RNA‐Seq Analysis of Genetic and Transcriptome Network Effects of Dual‐Trait Selection for Ethanol Preference and Withdrawal Using SOT and NOT Genetic Models

Abstract

Background

Genetic factors significantly affect alcohol consumption and vulnerability to withdrawal. Furthermore, some genetic models showing predisposition to severe withdrawal are also predisposed to low ethanol (EtOH) consumption and vice versa, even when tested independently in naïve animals.

Methods

Beginning with a C57BL/6J × DBA/2J F2 intercross founder population, animals were simultaneously selectively bred for both high alcohol consumption and low acute withdrawal (SOT line), or vice versa (NOT line). Using randomly chosen fourth selected generation (S4) mice ( N = 18‐22/sex/line), RNA‐Seq was employed to assess genome‐wide gene expression in ventral striatum. The MegaMUGA array was used to detect genome‐wide genotypic differences. Differential gene expression and the weighted gene co‐expression network analysis were implemented as described elsewhere (Genes Brain Behav 16, 2017, 462).

Results

The new selection of the SOT and NOT lines was similar to that reported previously (Alcohol Clin Exp Res 38, 2014, 2915). One thousand eight hundred and sixteen transcripts were detected as differentially expressed between the lines. For genes more highly expressed in the SOT line, there was enrichment in genes associated with cell adhesion, synapse organization, and postsynaptic membrane. The genes with a cell adhesion annotation included 23 protocadherins, Mpdz and Dlg2. Genes with a postsynaptic membrane annotation included Gabrb3, Gphn, Grid1, Grin2b, Grin2c, and Grm3. The genes more highly expressed in the NOT line were enriched in a network module (red) with annotations associated with mitochondrial function. Several of these genes were module hub nodes, and these included Nedd8, Guk1, Elof1, Ndufa8, and Atp6v1f.

Conclusions

Marked effects of selection on gene expression were detected. The NOT line was characterized by higher expression of hub nodes associated with mitochondrial function. Genes more highly expressed in the SOT aligned with previous findings, for example, Colville and colleagues (Genes Brain Behav 16, 2017, 462) that both high EtOH preference and consumption are associated with effects on cell adhesion and glutamate synaptic plasticity.

Abstract

SOT (Old English for drunkard) mice were selected for high alcohol preference/low withdrawal, with NOTs selected for the opposite phenotype. A cluster analysis showed genetic separation of the lines with SOTs genetically closer to the C57BL/6 founder, and NOTs genetically closer to the DBA/2 founder. The effects of selection on gene expression in SOTs and NOTs implicates genes involved in cell and synaptic interactions, energy metabolism and oxidative stress in alcohol preference and withdrawal.