Sex-specific variation in the genome-wide recombination rate

In most species that reproduce sexually, successful gametogenesis requires recombination during meiosis. The number and placement of crossovers (COs) vary among individuals, with females and males often presenting the most striking contrasts. Despite the recognition that the sexes recombine at different rates (heterochiasmy), existing data fail to answer the question of whether patterns of genetic variation in recombination rate are similar in the two sexes. To fill this gap, we measured the genome-wide recombination rate in both sexes from a panel of wild-derived inbred strains from multiple subspecies of house mice (Mus musculus) and from a few additional species of Mus. To directly compare recombination rates in females and males from the same genetic backgrounds, we applied established methods based on immunolocalization of recombination proteins to inbred strains. Our results reveal discordant patterns of genetic variation in the two sexes. Whereas male genome-wide recombination rates vary substantially among strains, female recombination rates measured in the same strains are more static. The direction of heterochiasmy varies within two subspecies, Mus musculus molossinus and Mus musculus musculus. The direction of sex differences in the length of the synaptonemal complex and CO positions is consistent across strains and does not track sex differences in genome-wide recombination rate. In males, contrasts between strains with high recombination rate and strains with low recombination rate suggest more recombination is associated with stronger CO interference and more double-strand breaks. The sex-specific patterns of genetic variation we report underscore the importance of incorporating sex differences into recombination research.     

Prevalence of Bartonella henselae and Bartonella clarridgeiae in cats in the south of Brazil: a molecular study

Bartonella spp are the causative agent of cat scratch disease in humans. Cats are the natural reservoir of these bacteria and may infect humans through scratches, bites or fleas. Blood samples from 47 cats aged up to 12 months were collected for this study. All animals were lodged in municipal animal shelters in the Vale do Sinos region, Rio Grande do Sul, Brazil. Bartonella spp were detected by genus-specific polymerase chain reaction (PCR) and when the PCR was positive, the species were determined by DNA sequencing. A Giemsa-stained blood smear was also examined for the presence of intraerythrocytic elements suggestive of Bartonella spp infection. Phylogenetic analysis was also performed for all positive samples. Using molecular detection methods, Bartonella spp were detected in 17.02% (8/47) of the samples. In seven out of eight samples confirmed to be positive for Bartonella spp, blood smear examination revealed the presence of intraerythrocytic elements suggestive of Bartonella spp. Phylogenetic analysis characterized positive samples as Bartonella henselae (5) or Bartonella clarridgeiae (3). To the best of our knowledge, this is the first molecular study demonstrating the presence of Bartonella spp in cats from the Southern Region of Brazil.     

Intraspecific variation of recombination rate in maize

Background

In sexually reproducing organisms, meiotic crossovers ensure the proper segregation of chromosomes and contribute to genetic diversity by shuffling allelic combinations. Such genetic reassortment is exploited in breeding to combine favorable alleles, and in genetic research to identify genetic factors underlying traits of interest via linkage or association-based approaches. Crossover numbers and distributions along chromosomes vary between species, but little is known about their intraspecies variation.

Results

Here, we report on the variation of recombination rates between 22 European maize inbred lines that belong to the Dent and Flint gene pools. We genotype 23 doubled-haploid populations derived from crosses between these lines with a 50 k-SNP array and construct high-density genetic maps, showing good correspondence with the maize B73 genome sequence assembly. By aligning each genetic map to the B73 sequence, we obtain the recombination rates along chromosomes specific to each population. We identify significant differences in recombination rates at the genome-wide, chromosome, and intrachromosomal levels between populations, as well as significant variation for genome-wide recombination rates among maize lines. Crossover interference analysis using a two-pathway modeling framework reveals a negative association between recombination rate and interference strength.

Conclusions

To our knowledge, the present work provides the most comprehensive study on intraspecific variation of recombination rates and crossover interference strength in eukaryotes. Differences found in recombination rates will allow for selection of high or low recombining lines in crossing programs. Our methodology should pave the way for precise identification of genes controlling recombination rates in maize and other organisms.     

Prevalence of Bartonella henselae antibody in Florida panthers

Serum samples from 28 free-ranging Florida panthers (Puma concolor coryi) and seven mountain lions from Texas (P. concolor stanleyana) living in south Florida (USA) between 1997 to 1998 were tested for antibodies to Bartonella henselae. Twenty percent (7/35) of the samples were reactive to B. henselae antisera with a subspecies prevalence of 18% (5/ 28) for Florida panthers and 28% (2/7) for cougars from Texas (USA). There was not a significant sex related difference in infection rates among the Florida panthers. Antibody prevalence was higher in panthers <2-yr of age (40%) compared to panthers >2-yr (13%). Compared to studies of antibody prevalence in mountain lions (P. concolor) from California (USA), overall seroprevalence was lower as was prevalence in panthers >2-yr-old. However, the seroprevalence in animals <2-yr from southern Florida was similar to prevalences reported in mountain lions or domestic felids in California.     

