Analysis of quantitative trait loci that influence animal behavior

Rgs 2 gene polymorphisms as modulators of anxiety in humans?

Rgs2 (regulator of G-protein signalling 2) gene recently was reported as a quantitative trait gene for anxious behaviour in mice and male Rgs2 knockout mice have been shown to be more anxious than wildtype mice. Therefore we investigated four non-coding single nucleotide polymorphisms in a sample of 173 patients with panic disorder and 173 matched controls of German descent. At the genotype level all four SNPs were associated with panic disorder (p = 0.02-0.05). At the haplotype level the strongest association was observed for a haplotype containing SNP3 and SNP 4 (subgroup men and men with agoraphobia: p = 0.01 and 0.03). This points towards a functional polymorphism at the 3' end of the gene. Our results support the hypothesis that variations of the Rgs2 gene play a role also for the development of anxiety in humans.

Identification of informative strains and provisional QTL mapping of amphetamine (AMPH)-induced locomotion in recombinant congenic strains (RCS) of mice

Amphetamine (AMPH)-induced locomotor activity is a rodent behavioral trait that reflects mesolimbic dopaminergic activity. To identify potential quantitative trait loci (QTL) associated with this behavior, we used 34 recombinant congenic strains (RCSs) of mice derived from A/J (A strains) and C57BL/6J (B strains) and measured AMPH-induced total distance traveled (AMPH-TDIST). Two strains in the A panel (A52 and A63) showed significantly elevated AMPH-TDIST compared to the parental A/J strain and behaved similarly to C57BL/6J. Simple sequence length polymorphism (SSLP) markers on chromosomes 1, 2, 3, 5, 6, 8, 9, 10 and 20 were significantly associated with AMPH-TDIST in the A strains. Within the B panel, two strains (B81 and B74) had significantly higher and two strains (B69 and B75) had significantly lower AMPH-TDIST than C57BL/6J. Markers associated with AMPH-TDIST in the B strains appeared on chromosomes 5, 17 and 20. Combining data from this approach and other genetic (mapping data in humans) and functional (cDNA expression) sources may help to identify suitable candidate genes relevant to human disorders where mesolimbic dopamine dysregulation has been postulated.

Complex Genetics of Interactions of Alcohol and CNS Function and Behavior

This work summarizes the proceedings of a symposium at the 2004 RSA Meeting in Vancouver, Canada. The organizers were R. W. Williams and D. B. Matthews; the Chair was M. F. Miles. The presentations were (1) WebQTL: A resource for analysis of gene expression variation and the genetic dissection of alcohol related phenotypes, by E. J. Chesler, (2) The marriage of microarray and qtl analyses: what's to gain, by J. K. Belknap, (3) Use of WebQTL to identify QTLs associated with footshock stress and ethanol related behaviors, by D. B. Matthews, (4) A high throughput strategy for the detection of quantitative trait genes, by R. J. Hitzemann, and (5) The use of gene arrays in conjunction with transgenic and selected animals to understand anxiety in alcoholism, by. B. Tabakoff.

The molecular genetic architecture of human personality: beyond self-report questionnaires

Molecular genetic studies of personality began with two high impact papers in 1996 that showed provisional associations between the dopamine DRD4 exon III repeat region and Novelty Seeking/Extraversion. These first two reports were shortly followed by an investigation linking Neuroticism/Harm Avoidance with the serotonin transporter (SLC6A4) promoter region polymorphism (5-HTTLPR). In the ensuing decade, thousands of subjects have been studied for association between these genes and personality, assessed by using self-report questionnaires, with erratic success in replication of the first findings for Novelty Seeking (DRD4) and Harm Avoidance (5-HTTLPR). Small effect sizes characteristic of non-Mendelian traits, polygenic patterns of inheritance and true heterogeneity between studies confound attempts to reach a consensus regarding the role of common polymorphisms in contributing to personality domains. Nevertheless, the current state of personality genetics is far from being bleak. Several new paradigms especially functional neuroimaging or 'imaging genomics' have strengthened the connection between 5-HTTLPR and anxiety-related personality traits. The demonstrations that early environmental information can considerably strengthen and even uncover associations between genes and behavior (Caspi's seminal studies and more recently the demonstration that early environment impacts on DRD4 and Novelty Seeking) are notable and herald a new era of personality genetics. Finally, consideration of the broader phenotypic expression of common polymorphisms (e.g. the 'social brain', altruism, etc.) and the use of new experimental paradigms including neurophysiological, neuropsychological and computer games that go beyond the narrow self-report questionnaire design will enable a deeper understanding of how common genetic polymorphisms modulate human behavior. Human personality, defined by Webster as the quality or state of being a person or the complex of characteristics that distinguishes an individual, surely requires a more encompassing view towards understanding its complex molecular genetic architecture.

The genetic contribution to canine personality

The domestic dog may be exceptionally well suited for behavioral genetic studies owing to its population history and the striking behavior differences among breeds. To explore to what extent and how behavioral traits are transmitted between generations, heritabilities and genetic correlations for behavioral traits were estimated in a cohort containing over 10,000 behaviorally tested German shepherd and Rottweiler dogs. In both breeds, the pattern of co-inheritance was found to be similar for the 16 examined behavioral traits. Furthermore, over 50% of the additive genetic variation of the behavioral traits could be explained by one underlying principal component, indicating a shared genetic component behind most of the examined behavioral traits. Only aggression appears to be inherited independently of the other traits. The results support a genetic basis for a broad personality trait previously named shyness-boldness dimension, and heritability was estimated to be 0.25 in the two breeds. Therefore, breeds of dogs appear to constitute a valuable resource for behavioral genetic research on the normal behavioral differences in broad personality traits.

