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Immunologic and structural relationships of the minor pilus subunits among Haemophilus influenzae isolates.

Two proteins, HifD and HifE, have been identified as structural components of Haemophilus influenzae pili. Both are localized at the pilus tip, and HifE appears to mediate pilus adherence to host cells. In this study we examined the immunologic and structural diversity of these pilus subunits among type b H. influenzae (Hib) and nontypeable H. influenzae (NTHI) strains. Western immunoblot analysis revealed that antibodies directed against the C terminus of HifD and HifE from Hib strain Eagan bound to HifD and HifE proteins, respectively, of all piliated Hib and NTHI strains tested. Whole-cell enzyme-linked immunosorbent assays showed that antibodies specific for native HifD or HifE of strain Eagan also bound to all piliated Hib strains but did not bind to the piliated NTHI strains. Antibodies against HifE of strain Eagan inhibited the binding of Hib to human erythrocytes but did not inhibit the binding of NTHI strains. Restriction fragment length polymorphism (RFLP) analysis was used to determine strain-to-strain structural differences within hifD and hifE genes, either by PCR or by nucleotide sequence analysis. DNA and derived amino acid sequence analyses of HifD and HifE confirmed the uniqueness of the RFLP types. The hifD and hifE genes of all type b strains showed identical restriction patterns. Analysis of hifD and hifE genes from the NTHI strains, however, revealed seven unique RFLP patterns, suggesting that these genes encode proteins with diverse primary structures. These results indicate that HifD and HifE are immunologically and structurally similar among the Hib strains but vary among the NTHI strains.

Adhesins, Bacterial↗

Single-nucleotide polymorphism-based population genetic analysis of Mycobacterium tuberculosis strains from 4 geographic sites.

We studied genetic relationships among 5069 Mycobacterium tuberculosis strains recovered from patients enrolled in 4 population-based studies in the United States and Europe, by analysis of 36 synonymous single-nucleotide polymorphisms (SNPs). All strains were assigned to 1 of 9 major genetic clusters based on sSNP profile. The same 9 genetic clusters were revealed by analysis of 227 nonsynonymous SNPs, 121 intergenic SNPs, and concatenated profiles of 578 SNPs available for a subset of 48 representative strains. IS6110 profiles, spoligotypes, and mycobacterial interspersed repetitive unit patterns were nonrandomly associated with SNP-based phylogenetic lineages, together indicating a strongly clonal population structure. Isolates of the 9 genetic clusters were not distributed with equal frequency in all localities, reflecting geographic subdivision. The SNP-based phylogenetic framework provides new insight into the worldwide evolution of M. tuberculosis and a gateway for investigating genotype-disease phenotype relationships in large samples of strains.

Bacterial Typing Techniques↗

Variable number of tandem repeats in clinical strains of Haemophilus influenzae.

An algorithm capable of identifying short repeat motifs was developed and used to screen the whole genome sequence available for Haemophilus influenzae, since some of these repeats have been shown to affect bacterial virulence. Various di- to hexanucleotide repeats were identified, confirming and extending previous findings on the existence of variable-number-of-tandem-repeat loci (VNTRs). Repeats with units of 7 or 8 nucleotides were not encountered. For all of the 3- to 6-nucleotide repeats in the H. influenzae chromosome, PCR tests capable of detecting allelic polymorphisms were designed. Fourteen of 18 of the potential VNTRs were indeed highly polymorphic when different strains were screened. Two of the potential VNTRs appeared to be short and homogeneous in length; another one may be specific for the H. influenzae Rd strain only. One of the primer sets generated fingerprint-type DNA banding patterns. The various repeat types differed with respect to intrinsic stability as well. It was noted for separate colonies derived from a single clinical specimen or strains passaged for several weeks on chocolate agar plates that the lengths of the VNTRs did not change. When several strains from different patients infected during an outbreak of lung disease were analyzed, increased but limited variation was encountered in all VNTR sites analyzed. One of the 5-nucleotide VNTRs proved to be hypervariable. This variability may reflect the molecular basis of a mechanism used by H. influenzae bacteria to successfully colonize and infect different human individuals.

Algorithms↗

Comparison of the hypervariable region of hepatitis C virus genomes in plasma and liver.

