title: Gene expression and localization analysis of Bombyx mori bidensovirus and its putative receptor in B. mori midgut.
abstract: Bombyx mori bidensovirus (BmBDV), which causes fatal flacherie disease in the silkworm, replicates only in midgut columnar cells. The viral resistance expressed by some silkworm strains, which is characterized as non-susceptibility irrespective of the viral dose, is determined by a single gene, nsd-2. We previously identified nsd-2 by positional cloning and found that this gene encodes a putative amino acid transporter that might function as a receptor for BmBDV. In this study, we investigated the relationship between the part of the midgut expressing nsd-2 (resistance gene), +(nsd-2) (susceptibility gene) and BmBDV propagation. Quantitative RT-PCR (qRT-PCR) analysis using total RNA isolated from the anterior, middle, and posterior parts of the midgut showed that nsd-2 and +(nsd-2) were strongly expressed in the posterior part of the midgut. The expression levels of both genes were very low in the anterior and middle parts. The qRT-PCR analysis showed that the expression levels of BmBDV-derived transcripts were correlated with the levels of +(nsd-2) expression. However, BmBDV-derived transcripts were clearly detected in all parts of the midgut. These results suggest that the infectivity of BmBDV depends mainly on the expression level of +(nsd-2) in the midgut and that viral infection is supported even by very faint expression of +(nsd-2). By contrast, the expression levels of +(nsd-2) were exceedingly low or undetectable in the middle part of the midgut, indicating that BmBDV infection might occur via another mechanism, independent of +(nsd-2), in the middle part of the midgut.
authors.affiliation: Department of Science of Biological Production, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan. Electronic address: katsuito@cc.tuat.ac.jp.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ito
authors.affiliation: Insect Mimetics Research Unit, National Institute of Agrobiological Sciences, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Shimura
authors.affiliation: Department of Agricultural and Environmental Biology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.affiliation: Faculty of Agriculture, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tsuda
authors.affiliation: Faculty of Agriculture, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8515, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Kobayashi
authors.affiliation: Department of Science of Biological Production, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tabunoki
authors.affiliation: Department of Science of Biological Production, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yokoyama
authors.affiliation: Department of Agricultural and Environmental Biology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Shimada
authors.affiliation: Insect-Plant Interaction Research Unit, National Institute of Agrobiological Sciences, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Kadono-Okuda
mesh_terms: D000818:Animals; D015153:Blotting, Western; D012831:Bombyx / Q000821:virology*; D017990:Densovirus / Q000472:pathogenicity* / Q000502:physiology; D004064:Digestive System / Q000382:microbiology; D020869:Gene Expression Profiling; D017344:Genes, Insect / Q000502:physiology*; D016679:Genome, Viral; D054884:Host-Pathogen Interactions; D007150:Immunohistochemistry; D060888:Real-Time Polymerase Chain Reaction; D059467:Transcriptome
keywords: Bidensovirus; Bombyx mori; Midgut; Silkworm; Virus receptor