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1.  Lead Exposure Disrupts Global DNA Methylation in Human Embryonic Stem Cells and Alters Their Neuronal Differentiation 
Toxicological Sciences  2014;139(1):142-161.
Exposure to lead (Pb) during childhood can result in learning disabilities and behavioral problems. Although described in animal models, whether Pb exposure also alters neuronal differentiation in the developing brains of exposed children is unknown. Here, we investigated the effects of physiologically relevant concentrations of Pb (from 0.4 to 1.9μM) on the capacity of human embryonic stem cells (hESCs) to progress to a neuronal fate. We found that neither acute nor chronic exposure to Pb prevented hESCs from generating neural progenitor cells (NPCs). NPCs derived from hESCs chronically exposed to 1.9μM Pb throughout the neural differentiation process generated 2.5 times more TUJ1-positive neurons than those derived from control hESCs. Pb exposure of hESCs during the stage of neural rosette formation resulted in a significant decrease in the expression levels of the neural marker genes PAX6 and MSI1. Furthermore, the resulting NPCs differentiated into neurons with shorter neurites and less branching than control neurons, as assessed by Sholl analysis. DNA methylation studies of control, acutely treated hESCs and NPCs derived from chronically exposed hESCs using the Illumina HumanMethylation450 BeadChip demonstrated that Pb exposure induced changes in the methylation status of genes involved in neurogenetic signaling pathways. In summary, our study shows that exposure to Pb subtly alters the neuronal differentiation of exposed hESCs and that these changes could be partly mediated by modifications in the DNA methylation status of genes crucial to brain development.
PMCID: PMC4023291  PMID: 24519525
Heavy metal; lead; human embryonic stem cell; neuronal differentiation; DNA methylation
2.  Massively parallel resequencing of the isogenic Drosophila melanogaster strain w1118; iso-2; iso-3 identifies hotspots for mutations in sensory perception genes 
Fly  2009;3(3):192-203.
We used the Illumina reversible-short sequencing technology to obtain 17-fold average depth (s.d. ~8) of ~94% of the euchromatic genome and ~1–5% of the heterochromatin sequence of the Drosophila melanogaster isogenic strain w1118; iso-2; iso-3. We show that this strain has a ~9 kb deletion that uncovers the first exon of the white (w) gene, ~4 kb of downstream promoter sequences, and most of the first intron, thus demonstrating that whole-genome sequencing can be used for mutation characterization. We chose this strain because there are thousands of transposon insertion lines and hundreds of isogenic deficiency lines available with this genetic background, such as the Exelixis, Inc., and the DrosDEL collections. We compared our sequence to Release 5 of the finished reference genome sequence which was made from the isogenic strain y1; cn1 bw1 sp1 and identified 356,614 candidate SNPs in the ~117 Mb unique sequence genome, which represents a substitution rate of ~1/305 nucleotides (~0.30%). The distribution of SNPs is not uniform, but rather there is a ~2-fold increase in SNPs on the autosome arms compared with the X chromosome and a ~7-fold increase when compared to the small 4th chromosome. This is consistent with previous analyses that demonstrated a correlation between recombination frequency and SNP frequency. An unexpected finding was a SNP hotpot in a ~20 Mb central region of the 4th chromosome, which might indicate higher than expected recombination frequency in this region of this chromosome. Interestingly, genes involved in sensory perception are enriched in SNP hotspots and genes encoding developmental genes are enriched in SNP coldspots, which suggests that recombination frequencies might be proportional to the evolutionary selection coefficient. There are currently 12 Drosophila species sequenced, and this represents one of many isogenic Drosophila melanogaster genome sequences that are in progress. Because of the dramatic increase in power in using isogenic lines rather than outbred individuals, the SNP information should be valuable as a test bed for understanding genotype-by-environment interactions in human population studies.
