Delta-like 1 participates in the specification of ventral midbrain progenitor derived dopaminergic neurons

Review on anti-alzheimer drug development: approaches, challenges and perspectives

Alzheimer is an irreversible progressive neurodegenerative disease that causes failure of cerebral neurons and disability of the affected person to practice normal daily life activities. There is no concrete evidence to identify the exact reason behind the disease, so several relevant hypotheses emerged, highlighting many possible therapeutic targets, such as acetylcholinesterase, cholinergic receptors, N-methyl d-aspartate receptors, phosphodiesterase, amyloid β protein, protein phosphatase 2A, glycogen synthase kinase-3 beta, β-secretase, γ-secretase, α-secretase, serotonergic receptors, glutaminyl cyclase, tumor necrosis factor-α, γ-aminobutyric acid receptors, and mitochondria. All of these targets have been involved in the design of new potential drugs. An extensive number of these drugs have been studied in clinical trials. However, only galantamine, donepezil, and rivastigmine (ChEIs), memantine (NMDA antagonist), and aducanumab and lecanemab (selective anti-Aβ monoclonal antibodies) have been approved for AD treatment. Many drugs failed in the clinical trials to such an extent that questions have been posed about the significance of some of the aforementioned targets. On the contrary, the data of other drugs were promising and shed light on the significance of their targets for the development of new potent anti-alzheimer drugs.

Spatiotemporal transcriptome atlas reveals the regional specification of the developing human brain

Different functional regions of brain are fundamental for basic neurophysiological activities. However, the regional specification remains largely unexplored during human brain development. Here, by combining spatial transcriptomics (scStereo-seq) and scRNA-seq, we built a spatiotemporal developmental atlas of multiple human brain regions from 6-23 gestational weeks (GWs). We discovered that, around GW8, radial glia (RG) cells have displayed regional heterogeneity and specific spatial distribution. Interestingly, we found that the regional heterogeneity of RG subtypes contributed to the subsequent neuronal specification. Specifically, two diencephalon-specific subtypes gave rise to glutamatergic and GABAergic neurons, whereas subtypes in ventral midbrain were associated with the dopaminergic neurons. Similar GABAergic neuronal subtypes were shared between neocortex and diencephalon. Additionally, we revealed that cell-cell interactions between oligodendrocyte precursor cells and GABAergic neurons influenced and promoted neuronal development coupled with regional specification. Altogether, this study provides comprehensive insights into the regional specification in the developing human brain.

Dorsoventral Arrangement of Lateral Hypothalamus Populations in the Mouse Hypothalamus: a Prosomeric Genoarchitectonic Analysis

The lateral hypothalamus (LH) has a heterogeneous cytoarchitectonic organization that has not been elucidated in detail. In this work, we analyzed within the framework of the prosomeric model the differential expression pattern of 59 molecular markers along the ventrodorsal dimension of the medial forebrain bundle in the mouse, considering basal and alar plate subregions of the LH. We found five basal (LH1-LH5) and four alar (LH6-LH9) molecularly distinct sectors of the LH with neuronal cell groups that correlate in topography with previously postulated alar and basal hypothalamic progenitor domains. Most peptidergic populations were restricted to one of these LH sectors though some may have dispersed into a neighboring sector. For instance, histaminergic Hdc-positive neurons were mostly contained within the basal LH3, Nts (neurotensin)- and Tac2 (tachykinin 2)-expressing cells lie strictly within LH4, Hcrt (hypocretin/orexin)-positive and Pmch (pro-melanin-concentrating hormone)-positive neurons appeared within separate LH5 subdivisions, Pnoc (prepronociceptin)-expressing cells were mainly restricted to LH6, and Sst (somatostatin)-positive cells were identified within the LH7 sector. The alar LH9 sector, a component of the Foxg1-positive telencephalo-opto-hypothalamic border region, selectively contained Satb2-expressing cells. Published studies of rodent LH subdivisions have not described the observed pattern. Our genoarchitectonic map should aid in systematic approaches to elucidate LH connectivity and function.

Newly regenerated dopaminergic neurons in 6-OHDA-lesioned adult zebrafish brain proliferate in the Olfactory bulb and telencephalon, but migrate to, differentiate and mature in the diencephalon

In order to understand the biological processes underlying dopaminergic neurons (DpN) regeneration in a 6-hydroxydopamine(6-OHDA)-induced adult zebrafish-based Parkinson's disease model, this study investigated the specific phases of neuroregeneration in a time-based manner. Bromodeoxyuridine (BrdU) was administered 24 h before the harvest of brain tissues at day three, five, seven, nine, 12 and 14 postlesion. Potential migration of proliferative cells was tracked over 14 days postlesion through double-pulse tracking [BrdU and 5-ethynyl-2'-deoxyuridine (EdU)] of cells and immunohistostaining of astrocytes [glial fibrillary acidic protein (GFAP)]. Gene expression of foxa2 and nurr1 (nr4a2a) at day three, nine, 14, 18, 22 and 30 postlesion was quantified using qPCR. Protein expression of foxa2 at day three, seven, 14 and 22 postlesion was validated using the western blot technique. Double labelling [EdU and tyrosine hydroxylase (TH)] of proliferative cells was performed to ascertain their fate after the neuroregeneration processes. It was found that whilst cell proliferation remained unchanged in the area of substantial DpN loss, the ventral diencephalon (vDn), there was a transient increase of cell proliferation in the olfactory bulb (OB) and telencephalon (Tel) seven days postlesion. BrdU-immunoreactive (ir)/ EdU-ir cells and activated astrocytes were later found to be significantly increased in the vDn and its nearby area (Tel) 14 days postlesion. There was a significant but transient downregulation of foxa2 at day three and nine postlesion, and nr4a2a at day three, nine and 14 postlesion. The expression of both genes remained unchanged in the OB and Tel. There was a transient downregulation of foxa2 protein expression at day three and seven postlesion. The significant increase of EdU-ir/ TH-ir cells in the vDn 30 days postlesion indicates maturation of proliferative cells (formed between day five-seven postlesion) into DpN. The present findings warrant future investigation of critical factors that govern the distinctive phases of DpN regeneration.

