Tomas Drgon

Rho1p, a yeast protein at the interface between cell polarization and morphogenesis

The enzyme that catalyzes the synthesis of the major structural component of the yeast cell wall, β(1→3)-D-glucan synthase (also known as 1,3-β-glucan synthase), requires a guanosine triphosphate (GTP) binding protein for activity. The GTP binding protein was identified as Rho1p. The rho1 mutants were defective in GTP stimulation of glucan synthase, and the defect was corrected by addition of purified or recombinant Rho1p. A protein missing in purified preparations from a rho1 strain was identified as Rho1p. Rho1p also regulates protein kinase C, which controls a mitogen-activated protein kinase cascade. Experiments with a dominant positive PKC1 gene showed that the two effects of Rho1p are independent of each other. The colocalization of Rho1p with actin patches at the site of bud emergence and the role of Rho1p in cell wall synthesis emphasize the importance of Rho1p in polarized growth and morphogenesis.

Human Brain Derived Neurotrophic Factor (BDNF) Genes, Splicing Patterns, and Assessments of Associations with Substance Abuse and Parkinson's Disease

Potential roles for variants in the human BDNF gene in human brain disorders are supported by findings that include: (a) influences that this trophic factor can exert on important neurons, brain regions, and neurotransmitter systems, (b) changes in BDNF expression that follow altered neuronal activity and drug treatments, and (c) linkages or associations between genetic markers in or near BDNF and human traits and disorders that include depression, schizophrenia, addictions, and Parkinsons disease. We now report assembly of more than 70 kb of BDNF genomic sequence, delineation of 7 noncoding and 1 coding human BDNF exons, elucidation of BDNF transcripts that are initiated at several alternative promoters, identification of BDNF mRNA splicing patterns, elucidation of novel sequences that could contribute to activity‐dependent BDNF mRNA transcription, targeting and/or translation, elucidation of tissue‐specific and brain‐region‐specific use of the alternative human BDNF promoters and splicing patterns, identification of single nucleotide polymorphism (SNP), and simple sequence length polymorphism (SSLP) BDNF genomic variants and identification of patterns of restricted haplotype diversity at the BDNF locus. We also identified type 2 BDNF‐locus transcripts that are coded by a novel gene that is overlapped with type 1 BDNF gene and transcribed in reverse orientation with several alternative splicing isoforms. Association studies of BDNF variants reveal no associations with Parkinsons disease. Comparisons between substance abusers and controls reveal modest associations. These findings increase interest in this diverse human gene. Published 2005 Wiley‐Liss, Inc.

Molecular genetics of nicotine dependence and abstinence: whole genome association using 520,000 SNPs

BackgroundClassical genetic studies indicate that nicotine dependence is a substantially heritable complex disorder. Genetic vulnerabilities to nicotine dependence largely overlap with genetic vulnerabilities to dependence on other addictive substances. Successful abstinence from nicotine displays substantial heritable components as well. Some of the heritability for the ability to quit smoking appears to overlap with the genetics of nicotine dependence and some does not. We now report genome wide association studies of nicotine dependent individuals who were successful in abstaining from cigarette smoking, nicotine dependent individuals who were not successful in abstaining and ethnically-matched control subjects free from substantial lifetime use of any addictive substance.ResultsThese data, and their comparison with data that we have previously obtained from comparisons of four other substance dependent vs control samples support two main ideas: 1) Single nucleotide polymorphisms (SNPs) whose allele frequencies distinguish nicotine-dependent from control individuals identify a set of genes that overlaps significantly with the set of genes that contain markers whose allelic frequencies distinguish the four other substance dependent vs control groups (p < 0.018). 2) SNPs whose allelic frequencies distinguish successful vs unsuccessful abstainers cluster in small genomic regions in ways that are highly unlikely to be due to chance (Monte Carlo p < 0.00001).ConclusionThese clustered SNPs nominate candidate genes for successful abstinence from smoking that are implicated in interesting functions: cell adhesion, enzymes, transcriptional regulators, neurotransmitters and receptors and regulation of DNA, RNA and proteins. As these observations are replicated, they will provide an increasingly-strong basis for understanding mechanisms of successful abstinence, for identifying individuals more or less likely to succeed in smoking cessation efforts and for tailoring therapies so that genotypes can help match smokers with the treatments that are most likely to benefit them.

