Unbiased homeologous recombination during pneumococcal transformation allows for multiple chromosomal integration events
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ABSTRACT:
SUBMITTER: Jan-Willem Veening
PROVIDER: S-BIAD26 | bioimages |
REPOSITORIES: bioimages
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Project description:The spread of antimicrobial resistance and vaccine escape in the human pathogen Streptococcus pneumoniae can be largely attributed to competence-induced transformation. Here, we studied this process at the single-cell level. We show that within isogenic populations, all cells become naturally competent and bind exogenous DNA. We find that transformation is highly efficient and that the chromosomal location of the integration site or whether the transformed gene is encoded on the leading or lagging strand has limited influence on recombination efficiency. Indeed, we have observed multiple recombination events in single recipients in real-time. However, because of saturation and because a single-stranded donor DNA replaces the original allele, transformation efficiency has an upper threshold of approximately 50% of the population. The fixed mechanism of transformation results in a fail-safe strategy for the population as half of the population generally keeps an intact copy of the original genome.
| S-EPMC7567608 | biostudies-literature
Project description:Feline leukemia virus (FeLV) is associated with a range of clinical signs in felid species. Differences in disease processes are closely related to genetic variation in the envelope (env) region of the genome of six defined subgroups. The primary hosts of FeLV are domestic cats of the Felis genus that also harbor endogenous FeLV (enFeLV) elements stably integrated in their genomes. EnFeLV elements display 86% nucleotide identity to exogenous, horizontally transmitted FeLV (FeLV-A). Variation between enFeLV and FeLV-A is primarily in the long terminal repeat (LTR) and env regions, which potentiates generation of the FeLV-B recombinant subgroup during natural infection. The aim of this study was to examine recombination behavior of exogenous FeLV (exFeLV) and enFeLV in a natural FeLV epizootic. We previously described that of 65 individuals in a closed colony, 32 had productive FeLV-A infection, and 22 of these individuals had detectable circulating FeLV-B. We cloned and sequenced the env gene of FeLV-B, FeLV-A, and enFeLV spanning known recombination breakpoints and examined between 1 and 13 clones in 22 animals with FeLV-B to assess sequence diversity and recombination breakpoints. Our analysis revealed that FeLV-A sequences circulating in the population, as well as enFeLV env sequences, are highly conserved. We documented many recombination breakpoints resulting in the production of unique FeLV-B genotypes. More than half of the cats harbored more than one FeLV-B variant, suggesting multiple recombination events between enFeLV and FeLV-A. We concluded that FeLV-B was predominantly generated de novo within each host, although we could not definitively rule out horizontal transmission, as nearly all cats harbored FeLV-B sequences that were genetically highly similar to those identified in other individuals. This work represents a comprehensive analysis of endogenous-exogenous retroviral interactions with important insights into host-virus interactions that underlie disease pathogenesis in a natural setting. IMPORTANCE Feline leukemia virus (FeLV) is a felid retrovirus with a variety of disease outcomes. Exogenous FeLV-A is the virus subgroup almost exclusively transmitted between cats. Recombination between FeLV-A and endogenous FeLV analogues in the cat genome may result in emergence of largely replication-defective but highly virulent subgroups. FeLV-B is formed when the 3' envelope (env) region of endogenous FeLV (enFeLV) recombines with that of the exogenous FeLV (exFeLV) during viral reverse transcription and integration. Both domestic cats and wild relatives of the Felis genus harbor enFeLV, which has been shown to limit FeLV-A disease outcome. However, enFeLV also contributes genetic material to the recombinant FeLV-B subgroup. This study evaluates endogenous-exogenous recombination outcomes in a naturally infected closed colony of cats to determine mechanisms and risk of endogenous retroviral recombination during exogenous virus exposure that leads to enhanced virulence. While FeLV-A and enFeLV env regions were highly conserved from cat to cat, nearly all individuals with emergent FeLV-B had unique combinations of genotypes, representative of a wide range of recombination sites within env. The findings provide insight into unique recombination patterns for emergence of new pathogens and can be related to similar viruses across species.
| S-EPMC8387034 | biostudies-literature
Project description:Exposure to environmental mutagens but also cell-endogenous processes can create DNA double-strand breaks (DSBs) in a cell's genome. DSBs need to be repaired accurately and timely to ensure genomic integrity and cell survival. One major DSB repair mechanism, called homologous recombination, relies on the nucleolytic degradation of the 5'-terminated strands in a process termed end resection. Here, we review new insights into end resection with a focus on the mechanistic interplay of the nucleases, helicases, and accessory factors involved.
