Biology subjects

Mulligan, M. K.

Publications and source records attributed to Mulligan, M. K..

At least 19 recordsLinked to original sources

bioRxiv2026

Paternal inheritance of a vulnerable opioid-taking phenotype in female rats

Risk for opioid use disorder (OUD) is substantially heritable, yet its genetic architecture remains only partly understood. This study examined oxycodone intake in two nearly isogenic rat strains, Wistar Kyoto More Immobile (WMI) and Less Immobile (WLI), and their reciprocal female F1 offspring. The parental strains differ in depression-like behavior and substance use vulnerability, with WMI rats consuming more oxycodone than WLI controls. Voluntary consumption was measured with an operant licking self-administration protocol that delivered 60 l drug per reward. Across four experimental stages, oxycodone concentrations increased from 0.025 to 0.1 mg/ml, and session durations increased from 1 to 4 hours. Female offspring showed a parent-of-origin effect. F1 females sired by WMI fathers (WLIxWMI) displayed accelerated escalation during the transition from 1-hour to 4-hour sessions in Stage 2 and consumed more oxycodone than reciprocal WMIxWLI females across expanded-access stages. This vulnerability was associated with increased licking during the drug-unavailable timeout period. In WMI and reciprocal WMIxWLI female, consumption was regulated by the drugs subjective value, as measured by lick microstructure, during Stages 1 and 2. This relationship was absent in WLIxWMI females during Stage 2. Together, these findings suggest that paternal WMI lineage is associated with a rapid transition to high oxycodone intake and cue-directed drug seeking, and identify a parent-of-origin effect that may contribute to female vulnerability to addiction.

animal behavior and cognition↗

bioRxiv2026

Cannabidiol dose modulates behavioral response to acute and repeated administration of Δ9-Tetrahydrocannabinol by strain and sex

Cannabis contains many bioactive compounds, including {Delta}9-Tetrahydrocannabinol (THC) and cannabidiol (CBD), which influence behavior through complex pharmacological interactions with endogenous targets. This study examines whether CBD influences THC-induced changes in motor activity, hypothermia, and antinociception traits across different THC:CBD ratios, sexes, and genetic backgrounds. Traits were measured in C57BL/6J (B6) and DBA/2J (D2) mice of both sexes following baseline intraperitoneal (i.p.) injection of vehicle (VEH) and two consecutive daily doses of VEH or THC (10 mg/kg) alone or in combination with 0.56, 5, or 10 mg/kg CBD (THC:0.56CBD, THC:5CBD, or THC:10CBD, respectively). Motor activity and hypothermia were quantified daily from 0 to 120 min following injection and antinociception was measured daily at 60 min. We found that CBD alters THC-induced changes in motor activity and hypothermia as a function of day, dose, time, sex, and strain. In D2 females, CBD dose-dependently attenuated the hypolocomotor effects of THC immediately following acute injection and enhanced these effects later at 75 min. Following repeated exposure, CBD dose-dependently enhanced THC-induced hypolocomotion in B6 females at 75 min and in D2 males at 30 min while attenuating THC-induced hypolocomotion in D2 females immediately following injection. In D2 females, CBD dose-dependently attenuated THC-induced hypothermia at 15 min and enhanced hypothermia relative to THC at 30 min in D2 males following acute injection. After repeated exposure, CBD dose-dependently enhanced THC-induced hypothermia in B6 females at 15 min and in D2 males from 30 to 120 mins, while attenuating hypothermia in D2 females at 30 min. No significant effects of CBD on antinociception were observed. Our results indicate that CBD can modulate some THC-induced traits acutely and after repeated exposure. Regulation of THC-induced behavioral responses is dependent on CBD dose, genetic background, and sex. A candidate gene search using brain gene expression in recombinant inbred mice revealed greater genetic variation in ion channel genes relative to key metabolic genes, suggesting an underlying pharmacodynamic mechanism. Future research and validation of molecular mechanisms underlying these differences is expected to enhance our understanding of potential health risks and clinical relevance of cannabis and cannabinoid compounds containing THC and CBD.

