Genetic association analyses of PHOX2B and ASCL1 in neuropsychiatric disorders: evidence for association of ASCL1 with Parkinson's disease

Activation of Embryonic Gene Transcription in Neural Precursor Cells Derived from the Induced Pluripotent Stem Cells of the Patients with Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases in the world. Despite numerous studies, the causes of this pathology remain completely unknown. This is, among other things, due to the difficulty of obtaining biological material for analysis. Neural cell cultures derived from the induced pluripotent stem cells (IPSCs) provide a great potential for studying molecular events underlying the pathogenesis of PD. This paper presents the results of bioinformatic analysis of the data obtained using RNA-seq technology in the study of neural precursors (NP) derived from IPSCs of the healthy donors and patients with PD carrying various mutations that are commonly associated with familial PD. This analysis showed that the level of transcription of multiple genes actively expressed in the nervous system at the embryonic stage of development was significantly increased in the NP cells obtained from the patients with PD, unlike in the case of healthy donors. Bioinformatic data have been, in general, confirmed using real-time PCR. The obtained data suggest that one of the causes of PD may be the shift of the gene expression pattern in neuronal cells towards embryonic gene expression pattern (termed dematuration).

The bHLH Transcription Factors in Neural Development and Therapeutic Applications for Neurodegenerative Diseases

The development of functional neural circuits in the central nervous system (CNS) requires the production of sufficient numbers of various types of neurons and glial cells, such as astrocytes and oligodendrocytes, at the appropriate periods and regions. Hence, severe neuronal loss of the circuits can cause neurodegenerative diseases such as Huntington's disease (HD), Parkinson's disease (PD), Alzheimer's disease (AD), and Amyotrophic Lateral Sclerosis (ALS). Treatment of such neurodegenerative diseases caused by neuronal loss includes some strategies of cell therapy employing stem cells (such as neural progenitor cells (NPCs)) and gene therapy through cell fate conversion. In this report, we review how bHLH acts as a regulator in neuronal differentiation, reprogramming, and cell fate determination. Moreover, several different researchers are conducting studies to determine the importance of bHLH factors to direct neuronal and glial cell fate specification and differentiation. Therefore, we also investigated the limitations and future directions of conversion or transdifferentiation using bHLH factors.

Genotype by environment interactions for chronic wasting disease in farmed US white-tailed deer

Despite implementation of enhanced management practices, chronic wasting disease in US white-tailed deer (Odocoileus virginianus) continues to expand geographically. Herein, we perform the largest genome-wide association analysis to date for chronic wasting disease (n = 412 chronic wasting disease-positive; n = 758 chronic wasting disease-nondetect) using a custom Affymetrix Axiom single-nucleotide polymorphism array (n = 121,010 single-nucleotide polymorphisms), and confirm that differential susceptibility to chronic wasting disease is a highly heritable (h2= 0.611 ± 0.056) polygenic trait in farmed US white-tailed deer, but with greater trait complexity than previously appreciated. We also confirm PRNP codon 96 (G96S) as having the largest-effects on risk (P ≤ 3.19E-08; phenotypic variance explained ≥ 0.025) across 3 US regions (Northeast, Midwest, South). However, 20 chronic wasting disease-positive white-tailed deer possessing codon 96SS genotypes were also observed, including one that was lymph node and obex positive. Beyond PRNP, we also detected 23 significant single-nucleotide polymorphisms (P-value ≤ 5E-05) implicating ≥24 positional candidate genes; many of which have been directly implicated in Parkinson's, Alzheimer's and prion diseases. Genotype-by-environment interaction genome-wide association analysis revealed a single-nucleotide polymorphism in the lysosomal enzyme gene ARSB as having the most significant regional heterogeneity of effects on chronic wasting disease (P ≤ 3.20E-06); with increasing copy number of the minor allele increasing susceptibility to chronic wasting disease in the Northeast and Midwest; but with opposite effects in the South. In addition to ARSB, 38 significant genotype-by-environment single-nucleotide polymorphisms (P-value ≤ 5E-05) were also detected, thereby implicating ≥ 36 positional candidate genes; the majority of which have also been associated with aspects of Parkinson's, Alzheimer's, and prion diseases.

Genetic Regulation of Vertebrate Forebrain Development by Homeobox Genes

Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.

