Visualization of Assembly Intermediates and Budding Vacuoles of Singapore Grouper Iridovirus in Grouper Embryonic Cells

by Yang Liu, Bich Ngoc Tran, Fan Wang, Puey Ounjai, Jinlu Wu & Choy L. Hew

Scientific Reports 6, Article number: 18696 (2016)

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.

Read online: Scientific Reports.

Frequency and amplitude control of cortical oscillations by phosphoinositide waves

by Ding Xiong, Shengping Xiao, Su Guo, Qinsong Lin, Fubito Nakatsu & Min Wu

Nature Chemical Biology (2016) doi:10.1038/nchembio.2000
Published online 11 January 2016

Rhythmicity is prevalent in the cortical dynamics of diverse single and multicellular systems. Current models of cortical oscillations focus primarily on cytoskeleton-based feedbacks, but information on signals upstream of the actin cytoskeleton is limited. In addition, inhibitory mechanisms—especially local inhibitory mechanisms, which ensure proper spatial and kinetic controls of activation—are not well understood. Here, we identified two phosphoinositide phosphatases, synaptojanin 2 and SHIP1, that function in periodic traveling waves of rat basophilic leukemia (RBL) mast cells. The local, phase-shifted activation of lipid phosphatases generates sequential waves of phosphoinositides. By acutely perturbing phosphoinositide composition using optogenetic methods, we showed that pulses of PtdIns(4,5)P2 regulate the amplitude of cyclic membrane waves while PtdIns(3,4)P2 sets the frequency. Collectively, these data suggest that the spatiotemporal dynamics of lipid metabolism have a key role in governing cortical oscillations and reveal how phosphatidylinositol 3-kinases (PI3K) activity could be frequency-encoded by a phosphatase-dependent inhibitory reaction.

Read online: Nature Chemical Biology.

Learn more about Wu Min‘s research.

Nanodroplet-Mediated Assembly of Platinum Nanoparticle Rings in Solution

Guanhua Lin†‡§∥, Xi Zhu, Utkarsh Anand†‡§∥, Qi Liu†‡§∥, Jingyu Lu†‡§∥, Zainul Aabdin†‡§∥, Haibin Su*⊥, and Utkur Mirsaidov*†‡§∥

Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551
Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546
§ Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore, 117543
NanoCore, National University of Singapore, 4 Engineering Drive 3, Singapore 117576
School of Materials Sciences and Engineering, Nanyang Technological University, Singapore 639798

Nano Lett., Article ASAP DOI: 10.1021/ acs.nanolett.5b04323 Publication Date (Web): January 4, 2016

Soft fluidlike nanoscale objects can drive nanoparticle assembly by serving as a scaffold for nanoparticle organization. The intermediate steps in these template-directed nanoscale assemblies are important but remain unresolved. We used real-time in situ transmission electron microscopy to follow the assembly dynamics of platinum nanoparticles into flexible ringlike chains around ethylenediaminetetraacetic acid nanodroplets dispersed in solution. In solution, these nanoring assemblies form via sequential attachment of the nanoparticles to binding sites located along the circumference of the nanodroplets, followed by the rearrangement and reorientation of the attached nanoparticles. Additionally, larger nanoparticle ring assemblies form via the coalescence of smaller ring assemblies. The intermediate steps of assembly reported here reveal how fluidlike nanotemplates drive nanoparticle organization, which can aid the future design of new nanomaterials.

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Learn more about Utkur Mirsaidov’s research.