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DNA methyltransferase 1 regulates reelin mRNA expression in mouse primary cortical cultures
Jai Sung Noh1, Rajiv P Sharma, Marin Veldic
1Psychiatric Institute, Department of Psychiatry, College of Medicine, University of Illinois, 1601 West Taylor Street, Chicago, IL 60612, USA.
Abstract:
The polygenic nature of complex psychiatric disorders suggests a common pathway that may be involved in the down-regulation of multiple genes through an epigenetic mechanism. To investigate the role of methylation in down-regulating the expression of mRNAs that may be associated with the schizophrenia phenotype, we have adopted a cell-culture model amenable to this line of investigation. We have administered methionine (2 mM) to primary cultures of cortical neurons prepared from embryonic day 16 mice and show that this treatment down-regulated reelin and glutamic acid decarboxylase 67 (GAD67) mRNA expression but not that corresponding to neuron-specific enolase mRNA. Moreover, methionine increased methylation of the reelin promoter, suggesting a possible mechanism for the observed change. These cultures contain a mixed population of neurons and glia. Approximately 83% of the neurons are GABAergic based on GAD immunoreactivity, and these neurons coexpress high levels of reelin and DNA methyltransferase (Dnmt) 1 immunoreactivity. To examine whether Dnmt1 regulates reelin gene expression, we used an antisense approach to reduce (knock down) Dnmt1 expression. The reduced Dnmt1 mRNA and protein were accompanied by increased reelin mRNA expression. More importantly, the Dnmt1 knockdown blocked the methionine-induced reelin and GAD67 mRNA down-regulation. These data support the hypothesis that the reduced amounts of reelin and GAD67 mRNAs documented in postmortem schizophrenia brain may be the consequence of a Dnmt1-mediated hypermethylation of the corresponding promoters.
Insights
Methionine treatment down-regulates reelin and GAD67 mRNA in neurons via DNA methyltransferase 1 (Dnmt1) activity. This epigenetic mechanism may explain reduced gene expression in schizophrenia.
Area of Science:
- Neuroscience
- Epigenetics
- Psychiatric Genetics
Background:
- Complex psychiatric disorders, like schizophrenia, exhibit polygenic inheritance, suggesting shared molecular pathways.
- Epigenetic mechanisms, particularly DNA methylation, are implicated in gene expression regulation relevant to psychiatric phenotypes.
- Previous studies suggest altered expression of reelin and glutamic acid decarboxylase 67 (GAD67) mRNAs in schizophrenia.
Purpose of the Study:
- To investigate the role of DNA methylation in down-regulating mRNA expression associated with the schizophrenia phenotype.
- To explore the involvement of DNA methyltransferase 1 (Dnmt1) in regulating reelin and GAD67 gene expression.
Main Methods:
- Primary mouse cortical neuron cultures were treated with methionine (2 mM).
- Messenger RNA (mRNA) expression levels of reelin, GAD67, and neuron-specific enolase were quantified.
- DNA methylation of the reelin promoter was assessed.
- Dnmt1 expression was reduced using an antisense approach (knockdown) to evaluate its regulatory role.
Main Results:
- Methionine treatment significantly down-regulated reelin and GAD67 mRNA expression, but not neuron-specific enolase mRNA.
- Methionine administration increased DNA methylation of the reelin promoter.
- Dnmt1 knockdown led to increased reelin mRNA expression and blocked the methionine-induced down-regulation of reelin and GAD67 mRNAs.
Conclusions:
- These findings support a model where Dnmt1-mediated hypermethylation of reelin and GAD67 promoters contributes to reduced mRNA levels.
- This epigenetic mechanism involving Dnmt1 may underlie the observed down-regulation of reelin and GAD67 mRNAs in postmortem schizophrenia brains.
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