Homologous Insertion Research Articles

Miniature Inverted-Repeat Transposable Elements: Small DNA Transposons That Have Contributed to Plant MICRORNA Gene Evolution

Angiosperms form the largest phylum within the Plantae kingdom and show remarkable genetic variation due to the considerable difference in the nuclear genome size of each species. Transposable elements (TEs), mobile DNA sequences that can amplify and change their chromosome position, account for much of the difference in nuclear genome size between individual angiosperm species. Considering the dramatic consequences of TE movement, including the complete loss of gene function, it is unsurprising that the angiosperms have developed elegant molecular strategies to control TE amplification and movement. Specifically, the RNA-directed DNA methylation (RdDM) pathway, directed by the repeat-associated small-interfering RNA (rasiRNA) class of small regulatory RNA, forms the primary line of defense to control TE activity in the angiosperms. However, the miniature inverted-repeat transposable element (MITE) species of TE has at times avoided the repressive effects imposed by the rasiRNA-directed RdDM pathway. MITE proliferation in angiosperm nuclear genomes is due to their preference to transpose within gene-rich regions, a pattern of transposition that has enabled MITEs to gain further transcriptional activity. The sequence-based properties of a MITE results in the synthesis of a noncoding RNA (ncRNA), which, after transcription, folds to form a structure that closely resembles those of the precursor transcripts of the microRNA (miRNA) class of small regulatory RNA. This shared folding structure results in a MITE-derived miRNA being processed from the MITE-transcribed ncRNA, and post-maturation, the MITE-derived miRNA can be used by the core protein machinery of the miRNA pathway to regulate the expression of protein-coding genes that harbor homologous MITE insertions. Here, we outline the considerable contribution that the MITE species of TE have made to expanding the miRNA repertoire of the angiosperms.

Investigating the origin of subtelomeric and centromeric AT-rich elements in Aspergillus flavus.

An in silico study of Aspergillus flavus genome stability uncovered significant variations in both coding and non-coding regions. The non-coding insertions uniformly consisted of AT-rich sequences that are evolutionarily maintained, albeit distributed at widely different sites in an array of A. flavus strains. A survey of ≥ 2kb AT-rich elements (AT ≥ 70%; ATEs) in non-centromeric regions uncovered two major categories of ATEs. The first category is composed of homologous insertions at ectopic, non-allelic sites that contain homology to transposable elements (TEs; Classes B, C, D, and E). Strains differed significantly in frequency, position, and TE type, but displayed a common enrichment in subtelomeric regions. The TEs were heavily mutated, with patterns consistent with the ancestral activity of repeat-induced point mutations (RIP). The second category consists of a conserved set of novel subtelomeric ATE repeats (Classes A, G, G, H, I and J) which lack discernible TEs and, unlike TEs, display a constant polarity relative to the telomere. Members of one of these classes are derivatives of a progenitor ATE that is predicted to have undergone extensive homologous recombination during evolution. A third category of ATEs consists of ~100 kb regions at each centromere. Centromeric ATEs and TE clusters within these centromeres display a high level of sequence identity between strains. These studies suggest that transposition and RIP are forces in the evolution of subtelomeric and centromeric structure and function.

Development of a gene-targeting system using CRISPR/Cas9 and utilization of pyrG as a novel selectable marker in Lentinula edodes.

First, we attempted to recombine the Shiitake (Lentinula edodes) pyrG (ura3) gene homologously by introducing a donor vector containing a carboxin resistance gene (lecbxR) flanked by homologous sequences of pyrG into protoplasts of the fungus. However, all the carboxin-resistant transformants only contained ectopic insertions of the exogenous gene and no homologous insertions. Agaricomycetes are generally known for their low efficiency of homologous recombination, and a similar result was shown for L. edodes. We then co-introduced a Cas9 plasmid vector containing a CRISPR/Cas9 expression cassette targeting pyrG and donor plasmid vector. As a result, ∆pyrG strains containing the expected homologous recombination were obtained. However, only two of the seven ∆pyrG strains had the Cas9 sequence; the others did not. Our results suggest that genome editing occurred via the transient expression of the CRISPR/Cas9 cassette in the Cas9 plasmid vector introduced into the fungal cell. Transforming pyrG into a ∆pyrG strain (strain I8) resulted in prototrophic strains with an efficiency of 6.5 strains/experiment.