Dopamine-related oxidative stress and mitochondrial dysfunction in dopaminergic neurons differentiated from deciduous teeth-derived stem cells of children with Down syndrome

Down syndrome (DS) is one of the common genetic disorders caused by the trisomy of human chromosome 21 (HSA21). Mitochondrial dysfunction and redox imbalance play important roles in DS pathology, and altered dopaminergic regulation has been demonstrated in the brain of individuals with DS. However, the pathological association of these elements is not yet fully understood. In this study, we analyzed dopaminergic neurons (DNs) differentiated from deciduous teeth-derived stem cells of children with DS or healthy control children. As previously observed in the analysis of a single case of DS, compared to controls, patient-derived DNs (DS-DNs) displayed shorter neurite outgrowth and fewer branches, as well as downregulated vesicular monoamine transporter 2 and upregulated dopamine transporter 1, both of which are key regulators of dopamine homeostasis in DNs. In agreement with these expression profiles, DS-DNs accumulated dopamine intracellularly and had increased levels of cellular and mitochondrial reactive oxygen species (ROS). DS-DNs showed downregulation of non-canonical Notch ligand, delta-like 1, which may contribute to dopamine accumulation and increased ROS levels through DAT1 upregulation. Furthermore, DS-DNs showed mitochondrial dysfunction in consistent with lower expression of peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) and upregulation of a HSA21-encoded negative regulator of PGC-1α, nuclear receptor-interacting protein 1. These results suggest that dysregulated dopamine homeostasis may participate in oxidative stress and mitochondrial dysfunction of the dopaminergic system in DS.

An atlas of transcriptionally defined cell populations in the rat ventral tegmental area

The ventral tegmental area (VTA) is a complex brain region that is essential for reward function and frequently implicated in neuropsychiatric disease. While decades of research on VTA function have focused on dopamine neurons, recent evidence has identified critical roles for GABAergic and glutamatergic neurons in reward processes. Additionally, although subsets of VTA neurons express genes involved in the synthesis and transport of multiple neurotransmitters, characterization of these combinatorial populations has largely relied on low-throughput methods. To comprehensively define the molecular architecture of the VTA, we performed single-nucleus RNA sequencing on 21,600 cells from the rat VTA. Analysis of neuronal subclusters identifies selective markers for dopamine and combinatorial neurons, reveals expression profiles for receptors targeted by drugs of abuse, and demonstrates population-specific enrichment of gene sets linked to brain disorders. These results highlight the heterogeneity of the VTA and provide a resource for further exploration of VTA gene expression.

Emerging Roles of DLK1 in the Stem Cell Niche and Cancer Stemness

DLK1 is a maternally imprinted, paternally expressed gene coding for the transmembrane protein Delta-like homologue 1 (DLK1), a non-canonical NOTCH ligand with well-described roles during development, and tumor-supportive functions in several aggressive cancer forms. Here, we review the many functions of DLK1 as a regulator of stem cell pools and tissue differentiation in tissues such as brain, muscle, and liver. Furthermore, we review recent evidence supporting roles for DLK1 in the maintenance of aggressive stem cell characteristics of tumor cells, specifically focusing on central nervous system tumors, neuroblastoma, and hepatocellular carcinoma. We discuss NOTCH -dependent as well as NOTCH-independent functions of DLK1, and focus particularly on the complex pattern of DLK1 expression and cleavage that is finely regulated from a spatial and temporal perspective. Progress in recent years suggest differential functions of extracellular, soluble DLK1 as a paracrine stem cell niche-secreted factor, and has revealed a role for the intracellular domain of DLK1 in cell signaling and tumor stemness. A better understanding of DLK1 regulation and signaling may enable therapeutic targeting of cancer stemness by interfering with DLK1 release and/or intracellular signaling.

Effect of NTN and Lmx1α on the Notch Signaling Pathway during the Differentiation of Human Bone Marrow Mesenchymal Stem Cells into Dopaminergic Neuron-Like Cells

Human bone marrow mesenchymal stem cells (h-BMSCs) have the potential to differentiate into dopaminergic neuron-like cells to treat Parkinson's disease. The Notch signaling pathway has been implicated in the regulation of cell fate decisions such as differentiation of BMSCs. This study investigated changes in the expression of Notch-related genes in the differentiation of BMSCs in vitro into dopaminergic (DA) neuron-like cells. BMSCs transfected with empty lentiviral vectors served as the control group and those transfected with NTN and Lmx1α recombinant lentiviral vectors served as the experimental group. After induction and culture of NTN and Lmx1α-transfected h-BMSCs for 21 days, the cells exhibited features of dopaminergic neuron-like cells, which were observed by transmission and scanning electron microscopy and verified by immunofluorescence of tyrosine hydroxylase (TH) and dopamine transporter (DAT). These induced cells could secrete dopamine and had basic action potentials. Expression of the neural stem cell (NSC) markers, including octamer-binding protein (Oct4), paired box gene 6 (Pax6), and sex determining region Y-box 1 (SOX1), increased on day 14 of induction and decreased on day 21 of induction during differentiation. The human Notch signaling pathway PCR array showed a differential expression of Notch-related genes during the differentiation of h-BMSCs into DA neuron-like cells in vitro relative to that in the control group. In conclusion, h-BMSCs overexpressing NTN and Lmx1α can successfully be induced to differentiate into dopaminergic neuron-like cells with a neuronal phenotype exhibiting fundamental biological functions in vitro, and NTN and Lmx1α may affect the expression of Notch-related genes during differentiation.

Dlk1 dosage regulates hippocampal neurogenesis and cognition

Neurogenesis in the adult brain gives rise to functional neurons, which integrate into neuronal circuits and modulate neural plasticity. Sustained neurogenesis throughout life occurs in the subgranular zone (SGZ) of the dentate gyrus in the hippocampus and is hypothesized to be involved in behavioral/cognitive processes such as memory and in diseases. Genomic imprinting is of critical importance to brain development and normal behavior, and exemplifies how epigenetic states regulate genome function and gene dosage. While most genes are expressed from both alleles, imprinted genes are usually expressed from either the maternally or the paternally inherited chromosome. Here, we show that in contrast to its canonical imprinting in nonneurogenic regions, Delta-like homolog 1 (Dlk1) is expressed biallelically in the SGZ, and both parental alleles are required for stem cell behavior and normal adult neurogenesis in the hippocampus. To evaluate the effects of maternally, paternally, and biallelically inherited mutations within the Dlk1 gene in specific behavioral domains, we subjected Dlk1-mutant mice to a battery of tests that dissociate and evaluate the effects of Dlk1 dosage on spatial learning ability and on anxiety traits. Importantly, reduction in Dlk1 levels triggers specific cognitive abnormalities that affect aspects of discriminating differences in environmental stimuli, emphasizing the importance of selective absence of imprinting in this neurogenic niche.

