Cocaine-mediated repression of the histone methyltransferase (HMT) G9a has recently been implicated in transcriptional, morphological and behavioral responses to chronic cocaine administration. Here, using a ribosomal affinity purification approach, we found that G9a repression by cocaine occurred in both Drd1-expressing (striatonigral) and Drd2-expressing (striatopallidal) medium spiny neurons. Conditional knockout and overexpression of G9a within these distinct cell types, however, revealed divergent behavioral phenotypes in response to repeated cocaine treatment. Our studies further indicated that such developmental deletion of G9a selectively in Drd2 neurons resulted in the unsilencing of transcriptional programs normally specific to striatonigral neurons and in the acquisition of Drd1-associated projection and electrophysiological properties. This partial striatopallidal to striatonigral 'switching' phenotype in mice indicates a new role for G9a in contributing to neuronal subtype identity and suggests a critical function for cell type–specific histone methylation patterns in the regulation of behavioral responses to environmental stimuli.
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This work was supported by grants from the US National Institute on Drug Abuse and National Institute of Mental Health, among others: P01DA08227 and P50MH96890 (E.J.N.), MH092306 (D.C., M.-H.H.) and J&J/IMHRO (M.-H.H.) and DA025962 (A.S.). The following provided additional support for this work: NARSAD Young Investigator Award (18194; A.S.) and the Seaver Foundation (A.S.).
The authors declare no competing financial interests.
Integrated supplementary information
G9a protein expression is significantly reduced in NAc of cocaine-addicted individuals. Western blot results for all 18 individuals are shown. G9a protein expression was normalized to GAPDH levels.
G9a KO in Drd1 and Drd2 MSNs results in non-significant trends for reduced expression levels of Glp in both cell types. In contrast, there was no change in Suv39h1 expression in either cell type.
Supplementary Figures 1 and 2 and Supplementary Table 1 (PDF 623 kb)
List of genes significantly regulated by cocaine, G9a KO, or both in striatal Drd1 neurons (XLS 270 kb)
List of genes significantly regulated by cocaine, G9a KO, or both in striatal Drd2 neurons (XLS 566 kb)
List of genes significantly enriched basally in Drd1 neurons in striatum (XLS 648 kb)
List of genes significantly enriched basally in Drd2 neurons in striatum (XLS 1008 kb)
List of Drd2 enriched genes displaying significant downregulation in Drd2 neurons in response to cocaine (XLS 33 kb)
List of Drd2 enriched genes displaying significant downregulation in Drd2 neurons in response to G9a KO (XLS 30 kb)
List of Drd2 enriched genes displaying significant downregulation in Drd2 neurons in response to cocaine plus G9a KO (XLS 40 kb)
List of Drd1 enriched genes displaying significant upregulation in Drd2 neurons in response to cocaine (XLS 33 kb)
List of Drd1 enriched genes displaying significant upregulation in Drd2 neurons in response to G9a KO (XLS 43 kb)
List of Drd1 enriched genes displaying significant upregulation in Drd2 neurons in response to cocaine plus G9a KO (XLS 47 kb)
mRNA primers (DOC 30 kb)
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Maze, I., Chaudhury, D., Dietz, D. et al. G9a influences neuronal subtype specification in striatum. Nat Neurosci 17, 533–539 (2014). https://doi.org/10.1038/nn.3670
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