PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-9 (9)
 

Clipboard (0)
None

Select a Filter Below

Journals
Authors
more »
Year of Publication
Document Types
1.  Colorectal Cancer “Methylator Phenotype”: Fact or Artifact?1 
Neoplasia (New York, N.Y.)  2005;7(4):331-335.
Abstract
It has been proposed that human colorectal tumors can be classified into two groups: one in which methylation is rare, and another with methylation of several loci associated with a “CpG island methylated phenotype (CIMP),” characterized by preferential proximal location in the colon, but otherwise poorly defined. There is considerable overlap between this putative methylator phenotype and the well-known mutator phenotype associated with microsatellite instability (MSI). We have examined hypermethylation of the promoter region of five genes (DAPK, MGMT, hMLH1, p16INK4a, and p14ARF) in 106 primary colorectal cancers. A graph depicting the frequency of methylated loci in the series of tumors showed a continuous, monotonically decreasing distribution quite different from the previously claimed discontinuity. We observed a significant association between the presence of three or more methylated loci and the proximal location of the tumors. However, if we remove from analysis the tumors with hMLH1 methylation or those with MSI, the significance vanishes, suggesting that the association between multiple methylations and proximal location was indirect due to the correlation with MSI. Thus, our data do not support the independent existence of the so-called methylator phenotype and suggest that it rather may represent a statistical artifact caused by confounding of associations.
PMCID: PMC1501152  PMID: 15967110
CpG methylation; phenotype; colorectal; cancer; microsatellite instability
2.  Automated Genotyping of a Highly Informative Panel of 40 Short Insertion-Deletion Polymorphisms Resolved in Polyacrylamide Gels for Forensic Identification and Kinship Analysis 
Objective
Short insertion-deletion polymorphisms (indels) are the second most abundant form of genetic variations in humans after SNPs. Since indel alleles differ in size, they can be typed using the same methodological approaches and equipment currently utilized for microsatellite genotyping, which is already operational in forensic laboratories. We have previously shown that a panel of 40 carefully chosen indels has excellent potential for forensic identification, with combined probability of identity (match probability) of 7.09 × 10–17 for Europeans.
Methods
We describe the successful development of a multiplex system for genotyping the 40-indel panel in long thin denaturing polyacrylamide gels with silver staining. We also demonstrate that the system can be easily fully automated with a simple large scanner and commercial software.
Results and Conclusion
The great advantage of the new system of typing is its very low cost. The total price for laboratory equipment is less than EUR 10,000.-, and genotyping of an individual patient will cost less than EUR 10.- in supplies. Thus, the 40-indel panel described here and the newly developed ‘low-tech’ analysis platform represent useful new tools for forensic identification and kinship analysis in laboratories with limited budgets, especially in developing countries.
doi:10.1159/000338854
PMCID: PMC3375136  PMID: 22851937
Insertion-deletion polymorphisms; Indels; DNA; Identification; Genome; Polyacrylamide gels
3.  The Genomic Ancestry of Individuals from Different Geographical Regions of Brazil Is More Uniform Than Expected 
PLoS ONE  2011;6(2):e17063.
Based on pre-DNA racial/color methodology, clinical and pharmacological trials have traditionally considered the different geographical regions of Brazil as being very heterogeneous. We wished to ascertain how such diversity of regional color categories correlated with ancestry. Using a panel of 40 validated ancestry-informative insertion-deletion DNA polymorphisms we estimated individually the European, African and Amerindian ancestry components of 934 self-categorized White, Brown or Black Brazilians from the four most populous regions of the Country. We unraveled great ancestral diversity between and within the different regions. Especially, color categories in the northern part of Brazil diverged significantly in their ancestry proportions from their counterparts in the southern part of the Country, indicating that diverse regional semantics were being used in the self-classification as White, Brown or Black. To circumvent these regional subjective differences in color perception, we estimated the general ancestry proportions of each of the four regions in a form independent of color considerations. For that, we multiplied the proportions of a given ancestry in a given color category by the official census information about the proportion of that color category in the specific region, to arrive at a “total ancestry” estimate. Once such a calculation was performed, there emerged a much higher level of uniformity than previously expected. In all regions studied, the European ancestry was predominant, with proportions ranging from 60.6% in the Northeast to 77.7% in the South. We propose that the immigration of six million Europeans to Brazil in the 19th and 20th centuries - a phenomenon described and intended as the “whitening of Brazil” - is in large part responsible for dissipating previous ancestry dissimilarities that reflected region-specific population histories. These findings, of both clinical and sociological importance for Brazil, should also be relevant to other countries with ancestrally admixed populations.
