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1.  Smoking and Major Depressive Disorder in Chinese Women 
PLoS ONE  2014;9(9):e106287.
To investigate the risk factors that contribute to smoking in female patients with major depressive disorder (MDD) and the clinical features in depressed smokers.
We examined the smoking status and clinical features in 6120 Han Chinese women with MDD (DSM-IV) between 30 and 60 years of age across China. Logistic regression was used to determine the association between clinical features of MDD and smoking status and between risk factors for MDD and smoking status.
Among the recurrent MDD patients there were 216(3.6%) current smokers, 117 (2.0%) former smokers and 333(5.6%) lifetime smokers. Lifetime smokers had a slightly more severe illness, characterized by more episodes, longer duration, more comorbid illness (panic and phobias), with more DSM-IV A criteria and reported more symptoms of fatigue and suicidal ideation or attempts than never smokers. Some known risk factors for MDD were also differentially represented among smokers compared to non-smokers. Smokers reported more stressful life events, were more likely to report childhood sexual abuse, had higher levels of neuroticism and an increased rate of familial MDD. Only neuroticism was significantly related to nicotine dependence.
Although depressed women smokers experience more severe illness, smoking rates remain low in MDD patients. Family history of MDD and environmental factors contribute to lifetime smoking in Chinese women, consistent with the hypothesis that the association of smoking and depression may be caused by common underlying factors.
PMCID: PMC4152240  PMID: 25180682
2.  Identification of structural variation in mouse genomes 
Frontiers in Genetics  2014;5:192.
Structural variation is variation in structure of DNA regions affecting DNA sequence length and/or orientation. It generally includes deletions, insertions, copy-number gains, inversions, and transposable elements. Traditionally, the identification of structural variation in genomes has been challenging. However, with the recent advances in high-throughput DNA sequencing and paired-end mapping (PEM) methods, the ability to identify structural variation and their respective association to human diseases has improved considerably. In this review, we describe our current knowledge of structural variation in the mouse, one of the prime model systems for studying human diseases and mammalian biology. We further present the evolutionary implications of structural variation on transposable elements. We conclude with future directions on the study of structural variation in mouse genomes that will increase our understanding of molecular architecture and functional consequences of structural variation.
PMCID: PMC4079067  PMID: 25071822
array comparative genome hybridization (aCGH); next-generation sequencing (NGS); structural variation (SV); paired-end mapping (PEM); inbred strains of mice; Heterogeneous Stock (HS); Sanger Mouse Genomes Project
3.  Genetic Interactions with Sex Make a Relatively Small Contribution to the Heritability of Complex Traits in Mice 
PLoS ONE  2014;9(5):e96450.
The extent to which sex-specific genetic effects contribute to phenotypic variation is largely unknown. We applied a novel Bayesian method, sparse partitioning, to detect gene by sex (GxS) and gene by gene (GxG) quantitative loci (QTLs) in 1,900 outbred heterogeneous stock mice. In an analysis of 55 phenotypes, we detected 16 GxS and 6 GxG QTLs. The increase in the amount of phenotypic variance explained by models including GxS was small, ranging from 0.14% to 4.30%. We conclude that GxS rarely make a large overall contribution to the heritability of phenotypes, however there are cases where these will be individually important.
PMCID: PMC4014490  PMID: 24811081
4.  Natural Polymorphisms in Tap2 Influence Negative Selection and CD4∶CD8 Lineage Commitment in the Rat 
PLoS Genetics  2014;10(2):e1004151.
Genetic variation in the major histocompatibility complex (MHC) affects CD4∶CD8 lineage commitment and MHC expression. However, the contribution of specific genes in this gene-dense region has not yet been resolved. Nor has it been established whether the same genes regulate MHC expression and T cell selection. Here, we assessed the impact of natural genetic variation on MHC expression and CD4∶CD8 lineage commitment using two genetic models in the rat. First, we mapped Quantitative Trait Loci (QTLs) associated with variation in MHC class I and II protein expression and the CD4∶CD8 T cell ratio in outbred Heterogeneous Stock rats. We identified 10 QTLs across the genome and found that QTLs for the individual traits colocalized within a region spanning the MHC. To identify the genes underlying these overlapping QTLs, we generated a large panel of MHC-recombinant congenic strains, and refined the QTLs to two adjacent intervals of ∼0.25 Mb in the MHC-I and II regions, respectively. An interaction between these intervals affected MHC class I expression as well as negative selection and lineage commitment of CD8 single-positive (SP) thymocytes. We mapped this effect to the transporter associated with antigen processing 2 (Tap2) in the MHC-II region and the classical MHC class I gene(s) (RT1-A) in the MHC-I region. This interaction was revealed by a recombination between RT1-A and Tap2, which occurred in 0.2% of the rats. Variants of Tap2 have previously been shown to influence the antigenicity of MHC class I molecules by altering the MHC class I ligandome. Our results show that a restricted peptide repertoire on MHC class I molecules leads to reduced negative selection of CD8SP cells. To our knowledge, this is the first study showing how a recombination between natural alleles of genes in the MHC influences lineage commitment of T cells.
