Defective limbic system in mice lacking the tailless gene

The nuclear receptor TLX (NR2E1) inhibits growth and progression of triple- negative breast cancer

Development of targeted therapies will be a critical step towards reducing the mortality associated with triple-negative breast cancer (TNBC). To achieve this, we searched for targets that met three criteria: (1) pharmacologically targetable, (2) expressed in TNBC, and (3) expression is prognostic in TNBC patients. Since nuclear receptors have a well-defined ligand-binding domain and are thus highly amenable to small-molecule intervention, we focused on this class of protein. Our analysis identified TLX (NR2E1) as a candidate. Specifically, elevated tumoral TLX expression was associated with prolonged recurrence-free survival and overall survival for breast cancer patients with either estrogen receptor alpha (ERα)-negative or basal-like tumors. Using two TNBC cell lines, we found that stable overexpression of TLX impairs in vitro proliferation. RNA-Seq analysis revealed that TLX reduced the expression of genes implicated in epithelial-mesenchymal transition (EMT), a cellular program known to drive metastatic progression. Indeed, TLX overexpression significantly decreased cell migration and invasion, and robustly decreased the metastatic capacity of TNBC cells in murine models. We identify SERPINB2 as a likely mediator of these effects. Taken together, our work indicates that TLX impedes the progression of TNBC. Several ligands have been shown to regulate the transcriptional activity of TLX, providing a framework for the future development of this receptor for therapeutic intervention.

Developmental regulation of neuronal gene expression by Elongator complex protein 1 dosage

Familial dysautonomia (FD), a hereditary sensory and autonomic neuropathy, is caused by a mutation in the Elongator complex protein 1 (ELP1) gene that leads to a tissue-specific reduction of ELP1 protein. Our work to generate a phenotypic mouse model for FD headed to the discovery that homozygous deletion of the mouse Elp1 gene leads to embryonic lethality prior to mid-gestation. Given that FD is caused by a reduction, not loss, of ELP1, we generated two new mouse models by introducing different copy numbers of the human FD ELP1 transgene into the Elp1 knockout mouse (Elp1-/-) and observed that human ELP1 expression rescues embryonic development in a dose-dependent manner. We then conducted a comprehensive transcriptome analysis in mouse embryos to identify genes and pathways whose expression correlates with the amount of ELP1. We found that ELP1 is essential for the expression of genes responsible for nervous system development. Further, gene length analysis of the differentially expressed genes showed that the loss of Elp1 mainly impacts the expression of long genes and that by gradually restoring Elongator, their expression is progressively rescued. Finally, through evaluation of co-expression modules, we identified gene sets with unique expression patterns that depended on ELP1 expression.

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.

TLX, an Orphan Nuclear Receptor With Emerging Roles in Physiology and Disease

TLX (NR2E1), an orphan member of the nuclear receptor superfamily, is a transcription factor that has been described to be generally repressive in nature. It has been implicated in several aspects of physiology and disease. TLX is best known for its ability to regulate the proliferation of neural stem cells and retinal progenitor cells. Dysregulation, overexpression, or loss of TLX expression has been characterized in numerous studies focused on a diverse range of pathological conditions, including abnormal brain development, psychiatric disorders, retinopathies, metabolic disease, and malignant neoplasm. Despite the lack of an identified endogenous ligand, several studies have described putative synthetic and natural TLX ligands, suggesting that this receptor may serve as a therapeutic target. Therefore, this article aims to briefly review what is known about TLX structure and function in normal physiology, and provide an overview of TLX in regard to pathological conditions. Particular emphasis is placed on TLX and cancer, and the potential utility of this receptor as a therapeutic target.

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.

Epigenetic control of region-specific transcriptional programs in mouse cerebellar and cortical astrocytes

Astrocytes from the cerebral cortex (CTX) and cerebellum (CB) share basic molecular programs, but also form distinct spatial and functional subtypes. The regulatory epigenetic layers controlling such regional diversity have not been comprehensively investigated so far. Here, we present an integrated epigenome analysis of methylomes, open chromatin, and transcriptomes of astroglia populations isolated from the cortex or cerebellum of young adult mice. Besides a basic overall similarity in their epigenomic programs, cortical astrocytes and cerebellar astrocytes exhibit substantial differences in their overall open chromatin structure and in gene-specific DNA methylation. Regional epigenetic differences are linked to differences in transcriptional programs encompassing genes of region-specific transcription factor networks centered around Lhx2/Foxg1 in CTX astrocytes and the Zic/Irx families in CB astrocytes. The distinct epigenetic signatures around these transcription factor networks point to a complex interconnected and combinatorial regulation of region-specific transcriptomes. These findings suggest that key transcription factors, previously linked to temporal, regional, and spatial control of neurogenesis, also form combinatorial networks important for astrocytes. Our study provides a valuable resource for the molecular basis of regional astrocyte identity and physiology.