animal behavior and cognition↗

bioRxiv2025

Early onset memory deficit of WMI rats compared to their nearly isogenic WLIs is reversed by enriched environment in females

We tested the hypothesis that environmental enrichment (EE) can attenuate early-onset cognitive decline in a stress-hyperresponsive rat strain. The novel genetic model, the Wistar Kyoto More Immobile (WMI) inbred rat strain demonstrates increased stress reactivity and enhanced depression-like behavior compared to its nearly isogenic control, the Wistar Kyoto Less Immobile strain (WLI). Middle-aged (12 months) WMI females exhibited diminished fear, and spatial memory in the contextual fear conditioning and Morris Water Maze paradigms, respectively, compared to young animals (6 months) of both strains and to middle-aged WLIs. Middle-aged WMI males showed a lesser age-induced deficit. EE from six to 12 months of age reversed these memory deficits in middle-aged WMI females and attenuated them in WMI males. Plasma levels of estradiol followed the same pattern as memory in WMI females following EE. RNA sequencing from female hippocampi revealed significant strain, age, and enrichment-induced differentially expressed genes. Among these, solute carrier family 35, member A4 (Slc35a4) and potassium inwardly rectifying channel, subfamily J, member 2 (Kcnj2) were confirmed to show hippocampal expression changes parallel to that of memory in the WMI. These genes have critical roles in the integrated stress response, cellular metabolism, and the effects of stress on neurovascular coupling, respectively. Pathway analyses revealed the involvement of oxidative phosphorylation and mitochondrial dysfunction in the hippocampal processes of aging and EE-induced reversal. These findings underscore the critical involvement of molecular stress responses in early-onset memory decline and suggest potential therapeutic targets for age-related cognitive impairment. HighlightsO_LIHeightened innate stress response and depression leads to early onset memory decline C_LIO_LIEnriched environment reverses memory decline of middle-aged females C_LIO_LIEnriched environment also reverses declining estrogen levels of middle-aged females C_LIO_LIMitochondrial dysfunction may underly mid-life cognitive and molecular changes C_LI

animal behavior and cognition↗

bioRxiv2024

Atp1a2 and Kcnj9 are candidate genes underlying oxycodone behavioral sensitivity and withdrawal in C57BL/6 substrains

Opioid use disorder is heritable, yet its genetic etiology is largely unknown. C57BL/6J and C57BL/6NJ mouse substrains exhibit phenotypic diversity in the context of limited genetic diversity which together can facilitate genetic discovery. Here, we found C57BL/6NJ mice were less sensitive to oxycodone (OXY)-induced locomotor activation versus C57BL/6J mice in a conditioned place preference paradigm. Narrow-sense heritability was estimated at 0.22-0.31, implicating suitability for genetic analysis. Quantitative trait locus (QTL) mapping in an F2 cross identified a chromosome 1 QTL explaining 7-12% of the variance in OXY locomotion and anxiety-like withdrawal in the elevated plus maze. A second QTL for EPM withdrawal behavior on chromosome 5 near Gabra2 (alpha-2 subunit of GABA-A receptor) explained 9% of the variance. To narrow the chromosome 1 locus, we generated recombinant lines spanning 163-181 Mb, captured the QTL for OXY locomotor traits and withdrawal, and fine-mapped a 2.45-Mb region (170.16-172.61 Mb). Transcriptome analysis identified five, localized striatal cis-eQTL transcripts and two were confirmed at the protein level (KCNJ9, ATP1A2). Kcnj9 codes for a potassium channel (GIRK3) that is a major effector of mu opioid receptor signaling. Atp1a2 codes for a subunit of a Na+/K+ ATPase enzyme that regulates neuronal excitability and shows functional adaptations following chronic opioid administration. To summarize, we identified two candidate genes underlying the physiological and behavioral properties of opioids, with direct preclinical relevance to investigators employing these widely used substrains and clinical relevance to human genetic studies of opioid use disorder.