Maternal influences on adult stress and anxiety-like behavior in C57BL/6J and BALB/cJ mice: a cross-fostering study

The quality of maternal care during early life has a dramatic impact on later stress reactivity and anxiety. Two inbred mouse strains, C57BL/6J and BALB/cJ, differ in levels of maternal care, stress reactivity, and anxiety-like behavior in adulthood. However, the relative contribution of early environmental factors and genetic predisposition to differences in these strains is not known. Maternal care, plasma corticosterone levels, emotionality, and hippocampal and paraventricular nucleus (PVN) glucocorticoid receptor mRNA levels were measured in adult C57BL/6J and BALB/cJ mice. Litters were then cross-fostered and anxiety-like behavior and stress reactivity was assessed in adulthood. Significantly less maternal care and elevated stress-induced corticosterone and emotionality was observed in BALB/cJ compared to C57BL/6J mice. Yet, no strain differences were found in hippocampal or paraventricular nucleus glucocorticoid receptor mRNA levels. Cross-fostering did alter anxiety-like behavior and basal corticosterone levels, which suggests that while genetic differences account for some of the variations between these two strains early rearing conditions also contribute.

A mouse model system for genetic analysis of sociability: C57BL/6J versus BALB/cJ inbred mouse strains

BACKGROUND

Impairments in social behaviors are highly disabling symptoms of autism, schizophrenia, and other psychiatric disorders. Mouse model systems are useful for identifying the many genes and environmental factors likely to affect complex behaviors, such as sociability (the tendency to seek social interaction). To progress toward developing such a model system, we tested the hypothesis that C57BL/6J inbred mice show higher levels of sociability than BALB/cJ inbred mice.

METHODS

Mice tested for sociability were 4- and 9-week-old, male and female C57BL/6J and BALB/cJ mice. On 2 consecutive days, the sociability of each test mouse toward an unfamiliar 4-week-old DBA/2J stimulus mouse was assessed with a social choice paradigm conducted in a three-chambered apparatus. Measures of sociability included the time that the test mouse spent near versus far from the stimulus mouse, the time spent directly sniffing the stimulus mouse, and the time spent in contact between test and stimulus mice in a free interaction.

RESULTS

C57BL/6J mice showed higher levels of sociability than BALB/cJ mice overall in each of these measures.

CONCLUSIONS

We propose that C57BL/6J and BALB/cJ mice will be a useful mouse model system for future genetic and neurobiological studies of sociability.

A genome scan with AFLP markers to detect fearfulness-related QTLs in Japanese quail

A quantitative trait loci (QTL) study was undertaken to identify genome regions involved in the control of fearfulness in Japanese quail (Coturnix japonica). An F2 cross was made between two quail lines divergently selected over 29 generations on duration of tonic immobility (DTI), a catatonic-like state of reduced responsiveness to a stressful stimulation. A total of 1065 animals were measured for the logarithm of DTI (LOGTI), the number of inductions (NI) necessary to induce the immobility reaction, open-field behaviour including locomotor activity (MOVE), latency before first movement (LAT), number of jumps (JUMP), dejections (DEJ) and shouts (SHOUT), corticosterone level after a contention stress (LOGCORT) and body weight at 2 weeks of age (BW2). A total of 310 animals were included in a genome scan using selective genotyping with 248 AFLP markers. A total of 21 suggestive or genome-wide significant QTL were observed. Two highly significant QTL were identified on linkage group 1 (GL1), one for LOGTI and one for NI. In the vicinity of the QTL for LOGTI, a nearly significant QTL for SHOUT and a suggestive QTL for LAT were also identified. On GL3, genome-wide significant QTL were observed for JUMP and DEJ as well as suggestive QTL for LOGTI, MOVE, SHOUT and LAT. A significant QTL for BW2 was observed on GL2 and a nearly significant one on GL1. These results may be useful in the understanding of fearfulness in quail and related species provided that fearfulness has the same genetic basis.

Maternal and Genetic Effects on Anxiety-Related Behavior of C3H/HeN, DBA/2J and NMRI Mice in a Motility-Box Following Blastocyst Transfer

Reciprocal embryo transfers were conducted to examine genetic and maternal effects on the behavior of inbred C3H/HeN and DBA/2J mice, and outbred NMRI mice using a motility-box. The behavioral variables measured were (i) horizontal locomotor activity assessed as the path and time spent during traveling; (ii) vertical activity assessed as the time spent with and numbers of rearings/leanings; (iii) and the time spent in the more anxiogenic central field. The transfer procedure per se resulted in a minor increase in vertical activity of inbred C3H/HeN mice, but had no effect in inbred DBA/2J mice. In contrast, outbred NMRI mice displayed a lower central field activity following embryo transfer indicating a higher anxiety level. Moreover, genetic differences between the mouse strains studied remained stable following embryo transfer for locomotor and vertical activity, but not central field activity depending on the recipient mother strain. Maternal effects were found for (i) vertical activity in the two inbred mouse strains, (ii) all behavioral variables studied in outbred NMRI mice, and (iii) an interaction with gender for the time spent in the anxiogenic central field. An additional fostering procedure revealed that the vertical activity of NMRI mice was modified towards the behavior of the recipient C3H/HeN strain by uterine factors, whereas the postnatal maternal effect of C3H/HeN mothers was the opposite. In summary, the effects of the embryo transfer procedure per se, stability of genetic characteristics following embryo transfer and maternal effects were related to the mouse strains used as donators and recipients, and the behavioral variables studied.

Computational, integrative, and comparative methods for the elucidation of genetic coexpression networks

Gene expression microarray data can be used for the assembly of genetic coexpression network graphs. Using mRNA samples obtained from recombinant inbred Mus musculus strains, it is possible to integrate allelic variation with molecular and higher-order phenotypes. The depth of quantitative genetic analysis of microarray data can be vastly enhanced utilizing this mouse resource in combination with powerful computational algorithms, platforms, and data repositories. The resulting network graphs transect many levels of biological scale. This approach is illustrated with the extraction of cliques of putatively coregulated genes and their annotation using gene ontology analysis and cis-regulatory element discovery. The causal basis for coregulation is detected through the use of quantitative trait locus mapping.