Nr2e1 deficiency aggravates insulin resistance and chronic inflammation of visceral adipose tissues in a diet-induced obese mice model

AIMS

To investigate the nuclear receptor subfamily 2 group E member 1 (Nr2e1) expression in adipose tissues of obese mice and assess the role of Nr2e1 in insulin resistance and chronic inflammation of the adipose tissues.

MAIN METHODS

An obese model was established in Nr2e1 knockout (KO) mice and their wild type (WT) littermates through a long-term high-fat diet (HFD) feeding regime. The epididymal fat weight, body weight, and daily food intake were recorded. The blood lipid profile, blood inflammatory factors, and the levels of fasting blood glucose (FBG) and fasting insulin were determined. We estimated insulin resistance by the homeostasis model assessment (HOMA). The expression of inflammatory factors and F4/80 was examined by polymerase chain reaction (PCR) and western blotting to assess adipose tissues inflammation. We also determined the molecules of insulin signaling and the nuclear factor kappa B (NF-κB) pathway by western blotting.

KEY FINDINGS

The Nr2e1 expression was upregulated in WT obese mice when compared with that in control mice. Despite a lower body weight and epididymal fat mass in Nr2e1^-/- mice, these rats showed increased inflammatory cytokines secretion, more pronounced hyperlipidemia, and impaired insulin sensitivity after HFD treatment. Further investigation revealed that Nr2e1 deletion affected the expression of insulin signaling and NF-κB pathway-related molecules in visceral adipose tissues.

SIGNIFICANCE

Nr2e1 may act as a potential target to improve insulin sensitivity and inflammation in obesity and related complications.

Nuclear receptors: Key regulators of somatic cell functions in the ovulatory process

The development of the ovarian follicle to its culmination by ovulation is an essential element of fertility. The final stages of ovarian follicular growth are characterized by granulosa cell proliferation and differentiation, and steroid synthesis under the influence of follicle-stimulating hormone (FSH). The result is a population of granulosa cells poised to respond to the ovulatory surge of luteinizing hormone (LH). Members of the nuclear receptor superfamily of transcription factors play indispensable roles in the regulation of these events. The key regulators of the final stages of follicular growth that precede ovulation from this family include the estrogen receptor beta (ESR2) and the androgen receptor (AR), with additional roles for others, including steroidogenic factor-1 (SF-1) and liver receptor homolog-1 (LRH-1). Following the LH surge, the mural and cumulus granulosa cells undergo rapid changes that result in expansion of the cumulus layer, and a shift in ovarian steroid hormone biosynthesis from estradiol to progesterone production. The nuclear receptor best associated with these events is LRH-1. Inadequate cumulus expansion is also observed in the absence of AR and ESR2, but not the progesterone receptor (PGR). The terminal stages of ovulation are regulated by PGR, which increases the abundance of the proteases that are directly responsible for rupture. It further regulates the prostaglandins and cytokines associated with the inflammatory-like characteristics of ovulation. LRH-1 regulates PGR, and is also a key regulator of steroidogenesis, cellular proliferation, and cellular migration, and cytoskeletal remodeling. In summary, nuclear receptors are among the panoply of transcriptional regulators with roles in ovulation, and several are necessary for normal ovarian function.

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.

The Orphan Nuclear Receptor TLX Represses Hes1 Expression, Thereby Affecting NOTCH Signaling and Lineage Progression in the Adult SEZ

In the adult subependymal zone (SEZ), neural stem cells (NSCs) apically contacting the lateral ventricle on activation generate progenitors proliferating at the niche basal side. We here show that Tailless (TLX) coordinates NSC activation and basal progenitor proliferation by repressing the NOTCH effector Hes1. Consistent with this, besides quiescence Hes1 expression also increases on Tlx mutation. Since HES1 levels are higher at the apical SEZ, NOTCH activation is increased in Tlx^−/− NSCs, but not in surrounding basal progenitors. Underscoring the causative relationship between higher HES1/NOTCH and increased quiescence, downregulation of Hes1 only in mutant NSCs normalizes NOTCH activation and resumes proliferation and neurogenesis not only in NSCs, but especially in basal progenitors. Since pharmacological blockade of NOTCH signaling also promotes proliferation of basal progenitors, we conclude that TLX, by repressing Hes1 expression, counteracts quiescence and NOTCH activation in NSCs, thereby relieving NOTCH-mediated lateral inhibition of proliferation in basal progenitors.