PMCID: PMC3839425  PMID: 19690466
personal genomes; Drosophila melanogaster; whole-genome SNP analysis
3.  A program for annotating and predicting the effects of single nucleotide polymorphisms, SnpEff 
Fly  2012;6(2):80-92.
We describe a new computer program, SnpEff, for rapidly categorizing the effects of variants in genome sequences. Once a genome is sequenced, SnpEff annotates variants based on their genomic locations and predicts coding effects. Annotated genomic locations include intronic, untranslated region, upstream, downstream, splice site, or intergenic regions. Coding effects such as synonymous or non-synonymous amino acid replacement, start codon gains or losses, stop codon gains or losses, or frame shifts can be predicted.
Here the use of SnpEff is illustrated by annotating ~356,660 candidate SNPs in ~117 Mb unique sequences, representing a substitution rate of ~1/305 nucleotides, between the Drosophila melanogaster w1118; iso-2; iso-3 strain and the reference y1; cn1 bw1 sp1 strain. We show that ~15,842 SNPs are synonymous and ~4,467 SNPs are non-synonymous (N/S ~0.28). The remaining SNPs are in other categories, such as stop codon gains (38 SNPs), stop codon losses (8 SNPs), and start codon gains (297 SNPs) in the 5′UTR. We found, as expected, that the SNP frequency is proportional to the recombination frequency (i.e., highest in the middle of chromosome arms). We also found that start-gain or stop-lost SNPs in Drosophila melanogaster often result in additions of N-terminal or C-terminal amino acids that are conserved in other Drosophila species. It appears that the 5′ and 3′ UTRs are reservoirs for genetic variations that changes the termini of proteins during evolution of the Drosophila genus.
As genome sequencing is becoming inexpensive and routine, SnpEff enables rapid analyses of whole-genome sequencing data to be performed by an individual laboratory.
PMCID: PMC3679285  PMID: 22728672
Drosophila melanogaster; Personal Genomes; next generation DNA sequencing; whole-genome SNP analysis
4.  Using Drosophila melanogaster as a Model for Genotoxic Chemical Mutational Studies with a New Program, SnpSift 
This paper describes a new program SnpSift for filtering differential DNA sequence variants between two or more experimental genomes after genotoxic chemical exposure. Here, we illustrate how SnpSift can be used to identify candidate phenotype-relevant variants including single nucleotide polymorphisms, multiple nucleotide polymorphisms, insertions, and deletions (InDels) in mutant strains isolated from genome-wide chemical mutagenesis of Drosophila melanogaster. First, the genomes of two independently isolated mutant fly strains that are allelic for a novel recessive male-sterile locus generated by genotoxic chemical exposure were sequenced using the Illumina next-generation DNA sequencer to obtain 20- to 29-fold coverage of the euchromatic sequences. The sequencing reads were processed and variants were called using standard bioinformatic tools. Next, SnpEff was used to annotate all sequence variants and their potential mutational effects on associated genes. Then, SnpSift was used to filter and select differential variants that potentially disrupt a common gene in the two allelic mutant strains. The potential causative DNA lesions were partially validated by capillary sequencing of polymerase chain reaction-amplified DNA in the genetic interval as defined by meiotic mapping and deletions that remove defined regions of the chromosome. Of the five candidate genes located in the genetic interval, the Pka-like gene CG12069 was found to carry a separate pre-mature stop codon mutation in each of the two allelic mutants whereas the other four candidate genes within the interval have wild-type sequences. The Pka-like gene is therefore a strong candidate gene for the male-sterile locus. These results demonstrate that combining SnpEff and SnpSift can expedite the identification of candidate phenotype-causative mutations in chemically mutagenized Drosophila strains. This technique can also be used to characterize the variety of mutations generated by genotoxic chemicals.
PMCID: PMC3304048  PMID: 22435069
personal genomes; Drosophila melanogaster; whole-genome SNP analysis; next-generation DNA sequencing
5.  Admixture mapping of lung cancer in 1812 African-Americans 
Carcinogenesis  2010;32(3):312-317.
