A cluster of genes, BAT1-BAT5, has been localized in the vicinity of the genes for TNF alpha and TNF beta. This gene is found near this cluster; it was mapped near the gene for C2 within a 120-kb region that included a HSP70 gene pair. These genes are all within the human major histocompatibility complex class III region. This gene was thought to be two different genes, NG36 and G9a, adjacent to each other but a recent publication shows that there is only a single gene. The protein encoded by this gene is thought to be involved in intracellular protein-protein interaction. There are three alternatively spliced transcript variants of this gene but only two are fully described.
G9a and G9a-like protein, another histone-lysine N-methyltransferase, catalyze the dimethylated state of H3K9me2. G9a is an important control mechanism for epigenetic regulation within the nucleus accumbens, particularly during the development of an addiction, since G9a opposes the induction of ΔFosB expression and is suppressed by ΔFosB. G9a exerts opposite effects to that of ΔFosB on drug-related behavior (e.g., self-administration) and synaptic remodeling (e.g., dendritic arborization – the development of additional tree-like dendritic branches and spines) in the nucleus accumbens, and therefore opposes ΔFosB's function as well as increases in its expression.
^Tachibana M, Sugimoto K, Fukushima T, Shinkai Y (Jul 2001). "Set domain-containing protein, G9a, is a novel lysine-preferring mammalian histone methyltransferase with hyperactivity and specific selectivity to lysines 9 and 27 of histone H3". The Journal of Biological Chemistry. 276 (27): 25309–17. PMID11316813. doi:10.1074/jbc.M101914200.
^ abNestler EJ (January 2014). "Epigenetic mechanisms of drug addiction". Neuropharmacology. 76 Pt B: 259–268. PMC3766384. PMID23643695. doi:10.1016/j.neuropharm.2013.04.004. Short-term increases in histone acetylation generally promote behavioral responses to the drugs, while sustained increases oppose cocaine’s effects, based on the actions of systemic or intra-NAc administration of HDAC inhibitors. ... Genetic or pharmacological blockade of G9a in the NAc potentiates behavioral responses to cocaine and opiates, whereas increasing G9a function exerts the opposite effect (Maze et al., 2010; Sun et al., 2012a). Such drug-induced downregulation of G9a and H3K9me2 also sensitizes animals to the deleterious effects of subsequent chronic stress (Covington et al., 2011). Downregulation of G9a increases the dendritic arborization of NAc neurons, and is associated with increased expression of numerous proteins implicated in synaptic function, which directly connects altered G9a/H3K9me2 in the synaptic plasticity associated with addiction (Maze et al., 2010).
G9a appears to be a critical control point for epigenetic regulation in NAc, as we know it functions in two negative feedback loops. It opposes the induction of ΔFosB, a long-lasting transcription factor important for drug addiction (Robison and Nestler, 2011), while ΔFosB in turn suppresses G9a expression (Maze et al., 2010; Sun et al., 2012a). ... Also, G9a is induced in NAc upon prolonged HDAC inhibition, which explains the paradoxical attenuation of cocaine’s behavioral effects seen under these conditions, as noted above (Kennedy et al., 2013). GABAA receptor subunit genes are among those that are controlled by this feedback loop. Thus, chronic cocaine, or prolonged HDAC inhibition, induces several GABAA receptor subunits in NAc, which is associated with increased frequency of inhibitory postsynaptic currents (IPSCs). In striking contrast, combined exposure to cocaine and HDAC inhibition, which triggers the induction of G9a and increased global levels of H3K9me2, leads to blockade of GABAA receptor and IPSC regulation.
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Shi Y, Sawada J, Sui G, Affar el B, Whetstine JR, Lan F, Ogawa H, Luke MP, Nakatani Y, Shi Y (Apr 2003). "Coordinated histone modifications mediated by a CtBP co-repressor complex". Nature. 422 (6933): 735–8. PMID12700765. doi:10.1038/nature01550.
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