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TLX autonomously controls quiescence in apical NSCs by repressing Hes1

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TLX controls basal progenitor proliferation via NOTCH-mediated lateral inhibition

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Downregulation of Hes1 in apical Tlx^−/− NSCs resumes proliferation and neurogenesis

Computer-Aided Discovery of Small Molecule Inhibitors of Transcriptional Activity of TLX (NR2E1) Nuclear Receptor

Orphan nuclear receptor TLX (NR2E1) plays a critical role in the regulation of neural stem cells (NSC) as well as in the development of NSC-derived brain tumors. In the last years, new data have emerged implicating TLX in prostate and breast cancer. Therefore, inhibitors of TLX transcriptional activity may have a significant impact on the treatment of several critical malignancies. However, the TLX protein possesses a non-canonical ligand-binding domain (LBD), which lacks a ligand-binding pocket (conventionally targeted in case of nuclear receptors) that complicates the development of small molecule inhibitors of TLX. Herein, we utilized a rational structure-based design approach to identify small molecules targeting the Atro-box binding site of human TLX LBD. As a result of virtual screening of ~7 million molecular structures, 97 compounds were identified and evaluated in the TLX-responsive luciferase reporter assay. Among those, three chemicals demonstrated 40–50% inhibition of luciferase-detected transcriptional activity of the TLX orphan nuclear receptor at a dose of 35 µM. The identified compounds represent the first class of small molecule inhibitors of TLX transcriptional activity identified via methods of computer-aided drug discovery.

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.

Nuclear receptors in neural stem/progenitor cell homeostasis

In the central nervous system, embryonic and adult neural stem/progenitor cells (NSCs) generate the enormous variety and huge numbers of neuronal and glial cells that provide structural and functional support in the brain and spinal cord. Over the last decades, nuclear receptors and their natural ligands have emerged as critical regulators of NSC homeostasis during embryonic development and adult life. Furthermore, substantial progress has been achieved towards elucidating the molecular mechanisms of nuclear receptors action in proliferative and differentiation capacities of NSCs. Aberrant expression or function of nuclear receptors in NSCs also contributes to the pathogenesis of various nervous system diseases. Here, we review recent advances in our understanding of the regulatory roles of steroid, non-steroid, and orphan nuclear receptors in NSC fate decisions. These studies establish nuclear receptors as key therapeutic targets in brain diseases.

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.

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.

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.

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.

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An evolutionarily conserved enhancer drives Tlx expression in neural stem cells

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SOX2 directly activates the identified enhancer and Tlx expression

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

Aggression in non-human vertebrates: Genetic mechanisms and molecular pathways

Aggression is an adaptive behavioral trait that is important for the establishment of social hierarchies and competition for mating partners, food, and territories. While a certain level of aggression can be beneficial for the survival of an individual or species, abnormal aggression levels can be detrimental. Abnormal aggression is commonly found in human patients with psychiatric disorders. The predisposition to aggression is influenced by a combination of environmental and genetic factors and a large number of genes have been associated with aggression in both human and animal studies. In this review, we compare and contrast aggression studies in zebrafish and mouse. We present gene ontology and pathway analyses of genes linked to aggression and discuss the molecular pathways that underpin agonistic behavior in these species. © 2015 Wiley Periodicals, Inc.

Combinatorial decoding of the invariant C. elegans embryonic lineage in space and time

Understanding how a single cell, the zygote, can divide and differentiate to produce the diverse animal cell types is a central goal of developmental biology research. The model organism Caenorhabditis elegans provides a system that enables a truly comprehensive understanding of this process across all cells. Its invariant cell lineage makes it possible to identify all of the cells in each individual and compare them across organisms. Recently developed methods automate the process of cell identification, allowing high-throughput gene expression characterization and phenotyping at single cell resolution. In this Review, we summarize the sequences of events that pattern the lineage including establishment of founder cell identity, the signaling pathways that diversify embryonic fate, and the regulators involved in patterning within these founder lineages before cells adopt their terminal fates. We focus on insights that have emerged from automated approaches to lineage tracking, including insights into mechanisms of robustness, context-specific regulation of gene expression, and temporal coordination of differentiation. We suggest a model by which lineage history produces a combinatorial code of transcription factors that act, often redundantly, to ensure terminal fate.

The TLX-miR-219 cascade regulates neural stem cell proliferation in neurodevelopment and schizophrenia iPSC model

Dysregulated expression of miR-219, a brain-specific microRNA, has been observed in neurodevelopmental disorders, such as schizophrenia (SCZ). However, its role in normal mammalian neural stem cells (NSCs) and in SCZ pathogenesis remains unknown. We show here that the nuclear receptor TLX, an essential regulator of NSC proliferation and self-renewal, inhibits miR-219 processing. miR-219 suppresses mouse NSC proliferation downstream of TLX. Moreover, we demonstrate upregulation of miR-219 and downregulation of TLX expression in NSCs derived from SCZ patient iPSCs and DISC1-mutant isogenic iPSCs. SCZ NSCs exhibit reduced cell proliferation. Overexpression of TLX or inhibition of miR-219 action rescues the proliferative defect in SCZ NSCs. Therefore, this study uncovers an important role for TLX and miR-219 in both normal neurodevelopment and in SCZ patient iPSC-derived NSCs. Moreover, this study reveals an unexpected role for TLX in regulating microRNA processing, independent of its well-characterized role in transcriptional regulation.