The head of Bartonella adhesin A is crucial for host cell interaction of Bartonella henselae

Human pathogenic Bartonella henselae cause cat scratch disease and vasculoproliferative disorders (e.g. bacillary angiomatosis). Expression of Bartonella adhesin A (BadA) is crucial for bacterial autoagglutination, adhesion to host cells, binding to extracellular matrix proteins and proangiogenic reprogramming via activation of hypoxia inducible factor (HIF)-1. Like the prototypic Yersinia adhesin A, BadA belongs to the class of trimeric autotransporter adhesins and is constructed modularly consisting of a head, a long and repetitive neck-stalk module and a membrane anchor. Until now, the exact biological role of these domains is not known. Here, we analysed the function of the BadA head by truncating the repetitive neck-stalk module of BadA (B. henselae badA(-)/pHN23). Like B. henselae Marseille wild type, B. henselae badA(-)/pHN23 showed autoagglutination, adhesion to collagen and endothelial cells and activation of HIF-1 in host cells. Remarkably, B. henselae badA(-)/pHN23 did not bind to fibronectin (Fn) suggesting a crucial role of the deleted stalk domain in Fn binding. Additionally, the recombinantly expressed BadA head adhered to human umbilical vein endothelial cells and to a lesser degree to epithelial (HeLa 229) cells. Our data suggest that the head represents the major functional domain of BadA responsible for host adhesion and angiogenic reprogramming.     

Assessment of Persistence of Bartonella henselae in Ctenocephalides felis

Bartonella henselae (Rhizobiales: Bartonellaceae) is a Gram-negative fastidious bacterium of veterinary and zoonotic importance. The cat flea Ctenocephalides felis (Siphonaptera: Pulicidae) is the main recognized vector of B. henselae, and transmission among cats and humans occurs mainly through infected flea feces. The present study documents the use of a quantitative molecular approach to follow the daily kinetics of B. henselae within the cat flea and its excreted feces after exposure to infected blood for 48 h in an artificial membrane system. B. henselae DNA was detected in both fleas and feces for the entire life span of the fleas (i.e., 12 days) starting from 24 h after initiation of the blood meal.     

Interactions of Bartonella henselae with vascular endothelial cells

The emerging human pathogen Bartonella henselae has the remarkable capacity to colonise vascular tissues and to stimulate vasoproliferative tumour growth. Although the molecular principle of bacterium-induced neovascularisation (angiogenesis) is still unclear, recent studies have indicated a novel mechanism of endothelial colonisation that involves the formation, engulfment and uptake of a large bacterial aggregate.     

Population Structure of Bartonella henselae in Algerian Urban Stray Cats

Whole blood samples from 211 stray cats from Algiers, Algeria, were cultured to detect the presence of Bartonella species and to evaluate the genetic diversity of B. henselae strains by multiple locus VNTR analysis (MLVA). Bartonella henselae was the only species isolated from 36 (17%) of 211 cats. B. henselae genotype I was the predominant genotype (64%). MLVA typing of 259 strains from 30 bacteremic cats revealed 52 different profiles as compared to only 3 profiles using MLST. Of these 52 profiles, 48 (92.3%) were identified for the first time. One-third of the cats harbored one MLVA profile only. As there was a correlation between the age of cats and the number of MLVA profiles, we hypothesized that the single profile in these cats was the profile of the initial infecting strain. Two-third of the cats harbored 2 to 6 MLVA profiles simultaneously. The similarity of MLVA profiles obtained from the same cat, neighbor-joining clustering and structure-neighbor clustering indicate that such a diversity likely results from two different mechanisms occurring either independently or simultaneously: independent infections and genetic drift from a primary strain.     

Serological Study of Bartonella henselae in Cat Scratch Disease in Japan

It has become clear that Bartonella henselae is a common cause of cat scratch disease (CSD). The indirect fluorescence antibody (IFA) test for detection of IgG and IgM antibodies to B. henselae concerning CSD showed that 5 (50%) of 10 patients with CSD had a serum IgG antibody titer of 1:128 or more and that 2 (20%) patients had a serum IgM antibody titer of 1:20 or more. One of 7 asymptomatic members of patients' families (14%) had IgG antibody to B. henselae at a titer of 1:256. IgM antibody to B. henselae was not detected in sera from the patients' families. Both IgG and IgM antibodies to B. henselae were not detected in sera from the healthy control group. These data suggest that B. henselae may be a cause of CSD in Japan.     