genetics↗

bioRxiv2024

Male and female variability in response to chronic stress and morphine in C57BL/6J, DBA/2J, and their BXD progeny

Drug addiction is a multifactorial syndrome in which genetic predispositions and exposure to environmental stressors constitute major risk factors for the early onset, escalation, and relapse of addictive behaviors. While it is well known that stress plays a key role in drug addiction, the genetic factors that make certain individuals particularly sensitive to stress and thereby more vulnerable to becoming addicted are unknown. In an effort to test a complex set of gene x environment interactions--specifically gene x chronic stress--here we leveraged a systems genetics resource: BXD recombinant inbred mice (BXD5, BXD8, BXD14, BXD22, BXD29, and BXD32) and their parental mouse lines, C57BL/6J and DBA/2J. Utilizing the chronic social defeat stress (CSDS) and chronic variable stress (CVS) paradigms, we first showed sexual dimorphism in the behavioral stress response between the mouse strains. Further, we observed an interaction between genetic background and vulnerability to prolonged exposure to non-social stressors. Finally, we found that DBA/2J and C57BL/6J mice pre-exposed to stress displayed differences in morphine sensitivity. Our results support the hypothesis that genetic variation in predisposition to stress responses influences morphine sensitivity and is likely to modulate the development of drug addiction.

neuroscience↗

bioRxiv2022

Divergent risky decision-making and impulsivity behaviors in two Lewis substrains of rats with low genetic difference

Substance use disorder (SUD) is associated with a cluster of cognitive disturbances that engender vulnerability to ongoing drug seeking and relapse. Two of these endophenotypes--risky decision-making and impulsivity--are amplified in individuals with substance use disorder and are augmented by repeated exposure to illicit drugs. Identifying genetic factors underlying variability in these traits is critical for early identification, prevention, and treatment of SUD-vulnerable individuals. Here, we compared risky decision-making and different facets of impulsivity between two fully inbred substrains of Lewis rats--LEW/NCrl and LEW/NHsd. We performed whole genome sequencing of both substrain to identify almost all relevant variants. We observed substantial differences in risky decision-making and impulsive behaviors. Relative to LEW/HHsd, the LEW/NCrl substrain accepts higher risk options in a decision-making task and higher rates of premature responses in the differential reinforcement of low rates of responding (DRL) task. These phenotypic differences were more pronounced in females than males. We defined a total of [~]9,000 polymorphisms between these substrains at 40X whole genome short-read coverage. Roughly half of variants are located within a single 1.5 Mb region of chromosome 8, but none impact protein-coding regions. In contrast, other variants are widely distributed, and of these 38 are predicted to cause protein-coding variants. In conclusion, Lewis rat substrains differ significantly in risk-taking and impulsivity and only a small number of easily mapped variants are likely to be causal. Sequencing combined with a reduced complexity cross (RCC) should enable identification of one or more variants underlying multiple complex addiction-relevant traits.

genomics↗

bioRxiv2022

Opiate responses are controlled by interactions of Oprm1 and Fgf12 loci in the murine BXD family: Correspondence to human GWAS finding