Dysregulation of microRNAs has been implicated in neurodevelopmental disorders, including schizophrenia. Here the authors show that the TLX-miR-219 cascade regulates the proliferation of neural stem cells during normal development, and this pathway is dysregulated in a schizophrenia iPSC model.

Tailless and Atrophin control Drosophila aggression by regulating neuropeptide signalling in the pars intercerebralis

Aggressive behaviour is widespread throughout the animal kingdom. However, its mechanisms are poorly understood, and the degree of molecular conservation between distantly related species is unknown. Here we show that knockdown of tailless (tll) increases aggression in Drosophila, similar to the effect of its mouse orthologue Nr2e1. Tll localizes to the adult pars intercerebralis (PI), which shows similarity to the mammalian hypothalamus. Knockdown of tll in the PI is sufficient to increase aggression and is rescued by co-expressing human NR2E1. Knockdown of Atrophin, a Tll co-repressor, also increases aggression, and both proteins physically interact in the PI. tll knockdown-induced aggression is fully suppressed by blocking neuropeptide processing or release from the PI. In addition, genetically activating PI neurons increases aggression, mimicking the aggression-inducing effect of hypothalamic stimulation. Together, our results suggest that a transcriptional control module regulates neuropeptide signalling from the neurosecretory cells of the brain to control aggressive behaviour.

TLX: An elusive receptor

TLX (tailless receptor) is a member of the nuclear receptor superfamily and belongs to a class of nuclear receptors for which no endogenous or synthetic ligands have yet been identified. TLX is a promising therapeutic target in neurological disorders and brain tumors. Thus, regulatory ligands for TLX need to be identified to complete the validation of TLX as a useful target and would serve as chemical probes to pursue the study of this receptor in disease models. It has recently been proved that TLX is druggable. However, to identify potent and specific TLX ligands with desirable biological activity, a deeper understanding of where ligands bind, how they alter TLX conformation and of the mechanism by which TLX mediates the transcription of its target genes is needed. While TLX is in the process of escaping from orphanhood, future ligand design needs to progress in parallel with improved understanding of (i) the binding cavity or surfaces to target with small molecules on the TLX ligand binding domain and (ii) the nature of the TLX coregulators in particular cell and disease contexts. Both of these topics are discussed in this review.

The Orphan Nuclear Receptor TLX/NR2E1 in Neural Stem Cells and Diseases

The human TLX gene encodes an orphan nuclear receptor predominantly expressed in the central nervous system. Tailess and Tlx, the TLX homologues in Drosophila and mouse, play essential roles in body-pattern formation and neurogenesis during early embryogenesis and perform crucial functions in maintaining stemness and controlling the differentiation of adult neural stem cells in the central nervous system, especially the visual system. Multiple target genes and signaling pathways are regulated by TLX and its homologues in specific tissues during various developmental stages. This review aims to summarize previous studies including many recent updates from different aspects concerning TLX and its homologues in Drosophila and mouse.

TLX-Its Emerging Role for Neurogenesis in Health and Disease

The orphan nuclear receptor TLX, also called NR2E1, is a factor important in the regulation of neural stem cell (NSC) self-renewal, neurogenesis, and maintenance. As a transcription factor, TLX is vital for the expression of genes implicated in neurogenesis, such as DNA replication, cell cycle, adhesion and migration. It acts by way of repressing or activating target genes, as well as controlling protein-protein interactions. Growing evidence suggests that dysregulated TLX acts in the initiation and progression of human disorders of the nervous system. This review describes recent knowledge about TLX expression, structure, targets, and biological functions, relevant to maintaining adult neural stem cells related to both neuropsychiatric conditions and certain nervous system tumours.

Nr2e1 Deficiency Augments Palmitate-Induced Oxidative Stress in Beta Cells

Nuclear receptor subfamily 2 group E member 1 (Nr2e1) has been regarded as an essential regulator of the growth of neural stem cells. However, its function elsewhere is unknown. In the present study, we generated Nr2e1 knockdown MIN6 cells and studied whether Nr2e1 knockdown affected basal beta cell functions such as proliferation, cell death, and insulin secretion. We showed that knockdown of Nr2e1 in MIN6 cells resulted in increased sensitivity to lipotoxicity, decreased proliferation, a partial G0/G1 cell-cycle arrest, and higher rates of apoptosis. Moreover, Nr2e1 deficiency exaggerates palmitate-induced impairment in insulin secretion. At the molecular level, Nr2e1 deficiency augments palmitate-induced oxidative stress. Nr2e1 deficiency also resulted in decreases in antioxidant enzymes and expression level of Nrf2. Together, this study indicated a potential protective effect of Nr2e1 on beta cells, which may serve as a target for the development of novel therapies for diabetes.