Pooled association genome scanning for alcohol dependence using 104,268 SNPs: Validation and use to identify alcoholism vulnerability loci in unrelated individuals from the collaborative study on the genetics of alcoholism

Association genome scanning can identify markers for the allelic variants that contribute to vulnerability to complex disorders, including alcohol dependence. To improve the power and feasibility of this approach, we report validation of “100k” microarray‐based allelic frequency assessments in pooled DNA samples. We then use this approach with unrelated alcohol‐dependent versus control individuals sampled from pedigrees collected by the Collaborative Study on the Genetics of Alcoholism (COGA). Allele frequency differences between alcohol‐dependent and control individuals are assessed in quadruplicate at 104,268 autosomal SNPs in pooled samples. One hundred eighty‐eight SNPs provide (1) the largest allele frequency differences between dependent versus control individuals; (2) t values ≥ 3 for these differences; and (3) clustering, so that 51 relatively small chromosomal regions contain at least three SNPs that satisfy criteria 1 and 2 above (Monte Carlo P = 0.00034). These positive SNP clusters nominate interesting genes whose products are implicated in cellular signaling, gene regulation, development, “cell adhesion,” and Mendelian disorders. The results converge with linkage and association results for alcohol and other addictive phenotypes. The data support polygenic contributions to vulnerability to alcohol dependence. These SNPs provide new tools to aid the understanding, prevention, and treatment of alcohol abuse and dependence.

Addiction molecular genetics: 639,401 SNP whole genome association identifies many “cell adhesion” genes†‡

Addictions are substantially heritable complex disorders. We now report whole genome association studies that identify 89 genes likely to contain variants that contribute to addiction vulnerability, using previously‐ and newly‐validated microarray based pooling assays. Each gene contains clustered single nucleotide polymorphisms (SNPs) that display significant allele frequency differences between abusers and controls in each of the two samples studied with 639,401 SNP arrays and confirmatory SNPs from each of two other abuser/control samples. These genes are implicated in interesting functions, including “cell adhesion” processes that help to establish and maintain neuronal connections of special relevance to addictions memory‐like features.

Molecular Genetics of Addiction and Related Heritable Phenotypes

Genome‐wide association (GWA) can elucidate molecular genetic bases for human individual differences in complex phenotypes that include vulnerability to addiction. Here, we review (a) evidence that supports polygenic models with (at least) modest heterogeneity for the genetic architectures of addiction and several related phenotypes; (b) technical and ethical aspects of importance for understanding GWA data, including genotyping in individual samples versus DNA pools, analytic approaches, power estimation, and ethical issues in genotyping individuals with illegal behaviors; (c) the samples and the data that shape our current understanding of the molecular genetics of individual differences in vulnerability to substance dependence and related phenotypes; (d) overlaps between GWA data sets for dependence on different substances; and (e) overlaps between GWA data for addictions versus other heritable, brain‐based phenotypes that include bipolar disorder, cognitive ability, frontal lobe brain volume, the ability to successfully quit smoking, neuroticism, and Alzheimers disease. These convergent results identify potential targets for drugs that might modify addictions and play roles in these other phenotypes. They add to evidence that individual differences in the quality and quantity of brain connections make pleiotropic contributions to individual differences in vulnerability to addictions and to related brain disorders and phenotypes. A “connectivity constellation” of brain phenotypes and disorders appears to receive substantial pathogenic contributions from individual differences in a constellation of genes whose variants provide individual differences in the specification of brain connectivities during development and in adulthood. Heritable brain differences that underlie addiction vulnerability thus lie squarely in the midst of the repertoire of heritable brain differences that underlie vulnerability to other common brain disorders and phenotypes.

Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score.

Improving and targeting nicotine replacement therapy (NRT) are cost-effective strategies for reducing adverse health consequences for smokers. Treatment studies document the efficacy of precessation NRT and support important roles for level of nicotine dependence and precessation smoking reduction in successful quitting. However, prior work has not identified the optimal precessation dose or means for personalizing NRT. Genome-wide association has identified groups of genomic markers associated with successful quitting, allowing us to develop a v1.0 “quit-success” genotype score. We now report influences of v1.0 quit-success genotype score, level of dependence and precessation smoking reduction in a smoking cessation trial that examined effects of 21 versus 42 mg/24 h precessation NRT. Four hundred seventy-nine smokers were randomized to 21 or 42 mg NRT, initiated 2 wks prior to target quit dates. We monitored self-reported abstinence and end-expired air carbon monoxide (CO). Genotyping used Affymetrix arrays (Santa Clara, CA, USA). The primary outcome was 10-wk continuous smoking abstinence. NRT dose, level of nicotine dependence and genotype scores displayed significant interactive effects on successful quitting. Successful abstinence also was predicted by CO reductions during precessation NRT. These results document ways in which smoking cessation strategies can be personalized based on levels of nicotine dependence, genotype scores and CO monitoring. These assessments, taken together, can help match most smokers with optimal NRT doses and help rapidly identify some who may be better treated using other methods.