Author Summary
Peptides from degraded cytoplasmic proteins are transported via TAP into the endoplasmic reticulum for loading onto MHC class I molecules. TAP is encoded by Tap1 and Tap2, which in rodents are located close to the MHC class I genes. In the rat, genetic variation in Tap2 gives rise to two different transporters: a promiscuous A variant (TAP-A) and a more restrictive B variant (TAP-B). It has been proposed that the class I molecule in the DA rat (RT1-Aa) has co-evolved with TAP-A and it has been shown that RT1-Aa antigenicity is changed when co-expressed with TAP-B. To study the contribution of different allelic combinations of RT1-A and Tap2 to the variation in MHC expression and T cell selection, we generated DA rats with either congenic or background alleles in the RT1-A and Tap2 loci. We found increased numbers of mature CD8SP cells in the thymus of rats which co-expressed RT1-Aa and TAP-B. This increase of CD8 cells could be explained by reduced negative selection, but did not correlate with RT1-Aa expression levels on thymic antigen presenting cells. Thus, our results identify a crucial role of the TAP and the quality of the MHC class I repertoire in regulating T cell selection.
PMCID: PMC3930506  PMID: 24586191
5.  Ectopic Cerebellar Cell Migration Causes Maldevelopment of Purkinje Cells and Abnormal Motor Behaviour in Cxcr4 Null Mice 
PLoS ONE  2014;9(2):e86471.
SDF-1/CXCR4 signalling plays an important role in neuronal cell migration and brain development. However, the impact of CXCR4 deficiency in the postnatal mouse brain is still poorly understood. Here, we demonstrate the importance of CXCR4 on cerebellar development and motor behaviour by conditional inactivation of Cxcr4 in the central nervous system. We found CXCR4 plays a key role in cerebellar development. Its loss leads to defects in Purkinje cell dentritogenesis and axonal projection in vivo but not in cell culture. Transcriptome analysis revealed the most significantly affected pathways in the Cxcr4 deficient developing cerebellum are involved in extra cellular matrix receptor interactions and focal adhesion. Consistent with functional impairment of the cerebellum, Cxcr4 knockout mice have poor coordination and balance performance in skilled motor tests. Together, these results suggest ectopic the migration of granule cells impairs development of Purkinje cells, causes gross cerebellar anatomical disruption and leads to behavioural motor defects in Cxcr4 null mice.
PMCID: PMC3917845  PMID: 24516532
6.  The Genetics of Major Depression 
Neuron  2014;81(3):484-503.
Major depression is the commonest psychiatric disorder and in the U.S. has the greatest impact of all biomedical diseases on disability. Here we review evidence of the genetic contribution to disease susceptibility and the current state of molecular approaches. Genome-wide association and linkage results provide constraints on the allele frequencies and effect sizes of susceptibility loci, which we use to interpret the voluminous candidate gene literature. We consider evidence for the genetic heterogeneity of the disorder and the likelihood that subtypes exist that represent more genetically homogenous conditions than have hitherto been analyzed.
Genetic analysis of major depression lags behind that of other disease. Genome-wide association and linkage results provide constraints on major depression’s genetic architecture, indicating that candidate gene studies are underpowered. The disorder is heterogeneous; subtypes likely exist that represent more homogenous conditions suitable for genetic dissection.
PMCID: PMC3919201  PMID: 24507187
7.  Associations of Educational Attainment, Occupation, Social Class and Major Depressive Disorder among Han Chinese Women 
PLoS ONE  2014;9(1):e86674.
The prevalence of major depressive disorder (MDD) is higher in those with low levels of educational attainment, the unemployed and those with low social status. However the extent to which these factors cause MDD is unclear. Most of the available data comes from studies in developed countries, and these findings may not extrapolate to developing countries. Examining the relationship between MDD and socio economic status in China is likely to add to the debate because of the radical economic and social changes occurring in China over the last 30 years.