MicroRNA-378 regulates neural stem cell proliferation and differentiation in vitro by modulating Tailless expression

Previous studies have suggested that microRNAs (miRNAs) play an important role in regulating neural stem cell (NSC) proliferation and differentiation. However, the precise role of miRNAs in NSC remains largely unexplored. In this study, we showed that miR-378 can target Tailless (TLX), a critical regulator of NSC, to regulate NSC proliferation and differentiation. By bioinformatic algorithms, miR-378 was found to have a predicted target site in the 3'-untranslated region of TLX, which was verified by a dual-luciferase reporter assay. The expression of miR-378 was increased during NSC differentiation and inversely correlated with TLX expression. qPCR and Western blot analysis also showed that miR-378 negatively regulated TLX mRNA and protein expression in neural stem cells (NSCs). Intriguingly, overexpression of miR-378 increased NSC differentiation and reduced NSC proliferation, whereas suppression of miR-378 led to decreased NSC differentiation and increased NSC proliferation. Moreover, the downstream targets of TLX, including p21, PTEN and Wnt/β-catenin were also found to be regulated by miR-378. Additionally, overexpression of TLX rescued the NSC proliferation deficiency induced by miR-378 overexpression and abolished miR-378-promoted NSC differentiation. Taken together, our data suggest that miR-378 is a novel miRNA that regulates NSC proliferation and differentiation via targeting TLX. Therefore, manipulating miR-378 in NSCs could be a novel strategy to develop novel interventions for the treatment of relevant neurological disorders.

Of Fighting Flies, Mice, and Men: Are Some of the Molecular and Neuronal Mechanisms of Aggression Universal in the Animal Kingdom?

Aggressive behavior is widespread in the animal kingdom, but the degree of molecular conservation between distantly related species is still unclear. Recent reports suggest that at least some of the molecular mechanisms underlying this complex behavior in flies show remarkable similarities with such mechanisms in mice and even humans. Surprisingly, some aspects of neuronal control of aggression also show remarkable similarity between these distantly related species. We will review these recent findings, address the evolutionary implications, and discuss the potential impact for our understanding of human diseases characterized by excessive aggression.

Combined serial analysis of gene expression and transcription factor binding site prediction identifies novel-candidate-target genes of Nr2e1 in neocortex development

Background

Nr2e1 (nuclear receptor subfamily 2, group e, member 1) encodes a transcription factor important in neocortex development. Previous work has shown that nuclear receptors can have hundreds of target genes, and bind more than 300 co-interacting proteins. However, recognition of the critical role of Nr2e1 in neural stem cells and neocortex development is relatively recent, thus the molecular mechanisms involved for this nuclear receptor are only beginning to be understood. Serial analysis of gene expression (SAGE), has given researchers both qualitative and quantitative information pertaining to biological processes. Thus, in this work, six LongSAGE mouse libraries were generated from laser microdissected tissue samples of dorsal VZ/SVZ (ventricular zone and subventricular zone) from the telencephalon of wild-type (Wt) and Nr2e1-null embryos at the critical development ages E13.5, E15.5, and E17.5. We then used a novel approach, implementing multiple computational methods followed by biological validation to further our understanding of Nr2e1 in neocortex development.

Results

In this work, we have generated a list of 1279 genes that are differentially expressed in response to altered Nr2e1 expression during in vivo neocortex development. We have refined this list to 64 candidate direct-targets of NR2E1. Our data suggested distinct roles for Nr2e1 during different neocortex developmental stages. Most importantly, our results suggest a possible novel pathway by which Nr2e1 regulates neurogenesis, which includes Lhx2 as one of the candidate direct-target genes, and SOX9 as a co-interactor.

Conclusions

In conclusion, we have provided new candidate interacting partners and numerous well-developed testable hypotheses for understanding the pathways by which Nr2e1 functions to regulate neocortex development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1770-3) contains supplementary material, which is available to authorized users.

The lysine acetyltransferase activator Brpf1 governs dentate gyrus development through neural stem cells and progenitors

Lysine acetylation has recently emerged as an important post-translational modification in diverse organisms, but relatively little is known about its roles in mammalian development and stem cells. Bromodomain- and PHD finger-containing protein 1 (BRPF1) is a multidomain histone binder and a master activator of three lysine acetyltransferases, MOZ, MORF and HBO1, which are also known as KAT6A, KAT6B and KAT7, respectively. While the MOZ and MORF genes are rearranged in leukemia, the MORF gene is also mutated in prostate and other cancers and in four genetic disorders with intellectual disability. Here we show that forebrain-specific inactivation of the mouse Brpf1 gene causes hypoplasia in the dentate gyrus, including underdevelopment of the suprapyramidal blade and complete loss of the infrapyramidal blade. We trace the developmental origin to compromised Sox2⁺ neural stem cells and Tbr2⁺ intermediate neuronal progenitors. We further demonstrate that Brpf1 loss deregulates neuronal migration, cell cycle progression and transcriptional control, thereby causing abnormal morphogenesis of the hippocampus. These results link histone binding and acetylation control to hippocampus development and identify an important epigenetic regulator for patterning the dentate gyrus, a brain structure critical for learning, memory and adult neurogenesis.