Highly soluble and stable ‘insertion domain’ of the capsid penton base protein provides complete protection against infections caused by fowl adenoviruses

In the current study, we have evaluated the protective efficacy of the ‘insertion domain’ which is commonly found in the capsid penton base protein of many adenoviruses. Using the ‘insertion domain’ of the penton base protein of a representative fowl adenovirus, fowl adenovirus serotype 4 (FAdV-4), we find that the ‘insertion domain’ can readily be expressed in a soluble form in the bacterial system, and can be purified in sufficient quantities through simple chromatographic methods. We demonstrate that the ‘insertion domain’, when employed as a subunit vaccine candidate, provides complete protection against hydropericardium syndrome, caused by FAdV-4, in chickens. The data presented here indicate that the protein, adjuvanted with Montanide™ ISA71 VG, provides complete protection in chickens against a lethal FAdV-4 challenge after administration of two doses (100 μg of the protein per dose) two weeks apart (the first dose at the 7th day of life and a booster dose at the age of 21 days). Furthermore, the purified protein can be stored at low temperatures without any observable loss in the protein integrity up to one year, tested so far. Due to the conserved nature of the ‘insertion domain’ across the penton base protein of fowl adenoviruses, it is suggested that homologous insertion domains could be employed as highly stable and cost-effective subunit vaccine candidates against infections caused by respective fowl adenoviruses.

Insertion orientation within the cassette affects gene-targeting success during ends-out recombination in the yeast Saccharomyces cerevisiae.

Gene-targeting is one of the most important molecular tools for genomic manipulations for research and industrial purposes. However, many factors influence targeting fidelity undermining the efforts for accurate, fast, and reliable construction of genetically modified yeast strains. Therefore, it is of great academic interest that we uncover as many as possible parameters affecting the recombination mechanisms that enable targeting. Since usually, researchers choose the orientation of the insertion (marker) within the module at random, it seemed interesting to see whether the same module will achieve essentially the same targeting efficiency when the same marker was oriented alternatively concerning the same target gene. Thus, two loci (URA3 and LEU2) and one allele (ura3-52) in a haploid yeast genetic background were targeted by artificial modules bearing homologous insertions in alternative orientations being flanked by long asymmetrical targeting homology to either replace or disrupt a genomic target. Results showed that insertion orientation within the targeting module strongly influences targeting in yeast, regardless of the targeting approach.

Disruption of the Snf1 Gene Enhances Cell Growth and Reduces the Metabolic Burden in Cellulase-Expressing and Lipid-Accumulating Yarrowia lipolytica.

Yarrowia lipolytica is known to be capable of metabolizing glucose and accumulating lipids intracellularly; however, it lacks the cellulolytic enzymes needed to break down cellulosic biomass directly. To develop Y. lipolytica as a consolidated bioprocessing (CBP) microorganism, we previously expressed the heterologous CBH I, CBH II, and EG II cellulase enzymes both individually and collectively in this microorganism. We concluded that the coexpression of these cellulases resulted in a metabolic drain on the host cells leading to reduced cell growth and lipid accumulation. The current study aims to build a new cellulase coexpressing platform to overcome these hinderances by (1) knocking out the sucrose non-fermenting 1 (Snf1) gene that represses the energetically expensive lipid and protein biosynthesis processes, and (2) knocking in the cellulase cassette fused with the recyclable selection marker URA3 gene in the background of a lipid-accumulating Y. lipolytica strain overexpressing ATP citrate lyase (ACL) and diacylglycerol acyltransferase 1 (DGA1) genes. We have achieved a homologous recombination insertion rate of 58% for integrating the cellulases-URA3 construct at the disrupted Snf1 site in the genome of host cells. Importantly, we observed that the disruption of the Snf1 gene promoted cell growth and lipid accumulation and lowered the cellular saturated fatty acid level and the saturated to unsaturated fatty acid ratio significantly in the transformant YL163t that coexpresses cellulases. The result suggests a lower endoplasmic reticulum stress in YL163t, in comparison with its parent strain Po1g ACL-DGA1. Furthermore, transformant YL163t increased in vitro cellulolytic activity by 30%, whereas the “total in vivo newly formed FAME (fatty acid methyl esters)” increased by 16% in comparison with a random integrative cellulase-expressing Y. lipolytica mutant in the same YNB-Avicel medium. The Snf1 disruption platform demonstrated in this study provides a potent tool for the further development of Y. lipolytica as a robust host for the expression of cellulases and other commercially important proteins.