Principal findings
We report results from 3,639 Chinese women with recurrent MDD and 3,800 controls. Highly significant odds ratios (ORs) were observed between MDD and full time employment (OR = 0.36, 95% CI = 0.25–0.46, logP = 78), social status (OR = 0.83, 95% CI = 0.77–0.87, logP = 13.3) and education attainment (OR = 0.90, 95% CI = 0.86–0.90, logP = 6.8). We found a monotonic relationship between increasing age and increasing levels of educational attainment. Those with only primary school education have significantly more episodes of MDD (mean 6.5, P-value = 0.009) and have a clinically more severe disorder, while those with higher educational attainment are likely to manifest more comorbid anxiety disorders.
In China lower socioeconomic position is associated with increased rates of MDD, as it is elsewhere in the world. Significantly more episodes of MDD occur among those with lower educational attainment (rather than longer episodes of disease), consistent with the hypothesis that the lower socioeconomic position increases the likelihood of developing MDD. The phenomenology of MDD varies according to the degree of educational attainment: higher educational attainment not only appears to protect against MDD but alters its presentation, to a more anxious phenotype.
PMCID: PMC3909008  PMID: 24497966
8.  Childhood Sexual Abuse and the Development of Recurrent Major Depression in Chinese Women 
PLoS ONE  2014;9(1):e87569.
Our prior study in Han Chinese women has shown that women with a history of childhood sexual abuse (CSA) are at increased risk for developing major depression (MD). Would this relationship be found in our whole data set?
Three levels of CSA (non-genital, genital, and intercourse) were assessed by self-report in two groups of Han Chinese women: 6017 clinically ascertained with recurrent MD and 5983 matched controls. Diagnostic and other risk factor information was assessed at personal interview. Odds ratios (ORs) were calculated by logistic regression.
We confirmed earlier results by replicating prior analyses in 3,950 new recurrent MD cases. There were no significant differences between the two data sets. Any form of CSA was significantly associated with recurrent MD (OR 4.06, 95% confidence interval (CI) [3.19–5.24]). This association strengthened with increasing CSA severity: non-genital (OR 2.21, 95% CI 1.58–3.15), genital (OR 5.24, 95% CI 3.52–8.15) and intercourse (OR 10.65, 95% CI 5.56–23.71). Among the depressed women, those with CSA had an earlier age of onset, longer depressive episodes. Recurrent MD patients those with CSA had an increased risk for dysthymia (OR 1.60, 95%CI 1.11–2.27) and phobia (OR 1.41, 95%CI 1.09–1.80). Any form of CSA was significantly associated with suicidal ideation or attempt (OR 1.50, 95% CI 1.20–1.89) and feelings of worthlessness or guilt (OR 1.41, 95% CI 1.02–2.02). Intercourse (OR 3.47, 95%CI 1.66–8.22), use of force and threats (OR 1.95, 95%CI 1.05–3.82) and how strongly the victims were affected at the time (OR 1.39, 95%CI 1.20–1.64) were significantly associated with recurrent MD.
In Chinese women CSA is strongly associated with recurrent MD and this association increases with greater severity of CSA. Depressed women with CSA have some specific clinical traits. Some features of CSA were associated with greater likelihood of developing recurrent MD.
PMCID: PMC3906190  PMID: 24489940
9.  The Architecture of Parent-of-Origin Effects in Mice 
Cell  2014;156(1-2):332-342.
The number of imprinted genes in the mammalian genome is predicted to be small, yet we show here, in a survey of 97 traits measured in outbred mice, that most phenotypes display parent-of-origin effects that are partially confounded with family structure. To address this contradiction, using reciprocal F1 crosses, we investigated the effects of knocking out two nonimprinted candidate genes, Man1a2 and H2-ab1, that reside at nonimprinted loci but that show parent-of-origin effects. We show that expression of multiple genes becomes dysregulated in a sex-, tissue-, and parent-of-origin-dependent manner. We provide evidence that nonimprinted genes can generate parent-of-origin effects by interaction with imprinted loci and deduce that the importance of the number of imprinted genes is secondary to their interactions. We propose that this gene network effect may account for some of the missing heritability seen when comparing sibling-based to population-based studies of the phenotypic effects of genetic variants.
Graphical Abstract
•Heritability of murine complex traits has a significant parent-of-origin effect•Many mouse quantitative trait loci show parent-of-origin effects•Gene knockouts induce parent-of-origin-like expression changes in reciprocal crosses
A surprisingly large proportion of traits exhibiting inheritance patterns based on parent of origin indicates a network of interactions between imprinted and nonimprinted genes. The results suggest that these interactions may account for some of the missing heritability seen when comparing sibling-based to population-based studies of the phenotypic effects of genetic variants.
PMCID: PMC3898482  PMID: 24439386
10.  Combined sequence-based and genetic mapping analysis of complex traits in outbred rats 
Nature genetics  2013;45(7):10.1038/ng.2644.