Lung cancer continues to be the leading cause of cancer death in the USA and the best example of a cancer with undisputed evidence of environmental risk. However, a genetic contribution to lung cancer has also been demonstrated by studies of familial aggregation, family-based linkage, candidate gene studies and most recently genome-wide association studies (GWAS). The African-American population has been underrepresented in these genetic studies and has patterns of cigarette use and linkage disequilibrium that differ from patterns in other populations. Therefore, studies in African-Americans can provide complementary data to localize lung cancer susceptibility genes and explore smoking dependence-related genes. We used admixture mapping to further characterize genetic risk of lung cancer in a series of 837 African-American lung cancer cases and 975 African-American controls genotyped at 1344 ancestry informative single-nucleotide polymorphisms. Both case-only and case–control analyses were conducted using ADMIXMAP adjusted for age, sex, pack-years of smoking, family history of lung cancer, history of emphysema and study site. In case-only analyses, excess European ancestry was observed over a wide region on chromosome 1 with the largest excess seen at rs6587361 for non-small-cell lung cancer (NSCLC) (Z-score = −4.33; P = 1.5 × 10−5) and for women with NSCLC (Z-score = −4.82; P = 1.4 × 10−6). Excess African ancestry was also observed on chromosome 3q with a peak Z-score of 3.33 (P = 0.0009) at rs181696 among ever smokers with NSCLC. These results add to the findings from the GWAS in Caucasian populations and suggest novel regions of interest.
PMCID: PMC3047238  PMID: 21115650
6.  Factors predicting inhaled corticosteroid responsiveness in African American patients with asthma 
African American patients suffer disproportionately from uncontrolled asthma. Treatment with an inhaled corticosteroid (ICS) is considered first-line therapy for persistent asthma.
To determine the degree to which African American patients respond to ICS medication and whether the level of response is influenced by other factors, including genetic ancestry.
Patients aged 12-56 years who received care from a large health system in southeast Michigan and who resided in Detroit were recruited to participate if they had a diagnosis of asthma. Patients were treated with 6 weeks of inhaled beclomethasone dipropionate, and pulmonary function was re-measured after treatment. Ancestry was determined by genotyping ancestry informative markers. The main outcome measure was ICS responsiveness defined as the change in pre-bronchodilator FEV1 over the 6-week course of treatment.
Among 147 participating African American patients with asthma, average improvement in FEV1 following 6 weeks of ICS treatment was 11.6%. The mean proportion of African ancestry in this group was 78.4%. The degree of baseline bronchodilator reversibility was the only factor consistently associated ICS responsiveness as measured by both an improvement in FEV1 and in patient reported asthma control (P=0.001 and P=0.021, respectively). The proportion of African ancestry was not significantly associated with ICS responsiveness.
While baseline pulmonary function parameters appear to be associated with the likelihood to respond to ICS treatment, the proportion of genetic African ancestry does not. This study suggests that genetic ancestry may not contribute to differences in ICS controller response among African American patients with asthma.
Clinical Implications
Although African American patients suffer disproportionately from asthma-related complications, response to ICS controller therapy does not appear to be dependent on an individual’s proportion of African ancestry.
Capsule summary
Personalized medicine will be most beneficial to groups disproportionately affected by disease complications. Here we find baseline bronchodilator reversibility but not African ancestry to be associated with ICS responsiveness among African American patients with asthma.