Nucleotide sequences of the hypervariable region of hepatitis C virus genomes obtained from plasma change rapidly during the course of infection and are believed to play a part in immunological escape and consequently in the development of persistent infection. It is not known, however, whether these changes also occur in the liver. To clarify this aspect, RNA was extracted from the plasma and liver tissue of eight patients with chronic hepatitis C. After cDNA synthesis, DNA fragments that included the hypervariable region were amplified by the polymerase chain reaction. Consensus nucleotide sequences were determined directly from the polymerase chain reaction products by the dideoxy chain termination method. The diversity of the hypervariable region was analyzed further by the polymerase chain reaction-single strand conformation polymorphism analysis. Consensus nucleotide sequences of the hypervariable region were identical between the plasma and the liver in each patient. The polymerase chain reaction-single strand conformation polymorphism analysis showed multiple DNA bands that represented different hypervariable region sequences. Comparison of the single strand conformation polymorphism patterns revealed that the number, the mobility, and the density of bands were the same between the plasma and the liver. It is concluded that the population and the diversity of hepatitis C virus quasispecies as detected by the hypervariable region sequence are the same between the plasma and the liver despite rapid mutations, indicating that rapid changes in the population of hepatitis C virus quasispecies also occur in the liver.

Amino Acid Sequence↗

A simple and rapid method for HLA-DP genotyping by digestion of PCR-amplified DNA with allele-specific restriction endonucleases.

We previously reported a simple and rapid method for HLA-DQA genotyping by digestion of polymerase chain reaction-amplified DQA genes with allele-specific restriction endonucleases. Here we report the application of this method to DP genotyping. The second exon of the HLA-DPB genes was selectively amplified from genomic DNAs of 72 HLA-D homozygous B-cell lines by the polymerase chain reaction method. Amplified DNAs were digested with ApaI, SacI, BstUI, FokI, and RsaI, which can recognize allelic sequence variations in the polymorphic segments of the DPB second exon and then subjected to electrophoresis in polyacrylamide gels. Sixteen different polymorphic patterns of the restriction fragments were found, and twelve were identical to patterns predicted from the known DNA sequences correlating with each HLA-DPw specificity defined by cellular typing. The other four patterns were distinct from those of the known DPw specificities, suggesting the presence of novel DP alleles. This polymerase chain reaction-restriction fragment length polymorphism method provides a simple and rapid technique for accurate definition of HLA-DP types at the nucleotide level, replacing the technically demanding method of primed lymphocyte typing.

Alleles↗

Testing the possible negative association of type 1 diabetes and atopic disease by analysis of the interleukin 4 receptor gene.

Variations in the interleukin 4 receptor A (IL4RA) gene have been reported to be associated with atopy, asthma, and allergy, which may occur less frequently in subjects with type 1 diabetes (T1D). Since atopy shows a humoral immune reactivity pattern, and T1D results from a cellular (T lymphocyte) response, we hypothesised that alleles predisposing to atopy could be protective for T1D and transmitted less often than the expected 50% from heterozygous parents to offspring with T1D. We genotyped seven exonic single nucleotide polymorphisms (SNPs) and the -3223 C>T SNP in the putative promoter region of IL4RA in up to 3475 T1D families, including 1244 Finnish T1D families. Only the -3223 C>T SNP showed evidence of negative association (P=0.014). There was some evidence for an interaction between -3233 C>T and the T1D locus IDDM2 in the insulin gene region (P=0.001 in the combined and P=0.02 in the Finnish data set). We, therefore, cannot rule out a genetic effect of IL4RA in T1D, but it is not a major one.

Alleles↗

mecA Locus diversity in methicillin-resistant Staphylococcus aureus isolates in Brisbane, Australia, and the development of a novel diagnostic procedure for the Western Samoan phage pattern clone.