Genetic mapping on fully sequenced individuals is transforming our understanding of the relationship between molecular variation and variation in complex traits. Here we report a combined sequence and genetic mapping analysis in outbred rats that maps 355 quantitative trait loci for 122 phenotypes. We identify 35 causal genes involved in 31 phenotypes, implicating novel genes in models of anxiety, heart disease and multiple sclerosis. The relation between sequence and genetic variation is unexpectedly complex: at approximately 40% of quantitative trait loci a single sequence variant cannot account for the phenotypic effect. Using comparable sequence and mapping data from mice, we show the extent and spatial pattern of variation in inbred rats differ significantly from those of inbred mice, and that the genetic variants in orthologous genes rarely contribute to the same phenotype in both species.
PMCID: PMC3821058  PMID: 23708188
11.  Clinical Features of Patients with Dysthymia in a Large Cohort of Han Chinese Women with Recurrent Major Depression 
PLoS ONE  2013;8(12):e83490.
Dysthymia is a form of chronic mild depression that has a complex relationship with major depressive disorder (MDD). Here we investigate the role of environmental risk factors, including stressful life events and parenting style, in patients with both MDD and dysthymia. We ask whether these risk factors act in the same way in MDD with and without dysthymia.
We examined the clinical features in 5,950 Han Chinese women with MDD between 30–60 years of age across China. We confirmed earlier results by replicating prior analyses in 3,950 new MDD cases. There were no significant differences between the two data sets. We identified sixteen stressful life events that significantly increase the risk of dysthymia, given the presence of MDD. Low parental warmth, from either mother or father, increases the risk of dysthymia. Highly threatening but short-lived threats (such as rape) are more specific for MDD than dysthymia. While for MDD more severe life events show the largest odds ratio versus controls, this was not seen for cases of MDD with or without dysthymia.
There are increased rates of stressful life events in MDD with dysthymia, but the impact of life events on susceptibility to dysthymia with MDD differs from that seen for MDD alone. The pattern does not fit a simple dose-response relationship, suggesting that there are moderating factors involved in the relationship between environmental precipitants and the onset of dysthymia. It is possible that severe life events in childhood events index a general susceptibility to chronic depression, rather than acting specifically as risk factors for dysthymia.
PMCID: PMC3873934  PMID: 24386213
12.  Suicidal Risk Factors of Recurrent Major Depression in Han Chinese Women 
PLoS ONE  2013;8(11):e80030.
The relationship between suicidality and major depression is complex. Socio- demography, clinical features, comorbidity, clinical symptoms, and stressful life events are important factors influencing suicide in major depression, but these are not well defined. Thus, the aim of the present study was to assess the associations between the above-mentioned factors and suicide ideation, suicide plan, and suicide attempt in 6008 Han Chinese women with recurrent major depression (MD). Patients with any suicidality had significantly more MD symptoms, a significantly greater number of stressful life events, a positive family history of MD, a greater number of episodes, a significant experience of melancholia, and earlier age of onset. Comorbidity with dysthymia, generalized anxiety disorder (GAD), social phobia, and animal phobia was seen in suicidal patients. The present findings indicate that specific factors act to increase the likelihood of suicide in MD. Our results may help improve the clinical assessment of suicide risk in depressed patients, especially for women.
PMCID: PMC3842272  PMID: 24312196
13.  Genome-wide association studies in mice 
Nature reviews. Genetics  2012;13(11):807-817.
Genome-wide association studies (GWASs) have transformed the field of human genetics and have led to the discovery of hundreds of genes that are implicated in human disease. The technological advances that drove this revolution are now poised to transform genetic studies in model organisms, including mice. However, the design of GWASs in mouse strains is fundamentally different from the design of human GWASs, creating new challenges and opportunities. This Review gives an overview of the novel study designs for mouse GWASs, which dramatically improve both the statistical power and resolution compared to classical gene-mapping approaches.
PMCID: PMC3625632  PMID: 23044826
14.  Meta-analyses of genome-wide linkage scans of anxiety-related phenotypes 
European Journal of Human Genetics  2012;20(10):1078-1084.
