Mef2 induction of the immediate early gene Hr38/Nr4a is terminated by Sirt1 to promote ethanol tolerance

Abstract

Drug naïve animals given a single dose of ethanol show changed responses to subsequent doses, including the development of ethanol tolerance and ethanol preference. These simple forms of behavioral plasticity are due in part to changes in gene expression and neuronal properties. Surprisingly little is known about how ethanol initiates changes in gene expression or what the changes do. Here we demonstrate a role in ethanol plasticity for Hr38, the sole Drosophila homolog of the mammalian Nr4a1/2/3 class of immediate early response transcription factors. Acute ethanol exposure induces transient expression of Hr38 and other immediate early neuronal activity genes. Ethanol activates the Mef2 transcriptional activator to induce Hr38, and the Sirt1 histone/protein deacetylase is required to terminate Hr38 induction. Loss of Hr38 decreases ethanol tolerance and causes precocious but short-lasting ethanol preference. Similarly, reduced Mef2 activity in all neurons or specifically in the mushroom body α/β neurons decreases ethanol tolerance; Sirt1 promotes ethanol tolerance in these same neurons. Genetically decreasing Hr38 expression levels in Sirt1 null mutants restores ethanol tolerance, demonstrating that both induction and termination of Hr38 expression are important for behavioral plasticity to proceed. These data demonstrate that Hr38 functions as an immediate early transcription factor that promotes ethanol behavioral plasticity.

Mushroom Body Specific Transcriptome Analysis Reveals Dynamic Regulation of Learning and Memory Genes After Acquisition of Long-Term Courtship Memory in Drosophila

“…In mouse, across many different studies, fear conditioning consistently invokes strong activation of immediate early genes such as c-Fos, which are known to be induced in response to neuron firing ( Mayford and Reijmers 2016 ). In insects, neuron activity induced genes have been more elusive, however, two genes, Hr38 and sr , are consistently upregulated in response to a variety of neuronal activation stimuli in flies and other insects ( Fujita et al 2013 ; Lutz and Robinson 2013 ; Chen et al 2016 ; Adhikari et al 2018 ). It is very interesting that we observe these two genes to be specifically activated in the MB in response to sexual rejection.…”

The Photoconvertible Fluorescent Probe, CaMPARI, Labels Active Neurons in Freely-Moving Intact Adult Fruit Flies

“…Previously, researchers have used intermediate early genes (IEGs) in mammals, such as Arc (Link et al, 1995;Guzowski et al, 1999) and cFos (Cole et al, 1989) as an indirect measure of neuronal activation, however, the use of IEGs is limited by the transient nature of their expression and lack of temporal resolution (Fields et al, 1997). In Drosophila, many IEGs are not conserved and the use of IEGs was limited to evaluating the expression of Hr38 (Fujita et al, 2013;Adhikari et al, 2019). Olfactory glomeruli were previously mapped in freelymoving flies using 2-deoxyglucose autoradiography (Rodrigues and Buchner, 1984).…”

Flying Together: Drosophila as a Tool to Understand the Genetics of Human Alcoholism

“…Follow-up validation of Drosophila orthologs revealed that loss-of-function mutations of the Mef2 transcription factor decrease EtOH sedation sensitivity but not rapid tolerance. Another group found that Mef2 reduction in neurons, or more specifically in mushroom body α/β neurons, reduces tolerance, corroborating the importance of this gene in alcohol responses [78]. The dissimilar fly tolerance results between these two groups may be an example of global gene manipulations causing different effects than manipulations limited to particular neuronal populations.…”

“…Finally, many genes and pathways have been implicated in flies that, to our knowledge, lack studies examining their human correlates, despite obvious homology, probable shared pathways, and evidence of links to AUDs in mammals. These include rut (discussed above) [11,142,197,198], the dopamine/ecdysteroid receptor gene DopEcR [223,224], the deacetylase gene Sirt1/Sir2 [78,81,160,225], various PKA genes [114,197,201], and happyhour, encoding a kinase that is a negative regulator of the (druggable) EGFR pathway mentioned above [158]. Further work is required to firmly establish the importance of some of these genes in Drosophila ethanol responses, whereas others are strongly implicated in flies but lack hypothesis-driven investigation in humans to advance the translational process.…”