Induction of Tyrosine Hydroxylase Gene Expression in Embryonal Carcinoma Stem Cells Using a Natural Tissue-Specific Inducer

A large number of studies have focused on the generation of dopaminergic neurons from pluripotent cells. Differentiation of stem cells into distinct cell types is influenced by tissue-specific microenvironment. Since, central nervous system undergoes further development during postnatal life, in the present study neonatal rat brain tissue extract (NRBE) was applied to direct the differentiation of embryonal carcinoma stem cell line, P19 into dopaminergic (DA) phenotypes. Additionally, a neuroprotective drug, deprenyl was used alone or in combination with the extract. Results from morphological, immunofluorescence, and qPCR analyses showed that during a period of one to three weeks, a large percentage of stem cells were differentiated into neural cells. The results also indicated the greater effect of NRBE on the differentiation of the cells into tyrosine hydroxylase-expressing cells. MS analysis of NRBE showed the enrichment of gene ontology terms related to cell differentiation and neurogenesis. Network analysis of the studied genes and some DA markers resulted in the suggestion of potential regulatory candidates such as AVP, ACHE, LHFPL5, and DLK1 genes. In conclusion, NRBE as a natural native inducer was apparently able to simulate the brain microenvironment and support neural differentiation of P19 cells.

Deletion of Dlk1 increases the vulnerability to developing anxiety-like behaviors and ethanol consumption in mice

Anxiety and alcohol use disorders (AUD) often present together, constituting a significant public health problem worldwide. In this study, we investigated the role of DLK1, a ligand of the Delta/NOTCH epidermal growth factor (EGF)-like protein family, reported to play a role in DA neurons differentiation in the striatum, as a neurobiological factor involved in the mechanisms regulating this psychiatric comorbidity. We exposed Dlk1 knockout mice (Dlk1-/- mice) to the open-field (OF), the light-dark box (LBD) and the elevated plus maze (EPM) tests, evaluating motivation to drink and ethanol consumption using the oral ethanol self-administration (OEA) paradigm. Quantitative real time polymerase chain reaction (qPCR) studies were carried out to evaluate alterations in targets closely related to DA neurotransmission in the reward system, tyrosine hydroxylase (Th) in the ventral tegmental area (VTA), and μ-opioid receptor (Oprm1) in the nucleus accumbens (NAc). No differences were observed in the total or peripheral distances travelled by Dlk1-/- compared to wild-type (WT) mice in OF. However, central distance travelled significantly decreased in Dlk1-/- mice. Deletion of Dlk1 increased anxiety-like behaviors in the LDB and EPM, and, Dlk1-/- mice also presented higher ethanol intake and motivation to drink (number of effective responses) in the OEA. In addition, Th and Oprm1 gene expression was reduced in the VTA and NAc of Dlk1-/- mice. We conclude that deletion of Dlk1 increases anxiety-related behaviors and vulnerability to ethanol consumption and modifies the gene expression of key targets closely related with DA neurotransmission involved in the reinforcing actions of ethanol.

Dual Effects of Human Placenta-Derived Neural Cells on Neuroprotection and the Inhibition of Neuroinflammation in a Rodent Model of Parkinson's Disease

Parkinson’s disease (PD) is the second most common age-related neurodegenerative disease in the elderly and the patients suffer from uncontrolled movement disorders due to loss of dopaminergic (DA) neurons on substantia nigra pars compacta (SNpc). We previously reported that transplantation of human fetal midbrain-derived neural precursor cells restored the functional deficits of a 6-hydroxy dopamine (6-OHDA)-treated rodent model of PD but its low viability and ethical issues still remain to be solved. Albeit immune privilege and neural differentiation potentials suggest mesenchymal stem cells (MSCs) from various tissues including human placenta MSCs (hpMSCs) for an alternative source, our understanding of their therapeutic mechanisms is still limited. To expand our knowledge on the MSC-mediated PD treatment, we here investigated the therapeutic mechanism of hpMSCs and hpMSC-derived neural phenotype cells (hpNPCs) using a PD rat model. Whereas both hpMSCs and hpNPCs protected DA neurons in the SNpc at comparable levels, the hpNPC transplantation into 6-OHDA treated rats exhibited longer lasting recovery in motor deficits than either the saline or the hpMSC treated rats. The injected hpNPCs induced delta-like ligand (DLL)1 and neurotrophic factors, and influenced environments prone to neuroprotection. Compared with hpMSCs, co-cultured hpNPCs more efficiently protected primary neural precursor cells from midbrain against 6-OHDA as well as induced their differentiation into DA neurons. Further experiments with conditioned media from hpNPCs revealed that the secreted factors from hpNPCs modulated immune responses and neural protection. Taken together, both DLL1-mediated contact signals and paracrine factors play critical roles in hpNPC-mediated improvement. First showing here that hpMSCs and their neural derivative hpNPCs were able to restore the PD-associated deficits via dual mechanisms, neuroprotection and immunosuppression, this study expanded our knowledge of therapeutic mechanisms in PD and other age-related diseases.

Targeting endogenous DLK1 exerts antitumor effect on hepatocellular carcinoma through initiating cell differentiation

Cancer stem cells (CSCs) are responsible for tumor initiation and progression. We previously showed that Delta-like homolog 1 (DLK1) may be a therapeutic target against the CSCs of human hepatocellular carcinoma (HCC). However, the therapeutic efficacy and underlying mechanism remain unclear. Here we demonstrated that knockdown of DLK1 using a tet-inducible short hairpin RNA (shRNA) system significantly inhibited proliferation, spheroid formation and in vivo xenograft tumor growth of human HCC cells. Furthermore, in an orthotopic xenograft mouse model, adenovirus-mediated DLK1 knockdown could significantly reduce tumor size, as shown by in vivo imaging approach. Subsequently, an adenoviral vector harboring mouse Dlk1 shRNA was applied. The results showed that Dlk1 knockdown also could inhibit tumor progression in a diethylnitrosamine (DEN) induced mouse HCC model. At cellular mechanism, DLK1 knockdown delayed the cell cycle G1-S transition, along with the decreased expression of cyclin E1 and D1. Significantly, DLK1 knockdown resulted in the decrease of molecular markers such as AFP and EpCAM for hepatic progenitor cells, but the increase of KRT18 and KRT19 for the differentiated hepatocytes. The collective data indicated that targeting endogenous DLK1 may exert antitumor effect on HCCs possibly through initiating cell differentiation.

Combined Nurr1 and Foxa2 roles in the therapy of Parkinson's disease

Use of the physiological mechanisms promoting midbrain DA (mDA) neuron survival seems an appropriate option for developing treatments for Parkinson's disease (PD). mDA neurons are specifically marked by expression of the transcription factors Nurr1 and Foxa2. We show herein that Nurr1 and Foxa2 interact to protect mDA neurons against various toxic insults, but their expression is lost during aging and degenerative processes. In addition to their proposed cell-autonomous actions in mDA neurons, forced expression of these factors in neighboring glia synergistically protects degenerating mDA neurons in a paracrine mode. As a consequence of these bimodal actions, adeno-associated virus (AAV)-mediated gene delivery of Nurr1 and Foxa2 in a PD mouse model markedly protected mDA neurons and motor behaviors associated with nigrostriatal DA neurotransmission. The effects of the combined gene delivery were dramatic, highly reproducible, and sustained for at least 1 year, suggesting that expression of these factors is a promising approach in PD therapy.