Cloning and Functional Analysis of Rat Tweety-Homolog 1 Gene Promoter

Tweety-homolog 1 protein (Ttyh1) is abundantly expressed in neurons in the healthy brain, and its expression is induced under pathological conditions. In hippocampal neurons in vitro, Ttyh1 was implicated in the regulation of primary neuron morphology. However, the mechanisms that underlie transcriptional regulation of the Ttyh1 gene in neurons remain elusive. The present study sought to identify the promoter of the Ttyh1 gene and functionally characterize cis-regulatory elements that are potentially involved in the transcriptional regulation of Ttyh1 expression in rat dissociated hippocampal neurons in vitro. We cloned a 592 bp rat Ttyh1 promoter sequence and designed deletion constructs of the transcription factors specificity protein 1 (Sp1), E2F transcription factor 3 (E2f3), and achaete-scute homolog 1 (Ascl1) that were fused upstream of a luciferase reporter gene in pGL4.10[luc2]. The luciferase reporter gene assay showed the possible involvement of Ascl1, Sp1, and responsive cis-regulatory elements in Ttyh1 expression. These findings provide novel information about Ttyh1 gene regulation in neurons.

bHLH transcription factors in neural development, disease, and reprogramming

The formation of functional neural circuits in the vertebrate central nervous system (CNS) requires that appropriate numbers of the correct types of neuronal and glial cells are generated in their proper places and times during development. In the embryonic CNS, multipotent progenitor cells first acquire regional identities, and then undergo precisely choreographed temporal identity transitions (i.e. time-dependent changes in their identity) that determine how many neuronal and glial cells of each type they will generate. Transcription factors of the basic-helix-loop-helix (bHLH) family have emerged as key determinants of neural cell fate specification and differentiation, ensuring that appropriate numbers of specific neuronal and glial cell types are produced. Recent studies have further revealed that the functions of these bHLH factors are strictly regulated. Given their essential developmental roles, it is not surprising that bHLH mutations and de-regulated expression are associated with various neurological diseases and cancers. Moreover, the powerful ability of bHLH factors to direct neuronal and glial cell fate specification and differentiation has been exploited in the relatively new field of cellular reprogramming, in which pluripotent stem cells or somatic stem cells are converted to neural lineages, often with a transcription factor-based lineage conversion strategy that includes one or more of the bHLH genes. These concepts are reviewed herein.

A Role for the Transcription Factor Nk2 Homeobox 1 in Schizophrenia: Convergent Evidence from Animal and Human Studies

Schizophrenia is a highly heritable disorder with diverse mental and somatic symptoms. The molecular mechanisms leading from genes to disease pathology in schizophrenia remain largely unknown. Genome-wide association studies (GWASs) have shown that common single-nucleotide polymorphisms associated with specific diseases are enriched in the recognition sequences of transcription factors that regulate physiological processes relevant to the disease. We have used a “bottom-up” approach and tracked a developmental trajectory from embryology to physiological processes and behavior and recognized that the transcription factor NK2 homeobox 1 (NKX2-1) possesses properties of particular interest for schizophrenia. NKX2-1 is selectively expressed from prenatal development to adulthood in the brain, thyroid gland, parathyroid gland, lungs, skin, and enteric ganglia, and has key functions at the interface of the brain, the endocrine-, and the immune system. In the developing brain, NKX2-1-expressing progenitor cells differentiate into distinct subclasses of forebrain GABAergic and cholinergic neurons, astrocytes, and oligodendrocytes. The transcription factor is highly expressed in mature limbic circuits related to context-dependent goal-directed patterns of behavior, social interaction and reproduction, fear responses, responses to light, and other homeostatic processes. It is essential for development and mature function of the thyroid gland and the respiratory system, and is involved in calcium metabolism and immune responses. NKX2-1 interacts with a number of genes identified as susceptibility genes for schizophrenia. We suggest that NKX2-1 may lie at the core of several dose dependent pathways that are dysregulated in schizophrenia. We correlate the symptoms seen in schizophrenia with the temporal and spatial activities of NKX2-1 in order to highlight promising future research areas.

Proneural bHLH genes in development and disease

Proneural genes encode evolutionarily conserved basic-helix-loop-helix transcription factors. In Drosophila, proneural genes are required and sufficient to confer a neural identity onto naïve ectodermal cells, inducing delamination and subsequent neuronal differentiation. In vertebrates, proneural genes are expressed in cells that already have a neural identity, but they are still required and sufficient to initiate neurogenesis. In all organisms, proneural genes control neurogenesis by regulating Notch-mediated lateral inhibition and initiating the expression of downstream differentiation genes. The general mode of proneural gene function has thus been elucidated. However, the regulatory mechanisms that spatially and temporally control proneural gene function are only beginning to be deciphered. Understanding how proneural gene function is regulated is essential, as aberrant proneural gene expression has recently been linked to a variety of human diseases-ranging from cancer to neuropsychiatric illnesses and diabetes. Recent insights into proneural gene function in development and disease are highlighted herein.