doi:10.1371/journal.pone.0017063
PMCID: PMC3040205  PMID: 21359226
4.  Virus-Host Coevolution: Common Patterns of Nucleotide Motif Usage in Flaviviridae and Their Hosts 
PLoS ONE  2009;4(7):e6282.
Virus-host biological interaction is a continuous coevolutionary process involving both host immune system and viral escape mechanisms. Flaviviridae family is composed of fast evolving RNA viruses that infects vertebrate (mammals and birds) and/or invertebrate (ticks and mosquitoes) organisms. These host groups are very distinct life forms separated by a long evolutionary time, so lineage-specific anti-viral mechanisms are likely to have evolved. Flaviviridae viruses which infect a single host lineage would be subjected to specific host-induced pressures and, therefore, selected by them. In this work we compare the genomic evolutionary patterns of Flaviviridae viruses and their hosts in an attempt to uncover coevolutionary processes inducing common features in such disparate groups. Especially, we have analyzed dinucleotide and codon usage patterns in the coding regions of vertebrate and invertebrate organisms as well as in Flaviviridae viruses which specifically infect one or both host types. The two host groups possess very distinctive dinucleotide and codon usage patterns. A pronounced CpG under-representation was found in the vertebrate group, possibly induced by the methylation-deamination process, as well as a prominent TpA decrease. The invertebrate group displayed only a TpA frequency reduction bias. Flaviviridae viruses mimicked host nucleotide motif usage in a host-specific manner. Vertebrate-infecting viruses possessed under-representation of CpG and TpA, and insect-only viruses displayed only a TpA under-representation bias. Single-host Flaviviridae members which persistently infect mammals or insect hosts (Hepacivirus and insect-only Flavivirus, respectively) were found to posses a codon usage profile more similar to that of their hosts than to related Flaviviridae. We demonstrated that vertebrates and mosquitoes genomes are under very distinct lineage-specific constraints, and Flaviviridae viruses which specifically infect these lineages appear to be subject to the same evolutionary pressures that shaped their host coding regions, evidencing the lineage-specific coevolutionary processes between the viral and host groups.
doi:10.1371/journal.pone.0006282
PMCID: PMC2707012  PMID: 19617912
5.  A Worldwide Phylogeography for the Human X Chromosome 
PLoS ONE  2007;2(6):e557.
Background
We reasoned that by identifying genetic markers on human X chromosome regions where recombination is rare or absent, we should be able to construct X chromosome genealogies analogous to those based on Y chromosome and mitochondrial DNA polymorphisms, with the advantage of providing information about both male and female components of the population.
Methodology/Principal Findings
We identified a 47 Kb interval containing an Alu insertion polymorphism (DXS225) and four microsatellites in complete linkage disequilibrium in a low recombination rate region of the long arm of the human X chromosome. This haplotype block was studied in 667 males from the HGDP-CEPH Human Genome Diversity Panel. The haplotypic diversity was highest in Africa (0.992±0.0025) and lowest in the Americas (0.839±0.0378), where no insertion alleles of DXS225 were observed. Africa shared few haplotypes with other geographical areas, while those exhibited significant sharing among themselves. Median joining networks revealed that the African haplotypes were numerous, occupied the periphery of the graph and had low frequency, whereas those from the other continents were few, central and had high frequency. Altogether, our data support a single origin of modern man in Africa and migration to occupy the other continents by serial founder effects. Coalescent analysis permitted estimation of the time of the most recent common ancestor as 182,000 years (56,700–479,000) and the estimated time of the DXS225 Alu insertion of 94,400 years (24,300–310,000). These dates are fully compatible with the current widely accepted scenario of the origin of modern mankind in Africa within the last 195,000 years and migration out-of-Africa circa 55,000–65,000 years ago.