QTL Analysis of Behavioral and Morphological Differentiation Between Wild and Laboratory Zebrafish (Danio rerio)

The zebrafish is an important model organism for neuro-anatomy and developmental genetics. It also offers opportunities for investigating the functional and evolutionary genetics of behaviour but these have yet to be exploited. The ecology of anti-predator behaviour has been widely studied in fish and has been shown to vary among populations and between wild and domesticated (laboratory) fish. Here, we utilise the strong behavioural differences present between a wild-derived strain of fish from Bangladesh and the laboratory strain AB. In total, 184 F2 fish were generated and tested for shoaling tendency and willingness to approach an unfamiliar object ('boldness'). Our results indicate the existence of QTL for boldness on chromosomes 9 and 16 and suggest another genomic region that influences anti-predator behaviour on chromosome 21. QTL for growth rate, weight and fat content, all of which are elevated in laboratory fish, were detected on chromosome 23. These initial results confirm the potential for QTL mapping of behavioural traits in zebrafish and also for dissecting the consequences of selection during domestication.

Genetics of Affective and Anxiety Disorders

The study of the genetics of complex behaviors has evolved dramatically from the days of the nature versus nurture debates that dominated much of the past century. Here we discuss advances in our understanding of the genetics of affective and anxiety disorders. In particular, we highlight our growing understanding of specific gene-environment interactions that occur during critical periods in development, setting the stage for later behavioral phenotypes. We review the recent literature in the field, focusing on recent advances in our understanding of the role of the serotonin system in establishing normal anxiety levels during development. We emphasize the importance of understanding the effect of genetic variation at the level of functional circuits and provide examples from the literature of how such an approach has been exploited to study novel genetic endpoints, including genetically based variation in response to medication, a potentially valuable phenotype that has not received much attention to date.

Impact of genomics on research in the rat

The need to translate genes to function has positioned the rat as an invaluable animal model for genomic research. The significant increase in genomic resources in recent years has had an immediate functional application in the rat. Many of the resources for translational research are already in place and are ready to be combined with the years of physiological knowledge accumulated in numerous rat models, which is the subject of this perspective. Based on the successes to date and the research projects under way to further enhance the infrastructure of the rat, we also project where research in the rat will be in the near future. The impact of the rat genome project has just started, but it is an exciting time with tremendous progress.

The ascent of mouse: advances in modelling human depression and anxiety

Psychiatry has proven to be among the least penetrable clinical disciplines for the development of satisfactory in vivo model systems for evaluating novel treatment approaches. However, mood and anxiety disorders remain poorly understood and inadequately treated. With the explosion in the use of genetically modified mice, enormous research efforts have been focused on developing mouse models of psychiatric disorders. The success of this approach is largely contingent on the usefulness of available behavioural models of depression- and anxiety-related behaviours in mice. Here, we assess the current status of research into developing appropriate tests for assessing such behaviours.

The genetic architecture of sucrose responsiveness in the honeybee (Apis mellifera L.)

One of the best examples of a natural behavioral syndrome is the pollen-hoarding syndrome in honeybees that ties together multiple behavioral phenotypes, ranging from foraging behavior to behavioral ontogeny and learning performance. A central behavioral factor is the bees' responsiveness to sucrose, measured as their proboscis extension reflex. This study examines the genetics of this trait in diploid worker and haploid male honeybees (drones) to learn more about the genetic architecture of the overall behavioral syndrome, using original strains selected for pollen-hoarding behavior. We show that a significant proportion of the phenotypic variability is determined by genotype in males and workers. Second, our data present overwhelming evidence for pleiotropic effects of previously identified quantitative trait loci for foraging behavior (pln-QTL) and epistatic interactions among them. Furthermore, we report on three genomic QTL scans (two reciprocal worker backcrosses and one drone hybrid population) derived from our selection strains. We present at least one significant and two putative new QTL directly affecting the sucrose response of honeybees. Thus, this study demonstrates the modular genetic architecture of behavioral syndromes in general, and elucidates the genetic architecture of the pollen-hoarding behavioral syndrome in particular. Understanding this behavioral syndrome is important for understanding the division of labor in social insects and social evolution itself.

Fine mapping of a major locus on chromosome 10 for exploratory and fear-like behavior in mice

Advanced intercross lines (AIL) and interval-specific congenic strains (ISCS) were used to fine map previously coarsely defined quantitative trait loci (QTL) on Chromosomes 1, 10, and 19, influencing behaviors in the open Field (OF) and light-dark (LD) paradigms in mice. F12(A x B) AIL mice (N = 1130) were phenotyped, genotyped, and mapped. The ISCS were studied only in the telomeric Chromosome 10 region of interest, containing the exploratory and excitability QTL1 (Exq1). The Chromosome 10 Exq1 and Chromosome 19 Exq4 loci mapped robustly in the AIL. The most significant QTL findings (2.0 LOD score intervals; peak; LOD score) came from the TD15 and LD transitions traits, yielding estimated intervals of 2.2 cM for Exq1 (71.3-73.5 cM; peak 72.3 cM; LOD 11.9) and 9.0 cM for Exq4 (29.0-38.2 cM; peak 34 cM; LOD 4.2). The replicated QTLs on Chromosome 1 failed to map in this AIL population. The ISCS data confirmed Exq1 loci in general. However, the ISCS data were complex and less definitive for localizing the Exq1 loci. These exploratory and fear-like behaviors result from inheriting "many small things," namely, QTL explaining 2%-7% of the phenotypic variance. These results highlight the challenges of positionally cloning loci of small effect for complex traits. In particular, fine-mapping success may depend on the genetic architecture underlying complex traits.