Modeling psychiatric disorders at the cellular and network levels

Although psychiatric disorders such as autism spectrum disorders, schizophrenia and bipolar disorder affect a number of brain regions and produce a complex array of clinical symptoms, basic phenotypes likely exist at the level of single neurons and simple networks. Being highly heritable, it is hypothesized that these disorders are amenable to cell-based studies in vitro. Using induced pluripotent stem cell-derived neurons and/or induced neurons from fibroblasts, limitless numbers of live human neurons can now be generated from patients with a genetic background permissive to the disease state. We predict that cell-based studies will ultimately contribute to our understanding of the initiation, progression and treatment of these psychiatric disorders.

Neuronal Per Arnt Sim (PAS) domain protein 4 (NPAS4) regulates neurite outgrowth and phosphorylation of synapsin I

Neuronal Per Arnt Sim domain protein 4 (NPAS4), a brain-specific basic helix-loop-helix transcription factor, has recently been shown to regulate the development of the GABAergic inhibitory synapses and transcription program for contextual memory formation in the hippocampus. We previously reported that chronic social isolation or restriction stress in mice resulted in an impairment in memory and emotional behavior, which was associated with a decrease in Npas4 mRNA levels. In this study, we investigated the role of NPAS4 in neuronal function in vitro and in vivo. Differentiation medium-induced neurite outgrowth was inhibited in Npas4 knockdown Neuro2a cells, whereas overexpression of NPAS4 accelerated the neurite outgrowth in Neuro2a cells. Furthermore, depolarization-induced neurite outgrowth was abolished in Npas4 KO hippocampal neurons. NPAS4 overexpression increased cyclin-dependent kinase 5 (CDK5)-dependent synapsin I phosphorylation in Neuro2a cells and primary cultured hippocampal neurons. A CDK5 inhibitor, roscovitine, inhibited the neurite outgrowth and the increase in phosphorylated synapsin I (p-SYN I) levels in Npas4-overexpressed Neuro2a cells. Interaction of NPAS4 with promoters of Cdk5 and NeuN genes was demonstrated by a chromatin immunoprecipitation assay. In an in vivo study, pentylenetetrazole-induced convulsions in mice resulted in an increase in NPAS4 and p-SYN I levels in the prefrontal cortex of wild-type mice, although no changes in p-SYN I levels were observed in Npas4 knock-out mice. These results suggest that NPAS4 plays an important role in the structural and functional plasticity of neurons.

Personality assessment and its association with genetic factors in captive Asian and African elephants

Elephants live in a complex society based on matrilineal groups. Management of captive elephants is difficult, partly because each elephant has a unique personality. For a better understanding of elephant well being in captivity, it would be helpful to systematically evaluate elephants' personalities and their underlying biological basis. We sent elephant' personality questionnaires to keepers of 75 elephants. We also used 196 elephant DNA samples to search for genetic polymorphisms in genes expressed in the brain that have been suggested to be related to personality traits. Three genes, androgen receptor (AR), fragile X related mental retardation protein interacting protein (NUFIP2), and acheate-scute homologs 1 (ASH1) contained polymorphic regions. We examined the association of personality with intraspecific genetic variation in 17 Asian and 28 African elephants. The results suggest that the ASH1 genotype was associated with neuroticism in Asian elephants. Subjects with short alleles had lower scores of neuroticism than those with long alleles. This is the first report of an association between a genetic polymorphism and personality in elephants.

Modeling psychiatric disorders through reprogramming

Psychiatric disorders, including autism spectrum disorders and schizophrenia, are extremely heritable complex genetic neurodevelopmental disorders. It is now possible to directly reprogram fibroblasts from psychiatric patients into human induced pluripotent stem cells (hiPSCs) and subsequently differentiate these disorder-specific hiPSCs into neurons. This means that researchers can generate nearly limitless quantities of live human neurons with genetic backgrounds that are known to result in psychiatric disorders, without knowing which genes are interacting to produce the disease state in each patient. With these new human-cell-based models, scientists can investigate the precise cell types that are affected in these disorders and elucidate the cellular and molecular defects that contribute to disease initiation and progression. Here, we present a short review of experiments using hiPSCs and other sophisticated in vitro approaches to study the pathways underlying psychiatric disorders.