Exploring the molecular genetic cascades responsible for behavioral responses to opioids can improve our understanding of drug use initiation. We generated high-precision time-series data for 105 morphine-and naloxone-related traits across [~]700 young adult BXD mice (64 diverse strains and both sexes) for 3 hours after a single morphine injection. Variations in responses were mapped using high-precision genome sequencing-based genotypes. The initial locomotor responses to morphine mapped precisely to the {micro} opioid receptor gene (Oprm1) on chromosome (Chr) 10 with a peak linkage of 12.4 (-logP, genome-wide significance level is approximately 3.8). The B allele inherited from C57BL/6J was associated with up to 60% higher activity. This effect climaxed at 75 min but was exhausted by 160 min. A second major modulator of opioid-induced locomotion emerged after approximately 100 min. This locus, also associated with a high B allele, was located on Chr 16 with peak linkage of 10.6 (-logP) in females. This locus included only one compelling candidate, fibroblast growth factor 12 (Fgf12), a 600 Kb gene that controls sodium current kinetics at the axon hillock. A strong and transient epistatic interaction existed between the Oprm1 and Fgf12 loci during a short time window (45-75 min). The combination of a B haplotype at Oprm1 with a D haplotype from DBA/2J at Fgf12 was associated with unusually high activity. In a complementary study in heterogeneous stock rats, we demonstrated that Oprm1 and Fgf12 were co-expressed in one specific subtype of Drd1+ medium spiny neuron. A Bayesian network analysis supported an Oprm1-to-Fgf12 network that involves a MAP kinase cascade that modulates FGF12 phosphorylation and locomotor activation. OPRM1 and FGF12 networks in human GWAS data highlight enrichment of signals associated with substance use disorder. This study represents the first demonstration of a time-dependent epistatic interaction modulating drug response in mammals and the first linkage of Fgf12 to opioid-induced behavior.

genetics↗

bioRxiv2022

LMM-MQM time series mapping - An application in a murine advanced intercross line identifies novel growth QTLs

The Berlin Fat Mouse Inbred line 860 (BFMI860) is a mouse model for juvenile obesity. Previously, a recessive major effect locus (jObes1) was identified on chromosome 3 explaining around 26% of the body weight variance in an BFMI860xC57BL/6NCrl advanced intercross line. The aim of this study was to discover additional QTL. Time series body weight data were modeled using linear mixed models (LMM), while a multiple QTL mapping (MQM) approach compensated for the jObes1 locus effect. LMM-MQM identified five additional loci significantly associated with body weight. Variance explained by the jObes1 locus increased to 38.1% when using LMM-MQM mapping, while the additional loci explained between 2.0% and 3.9% of the body weight variance. Several positional candidate genes within the novel QTL regions were found in KEGG pathways for insulin signaling and insulin resistance. Strong distortion with preference for the BFMI allele was observed within a newly identified QTL containing the well-known Foxo1 regulator of adipocyte differentiation. Here, we present a novel method for QTL detection in time series data: LMM-MQM time series mapping. We show that our method is more powerful in detecting QTLs compared to single timepoint mapping approaches. Thus, the time series structure should be considered for optimal detection of small effect QTLs. LMM-MQM time series mapping can be used to find genetic determinants of all kind of "phenotypes over time" be it lactation curves in cattle, plant biomass, drug clearance in human clinical trials, or cognitive decline during disease.

genetics↗

bioRxiv2021

A quantitative trait variant in Gabra2 underlies increased methamphetamine stimulant sensitivity

Psychostimulant (methamphetamine, cocaine) use disorders have a genetic component that remains mostly unknown. Here, we conducted genome-wide quantitative trait locus (QTL) analysis of methamphetamine stimulant sensitivity. To facilitate gene identification, we employed a Reduced Complexity Cross between closely related C57BL/6 mouse substrains and examined maximum speed and distance traveled over 30 min following methamphetamine (2 mg/kg, i.p.). For maximum methamphetamine-induced speed following the second and third administration, we identified a single genome-wide significant QTL on chromosome 11 that peaked near the Cyfip2 locus [LOD = 3.5, 4.2; peak = 21 cM (36 Mb)]. For methamphetamine-induced distance traveled, we identified a single genome-wide significant QTL on chromosome 5 that peaked near a functional intronic indel in Gabra2 that codes for the alpha-2 subunit of the GABA-A receptor [LOD = 5.2; peak = 35 cM (67 Mb)]. Striatal cis-expression QTL mapping corroborated Gabra2 as a functional candidate gene underlying methamphetamine-induced distance traveled. CRISPR/Cas9-mediated correction of the mutant intronic deletion on the C57BL/6J background to the wild-type C57BL/6NJ allele was sufficient to reduce methamphetamine-induced locomotor activity toward the wild-type C57BL/6NJ-like level, thus validating the quantitative trait variant (QTV). These studies demonstrate the power and efficiency of Reduced Complexity Crosses in identifying causal genes and variants underlying complex traits. Functionally restoring Gabra2 expression decreased methamphetamine stimulant sensitivity and supports preclinical and human genetic studies implicating the GABA-A receptor in psychostimulant addiction-relevant traits. Importantly, our findings have major implications for investigators studying psychostimulants in the C57BL/6J strain - the gold standard strain in biomedical research.