An emerging public health phenomenon is the increasing incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections that are acquired outside of health care facilities. One lineage of community-acquired MRSA (CA-MRSA) is known as the Western Samoan phage pattern (WSPP) clone. The central aim of this study was to develop an efficient genotyping procedure for the identification of WSPP isolates. The approach taken was to make use of the highly variable region downstream of mecA in combination with a single nucleotide polymorphism (SNP) defined by the S. aureus multilocus sequence typing (MLST) database. The premise was that a combinatorial genotyping method that interrogated both a highly variable region and the genomic backbone would deliver a high degree of informative power relative to the number of genetic polymorphisms interrogated. Thirty-five MRSA isolates were used for this study, and their gene contents and order downstream of mecA were determined. The CA-MRSA isolates were found to contain a truncated mecA downstream region consisting of mecA-HVR-IS431 mec-dcs-Ins117, and a PCR-based method for identifying this structure was developed. The hospital-acquired isolates were found to contain eight different mecA downstream regions, three of which were novel. The Minimum SNPs computer software program was used to mine the S. aureus MLST database, and the arcC 272G polymorph was identified as 82% discriminatory for ST-30. A real-time PCR assay was developed to interrogate this SNP. We found that the assay for the truncated mecA downstream region in combination with the interrogation of arcC position 272 provided an unambiguous identification of WSPP isolates.

Bacterial Proteins↗

MDR and PRP: a comparison of methods for high-order genotype-phenotype associations.

Complex diseases such as cardiovascular disease are likely due to the effects of high-order interactions among multiple genes and demographic factors. Therefore, in order to understand their underlying biological mechanisms, we need to consider simultaneously the effects of genotypes across multiple loci. Statistical methods such as multifactor dimensionality reduction (MDR), the combinatorial partitioning method (CPM), recursive partitioning (RP), and patterning and recursive partitioning (PRP) are designed to uncover complex relationships without relying on a specific model for the interaction, and are therefore well-suited to this data setting. However, the theoretical overlap among these methods and their relative merits have not been well characterized. In this paper we demonstrate mathematically that MDR is a special case of RP in which (1) patterns are used as predictors (PRP), (2) tree growth is restricted to a single split, and (3) misclassification error is used as the measure of impurity. Both approaches are applied to a case-control study assessing the effect of eleven single nucleotide polymorphisms on coronary artery calcification in people at risk for cardiovascular disease.

Cardiovascular Diseases↗

Genomic regulation of natural variation in cortical and noncortical brain volume.

BACKGROUND: The relative growth of the neocortex parallels the emergence of complex cognitive functions across species. To determine the regions of the mammalian genome responsible for natural variations in cortical volume, we conducted a complex trait analysis using 34 strains of recombinant inbred (Rl) strains of mice (BXD), as well as their two parental strains (C57BL/6J and DBA/2J). We measured both neocortical volume and total brain volume in 155 coronally sectioned mouse brains that were Nissl stained and embedded in celloidin. After correction for shrinkage, the measured cortical and noncortical brain volumes were entered into a multiple regression analysis, which removed the effects of body size and age from the measurements. Marker regression and interval mapping were computed using WebQTL. RESULTS: An ANOVA revealed that more than half of the variance of these regressed phenotypes is genetically determined. We then identified the regions of the genome regulating this heritability. We located genomic regions in which a linkage disequilibrium was present using WebQTL as both a mapping engine and genomic database. For neocortex, we found a genome-wide significant quantitative trait locus (QTL) on chromosome 11 (marker D11Mit19), as well as a suggestive QTL on chromosome 16 (marker D16Mit100). In contrast, for noncortex the effect of chromosome 11 was markedly reduced, and a significant QTL appeared on chromosome 19 (D19Mit22). CONCLUSION: This classic pattern of double dissociation argues strongly for different genetic factors regulating relative cortical size, as opposed to brain volume more generally. It is likely, however, that the effects of proximal chromosome 11 extend beyond the neocortex strictly defined. An analysis of single nucleotide polymorphisms in these regions indicated that ciliary neurotrophic factor (Cntf) is quite possibly the gene underlying the noncortical QTL. Evidence for a candidate gene modulating neocortical volume was much weaker, but Otx1 deserves further consideration.

Animals↗

A proposal for standardization in forensic canine DNA typing: allele nomenclature of six canine-specific STR loci.

