Pathogenic SYNGAP1 mutations impair cognitive development by disrupting maturation of dendritic spine synapses.

Mutations that cause intellectual disability (ID) and autism spectrum disorder (ASD) are commonly found in genes that encode for synaptic proteins. However, it remains unclear how mutations that disrupt synapse function impact intellectual ability. In the SYNGAP1 mouse model of ID/ASD, we found that dendritic spine synapses develop prematurely during the early postnatal period. Premature spine maturation dramatically enhanced excitability in the developing hippocampus, which corresponded with the emergence of behavioral abnormalities. Inducing SYNGAP1 mutations after critical developmental windows closed had minimal impact on spine synapse function, whereas repairing these pathogenic mutations in adulthood did not improve behavior and cognition. These data demonstrate that SynGAP protein acts as a critical developmental repressor of neural excitability that promotes the development of life-long cognitive abilities. We propose that the pace of dendritic spine synapse maturation in early life is a critical determinant of normal intellectual development.

EZH1 is an antipsychotic-sensitive epigenetic modulator of social and motivational behavior that is dysregulated in schizophrenia.

BACKGROUND: With the capacity to modulate gene networks in an environmentally-sensitive manner, the role of epigenetic systems in mental disorders has come under intense investigation. Dysregulation of epigenetic effectors, including microRNAs and histone-modifying enzymes, may better explain the role of environmental risk factors and the observed heritability rate that cannot be fully attributed to known genetic risk alleles. Here, we aimed to identify novel epigenetic targets of the schizophrenia-associated microRNA 132 (miR-132). METHODS: Histone modifications were quantified by immunodetection in response to viral-mediated overexpression of miR-132 while a luminescent reporter system was used to validate targets of miR-132 in vitro. Genome-wide profiling, quantitative PCR and NanoSting were used to quantify gene expression in post-mortem human brains, neuronal cultures and prefrontal cortex (PFC) of mice chronically exposed to antipsychotics. Following viral-mediated depletion of Enhancer of Zeste 1 (EZH1) in the murine PFC, behaviors including sociability and motivation were assessed using a 3-chambered apparatus and forced-swim test, respectively. RESULTS: Overexpression of miR-132 decreased global histone 3 lysine 27 tri-methylation (H3K27me3), a repressive epigenetic mark. Moreover, the polycomb-associated H3K27 methyltransferase, EZH1, is regulated by miR-132 and upregulated in the PFC of schizophrenics. Unlike its homolog EZH2, expression of EZH1 in the murine PFC decreased following chronic exposure to antipsychotics. Viral-mediated depletion of EZH1 in the mouse PFC attenuated sociability, enhanced motivational behaviors, and affected gene expression pathways related to neurotransmission and behavioral phenotypes. CONCLUSIONS: EZH1 is dysregulated in schizophrenia, sensitive to antipsychotic medications, and a brain-enriched miR-132 target that controls neurobehavioral phenotypes.

MicroRNA-132 dysregulation in schizophrenia has implications for both neurodevelopment and adult brain function.

Schizophrenia is characterized by affective, cognitive, neuromorphological, and molecular abnormalities that may have a neurodevelopmental origin. MicroRNAs (miRNAs) are small noncoding RNA sequences critical to neurodevelopment and adult neuronal processes by coordinating the activity of multiple genes within biological networks. We examined the expression of 854 miRNAs in prefrontal cortical tissue from 100 control, schizophrenic, and bipolar subjects. The cyclic AMP-responsive element binding- and NMDA-regulated microRNA miR-132 was significantly down-regulated in both the schizophrenic discovery cohort and a second, independent set of schizophrenic subjects. Analysis of miR-132 target gene expression in schizophrenia gene-expression microarrays identified 26 genes up-regulated in schizophrenia subjects. Consistent with NMDA-mediated hypofunction observed in schizophrenic subjects, administration of an NMDA antagonist to adult mice results in miR-132 down-regulation in the prefrontal cortex. Furthermore, miR-132 expression in the murine prefrontal cortex exhibits significant developmental regulation and overlaps with critical neurodevelopmental processes during adolescence. Adult prefrontal expression of miR-132 can be down-regulated by pharmacologic inhibition of NMDA receptor signaling during a brief postnatal period. Several key genes, including DNMT3A, GATA2, and DPYSL3, are regulated by miR-132 and exhibited altered expression either during normal neurodevelopment or in tissue from adult schizophrenic subjects. Our data suggest miR-132 dysregulation and subsequent abnormal expression of miR-132 target genes contribute to the neurodevelopmental and neuromorphological pathologies present in schizophrenia.