Lysine acetylation refers to addition of the acetyl group to lysine residues after protein synthesis. Little is known about how this modification plays a role in the brain and neural stem cells. It is catalyzed by a group of enzymes known as lysine acetyltransferases. A novel epigenetic regulator called BRPF1 acts as a master activator of three different lysine acetyltransferases and also contains multiple structural domains for histone binding. In this study, we show that forebrain-specific inactivation of the mouse Brpf1 gene causes abnormal development of the dentate gyrus, a key component of the hippocampus. We trace the developmental origin to compromised neural stem cells and progenitors, and demonstrate that Brpf1 loss deregulates neuronal migration and cell cycle progression during development of the dentate gyrus. This is the first report on an epigenetic regulator whose loss has such a profound impact on the hippocampus, especially the dentate gyrus, a brain structure critical for learning, memory and adult neurogenesis.

The Concise Guide to PHARMACOLOGY 2013/14: nuclear hormone receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full.

Nuclear hormone receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets.

It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

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

The orphan nuclear receptor TLX, also known as NR2E1, is an essential regulator of neural stem cell (NSC) self-renewal, maintenance, and neurogenesis. In vertebrates, TLX is specifically localized to the neurogenic regions of the forebrain and retina throughout development and adulthood. TLX regulates the expression of genes involved in multiple pathways, such as the cell cycle, DNA replication, and cell adhesion. These roles are primarily performed through the transcriptional repression or activation of downstream target genes. Emerging evidence suggests that the misregulation of TLX might play a role in the onset and progression of human neurological disorders making this factor an ideal therapeutic target. Here, we review the current understanding of TLX function, expression, regulation, and activity significant to NSC maintenance, adult neurogenesis, and brain plasticity. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Nuclear receptor TLX stimulates hippocampal neurogenesis and enhances learning and memory in a transgenic mouse model

The role of the nuclear receptor TLX in hippocampal neurogenesis and cognition has just begun to be explored. In this study, we generated a transgenic mouse model that expresses TLX under the control of the promoter of nestin, a neural precursor marker. Transgenic TLX expression led to mice with enlarged brains with an elongated hippocampal dentate gyrus and increased numbers of newborn neurons. Specific expression of TLX in adult hippocampal dentate gyrus via lentiviral transduction increased the numbers of BrdU(+) cells and BrdU(+)NeuN(+) neurons. Furthermore, the neural precursor-specific expression of the TLX transgene substantially rescued the neurogenic defects of TLX-null mice. Consistent with increased neurogenesis in the hippocampus, the TLX transgenic mice exhibited enhanced cognition with increased learning and memory. These results suggest a strong association between hippocampal neurogenesis and cognition, as well as significant contributions of TLX to hippocampal neurogenesis, learning, and memory.

Orphan nuclear receptor TLX regulates astrogenesis by modulating BMP signaling

Neural stem cells (NSCs) are self-renewing multipotent progenitors that generate both neurons and glia. The precise control of NSC behavior is fundamental to the architecture and function of the central nervous system. We previously demonstrated that the orphan nuclear receptor TLX is required for postnatal NSC activation and neurogenesis in the neurogenic niche. Here, we show that TLX modulates bone morphogenetic protein (BMP)-SMAD signaling to control the timing of postnatal astrogenesis. Genes involved in the BMP signaling pathway, such as Bmp4, Hes1, and Id3, are upregulated in postnatal brains lacking Tlx. Chromatin immunoprecipitation and electrophoretic mobility shift assays reveal that TLX can directly bind the enhancer region of Bmp4. In accordance with elevated BMP signaling, the downstream effectors SMAD1/5/8 are activated by phosphorylation in Tlx mutant mice. Consequently, Tlx mutant brains exhibit an early appearance and increased number of astrocytes with marker expression of glial fibrillary acidic protein (GFAP) and S100B. Taken together, these results suggest that TLX tightly controls postnatal astrogenesis through the modulation of BMP-SMAD signaling pathway activity.