genetics↗

bioRxiv2021

Genetic modulation of initial sensitivity to Δ9-tetrahydrocannabinol (THC) among the BXD family of mice

Cannabinoid receptor 1 activation by the major psychoactive component in cannabis, {Delta}9-tetrahydrocannabinol (THC), produces motor impairments, hypothermia, and analgesia upon acute exposure. In previous work, we demonstrated significant sex and strain differences in acute responses to THC following administration of a single dose (10 mg/kg, i.p.) in C57BL/6J (B6) and DBA/2J (D2) inbred mice. To determine the extent to which these differences are heritable, we quantified acute responses to a single dose of THC (10 mg/kg, i.p.) in males and females from 20 members of the BXD family of inbred strains derived by crossing and inbreeding B6 and D2 mice. Acute THC responses (initial sensitivity) were quantified as changes from baseline for: 1. spontaneous activity in the open field (mobility), 2. body temperature (hypothermia), and 3. tail withdrawal latency to a thermal stimulus (analgesia/antinociception). Initial sensitivity to the immobilizing, hypothermic, and antinociceptive effects of THC varied substantially across the BXD family. Heritability was highest for mobility and hypothermia traits, indicating that segregating genetic variants modulate initial sensitivity to THC. We identified genomic loci and candidate genes, including Ndufs2, Scp2, Rps6kb1 or P70S6K, Pde4d, and Pten, that may control variation in THC initial sensitivity. We also detected strong correlations between initial responses to THC and legacy phenotypes related to intake or response to other drugs of abuse (cocaine, ethanol, and morphine). Our study demonstrates the feasibility of mapping genes and variants modulating THC responses in the BXDs to systematically define biological processes and liabilities associated with drug use and abuse.

genetics↗

bioRxiv2020

TailTimer: an open-source device for automating the rodent tail immersion assay

The tail immersion assay is a widely used method for measuring acute thermal pain in a way which is quantifiable and reproducible. It is non-invasive and measures response to a stimulus that may be encountered by an animal in its natural environment. However, tail withdrawal latency data are usually collected manually, and precise temperatures of the water at the time of measurement are most often not recorded. These two factors can reduce the reproducibility of tail immersion assay data. We designed a device, TailTimer, which uses the Raspberry Pi single-board computer and a temperature sensor, to automatically record both tail withdrawal latency and water temperature. The device has a radio frequency identification (RFID) system that can record the ID of animals. Our software recognizes several specific RFID keys as user interface commands, which allows TailTimer to be operated via RFID fobs. We also programmed the device to only allow tests to be conducted when the water is within {+/-} 0.25 {degrees}C of the target temperature. Data recorded using the TailTimer device showed a linear relationship between tail withdrawal latency and water temperature when tested between 47 - 50 {degrees}C. We also observed a profound effect of water mixing speed on tail withdrawal latency. Our data further revealed significant strain and sex differences, valorizing TailTimer in its ability to detect genetically-determined variations in thermal pain sensitivity. Significance StatementQuantification of tail withdrawal latency in response to thermal pain has essentially remained the same since the method was first introduced decades ago and relies on manual recording of water temperature and tail withdrawal latency. Such manual methods engender relatively substantial variability and are potential contributors to some of the discrepancies present among relevant research. The open source TailTimer device we report here is simple and inexpensive to manufacture. The RFID-based user interface is ergonomic, especially in animal facilities where space is limited and gloves are mandatory. We anticipate that the increased reproducibility of tail withdrawal latency provided by TailTimer will augment its utility in nociception and addiction research.