Conclusions/Significance
A haplotypic block combining an Alu insertion polymorphism and four microsatellite markers on the human X chromosome is a useful marker to evaluate genetic diversity of human populations and provides a highly informative tool for evolutionary studies.
doi:10.1371/journal.pone.0000557
PMCID: PMC1891433  PMID: 17593958
6.  Global Pharmacogenomics: Distribution of CYP3A5 Polymorphisms and Phenotypes in the Brazilian Population 
PLoS ONE  2014;9(1):e83472.
The influence of self-reported “race/color”, geographical origin and genetic ancestry on the distribution of three functional CYP3A5 polymorphisms, their imputed haplotypes and inferred phenotypes was examined in 909 healthy, adult Brazilians, self-identified as White, Brown or Black (“race/color” categories of the Brazilian census). The cohort was genotyped for CYP3A5*3 (rs776746), CYP3A5*6 (rs10264272) and CYP3A5*7 (rs41303343), CYP3A5 haplotypes were imputed and CYP3A5 metabolizer phenotypes were inferred according to the number of defective CYP3A5 alleles. Estimates of the individual proportions of Amerindian, African and European ancestry were available for the entire cohort. Multinomial log-linear regression models were applied to infer the statistical association between the distribution of CYP3A5 alleles, haplotypes and phenotypes (response variables), and self-reported Color, geographical region and ancestry (explanatory variables). We found that Color per se or in combination with geographical region associates significantly with the distribution of CYP3A5 variant alleles and CYP3A5 metabolizer phenotypes, whereas geographical region per se influences the frequency distribution of CYP3A5 variant alleles. The odds of having the default CYP3A5*3 allele and the poor metabolizer phenotype increases continuously with the increase of European ancestry and decrease of African ancestry. The opposite trend is observed in relation to CYP3A5*6, CYP3A5*7, the default CYP3A5*1 allele, and both the extensive and intermediate phenotypes. No significant effect of Amerindian ancestry on the distribution of CYP3A5 alleles or phenotypes was observed. In conclusion, this study strongly supports the notion that the intrinsic heterogeneity of the Brazilian population must be acknowledged in the design and interpretation of pharmacogenomic studies, and dealt with as a continuous variable, rather than proportioned in arbitrary categories that do not capture the diversity of the population. The relevance of this work extrapolates the Brazilian borders, and extends to other admixed peoples of the Americas, with ancestral roots in Europe, Africa and the American continent.
doi:10.1371/journal.pone.0083472
PMCID: PMC3888384  PMID: 24427273
7.  Oxidative Stress and DNA Lesions: The Role of 8-Oxoguanine Lesions in Trypanosoma cruzi Cell Viability 
The main consequence of oxidative stress is the formation of DNA lesions, which can result in genomic instability and lead to cell death. Guanine is the base that is most susceptible to oxidation, due to its low redox potential, and 8-oxoguanine (8-oxoG) is the most common lesion. These characteristics make 8-oxoG a good cellular biomarker to indicate the extent of oxidative stress. If not repaired, 8-oxoG can pair with adenine and cause a G:C to T:A transversion. When 8-oxoG is inserted during DNA replication, it could generate double-strand breaks, which makes this lesion particularly deleterious. Trypanosoma cruzi needs to address various oxidative stress situations, such as the mammalian intracellular environment and the triatomine insect gut where it replicates. We focused on the MutT enzyme, which is responsible for removing 8-oxoG from the nucleotide pool. To investigate the importance of 8-oxoG during parasite infection of mammalian cells, we characterized the MutT gene in T. cruzi (TcMTH) and generated T. cruzi parasites heterologously expressing Escherichia coli MutT or overexpressing the TcMTH enzyme. In the epimastigote form, the recombinant and wild-type parasites displayed similar growth in normal conditions, but the MutT-expressing cells were more resistant to hydrogen peroxide treatment. The recombinant parasite also displayed significantly increased growth after 48 hours of infection in fibroblasts and macrophages when compared to wild-type cells, as well as increased parasitemia in Swiss mice. In addition, we demonstrated, using western blotting experiments, that MutT heterologous expression can influence the parasite antioxidant enzyme protein levels. These results indicate the importance of the 8-oxoG repair system for cell viability.
