title: Visualization of Assembly Intermediates and Budding Vacuoles of Singapore Grouper Iridovirus in Grouper Embryonic Cells.
abstract: Iridovirid infection is associated with the catastrophic loss in aquaculture industry and the population decline of wild amphibians and reptiles, but none of the iridovirid life cycles have been well explored. Here, we report the detailed visualization of the life cycle of Singapore grouper iridovirus (SGIV) in grouper cells by cryo-electron microscopy (cryoEM) and tomography (ET). EM imaging revealed that SGIV viral particles have an outer capsid layer, and the interaction of this layer with cellular plasma membrane initiates viral entry. Subsequent viral replication leads to formation of a viral assembly site (VAS), where membranous structures emerge as precursors to recruit capsid proteins to form an intermediate, double-shell, crescent-shaped structure, which curves to form icosahedral capsids. Knockdown of the major capsid protein eliminates the formation of viral capsids. As capsid formation progresses, electron-dense materials known to be involved in DNA encapsidation accumulate within the capsid until it is fully occupied. Besides the well-known budding mechanism through the cell periphery, we demonstrate a novel budding process in which viral particles bud into a tubular-like structure within vacuoles. This budding process may denote a new strategy used by SGIV to disseminate viral particles into neighbor cells while evading host immune response.
authors.affiliation: Mechanobiology Institute, National University of Singapore, Singapore 114543.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Biological Sciences; National University of Singapore, Singapore 114543.
authors.forename: Bich Ngoc
authors.initials: BN
authors.lastname: Tran
authors.affiliation: Mechanobiology Institute, National University of Singapore, Singapore 114543.
authors.forename: Fan
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Biology, Faculty of Science, Mahidol University, 272 Rama VI Rd. Rajdevi, Bangkok, Thailand 10400.
authors.forename: Puey
authors.initials: P
authors.lastname: Ounjai
authors.affiliation: Mechanobiology Institute, National University of Singapore, Singapore 114543.
authors.forename: Jinlu
authors.initials: J
authors.lastname: Wu
authors.affiliation: Mechanobiology Institute, National University of Singapore, Singapore 114543.|Department of Biological Sciences; National University of Singapore, Singapore 114543.
authors.forename: Choy L
authors.initials: CL
authors.lastname: Hew
mesh_terms: D000818:Animals; D002213:Capsid / Q000378:metabolism / Q000648:ultrastructure; D036022:Capsid Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D020285:Cryoelectron Microscopy; D005399:Fishes; D055785:Gene Knockdown Techniques; D005814:Genes, Viral; D017994:Iridovirus / Q000502:physiology* / Q000648:ultrastructure*; D014771:Virion; D019065:Virus Assembly; D057074:Virus Release; D014779:Virus Replication
chemical_list: D036022:Capsid Proteins