Induction of Broad and Polyfunctional HIV-1-Specific T Cell Responses by the Multiepitopic Protein TMEP-B Vectored by MVA Virus.

A human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) vaccine able to induce long-lasting immunity remains a major challenge. We previously designed a T cell multiepitopic immunogen including protective conserved epitopes from HIV-1 Gag, Pol and Nef proteins (TMEP-B), that induced potent HIV-1-specific CD8 T cells when vectored by DNA and combined with the vaccine candidate modified vaccinia virus Ankara (MVA)-B. Here, we described the vectorization of TMEP-B in MVA (MVA-TMEP) and evaluated the T cell immunogenicity profile elicited in mice when administered in homologous (MVA/MVA) or heterologous (DNA/MVA) prime/boost vector regimens or using homologous or heterologous inserts. The heterologous vector regimen was superior to the homologous protocol in inducing T cell responses. DNA-TMEP-primed animals boosted with MVA-TMEP or MVA-B exhibited the highest magnitudes of HIV-1-specific CD8, CD4 and T follicular helper (Tfh) cells, with MVA-TMEP significantly expanding Gag-specific CD8 T cell responses. In the homologous vector regimen, all groups exhibited similar HIV-1-specific CD8 and CD4 T cell responses, but both MVA-B/MVA-B and MVA-TMEP/MVA-TMEP combinations elicited higher Gag-Pol-Nef (GPN)-specific CD8 T cell responses compared to MVA-TMEP/MVA-B. Our results revealed an enhanced induction of HIV-1-specific T cell responses by TMEP-B when vectored in both DNA and MVA, and supported their use in combined prime/boost strategies for HIV-1 prevention and/or therapy.

Development of an Improved Method for Genetic Fate Mapping of Brain Microglia

As the resident macrophage cells of the brain, microglia are crucial for the phagocytosis of infectious agents, apoptotic cells and synapses. Developmentally, microglia originate from the embryonic yolk sac and serve important roles in the sculpting of neonatal neural circuits. In the context of severe brain injury or infection, bone‐marrow derived macrophages invade neural tissue, making it difficult to distinguish between invading macrophages and resident microglia. Although bone‐marrow derived macrophages can adopt some features of endogenous microglia, they are not able to fully recapitulate all of their properties, suggesting that there may be important functional differences between these two populations of cells. To distinguish between resident microglia and circulating myelogenous macrophages, we generated a P2ry12‐CreER mouse line. P2RY12 is a microglial‐specific nucleotide sensing GPCR that is important for microglial response to tissue damage. The P2ry12‐CreER line was generated by CRISPR‐facilitated homologous recombination and insertion of a 2A‐CreER sequence into the 3’ end of the P2RY12 coding sequence. Using immunofluorescent labeling and flow cytometry, we determined whether this recombination was specific to parenchymal microglia, as compared to meningeal, choroid plexus or perivascular macrophages. We also describe preliminary experiments that involve transcriptional profiling of P2ry12‐CreER recombined cells, using a Cre‐dependent Rpl22‐HA mouse line. Finally, using mouse models of neonatal and adult stroke, we used the P2ry12‐CreER line to fate map true brain microglia in the context of brain injury. Altogether, these results demonstrate the utility of this novel mouse line for genetic recombination, gene expression and fate‐mapping studies of brain microglia.Support or Funding InformationNIH K08NS096192This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Genome-Wide Identification and Analysis of High-Copy-Number LTR Retrotransposons in Asian Pears.

A large proportion of the genome of ‘Suli’ pear (Pyrus pyrifolia) contains long terminal repeat retrotransposons (LTR-RTs), which suggests that LTR-RTs have played important roles in the evolution of Pyrus. Further analysis of retrotransposons, particularly of high-copy-number LTR-RTs in different species, will provide new insights into the evolutionary history of Pyrus. A total of 4912 putative LTR-RTs classified into 198 subfamilies were identified in the ‘Suli’ pear genome. Six Asian pear accessions, including cultivars and wild species, were resequenced. The comparison of copy number for each LTR-RT subfamily was evaluated in Pyrus accessions, and data showed up to four-fold differences for some subfamilies. This contrast suggests different fates for retrotransposon families in the evolution of Pyrus. Fourteen high-copy-number subfamilies were identified in Asian pears, and more than 50% of the LTR-RTs in the genomes of all Pyrus accessions were from these 14 identified LTR-RT subfamilies. Their average insertion time was 3.42 million years ago, which suggests that these subfamilies were recently inserted into the genome. Many homologous and specific retrotransposon insertion sites were identified in oriental and occidental pears, suggesting that the duplication of retrotransposons has occurred throughout almost the entire origin and evolution of Pyrus species. The LTR-RTs show high heterogeneity, and their copy numbers vary in different Pyrus species. Thus, our findings suggest that LTR-RTs are an important source of genetic variation among Pyrus species.

