Shinji Masui

The University of Tokyo, Tōkyō, Japan

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Publications (6)12.12 Total impact

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    ABSTRACT: Wolbachia are intracellular symbionts mainly found in arthropods, causing various sexual alterations on their hosts by unknown mechanisms. Here we report the results that strongly suggest that Wolbachia have virus-like particles of phage WO, which was previously identified as a prophage-like element in the Wolbachia genome. Wolbachia (strain wTai) infection in an insect was detected with the antibody against Wsp, an outer surface protein of Wolbachia, by fluorescence microscopy and immunoelectron-microscopy for the first time. Virus-like particles in Wolbachia were observed by electron-microscopy. The 0.22-microm filtrate of insect ovary contained DAPI-positive particles, and PCR analysis demonstrated that a phage WO DNA passed through the filter while Wolbachia DNA were eliminated, suggesting that the DAPI-positive particles were phage WO.
    Biochemical and Biophysical Research Communications 06/2001; 283(5):1099-104. DOI:10.1006/bbrc.2001.4906 · 2.30 Impact Factor
  • S Masui · S Kamoda · T Sasaki · H Ishikawa
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    ABSTRACT: Wolbachia are obligatory intracellular and maternally inherited bacteria, known to infect many species of arthropod. In this study, we discovered a bacteriophage-like genetic element in Wolbachia, which was tentatively named bacteriophage WO. The phylogenetic tree based on phage WO genes of several Wolbachia strains was not congruent with that based on chromosomal genes of the same strains, suggesting that phage WO was active and horizontally transmitted among various Wolbachia strains. All the strains of Wolbachia used in this study were infected with phage WO. Although the phage genome contained genes of diverse origins, the average G+C content and codon usage of these genes were quite similar to those of a chromosomal gene of Wolbachia. These results raised the possibility that phage WO has been associated with Wolbachia for a very long time, conferring some benefit to its hosts. The evolution and possible roles of phage WO in various reproductive alterations of insects caused by Wolbachia are discussed.
    Journal of Molecular Evolution 12/2000; 51(5):491-7. DOI:10.1007/s002390010112 · 1.68 Impact Factor
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    Shinji Masui · Tetsuhiko Sasaki · Hajime Ishikawa
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    ABSTRACT: Wolbachia species are intracellular bacteria known to cause reproductive abnormalities in their hosts. In this study, we identified Wolbachia genes encoding homologs to the type IV secretion system by which many pathogenic bacteria secrete macromolecules. The genes identified encoded most of the essential components of the secretion system and were cotranscribed as an operon.
    Journal of Bacteriology 12/2000; 182(22):6529-31. DOI:10.1128/JB.182.22.6529-6531.2000 · 2.81 Impact Factor
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    S Kamoda · S Masui · H Ishikawa · T Sasaki
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    ABSTRACT: Wolbachia are cytoplasmically inherited bacteria found in many arthropods. They induce various reproductive alterations in their hosts, including cytoplasmic incompatibility, thelytokous parthenogenesis, feminization and male-killing. In this study, we examined Wolbachia infection and its effects on the host cricket Teleogryllus taiwanemma. In a phylogenetic study based on the wsp gene coding for a Wolbachia surface protein, the Wolbachia strain harboured by T. taiwanemma was clustered together with those harboured by Laodelphax striatellus, Tribolium confusum, Acraea encedon, Trichogramma deion and Adalia bipunctata. Crossing experiments using the Wolbachia-infected and uninfected strains of cricket showed that the infection is associated with the expression of unidirectional cytoplasmic incompatibility: the egg hatch rate in the incompatible cross between the infected males and uninfected females was 20.3 %. We also examined the distribution of Wolbachia within the host using polymerase chain reaction assays; they were detected in the antennae, heads, forewings, hindwings, testes, ovaries, Malpighian tubules, foot muscles and fat bodies. Quantitative polymerase chain reaction assays showed that the bacterial density was highest in the fat bodies, followed by the ovaries and testes. Wolbachia were not detected in the haemolymph or in mature spermatozoa. The spermatozoa of the infected male may be modified by the presence of Wolbachia during its development. To examine this possibility, we compared the profiles of sperm proteins between the infected and uninfected males using two-dimensional gel electrophoresis. However, no differences in the protein profiles were observed.
    Journal of Experimental Biology 09/2000; 203(Pt 16):2503-9. · 2.90 Impact Factor
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    ABSTRACT: Wolbachia are maternally inherited intracellular rickettsia-like bacteria known to infect a wide range of arthropods. They are associated with a number of different reproductive phenotypes in their hosts, such as cytoplasmic incompatibility, parthenogenesis, and feminization. We report on a novel insertion sequence (IS), ISW1, which was identified in the region downstream of groEL of a Wolbachia strain, wTai. The 573-bp-long ISW1 sequence is the first IS element observed in this organism, displays significant similarity to IS200, and lacks terminal inverted repeats. There were more than 20 copies of ISW1 on the chromosome of wTai. Sequence analysis of nine distinct ISW1 copies and their flanking regions showed that the copies were identical and suggested that ISW1 has no preference for its insertion sites. Possible roles of ISW1 in the adaptation of Wolbachia to intracellular environments and in various reproductive alterations caused by this bacterium are discussed.
    Plasmid 08/1999; 42(1):13-9. DOI:10.1006/plas.1999.1407 · 1.58 Impact Factor
  • Shinji Masui · Tetsuhiko Sasaki · Hajime Ishikawa
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    ABSTRACT: Wolbachia, a member of rickettsia found in the cells of many arthropod species, are cytoplasmically inherited bacteria which interfere with host's sexuality and reproduction. Wolbachia strains have been phylogenetically divided into A and B groups based on the nucleotide sequences of their ftsZ genes. In an attempt to further define the phylogenetical relationship among these endosymbionts, we cloned and sequenced the entire length of the groE operon of a Wolbachia harbored by a cricket. The operon encoded two heat shock proteins, which represented the third and fourth proteins of any Wolbachia ever characterized. Also, 800 bp stretches of the groE operons of several other Wolbachia were sequenced, and a phylogenetic tree was constructed based on the results. The groE tree defined the relationship among A group Wolbachia strains that had not been successfully resolved by the ftsZ tree, and suggested unexpected horizontal transmission of these bacteria.
    ZOOLOGICAL SCIENCE 09/1997; 14(4):701-6. DOI:10.2108/zsj.14.701 · 0.86 Impact Factor