Quantitative trait locus analysis identifies Gabra3 as a regulator of behavioral despair in mice.

The Tail Suspension Test (TST), which measures behavioral despair, is widely used as an animal model of human depressive disorders and antidepressant efficacy. In order to identify novel genes involved in the regulation of TST performance, we crossed an inbred strain exhibiting low immobility in the TST (RIIIS/J) with two high-immobility strains (C57BL/6J and NZB/BlNJ) to create two distinct F2 hybrid populations. All F2 offspring (n = 655) were genotyped at high density with a panel of SNP markers. Whole-genome interval mapping of the F2 populations identified statistically significant quantitative trait loci (QTLs) on mouse chromosomes (MMU) 4, 6, and X. Microarray analysis of hippocampal gene expression in the three parental strains was used to identify potential candidate genes within the MMUX QTLs identified in the NZB/BlNJ x RIIIS/J cross. Expression of Gabra3, which encodes the GABA(A) receptor alpha3 subunit, was robust in the hippocampus of B6 and RIIIS mice but absent from NZB hippocampal tissue. To verify the role of Gabra3 in regulating TST behavior in vivo, mice were treated with SB-205384, a positive modulator of the alpha3 subunit. SB-205384 significantly reduced TST immobility in B6 mice without affecting general activity, but it had no effect on behavior in NZB mice. This work suggests that GABRA3 regulates a behavioral endophenotype of depression and establishes this gene as a viable new target for the study and treatment of human depression.

BK calcium-activated potassium channels regulate circadian behavioral rhythms and pacemaker output.

Spontaneous action potentials in the suprachiasmatic nucleus (SCN) are necessary for normal circadian timing of behavior in mammals. The SCN exhibits a daily oscillation in spontaneous firing rate (SFR), but the ionic conductances controlling SFR and the relationship of SFR to subsequent circadian behavioral rhythms are not understood. We show that daily expression of the large conductance Ca(2+)-activated K(+) channel (BK) in the SCN is controlled by the intrinsic circadian clock. BK channel-null mice (Kcnma1(-/-)) have increased SFRs in SCN neurons selectively at night and weak circadian amplitudes in multiple behaviors timed by the SCN. Kcnma1(-/-) mice show normal expression of clock genes such as Arntl (Bmal1), indicating a role for BK channels in SCN pacemaker output, rather than in intrinsic time-keeping. Our findings implicate BK channels as important regulators of the SFR and suggest that the SCN pacemaker governs the expression of circadian behavioral rhythms through SFR modulation.

Genetic regulation of behavioral and neuronal responses to fluoxetine.

Despite widespread use of antidepressants, the factors underlying the behavioral response to antidepressants are unknown. It has been shown that antidepressant treatment promotes the proliferation and survival of neurons in the adult hippocampus via enhanced serotonergic signaling, but it is unclear whether hippocampal neurogenesis is responsible for the behavioral response to antidepressants. Furthermore, a large subpopulation of patients fails to respond to antidepressant treatment due to presumed underlying genetic factors. In the present study, we have used the phenotypic and genotypic variability of inbred mouse strains to show that there is a genetic component to both the behavioral and neuronal effects of chronic fluoxetine treatment, and that this antidepressant induces an increase in hippocampal cell proliferation only in the strains that also show a positive behavioral response to treatment. Furthermore, the behavioral and neuronal responses are associated with an upregulation of genes known to promote neuronal proliferation and survival. These results suggest that inherent genetic predisposition to increased serotonin-induced neurogenesis may be a determinant of antidepressant efficacy.

