title: Mechanisms of nodule-specific melanization in the hemocoel of the silkworm, Bombyx mori.
abstract: In the insect immune system, nodules are known to be a product of the cellular response against microorganisms and may be a preferential target for melanization. However, the mechanism of nodule-preferential melanization remains to be explored. In this study, we identified several mechanisms of nodule-preferential melanization by analyzing congregation and the activation of several factors involved in the prophenoloxidase (proPO)-activating system in the silkworm, Bombyx mori. Microorganism-binding assays revealed that B. mori larval plasma have an effective invading microorganism-surveillance network consisting of at least six pattern-recognition receptors (PRRs). We also found that a hemolymph serine proteinase, BmHP14, can bind to Saccharomyces cerevisiae. Pull-down assays showed that PRR C-type lectins form protein complexes with serine proteinase homologs, BmSPH1 and BmSPH2, which leads to the activated forms of BmSPH1 and BmSPH2 being gathered on microorganisms and trapped in nodules. Immunostaining analysis revealed that most factors in the proPO-activating system and some factors in the triggering system for antimicrobial peptide production exist in the granules of hemocytes which can gather in nodules. Western blot analysis showed that factors in the proPO-activating system are congregated in formed nodules by their concentration in plasma and aggregating hemocytes.
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Min
authors.initials: M
authors.lastname: Shu
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Dingze
authors.initials: D
authors.lastname: Mang
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Gege Sun
authors.initials: GS
authors.lastname: Fu
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Shiho
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Haruka
authors.initials: H
authors.lastname: Endo
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Kikuta
authors.affiliation: Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, Naka-cho, Koganei, Tokyo 184-8588, Japan. Electronic address: ryoichi@cc.tuat.ac.jp.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Sato
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D015153:Blotting, Western; D012831:Bombyx / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D006434:Hemocytes / Q000378:metabolism; D007106:Immune Sera; D007150:Immunohistochemistry; D008543:Melanins / Q000378:metabolism*; D016982:Micrococcus luteus / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D007106:Immune Sera; D008543:Melanins
keywords: Bombyx mori; Melanization; Nodule; Pattern recognition receptors; Serine proteinase; Serine proteinase homolog