Laboratory of Addiction Genetics
The focus of the Laboratory of Addiction Genetics is to understand the genetic basis of behavioral and molecular traits relevant to substance abuse and dependence in mice. The ultimate goal is to improve our understanding of the neurobiological mechanisms of addiction and to translate these findings toward preventative and treatment strategies in humans. We currently utilize both a) forward genetic strategies [e.g., quantitative trait locus; (QTL) mapping] as discovery tools for revealing novel genes, pathways, and networks contributing to complex traits and b) reverse genetics (e.g., knockouts and TALENs) to directly validate the genes and mechanisms in vivo.
1. K99/R00: “Genetic basis of opioid reward and aversion in mice.”
A current focus is to determine the genetic basis of the rewarding properties of opioids in mice by combining quantitative trait locus (QTL) analysis of conditioned place preference (CPP) and transcriptome analysis via RNA-sequencing in genetic reference populations that yield high resolution QTLs. This multi-pronged approach to gene mapping will accelerate the nomination of candidate genes for validation via direct gene targeting. We are dissecting multiple behaviors that are expressed during opioid administration and CPP in real time (locomotor, visits, visit time, ultrasonic vocalizations, placebo-like responses) and applying factor analysis toward defining behavioral sets and inferring motivational meaning of these factors. We will estimate heritability for these trait sets and apply QTL mapping toward those most influenced by genetic factors. Elucidating the genetic basis of the motivational properties of opioids and other drugs of abuse will have direct application toward preventative/treatment strategies of addiction in humans, toward other substances of abuse (ethanol and food), and toward other conditions affected by the mesocorticolimbic pathway (Parkinson’s, depression, schizophrenia).
2. Deciphering the roles of casein kinase 1-epsilon and –delta in the motivational properties of substances of abuse and dopaminergic signaling.
Dr. Bryant recently provided direct genetic and pharmacological evidence that casein kinase 1-epsilon (Csnk1e) inhibits whereas casein kinase 1-delta (Csnk1d) facilitates the locomotor response to psychostimulants and opioids (Bryant et al., 2012; Neuropsychopharmacology). These observations suggest at least two possibilities regarding the molecular and cellular mechanisms of these two highly related isoforms on behavior: 1) Csnk1e and Csnk1d modulate different signaling pathways to produce their opposing behavioral effects and 2) Csnk1e and Csnk1d are expressed in different cell types and thus, modulate different circuitry to exert opposing effects on behavior. We are currently testing these two hypotheses by examining dopamine signaling (DARPP-32) and generating cell type-specific knockout mice to examine the effects of ablating Csnk1e versus Csnk1d on signaling and behavior.
3. Candidate gene testing of Rufy1 and Hnrnph1 for methamphetamine sensitivity
Dr. Bryant recently generated a panel of 17 interval-specific congenic mice to identify a 0.25 Mb locus on chromosome 11 that regulates the locomotor stimulant response to methamphetamine (MA) (manuscript in preparation). This genomic region contains only two possible quantitative trait genes that could be responsible for the QTL: Rufy1 and Hnrnph1. Rufy1, also known as Rabip4, codes for an early endosomal protein that interacts with Rab proteins including Rab4 and Rab5. We hypothesize that a known coding polymorphism within Rufy1 alters methamphetamine-induced trafficking of its primary molecular targets – the monoamine transporters – which in turn affects dopamine release, uptake, and behavior. We are directly targeting Rufy1 in vivo using TALENs technology and will directly test the role of Rufy1 in methamphetamine-induced transporter trafficking, dopamine uptake/release, and behavior. We are also targeting the second gene within the QTL interval, Hnrnph1, and examining its effect on gene transcription and behavior. Hnrnph1 is a heterogenous nuclear ribonucleoprotein that has been shown to regulate processing of microRNAs (miRNAs) and thus, could affect the expression of gene networks. The results of these studies will lead to the identification of the quantitative trait gene (QTG) that underlies the QTL responsible for genetic variation in methamphetamine sensitivity. Future directions will include examining this QTG in other conditions that could potentially be affected by dopaminergic function (Parkinson’s, ADHD, schizophrenia) and determining its role in regulating the motivational responses to methamphetamine and other substances of abuse.
4. Genetic basis of the placebo response
Last, Dr. Bryant has a longstanding interest in using mice to study the neurobiological basis of the “placebo effect” (Bryant et al., 2009; Drug and Alcohol Dependence), a phenomenon that has been hypothesized to be mediated by the reward expectation. He plans to develop and apply a forward genetic analysis toward Pavlovian conditioning mouse models across a variety of conditions that are notoriously sensitive to the placebo effect, including pain, anxiety, depression, and Parkinson’s Disease.