animal behavior and cognition↗

bioRxiv2020

RatsPub: a webservice aided by deep learning to mine PubMed for addiction-related genes

Interpreting and integrating results from omics studies typically requires a comprehensive and time consuming survey of extant literature. Here, we introduce GeneCup, an easy to use literature mining web service that searches all PubMed abstracts for user-provided gene symbols in conjunction with a set of custom keywords organized into a customized ontology, as well as results from human genome-wide association studies (GWAS). As an example, we organized over 300 keywords related to drug addiction into seven categories. The literature search is conducted by querying the NIH PubMed server using a programming interface, which is followed by retrieving abstracts from a local copy of the PubMed archive. The main results presented to the user are individual sentences containing the gene symbol, organized by the keywords they also contain. These sentences are presented through an interactive graphical interface or as tables. GWAS results are displayed using a similar method. All results are linked to the original abstract in PubMed. In addition, a convolutional neural network is employed to distinguish sentences describing systemic stress from those describing cellular stress. The automated and comprehensive search strategy provided by GeneCup facilitates the integration of new discoveries from omic studies with existing literature. GeneCup is free and open source software. The source code of GeneCup and the link to a running instance is available at https://github.com/hakangunturkun/GeneCup

bioinformatics↗

bioRxiv2020

Systems genetic analysis of binge-like eating in a C57BL/6J x DBA/2J-F2 cross

ObjectiveBinge eating is a heritable quantitative trait associated with eating disorders (ED) and refers to the rapid consumption of a large quantity of energy-dense food that is associated with loss of control, anxiety, and depression. Binge Eating Disorder is the most common ED in adults in the US; however, the genetic basis is unknown. We previously identified robust mouse inbred strain differences between C57BL/6J and DBA/2J in binge-like eating (BLE) of sweetened palatable food (PF) in an intermittent access, conditioned place preference paradigm. MethodsTo map the genetic basis of BLE, we phenotyped and genotyped 128 C57BL/6J x DBA/2J-F2 mice. ResultsWe identified a quantitative trait locus (QTL) on chromosome 13 influencing progressive changes in body weight across training days (LOD = 5.5; 26-39 cM). We also identified two sex-combined QTLs influencing PF intake on chromosome 5 (LOD = 5.6; 1.5-LOD interval = 21-28 cM) and 6 (LOD = 5.3; 1.5-LOD interval = 50-59 cM). Furthermore, sex-specific analyses revealed that the chromosome 6 locus was driven by males (1.5-LOD interval: 52-59 cM) and identified a female-selective QTL for BLE on chromosome 18 (LOD = 4.1; 1.5-LOD interval: 23-35 cM). Systems genetic analysis of the chromosome 6 locus for BLE using GeneNetwork legacy trait datasets from BXD recombinant inbred strains identified Adipor2 and Plxnd1 as two positional, functional, biological candidate genes. DiscussionWe identified genetic loci influencing BLE. Future studies will phenotype BXD recombinant inbred strains to fine map loci and support candidate gene nomination and validation.