Elevated α-synuclein caused by SNCA gene triplication impairs neuronal differentiation and maturation in Parkinson's patient-derived induced pluripotent stem cells

We have assessed the impact of α-synuclein overexpression on the differentiation potential and phenotypic signatures of two neural-committed induced pluripotent stem cell lines derived from a Parkinson's disease patient with a triplication of the human SNCA genomic locus. In parallel, comparative studies were performed on two control lines derived from healthy individuals and lines generated from the patient iPS-derived neuroprogenitor lines infected with a lentivirus incorporating a small hairpin RNA to knock down the SNCA mRNA. The SNCA triplication lines exhibited a reduced capacity to differentiate into dopaminergic or GABAergic neurons and decreased neurite outgrowth and lower neuronal activity compared with control cultures. This delayed maturation phenotype was confirmed by gene expression profiling, which revealed a significant reduction in mRNA for genes implicated in neuronal differentiation such as delta-like homolog 1 (DLK1), gamma-aminobutyric acid type B receptor subunit 2 (GABABR2), nuclear receptor related 1 protein (NURR1), G-protein-regulated inward-rectifier potassium channel 2 (GIRK-2) and tyrosine hydroxylase (TH). The differentiated patient cells also demonstrated increased autophagic flux when stressed with chloroquine. We conclude that a two-fold overexpression of α-synuclein caused by a triplication of the SNCA gene is sufficient to impair the differentiation of neuronal progenitor cells, a finding with implications for adult neurogenesis and Parkinson's disease progression, particularly in the context of bioenergetic dysfunction.

Serum DLK1 is a potential prognostic biomarker in patients with hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most prevalent cancer and the third most frequent cause of cancer-related death in developing countries, especially in East Asia and South Africa, and the identification of new biomarkers for early diagnosis and prognosis is needed. Delta-like 1 homologue (Drosophila) (DLK1) is expressed in malignancies and promotes cancer cell stemness and tumourigenicity, which makes this molecule a potential target for therapies directed against cancer stem/progenitor cells. Here, we aimed to assess the predictive value of DLK1 as a diagnostic and prognostic biomarker in HCC. With this purpose, serum DLK1 levels were detected using an enzyme-linked immunosorbent assay (ELISA) in serum specimens from 397 HCC patients, 114 healthy individuals, 43 patients with chronic hepatitis B virus (HBV) infection and 24 cirrhotic liver patients with HBV infection, and the correlation between DLK1 levels and clinical features was evaluated. Our data showed that the serum DLK1 level was significantly higher in HCC patients than in healthy individuals or patients with chronic HBV infection (HBV carriers) (P < 0.05). Moreover, the serum DLK1 levels were positively correlated with tumour size and α-fetoprotein (AFP) levels, but not with gender, age, histological grade, HBV infection, intrahepatic metastasis or cirrhosis in HCC patients. Kaplan-Meier analysis indicated that higher DLK1 levels were associated with shorter survival in HCC patients. These results suggest that the serum levels of DLK1 may serve as a prognostic biomarker for HCC patients.

Characterization of fetal antigen 1/delta-like 1 homologue expressing cells in the rat nigrostriatal system: effects of a unilateral 6-hydroxydopamine lesion

Fetal antigen 1/delta-like 1 homologue (FA1/dlk1) belongs to the epidermal growth factor superfamily and is considered to be a non-canonical ligand for the Notch receptor. Interactions between Notch and its ligands are crucial for the development of various tissues. Moreover, FA1/dlk1 has been suggested as a potential supplementary marker of dopaminergic neurons. The present study aimed at investigating the distribution of FA1/dlk1-immunoreactive (-ir) cells in the early postnatal and adult midbrain as well as in the nigrostriatal system of 6-hydroxydopamine (6-OHDA)-lesioned hemiparkinsonian adult rats. FA1/dlk1-ir cells were predominantly distributed in the substantia nigra (SN) pars compacta (SNc) and in the ventral tegmental area. Interestingly, the expression of FA1/dlk1 significantly increased in tyrosine hydroxylase (TH)-ir cells during early postnatal development. Co-localization and tracing studies demonstrated that FA1/dlk1-ir cells in the SNc were nigrostriatal dopaminergic neurons, and unilateral 6-OHDA lesions resulted in loss of both FA1/dlk1-ir and TH-ir cells in the SNc. Surprisingly, increased numbers of FA1/dlk1-ir cells (by 70%) were detected in dopamine-depleted striata as compared to unlesioned controls. The higher number of FA1/dlk1-ir cells was likely not due to neurogenesis as colocalization studies for proliferation markers were negative. This suggests that FA1/dlk1 was up-regulated in intrinsic cells in response to the 6-OHDA-mediated loss of FA1/dlk1-expressing SNc dopaminergic neurons and/or due to the stab wound. Our findings hint to a significant role of FA1/dlk1 in the SNc during early postnatal development. The differential expression of FA1/dlk1 in the SNc and the striatum of dopamine-depleted rats could indicate a potential involvement of FA1/dlk1 in the cellular response to the degenerative processes.

Zebrafish as a systems toxicology model for developmental neurotoxicity testing

The developing brain is extremely sensitive to many chemicals. Exposure to neurotoxicants during development has been implicated in various neuropsychiatric and neurological disorders, including autism spectrum disorder, attention deficit hyperactive disorder, schizophrenia, Parkinson's disease, and Alzheimer's disease. Although rodents have been widely used for developmental neurotoxicity testing, experiments using large numbers of rodents are time-consuming, expensive, and raise ethical concerns. Using alternative non-mammalian animal models may relieve some of these pressures by allowing testing of large numbers of subjects while reducing expenses and minimizing the use of mammalian subjects. In this review, we discuss some of the advantages of using zebrafish in developmental neurotoxicity testing, focusing on central nervous system development, neurobehavior, toxicokinetics, and toxicodynamics in this species. We also describe some important examples of developmental neurotoxicity testing using zebrafish combined with gene expression profiling, neuroimaging, or neurobehavioral assessment. Zebrafish may be a systems toxicology model that has the potential to reveal the pathways of developmental neurotoxicity and to provide a sound basis for human risk assessments.

