Mittleman, G. | bioRxiv Science

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↗

bioRxiv2020

Discovery of a role for Rab3b in habituation and cocaine induced locomotor activation in mice using heterogeneous functional genomic analysis

Substance use disorders are prevalent and present a tremendous societal cost but the mechanisms underlying addiction behavior are poorly understood and few biological treatments exist. One strategy to identify novel molecular mechanisms of addiction is through functional genomic experimentation. However, results from individual experiments are often noisy. To address this problem, the convergent analysis of multiple genomic experiments can prioritize signal from these studies. In the present study, we examine genetic loci identified in the recombinant inbred (BXD RI) genetic reference population that modulate the locomotor response to cocaine. We then applied the GeneWeaver software system for heterogeneous functional genomic analysis to integrate and aggregate multiple studies of addiction genomics, resulting in the identification of Rab3b, as a functional correlate of the locomotor response to cocaine in rodents. This gene encodes a member of the RAB family of Ras-like GTPases known to be involved in trafficking of secretory and endocytic vesicles in eukaryotic cells. The convergent evidence for a role of Rab3b was included co-occurrence in previously published genetic mapping studies of cocaine related behaviors; methamphetamine response and Cartpt (Cocaine- and amphetamine-regulated transcript prepropeptide) abundance; evidence related to other addictive substances; density of polymorphisms; and its expression pattern in reward pathways. To evaluate this finding, we examined the effect of RAB3 complex perturbation in cocaine response. B6;129-Rab3btm1Sud Rab3ctm1sud Rab3dtm1sud triple null mice (Rab3bcd-/-) exhibited significant deficits in habituation, and increased acute and repeated cocaine responses. This previously unidentified mechanism of the behavioral predisposition and response to cocaine is an example of many that can be identified and validated using aggregate genomic studies. Many genetic and genomic studies have been performed over the past few decades, representing a wealth of data on the underlying neurobiological and genetic basis of multiple complex behaviors. However, these studies, particularly legacy studies using older technologies and resources lack precision. By aggregating multiple studies, convergent evidence for shared molecular mechanisms of multiple behaviors can be found, for example the widely reported relations among psychostimulant use and novelty response behavior. Here a legacy genetic mapping result for a cocaine related trait mapped in mice was refined using data from 113 different experimental gene sets related to addiction in the GeneWeaver system for heterogeneous functional genomic analysis. Convergent evidence revealed a role for Rab3b in this and other traits including multiple psychostimulant responses and CART expression. Experimental perturbation of the RAB complex revealed effects on habituation to a novel environment, cocaine induced activation and Carpt expression. The analysis of aggregate data thus revealed a molecular mechanism that influences the relationship between response to novel situations and cocaine-related phenotypes.

neuroscience↗