Preference Phenotype Research Articles

Topical menthol, a pharmacological cold mimic, induces cold sensitivity, adaptive thermogenesis and brown adipose tissue activation in mice.

Brown adipose tissue (BAT) thermogenesis has profound energy-expanding potential, which makes it an attractive target tissue to combat ever-increasing obesity and its other associated metabolic complications. Although it is fairly accepted that cold is a potent inducer of BAT activation and function, there are limited studies on the mechanisms of pharmacological cold-mimicking agents, such as the TRPM8 agonist, menthol, on BAT thermogenesis and activation. Herein, we sought to determine the effect of topical application of menthol (10% w/v [4 g/kg] cream formulation/day for 15 days) on temperature sensitivity behaviour (thermal gradient assay, nesting behaviour), adaptive thermogenesis (infrared thermography, core body temperature), BAT sympathetic innervation (tyrosine hydroxylase immunohistochemistry) and activation (18F-FDG PET-CT analysis, Uncoupling Protein 1 immunohistochemistry and BAT gene expression), whole-body energy expenditure (indirect calorimetry) and other metabolic variables in male C57BL/6N mice. We show that male C57BL/6N mice: (a) develop a warm-seeking and cold-avoiding thermal preference phenotype; (b) display increased locomotor activity and adaptive thermogenesis; (c) show augmented sympathetic innervation in BAT and its activation; (d) exhibit enhanced gluconeogenic capacity (increased glucose excursion in response to pyruvate) and insulin sensitivity; and (e) show enhanced whole-body energy expenditure and induced lipid-utilizing phenotype after topical menthol application. Taken together, our findings highlight that pharmacological cold mimicking using topical menthol application presents a potential therapeutic strategy to counter weight gain and related complications.

No Association Between the 5-HTTLPR Polymorphism and Diurnal Preference in Koreans

Objective: Recent studies have extended the study of diurnal preferences to the genetic level. Most studies have focused on clock genes, but some studies have searched for the possibilities of other genes associated with the circadian rhythm. Considering that the circadian rhythm is associated with the serotonergic system, investigating the association between major genes of the serotonin system and the diurnal preference phenotype is essential. In this study, we evaluated whether the 5-HTTLPR polymorphism is associated with diurnal preference in a Korean population.Methods: In total, 509 healthy subjects were genotyped for the 5-HTTLPR polymorphism. The Korean version of the Composite Scale of Morningness (CSM) was used to measure the phenotype patterns of diurnal preference. In addition, scores of three subscales—morningness, activity planning, and morning alertness—were extracted from the CSM.Results: No significant associations were observed between CSM scores and the 5-HTTLPR genotype or allele carrier status.Conclusion: The results of this study suggests that 5-HTTLPR has no effect on diurnal preference in a healthy Korean population. Further studies with a large number of subjects from multiple ethnicities are necessary to fully evaluate the association between 5-HTTLPR and diurnal preference.

Juvenile social experience and practice have a switch-like influence on adult mate preferences in an insect.

Social causes of variation in animal communication systems have important evolutionary consequences, including speciation. The relevance of these effects depends on how widespread they are among animals. There is evidence for such effects not only in birds and mammals, but also frogs and some insects and spiders. Here, we analyze the social ontogeny of adult mate preferences in an insect, Enchenopa treehoppers. In these communal plant-feeding insects, individuals reared in isolation or in groups differ in their mate preferences, and the group-reared phenotype can be rescued by playbacks to isolation-reared individuals. We ask about the relative role of signaling experience and signaling practice during ontogeny on the development of adult mating preferences in Enchenopa females. Taking advantage of variation in the signal experience and signaling practice of isolation-reared individuals, we find switch-like effects for experience and practice on female mate preference phenotypes, with individuals having some experience and practice as juveniles best rescuing the group-reared preference phenotype. We discuss how understanding the nature and distribution of social-ontogenetic causes of variation in mate preferences and other sexual traits will bring new insights into how within- and between-population variation influences the evolution of communication systems.

Genetic dissection of assortative mating behavior.