Target-Specific Precision of CRISPR-Mediated Genome Editing

SummaryThe CRISPR-Cas9 system has successfully been adapted to edit the genome of various organisms. However, our ability to predict the editing outcome at specific sites is limited. Here, we examined indel profiles at over 1,000 genomic sites in human cells and uncovered general principles guiding CRISPR-mediated DNA editing. We find that precision of DNA editing (i.e., recurrence of a specific indel) varies considerably among sites, with some targets showing one highly preferred indel and others displaying numerous infrequent indels. Editing precision correlates with editing efficiency and a preference for single-nucleotide homologous insertions. Precise targets and editing outcome can be predicted based on simple rules that mainly depend on the fourth nucleotide upstream of the protospacer adjacent motif (PAM). Indel profiles are robust, but they can be influenced by chromatin features. Our findings have important implications for clinical applications of CRISPR technology and reveal general patterns of broken end joining that can provide insights into DNA repair mechanisms.

Comparison of the Mitochondrial Genome Sequences of Six Annulohypoxylon stygium Isolates Suggests Short Fragment Insertions as a Potential Factor Leading to Larger Genomic Size.

Mitochondrial DNA (mtDNA) is a core non-nuclear genetic material found in all eukaryotic organisms, the size of which varies extensively in the eumycota, even within species. In this study, mitochondrial genomes of six isolates of Annulohypoxylon stygium (Lév.) were assembled from raw reads from PacBio and Illumina sequencing. The diversity of genomic structures, conserved genes, intergenic regions and introns were analyzed and compared. Genome sizes ranged from 132 to 147 kb and contained the same sets of conserved protein-coding, tRNA and rRNA genes and shared the same gene arrangements and orientation. In addition, most intergenic regions were homogeneous and had similar sizes except for the region between cytochrome b (cob) and cytochrome c oxidase I (cox1) genes which ranged from 2,998 to 8,039 bp among the six isolates. Sixty-five intron insertion sites and 99 different introns were detected in these genomes. Each genome contained 45 or more introns, which varied in distribution and content. Introns from homologous insertion sites also showed high diversity in size, type and content. Comparison of introns at the same loci showed some complex introns, such as twintrons and ORF-less introns. There were 44 short fragment insertions detected within introns, intergenic regions, or as introns, some of them located at conserved domain regions of homing endonuclease genes. Insertions of short fragments such as small inverted repeats might affect or hinder the movement of introns, and these allowed for intron accumulation in the mitochondrial genomes analyzed, and enlarged their size. This study showed that the evolution of fungal mitochondrial introns is complex, and the results suggest short fragment insertions as a potential factor leading to larger mitochondrial genomes in A. stygium.

Going, going, gone: predicting the fate of genomic insertions in plant RNA viruses.

Horizontal gene transfer is common among viruses, while they also have highly compact genomes and tend to lose artificial genomic insertions rapidly. Understanding the stability of genomic insertions in viral genomes is therefore relevant for explaining and predicting their evolutionary patterns. Here, we revisit a large body of experimental research on a plant RNA virus, tobacco etch potyvirus (TEV), to identify the patterns underlying the stability of a range of homologous and heterologous insertions in the viral genome. We obtained a wide range of estimates for the recombination rate-the rate at which deletions removing the insertion occur-and these appeared to be independent of the type of insertion and its location. Of the factors we considered, recombination rate was the best predictor of insertion stability, although we could not identify the specific sequence characteristics that would help predict insertion instability. We also considered experimentally the possibility that functional insertions lead to higher mutational robustness through increased redundancy. However, our observations suggest that both functional and non-functional increases in genome size decreased the mutational robustness. Our results therefore demonstrate the importance of recombination rates for predicting the long-term stability and evolution of viral RNA genomes and suggest that there are unexpected drawbacks to increases in genome size for mutational robustness.