The tail suspension test as a model for assessing antidepressant activity: review of pharmacological and genetic studies in mice

Since its introduction almost 20 years ago, the tail suspension test has become one of the most widely used models for assessing antidepressant-like activity in mice. The test is based on the fact that animals subjected to the short-term, inescapable stress of being suspended by their tail, will develop an immobile posture. Various antidepressant medications reverse the immobility and promote the occurrence of escape-related behaviour. This review focuses on the utility this test as part of a research program aimed at understanding the mechanism of action of antidepressants. We discuss the inherent difficulties in modeling depression in rodents. We describe how the tail suspension differs from the closely related forced swim test. Further, we address some key issues associated with using the TST as a model of antidepressant action. We discuss issues regarding whether it satisfies criteria to be a valid model for assessing depression-related behavioural traits. We elaborate on the tests' ease of use, strain differences observed in the test and gender effects in the test. We focus on the utility of the test for genetic analysis. Furthermore, we discuss the concept of whether immobility maybe a behavioural trait relevant to depression. All of the available pharmacological data using the test in genetically modified mice is collated. Special attention is given to selective breeding programs such as the Rouen 'depressed' mice which have been bred for high and low immobility in the tail suspension test. We provide an extensive pooling of the pharmacological studies published to date using the test. Finally, we provide novel pharmacological validation of an automated system (Bioseb) for assessing immobility. Taken together, we conclude that the tail suspension test is a useful test for assessing the behavioural effects of antidepressant compounds and other pharmacological and genetic manipulations relevant to depression.

Using progenitor strain information to identify quantitative trait nucleotides in outbred mice

We have developed a fast and economical strategy for dissecting the genetic architecture of quantitative trait loci at a molecular level. The method uses two pieces of information: mapping data from crosses that involve more than two inbred strains and sequence variants in the progenitor strains within the interval containing a quantitative trait locus (QTL). By testing whether the strain distribution pattern in the progenitor strains is consistent with the observed genetic effect of the QTL we can assign a probability that any sequence variant is a quantitative trait nucleotide (QTN). It is not necessary to genotype the animals except at a skeleton of markers; the genotypes at all other polymorphisms are estimated by a multipoint analysis. We apply the method to a 4.8-Mb region on mouse chromosome 1 that contains a QTL influencing anxiety segregating in a heterogeneous stock and show that, under the assumption that a single QTN is present and lies in a region conserved between the human and mouse genomes, it is possible to reduce the number of variants likely to be the quantitative trait nucleotide from many thousands to <20.

Heritability, correlations and in silico mapping of locomotor behavior and neurochemistry in inbred strains of mice

The midbrain dopamine system mediates normal and pathologic behaviors related to motor activity, attention, motivation/reward and cognition. These are complex, quantitative traits whose variation among individuals is modulated by genetic, epigenetic and environmental factors. Conventional genetic methods have identified several genes important to this system, but the majority of factors contributing to the variation remain unknown. To understand these genetic and environmental factors, we initiated a study measuring 21 behavioral and neurochemical traits in 15 common inbred mouse strains. We report trait data, heritabilities and genetic and non-genetic correlations between pheno-types. In general, the behavioral traits were more heritable than neurochemical traits, and both genetic and non-genetic correlations within these trait sets were high. Surprisingly, there were few significant correlations between the behavioral and the individual neurochemical traits. However, striatal serotonin and one measure of dopamine turnover (DOPAC/DA) were highly correlated with most behavioral measures. The variable accounting for the most variation in behavior was mouse strain and not a specific neurochemical measure, suggesting that additional genetic factors remain to be determined to account for these behavioral differences. We also report the prospective use of the in silico method of quantitative trait loci (QTL) analysis and demonstrate difficulties in the use of this method, which failed to detect significant QTLs for the majority of these traits. These data serve as a framework for further studies of correlations between different midbrain dopamine traits and as a guide for experimental cross designs to identify QTLs and genes that contribute to these traits.

Digit ratio (2D:4D) and behavioral differences between inbred mouse strains

Digit ratio (2D:4D) is a trait, which is sexually differentiated in a variety of species. In humans, males typically have shorter second digits (2Ds) (index fingers) compared to fourth digits (4Ds) (ring fingers) whereas females' fingers are more equal in length. Smaller, more masculine, digit ratios are thought to be associated with higher prenatal testosterone levels, greater sensitivity to prenatal androgens or both. Men with more masculine digit ratios have shown increased ability, achievement and speed in sports and tend to report that they are more physically aggressive. Previous research has shown the same sexually differentiated pattern in the hind paws of laboratory mice as in human hands, males have lower 2D:4D than females. We measured hind paw digit ratio in mice of eight inbred strains. These measurements were made while blind to strain, sex and whether the paw was from the left or right side. We found large differences in digit ratio between the strains and suggest that inbred mice are a promising system for investigating the correlation between digit ratio and behavioral traits.

Supportive evidence for an allelic association of the human KCNJ10 potassium channel gene with idiopathic generalized epilepsy

PURPOSE

Quantitative trait loci (QTL) mapping in mice revealed a seizure-related QTL (Szs1), for which the inward-rectifying potassium channel Kcnj10 is the most compelling candidate gene. Association analysis of the human KCNJ10 gene identified a common KCNJ10 missense variation (Arg271Cys) that influences susceptibility to focal and generalized epilepsies. The present replication study tested the initial finding that the KCNJ10 Cys271 allele is associated with seizure resistance to common syndromes of idiopathic generalized epilepsy (IGE).

METHODS

The study sample comprised 563 German IGE patients and 660 healthy population controls. To search for seizure type-specific effects, two IGE subgroups were formed, comprising 258 IGE patients with typical absences (IAE group) and 218 patients with juvenile myoclonic epilepsy (JME group). A TaqMan nuclease assay was used to genotype the KCNJ10 single nucleotide polymorphism c.1037C > T (dbSNP: rs1130183) that alters amino acid at position 271 from arginine to cysteine.