Genetic factors underlying trait neuroticism, reflecting a tendency towards negative affective states, may overlap genetic susceptibility for anxiety disorders and help explain the extensive comorbidity amongst internalizing disorders. Genome-wide linkage (GWL) data from several studies of neuroticism and anxiety disorders have been published, providing an opportunity to test such hypotheses and identify genomic regions that harbor genes common to these phenotypes. In all, 11 independent GWL studies of either neuroticism (n=8) or anxiety disorders (n=3) were collected, which comprised of 5341 families with 15 529 individuals. The rank-based genome scan meta-analysis (GSMA) approach was used to analyze each trait separately and combined, and global correlations between results were examined. False discovery rate (FDR) analysis was performed to test for enrichment of significant effects. Using 10 cM intervals, bins nominally significant for both GSMA statistics, PSR and POR, were found on chromosomes 9, 11, 12, and 14 for neuroticism and on chromosomes 1, 5, 15, and 16 for anxiety disorders. Genome-wide, the results for the two phenotypes were significantly correlated, and a combined analysis identified additional nominally significant bins. Although none reached genome-wide significance, an excess of significant PSRP-values were observed, with 12 bins falling under a FDR threshold of 0.50. As demonstrated by our identification of multiple, consistent signals across the genome, meta-analytically combining existing GWL data is a valuable approach to narrowing down regions relevant for anxiety-related phenotypes. This may prove useful for prioritizing emerging genome-wide association data for anxiety disorders.
PMCID: PMC3449070  PMID: 22473089
anxiety; neuroticism; panic disorder; linkage; meta-analysis
15.  Ablating Adult Neurogenesis in the Rat Has No Effect on Spatial Processing: Evidence from a Novel Pharmacogenetic Model 
PLoS Genetics  2013;9(9):e1003718.
The function of adult neurogenesis in the rodent brain remains unclear. Ablation of adult born neurons has yielded conflicting results about emotional and cognitive impairments. One hypothesis is that adult neurogenesis in the hippocampus enables spatial pattern separation, allowing animals to distinguish between similar stimuli. We investigated whether spatial pattern separation and other putative hippocampal functions of adult neurogenesis were altered in a novel genetic model of neurogenesis ablation in the rat. In rats engineered to express thymidine kinase (TK) from a promoter of the rat glial fibrillary acidic protein (GFAP), ganciclovir treatment reduced new neurons by 98%. GFAP-TK rats showed no significant difference from controls in spatial pattern separation on the radial maze, spatial learning in the water maze, contextual or cued fear conditioning. Meta-analysis of all published studies found no significant effects for ablation of adult neurogenesis on spatial memory, cue conditioning or ethological measures of anxiety. An effect on contextual freezing was significant at a threshold of 5% (P = 0.04), but not at a threshold corrected for multiple testing. The meta-analysis revealed remarkably high levels of heterogeneity among studies of hippocampal function. The source of this heterogeneity remains unclear and poses a challenge for studies of the function of adult neurogenesis.
Author Summary
Adult neurogenesis occurs in the rodent brain, but its function remains unclear. Current theories support the view that adult neurogenesis in the hippocampus supports pattern separation in the hippocampus, thereby allowing animals to distinguish between similar, overlapping inputs. However the effects of pharmacological, radiation and genetic ablation of adult neurogenesis on putative hippocampal functions have been inconsistent. We developed a novel genetic model to ablate adult neurogenesis in the rat. We found that we could reduce adult neurogenesis by 98%. Rats without adult neurogenesis showed no significant difference from controls in learning and memory tasks nor spatial pattern separation. We investigated the sources of heterogeneity in published results using a meta-analysis. The source of this heterogeneity remains unclear and poses a challenge for studies of the function of adult neurogenesis.
PMCID: PMC3764151  PMID: 24039591
16.  Genome-wide Generation and Systematic Phenotyping of Knockout Mice Reveals New Roles for Many Genes 
Cell  2013;154(2):452-464.
Mutations in whole organisms are powerful ways of interrogating gene function in a realistic context. We describe a program, the Sanger Institute Mouse Genetics Project, that provides a step toward the aim of knocking out all genes and screening each line for a broad range of traits. We found that hitherto unpublished genes were as likely to reveal phenotypes as known genes, suggesting that novel genes represent a rich resource for investigating the molecular basis of disease. We found many unexpected phenotypes detected only because we screened for them, emphasizing the value of screening all mutants for a wide range of traits. Haploinsufficiency and pleiotropy were both surprisingly common. Forty-two percent of genes were essential for viability, and these were less likely to have a paralog and more likely to contribute to a protein complex than other genes. Phenotypic data and more than 900 mutants are openly available for further analysis.
Graphical Abstract
•Large openly available resource of targeted mouse mutants and phenotypic data•Screen for broad range of disease features and traits•Many novel phenotypes suggest functions for both studied and unstudied genes•Haploinsufficiency and pleiotropy are common
More than 900 new mutant mice lines and a multifaceted phenotypic screening platform reveal unanticipated pleiotropies, widespread effects of haploinsufficiency, potential disease models, and functions for unstudied genes.
PMCID: PMC3717207  PMID: 23870131
17.  Causes and Consequences of Chromatin Variation between Inbred Mice 
PLoS Genetics  2013;9(6):e1003570.