In this study a proposal for the allele nomenclature of six polymorphic short tandem repeat (STR) loci (PEZ3, PEZ6, PEZ8, PEZ10, FHC2161, and FHC2328) for canine genotyping (Canis lupus familiaris) is presented. The nomenclature is based on the sequence data of the polymorphic region of the microsatellite markers as recommended by the DNA commission of the International Society of Forensic Haemogenetics (ISFH) in 1994 for human DNA typing. To cover commonly and rarely occurring alleles, a selection of homozygous and heterozygous animals were analyzed and subjected to sequence studies. The alleles consisted of simple tri- and tetra-nucleotide repeat patterns as well as compound and highly complex repeat patterns. Several alleles revealing the same fragment size but different repeat structures were found. The allele designation described here was adopted to the number of repeats, including all variable regions within the amplified fragment. In a second step the most commonly occurring alleles were added to an allelic ladder for each marker allowing a reliable typing of all alleles differing in size. A total number of 142 unrelated dogs from surrounding municipal animal homes, private households, and canines in police duty were analyzed. The data were added to a population database providing allele frequencies for each marker.

Alleles↗

Polymorphic corneal amyloidosis: a disorder due to a novel mutation in the transforming growth factor beta-induced (BIGH3) gene.

PURPOSE: To characterize the clinicopathologic phenotype as well as the molecular genetic basis of an autosomal dominant form of corneal amyloidosis. DESIGN: Clinicopathologic and molecular genetic study of a family with a form of corneal amyloidosis. PARTICIPANTS: Forty-nine individuals from one family were studied. METHODS: The medical records of affected family members were reviewed, and corneal tissue from those who had undergone penetrating keratoplasty (PK) was examined. Several family members were examined clinically, and corneas were photographed. Deoxyribonucleic acid from blood or buccal swabs was extracted from each consenting family member to determine the status of their transforming growth factor beta-induced (TGFBI) gene. The coding region of the TGFBI gene was analyzed for mutations in the proband's DNA, and compared with the nucleotide sequences of normal individuals. This was performed by amplifying and sequencing all exons of the TGFBI gene. In all other family members, only exons 4, 8, 11, and 12 of the gene were amplified, sequenced, and analyzed for mutations. MAIN OUTCOME MEASURES: Clinicopathologic manifestations in relation to mutational status of the TGFBI gene. RESULTS: Slit-lamp biomicroscopy revealed bilateral multiple polymorphic, polygonal, refractile, chipped ice-appearing gray and white opacities. There were also occasional deep filamentous lines that did not form a distinct lattice pattern. Corneal tissue of affected individuals who underwent PK contained widespread deposits of amyloid within the corneal stroma, particularly in the deep central stroma. Twelve members of the family were found to have a heterozygous single mutation in the TGFBI gene leading to a predicted amino acid substitution of aspartic acid for alanine (A546D). Nine of these individuals had ophthalmologist-documented corneal disease. The remaining 3, who were 11, 14, and 15 years old, were asymptomatic. In addition, 4 inconsequential polymorphisms with the nucleotide changes 387 G/A (R129R), 981 G/A (V327V), 1416 T/C (L472L), and 1620 C/T (F540F) were found. CONCLUSION: A distinct, progressive form of corneal amyloidosis with an autosomal dominant mode of inheritance is characterized clinically by the presence of refractile polymorphic corneal opacities. We have designated this entity, which is caused by an A546D mutation in the TGFBI gene, polymorphic corneal amyloidosis.

Adolescent↗

Use of a dense single nucleotide polymorphism map for in silico mapping in the mouse.

Rapid expansion of available data, both phenotypic and genotypic, for multiple strains of mice has enabled the development of new methods to interrogate the mouse genome for functional genetic perturbations. In silico mapping provides an expedient way to associate the natural diversity of phenotypic traits with ancestrally inherited polymorphisms for the purpose of dissecting genetic traits. In mouse, the current single nucleotide polymorphism (SNP) data have lacked the density across the genome and coverage of enough strains to properly achieve this goal. To remedy this, 470,407 allele calls were produced for 10,990 evenly spaced SNP loci across 48 inbred mouse strains. Use of the SNP set with statistical models that considered unique patterns within blocks of three SNPs as an inferred haplotype could successfully map known single gene traits and a cloned quantitative trait gene. Application of this method to high-density lipoprotein and gallstone phenotypes reproduced previously characterized quantitative trait loci (QTL). The inferred haplotype data also facilitates the refinement of QTL regions such that candidate genes can be more easily identified and characterized as shown for adenylate cyclase 7.