RESULTS

Replication analysis revealed a significant decrease of the Cys271 allele frequency in 446 IGE patients compared to controls (chi2 = 3.52, d.f. = 1, P = 0.030, one-sided; OR(Cys271+) = 0.69; 95% CI: 0.50-0.95). Among the IGE subgroups, lack of the Cys271 allele was accentuated in the JME group (chi2 = 5.20, d.f. = 1, P = 0.011, one-sided).

CONCLUSION

Our results support previous evidence that the common KCNJ10 Arg271Cys missense variation influences seizure susceptibility of common IGE syndromes.

The Flinders Sensitive Line rat: a selectively bred putative animal model of depression

The Flinders Sensitive Line (FSL) rats were originally selectively bred for increased responses to an anticholinesterase agent. The FSL rat partially resembles depressed individuals because it exhibits reduced appetite and psychomotor function but exhibits normal hedonic responses and cognitive function. The FSL rat also exhibits sleep and immune abnormalities that are observed in depressed individuals. Neurochemical and/or pharmacological evidence suggests that the FSL rat exhibits changes consistent with the cholinergic, serotonergic, dopaminergic, NPY, and circadian rhythm models but not the noradrenergic, HPA axis or GABAergic models of depression. However, evidence for the genetic basis of these changes is lacking and it remains to be determined which, if any, of the neurochemical changes are primary to the behavioral alterations. The FSL rat model has been very useful as a screen for antidepressants because known antidepressants reduced swim test immobility when given chronically and psychomotor stimulants did not. Furthermore, rolipram and a melatonin agonist were shown to have anti-immobility effects in the FSL rats and later to have antidepressant effects in humans. Thus, the FSL rat model of depression exhibits some behavioral, neurochemical, and pharmacological features that have been reported in depressed individuals and has been very effective in detecting antidepressants.

Strategies for mapping and cloning quantitative trait genes in rodents

Over the past 15 years, more than 2,000 quantitative trait loci (QTLs) have been identified in crosses between inbred strains of mice and rats, but less than 1% have been characterized at a molecular level. However, new resources, such as chromosome substitution strains and the proposed Collaborative Cross, together with new analytical tools, including probabilistic ancestral haplotype reconstruction in outbred mice, Yin-Yang crosses and in silico analysis of sequence variants in many inbred strains, could make QTL cloning tractable. We review the potential of these strategies to identify genes that underlie QTLs in rodents.

Lineage is an epigenetic modifier of QTL influencing behavioral coping with stress

A genome-wide scan was carried out on a segregating F2 population of rats derived from reciprocal intercrosses between two inbred strains of rats, Fisher 344 (F344) and Wistar Kyoto (WKY) that differ significantly in their behavioral coping responses to stress measured by the defensive burying (DB) test. The DB test measures differences in coping strategies by assaying an animal's behavioral response to an immediate threat. We have previously identified three X-linked loci contributing to the phenotypic variance in behavioral coping. Here we report on six significant autosomal quantitative trait loci (QTL) related to different behaviors in the DB test:one for the number of shocks received, three for number of prod approaches, one for latency to bury, and one pleiotropic locus affecting both approach and latency. These QTL contributing to different aspects of coping behaviors show that the effect of genotype on phenotype is highly dependent on lineage. The WKY lineage was particularly influential, with five out of the six QTL affecting coping behavior only in rats of the WKY lineage, and one locus affecting only those in the F344 lineage. Thus, epigenetic factors, primarily of WKY origin, may significantly modulate the genetic contribution to variance in behavioral responses to stress in the DB test.

Complex trait analysis of gene expression uncovers polygenic and pleiotropic networks that modulate nervous system function

Patterns of gene expression in the central nervous system are highly variable and heritable. This genetic variation among normal individuals leads to considerable structural, functional and behavioral differences. We devised a general approach to dissect genetic networks systematically across biological scale, from base pairs to behavior, using a reference population of recombinant inbred strains. We profiled gene expression using Affymetrix oligonucleotide arrays in the BXD recombinant inbred strains, for which we have extensive SNP and haplotype data. We integrated a complementary database comprising 25 years of legacy phenotypic data on these strains. Covariance among gene expression and pharmacological and behavioral traits is often highly significant, corroborates known functional relations and is often generated by common quantitative trait loci. We found that a small number of major-effect quantitative trait loci jointly modulated large sets of transcripts and classical neural phenotypes in patterns specific to each tissue. We developed new analytic and graph theoretical approaches to study shared genetic modulation of networks of traits using gene sets involved in neural synapse function as an example. We built these tools into an open web resource called WebQTL that can be used to test a broad array of hypotheses.

Human personality traits are associated with individual environmental traits in male adolescents--a pilot study

The human personality seems to be formed by biological (internal) and environmental (external) factors, which function interactively. This pilot study examined the relationship between fundamental personality traits and individual environmental traits in healthy adolescents. A complex relationship between personality traits and candidate environmental traits was found in this sample. Parental smoking, one of the hypothetical environmental traits, was significantly associated with the sociability personality trait of adolescent offspring. Another hypothetical environmental trait-parent/child attachment status-"was related to novelty-seeking personality. Unexpectedly, these associations were observed only in male but not in female adolescents. The present study suggested that (1) parental smoking behavior might directly or indirectly affect offspring social behavior and related personality by nongenetic transmission; (2) past and present data indicated that the triad of a poor parent/child relationship, novelty-seeking personality, and risky/delinquent behavior is closely connected. Investigations of environmental traits at a nonclinical level may lead us to understand the overall human personality, as with research on genes and biological traits that are implicated in the formation of mental activity.