Variation at regulatory elements, identified through hypersensitivity to digestion by DNase I, is believed to contribute to variation in complex traits, but the extent and consequences of this variation are poorly characterized. Analysis of terminally differentiated erythroblasts in eight inbred strains of mice identified reproducible variation at approximately 6% of DNase I hypersensitive sites (DHS). Only 30% of such variable DHS contain a sequence variant predictive of site variation. Nevertheless, sequence variants within variable DHS are more likely to be associated with complex traits than those in non-variant DHS, and variants associated with complex traits preferentially occur in variable DHS. Changes at a small proportion (less than 10%) of variable DHS are associated with changes in nearby transcriptional activity. Our results show that whilst DNA sequence variation is not the major determinant of variation in open chromatin, where such variants exist they are likely to be causal for complex traits.
Author Summary
Regulatory sites of the genome affect gene expression and complex traits, including disease susceptibility. Variable regulatory sites are potentially interesting because they are a likely cause of phenotypic variation, providing a bridge between sequence and transcriptional variation. In this paper we identify regions of the genome where DNA is not wrapped up in chromatin (hence potentially regulatory) in eight inbred strains of mice. We compare sites that vary among strains and compare them to non-variable sites. We show that more than half of variable sites cannot be attributed to local sequence variation. Functional consequences (in terms of readily detectable changes in gene expression) are associated with less than 10% of variable DNase I hypersensitive sites. We show that variable sites are enriched for sequence variants contributing to complex traits in mice.
PMCID: PMC3681629  PMID: 23785304
18.  Candidate and non-candidate genes in behavior genetics 
► Common variants of small effect contribute to psychiatric disease. ► Rare de novo mutations occur in the exons of patients with schizophrenia and autism. ► Effect sizes of loci influencing brain size are comparable to those of other phenotypes. ► The literature of imaging genetic studies contains many false positives. ► Studies on gene by environment interaction are mostly underpowered.
In this review we discuss recent developments in psychiatric genetics: on the one hand, studies using whole genome approaches (genome-wide association studies (GWAS) and exome sequencing) are coming close to finding genes and molecular variants that contribute to disease susceptibility; on the other candidate genes, such as the serotonin transporter, continue to dominate in genetic studies of brain imaging phenotypes and in protracted searches for gene by environment interactions. These two areas intersect, in that new information about genetic effects from whole genome approaches, should (but does not always) inform the single locus analyses.
PMCID: PMC3752971  PMID: 22878161
19.  Mutation of the Diamond-Blackfan Anemia Gene Rps7 in Mouse Results in Morphological and Neuroanatomical Phenotypes 
PLoS Genetics  2013;9(1):e1003094.
The ribosome is an evolutionarily conserved organelle essential for cellular function. Ribosome construction requires assembly of approximately 80 different ribosomal proteins (RPs) and four different species of rRNA. As RPs co-assemble into one multi-subunit complex, mutation of the genes that encode RPs might be expected to give rise to phenocopies, in which the same phenotype is associated with loss-of-function of each individual gene. However, a more complex picture is emerging in which, in addition to a group of shared phenotypes, diverse RP gene-specific phenotypes are observed. Here we report the first two mouse mutations (Rps7Mtu and Rps7Zma) of ribosomal protein S7 (Rps7), a gene that has been implicated in Diamond-Blackfan anemia. Rps7 disruption results in decreased body size, abnormal skeletal morphology, mid-ventral white spotting, and eye malformations. These phenotypes are reported in other murine RP mutants and, as demonstrated for some other RP mutations, are ameliorated by Trp53 deficiency. Interestingly, Rps7 mutants have additional overt malformations of the developing central nervous system and deficits in working memory, phenotypes that are not reported in murine or human RP gene mutants. Conversely, Rps7 mouse mutants show no anemia or hyperpigmentation, phenotypes associated with mutation of human RPS7 and other murine RPs, respectively. We provide two novel RP mouse models and expand the repertoire of potential phenotypes that should be examined in RP mutants to further explore the concept of RP gene-specific phenotypes.