Identification of the circadian transcriptome in adult mouse skeletal muscle.

Circadian rhythms are approximate 24-h behavioral and physiological cycles that function to prepare an organism for daily environmental changes. The basic clock mechanism is a network of transcriptional-translational feedback loops that drive rhythmic expression of genes over a 24-h period. The objectives of this study were to identify transcripts with a circadian pattern of expression in adult skeletal muscle and to determine the effect of the Clock mutation on gene expression. Expression profiling on muscle samples collected every 4 h for 48 h was performed. Using COSOPT, we identified a total of 215 transcripts as having a circadian pattern of expression. Real-time PCR results verified the circadian expression of the core clock genes, Bmal1, Per2, and Cry2. Annotation revealed cycling genes were involved in a range of biological processes including transcription, lipid metabolism, protein degradation, ion transport, and vesicular trafficking. The tissue specificity of the skeletal muscle circadian transcriptome was highlighted by the presence of known muscle-specific genes such as Myod1, Ucp3, Atrogin1 (Fbxo32), and Myh1 (myosin heavy chain IIX). Expression profiling was also performed on muscle from the Clock mutant mouse and sarcomeric genes such as actin and titin, and many mitochondrial genes were significantly downregulated in the muscle of Clock mutant mice. Defining the circadian transcriptome in adult skeletal muscle and identifying the significant alterations in gene expression that occur in muscle of the Clock mutant mouse provide the basis for understanding the role of circadian rhythms in the daily maintenance of skeletal muscle.

Circadian clock mutation disrupts estrous cyclicity and maintenance of pregnancy.

Classic experiments have shown that ovulation and estrous cyclicity are under circadian control and that surgical ablation of the suprachiasmatic nuclei (SCN) results in estrous acyclicity in rats. Here, we characterized reproductive function in the circadian Clock mutant mouse and found that the circadian Clock mutation both disrupts estrous cyclicity and interferes with the maintenance of pregnancy. Clock mutant females have extended, irregular estrous cycles, lack a coordinated luteinizing hormone (LH) surge on the day of proestrus, exhibit increased fetal reabsorption during pregnancy, and have a high rate of full-term pregnancy failure. Clock mutants also show an unexpected decline in progesterone levels at midpregnancy and a shortened duration of pseudopregnancy, suggesting that maternal prolactin release may be abnormal. In a second set of experiments, we interrogated the function of each level of the hypothalamic-pituitary-gonadal (HPG) axis in order to determine how the Clock mutation disrupts estrous cyclicity. We report that Clock mutants fail to show an LH surge following estradiol priming in spite of the fact that hypothalamic levels of gonadotropin-releasing hormone (GnRH), pituitary release of LH, and serum levels of estradiol and progesterone are all normal in Clock/Clock females. These data suggest that Clock mutants lack an appropriate circadian daily-timing signal required to coordinate hypothalamic hormone secretion. Defining the mechanisms by which the Clock mutation disrupts reproductive function offers a model for understanding how circadian genes affect complex physiological systems.

Epigenetic mechanisms in schizophrenia.

Epigenetic modifications, including DNA methylation, histone modifications, and non-coding RNAs, have been implicated in a number of complex diseases. Schizophrenia and other major psychiatric and neurodevelopmental disorders are associated with abnormalities in multiple epigenetic mechanisms, resulting in altered gene expression during development and adulthood. Polymorphisms and copy number variants in schizophrenia risk genes contribute to the high heritability of the disease, but environmental factors that lead to epigenetic modifications may either reduce or exacerbate the expression of molecular and behavioral phenotypes associated with schizophrenia and related disorders. In the present paper, we will review the current understanding of molecular dysregulation in schizophrenia, including disruption of the dopamine, NMDA, and GABA signaling pathways, and discuss the role of epigenetic factors underlying disease pathology.