Assessment of two CRISPR-Cas9 genome editing protocols for rapid generation of Trypanosoma cruzi gene knockout mutants

CRISPR/Cas9 technology has been used to edit genomes in a variety of organisms. Using the GP72 gene as a target sequence, we tested two distinct approaches to generate Trypanosoma cruzi knockout mutants using the Cas9 nuclease and in vitro transcribed single guide RNA. Highly efficient rates of disruption of GP72 were achieved either by transfecting parasites stably expressing Streptococcus pyogenes Cas9 with single guide RNA or by transfecting wild type parasites with recombinant Staphylococcus aureus Cas9 previously associated with single guide RNA. In both protocols, we used single-stranded oligonucleotides as a repair template for homologous recombination and insertion of stop codons in the target gene.

Roles of Streptococcus pneumoniae CiaR in regulating the expression of pbps genes and csRNAs and its correlation with drug resistance

Objective To construct a ciaR gene-knockout (ΔciaR) mutant of Streptococcus pneumoniae (S.pneumoniae) and to investigate the effects of CiaR in CiaH/CiaR, a streptococcal two-component signal-transducing system, on the expression of genes encoding penicillin-binding proteins (pbps genes) and cia-dependent small RNAs (csRNAs). Methods Electrophoretic mobility shift assay (ESMA) was performed to detect the recombinant CiaR (rCiaR)-binding pbps genes. A suicide plasmid pEVP3ciaR for ciaR gene knockout was constructed and then a ΔciaR mutant was obtained through homologous recombination and insertion inactivation of the suicide plasmid, and screening with chloromycin. The mutant was identified using PCR and sequencing analysis. E-test was used to detect the minimal inhibitory concentrations (MIC) of penicillin (PCN) and cefotaxime (CTX) against S. pneumoniae strains. Changes and differences in the expression of pbps genes and csRNAs in the ΔciaR mutant and its wild-type strain before and after treatment with 1/4 MIC of PCN or CTX were detected using real-time quantitative RT-PCR. Results The rCiaR could bind to the promoter regions in pbp1a, pbp1b and pbp2b genes of S. pneumoniae. The ciaR gene in ΔciaR mutant was inactivated by insertion according to the results of PCR and sequencing analysis. After treatment with 1/4 MIC of PCN or CTX, the expression of pbps genes at mRNA level (pbps-mRNAs) in the ΔciaR mutant was significantly increased (P<0.05), but the levels of csRNAs were significantly decreased (P<0.05); whereas a significantly decreased pbps-mRNAs (P<0.05) and increased csRNAs (P<0.05) were observed in its wild-type strain. The result of E-test showed that the MICs of PCN and CTX against ΔciaR mutant were increased by 250-fold as compared with those against its wild-type strain. Conclusion The CiaR can enhance the drug resistance of S. pneumoniae to PCN and CTX through down-regulating the expression of PBP1a, PBP1b and PBP2b and up-regulating the expression of csRNAs to inhibit the expression of PBPs. Key words: Streptococcus pneumoniae; Drug resistance; Response regulation protein/CiaR; Gene knockout; PBPs/csRNAs

Efficient generation of targeted and controlled mutational events in porcine cells using nuclease-directed homologous recombination

BackgroundNuclease-based genome editing has rapidly sped the creation of new models of human disease. These techniques also hold great promise for the future of clinical xenotransplantation and cell-based therapies for cancer or immunodeficient pathology. However, to fully realize the potential of nuclease editing tools, the efficiency and precision of their application must be optimized. The object of this study was to use nonintegrating selection and nuclease-directed homologous recombination to efficiently control the genetic modification of the porcine genome. MethodsClustered randomly integrating spaced palindromic repeats and associated Cas9 protein (CRISPR/Cas9)-directed mutagenesis with a single-guide RNA target was designed to target the alpha-1,3-galactosyltransferase locus (GGTA1) of the porcine genome. A vector expressing a single-guide RNA, Cas9 protein, and green fluorescent protein was used to increase plasmid-delivered mutational efficiency when coupled with fluorescence sorting. Single and double-strand DNA oligonucleotides with a restriction site replacing the start codon were created with variable homology lengths surrounding the mutational event site. Finally, a transgene construct was flanked with 50 base pairs of homology directed immediately 5′ to a nuclease cut site. These products were introduced to cells with a constant concentration of CRISPR/cas9 vector. Phenotype-specific mutational efficiency was measured by flow cytometer. Controlled homologous insertion was measured by Sanger sequence, restriction enzyme digest and flow cytometry. ResultsExpression of a fluorescence protein on the Cas9 vector functioned as a nonintegrating selection marker. Selection by this marker increased phenotype-silencing mutation rates from 3.5% to 82% (P = 0.0002). Insertion or deletion mutation increased from 11% to 96% (P = 0.0007). Co-transfection with homologous DNA oligonucleotides increased the aggregate phenotype-silencing mutation rates up to 22% and increased biallelic events. Single-strand DNA was twice as efficient as double-strand DNA. Furthermore, nuclease-mediated insertion by homology-directed repair successfully drove locus-specific transgene expression in the porcine genome. ConclusionsA nonintegrating selection strategy based on fluorescence expression can increase the mutational efficiency of the CRISPR/Cas9 system. The precision of this system can be increased by the addition of a very short homologous template sequence and can serve as a method for locus-specific transgene delivery. Together these strategies may be used to efficiently control mutational events. This system may be used to better use the potential of nuclease-mediated genomic editing.