Molecular mechanisms of dopaminergic subset specification: fundamental aspects and clinical perspectives

Dopaminergic (DA) neurons in the ventral mesodiencephalon control locomotion and emotion and are affected in psychiatric and neurodegenerative diseases, such as Parkinson's disease (PD). A clinical hallmark of PD is the specific degeneration of DA neurons located within the substantia nigra (SNc), whereas neurons in the ventral tegmental area remain unaffected. Recent advances have highlighted that the selective vulnerability of the SNc may originate in subset-specific molecular programming during DA neuron development, and significantly increased our understanding of the molecular code that drives specific SNc development. We here present an up-to-date overview of molecular mechanisms that direct DA subset specification, integrating our current knowledge about subset-specific roles of transcription factors, signaling pathways and morphogenes. We discuss strategies to further unravel subset-specific gene-regulatory networks, and the clinical promise of fundamental knowledge about subset specification of DA neurons, with regards to cell replacement therapy and cell-type-specific vulnerability in PD.

Prenatal maternal immune activation causes epigenetic differences in adolescent mouse brain

Epigenetic processes such as DNA methylation have been implicated in the pathophysiology of neurodevelopmental disorders including schizophrenia and autism. Epigenetic changes can be induced by environmental exposures such as inflammation. Here we tested the hypothesis that prenatal inflammation, a recognized risk factor for schizophrenia and related neurodevelopmental conditions, alters DNA methylation in key brain regions linked to schizophrenia, namely the dopamine rich striatum and endocrine regulatory centre, the hypothalamus. DNA methylation across highly repetitive elements (long interspersed element 1 (LINE1) and intracisternal A-particles (IAPs)) were used to proxy global DNA methylation. We also investigated the Mecp2 gene because it regulates transcription of LINE1 and has a known association with neurodevelopmental disorders. Brain tissue was harvested from 6 week old offspring of mice exposed to the viral analog PolyI:C or saline on gestation day 9. We used Sequenom EpiTYPER assay to quantitatively analyze differences in DNA methylation at IAPs, LINE1 elements and the promoter region of Mecp2. In the hypothalamus, prenatal exposure to PolyI:C caused significant global DNA hypomethylation (t=2.44, P=0.019, PolyI:C mean 69.67%, saline mean 70.19%), especially in females, and significant hypomethylation of the promoter region of Mecp2, (t=3.32, P=0.002; PolyI:C mean 26.57%, saline mean 34.63%). IAP methylation was unaltered. DNA methylation in the striatum was not significantly altered. This study provides the first experimental evidence that exposure to inflammation during prenatal life is associated with epigenetic changes, including Mecp2 promoter hypomethylation. This suggests that environmental and genetic risk factors associated with neurodevelopmental disorders may act upon similar pathways. This is important because epigenetic changes are potentially modifiable and their investigation may open new avenues for treatment.

Delta-like 1 homologue (DLK1) protein in neurons of the arcuate nucleus that control weight homeostasis and effect of fasting on hypothalamic DLK1 mRNA

Delta-like 1 homologue (DLK1; also called preadipocyte factor 1) is an epidermal growth factor repeat-containing transmembrane protein that is cleaved by tumor necrosis factor-α-converting enzyme to generate a biologically active soluble form. DLK1 is involved in the differentiation of several cell types, including adipocytes. Lack of the dlk1 gene results in adiposity, and polymorphism within the gene encoding DLK1 is associated with human obesity. The dlk1 gene is expressed in restricted areas of the adult brain, with an enrichment of cell bodies expressing DLK1 mRNA in the hypothalamus. Antibodies to DLK1 were used to study the cellular localization and chemical identity of DLK1-immunoreactive neuronal cell bodies in rat hypothalamus. DLK1 immunoreactivity was demonstrated in the cell soma and dendrites of cell bodies in the suprachiasmatic, supraoptic, paraventricular, dorsomedial, arcuate nuclei and in the perifornical/lateral hypothalamic area. In the arcuate nucleus (Arc), DLK1 immunoreactivity was mainly seen in many neurons of the ventromedial and to a lesser extent in its ventrolateral division. Double labeling showed that 93.7% of orexigenic agouti-related peptide (AgRP) and 94.1% of neuropeptide Y (NPY) neurons located in the ventromedial part of the Arc were DLK1 positive, whereas 36.1% of anorexigenic pro-opiomelanocortin and 34.6% of cocaine- and amphetamine-regulated transcript neurons of the Arc contained DLK1 immunoreactivity. DLK1 mRNA was downregulated in the hypothalamus of fasted animals. Presence of DLK1 in the majority of orexigenic Arc NPY/AgRP neurons and regulation of DLK1 mRNA by nutritional challenge suggest that DLK1 has a role in hypothalamic regulation of body weight control. © 2014 S. Karger AG, Basel.

Delta-like 1 homologue is a hypothalamus-enriched protein that is present in orexin-containing neurones of the lateral hypothalamic area

Delta-like 1 homologue (DLK1), also known as preadipocyte factor-1, fetal antigen 1 or pG2, is a transmembrane protein belonging to the epidermal growth factor-like superfamily. The protein becomes soluble and biologically active after cleavage of the tumour necrosis factor-α-converting enzyme. DLK1 is involved in the differentiation of several cell types, including adipocytes. Lack of the dlk1 gene in mice results in adiposity and a polymorphism within the gene encoding DLK1 has been associated with obesity. The dlk1 gene is expressed in restricted areas of the central nervous system with an enrichment of cell bodies expressing DLK1 mRNA in the hypothalamus. Goat and rabbit antisera to DLK1 were used to study the cellular localisation and chemical identity of DLK1-immunoreactive neuronal cell bodies in rat hypothalamus. DLK1 immunoreactivity was demonstrated in the cell bodies of the suprachiasmatic, supraoptic, paraventricular, arcuate nuclei and in the lateral hypothalamus. At the subcellular level, DLK1 immunoreactivity was observed in the cell soma and dendrites, although not in axonal fibres or nerve terminals. Double-labelling of sections from the lateral hypothalamic/perifornical area of colchicine-treated rats (a treatment that increases the content of immunoreactive material in the cell soma) showed that DLK1 was present in the virually all orexin- and dynorphin-containing neurones. By contrast, DLK1 was not demonstrated in any melanin-concentrating hormone or cocaine- and amphetamine-regulated transcript-containing neurones of the lateral hypothalamic/perifornical area. The presence of DLK1 in a population of lateral hypothalamic neurones suggests a functional role for DLK1 in orexin/hypocretin/dynorphin neurones.

Impact of Immunity in Autism Spectrum Disorders

Autism spectrum disorders (ASDs) are childhood psychopathologies characterized by having difficulties in social interaction, verbal and non-verbal communication as well as sensor motor movements. Evidence suggests that in ASDs environmental toxicant exposure, genetic and mitochondrial dysfunction are involved associated with abnormal immune response with allergic problems and elevated serum IgE. ASDs present the major cytokine and chemokine dysfunction in CNS and is mediated by an increase of pro-inflammatory cytokine levels in the brain, such as TNF, IL-1, IFN-γ, IL-6, IL-8 and others. Mast cells, which are also implicated in ASDs, are worsened by stress and produce proinflammatory cytokines and can be stimulated by neurotensin in the brain and gut, contributing also to the inflammatory response. However, the exact etiology of ASDs remains largely unknown.

