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Cryotomography of budding influenza A virus reveals filaments with diverse morphologies that mostly do not bear a genome at their distal end.

Vijayakrishnan S, Loney C, Jackson D, Suphamungmee W, Rixon FJ, Bhella D - PLoS Pathog. (2013)

Bottom Line: Long filaments that did not have bulbs were infrequently seen to bear an ordered complement of RNPs at their distal ends.Bacilliform virions contained an ordered complement of RNPs while longer filamentous particles were narrower and mostly appeared to lack this feature, but often contained fibrillar material along their entire length.The important ultrastructural differences between these diverse classes of particles raise the possibility of distinct morphogenetic pathways and functions during the infectious process.

View Article: PubMed Central - PubMed

Affiliation: MRC Centre for Virus Research, University of Glasgow, Glasgow, United Kingdom.

ABSTRACT
Influenza viruses exhibit striking variations in particle morphology between strains. Clinical isolates of influenza A virus have been shown to produce long filamentous particles while laboratory-adapted strains are predominantly spherical. However, the role of the filamentous phenotype in the influenza virus infectious cycle remains undetermined. We used cryo-electron tomography to conduct the first three-dimensional study of filamentous virus ultrastructure in particles budding from infected cells. Filaments were often longer than 10 microns and sometimes had bulbous heads at their leading ends, some of which contained tubules we attribute to M1 while none had recognisable ribonucleoprotein (RNP) and hence genome segments. Long filaments that did not have bulbs were infrequently seen to bear an ordered complement of RNPs at their distal ends. Imaging of purified virus also revealed diverse filament morphologies; short rods (bacilliform virions) and longer filaments. Bacilliform virions contained an ordered complement of RNPs while longer filamentous particles were narrower and mostly appeared to lack this feature, but often contained fibrillar material along their entire length. The important ultrastructural differences between these diverse classes of particles raise the possibility of distinct morphogenetic pathways and functions during the infectious process.

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Tomograms of purified A/Udorn/72 virions (A).Three distinct morphologies were observed: short-rods (B), longer filaments (C) and spherical virions (D). Length and diameter measurements from 96 particles were plotted (E) showing that filamentous particles had a narrower diameter compared to the shorter rod-shaped particles (that we term bacilliform virions). Long filaments that extended beyond the field of view were plotted with a filled square. Spherical virion dimensions (those with an axial ratio <1.2) were plotted with a hollow circle. See also movie S5 and figures S6 and S7.
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ppat-1003413-g007: Tomograms of purified A/Udorn/72 virions (A).Three distinct morphologies were observed: short-rods (B), longer filaments (C) and spherical virions (D). Length and diameter measurements from 96 particles were plotted (E) showing that filamentous particles had a narrower diameter compared to the shorter rod-shaped particles (that we term bacilliform virions). Long filaments that extended beyond the field of view were plotted with a filled square. Spherical virion dimensions (those with an axial ratio <1.2) were plotted with a hollow circle. See also movie S5 and figures S6 and S7.

Mentions: Experiments to image cell associated filamentous structures did not yield data on particles released into the media and in particular smaller virions were only rarely seen (Fig S6A, B). To provide a structural view of all classes of particle produced by infected cells and to compare the morphology of cell-associated filaments with virions and filaments released into the media we performed CET of purified virus particles (Fig. 7A, movie S5). These preparations were predominantly filamentous and very few Archetti bodies were seen (Fig S6C). Some filamentous structures were found to have varicosities along their lengths however these were more irregular in shape and did not resemble the Archetti bodies seen in our study of infected cells (Fig S6D). In our analysis of virus infected cells Archetti varicosities were predominantly seen to be at the termini of budding filaments, confocal imaging on the other hand appears to show filaments with varicosities along their length. Given the greater clarity of the CET data, we conclude that in most cases such features seen in confocal imaging are most likely the result of several Archetti filaments clustering together to give the appearance of a single entity. Very long filaments and Archetti bodies were seen to be fragile and liable to shear, it is likely then that the majority of longer filaments and Archetti bodies were lost during the purification process and were therefore not frequently seen in our study of purified filamentous particles.