The evolution of new species is made easier when traits under divergent ecological selection are also mating cues. Such ecological mating cues are now considered more common than previously thought, but we still know little about the genetic changes underlying their evolution or more generally about the genetic basis for assortative mating behaviors. Both tight physical linkage and the existence of large-effect preference loci will strengthen genetic associations between behavioral and ecological barriers, promoting the evolution of assortative mating. The warning patterns of Heliconius melpomene and H. cydno are under disruptive selection due to increased predation of nonmimetic hybrids and are used during mate recognition. We carried out a genome-wide quantitative trait locus (QTL) analysis of preference behaviors between these species and showed that divergent male preference has a simple genetic basis. We identify three QTLs that together explain a large proportion (approximately 60%) of the difference in preference behavior observed between the parental species. One of these QTLs is just 1.2 (0–4.8) centiMorgans (cM) from the major color pattern gene optix, and, individually, all three have a large effect on the preference phenotype. Genomic divergence between H. cydno and H. melpomene is high but broadly heterogenous, and admixture is reduced at the preference–optix color pattern locus but not the other preference QTLs. The simple genetic architecture we reveal will facilitate the evolution and maintenance of new species despite ongoing gene flow by coupling behavioral and ecological aspects of reproductive isolation.

Early neurogenomic response associated with variation in guppy female mate preference.

Understanding the evolution of mate choice requires dissecting the mechanisms of female preference, particularly how these differ among social contexts and preference phenotypes. Here we study the female neurogenomic response after only 10 minutes of mate exposure in both a sensory component (optic tectum) and a decision-making component (telencephalon) of the brain. By comparing the transcriptional response between females with and without preferences for colorful males, we identified unique neurogenomic elements associated with the female preference phenotype that are not present in females without preference. Network analysis revealed different properties for this response at the sensory-processing and the decision-making levels, and showed that this response is highly centralized in the telencephalon. Furthermore, we identified an additional set of genes that vary in expression across social contexts, beyond mate evaluation. We show that transcription factors among those loci are predicted to regulate the transcriptional response of the genes we found to be associated with female preference.

Identification of SNPs, QTLs, and dominant markers associated with wheat grain flavor using genotyping-by-sequencing

Consumer acceptance of whole wheat products can be hindered by the flavor, aroma, and texture. A laboratory mouse model system was used to examine flavor using a two-choice feeding system employing a common check variety and the Student's t statistic as a consumption phenotype. Samples were from a doubled haploid population derived from “Yummy” (Louise) and “yucky” (Yumai34) soft white spring wheat parents. Genotyping-by-sequencing (GBS) identified 655 single nucleotide polymorphic (SNP) markers that differed between the two parents, which were used to create a genetic map with 24 linkage groups. Thirty-nine SNP markers exhibited a significant marker-trait association with consumption, and four significant QTL were detected. Additionally, a novel approach that identified dominant markers successfully found both Louise- and Yumai34-dominant GBS sequence tags. The Louise-dominant markers exhibited high levels of marker-trait association with the Student's t statistic flavor preference phenotype. In total, markers mapped to seven genic regions. In particular, dominant markers on 4DL exhibited the greatest F-values and provided the strongest evidence that genes involved in wheat flavor were located there. This work furthers the understanding of the genetics involved in wheat grain flavor and will aid in the development of varieties with greater consumer acceptance for whole-wheat products.

Identifying genetic markers of wheat (Triticum aestivum) associated with flavor preference using a laboratory mouse model

Whole wheat products provide critical nutrients for human health, but flavor of whole wheat products may hinder consumer acceptance. However, flavor differences among wheat varieties are not well understood. Using a mouse model system, flavor of whole wheat grain was examined using a two-choice feeding system. A bi-parental recombinant inbred line (RIL) population derived from Clark's Cream x NY6432-18 was used for mapping flavor preference. Clark's Cream is a hard white, and NY6432-18 is a soft white wheat. “Yummy” (cv. Diva soft white) and “yucky” (cv. Macon hard white) varieties were used as ‘checks’ for evaluating each RIL. Marker-trait association was performed using the Student's t as a preference phenotype from each check-RIL comparison. Twenty-two significant marker associations were found. Because mice prefer softer kernel texture, the effect of the Puroindoline b haplotype and phenotypic kernel texture were used as covariates in analyses. Twenty-eight markers exhibited significant associations in the two covariate analyses, with an additional five having significant associations in both covariate analyses. The results indicate that there is an identifiable genetic basis for flavor preference independent of kernel texture. Identifying flavor genes in wheat grain may help facilitate the development of varieties with greater palatability for whole-wheat products.