Behavioral Characterization of Wild Derived Male Mice (Mus musculus musculus) of the PWD/Ph Inbred Strain: High Exploration Compared to C57BL/6J

PWD/Ph is an inbred mouse strain derived from wild mice trapped in central Czech Republic. These mice are of the Mus musculus musculus subspecies, whose ancestors separated from those of Mus musculus domesticus about one million years ago. There is a high degree of variation in the genomic sequence and a wide range of phenotypes between PWD/Ph and standard laboratory inbred mouse strains, the genomes of which are principally Mus musculus domesticus in origin, making PWD/Ph mice an useful resource for complex trait research. As a first step in taking advantage of this resource, a preliminary characterization of the behavior of PWD/Ph mice was performed. Groups of 10 PWD/Ph and C57BL/6J male mice were tested in the open field, novel object exploration task and Morris water maze. PWD/Ph were marginally more anxious than C57BL/6J mice in the open field but subsequently displayed much higher levels of exploration and lower anxiety than C57BL/6J mice following introduction of a novel object. As C57BL/6J itself is rated as highly explorative among classical inbred strains, PWD/Ph probably represents an extreme among mouse strains for this specific behavior. PWD/Ph and C57BL/6J mice differed in their water escape training profiles in the Morris water maze, perhaps reflecting different motivational factors. However, there were no differences in overall cognitive ability (spatial learning) as both groups learned to find the hidden platform and performed equally well when the location of the platform was changed. This is the first quantification of the behavior of PWD/Ph mice and the results are promising for the potential of the consomic panel currently being generated with PWD/Ph and C57BL/6J as a tool for the molecular dissection of behavior.

Genetic dissection of a behavioral quantitative trait locus shows that Rgs2 modulates anxiety in mice

Here we present a strategy to determine the genetic basis of variance in complex phenotypes that arise from natural, as opposed to induced, genetic variation in mice. We show that a commercially available strain of outbred mice, MF1, can be treated as an ultrafine mosaic of standard inbred strains and accordingly used to dissect a known quantitative trait locus influencing anxiety. We also show that this locus can be subdivided into three regions, one of which contains Rgs2, which encodes a regulator of G protein signaling. We then use quantitative complementation to show that Rgs2 is a quantitative trait gene. This combined genetic and functional approach should be applicable to the analysis of any quantitative trait.

On the Integration of Alcohol-Related Quantitative Trait Loci and Gene Expression Analyses

BACKGROUND

Quantitative trait loci (QTLs) have been detected for a wide variety of ethanol-related phenotypes, including acute and chronic ethanol withdrawal, acute locomotor activation, and ethanol preference. This study was undertaken to determine whether the process of moving from QTL to quantitative trait gene (QTG) could be accelerated by the integration of functional genomics (gene expression) into the analysis strategy.

METHODS

Six ethanol-related QTLs, all detected in C57BL/6J and DBA/2J intercrosses were entered into the analysis. Each of the QTLs had been confirmed in independent genetic models at least once; the cumulative probabilities for QTL existence ranged from 10 to 10. Brain gene expression data for the C57BL/6 and DBA/2 strains (n = 6 per strain) and an F2 intercross sample (n = 56) derived from these strains were obtained by using the Affymetrix U74Av2 and 430A arrays; additional data with the U74Av2 array were available for the extended amygdala, dorsomedial striatum, and hippocampus. Low-level analysis was performed by using multiple methods to determine the likelihood that a transcript was truly differentially expressed. For the 430A array data, the F2 sample was used to determine which of the differentially expressed transcripts within the QTL intervals were cis-regulated and, thus, strong candidates for QTGs.

RESULTS

Within the 6 QTL intervals, 39 transcripts (430A array) were identified as being highly likely to be differentially expressed between the C57BL/6 and DBA/2 strains at a false discovery rate of 0.01 or better. Twenty-eight of these transcripts showed significant (logarithm of odds > or =3.6) to highly significant (logarithm of odds >7) cis-regulation. The process correctly detected Mpdz (chromosome 4) as a candidate QTG for acute withdrawal.

CONCLUSIONS

Although improvements are needed in the expression databases, the integration of QTL and gene expression analyses seems to have potential as a high-throughput strategy for moving from QTL to QTG.

Mapping quantitative trait loci for anxiety in chromosome substitution strains of mice

Anxious behavior in the mouse is a complex quantitative phenotype that varies widely among inbred mouse strains. We examined a panel of chromosome substitution strains bearing individual A/J chromosomes in an otherwise C57BL/6J background in open-field and light-dark transition tests. Our results confirmed previous reports of quantitative trait loci (QTL) on chromosomes 1, 4, and 15 and identified novel loci on chromosomes 6 and 17. The studies were replicated in two separate laboratories. Systematic differences in the overall activity level were found between the two facilities, but the presence of the QTL was confirmed in both laboratories. We also identified specific effects on open-field defecation and center avoidance and distinguished them from overall open-field activity.

N-ethyl-N-nitrosourea mouse mutants in the dissection of behavioural and psychiatric disorders

Twin and adoption studies have consistently implicated genetics in the aetiology of psychiatric and behavioural disorders. The identification of the genes and molecular pathways that are associated with these traits using linkage studies has been difficult because psychiatric disorders are almost always non-mendelian, heterogeneous, involve multiple genetic loci and are influenced significantly by environmental factors. Mouse models that are based on intermediate signatures of psychiatric disease and pharmacological responsiveness hold promise as a complementary approach to dissecting the molecular basis of neurobehavioural disorders. This has been made possible by the development and refinement of gene targeting technologies and the use of super-efficient chemical mutagens. N-ethyl-N-nitrosourea (ENU) mutagenesis in the mouse, when coupled to a battery of sensitive behavioural screens, is an effective way of creating and identifying novel mouse behavioural mutants. Here, the concept of screening for ENU mutants is introduced while progress with two behavioural screens, an "anxiety" screen and a circadian screen, are presented. It is hoped that the study of mouse mutants that have arisen from these screens will provide new insights into the genetic basis of abnormal behaviour and that they might lead to the development of novel therapeutic compounds for human psychiatric disease.