Author Summary
The parasite Trypanosoma cruzi is the causative agent of Chagas disease, a malady endemic throughout Latin America. Studying the DNA repair machinery of this parasite could provide us with good insights about T. cruzi biology and virulence. We focused on the 8-oxoguanine (8-oxoG) DNA lesion and its repair system. This lesion is considered particularly deleterious because it can generate DNA double strand breaks if inserted during the DNA replication. Our approach to investigating the importance of the 8-oxoG repair system in T. cruzi was to generate a parasite population expressing the Escherichia coli MutT enzyme, which is responsible for removing 8-oxo-dGTP from the nucleotide pool. Different parameters such as growth curves, cell infection experiments, antioxidants, enzymes expression, and DNA lesion quantification were used to study this modified parasite in comparison with a control WT population. We also characterized a gene in T. cruzi that has functional homology with the E. coli MutT gene. The overexpression of this gene in T. cruzi caused the same phenotypes observed when we expressed the heterologous gene. Overall, the results indicate the importance of this DNA repair enzyme for T. cruzi resistance to oxidative stress and improving its proliferative ability in the vertebrate host.
doi:10.1371/journal.pntd.0002279
PMCID: PMC3681716  PMID: 23785540
8.  Molecular Characterization of the Schistosoma mansoni Zinc Finger Protein SmZF1 as a Transcription Factor 
Background
During its development, the parasite Schistosoma mansoni is exposed to different environments and undergoes many morphological and physiological transformations as a result of profound changes in gene expression. Characterization of proteins involved in the regulation of these processes is of importance for the understanding of schistosome biology. Proteins containing zinc finger motifs usually participate in regulatory processes and are considered the major class of transcription factors in eukaryotes. It has already been shown, by EMSA (Eletrophoretic Mobility Shift Assay), that SmZF1, a S. mansoni zinc finger (ZF) protein, specifically binds both DNA and RNA oligonucleotides. This suggests that this protein might act as a transcription factor in the parasite.
Methodology/Principal Findings
In this study we extended the characterization of SmZF1 by determining its subcellular localization and by verifying its ability to regulate gene transcription. We performed immunohistochemistry assays using adult male and female worms, cercariae and schistosomula to analyze the distribution pattern of SmZF1 and verified that the protein is mainly detected in the cells nuclei of all tested life cycle stages except for adult female worms. Also, SmZF1 was heterologously expressed in mammalian COS-7 cells to produce the recombinant protein YFP-SmZF1, which was mainly detected in the nucleus of the cells by confocal microscopy and Western blot assays. To evaluate the ability of this protein to regulate gene transcription, cells expressing YFP-SmZF1 were tested in a luciferase reporter system. In this system, the luciferase gene is downstream of a minimal promoter, upstream of which a DNA region containing four copies of the SmZF1 putative best binding site (D1-3DNA) was inserted. SmZF1 increased the reporter gene transcription by two fold (p≤0.003) only when its specific binding site was present.
Conclusion
Taken together, these results strongly support the hypothesis that SmZF1 acts as a transcription factor in S. mansoni.