Fixed prey cue preferences among Dusky Pigmy Rattlesnakes (Sistrurus miliarius barbouri) raised on different long-term diets

Chemoreception is often crucial to the interaction between predators and their prey. Investigating the mechanisms controlling predator chemical preference gives insight into how selection molds traits directly involved in ecological interactions between species. In snakes, prey cue preferences are influenced by both direct genetic control and experience-based plasticity. We assessed prey preference in a group of Dusky Pigmy Rattlesnakes that had eaten only mice or lizards over a 5 year period to test whether genetics or plasticity primarily determine the preference phenotype. Our results provide evidence for genetic determination of preference for lizard chemical cues in pigmy rattlesnakes. Snakes preferred the scent of lizards, regardless of their initial diet, and the response to mouse scent did not differ from the water-only control. We discuss these findings in light of previous studies that manipulated snake diets over shorter timescales.

Alleviating waiting impulsivity and perseverative responding by μ-opioid receptor antagonism in two inbred mouse strains.

Recent evidence has implicated the opioid system in exaggerated ethanol consumption and impulsivity deficits. The opioid receptor antagonist naltrexone (NTX) has proven efficient in reducing alcohol consumption; however, its role on impulsive behaviour is not fully characterised. The aim of this study was to investigate the effects of NTX on two measures of impulsive behaviour in two inbred mouse strains that differ in ethanol preference and impulsive phenotype. Two separate groups of C57BL/6J (B6, n = 24) and DBA2/J (D2, n = 24) male mice were exposed to intermittent ethanol (IEE; 2g/kg) during early (PND 30-45, IEE_Early) or late (PND 45-60, IEE_Late) adolescence or the respective saline control. The ability of NTX (10mg/kg) alone, or co-administered with ethanol (0.5g/kg), to diminish waiting impulsivity in the five-choice serial reaction time task (5-CSRTT), or improve decision-making in a mouse version of the Iowa Gambling Task (mIGT), was examined in adulthood. In the 5-CSRTT, NTX diminished impulsivity in both strains of mice, irrespective of previous ethanol experience. In the mIGT, NTX failed to alter risky decision-making but decreased perseverative responding. Blocking the actions of endogenous opioids may attenuate waiting impulsivity, in addition to alleviating perseverative responding. In a broader context, μ-opiate antagonism may be of potential interest for impulse-control disorders.

Selection for Drinking in the Dark Alters Brain Gene Coexpression Networks

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. 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. 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. 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.

Ethanol‐Responsive Genes (Crtam, Zbtb16, and Mobp) Located in the Alcohol‐QTL Region of Chromosome 9 Are Associated With Alcohol Preference in Mice

Previously, our group identified cytotoxic and regulatory T-cell molecule (Crtam), zinc finger and BTB domain containing 16 (Zbtb16), and myelin-associated oligodendrocytic basic protein (Mobp) as ethanol-responsive genes in the mouse brain by gene expression profiling. In this study, we used a genetic co-segregation analysis to assess the association of Crtam, Zbtb16, and Mobp with the alcohol preference (AP) phenotype in the alcohol-preferring C57BL/6J (B6) and alcohol avoiding DBA/2J (D2) strains of mice. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to confirm previous microarray analysis results that Crtam, Zbtb16, and Mobp brain mRNA levels in the B6 and D2 strains are altered by ethanol treatment. The association of the 3 genes with AP was assessed in a F(2) population (n = 427) derived from the reciprocal crosses involving the B6 and D2 strains. Each F(2) individual was assessed for their AP using the 2 bottle choice test and genotyped for Crtam, Zbtb16, and Mobp single nucleotide polymorphisms (SNPs) that differ between B6 and D2 mice. Semi-quantitative RT-PCR analysis confirmed that Crtam, Zbtb16, and Mobp are ethanol-responsive genes. The SNP analyses show that alleles of the 3 genes co-segregate with the AP phenotype in F(2) mice, where individuals homozygous for the B6 allele have higher AP than those homozygous for the D2 allele. Also, the Crtam-Zbtb16 loci that are tightly linked and the Mobp locus act in an additive fashion in determining the relative AP phenotype. Our results are consistent with the hypothesis that Crtam, Zbtb16, and Mobp may be involved in AP in mice. The nature of this association remains to be established and may reflect a direct effect of these genes or an indirect effect caused by linked genes on mouse chromosome 9.

