Selection for Drinking in the Dark Alters Brain Gene Coexpression Networks

Authors

  • Ovidiu D. Iancu,

    Corresponding author
    • Department of Behavioral Neuroscience , Oregon Health & Science University, Portland, Oregon
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  • Denesa Oberbeck,

    1. Department of Behavioral Neuroscience , Oregon Health & Science University, Portland, Oregon
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  • Priscila Darakjian,

    1. Department of Behavioral Neuroscience , Oregon Health & Science University, Portland, Oregon
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  • Pamela Metten,

    1. Department of Behavioral Neuroscience , Oregon Health & Science University, Portland, Oregon
    2. Portland Alcohol Research Center , Research Service, Veterans Affairs Medical Center, Portland, Oregon
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  • Shannon McWeeney,

    1. Oregon Clinical and Translational Research Institute , Oregon Health & Science University, Portland, Oregon
    2. Division of Biostatistics, Public Health & Preventative Medicine , Oregon Health & Science University, Portland, Oregon
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  • John C. Crabbe,

    1. Department of Behavioral Neuroscience , Oregon Health & Science University, Portland, Oregon
    2. Portland Alcohol Research Center , Research Service, Veterans Affairs Medical Center, Portland, Oregon
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  • Robert Hitzemann

    1. Department of Behavioral Neuroscience , Oregon Health & Science University, Portland, Oregon
    2. Portland Alcohol Research Center , Research Service, Veterans Affairs Medical Center, Portland, Oregon
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Reprint requests: Ovidiu D. Iancu, 3181 SW Sam Jackson Park Rd., Portland, OR 97239-3098; Tel.: 503-329-5945; Fax: 503-494-6877; E-mail: iancuo@ohsu.edu

Abstract

Background

Heterogeneous stock (HS/NPT) mice have been used to create lines selectively bred in replicate for elevated drinking in the dark (DID). Both selected lines routinely reach a blood ethanol (EtOH) concentration (BEC) of 1.00 mg/ml or greater at the end of the 4-hour period of access in Day 2. The mechanisms through which genetic differences influence DID are currently unclear. Therefore, the current study examines the transcriptome, the first stage at which genetic variability affects neurobiology. Rather than focusing solely on differential expression (DE), we also examine changes in the ways that gene transcripts collectively interact with each other, as revealed by changes in coexpression patterns.

Methods

Naïve mice (N = 48/group) were genotyped using the Mouse Universal Genotyping Array, which provided 3,683 informative markers. Quantitative trait locus (QTL) analysis used a marker-by-marker strategy with the threshold for a significant logarithm of odds (LOD) set at 10.6. Gene expression in the ventral striatum was measured using the Illumina Mouse 8.2 array. Differential gene expression and the weighted gene coexpression network analysis (WGCNA) were implemented largely as described elsewhere.

Results

Significant QTLs for elevated BECs after DID were detected on chromosomes 4, 14, and 16; the latter 2 were associated with gene-poor regions. None of the QTLs overlapped with known QTLs for EtOH preference drinking. Ninety-four transcripts were detected as being differentially expressed in both selected lines versus HS controls; there was no overlap with known preference genes. The WGCNA revealed 2 modules as showing significant effects of both selections on intramodular connectivity. A number of genes known to be associated with EtOH phenotypes (e.g., Gabrg1, Glra2, Grik1, Npy2r, and Nts) showed significant changes in connectivity.

Conclusions

We found marked and consistent effects of selection on coexpression patterns; DE changes were more modest and less concordant. The QTLs and differentially expressed genes detected here are distinct from the preference phenotype. This is consistent with behavioral data and suggests that the DID and preference phenotypes are markedly different genetically.

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