How species evolve collectively: implications of gene flow and selection for the spread of advantageous alleles

The traditional view that species are held together through gene flow has been challenged by observations that migration is too restricted among populations of many species to prevent local divergence. However, only very low levels of gene flow are necessary to permit the spread of highly advantageous alleles, providing an alternative means by which low-migration species might be held together. We re-evaluate these arguments given the recent and wide availability of indirect estimates of gene flow. Our literature review of F(ST) values for a broad range of taxa suggests that gene flow in many taxa is considerably greater than suspected from earlier studies and often is sufficiently high to homogenize even neutral alleles. However, there are numerous species from essentially all organismal groups that lack sufficient gene flow to prevent divergence. Crude estimates on the strength of selection on phenotypic traits and effect sizes of quantitative trait loci (QTL) suggest that selection coefficients for leading QTL underlying phenotypic traits may be high enough to permit their rapid spread across populations. Thus, species may evolve collectively at major loci through the spread of favourable alleles, while simultaneously differentiating at other loci due to drift and local selection.

A strategy for the integration of QTL, gene expression, and sequence analyses

Although hundreds if not thousands of quantitative trait loci (QTL) have been described for a wide variety of complex traits, only a very small number of these QTLs have been reduced to quantitative trait genes (QTGs) and quantitative trait nucleotides (QTNs). A strategy, Multiple Cross Mapping (MCM), is described for detecting QTGs and QTNs that is based on leveraging the information contained within the haplotype structure of the mouse genome. As described in the current report, the strategy utilizes the six F(2) intercrosses that can be formed from the C57BL/6J (B6), DBA/2J (D2), BALB/cJ (C), and LP/J (LP) inbred mouse strains. Focusing on the phenotype of basal locomotor activity, it was found that in all three B6 intercrosses, a QTL was detected on distal Chromosome (Chr) 1; no QTL was detected in the other three intercrosses, and thus, it was assumed that at the QTL, the C, D2, and LP strains had functionally identical alleles. These intercross data were used to form a simple algorithm for interrogating microsatellite, single nucleotide polymorphism (SNP), brain gene expression, and sequence databases. The results obtained point to Kcnj9 (which has a markedly lower expression in the B6 strain) as being the likely QTG. Further, it is suggested that the lower expression in the B6 strain results from a polymorphism in the 5'-UTR that disrupts the binding of at least three transcription factors. Overall, the method described should be widely applicable to the analysis of QTLs.

Maternal behavior modulates X-linked inheritance of behavioral coping in the defensive burying test

BACKGROUND

Complex behavioral traits such as coping strategies in response to stress are usually formed by genetic and environmental influences.

METHODS

By exploiting the phenotypic and genotypic differences between the Wistar Kyoto (WKY) and Fischer 344 (F344) inbred rat strains, we recently identified three X chromosome-linked quantitative trait loci contributing to differences in coping strategies in the defensive burying (DB) paradigm. In this article we study the influence of postnatal maternal environment in these behaviors by characterizing the maternal behavior of these strains and the effect of cross-fostering on DB behavior of male offspring from reciprocal crossing (F1).

RESULTS

Maternal behavior of WKY rats can be quantitatively characterized by less contact and more periods of neglect of their F1 pups. In contrast, F344 mothers engaged in more active behaviors such as licking/grooming and arched-back nursing. Cross-fostering male F1 pups at birth did not influence the latency to bury measure in DB; however, duration of burying and prod approaches were influenced by both genotype and maternal environment in an additive manner.

CONCLUSIONS

These results demonstrate that different measures of behavioral coping in the DB paradigm are influenced by maternal environment to differing degrees and in addition by genetic factors.

The genetic basis of neuroticism

Gray has drawn upon genetic evidence to argue for the existence of rodent emotionality, a model of human neuroticism. With the advent of molecular mapping techniques it has become possible to test this hypothesis. Here I review the progress that has been made, largely in animal genetic studies, demonstrating that a common set of genes act pleiotropically on measures of emotionality. More recently, evidence has emerged supporting the view that the same genes influence variation in both rodent and human phenotypes.

Hippocampal gene expression profiling across eight mouse inbred strains: towards understanding the molecular basis for behaviour

Mouse inbred strains differ in many aspects of their phenotypes, and it is known that gene expression does so too. This gives us an opportunity to isolate the genetic aspect of variation in expression and compare it to other phenotypic variables. We have investigated these issues using an eight-strain expression profile comparison with four replicates per strain on Affymetrix MGU74av2 GeneChips focusing on one well-defined brain tissue (the hippocampus). We identified substantial strain-specific variation in hippocampal gene expression, with more than two hundred genes showing strain differences by a very conservative criterion. Many such genetically driven differences in gene expression are likely to result in functional differences including differences in behaviour. A large panel of inbred strains could be used to identify genes functionally involved in particular phenotypes, similar to genetic correlation. The genetic correlation between expression profiles and function is potentially very powerful, especially given the current large-scale generation of phenotypic data on multiple strains (the Mouse Phenome Project). As an example, the strongest genetic correlation between more than 200 probe sets showing significant differences among our eight inbred strains and a ranking of these strains by aggression phenotype was found for Comt, a gene known to be involved in aggression.

In search of a depressed mouse: utility of models for studying depression-related behavior in genetically modified mice

The ability to modify mice genetically has been one of the major breakthroughs in modern medical science affecting every discipline including psychiatry. It is hoped that the application of such technologies will result in the identification of novel targets for the treatment of diseases such as depression and to gain a better understanding of the molecular pathophysiological mechanisms that are regulated by current clinically effective antidepressant medications. The advent of these tools has resulted in the need to adopt, refine and develop mouse-specific models for analyses of depression-like behavior or behavioral patterns modulated by antidepressants. In this review, we will focus on the utility of current models (eg forced swim test, tail suspension test, olfactory bulbectomy, learned helplessness, chronic mild stress, drug-withdrawal-induced anhedonia) and research strategies aimed at investigating novel targets relevant to depression in the mouse. We will focus on key questions that are considered relevant for examining the utility of such models. Further, we describe other avenues of research that may give clues as to whether indeed a genetically modified animal has alterations relevant to clinical depression. We suggest that it is prudent and most appropriate to use convergent tests that draw on different antidepressant-related endophenotypes, and complimentary physiological analyses in order to provide a program of information concerning whether a given phenotype is functionally relevant to depression-related pathology.