N-Methyl-D-aspartate receptor subunit expression in GnRH neurons changes during reproductive senescence in the female rat.

During reproductive senescence in females, the function of GnRH neurons becomes compromised, and this may play a role in the transition from normal estrous cycles to acyclicity. One hypothalamic component of this dysregulation is an alteration in the stimulatory effects of glutamate, acting via N-methyl-D-aspartate receptors (NMDARs), on GnRH release. The present study examined whether GnRH neurons express the subunits necessary to make functional NMDARs, and how subunit expression may change during aging in association with compromised reproductive physiology. Colocalization of the three NMDAR subunits that are most abundant in the hypothalamus (NR1, NR2A, or NR2B) with GnRH perikarya was determined in female rats at different stages of the reproductive life cycle: young (3-4 months) rats with regular estrous cycles, middle-aged (8-10 months) rats with regular estrous cycles, middle-aged rats with irregular estrous cycles, and middle-aged acyclic rats in persistent estrus. The number, percent, and localization of GnRH perikarya expressing NR1, NR2A, or NR2B were mapped and quantified by double label immunofluorescence microscopy. Overall, each of the NMDAR subunits was present in a majority of GnRH neurons. There were no age- or reproductive status-related changes in coexpression of NR1 or NR2A subunits in GnRH neurons. However, coexpression of the NR2B subunit, which affects several functional channel characteristics, was significantly lower in young compared with middle-aged rats, irrespective of reproductive status. This may result in an age-related increase in the ratio of the NR2B to the NR1 and NR2A subunits on GnRH neurons. These data indicate that the majority of GnRH neurons express the proteins needed to receive direct NMDAR-mediated glutamatergic input, and that a change in the stoichiometry of the NMDAR pentamer occurs during aging that precedes, and may have consequences for, altered neuroendocrine function.

Central circadian control of female reproductive function.

Over the past two decades, it has become clear just how much of our physiology is under the control of the suprachiasmatic nucleus (SCN) and the cell-intrinsic molecular clock that ticks with a periodicity of approximately 24 h. The SCN prepares our digestive system for meals, our adrenal axis for the stress of waking up in the morning, and the genes expressed in our muscles when we prepare to exercise. Long before molecular studies of genes such as Clock, Bmal1, and the Per homologs were possible, it was obvious that female reproductive function was under strict circadian control at every level of the hypothalamic-pituitary-gonadal axis, and in the establishment and successful maintenance of pregnancy. This review highlights our current understanding of the role that the SCN plays in regulating female reproductive physiology, with a special emphasis on the advances made possible through the use of circadian mutant mice.

Evaluating genetic markers and neurobiochemical analytes for fluoxetine response using a panel of mouse inbred strains.

RATIONALE: Identification of biomarkers that establish diagnosis or treatment response is critical to the advancement of research and management of patients with depression. OBJECTIVE: Our goal was to identify biomarkers that can potentially assess fluoxetine response and risk to poor treatment outcome. METHODS: We measured behavior, gene expression, and the levels of 36 neurobiochemical analytes across a panel of genetically diverse mouse inbred lines after chronic treatment with water or fluoxetine. RESULTS: Glyoxylase 1 (GLO1) and guanine nucleotide-binding protein 1 (GNB1) mostly account for baseline anxiety-like and depressive-like behavior, indicating a common biological link between depression and anxiety. Fluoxetine-induced biochemical alterations discriminated positive responders, while baseline neurobiochemical differences differentiated negative responders (p < 0.006). Results show that glial fibrillary acidic protein, S100 beta protein, GLO1, and histone deacetylase 5 contributed most to fluoxetine response. These proteins are linked within a cellular growth/proliferation pathway, suggesting the involvement of cellular genesis in fluoxetine response. Furthermore, a candidate genetic locus that associates with baseline depressive-like behavior contains a gene that encodes for cellular proliferation/adhesion molecule (Cadm1), supporting a genetic basis for the role of neuro/gliogenesis in depression. CONCLUSION: We provided a comprehensive analysis of behavioral, neurobiochemical, and transcriptome data across 30 mouse inbred strains that has not been accomplished before. We identified biomarkers that influence fluoxetine response, which, altogether, implicate the importance of cellular genesis in fluoxetine treatment. More broadly, this approach can be used to assess a wide range of drug response phenotypes that are challenging to address in human samples.