Adenylyl Cyclases↗

Multilocus patterns of nucleotide variability and the demographic and selection history of Drosophila melanogaster populations.

Uncertainty about the demographic history of populations can hamper genome-wide scans for selection based on population genetic models. To obtain a portrait of the effects of demographic history on genome variability patterns in Drosophila melanogaster populations, we surveyed noncoding DNA polymorphism at 10 X-linked loci in large samples from three African and two non-African populations. All five populations show significant departures from expectations under the standard neutral model. We detect weak but significant differentiation between East (Kenya and Zimbabwe) and West/Central sub-Saharan (Gabon) African populations. A skew toward high-frequency-derived polymorphisms, elevated levels of linkage disequilibrium (LD) and significant heterogeneity in levels of polymorphism and divergence in the Gabon sample suggest that this population is further from mutation-drift equilibrium than the two Eastern African populations. Both non-African populations harbor significantly higher levels of LD, a large excess of high-frequency-derived mutations and extreme heterogeneity among loci in levels of polymorphism and divergence. Rejections of the neutral model in D. melanogaster populations using these and similar features have been interpreted as evidence for an important role for natural selection in shaping genome variability patterns. Based on simulations, we conclude that simple bottleneck models are sufficient to account for most, if not all, polymorphism features of both African and non-African populations. In contrast, we show that a steady-state recurrent hitchhiking model fails to account for several aspects of the data. Demographic departures from equilibrium expectations in both ancestral and derived populations thus represent a serious challenge to detecting positive selection in genome-wide scans using current methodologies.

Animals↗

Natural selection on Plasmodium surface proteins.

Numbers of synonymous (ds) and nonsynonymous (dN) nucleotide substitutions per site were analysed in eight polymorphic Plasmodium genes: circumsporozoite protein gene (CSP), sporozoite surface protein 2 (thrombospondin related anonymous protein, TRAP), merozoite surface antigen 2 (MSA-2), apical membrane antigen 1 (PF83), liver-stage antigen-1 (LSA-1), knob-associated histidine-rich protein (KAHRP), ring-infected erythrocyte surface antigen (RESA) and S-antigen. In certain regions of genes coding for proteins of the sporozoite and merozoite surface (CSP, TRAP, MSA-2 and PF83), dN was significantly greater than dS. This unusual pattern of nucleotide substitution is indicative of positive Darwinian selection acting to promote diversity at the amino-acid level; thus our results suggest that the sporozoite and merozoite surface proteins are under positive selection, presumably exerted by the host immune system. No such pattern of substitution was observed on LSA-1, KAHRP, RESA, or S-antigen. Observed patterns of nucleotide substitution were not explicable by nucleotide content bias. G + C content in the 5' nonrepeat region of CSP in nine Plasmodium species was positively correlated with that in the 3' nonrepeat region; however, there was no relationship between G + C content and the ratio dS/dN in either CSP or a larger sample of all regions of all genes analysed.

Animals↗

Changes in temporal and spatial patterns of outer surface lipoprotein expression generate population heterogeneity and antigenic diversity in the Lyme disease spirochete, Borrelia burgdorferi.

Borrelia burgdorferi differentially expresses many of the OspE/F/Elp paralogs during tick feeding. These findings, combined with the recent report that stable B. burgdorferi infection of mammals occurs only after 53 h of tick attachment, prompted us to further analyze the expression of the OspE/F/Elp paralogs during this critical period of transmission. Indirect immunofluorescence analysis revealed that OspE, p21, ElpB1, ElpB2, and OspF/BbK2.11 are expressed in the salivary glands of ticks allowed to feed on mice for 53 to 58 h. Interestingly, many of the spirochetes in the salivary glands that expressed abundant amounts of these antigens were negative for OspA and OspC. Although prior reports have indicated that OspE/F/Elp orthologs are surface exposed, none of the individual lipoproteins or combinations of the lipoproteins protected mice from challenge infections. To examine why these apparently surface-exposed lipoproteins were not protective, we analyzed their genetic stability during infection and their cellular locations after cultivation in vitro and within dialysis membrane chambers, mimicking a mammalian host-adapted state. Combined restriction fragment length polymorphism and nucleotide sequence analyses revealed that the genes encoding these lipoproteins are stable for at least 8 months postinfection. Interestingly, cellular localization experiments revealed that while all of these proteins can be surface localized, there were significant populations of spirochetes that expressed these lipoproteins only in the periplasm. Furthermore, host-specific signals were found to alter the expression patterns and final cellular location of these lipoproteins. The combined data revealed a remarkable heterogeneity in populations of B. burgdorferi during tick transmission and mammalian infection. The diversity is generated not only by temporal changes in antigen expression but also by modulation of the surface lipoproteins during infection. The ability to regulate the temporal and spatial expression patterns of lipoproteins throughout infection likely contributes to persistent infection of mammals by B. burgdorferi.