From hormones to immunity: the physiology of immunology

Discoveries in the physiology of immunology have increased at an increasing rate during the past two decades. It is now recognized that the immune system is just another physiological system that regulates, and is regulated by, other physiological systems such as the brain. These advances make it clear that recent findings in genomic biology must be interpreted in the context of the environment in which animals and humans live. Lack of a strong genetic basis for significant human mental health disorders, such as major depression, points to the critical importance of interactions. Several examples of environmental x genetic x disease interactions are presented. Regulation of cells of the hematopoietic lineage by two genes that control over 80% of postnatal growth, growth hormone and IGF-I, are then highlighted. The reciprocal relationship of how proinflammatory cytokines from the immune system regulate the growth hormone/IGF-I axis is also summarized. Particular emphasis is placed upon TNFalpha-induced IGF-I resistance in neurons, muscle cells and epithelial cells. This cytokine regulation of hormone action may ultimately be more important for human and animal health than direct effects of growth hormone and IGF-I on hematopoietic cells. Wasting of AIDS patients is given as an important clinical example of how TNFalpha from an activated immune system reduces IGF-I sensitivity in multiple physiologic systems, including muscle, nervous and hematopoietic tissues.

Abnormal anxiety-related behavior in serotonin transporter null mutant mice: the influence of genetic background

Serotonin transporter (5-HTT) null mutant mice provide a model system to study the role genetic variation in the 5-HTT plays in the regulation of emotion. Anxiety-like behaviors were assessed in 5-HTT null mutants with the mutation placed on either a B6 congenic or a 129S6 congenic background. Replicating previous findings, B6 congenic 5-HTT null mutants exhibited increased anxiety-like behavior and reduced exploratory locomotion on the light <--> dark exploration and elevated plus-maze tests. In contrast, 129S6 congenic 5-HTT null mutant mice showed no phenotypic abnormalities on either test. 5-HTT null mutants on the 129S6 background showed reduced 5-HT(1A) receptor binding (as measured by quantitative autoradiography) and reduced 5-HT(1A) receptor function (as measured by 8-OH-DPAT-induced hypothermia). These data confirm that the 5-HTT null mutation produced alterations in brain 5-HT function in mice on the 129S6 background, thereby discounting the possibility that the absence of an abnormal anxiety-like phenotype in these mice was due to a suppression of the mutation by 129 modifier genes. Anxiety-like behaviors in the light <--> dark exploration and elevated plus-maze tests were significantly higher in 129S6 congenic +/+ mice as compared to B6 congenic +/+ mice. This suggests that high baseline anxiety-like behavior in the 129S6 strain might have precluded detection of the anxiety-like effects of the 5-HTT null mutation on this background. Present findings provide further evidence linking genetic variation in the 5-HTT to abnormalities in mood and anxiety. Furthermore, these data highlight the utility of conducting behavioral phenotyping of mutant mice on multiple genetic backgrounds.

Allelic variations in gene expression

PURPOSE OF REVIEW

Genetic variants determine phenotypic variability. Many genetic studies suggest that protein structural variations predispose the population to more than 1000 different hereditary diseases. Unfortunately, despite the study of genetic polymorphisms for many decades, the milder phenotypic variations believed to account for most human physical and behavioral differences and underlying the most common human genetic diseases (including cancers) cannot be accounted for easily by these variations in the protein coding sequences. Thus, it has been hypothesized that the study of natural differential expression presenting within and among populations may enhance understanding of human phenotypic variation.

RECENT FINDINGS

During the last year, reports identifying variations in gene expression in different organisms and finding subtle changes of gene expression associated with common genetic disease have pointed to variations in gene expression as playing a central role in molecular evolution and human disease. Advances in the functional analysis of gene regulatory networks-in particular, new methods for distinguishing cis-acting components from trans-acting factors-have provided the impetus for these discoveries.

SUMMARY

This review represents current knowledge about allelic variation in gene expression and its increasingly important role in understanding the genotype-phenotype relation. Characterization of these allelic variations may open largely uncharted territory in genomics for biomedical researchers and may eventually lead to the discovery of the causative genes of common hereditary diseases and their mechanism of action.

The nicotinic acetylcholine receptor subunit alpha 5 mediates short-term effects of nicotine in vivo

Nicotine, acting at pentameric neuronal nicotinic acetylcholine receptors (nAChRs), is the primary addictive component in tobacco. At low doses, it affects attention, learning, memory, anxiety, cardiovascular responses, thermoregulation, and nociception. At high doses, nicotine produces more drastic behaviors and eventually induces tonic-clonic seizures in rodents. In mammals, several subunits of the nAChRs have been cloned, including eight alpha and three beta subunits. To study the physiological role of the alpha 5 subunit, we have generated alpha 5-deficient mice. These mice have a generally healthy appearance and are normal in a standard battery of behavioral tests. However, the sensitivity of alpha 5 mutant mice to nicotine-induced behaviors and seizures is dramatically reduced compared with their wild-type littermates. These animals have a normal brain anatomy and normal levels of mRNA for other nAChR subunits, namely alpha 4, alpha 6, alpha 7, beta 2, and beta 4. In addition, (125)I-epibatidine and [(125)I]alpha-bungarotoxin binding in the brains of alpha 5-deficient mice is normal. Together, these results suggest a direct involvement of the alpha 5 subunit in the observed phenotypes.

Untangling genetic networks of panic, phobia, fear and anxiety

As is the case for normal individual variation in anxiety levels, the conditions panic disorder, agoraphobia and other phobias have a significant genetic basis. Recent reports have started to untangle the genetic relationships between predispositions to anxiety and anxiety disorders.