MicroRNA dysregulation in psychiatric disease.

MicroRNAs (miRNAs) are small regulatory RNAs that individually regulate up to several hundred genes, and collectively may regulate as much as two-thirds of the transcriptome. Recent evidence supports a role for miRNA dysregulation in psychiatric and neurological disorders, including schizophrenia, bipolar disorder, and autism. Small changes in miRNA expression can fine-tune the expression of multiple genes within a biological network, suggesting that miRNA dysregulation may underlie many of the molecular changes observed in psychiatric disease, and that therapeutic regulation of miRNA levels may represent a novel treatment option.

Phenotypic characterization of a genetically diverse panel of mice for behavioral despair and anxiety.

BACKGROUND: Animal models of human behavioral endophenotypes, such as the Tail Suspension Test (TST) and the Open Field assay (OF), have proven to be essential tools in revealing the genetics and mechanisms of psychiatric diseases. As in the human disorders they model, the measurements generated in these behavioral assays are significantly impacted by the genetic background of the animals tested. In order to better understand the strain-dependent phenotypic variability endemic to this type of work, and better inform future studies that rely on the data generated by these models, we phenotyped 33 inbred mouse strains for immobility in the TST, a mouse model of behavioral despair, and for activity in the OF, a model of general anxiety and locomotor activity. RESULTS: We identified significant strain-dependent differences in TST immobility, and in thigmotaxis and distance traveled in the OF. These results were replicable over multiple testing sessions and exhibited high heritability. We exploited the heritability of these behavioral traits by using in silico haplotype-based association mapping to identify candidate genes for regulating TST behavior. Two significant loci (-logp >7.0, gFWER adjusted p value <0.05) of approximately 300 kb each on MMU9 and MMU10 were identified. The MMU10 locus is syntenic to a major human depressive disorder QTL on human chromosome 12 and contains several genes that are expressed in brain regions associated with behavioral despair. CONCLUSIONS: We report the results of phenotyping a large panel of inbred mouse strains for depression and anxiety-associated behaviors. These results show significant, heritable strain-specific differences in behavior, and should prove to be a valuable resource for the behavioral and genetics communities. Additionally, we used haplotype mapping to identify several loci that may contain genes that regulate behavioral despair.

Integrative analysis of low- and high-resolution eQTL.

The study of expression quantitative trait loci (eQTL) is a powerful way of detecting transcriptional regulators at a genomic scale and for elucidating how natural genetic variation impacts gene expression. Power and genetic resolution are heavily affected by the study population: whereas recombinant inbred (RI) strains yield greater statistical power with low genetic resolution, using diverse inbred or outbred strains improves genetic resolution at the cost of lower power. In order to overcome the limitations of both individual approaches, we combine data from RI strains with genetically more diverse strains and analyze hippocampus eQTL data obtained from mouse RI strains (BXD) and from a panel of diverse inbred strains (Mouse Diversity Panel, MDP). We perform a systematic analysis of the consistency of eQTL independently obtained from these two populations and demonstrate that a significant fraction of eQTL can be replicated. Based on existing knowledge from pathway databases we assess different approaches for using the high-resolution MDP data for fine mapping BXD eQTL. Finally, we apply this framework to an eQTL hotspot on chromosome 1 (Qrr1), which has been implicated in a range of neurological traits. Here we present the first systematic examination of the consistency between eQTL obtained independently from the BXD and MDP populations. Our analysis of fine-mapping approaches is based on 'real life' data as opposed to simulated data and it allows us to propose a strategy for using MDP data to fine map BXD eQTL. Application of this framework to Qrr1 reveals that this eQTL hotspot is not caused by just one (or few) 'master regulators', but actually by a set of polymorphic genes specific to the central nervous system.