Animals↗

Identification of a partial cDNA clone for the human receptor for complement fragments C3b/C4b.

Redundant oligonucleotides were synthesized based on amino acid sequences of tryptic peptides from the purified receptor for human complement fragments C3b/C4b (CR1). These probes were used to screen a size-selected human tonsilar cDNA library. A single positive clone was identified that hybridized to three oligonucleotide probes. The cDNA insert was 1.5 kilobases in length and contained sequences homologous to those of the oligonucleotide probes as well as nucleotide sequences corresponding to another independent CR1 tryptic peptide. Blot-hybridization analysis using fragments of the cDNA insert as probes revealed two distinct species of the CR1 message of 9 and 11 kilobases in human tonsil mRNA. The two EcoRI fragments of the CR1 cDNA insert hybridized to each other, suggesting the presence of homologous sequences. When used as probes in Southern blot analysis of human DNA, each fragment identified similar but not identical patterns of multiple restriction fragments, indicating either a series of homologous domains in a single CR1 gene or the presence of multiple CR1 genes. Furthermore, an additional BamHI fragment was found to segregate with the expression of the S allotype of the CR1 protein in a family. Thus, the molecular weight difference in the polymorphic variants of the CR1 protein is based on differences in nucleotide sequences.

Base Sequence↗

Mutational analysis of OB gene in obese and type 2 diabetes affected subjects.

Peripheral blood DNA from 12 subjects affected by familial obesity and from 35 subjects affected by type 2 diabetes were analysed for mutations in the coding sequence of the OB gene. Mutational analysis, conducted using the single strand conformation polymorphism (SSCP) technique, followed by direct sequencing did not reveal the presence of nucleotide variants in the coding region of the OB gene. The lack of mutations in the coding sequence is consistent with previous data suggesting that mutations in the coding sequence of the OB gene are not common in human familial obesity. In 2 samples displaying a non-informative pattern of SSCP and in 8 additional samples the nucleotide sequence of portion of the intron 2 bordering the coding sequence of exon 2 identified a G in the positions +14IVS and +18IVS, according to a sequence reported previously, but in contrast with some others. All samples were homozygous for these intron variants.

Adult↗

A single-amino-acid change of the gustatory receptor gene, Gr5a, has a major effect on trehalose sensitivity in a natural population of Drosophila melanogaster.

Variation in trehalose sensitivity and nucleotide sequence polymorphism of the Gr5a gene encoding the gustatory receptor to sugar trehalose were investigated in 152 male lines of Drosophila melanogaster collected from a natural population. Among the observed 59 segregating sites, some pairs of sites showed significant linkage disequilibrium. A single SNP, which results in the Ala218Thr amino acid change, was significantly associated with trehalose sensitivity, as previously suggested. Threonine at amino acid position 218 was found to be the ancestral form in D. melanogaster, suggesting that low trehalose sensitivity was an ancestral form with respect to the receptor function. There was large genetic variation in trehalose sensitivity. It was continuously distributed, indicating that trehalose sensitivity measured by the behavioral assay is a quantitative trait. These results suggest that apart from the Gr5a gene, other genetic factors contribute to variation in trehalose sensitivity. Nucleotide diversity (pi) and nucleotide variation (theta) per site were 0.00874 and 0.00590, respectively. Fu and Li's test and the MK test showed no significant departure from the expectation of selective neutrality in the Gr5a gene. However, we rejected selective neutrality by Tajima's test and Fay and Wu's test with the observed level of recombination. We discuss possible causes of the observed pattern of nucleotide variation in the gustatory receptor Gr5a gene.

Amino Acid Substitution↗