Author Summary
Ribosomes are composed of two subunits that each consist of a large number of proteins, and their function of translating mRNA into protein is essential for cell viability. Naturally occurring or genetically engineered mutations within an individual ribosomal protein provide a valuable resource, since the resulting abnormal phenotypes reveal the function of each ribosomal protein. A number of mutations recently identified in mammalian ribosomal subunit genes have confirmed that homozygous loss of function consistently results in lethality; however, haploinsufficiency causes a variety of tissue-specific phenotypes. In this paper, we describe the first mutant alleles of the gene encoding ribosomal protein S7 (Rps7) in mouse. Rps7 haploinsufficiency causes decreased size, abnormal skeletal morphology, mid-ventral white spotting, and eye malformations, phenotypes that also occur with haploinsufficiency for other ribosomal subunits. Additionally, significant apoptosis occurs within the developing central nervous system (CNS) along with subtle behavioral phenotypes, suggesting RPS7 is required for CNS development. Mutation of human RPS7 has been implicated in Diamond-Blackfan anemia (DBA), yet the murine alleles do not present an analogous phenotype. The phenotypes we observe in the Rps7 mouse mutants indicate RPS7 should be considered as a candidate for a broader spectrum of human diseases.
PMCID: PMC3561062  PMID: 23382688
20.  Prioritization and Association Analysis of Murine-Derived Candidate Genes in Anxiety-Spectrum Disorders 
Biological psychiatry  2011;70(9):888-896.
Anxiety disorders are common psychiatric conditions that are highly comorbid with each other and related phenotypes such as depression, likely due to a shared genetic basis. Fear-related behaviors in mice have long been investigated as potential models of anxiety disorders, making integration of information from both murine and human genetic data a powerful strategy for identifying potential susceptibility genes for these conditions.
We combined genome-wide association analysis of fear-related behaviours with strain distribution pattern analysis in heterogeneous stock mice to identify a preliminary list of 52 novel candidate genes. We ranked these according to three complementary sources of prior anxiety-related genetic data: (1) extant linkage and knock-out studies in mice, (2) a meta-analysis of human linkage scans, and (3) a preliminary human genomewide association study. We genotyped tagging SNPs covering the nine top-ranked regions in a two-stage association study of 1316 subjects from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders chosen for high or low genetic loading for anxiety-spectrum phenotypes (anxiety disorders, neuroticism, and major depression).
Multiple SNPs in the PPARGC1A gene demonstrated association in both stages that survived gene-wise correction for multiple testing.
Integration of genetic data across human and murine studies suggests PPARGC1A as a potential susceptibility gene for anxiety-related disorders.
PMCID: PMC3191234  PMID: 21871609
anxiety disorder; depression; internalizing; candidate gene; genetic association; data integration
21.  Cofilin-1: A Modulator of Anxiety in Mice 
PLoS Genetics  2012;8(10):e1002970.
The genes involved in conferring susceptibility to anxiety remain obscure. We developed a new method to identify genes at quantitative trait loci (QTLs) in a population of heterogeneous stock mice descended from known progenitor strains. QTLs were partitioned into intervals that can be summarized by a single phylogenetic tree among progenitors and intervals tested for consistency with alleles influencing anxiety at each QTL. By searching for common Gene Ontology functions in candidate genes positioned within those intervals, we identified actin depolymerizing factors (ADFs), including cofilin-1 (Cfl1), as genes involved in regulating anxiety in mice. There was no enrichment for function in the totality of genes under each QTL, indicating the importance of phylogenetic filtering. We confirmed experimentally that forebrain-specific inactivation of Cfl1 decreased anxiety in knockout mice. Our results indicate that similarity of function of mammalian genes can be used to recognize key genetic regulators of anxiety and potentially of other emotional behaviours.
Author Summary
Thousands of small effect loci are believed to contribute to behavioural variation in mammals. Their abundance and small size frustrate gene identification and make it difficult to know which among them are central to the responsible biological mechanisms. Using imputed genome sequences from 2,000 outbred mice and by testing for an enrichment of functional annotations, we identify 167 candidate genes involved in anxiety. Unexpectedly, annotations implicate actin depolymerizing factors (ADFs), including cofilin-1 (Cfl1), as being involved with the expression of anxiety phenotypes in mice. We confirmed that forebrain-specific inactivation of Cfl1 decreased anxiety in knockout mice.
PMCID: PMC3464202  PMID: 23055942
22.  Genetics of arthritis severity: a genome-wide and species-wide dissection in HS mice 
Arthritis and Rheumatism  2011;63(9):2630-2640.
Susceptibility to inflammatory arthritis is determined by a complex set of environmental and genetic factors, but only a portion of the genetic effect can be explained. Conventional genome-wide screens of arthritis models using crosses between inbred mice have been hampered by the low resolution of results and by the restricted range of natural genetic variation sampled. We sought to address these limitations by performing a genome-wide screen for determinants of arthritis severity using a genetically heterogeneous cohort of mice.
Heterogeneous Stock (HS) mice derive from eight founder inbred strains by serial intercrossing (N>60), resulting in fine-grained genetic variation. With a cohort of 570 HS mice, we performed a genome-wide screen for determinants of severity in the K/BxN serum-transfer arthritis model.