Circadian and CLOCK-controlled regulation of the mouse transcriptome and cell proliferation.

Circadian rhythms of cell and organismal physiology are controlled by an autoregulatory transcription-translation feedback loop that regulates the expression of rhythmic genes in a tissue-specific manner. Recent studies have suggested that components of the circadian pacemaker, such as the Clock and Per2 gene products, regulate a wide variety of processes, including obesity, sensitization to cocaine, cancer susceptibility, and morbidity to chemotherapeutic agents. To identify a more complete cohort of genes that are transcriptionally regulated by CLOCK and/or circadian rhythms, we used a DNA array interrogating the mouse protein-encoding transcriptome to measure gene expression in liver and skeletal muscle from WT and Clock mutant mice. In WT tissue, we found that a large percentage of expressed genes were transcription factors that were rhythmic in either muscle or liver, but not in both, suggesting that tissue-specific output of the pacemaker is regulated in part by a transcriptional cascade. In comparing tissues from WT and Clock mutant mice, we found that the Clock mutation affects the expression of many genes that are rhythmic in WT tissue, but also profoundly affects many nonrhythmic genes. In both liver and skeletal muscle, a significant number of CLOCK-regulated genes were associated with the cell cycle and cell proliferation. To determine whether the observed patterns in cell-cycle gene expression in Clock mutants resulted in functional dysregulation, we compared proliferation rates of fibroblasts derived from WT or Clock mutant embryos and found that the Clock mutation significantly inhibits cell growth and proliferation.

Vasopressin regulation of the proestrous luteinizing hormone surge in wild-type and Clock mutant mice.

In the female mouse, ovulation and estrous cyclicity are under both hormonal and circadian control. We have shown that mice with a mutation in the core circadian gene Clock have abnormal estrous cycles and do not have a luteinizing hormone (LH) surge on the afternoon of proestrus due to a defect at the hypothalamic level. In the present study, we tested the hypotheses that vasopressin (AVP) can act as a circadian signal to regulate the proestrous release of LH, and that this signal is deficient in the Clock mutant. We found that Avp expression in the suprachiasmatic nucleus (SCN) and AVP 1a receptor (Avpr1a) expression in the hypothalamus is reduced in Clock mutant mice compared to wild-type mice. Intracerebroventricular (i.c.v.) injection of AVP on the afternoon of proestrus is sufficient to induce LH secretion, which reaches surge levels in 50% of Clock mutant mice. The effect of AVP on the Clock mutant LH surge is mediated by AVPR1A, as co-infusion of AVP and an AVPR1A-specific antagonist prevents AVP induction of LH release, although infusion of an AVPR1A antagonist into wild-type mice failed to prevent a proestrous LH surge. These results suggest that reduced hypothalamic AVP signaling plays a role in the absence of the proestrous LH surge in Clock mutant mice. The results also support the hypothesis that AVP produced by the SCN may be a circadian signal that regulates LH release.

Coordinated transcription of key pathways in the mouse by the circadian clock.

In mammals, circadian control of physiology and behavior is driven by a master pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. We have used gene expression profiling to identify cycling transcripts in the SCN and in the liver. Our analysis revealed approximately 650 cycling transcripts and showed that the majority of these were specific to either the SCN or the liver. Genetic and genomic analysis suggests that a relatively small number of output genes are directly regulated by core oscillator components. Major processes regulated by the SCN and liver were found to be under circadian regulation. Importantly, rate-limiting steps in these various pathways were key sites of circadian control, highlighting the fundamental role that circadian clocks play in cellular and organismal physiology.