Role of Potassium Channel Gene Kcnj10 in Ethanol Preference in C57bl/6J and DBA/2J Mice

Inwardly-rectifying potassium channel protein Kir4.1 is encoded by Kcnj10 which maps to a quantitative trait locus on chromosome 1 for the voluntary alcohol consumption phenotype in mice. Kcnj10 brain expression differences have been established between ethanol-preferring C57Bl/6J and ethanol-avoiding BALB/cJ mice, but its differential expression in other tissues and strains have largely been overlooked. A nonsynonymous single nucleotide polymorphism exists between C57Bl/6J and ethanol-avoiding DBA/2J mice which changes amino acid 262 from threonine (C57Bl/6J) to serine (DBA/2J). This Kcnj10 SNP and its expression may serve as valuable markers in predicting the ethanol preference phenotype in mice. The evolutionary divergence of the Kir gene family was characterized using phylogenetic analysis involving the 16 mouse Kir channels. Kcnj10 expression differences in the brain, liver, lung, heart, spleen, kidney, testes, and muscle of male C57Bl/6J and DBA/2J mice at different developmental stages were examined using semiquantitative RT-PCR analysis. A SNP analysis was conducted to assess the association of Kcnj10 Thr262Ser SNP and the ethanol preference phenotype in F2 mice derived from the reciprocal crosses of the C57Bl/6J and DBA/2J strains. Evolutionary analysis supports gene duplication and genetic recombination as likely sources of diversity within the Kir gene family. Semiquantitative RT-PCR analysis revealed significantly higher Kcnj10 expression in the brain, spleen, and kidney of both strains when compared to other tissues from the same strain. There were no significant differences in tissue-specific mRNA levels between strains except in the testes. Genotype distributions of the Kcnj10 Thr262Ser SNP were different between low- and high-drinkers. A significant difference in the average ethanol preference level of each genotype was also observed. Our results suggest a role for Kcnj10 in ethanol preference determination in mice. However, further experiments are needed to establish if this association is due to the nonsynonymous SNP or other additional factors associated with Kcnj10.

Expression Profiling and QTL Analysis: a Powerful Complementary Strategy in Drug Abuse Research

Alcoholism is a complex disease exhibiting a multifactorial mode of transmission. To simplify the genetic and phenotypic complexity of the alcoholic phenotype, alcohol-preferring (P) and -non-preferring (NP) rats were developed on the basis of alcohol preference and consumption as an animal model of alcoholism. Total gene expression analysis (TOGA) and quantitative trait loci (QTL) analysis were applied to selectively bred, inbred P and NP rats as complementary studies to identify genetic factors that contribute to alcohol preference and consumption. TOGA analysis was utilized to screen for differential expression in several brain regions involved in the mesocorticolimbic dopamine (DA) system. Genes exhibiting differences in expression were then screened for an association to the alcohol preference phenotype, the quantitative trait of a previously identified QTL. By evaluating differences in gene expression for linkage to a quantitative trait, this combined approach was implemented to identify alpha-synuclein, a candidate gene for alcohol preference.

Genetic segregation of brain gene expression identifies retinaldehyde binding protein 1 and syntaxin 12 as potential contributors to ethanol preference in mice.

Genetic strains of mice represent an important resource for research on the biological determinants of complex diseases and behavioral phenotypes. To date, the approaches used have had little success in identifying causal genes. We have evaluated brain gene expression in C57BL/6J (B6) and DBA/2J (D2) inbred mouse strains using differential display to identify a number of sequences showing significant expression differences between the two strains. These differences were confirmed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. Knowing that B6 and D2 mouse strains differ for a number of behavioral phenotypes, we asked whether this difference in brain gene expression could explain any of these traits. Here, we show that the expression of two of these genes, retinaldehyde binding protein 1 (Rlbp1) and syntaxin 12 (Stx12), co-segregate with the ethanol preference phenotype in a B6D2 F2 population. Our results suggest a potential role for Rlbp1 and Stx12 in ethanol preference in mice, a conclusion supported by the location of these genes in quantitative trait loci (QTL) regions for this phenotype. This experimental approach has the potential for a broad application in the assessment of the roles of differentially expressed genes in a variety of complex phenotypes, with the advantage of identifying novel and potentially causal candidate genes directly.