| S-EPMC9006674 | biostudies-literature
Project description:Recombination is a major force for generating human immunodeficiency virus type 1 (HIV-1) diversity and produces numerous recombinants circulating in the human population. We previously established a cell-based system using green fluorescent protein gene (gfp) as a reporter to study the mechanisms of HIV-1 recombination. We now report an improved system capable of detecting recombination using authentic viral sequences. Frameshift mutations were introduced into the gag gene so that parental viruses do not express full-length Gag; however, recombination can generate a progeny virus that expresses a functional Gag. We demonstrate that this Gag reconstitution assay can be used to detect recombination between two group M HIV-1 variants of the same or of different subtypes. Using both gfp and gag assays, we found that, similar to group M viruses, group O viruses also recombine frequently. When recombination between a group M virus and a group O virus was examined, we found three distinct barriers for intergroup recombination. First, similar to recombination within group M viruses, intergroup recombination is affected by the identity of the dimerization initiation signal (DIS); variants with the same DIS recombined at a higher rate than those with different DIS. Second, using the gfp recombination assay, we showed that intergroup recombination occurs much less frequently than intragroup recombination, even though the gfp target sequence is identical in all viruses. Finally, Gag reconstitution between variants from different groups is further reduced compared with green fluorescent protein, indicating that sequence divergence interferes with recombination efficiency in the gag gene. Compared with identical sequences, we estimate that recombination rates are reduced by 3-fold and by 10- to 13-fold when the target regions in gag contain 91% and 72-73% sequence identities, respectively. These results show that there are at least three distinct mechanisms preventing exchange of genetic information between divergent HIV-1 variants from different groups.
| S-EPMC3065980 | biostudies-literature
Project description:Engagement of promoters with distal elements in long-range looping interactions has been implicated in regulation of Ig class switch recombination (CSR). The principles determining the spatial and regulatory relationships among Igh transcriptional elements remain poorly defined. We examined the chromosome conformation of C region (CH) loci that are targeted for CSR in a cytokine-dependent fashion in mature B lymphocytes. Germline transcription (GLT) of the ?1 and ? CH loci is controlled by two transcription factors, IL-4-inducible STAT6 and LPS-activated NF-?B. We showed that although STAT6 deficiency triggered loss of GLT, deletion of NF-?B p50 abolished both GLT and ?1 locus:enhancer looping. Thus, chromatin looping between CH loci and Igh enhancers is independent of GLT production and STAT6, whereas the establishment and maintenance of these chromatin contacts requires NF-?B p50. Comparative analysis of the endogenous ?1 locus and a knock-in heterologous promoter in mice identified the promoter per se as the interactive looping element and showed that transcription elongation is dispensable for promoter/enhancer interactions. Interposition of the LPS-responsive heterologous promoter between the LPS-inducible ?3 and ?2b loci altered GLT expression and essentially abolished direct IgG2b switching while maintaining a sequential ???3??2b format. Our study provides evidence that promoter/enhancer looping interactions can introduce negative constraints on distal promoters and affect their ability to engage in germline transcription and determine CSR targeting.
| S-EPMC4440573 | biostudies-literature
Project description:Although DNA non-homologous end-joining repairs most DNA double-strand breaks (DSBs) in G2 phase, late repairing DSBs undergo resection and repair by homologous recombination (HR). Based on parallels to the situation in G1 cells, previous work has suggested that DSBs that undergo repair by HR predominantly localize to regions of heterochromatin (HC). By using H3K9me3 and H4K20me3 to identify HC regions, we substantiate and extend previous evidence, suggesting that HC-DSBs undergo repair by HR. Next, we examine roles for 53BP1 and BRCA1 in this process. Previous studies have shown that 53BP1 is pro-non-homologous end-joining and anti-HR. Surprisingly, we demonstrate that in G2 phase, 53BP1 is required for HR at HC-DSBs with its role being to promote phosphorylated KAP-1 foci formation. BRCA1, in contrast, is dispensable for pKAP-1 foci formation but relieves the barrier caused by 53BP1. As 53BP1 is retained at irradiation-induced foci during HR, we propose that BRCA1 promotes displacement but retention of 53BP1 to allow resection and any necessary HC modifications to complete HR. In contrast to this role for 53BP1 in HR in G2 phase, we show that it is dispensable for HR in S phase, where HC regions are likely relaxed during replication.