genetics↗

bioRxiv2020

Gabra2 is a genetic modifier of Dravet syndrome in mice

Pathogenic variants in epilepsy genes result in a spectrum of clinical presentation, ranging from benign phenotypes to intractable epilepsies with significant co-morbidities and increased risk of sudden unexpected death in epilepsy (SUDEP). One source of this phenotypic heterogeneity is modifier genes that affect penetrance, dominance or expressivity of a primary pathogenic variant. Mouse models of epilepsy also display varying degrees of clinical severity on different genetic backgrounds. Mice with heterozygous deletion of Scn1a (Scn1a+/-) model Dravet syndrome, a severe epilepsy most often caused by SCN1A haploinsufficiency. Scn1a+/- heterozygous mice recapitulate key features of Dravet syndrome, including febrile and afebrile spontaneous seizures, SUDEP, and cognitive and behavioral deficits. The Scn1a+/- mouse model also exhibits strain-dependent phenotype severity. Scn1a+/- mice maintained on the 129S6/SvEvTac (129) strain have normal lifespan and no overt seizures. In contrast, admixture with C57BL/6J (B6) results in severe epilepsy and premature lethality in [B6x129]F1.Scn1a+/- mice. In previous work, we identified Dravet Survival Modifier loci (Dsm1-Dsm5) responsible for strain-dependent differences in survival. Gabra2, encoding the GABAA 2 subunit, was nominated as the top candidate modifier at the Dsm1 locus on chromosome 5. Direct measurement of GABAA receptors found lower abundance of 2-containing receptors in hippocampal synapses of B6 mice relative to 129. We also identified a B6-specific single nucleotide intronic deletion within Gabra2 that lowers mRNA and protein by nearly 50%. Repair of this de novo deletion reestablished normal levels of Gabra2 transcript and protein expression. In the current study, we used B6 mice with the repaired Gabra2 allele to validate it as a modifier of phenotype severity in Scn1a+/- mice. Repair of Gabra2 restored transcript and protein expression, increased abundance of 2-containing GABAA receptors in hippocampal synapses, and improved seizure and survival phenotypes of Scn1a+/- mice. These findings validate Gabra2 as a genetic modifier of Dravet syndrome.

genetics↗

bioRxiv2019

Modulation of longevity by diet, and youthful body weight, but not by weight gain after maturity

Diet and environment profoundly modulate lifespan. We measured longevity as a function of diet and weight gain across a genetically diverse family of mice. We followed 1348 females from two parental strains--C57BL/6J and DBA/2J--and 146 cohorts of BXD isogenic progeny strains (n = 73) across their lifespan on a low fat chow diet (CD, 18% calories from fat) and on a high fat diet (HFD, 60% calories from fat). On average, HFD shortens lifespan by 85 days or 12%, roughly equivalent to an 8-10 year decrease in humans. However, strain variation in the response of diet on longevity is remarkably high, ranging from a longevity loss of 54% in BXD65 to a gain of 37% in BXD8. Baseline weights and early weight gain are both associated with a mean decrease in longevity of [~]4 days/g. By 500 days-of-age, cases fed HFD gained four times as much weight as control on average. However, strain-specific variation was substantial, thus weight gain did not correlate well with lifespan. In summary, high fat had a strong negative effect on longevity, but genetic interactions effects were even stronger. This highlights the unequivocal importance of genetic differences in making dietary recommendations.

genetics↗

bioRxiv2019

Kcnn3 as a target for treating aberrant behaviors in stressed, ethanol-dependent mice

Anxiety and mood disorders are often comorbid with alcohol use disorder (AUD) and are considered critical in the development, maintenance, and reinstatement of alcohol dependence and harmful alcohol-seeking behaviors. Because of this high comorbidity, it is necessary to determine shared and unique genetic factors driving heavy ethanol drinking and anxiety-related behaviors. We used a model of stress-induced escalation of drinking in ethanol dependent C57BL/6J mice to measure anxiety-like behaviors on the marble burying and novelty-suppressed feeding task (NSFT) during abstinence. In order to identify novel pharmacogenetic targets that may lead to more effective treatment, a targeted bioinformatics analysis was used to quantify the expression of K+ channel genes in the amygdala that covary with anxiety-related phenotypes in the well phenotyped and fully sequenced family of BXD strains. A pharmacological approach was used to validate the key bioinformatics finding in ethanol-dependent, stressed C57BL/6J mice during the NSFT. Amygdalar expression of Kcnn3 correlated significantly with just over 40 anxiety-associated phenotypes. Further examination of Kcnn3 expression revealed a strong eigentrait for anxiety-like behaviors in this family. Kcnn3 expression in the amygdala correlated negatively with binge-like and voluntary ethanol drinking. C57BL/6J mice treated with chronic intermittent ethanol exposure and repeated swim stress consumed more ethanol in their home cages and showed hypophagia on the NSFT during prolonged abstinence. Pharmacologically targeting KCNN3 protein with the KCa2 channel positive modulator 1-EBIO decreased ethanol drinking and reduced latency to approach food during the NSFT in ethanol-dependent, stressed mice. Collectively these validation studies provide central nervous system mechanistic links into to the covariance of stress, anxiety, and AUD in the BXD strains. Further this analytical approach is effective in defining targets for treating alcohol dependence and comorbid mood and anxiety disorders.