Linkage Disequilibrium, Haplotype and Association Studies of a Chromosome 4 GABA Receptor Gene Cluster: Candidate Gene Variants for Addictions

Strong genetic contributions to individual differences in vulnerability to addictions are well supported by classical genetic studies. Linkage and association genome scans for addiction vulnerability have provided converging evidence for several chromosomal regions which are likely to harbor allelic variants that contribute to such vulnerability. We and others have delineated a candidate addiction‐associated chromosome 4p12 “rSA3” region based on convergent data from association genome scanning studies in polysubstance abusers [Uhl et al. ( 2001 ); Am J Hum Genet 69(6):1290–1300], linkage‐based studies in alcoholism [Long et al. ( 1998 ); Am J Med Genet 81(3):216–221; Reich et al. ( 1998 ); Am J Med Genet 81(3):207–215] and association‐based studies for alcoholism and association‐based studies for individual differences in electroencephalographic (EEG) spectral power phenotypes [Porjesz et al. ( 2002 ); Proc Natl Acad Sci USA 99(6):3729–3733; Edenberg et al. ( 2004 ); Am J Hum Genet 74(4):705–714]. The rSA3 region contains interesting candidate genes that encode the alpha 2, alpha 4, beta 1, and gamma 1 receptor subunits for the principal brain inhibitory neurotransmitter, γ‐aminobutyric acid (GABA) [Covault et al. ( 2004 ); Am J Med Genet Part B 129B:104–109; Edenberg et al. ( 2004 ); Am J Hum Genet 74(4):705–714; Lappalainen et al. ( 2005 ); Alcohol Clin Exp Res 29(4):493–498]. We now report assessment of single nucleotide polymorphism (SNP) genotypes in this region in three samples of substance abusers and controls. These results delineate the haplotypes and patterns of linkage disequilibrium in this region, focus attention of the GABRA2 gene and identify modest associations between GABRA2 genotypes and addiction phenotypes. These results are consistent with modest roles for GABRA2 variants in addiction vulnerabilities.

Characterization of the rRNA Locus of Pfiesteria piscicida and Development of Standard and Quantitative PCR-Based Detection Assays Targeted to the Nontranscribed Spacer

ABSTRACT Pfiesteria piscicida is a heterotrophic dinoflagellate widely distributed along the middle Atlantic shore of the United States and associated with fish kills in the Neuse River (North Carolina) and the Chesapeake Bay (Maryland and Virginia). We constructed a genomic DNA library from clonally cultured P. piscicida and characterized the nontranscribed spacer (NTS), small subunit, internal transcribed spacer 1 (ITS1), 5.8S region, ITS2, and large subunit of the rRNA gene cluster. Based on the P. piscicida ribosomal DNA sequence, we developed a PCR-based detection assay that targets the NTS. The assay specificity was assessed by testing clonal P. piscicida and Pfiesteria shumwayae, 35 additional dinoflagellate species, and algal prey (Rhodomonas sp.). Only P. piscicida and nine presumptive P. piscicida isolates tested positive. All PCR-positive products yielded identical sequences for P. piscicida, suggesting that the PCR-based assay is species specific. The assay can detect a single P. piscicida zoospore in 1 ml of water, 10 resting cysts in 1 g of sediment, or 10 fg of P. piscicida DNA in 1 μg of heterologous DNA. An internal standard for the PCR assay was constructed to identify potential false-negative results in testing of environmental sediment and water samples and as a competitor for the development of a quantitative competitive PCR assay format. The specificities of both qualitative and quantitative PCR assay formats were validated with >200 environmental samples, and the assays provide simple, rapid, and accurate methods for the assessment of P. piscicida in water and sediments.

Genome-Wide Association for Nicotine Dependence and Smoking Cessation Success in NIH Research Volunteers

Phenotypes related to both nicotine dependence and ability to successfully quit smoking display substantial heritabilities in classical and molecular genetic studies. Twin studies suggest that some genetic components for dependence overlap with genetic components of ability to quit, but that many components do not overlap. Initial genome-wide association (GWA) studies have demonstrated haplotypes that distinguish nicotine-dependent from nondependent smokers. These haplotypes overlap partially with those that distinguish individuals who successfully quit smoking from those who were not able to quit smoking in clinical trials for smoking cessation. We now report novel genome-wide association results from National Institutes of Health research volunteers who reported smoking histories, symptoms of nicotine dependence, and ability to successfully quit smoking outside the context of a clinical trial. These results buttress data from several prior GWA studies. The data from these volunteers support the idea that previously reported studies of genes associated with smoking cessation success in clinical trial participants may also apply to smokers who are more or less able to initiate and sustain abstinence outside of clinical trial settings.