Mouse model reveals the role of RERE in cerebellar foliation and the migration and maturation of Purkinje cells

Nuclear receptors and their coregulators play a critical role in brain development by regulating the spatiotemporal expression of their target genes. The arginine-glutamic acid dipeptide repeats gene (Rere) encodes a nuclear receptor coregulator previously known as Atrophin 2. In the developing cerebellum, RERE is expressed in the molecular layer, the Purkinje cell layer and the granule cell layer but not in granule cell precursors. To study RERE's role in cerebellar development, we used RERE-deficient embryos bearing a null allele (om) and a hypomorphic allele (eyes3) of Rere (Rere^om/eyes3). In contrast to wild-type embryos, formation of the principal fissures in these RERE-deficient embryos was delayed and the proliferative activity of granule cell precursors (GCPs) was reduced at E18.5. This reduction in proliferation was accompanied by a decrease in the expression of sonic hedgehog (SHH), which is secreted from Purkinje cells and is required for normal GCP proliferation. The maturation and migration of Purkinje cells in Rere^om/eyes3 embryos was also delayed with decreased numbers of post-migratory Purkinje cells in the cerebellum. During the postnatal period, RERE depletion caused incomplete division of lobules I/II and III due to truncated development of the precentral fissure in the cerebellar vermis, abnormal development of lobule crus I and lobule crus II in the cerebellar hemispheres due to attenuation of the intercrural fissure, and decreased levels of Purkinje cell dendritic branching. We conclude that RERE-deficiency leads to delayed development of the principal fissures and delayed maturation and migration of Purkinje cells during prenatal cerebellar development and abnormal cerebellar foliation and Purkinje cell maturation during postnatal cerebellar development.

The orphan nuclear receptors at their 25-year reunion

The nuclear receptor superfamily includes many receptors, identified based on their similarity to steroid hormone receptors but without a known ligand. The study of how these receptors are diversely regulated to interact with genomic regions to control a plethora of biological processes has provided critical insight into development, physiology, and the molecular pathology of disease. Here we provide a compendium of these so-called orphan receptors and focus on what has been learned about their modes of action, physiological functions, and therapeutic promise.

Pax6 is required for normal cell-cycle exit and the differentiation kinetics of retinal progenitor cells

The coupling between cell-cycle exit and onset of differentiation is a common feature throughout the developing nervous system, but the mechanisms that link these processes are mostly unknown. Although the transcription factor Pax6 has been implicated in both proliferation and differentiation of multiple regions within the central nervous system (CNS), its contribution to the transition between these successive states remains elusive. To gain insight into the role of Pax6 during the transition from proliferating progenitors to differentiating precursors, we investigated cell-cycle and transcriptomic changes occurring in Pax6 (-) retinal progenitor cells (RPCs). Our analyses revealed a unique cell-cycle phenotype of the Pax6-deficient RPCs, which included a reduced number of cells in the S phase, an increased number of cells exiting the cell cycle, and delayed differentiation kinetics of Pax6 (-) precursors. These alterations were accompanied by coexpression of factors that promote (Ccnd1, Ccnd2, Ccnd3) and inhibit (P27 (kip1) and P27 (kip2) ) the cell cycle. Further characterization of the changes in transcription profile of the Pax6-deficient RPCs revealed abrogated expression of multiple factors which are known to be involved in regulating proliferation of RPCs, including the transcription factors Vsx2, Nr2e1, Plagl1 and Hedgehog signaling. These findings provide novel insight into the molecular mechanism mediating the pleiotropic activity of Pax6 in RPCs. The results further suggest that rather than conveying a linear effect on RPCs, such as promoting their proliferation and inhibiting their differentiation, Pax6 regulates multiple transcriptional networks that function simultaneously, thereby conferring the capacity to proliferate, assume multiple cell fates and execute the differentiation program into retinal lineages.

Histone H3.3. mutations drive pediatric glioblastoma through upregulation of MYCN

Children and young adults with glioblastoma (GBM) have a median survival rate of only 12 to 15 months, and these GBMs are clinically and biologically distinct from histologically similar cancers in older adults. They are defined by highly specific mutations in the gene encoding the histone H3.3 variant H3F3A , occurring either at or close to key residues marked by methylation for regulation of transcription—K27 and G34. Here, we show that the cerebral hemisphere-specific G34 mutation drives a distinct expression signature through differential genomic binding of the K36 trimethylation mark (H3K36me3). The transcriptional program induced recapitulates that of the developing forebrain, and involves numerous markers of stem-cell maintenance, cell-fate decisions, and self-renewal.Critically, H3F3A G34 mutations cause profound upregulation of MYCN , a potent oncogene that is causative of GBMs when expressed in the correct developmental context. This driving aberration is selectively targetable in this patient population through inhibiting kinases responsible for stabilization of the protein.