The IncP-6 Plasmid p10265-KPC from Pseudomonas aeruginosa Carries a Novel ΔISEc33-Associated bla KPC-2 Gene Cluster.

Pseudomonas aeruginosa strain 10265 was recovered from a patient with pneumonia in a Chinese public hospital, and it displays the carbapenem resistance phenotype due to the acquisition of a non-conjugative but mobilizable IncP-6-type plasmid p10265-KPC. p10265-KPC carries a Tn5563-borne defective mer locus, and a novel ΔISEc33-associated blaKPC-2 gene cluster without paired inverted repeats and paired direct repeats at both ends. Mobilization of this ΔISEc33-associated element in p10265-KPC would be attributed to homologous recombination-based insertion of a foreign structure Tn3-ISApu1-orf7-ISApu2- ISKpn27-ΔblaTEM-1-blaKPC-2-ΔISKpn6- korC-orf6-klcA-ΔrepB into a pre-existent intact ISEc33, making ISEc33 truncated at the 3′ end. The previously reported pCOL-1 represents the first sequenced KPC-producing IncP-6 plasmid, while p10265-KPC is the second one. These two plasmids carry two distinct blaKPC-2 gene clusters, which are inserted into the different sites of the IncP-6 backbone and have different evolutionary histories of assembly and mobilization. This is the first report of identification of the IncP-6-type resistance plasmid in China.

Vaccination With Heterologous HIV-1 Envelope Sequences and Heterologous Adenovirus Vectors Increases T-Cell Responses to Conserved Regions: HVTN 083.

Increasing the breadth of human immunodeficiency virus type 1 (HIV-1) vaccine-elicited immune responses or targeting conserved regions may improve coverage of circulating strains. HIV Vaccine Trials Network 083 tested whether cellular immune responses with these features are induced by prime-boost strategies, using heterologous vectors, heterologous inserts, or a combination of both. A total of 180 participants were randomly assigned to receive combinations of adenovirus vectors (Ad5 or Ad35) and HIV-1 envelope (Env) gene inserts (clade A or B) in a prime-boost regimen. T-cell responses to heterologous and homologous insert regimens targeted a similar number of epitopes (ratio of means, 1.0; 95% confidence interval [CI], .6-1.6; P = .91), but heterologous insert regimens induced significantly more epitopes that were shared between EnvA and EnvB than homologous insert regimens (ratio of means, 2.7; 95% CI, 1.2-5.7; P = .01). Participants in the heterologous versus homologous insert groups had T-cell responses that targeted epitopes with greater evolutionary conservation (mean entropy [±SD], 0.32 ± 0.1 bits; P = .003), and epitopes recognized by responders provided higher coverage (49%; P = .035). Heterologous vector regimens had higher numbers of total, EnvA, and EnvB epitopes than homologous vector regimens (P = .02, .044, and .045, respectively). These data demonstrate that vaccination with heterologous insert prime boosting increased T-cell responses to shared epitopes, while heterologous vector prime boosting increased the number of T-cell epitopes recognized. NCT01095224.