Microsatellite variation and recombination rate in the human genome

Background (purifying) selection on deleterious mutations is expected to remove linked neutral mutations from a population, resulting in a positive correlation between recombination rate and levels of neutral genetic variation, even for markers with high mutation rates. We tested this prediction of the background selection model by comparing recombination rate and levels of microsatellite polymorphism in humans. Published data for 28 unrelated Europeans were used to estimate microsatellite polymorphism (number of alleles, heterozygosity, and variance in allele size) for loci throughout the genome. Recombination rates were estimated from comparisons of genetic and physical maps. First, we analyzed 61 loci from chromosome 22, using the complete sequence of this chromosome to provide exact physical locations. These 61 microsatellites showed no correlation between levels of variation and recombination rate. We then used radiation-hybrid and cytogenetic maps to calculate recombination rates throughout the genome. Recombination rates varied by more than one order of magnitude, and most chromosomes showed significant suppression of recombination near the centromere. Genome-wide analyses provided no evidence for a strong positive correlation between recombination rate and polymorphism, although analyses of loci with at least 20 repeats suggested a weak positive correlation. Comparisons of microsatellites in lowest-recombination and highest-recombination regions also revealed no difference in levels of polymorphism. Together, these results indicate that background selection is not a major determinant of microsatellite variation in humans.     

Bartonella henselae in captive and hunter-harvested beluga (Delphinapterus leucas)

Previously, we reported the isolation of Bartonella henselae from the blood of harbor porpoises (Phocoena phocoena) and loggerhead sea turtles (Caretta caretta) from the North Carolina coast. Hematologic, pathologic, and microbiologic findings surrounding the death of a juvenile captive beluga in Vancouver initiated an outbreak investigation designed to define the molecular prevalence of Bartonella infection in belugas. Using polymerase chain reaction analyses targeting the intergenic spacer region (ITS), two B. henselae ITS strains were identified in 78% of captive and free-ranging hunter-harvested belugas. These findings may have public health implications and may influence aquarium management procedures for captive marine mammals.     

The role of the host immune response in pathogenesis of Bartonella henselae

Bartonella henselae can infect humans resulting in a wide range of disease syndromes including cat-scratch disease, fever with bacteremia, endocarditis, bacillary angiomatosis, and bacillary peliosis hepatis, among others. The nature and severity of the clinical presentation correlates well with the status of the hosts' immune system. Individuals with impaired immune function, including HIV infection, progress to systemic infections more often. Patients with intact immune function who become infected with B. henselae usually get cat-scratch disease, a disease that usually involves lymphadenopathy resulting from a strong cellular immune response to the bacterium. However, immunocompromised patients often progress to bacillary angiomatosis or bacillary peliosis hepatis. The reduced ability of the hosts immune response to control bacterial infection apparently results in a bacteremia of longer duration, and in some patients the presence of angiogenic lesions that are unique among bacterial infections to Bartonella. Recently, the role of immune effector cells that produce angiogenic cytokines upon stimulation with B. henselae has been proposed. Here, the current status of the role of the immune response in both controlling infection and in B. henselae-triggered immunopathogenesis is presented.     

Isolation of Bartonella henselae from domestic cats in an Italian urban area

Bartonella henselae is the causative agent of Cat Scratch Disease (CSD) in humans. Cat is considered the reservoir of the bacterium. Identification of bacteriemic cats is the basic tool in the prophylaxis of CSD. Blood samples were collected between January 1999-December 2000 from 248 domestic cats living in an urban area (Reggio Emilia) in Northern Italy and tested for Bartonella henselae bacteriemia. Cultural and PCR methods were used. PCR was used directly on cat blood as well as to identify the Bartonella strain growth in culture. 24 (9.7 %) cats were found bacteriemic, most of which aged <1 year. A higher sensitivity was demonstrated by cultural method compared with PCR.     

Seroepidemiological Survey of Bartonella (Rochalimaea) henselae in Domestic Cats in Japan

A total of 199 domestic cat serum samples from 3 geographical areas (northeastern, central and southwestern) of Japan collected between 1992 to 1994 were examined for serum antibody against Bartonella henselae using an immunofluorescent assay. The antibody prevalence was 15.1% (30/199). A significant difference in the prevalence of B. henselae antibody was observed between the northeastern area (6.3%:3/48) and the central area (22.0%: 13/59) in Japan. There was no significant difference between the average age of seropositive cats (4.39 ±3.26 years) and that of seronegative cats (4.03 ±3.84 years), and also between the frequency of seropositive male cats (16.5%: 15/91) and that of seropositive female cats (11.8%:9/76). This is the first report of B. henselae antibodies in cats in Japan.     