Prolonged membrane depolarization enhances midbrain dopamine neuron differentiation via epigenetic histone modifications

Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiological and clinical implications of this neuronal subtype. We show that prolonged membrane depolarization induced by KCl treatment promotes DA neuron differentiation from neural precursor cells (NPCs) derived from embryonic ventral midbrain (VM). Interestingly, the depolarization-induced increase of DA neuron yields was not abolished by L-type calcium channel blockers, along with no depolarization-mediated change of intracellular calcium level in the VM-derived NPCs (VM-NPCs), suggesting that the depolarization effect is due to a calcium-independent mechanism. Experiments with labeled DA neuron progenitors indicate that membrane depolarization acts at the differentiation fate determination stage and promotes the expression of DA phenotype genes (tyrosine hydroxylase [TH] and DA transporter [DAT]). Recruitment of Nurr1, a transcription factor crucial for midbrain DA neuron development, to the promoter of TH gene was enhanced by depolarization, along with increases of histone 3 acetylation (H3Ac) and trimethylation of histone3 on lysine 4 (H3K4m3), and decreases of H3K9m3 and H3K27m3 in the consensus Nurr1 binding regions of TH promoter. Depolarization stimuli on differentiating VM-NPCs also induced dissociation of methyl CpG binding protein 2 and related repressor complex molecules (repressor element-1 silencing transcription factor corepressor and histone deacetylase 1) from the CpG sites of TH and DAT promoters. Based on these findings, we suggest that membrane depolarization promotes DA neuron differentiation by opening chromatin structures surrounding DA phenotype genes and inhibiting the binding of corepressors, thus allowing transcriptional activators such as Nurr1 to access DA neuron differentiation gene promoter regions.

DLK1 is a somato-dendritic protein expressed in hypothalamic arginine-vasopressin and oxytocin neurons

Delta-Like 1 Homolog, Dlk1, is a paternally imprinted gene encoding a transmembrane protein involved in the differentiation of several cell types. After birth, Dlk1 expression decreases substantially in all tissues except endocrine glands. Dlk1 deletion in mice results in pre-natal and post-natal growth deficiency, mild obesity, facial abnormalities, and abnormal skeletal development, suggesting involvement of Dlk1 in perinatal survival, normal growth and homeostasis of fat deposition. A neuroendocrine function has also been suggested for DLK1 but never characterised. To evaluate the neuroendocrine function of DLK1, we first characterised Dlk1 expression in mouse hypothalamus and then studied post-natal variations of the hypothalamic expression. Western Blot analysis of adult mouse hypothalamus protein extracts showed that Dlk1 was expressed almost exclusively as a soluble protein produced by cleavage of the extracellular domain. Immunohistochemistry showed neuronal DLK1 expression in the suprachiasmatic (SCN), supraoptic (SON), paraventricular (PVN), arcuate (ARC), dorsomedial (DMN) and lateral hypothalamic (LH) nuclei. DLK1 was expressed in the dendrites and perikarya of arginine-vasopressin neurons in PVN, SCN and SON and in oxytocin neurons in PVN and SON. These findings suggest a role for DLK1 in the post-natal development of hypothalamic functions, most notably those regulated by the arginine-vasopressin and oxytocin systems.

Retinoic acid-dependent and -independent gene-regulatory pathways of Pitx3 in meso-diencephalic dopaminergic neurons

Development of meso-diencephalic dopamine (mdDA) neurons requires the combined actions of the orphan nuclear receptor Nurr1 and the paired-like homeobox transcription factor Pitx3. Whereas all mdDA neurons require Nurr1 for expression of Th and survival, dependence on Pitx3 is displayed only by the mdDA subpopulation that will form the substantia nigra (SNc). Previously, we have demonstrated that Pitx3(-/-) embryos lack the expression of the retinoic acid (RA)-generating enzyme Ahd2, which is normally selectively expressed in the Pitx3-dependent DA neurons of the SNc. Restoring RA signaling in Pitx3(-/-) embryos revealed a selective dependence of SNc neurons on the presence of RA for differentiation into Th-positive neurons and maintenance throughout embryonic development. Whereas these data are suggestive of an important developmental role for RA in neurons of the SNc, it remained unclear whether other Nurr1 and Pitx3 target genes depend on RA signaling in a manner similar to Th. In the search for genes that were affected in Pitx3-deficient mdDA neurons and restored upon embryonic RA treatment, we provide evidence that Delta-like 1, D2R (Drd2) and Th are regulated by Pitx3 and RA signaling, which influences the mdDA terminal differentiated phenotype. Furthermore, we show that regulation of Ahd2-mediated RA signaling represents only one aspect of the Pitx3 downstream cascade, as Vmat2, Dat, Ahd2 (Aldh1a1), En1, En2 and Cck were unaffected by RA treatment and are (subset) specifically modulated by Pitx3. In conclusion, our data reveal several RA-dependent and -independent aspects of the Pitx3-regulated gene cascade, suggesting that Pitx3 acts on multiple levels in the molecular subset-specification of mdDA neurons.

Estrogen inhibits Dlk1/FA1 production: a potential mechanism for estrogen effects on bone turnover

We have recently identified delta-like 1/fetal antigen 1 (Dlk1/FA1) as a novel regulator of bone mass that functions to mediate bone loss under estrogen deficiency in mice. In this report, we investigated the effects of estrogen (E) deficiency and E replacement on serum (s) levels of Dlk1/FA1 (s-Dlk1FA1) and its correlation with bone turnover markers. s-Dlk1/FA1 and bone turnover markers (serum cross-linked C-telopeptide [s-CTX] and serum osteocalcin) were measured in two cohorts: a group of pre- and postmenopausal women (n = 100) and a group of postmenopausal women, where half had received estrogen-replacement therapy (ERT, n = 166). s-Dlk1/FA1 and s-CTX were elevated in postmenopausal E-deficient women compared with premenopausal E-replete women (both p < 0.001). s-Dlk1/FA1 was correlated with s-CTX (r = 0.30, p < 0.01). ERT in postmenopausal women decreased s-Dlk1/FA1, as well as s-CTX and s-osteoclacin (all p < .0001). Changes in s-Dlk1 were significantly correlated with those observed in s-CTX (r = 0.18, p < 0.05) and s-osteocalcin (r = 0.28, p < 0.001). In conclusion, s-Dlk1/FA1 is influenced by E-deficiency and is correlated with bone turnover. Increased levels of s-Dlk1/FA1 in postmenopausal women may be a mechanism mediating the effects of estrogen deficiency on bone turnover.