Efficient discovery of ASCL1 regulatory sequences through transgene pooling

Zebrafish transgenesis is a powerful and increasingly common strategy to assay vertebrate transcriptional regulatory control. Several challenges remain, however, to the broader application of this technique; they include increasing the rate with which transgenes can be analyzed and maximizing the informational value of the data generated. Presently, many rely on the injection of individual constructs and the analysis of resulting reporter expression in mosaic G0 embryos. Here, we contrast these approaches, examining whether injecting pooled transgene constructs can increase the efficiency with which regulatory sequences can be assayed, restricting analysis to the offspring of germ line transmitting transgenic zebrafish in an effort to reduce potential subjectivity. We selected a 64kb interval encompassing the human ASCL1 locus as our model interval and report the analysis of 9 highly conserved putative enhancers therein. We identified 32 transgene-positive zebrafish, transmitting one or more independent constructs displaying ASCL1-like regulatory control. Through examination of embryos harboring one or more transgenes, we demonstrate that five of the nine sequences account for the observed control and describe their likely roles in ASCL1 regulation. These data demonstrate the utility of this approach and its potential for further adaptation and higher throughput application.

Examination of the MSX1 gene in patients with Parkinson's disease

BACKGROUND

Several genetic variants in transcription factor genes have been reported to be associated with Parkinson's disease (PD). The muscle segment homeobox drosophila homolog of 1 gene (MSX1) is a major upstream regulator of the dopaminergic neuronal subtype specification.

AIMS OF THE STUDY

To determine whether genetic variation in the coding region of the MSX1 gene plays a role in the etiology of PD.

METHODS

We searched for genetic variations in the coding region of the MSX1 gene in 202 patients with PD and 200 normal controls by PCR-single-strand conformation polymorphism (PCR-SSCP) and sequencing.

RESULTS

No mutation in the MSX1 gene was identified in our cohort.

CONCLUSIONS

Mutations in the coding region of the MSX1 gene play little or no role in the development of PD.

Molecular genetics of bipolar disorder and depression

In this review, all papers relevant to the molecular genetics of bipolar disorder published from 2004 to the present (mid 2006) are reviewed, and major results on depression are summarized. Several candidate genes for schizophrenia may also be associated with bipolar disorder: G72, DISC1, NRG1, RGS4, NCAM1, DAO, GRM3, GRM4, GRIN2B, MLC1, SYNGR1, and SLC12A6. Of these, association with G72 may be most robust. However, G72 haplotypes and polymorphisms associated with bipolar disorder are not consistent with each other. The positional candidate approach showed an association between bipolar disorder and TRPM2 (21q22.3), GPR50 (Xq28), Citron (12q24), CHMP1.5 (18p11.2), GCHI (14q22-24), MLC1 (22q13), GABRA5 (15q11-q13), BCR (22q11), CUX2, FLJ32356 (12q23-q24), and NAPG (18p11). Studies that focused on mood disorder comorbid with somatic symptoms, suggested roles for the mitochondrial DNA (mtDNA) 3644 mutation and the POLG mutation. From gene expression analysis, PDLIM5, somatostatin, and the mtDNA 3243 mutation were found to be related to bipolar disorder. Whereas most previous positive findings were not supported by subsequent studies, DRD1 and IMPA2 have been implicated in follow-up studies. Several candidate genes in the circadian rhythm pathway, BmaL1, TIMELESS, and PERIOD3, are reported to be associated with bipolar disorder. Linkage studies show many new linkage loci. In depression, the previously reported positive finding of a gene-environmental interaction between HTTLPR (insertion/deletion polymorphism in the promoter of a serotonin transporter) and stress was not replicated. Although the role of the TPH2 mutation in depression had drawn attention previously, this has not been replicated either. Pharmacogenetic studies show a relationship between antidepressant response and HTR2A or FKBP5. New technologies for comprehensive genomic analysis have already been applied. HTTLPR and BDNF promoter polymorphisms are now found to be more complex than previously thought, and previous papers on these polymorphisms should be treated with caution. Finally, this report addresses some possible causes for the lack of replication in this field.

A novel scale including strabismus and 'cuspidal ear' for distinguishing schizophrenia patients from controls using minor physical anomalies

The present study explored minor physical anomaly items relevant to schizophrenia in order to establish a scale that can distinguish schizophrenia from controls using newly identified items along with items from the refined Waldrop scale. Seven items were significantly more frequent among schizophrenia patients (N=218) than controls (N=226). Among these seven items, two novel features, strabismus and 'cuspidal ear' showed markedly different prevalence rates between schizophrenia and control groups. A six-item scale, including the newly identified strabismus and cuspidal ear, was selected for most accurately discriminating patients with schizophrenia from controls. This scale correctly classified 59.6% of patients and 78.9% of control subjects. This new scale is procedurally more exacting and quantitative, and more relevant to schizophrenia than the original Waldrop scale. The validity of this scale should be sound since it was tested on a larger number of cohorts than used in previous research. Our scale can be used as a biomarker for predicting risk for future development of schizophrenia. The scale may also facilitate the identification of schizophrenia susceptibility genetic/environmental factors by stratifying etiologically heterogeneous patients according to physical abnormalities.