| S-EPMC3834810 | biostudies-other
Project description:BackgroundSaffold cardiovirus (SAFV) is a new human cardiovirus with 11 identified genotypes. Little is known about the natural history and pathogenicity of SAFVs.Methodology/principal findingsWe sequenced the genome of five SAFV-1 strains which were identified from fecal samples taken from children with viral diarrhea in Beijing, China between March 2006 and November 2007, and analyzed the phylogenetic and phylodynamic properties of SAFVs using the genome sequences of every known SAFV genotypes. We identified multiple recombination events in our SAFV-1 strains, specifically recombination between SAFV-2, -3, -4, -9, -10 and the prototype SAFV-1 strain in the VP4 region and recombination between SAFV-4, -6, -8, -10, -11 and prototype SAFV-1 in the VP1/2A region. Notably, recombination in the structural gene VP4 is a rare event in Cardiovirus. The ratio of nonsynonymous substitutions to synonymous substitutions indicates a purifying selection of the SAFV genome. Phylogenetic and molecular clock analysis indicates the existence of at least two subclades of SAFV-1 with different origins. Subclade 1 includes two strains isolated from Pakistan, whereas subclade 2 includes the prototype strain and strains isolated in China, Pakistan, and Afghanistan. The most recent common ancestor of all SAFV genotypes dates to the 1710s, and SAFV-1, -2, and -3 to the 1940s, 1950s, and 1960s, respectively. No obvious relationship between variation and pathogenicity exists in the critical domains of the CD and EF loops of viral capsid proteins or the multi-functional proteins L based on amino acid sequence identity comparison between SAFV genotypes.Conclusions/significanceOur findings suggest that intertypic recombination plays an important role in the diversity of SAFVs, highlighting the diversity of the five strains with the previously described SAFV-1 strains.
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Project description:Phylogenetic recombination detection is a fundamental task in bioinformatics and evolutionary biology. Most of the computational tools developed to attack this important problem are not integrated into the growing suite of R packages for statistical analysis of molecular sequences. Here, we present an R package, rbrothers, that makes a Bayesian multiple change-point model, one of the most sophisticated model-based phylogenetic recombination tools, available to R users. Moreover, we equip the Bayesian change-point model with a set of pre- and post- processing routines that will broaden the application domain of this recombination detection framework. Specifically, we implement an algorithm that forms the set of input trees required by multiple change-point models. We also provide functionality for checking Markov chain Monte Carlo convergence and creating estimation result summaries and graphics. Using rbrothers, we perform a comparative analysis of two Salmonella enterica genes, fimA and fimH, that encode major and adhesive subunits of the type 1 fimbriae, respectively. We believe that rbrothers, available at R-Forge: http://evolmod.r-forge.r-project.org/, will allow researchers to incorporate recombination detection into phylogenetic workflows already implemented in R.
| S-EPMC3694826 | biostudies-literature
Project description:Birds are characterized by female heterogamety; females carry the Z and W sex chromosomes, while males have two copies of the Z chromosome. We suggest here that full differentiation of the Z and W sex chromosomes of birds did not take place until after the split of major contemporary lineages, in the late Cretaceous. The ATP synthase alpha-subunit gene is now present in one copy each on the nonrecombining part of the W chromosome (ATP5A1W) and on the Z chromosome (ATP5A1Z). This gene seems to have evolved on several independent occasions, in different lineages, from a state of free recombination into two sex-specific and nonrecombining variants. ATP5A1W and ATP5A1Z are thus more similar within orders, relative to what W (or Z) are between orders. Moreover, this cessation of recombination apparently took place at different times in different lineages (estimated at 13, 40, and 65 million years ago in Ciconiiformes, Galliformes, and Anseriformes, respectively). We argue that these observations are the result of recent and traceable steps in the process where sex chromosomes gradually cease to recombine and become differentiated. Our data demonstrate that this process, once initiated, may occur independently in parallel in sister lineages.
| S-EPMC1461649 | biostudies-other
Project description:Meiotic homologous recombination is a specialized process that involves homologous chromosome pairing and strand exchange to guarantee proper chromosome segregation and genetic diversity. The formation and repair of DNA double-strand breaks (DSBs) during meiotic recombination differs from those during mitotic recombination in that the homologous chromosome rather than the sister chromatid is the preferred repair template. The processing of single-stranded DNA (ssDNA) formed on intermediate recombination structures is central to driving the specific outcomes of DSB repair during meiosis. Replication protein A (RPA) is the main ssDNA-binding protein complex involved in DNA metabolism. However, the existence of RPA orthologs in plants and the recent discovery of meiosis specific with OB domains (MEIOB), a widely conserved meiosis-specific RPA1 paralog, strongly suggest that multiple RPA complexes evolved and specialized to subdivide their roles during DNA metabolism. Here we review ssDNA formation and maturation during mitotic and meiotic recombination underlying the meiotic specific features. We describe and discuss the existence and properties of MEIOB and multiple RPA subunits in plants and highlight how they can provide meiosis-specific fates to ssDNA processing during homologous recombination. Understanding the functions of these RPA homologs and how they interact with the canonical RPA subunits is of major interest in the fields of meiosis and DNA repair.
| S-EPMC4830875 | biostudies-literature