Role of the non-canonical notch ligand delta-like protein 1 in hormone-producing cells of the adult male mouse pituitary

To better understand the role of the non-canonical Notch ligand delta-like protein 1 (DLK1), in hormone-producing cells, we studied the cell distribution and subcellular localisation of DLK1 in the pituitary of male adult 129/SvJ mice, and analysed the variations in the hormone-producing cells associated with the lack of this gene in Dlk1 knockout mice. The results obtained showed the presence of DLK1-immunoreactive (ir) cells in all hormone-producing cells of the anterior pituitary. Immunoelectron microscopy showed DLK1-ir in the rough endoplasmic reticulum and inside secretory vesicles, suggesting that DLK1 is released together with pituitary hormones. Moreover, we found that prolactin (PRL)-DLK1-ir cells are in intimate contact with follicle-stimulating hormone (FSH)-ir-DLK1-negative cells. In Dlk1 knockout mice, we detected a significantly lower number of gowth hormone (GH)-ir cells, a reduction in the FSH and PRL immunostaining intensity, and a significant decrease in FSH mRNA expression compared to wild-type mice. An increase in pituitary GH mRNA expression and serum leptin levels was also found. These findings provide evidence supporting several regulatory functions of DLK1 in the pituitary gland.

Postnatal loss of Dlk1 imprinting in stem cells and niche astrocytes regulates neurogenesis

The gene for the atypical Notch ligand Delta-like homologue 1 (Dlk1) encodes membrane-bound and secreted isoforms functioning in multiple developmental processes in vitro and in vivo. Dlk1, a member of a cluster of imprinted genes, is expressed from the paternally-inherited chromosome^1,2. Here we show that mice deficient in Dlk1 exhibit defects in postnatal neurogenesis within the subventricular zone (SVZ), a developmental continuum resulting in depletion of mature neurons in the olfactory bulb. We show that DLK1 is a factor secreted by niche-astrocytes, while its membrane-bound isoform is present in neural stem cells (NSCs) being required for the inductive effect of secreted DLK1 on self-renewal. Surprisingly, we find a requirement for Dlk1 expressed from both maternal and paternally inherited chromosomes. Selective absence of Dlk1 imprinting in both NSCs and niche astrocytes is associated with postnatal acquisition of DNA methylation at the germ line-derived imprinting control region (IG-DMR). The results emphasize molecular relationships between NSCs and niche-astrocytes identifying a signalling system coded by a single gene functioning co-ordinately in both cell types. The modulation of genomic imprinting in a stem cell environment adds a new level of epigenetic regulation to the establishment and maintenance of the niche raising wider questions about the adaptability, function, and evolution of imprinting within specific developmental contexts.

Genomic imprinting as an adaptative model of developmental plasticity

Developmental plasticity can be defined as the ability of one genotype to produce a range of phenotypes in response to environmental conditions. Such plasticity can be manifest at the level of individual cells, an organ, or a whole organism. Imprinted genes are a group of approximately 100 genes with functionally monoallelic, parental-origin specific expression. As imprinted genes are critical for prenatal growth and metabolic axis development and function, modulation of imprinted gene dosage has been proposed to play a key role in the plastic development of the unborn foetus in response to environmental conditions. Evidence is accumulating that imprinted dosage may also be involved in controlling the plastic potential of individual cells or stem cell populations. Imprinted gene dosage can be modulated through canonical, transcription factor mediated mechanisms, or through the relaxation of imprinting itself, reactivating the normally silent allele.

LRRK2 controls synaptic vesicle storage and mobilization within the recycling pool

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the single most common cause of inherited Parkinson's disease. Little is known about its involvement in the pathogenesis of Parkinson's disease mainly because of the lack of knowledge about the physiological role of LRRK2. To determine the function of LRRK2, we studied the impact of short hairpin RNA-mediated silencing of LRRK2 expression in cortical neurons. Paired recording indicated that LRRK2 silencing affects evoked postsynaptic currents. Furthermore, LRRK2 silencing induces at the presynaptic site a redistribution of vesicles within the bouton, altered recycling dynamics, and increased vesicle kinetics. Accordingly, LRRK2 protein is present in the synaptosomal compartment of cortical neurons in which it interacts with several proteins involved in vesicular recycling. Our results suggest that LRRK2 modulates synaptic vesicle trafficking and distribution in neurons and in consequence participates in regulating the dynamics between vesicle pools inside the presynaptic bouton.

DeltaA/DeltaD regulate multiple and temporally distinct phases of notch signaling during dopaminergic neurogenesis in zebrafish

Dopaminergic neurons develop at distinct anatomical sites to form some of the major neuromodulatory systems in the vertebrate brain. Despite their relevance in neurodegenerative diseases and the interests in reconstitutive therapies from stem cells, mechanisms of the neurogenic switch from precursor populations to dopaminergic neurons are not well understood. Here, we investigated neurogenesis of different dopaminergic and noradrenergic neuron populations in the zebrafish embryo. Birth-dating analysis by EdU (5-ethynyl-2'-deoxyuridine) incorporation revealed temporal dynamics of catecholaminergic neurogenesis. Analysis of Notch signaling mutants and stage-specific pharmacological inhibition of Notch processing revealed that dopaminergic neurons form by temporally distinct mechanisms: dopaminergic neurons of the posterior tuberculum derive directly from neural plate cells during primary neurogenesis, whereas other dopaminergic groups form in continuous or wavelike neurogenesis phases from proliferating precursor pools. Systematic analysis of Notch ligands revealed that the two zebrafish co-orthologs of mammalian Delta1, DeltaA and DeltaD, control the neurogenic switch of all early developing dopaminergic neurons in a partially redundant manner. DeltaA/D may also be involved in maintenance of dopaminergic precursor pools, as olig2 expression in ventral diencephalic dopaminergic precursors is affected in dla/dld mutants. DeltaA/D act upstream of sim1a and otpa during dopaminergic specification. However, despite the fact that both dopaminergic and corticotropin-releasing hormone neurons derive from sim1a- and otpa-expressing precursors, DeltaA/D does not act as a lineage switch between these two neuronal types. Rather, DeltaA/D limits the size of the sim1a- and otpa-expressing precursor pool from which dopaminergic neurons differentiate.