Author Summary
Schistosomes are parasites that exhibit a complex life cycle during which they progress through many morphological and physiological transformations. These transformations are likely accompanied by alterations in gene expression, making genetic regulation important for parasite development. Here we describe a Schistosoma mansoni protein (SmZF1) that may act as a parasite transcription factor. These factors are key proteins for gene regulation. We have previously demonstrated that SmZF1 is able to bind DNA and that its mRNA is present at different stages during the parasite life cycle. In this study we aimed to define if this protein can function as a transcription factor in S. mansoni. SmZF1 was detected in the nucleus of adult male worms, cercariae and schistosomula cells. It was not, however, observed in female cells, suggesting it to be gender specific. We used mammalian cells expressing recombinant SmZF1 to analyze if SmZF1 protein is able to activate/repress gene transcription and demonstrated that it increased the expression of a reporter gene by two-fold. The results obtained confirm SmZF1 as a S. mansoni transcription factor.
doi:10.1371/journal.pntd.0000547
PMCID: PMC2770324  PMID: 19901992
9.  Ancestral Genomes, Sex, and the Population Structure of Trypanosoma cruzi 
PLoS Pathogens  2006;2(3):e24.
Acquisition of detailed knowledge of the structure and evolution of Trypanosoma cruzi populations is essential for control of Chagas disease. We profiled 75 strains of the parasite with five nuclear microsatellite loci, 24Sα RNA genes, and sequence polymorphisms in the mitochondrial cytochrome oxidase subunit II gene. We also used sequences available in GenBank for the mitochondrial genes cytochrome B and NADH dehydrogenase subunit 1. A multidimensional scaling plot (MDS) based in microsatellite data divided the parasites into four clusters corresponding to T. cruzi I (MDS-cluster A), T. cruzi II (MDS-cluster C), a third group of T. cruzi strains (MDS-cluster B), and hybrid strains (MDS-cluster BH). The first two clusters matched respectively mitochondrial clades A and C, while the other two belonged to mitochondrial clade B. The 24Sα rDNA and microsatellite profiling data were combined into multilocus genotypes that were analyzed by the haplotype reconstruction program PHASE. We identified 141 haplotypes that were clearly distributed into three haplogroups (X, Y, and Z). All strains belonging to T. cruzi I (MDS-cluster A) were Z/Z, the T. cruzi II strains (MDS-cluster C) were Y/Y, and those belonging to MDS-cluster B (unclassified T. cruzi) had X/X haplogroup genotypes. The strains grouped in the MDS-cluster BH were X/Y, confirming their hybrid character. Based on these results we propose the following minimal scenario for T. cruzi evolution. In a distant past there were at a minimum three ancestral lineages that we may call, respectively, T. cruzi I, T. cruzi II, and T. cruzi III. At least two hybridization events involving T. cruzi II and T. cruzi III produced evolutionarily viable progeny. In both events, the mitochondrial recipient (as identified by the mitochondrial clade of the hybrid strains) was T. cruzi II and the mitochondrial donor was T. cruzi III.
Synopsis
The parasite protozoan Trypanosoma cruzi causes Chagas disease, a malady that afflicts almost 20 million people in South America and Central America. Although the genome sequencing of T. cruzi has been recently completed, little is known about its population structure and evolution. Since 1999, two major evolutionary lineages presenting distinct epidemiological characteristics have been recognized in the parasite: T. cruzi I and T. cruzi II, the latter being much more associated with severe chronic cases of the disease. We describe new and important aspects of the population structure of the parasite, especially the characterization of a third ancestral lineage that we propose to call T. cruzi III. Through careful dissection of the genetic constitution of blocks of genes that are stably transmitted from generation to generation of the parasite we deduced at least two occurrences of the formation of hybrid strains from the parental lineages T. cruzi II and T. cruzi III, including the strain CLBrener, whose genome was sequenced. We did not find any hybrids originating from T. cruzi I. A fascinating finding was that both hybrids studied had the same mitochondrial DNA type as the T. cruzi III ancestral lineage, which was quite different from T.cruzi II.
doi:10.1371/journal.ppat.0020024
PMCID: PMC1434789  PMID: 16609729

Results 1-9 (9)