PMCID: PMC2998569  PMID: 20864153
inhaled corticosteroids; asthma; race-ethnicity; continental population groups; ancestry; urban health
7.  Dietary fatty acids, luminal modifiers, and risk of colorectal cancer 
Inconsistent observations in epidemiologic studies on the association between total fat intake and colorectal cancer may be ascribed to opposing effects of individual fatty acids and the presence of other dietary constituents that modify luminal or systemic lipid exposure. We analyzed the data from a population-based case-control study that included 1163 cases and 1501 controls to examine the effects of individual fatty acid groups on colorectal cancer risk as well as their interactions with calcium and fiber intake. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by unconditional logistic regression model according to quartile levels of energy-adjusted fatty acid intake. In the bivariable analyses, the risk of colorectal cancer increased with trans fatty acid (TFA) intake (OR for top vs bottom quartile =1.46, 95% CI 1.17-1.59, p-value for a trend <0.001 ), but the associations was substantially attenuated in multivariable analyses (p-value for a trend =0.176). However, a significant linear trend in the multivariable OR (p=0.029) for TFA was present for subjects with lower calcium intake. Furthermore, multivariable ORs progressively decreased with increasing both omega-3 and omega-6 polyunsaturated fatty acid intake (P-values for linear trend: 0.033 and 0.011, respectively) for subjects with lower dietary fiber intake. These interactions were also significant or marginally significant (P = 0.085 for TFA, 0.029 for omega-3 and 0.068 for omega-6). Our results suggest that populations with lower intake of luminal modifiers, i.e., calcium and fiber, may have differential risks of colorectal cancer associated with dietary fatty acid intake.
PMCID: PMC2891322  PMID: 19998336
Fatty acids; colorectal cancer; case-control study; calcium; fiber
8.  Results from a Prostate Cancer Admixture Mapping Study in African American Men 
Human genetics  2009;126(5):637-642.
There are considerable racial disparities in prostate cancer risk, with a 60% higher incidence rate among African American (AA) men compared with European American (EA) men, and a 2.4 fold higher mortality rate in AA men than in EA men. Recently, studies have implicated several African-ancestry associated prostate cancer susceptibility loci on chromosome 8q24. In the current study, we performed admixture mapping in AA men from two independent case-control studies of prostate cancer to confirm the 8q24 ancestry association and also identify other genomic regions that may harbor prostate cancer susceptibility genes. A total of 482 cases and 261 controls were genotyped for 1,509 ancestry informative markers across the genome. The mean estimated individual admixture proportions were 20% European and 80% African. The most significant observed increase in European ancestry occurred at rs2141360 on chromosome 7q31 in both the case-only (p=0.0000035) and case-control analyses. The most significant observed increase in African ancestry across the genome occurred at a locus on chromosome 5q35 identified by SNPs rs7729084 (case-only analysis: p=0.002), and rs12474977 (case-control analysis: p=0.004), which are separated by 646 kb and were adjacent to one another on the panel. On chromosome 8, rs4367565 was associated with the greatest excess African ancestry in both the case-only and case-control analyses (case-only and case-control p=0.02), confirming previously reported African-ancestry associations with chromosome 8q24. In conclusion, we confirmed ancestry associations on 8q24, and identified additional ancestry-associated regions potentially harboring prostate cancer susceptibility loci.
PMCID: PMC2975267  PMID: 19568772
Prostate Cancer; Admixture Mapping; Ancestry; PODXL; DOCK4
9.  Tobacco and estrogen metabolic polymorphisms and risk of non-small cell lung cancer in women 
Carcinogenesis  2009;30(4):626-635.