neuroscience↗

bioRxiv2019

The expanded BXD family of mice: A cohort for experimental systems genetics and precision medicine

The challenge of precision medicine is to model complex interactions among DNA variants, sets of phenotypes, and complex environmental factors and confounders. We have expanded the BXD family, creating a powerful and extensible test bed for experimental precision medicine and an ideal cohort to study gene-by-environmental interactions.\n\nThese BXD segregate for over 6 million variants, with a mean minor allele frequency close to 0.5. We have increased the family two-fold to 150 inbred strains, all derived from C57BL/6J and DBA/2J. We have also generated updated and comprehensive genotypes and an unrivaled deep phenome.\n\nApproximately 10,000 recombinations have been located, allowing precision of quantitative trait loci mapping of {+/-}2.0 Mb over much of the genome and {+/-}0.5 Mb for Mendelian loci. The BXD phenome includes more than 100 omics data sets and >7000 quantitative and clinical phenotypes, all of which is publicly available.\n\nThe BXD family is an enduring, collaborative, and replicable resource to test causal and mechanistic links between genomes and phenomes at many stages and under a wide variety of treatments and interventions.

genomics↗

bioRxiv2019

Identification of a functional non-coding variant in the GABAA receptor α2 subunit of the C57BL/6J mouse reference genome: Major implications for neuroscience research

GABA type-A (GABA-A) receptors containing the 2 subunit (Gabra2) are expressed in most brain regions and are critical in modulating inhibitory synaptic function. Genetic variation at the GABRA2 locus has been implicated in epilepsy, affective and psychiatric disorders, alcoholism and drug abuse. Gabra2 expression varies as a function of genotype and is modulated by sequence variants in several brain structures and populations, including F2 crosses originating from C57BL/6J (B6J) and the BXD recombinant inbred family derived from B6J and DBA/2J. Here we demonstrate a global reduction of Gabra2 brain mRNA and protein in the B6J strain relative to other inbred strains, and identify and validate the causal mutation in B6J. The mutation is a single base pair intronic deletion located adjacent to a splice acceptor site that only occurs in the B6J reference genome. The deletion became fixed in B6J between 1976 and 1991 and is now pervasive in many engineered lines, BXD strains generated after 1991, the Collaborative Cross, and the majority of consomic lines. Repair of the deletion using CRISPR-Cas9 mediated gene editing on a B6J genetic background completely restored brain levels of Gabra2 mRNA and protein. Comparison of transcript expression in hippocampus, cortex, and striatum between B6J and repaired genotypes revealed alterations in GABA-A receptor subunit expression, especially in striatum. These results suggest that naturally occurring variation in GABRA2 levels between B6J and other substrains or inbred strains may also explain strain differences in anxiety-like or alcohol and drug response traits related to striatal function. Characterization of the B6J private mutation in the Gabra2 gene is of critical importance to molecular genetic studies in neurobiological research as this strain is widely used to generate genetically engineered mice and murine genetic populations, and is the most widely utilized strain for evaluation of anxiety-like, depression-like, pain, epilepsy, and drug response traits that may be partly modulated by Gabra2 function.

genetics↗