Correlation between the ciaH gene of Streptococcus pneumoniae and the resistance to β-lactam antibiotics

Objective To construct a mutant strain of Streptococcus pneumoniae (S.pneumoniae) with ciaH gene-knockout (ΔciaH) and to analyze the correlation between the ciaH gene and the bacterial resistance against β-lactam antibiotics. Methods The ciaH gene segament of S. pneumoniae strain ATCC6306 was amplified by PCR. The PCR product was sequenced after T-A cloning. A suicide plasmid pEVP3ciaH was constructed for the deletion of ciaH gene and then transformed into the ATCC6306 strain by using the CaCl2 method. The mutant strain of S. pneumonia strain ATCC6306 with ciaH gene-knockout (ΔciaH) was generated through homologous recombination, insertion inactivation and amphemycin screening, which was further identified by PCR, sequencing analysis and laser confocal microscopy. Double agar dilution method was used to detect the minimal inhibitory concentrations (MICs) of penicillin G (PCN) and cefotaxime (CTX) against the ΔciaH mutant strain and the wild type strain. The differences between the MICs were further analyzed. The changes of ciaH gene expression at mRNA level after treatment with 1/4 MIC of PCN or CTX were detected by real-time fluorescent quantitative RT-PCR (qRT-PCR). Results The ciaH gene in the genomic DNA of the generated ΔciaH mutant strain was inactivated by insertion as indicated by PCR and sequencing analysis. Results of the immunofluorescence assay showed that the ΔciaH mutant strain did not express the CiaH protein. The MICs of PCN and CTX against the ΔciaH mutant strain were 32 μg/ml and 64 μg/ml, respectively, which were significantly higher than that of the wild type strain (0.06 μg/ml and 1 μg/ml) (P<0.01). The expression of ciaH gene at mRNA level was significantly elevated after treatment S. pneumoniae ATCC6306 strain with 1/4 MIC PCN or CTX (P<0.01). Conclusion The CiaH protein in the CiaH/CiaR two-component signaling system is involved in the resistance of S. pneumoniae against β-lactam antibiotics. Key words: Streptococcus pneumoniae; Two-component signaling system; CiaH protein; β-lactam antibiotics; Drug resistance

Safety and Immunogenicity of a Recombinant Adenovirus Serotype 35-Vectored HIV-1 Vaccine in Adenovirus Serotype 5 Seronegative and Seropositive Individuals.

Recombinant adenovirus serotype 5 (rAd5)-vectored HIV-1 vaccines have not prevented HIV-1 infection or disease and pre-existing Ad5 neutralizing antibodies may limit the clinical utility of Ad5 vectors globally. Using a rare Ad serotype vector, such as Ad35, may circumvent these issues, but there are few data on the safety and immunogenicity of rAd35 directly compared to rAd5 following human vaccination. HVTN 077 randomized 192 healthy, HIV-uninfected participants into one of four HIV-1 vaccine/placebo groups: rAd35/rAd5, DNA/rAd5, and DNA/rAd35 in Ad5-seronegative persons; and DNA/rAd35 in Ad5-seropositive persons. All vaccines encoded the HIV-1 EnvA antigen. Antibody and T-cell responses were measured 4 weeks post boost immunization. All vaccines were generally well tolerated and similarly immunogenic. As compared to rAd5, rAd35 was equally potent in boosting HIV-1-specific humoral and cellular immunity and responses were not significantly attenuated in those with baseline Ad5 seropositivity. Like DNA, rAd35 efficiently primed rAd5 boosting. All vaccine regimens tested elicited cross-clade antibody responses, including Env V1/V2-specific IgG responses. Vaccine antigen delivery by rAd35 is well-tolerated and immunogenic as a prime to rAd5 immunization and as a boost to prior DNA immunization with the homologous insert. Further development of rAd35-vectored prime-boost vaccine regimens is warranted.

Application of CRISPR/cas9-Directed Homologous Recombination to the Generation of Human Tumor Cells with Conditional Knockout of an X-Linked MicroRNA Locus

Studying the cellular function of microRNAs requires genetic strategies to generate their loss-of-function. Recently, a novel approach of targeted genomic deletion was proposed, which is based on induction of site-specific DNA cuts with Cas9/gRNA ribonucleoprotein complexes, combined with homologous recombination-dependent insertion of cassettes that contain sequences for Cre-lox or FLP-FRT systems. Here, we provide a technical report describing application of this CRISPR/Cas9-directed homologous recombination procedure to the generation of human tumor cells in which conditional knockout of an X-linked cluster of microRNAs (miR-105/miR-767) can be induced. We describe the successive steps of genetic engineering and cell clone selection that allowed us to generate cells with the expected genome editing.