To explore the potential role for estrogen in lung cancer susceptibility, candidate single-nucleotide polymorphism (SNPs) in tobacco and estrogen metabolism genes were evaluated. Population-based cases (n = 504) included women aged 18–74, diagnosed with NSCLC in metropolitan Detroit between November 2001 and October 2005. Population-based controls (n = 527) were identified through random digit dialing and matched on race and age. Eleven SNPs in 10 different genes were examined in relation to risk: CYP1A1 Msp1, CYP1A1 Ile462Val, CYP1B1 Leu432Val, CYP17, CYP19A1, XRCC1 Gln399Arg, COMT Val158Met, NQO1 Pro187Ser, GSTM1, GSTT1 and GSTP1 Ile105Val. Lung cancer risk associated with individual SNPs was seen for GSTP1 [A allele; odds ratio (OR) = 1.85; 95% confidence interval (CI), 1.04–3.27] and XRCC1 (A/A genotype; OR = 1.68; 95% CI, 1.01–2.79) in white women and CYP1B1 (G allele; OR = 11.1; 95% CI, 1.18–104) in black women smokers. White women smokers carrying two risk genotypes at the following loci were at increased risk of lung cancer compared with individuals not carrying risk alleles at these loci: CYP17 and GSTM1, COMT and GSTM1, CYP17 and GSTT1, XRCC1 and GSTP1, CYP1B1 and XRCC1 and COMT and XRCC1. The most parsimonious model of lung cancer risk in white smoking women included age, family history of lung cancer, history of chronic lung disease, pack-years, body mass index, XRCC1 A/A genotype, GSTM1 null and COMT A/G or G/G genotype. These findings support the need for continued study of estrogen in relation to lung cancer risk. Polymorphisms in the tobacco metabolism, estrogen metabolism and DNA repair pathways will be useful in developing more predictive models of individual risk.
PMCID: PMC2664455  PMID: 19174490
10.  BDNF Val66Met Polymorphism Influences Age Differences in Microstructure of the Corpus Callosum 
Brain-derived neurotrophic factor (BDNF) plays an important role in neuroplasticity and promotes axonal growth, but its secretion, regulated by a BDNF gene, declines with age. The low-activity (met) allele of common polymorphism BDNF val66met is associated with reduced production of BDNF. We examined whether age-related reduction in the integrity of cerebral white matter (WM) depends on the BDNF val66met genotype. Forty-one middle-aged and older adults participated in the study. Regional WM integrity was assessed by fractional anisotropy (FA) computed from manually drawn regions of interest in the genu and splenium of the corpus callosum on diffusion tensor imaging scans. After controlling for effects of sex and hypertension, we found that only the BDNF 66met carriers displayed age-related declines in the splenium FA, whereas no age-related declines were shown by BDNF val homozygotes. No genotype-related differences were observed in the genu of the corpus callosum. This finding is consistent with a view that genetic risk for reduced BDNF affects posterior regions that otherwise are considered relatively insensitive to normal aging. Those individuals with a genetic predisposition for decreased BDNF expression may not be able to fully benefit from BDNF-based plasticity and repair mechanisms.
PMCID: PMC2737488  PMID: 19738930
brain; diffusion tensor imaging; genetics; MRI; white matter; aging; brain-derived neurotrophic factor; single nucleotide polymorphism
11.  Brain-Derived Neurotrophic Factor Val66Met and Blood Glucose: A Synergistic Effect on Memory 
Age-related declines in episodic memory performance are frequently reported, but their mechanisms remain poorly understood. Although several genetic variants and vascular risk factors have been linked to mnemonic performance in general and age differences therein, it is unknown whether and how they modify age-related memory declines. To address that question, we investigated the effect of Brain-Derived Neurotrophic Factor (BDNF) Val66Met polymorphism that affects secretion of BDNF, and fasting blood glucose level (a vascular risk factor) on episodic memory in a sample of healthy volunteers (age 19–77). We found that advanced age and high-normal blood glucose levels were associated with reduced recognition memory for name-face associations and poorer prose recall. However, elevated blood glucose predicted lower memory scores only in carriers of the BDNF 66Met allele. The effect on associative memory was stronger than on free recall. These findings indicate that even low-level vascular risk can produce negative cognitive effects in genetically susceptible individuals. Alleviation of treatable vascular risks in such persons may have a positive effect on age-related cognitive declines.
PMCID: PMC2572208  PMID: 18958212
aging; BDNF; memory; vascular risk; single nucleotide polymorphism; paired-associates; recognition; free recall

Results 1-11 (11)