionary origins to the time at which animal life arose. Typical nuclear receptors contain two major domains: a DNA-binding domain and a C-terminal domain that may bind a lipophilic hormone. Many of these nuclear receptors play varied roles in animal development, including coordination of life cycle events and cellular differentiation. The well-studied genetic model systems of Drosophila, C. elegans, and mouse permit an evaluation of the extent to which nuclear receptor function in development is conserved or exapted (repurposed) over animal evolution. While there are some specific examples of conserved functions and pathways, there are many clear examples of exaptation. Overall, the evolutionary theme of exaptation appears to be favored over strict functional conservation. Despite strong conservation of DNA-binding domain sequences and activity, the nuclear receptors prove to be highly-flexible regulators of animal development.

Stem Cell Transcriptome Responses and Corresponding Biomarkers That Indicate the Transition from Adaptive Responses to Cytotoxicity

Analysis of transcriptome changes has become an established method to characterize the reaction of cells to toxicants. Such experiments are mostly performed at compound concentrations close to the cytotoxicity threshold. At present, little information is available on concentration-dependent features of transcriptome changes, in particular, at the transition from noncytotoxic concentrations to conditions that are associated with cell death. Thus, it is unclear in how far cell death confounds the results of transcriptome studies. To explore this gap of knowledge, we treated pluripotent stem cells differentiating to human neuroepithelial cells (UKN1 assay) for short periods (48 h) with increasing concentrations of valproic acid (VPA) and methyl mercury (MeHg), two compounds with vastly different modes of action. We developed various visualization tools to describe cellular responses, and the overall response was classified as "tolerance" (minor transcriptome changes), "functional adaptation" (moderate/strong transcriptome responses, but no cytotoxicity), and "degeneration". The latter two conditions were compared, using various statistical approaches. We identified (i) genes regulated at cytotoxic, but not at noncytotoxic, concentrations and (ii) KEGG pathways, gene ontology term groups, and superordinate biological processes that were only regulated at cytotoxic concentrations. The consensus markers and processes found after 48 h treatment were then overlaid with those found after prolonged (6 days) treatment. The study highlights the importance of careful concentration selection and of controlling viability for transcriptome studies. Moreover, it allowed identification of 39 candidate "biomarkers of cytotoxicity". These could serve to provide alerts that data sets of interest may have been affected by cell death in the model system studied.

Regulation of behaviour by the nuclear receptor TLX

The orphan nuclear receptor Tlx (Nr2e1) is a key regulator of both embryonic and adult hippocampal neurogenesis. Several different mouse models have been developed which target Tlx in vivo including spontaneous deletion models (from birth) and targeted and conditional knockouts. Although some conflicting findings have been reported, for the most part studies have demonstrated that Tlx is important in regulating processes that underlie neurogenesis, spatial learning, anxiety-like behaviour and interestingly, aggression. More recent data have demonstrated that disrupting Tlx during early life induces hyperactivity and that Tlx plays a role in emotional regulation. Moreover, there are sex- and age-related differences in some behaviours in Tlx knockout mice during adolescence and adulthood. Here, we discuss the role of Tlx in motor-, cognitive-, aggressive- and anxiety-related behaviours during adolescence and adulthood. We examine current evidence which provides insight into Tlx during neurodevelopment, and offer our thoughts on the function of Tlx in brain and behaviour. We further hypothesize that Tlx is a key target in understanding the emergence of neurobiological disorders during adolescence and early adulthood.

Enhancer Analysis Unveils Genetic Interactions between TLX and SOX2 in Neural Stem Cells and In Vivo Reprogramming

The orphan nuclear receptor TLX is a master regulator of postnatal neural stem cell (NSC) self-renewal and neurogenesis; however, it remains unclear how TLX expression is precisely regulated in these tissue-specific stem cells. Here, we show that a highly conserved cis-element within the Tlx locus functions to drive gene expression in NSCs. We demonstrate that the transcription factors SOX2 and MYT1 specifically interact with this genomic element to directly regulate Tlx enhancer activity in vivo. Knockdown experiments further reveal that SOX2 dominantly controls endogenous expression of TLX, whereas MYT1 only plays a modulatory role. Importantly, TLX is essential for SOX2-mediated in vivo reprogramming of astrocytes and itself is also sufficient to induce neurogenesis in the adult striatum. Together, these findings unveil functional genetic interactions among transcription factors that are critical to NSCs and in vivo cell reprogramming.

•

An evolutionarily conserved enhancer drives Tlx expression in neural stem cells

•

SOX2 directly activates the identified enhancer and Tlx expression

•

SOX2-mediated in vivo reprogramming of astrocytes to neuroblasts requires TLX