SIGNIFICANCE

We provide the mechanistic explanation for how the fi rst histone gene mutation inhuman disease biology acts to deliver MYCN, a potent tumorigenic initiator, into a stem-cell compartment of the developing forebrain, selectively giving rise to incurable cerebral hemispheric GBM. Using synthetic lethal approaches to these mutant tumor cells provides a rational way to develop novel and highly selective treatment strategies

An allelic series of mice reveals a role for RERE in the development of multiple organs affected in chromosome 1p36 deletions

Individuals with terminal and interstitial deletions of chromosome 1p36 have a spectrum of defects that includes eye anomalies, postnatal growth deficiency, structural brain anomalies, seizures, cognitive impairment, delayed motor development, behavior problems, hearing loss, cardiovascular malformations, cardiomyopathy, and renal anomalies. The proximal 1p36 genes that contribute to these defects have not been clearly delineated. The arginine-glutamic acid dipeptide (RE) repeats gene (RERE) is located in this region and encodes a nuclear receptor coregulator that plays a critical role in embryonic development as a positive regulator of retinoic acid signaling. Rere-null mice die of cardiac failure between E9.5 and E11.5. This limits their usefulness in studying the role of RERE in the latter stages of development and into adulthood. To overcome this limitation, we created an allelic series of RERE-deficient mice using an Rere-null allele, om, and a novel hypomorphic Rere allele, eyes3 (c.578T>C, p.Val193Ala), which we identified in an N-ethyl-N-nitrosourea (ENU)-based screen for autosomal recessive phenotypes. Analyses of these mice revealed microphthalmia, postnatal growth deficiency, brain hypoplasia, decreased numbers of neuronal nuclear antigen (NeuN)-positive hippocampal neurons, hearing loss, cardiovascular malformations–aortic arch anomalies, double outlet right ventricle, and transposition of the great arteries, and perimembranous ventricular septal defects–spontaneous development of cardiac fibrosis and renal agenesis. These findings suggest that RERE plays a critical role in the development and function of multiple organs including the eye, brain, inner ear, heart and kidney. It follows that haploinsufficiency of RERE may contribute–alone or in conjunction with other genetic, environmental, or stochastic factors–to the development of many of the phenotypes seen in individuals with terminal and interstitial deletions that include the proximal region of chromosome 1p36.

Neurogenetics of aggressive behavior: studies in rodents

Aggressive behavior is observed in many animal species, such as insects, fish, lizards, frogs, and most mammals including humans. This wide range of conservation underscores the importance of aggressive behavior in the animals' survival and fitness, and the likely heritability of this behavior. Although typical patterns of aggressive behavior differ between species, there are several concordances in the neurobiology of aggression among rodents, primates, and humans. Studies with rodent models may eventually help us to understand the neurogenetic architecture of aggression in humans. However, it is important to recognize the difference between the ecological and ethological significance of aggressive behavior (species-typical aggression) and maladaptive violence (escalated aggression) when applying the findings of aggression research using animal models to human or veterinary medicine. Well-studied rodent models for aggressive behavior in the laboratory setting include the mouse (Mus musculus), rat (Rattus norvegicus), hamster (Mesocricetus auratus), and prairie vole (Microtus ochrogaster). The neural circuits of rodent aggression have been gradually elucidated by several techniques, e.g., immunohistochemistry of immediate-early gene (c-Fos) expression, intracranial drug microinjection, in vivo microdialysis, and optogenetics techniques. Also, evidence accumulated from the analysis of gene-knockout mice shows the involvement of several genes in aggression. Here, we review the brain circuits that have been implicated in aggression, such as the hypothalamus, prefrontal cortex (PFC), dorsal raphe nucleus (DRN), nucleus accumbens (NAc), and olfactory system. We then discuss the roles of glutamate and γ-aminobutyric acid (GABA), excitatory and inhibitory amino acids in the brain, as well as their receptors, in controlling aggressive behavior, focusing mainly on recent findings. At the end of this chapter, we discuss how genes can be identified that underlie individual differences in aggression, using the so-called forward genetics approach.

Unlocking mechanisms in interleukin-1β-induced changes in hippocampal neurogenesis--a role for GSK-3β and TLX

Glycogen synthase kinase-3β (GSK-3β) and the orphan nuclear receptor tailless homolog (TLX) are key regulators of hippocampal neurogenesis, which has been reported to be dysregulated in both neurodegenerative and psychiatric disorders. Inflammation is also implicated in the neuropathology of these disorders because of increased levels of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the brain. At elevated levels, IL-1β signaling through the IL-1 receptor type 1 has been shown to be detrimental to hippocampal neurogenesis. TLX is required to maintain neural stem/progenitor cells (NSPCs) in an undifferentiated state and is involved in NSPC fate determination, while GSK-3β negatively regulates Wnt signaling, a vital pathway promoting neurogenesis. This study shows that GSK-3β inhibition using a small-molecule inhibitor and the mood stabilizer lithium restores the IL-1β-induced decrease in NSPC proliferation and neuronal differentiation of embryonic rat hippocampal NSPCs to control levels. The IL-1β-induced effect on NSPCs is paralleled by a decrease in TLX expression that can be prevented by GSK-3β inhibition. The present results suggest that GSK-3β ameliorates the anti-proliferative and pro-gliogenic effects of IL-1β, and that TLX is vulnerable to inflammatory insult. Strategies to reduce GSK-3β activity or to increase TLX expression may facilitate the restoration of hippocampal neurogenesis in neuroinflammatory conditions where neurogenesis is impaired.