A QUICK screen for Lrrk2 interaction partners--leucine-rich repeat kinase 2 is involved in actin cytoskeleton dynamics

Mutations in human leucine-rich repeat kinase 2 (Lrrk2), a protein of yet unknown function, are linked to Parkinson's disease caused by degeneration of midbrain dopaminergic neurons. The protein comprises several domains including a GTPase and a kinase domain both affected by several pathogenic mutations. To elucidate the molecular interaction network of endogenous Lrrk2 under stoichiometric constraints, we applied QUICK (quantitative immunoprecipitation combined with knockdown) in NIH3T3 cells. The identified interactome reveals actin isoforms as well as actin-associated proteins involved in actin filament assembly, organization, rearrangement, and maintenance, suggesting that the biological function of Lrrk2 is linked to cytoskeletal dynamics. In fact, we demonstrate Lrrk2 de novo binding to F-actin and its ability to modulate its assembly in vitro. When tested in intact cells, knockdown of Lrrk2 causes morphological alterations in NIH3T3 cells. In developing dopaminergic midbrain primary neurons, Lrrk2 knockdown results in shortened neurite processes, indicating a physiological role of Lrrk2 in cytoskeletal organization and dynamics of dopaminergic neurons. Hence, our results demonstrate that molecular interactions as well as the physiological function of Lrrk2 are closely related to the organization of the actin-based cytoskeleton, a crucial feature of neuronal development and neuron function.

MicroRNA-15a fine-tunes the level of Delta-like 1 homolog (DLK1) in proliferating 3T3-L1 preadipocytes

Delta like 1 homolog (Dlk1) exists in both transmembrane and soluble molecular forms, and is implicated in cellular growth and plays multiple roles in development, tissue regeneration, and cancer. Thus, DLK1 levels are critical for cell function, and abnormal DLK1 expression can be lethal; however, little is known about the underlying mechanisms. We here report that miR-15a modulates DLK1 levels in preadipocytes thus providing a mechanism for DLK1 regulation that further links it to cell cycle arrest and cancer since miR-15a is deregulated in these processes. In preadipocytes, miR-15a increases with cell density, and peaks at the same stage where membrane DLK1(M) and soluble DLK1(S) are found at maximum levels. Remarkably, miR-15a represses the amount of all Dlk1 variants at the mRNA level but also the level of DLK1(M) protein while it increases the amount of DLK1(S) supporting a direct repression of DLK1 and a parallel effect on the protease that cleaves off the DLK1 from the membrane. In agreement with previous studies, we found that miR-15a represses cell numbers, but additionally, we report that miR-15a also increases cell size. Conversely, anti-miR-15a treatment decreases cell size while increasing cell numbers, scenarios that were completely rescued by addition of purified DLK1(S). Our data thus imply that miR-15a regulates cell size and proliferation by fine-tuning Dlk1 among others, and further emphasize miR-15a and DLK1 levels to play important roles in growth signaling networks.

Identification of Dlk1, Ptpru and Klhl1 as novel Nurr1 target genes in meso-diencephalic dopamine neurons

The orphan nuclear receptor Nurr1 is essential for the development of meso-diencephalic dopamine (mdDA) neurons and is required, together with the homeobox transcription factor Pitx3, for the expression of genes involved in dopamine metabolism. In order to elucidate the molecular mechanisms that underlie the neuronal deficits in Nurr1(-/-) mice, we performed combined gene expression microarrays and ChIP-on-chip analysis and thereby identified Dlk1, Ptpru and Klhl1 as novel Nurr1 target genes in vivo. In line with the previously described cooperativity between Nurr1 and Pitx3, we show that the expression of Ptpru and Klhl1 in mdDA neurons is also dependent on Pitx3. Furthermore, we demonstrate that Nurr1 interacts with the Ptpru promoter directly and requires Pitx3 for full expression of Ptpru in mdDA neurons. By contrast, the expression of Dlk1 is maintained in Pitx3(-/-) embryos and is even expanded into the rostral part of the mdDA area, suggesting a unique position of Dlk1 in the Nurr1 and Pitx3 transcriptional cascades. Expression analysis in Dlk1(-/-) embryos reveals that Dlk1 is required to prevent premature expression of Dat in mdDA neuronal precursors as part of the multifaceted process of mdDA neuronal differentiation driven by Nurr1 and Pitx3. Taken together, the involvement of Nurr1 and Pitx3 in the expression of novel target genes involved in important neuronal processes such as neuronal patterning, axon outgrowth and terminal differentiation, opens up new avenues to study the properties of mdDA neurons during development and in neuronal pathology as observed in Parkinson's disease.

Mecp2-null mice provide new neuronal targets for Rett syndrome

Background

Rett syndrome (RTT) is a complex neurological disorder that is one of the most frequent causes of mental retardation in women. A great landmark in research in this field was the discovery of a relationship between the disease and the presence of mutations in the gene that codes for the methyl-CpG binding protein 2 (MeCP2). Currently, MeCP2 is thought to act as a transcriptional repressor that couples DNA methylation and transcriptional silencing. The present study aimed to identify new target genes regulated by Mecp2 in a mouse model of RTT.

Methodology/Principal Findings

We have compared the gene expression profiles of wild type (WT) and Mecp2-null (KO) mice in three regions of the brain (cortex, midbrain, and cerebellum) by using cDNA microarrays. The results obtained were confirmed by quantitative real-time PCR. Subsequent chromatin immunoprecipitation assays revealed seven direct target genes of Mecp2 bound in vivo (Fkbp5, Mobp, Plagl1, Ddc, Mllt2h, Eya2, and S100a9), and three overexpressed genes due to an indirect effect of a lack of Mecp2 (Irak1, Prodh and Dlk1). The regions bound by Mecp2 were always methylated, suggesting the involvement of the methyl-CpG binding domain of the protein in the mechanism of interaction.

Conclusions

We identified new genes that are overexpressed in Mecp2-KO mice and are excellent candidate genes for involvement in various features of the neurological disease. Our results demonstrate new targets of MeCP2 and provide us with a better understanding of the underlying mechanisms of RTT.

Prevention of interferon-stimulated gene expression using microRNA-designed hairpins

RNA interference allows selective gene silencing, and is widely used for functional analysis of individual genes in vertebrate cells and represents an attractive therapeutic option for treating central nervous system diseases. However, growing evidence exists that the expression of short hairpin RNAs (shRNAs) can trigger cellular immune response resulting in unspecific cellular phenotypes and severe side effects. We found that lentiviral vector (LV)-mediated expression of shRNAs in primary cortical cultures resulted in strong expression of the interferon-stimulated gene oligoadenylate synthetase 1 (Oas1), which was accompanied by accelerated apoptosis and substantial net neuron loss. Modification of the shRNA construct by implementing features of the naturally occurring microRNA-30 (miR-30) precursor avoided Oas1 induction in transduced primary cultures, whereby modification of the passenger strand seems to be a crucial feature to circumvent interferon-stimulated gene expression. This work represents the first experimental study showing that an miR-30-based shRNA construct prevents Oas1 pathway associated off-target effects, which we consider as an essential prerequisite for shRNA use in future gene therapeutic approaches.