We mapped regions on chromosomes 1, 2, 4, 6, 7 and 15 that contain QTLs influencing arthritis severity at a resolution of a few Mb. In several instances, these regions proved to contain 2 QTLs: the region on chromosome 2 includes the C5 fraction of complement known to be required for K/BxN arthritis, but also contained a second adjacent QTL, for which an intriguing candidate is Ptgs1 (Cox-1). Interesting candidates on Chr4 include the Padi gene family, encoding peptidyl-arginine-deiminases responsible for citrulline protein modification; suggestively, Padi2 and Padi4 RNA expression was correlated with arthritis severity in HS mice.
These results provide a broad overview of the genetic variation that controls the severity of K/BxN arthritis and suggest intriguing candidate genes for further study.
PMCID: PMC3371645  PMID: 21560115
23.  Epilogue: Lessons from the CONVERGE study of major depressive disorder in China 
Journal of Affective Disorders  2012;140-334(1):1-5.
This review summarizes the first clinical reports from the CONVERGE consortium: China, Oxford and VCU Experimental Research on Genetic Epidemiology. CONVERGE sets out to investigate the nature and mode of action of the genetic and environmental risk factors for major depressive disorder (MDD). CONVERGE aims to collect 6000 cases of recurrent MDD and 6000 controls. The consortium includes hospitals in 30 cities, all with populations exceeding 5 million, and has collected over 2000 cases and controls. High quality phenotype data on MDD collected in China is now available to determine the source and nature of this highly heterogeneous condition. Analyses reported in a series of papers indicate that the clinical features and risk factors of MDD are sufficiently similar to those in the West that we can confidently predict that the results of subsequent analyses will be widely applicable.
PMCID: PMC3387371  PMID: 21955396
Major depressive disorder; China; Co-morbidity; Anxiety
24.  Sequence based characterization of structural variation in the mouse genome 
Nature  2011;477(7364):326-329.
Structural variation is widespread in mammalian genomes1,2 and is an important cause of disease3, but just how abundant and important structural variants (SVs) are in shaping phenotypic variation remains unclear4,5. Without knowing how many SVs there are, and how they arise, it is difficult to discover what they do. Combining experimental with automated analyses, we identified 0.71M SVs at 0.28M sites in the genomes of thirteen classical and four wild-derived inbred mouse strains. The majority of SVs are less than 1 kilobase in size and 98% are deletions or insertions. The breakpoints of 0.16M SVs were mapped to base pair resolution allowing us to infer that insertion of retrotransposons causes more than half of SVs. Yet, despite their prevalence, SVs are less likely than other sequence variants to cause gene-expression or quantitative phenotypic variation. We identified 24 SVs that disrupt coding exons, acting as rare variants of large effect on gene function. One third of the genes so affected have immunological functions.
PMCID: PMC3428933  PMID: 21921916
25.  Development, validation and evaluation of a rapid PCR-nucleic acid lateral flow immuno-assay for the detection of Plasmodium and the differentiation between Plasmodium falciparum and Plasmodium vivax 
Malaria Journal  2012;11:279.
Molecular tools are very sensitive and specific and could be an alternative for the diagnosis of malaria. The complexity and need for expensive equipment may hamper implementation and, therefore, simplifications to current protocols are warranted.
A PCR detecting the different Plasmodium species and differentiating between Plasmodium falciparum and Plasmodium vivax was developed and combined with a nucleic acid lateral flow immuno-assay (PCR-NALFIA) for amplicon detection. The assay was thoroughly evaluated for the analytical sensitivity and specificity in the laboratory, the robustness and reproducibility in a ring trial and accuracy and predictive value in a field trial.
The analytical sensitivity and specificity were 0.978 (95% CI: 0.932–0.994) and 0.980 (95% CI: 0.924-0.997), respectively, and were slightly less sensitive for the detection of P. vivax than for P. falciparum. The reproducibility tested in three laboratories was very good (k = 0.83). This evaluation showed that the PCR machine used could influence the results. Accuracy was evaluated in Thailand and compared to expert microscopy and rapid diagnostic tests (RDTs). The overall and P. falciparum-specific sensitivity and specificity was good ranging from 0.86-1 and 0.95-0.98 respectively, compared to microscopy. Plasmodium vivax detection was better than the sensitivity of RDT, but slightly less than microscopy performed in this study.
PCR-NALFIA is a sensitive, specific and robust assay able to identify Plasmodium species with good accuracy. Extensive testing including a ring trial can identify possible bottlenecks before implementation and is therefore essential to perform in additon to other evaluations.
PMCID: PMC3459699  PMID: 22900750

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