Genetic variation versus recombination rate in a structured population of mice

The correlation between genetic variation and recombination rate was investigated in a structured mouse population. Nucleotide sequence data from 19 autosomal DNA loci from eight inbred strains of mouse (Mus musculus) sampled from three major subspecies were analyzed. The recombination rate was estimated from the comparison of genetic and physical map distances between markers flanking a 10-cM region of each locus. The strains were categorized into four groups (subpopulations) based on geography. By partitioning the genetic diversity into within-group and among-group variation, we detected a positive correlation between the recombination rate and nucleotide diversity within groups. The level of nucleotide differentiation among groups (G(ST)) showed a negative correlation with the rate of recombination. There was no significant correlation between recombination rate and nucleotide diversity when data from different subpopulations were pooled. No correlation was detected between recombination rate and nucleotide divergence of M. musculus and M. spicilegus. These patterns deviate from the strict neutral expectation under the constant nucleotide substitution rate, and they are likely to have been formed either by a hitchhiking effect of positively selected mutants or by background selection of deleterious mutants occurring in a subdivided population. Our series of comparisons show that because a real population always has some structure, incorporation of its information is important in detecting non-neutral evolution.     

Heme degrading protein HemS is involved in oxidative stress response of Bartonella henselae

Bartonellae are hemotropic bacteria, agents of emerging zoonoses. These bacteria are heme auxotroph Alphaproteobacteria which must import heme for supporting their growth, as they cannot synthesize it. Therefore, Bartonella genome encodes for a complete heme uptake system allowing the transportation of this compound across the outer membrane, the periplasm and the inner membranes. Heme has been proposed to be used as an iron source for Bartonella since these bacteria do not synthesize a complete system required for iron Fe3? uptake. Similarly to other bacteria which use heme as an iron source, Bartonellae must transport this compound into the cytoplasm and degrade it to allow the release of iron from the tetrapyrrole ring. For Bartonella, the gene cluster devoted to the synthesis of the complete heme uptake system also contains a gene encoding for a polypeptide that shares homologies with heme trafficking or degrading enzymes. Using complementation of an E. coli mutant strain impaired in heme degradation, we demonstrated that HemS from Bartonella henselae expressed in E. coli allows the release of iron from heme. Purified HemS from B. henselae binds heme and can degrade it in the presence of a suitable electron donor, ascorbate or NADPH-cytochrome P450 reductase. Knocking down the expression of HemS in B. henselae reduces its ability to face H?O? induced oxidative stress.     

Unusual trafficking pattern of Bartonella henselae -containing vacuoles in macrophages and endothelial cells

Bartonella henselae, the agent of cat-scratch disease and vasculoproliferative disorders in humans, is a fastidious facultative intracellular pathogen, whose interaction with macrophages and endothelial cells (ECs) is crucial in the pathogenesis of these diseases. However, little is known about the subcellular compartment in which B. henselae resides. Two hours after infection of murine macrophages and human ECs, the majority of B. henselae-containing vacuoles (BCVs) lack typical endocytic marker proteins, fail to acidify, and do not fuse with lysosomes, suggesting that B. henselae resides in a non-endocytic compartment. In contrast to human umbilical vein endothelial cells, bacterial death and lysosomal fusion with BCVs is apparent in J774A.1 macrophages at 24 h. This phenomenon of delayed lysosomal fusion requires bacterial viability, and is confined to the BCV itself. Using magnetic selection, we enriched for transposon-mutagenized B. henselae trapped in lysosomes of macrophages 2 h after infection. Genes affected appear to be relevant to the intracellular lifestyle in macrophages and ECs and include some previously implicated in Bartonella pathogenicity. We conclude that B. henselae has a specific capacity to actively avoid the host endocytic pathway after entry of macrophages and ECs, from within a specialized non-endocytic membrane-bound vacuole.     

Emergence of distinct genetic variants in the population of primary Bartonella henselae isolates

Bartonella henselae isolates from different hosts display a marked genetic heterogeneity, as determined by pulsed-field gel electrophoresis (PFGE). The aim of the present study was to determine whether different genetic variants may coexist within the population of distinct B. henselae isolates and could be detected by PFGE. Three primary B. henselae isolates and the B. henselae reference strains ATCC 49793 and 49882 were subjected as single colony derived cultures in quadruplicate to PFGE analysis upon restriction with SmaI or NotI. Up to 4 fragment differences were found among the cultures obtained from each primary isolate, indicating the coexistence of genetic variants in the population of primary B. henselae isolates. The clonal relatedness of the genetic variants was confirmed by arbitrarily primed PCR and multi-locus sequence typing. In contrast to the primary isolates, no variants were detected among the single colony derived cultures of the high-passage ATCC strains. We hypothesized that the coexistence of different genetic variants may represent a feature that is restricted to primary or low-passage B. henselae isolates. The primary isolates were serially passed in vitro and then subjected as single colony derived cultures to PFGE analysis, which now revealed identical patterns among the quadruplicate cultures of each high-passage isolate. These results suggest that the population of a primary B. henselae isolate is composed of distinct genetic variants, which may disappear upon repeated passages on artificial culture media. Generation of genetic variants by B. henselae may represent an escape mechanism to circumvent the host specific immune responses.