Cryotomography of budding influenza A virus reveals filaments with diverse morphologies that mostly do not bear a genome at their distal end.

Vijayakrishnan S, Loney C, Jackson D, Suphamungmee W, Rixon FJ, Bhella D - PLoS Pathog. (2013)

Tomograms of purified A/Udorn/72 virions (A).Three distinct morphologies were observed: short-rods (B), longer filaments (C) and spherical virions (D). Length and diameter measurements from 96 particles were plotted (E) showing that filamentous particles had a narrower diameter compared to the shorter rod-shaped particles (that we term bacilliform virions). Long filaments that extended beyond the field of view were plotted with a filled square. Spherical virion dimensions (those with an axial ratio <1.2) were plotted with a hollow circle. See also movie S5 and figures S6 and S7.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3675018&req=5

ppat-1003413-g007: Tomograms of purified A/Udorn/72 virions (A).Three distinct morphologies were observed: short-rods (B), longer filaments (C) and spherical virions (D). Length and diameter measurements from 96 particles were plotted (E) showing that filamentous particles had a narrower diameter compared to the shorter rod-shaped particles (that we term bacilliform virions). Long filaments that extended beyond the field of view were plotted with a filled square. Spherical virion dimensions (those with an axial ratio <1.2) were plotted with a hollow circle. See also movie S5 and figures S6 and S7.
Mentions: Experiments to image cell associated filamentous structures did not yield data on particles released into the media and in particular smaller virions were only rarely seen (Fig S6A, B). To provide a structural view of all classes of particle produced by infected cells and to compare the morphology of cell-associated filaments with virions and filaments released into the media we performed CET of purified virus particles (Fig. 7A, movie S5). These preparations were predominantly filamentous and very few Archetti bodies were seen (Fig S6C). Some filamentous structures were found to have varicosities along their lengths however these were more irregular in shape and did not resemble the Archetti bodies seen in our study of infected cells (Fig S6D). In our analysis of virus infected cells Archetti varicosities were predominantly seen to be at the termini of budding filaments, confocal imaging on the other hand appears to show filaments with varicosities along their length. Given the greater clarity of the CET data, we conclude that in most cases such features seen in confocal imaging are most likely the result of several Archetti filaments clustering together to give the appearance of a single entity. Very long filaments and Archetti bodies were seen to be fragile and liable to shear, it is likely then that the majority of longer filaments and Archetti bodies were lost during the purification process and were therefore not frequently seen in our study of purified filamentous particles.

Bottom Line: Long filaments that did not have bulbs were infrequently seen to bear an ordered complement of RNPs at their distal ends.Bacilliform virions contained an ordered complement of RNPs while longer filamentous particles were narrower and mostly appeared to lack this feature, but often contained fibrillar material along their entire length.The important ultrastructural differences between these diverse classes of particles raise the possibility of distinct morphogenetic pathways and functions during the infectious process.

View Article: PubMed Central - PubMed

Affiliation: MRC Centre for Virus Research, University of Glasgow, Glasgow, United Kingdom.

ABSTRACT
Influenza viruses exhibit striking variations in particle morphology between strains. Clinical isolates of influenza A virus have been shown to produce long filamentous particles while laboratory-adapted strains are predominantly spherical. However, the role of the filamentous phenotype in the influenza virus infectious cycle remains undetermined. We used cryo-electron tomography to conduct the first three-dimensional study of filamentous virus ultrastructure in particles budding from infected cells. Filaments were often longer than 10 microns and sometimes had bulbous heads at their leading ends, some of which contained tubules we attribute to M1 while none had recognisable ribonucleoprotein (RNP) and hence genome segments. Long filaments that did not have bulbs were infrequently seen to bear an ordered complement of RNPs at their distal ends. Imaging of purified virus also revealed diverse filament morphologies; short rods (bacilliform virions) and longer filaments. Bacilliform virions contained an ordered complement of RNPs while longer filamentous particles were narrower and mostly appeared to lack this feature, but often contained fibrillar material along their entire length. The important ultrastructural differences between these diverse classes of particles raise the possibility of distinct morphogenetic pathways and functions during the infectious process.

Show MeSH
Related in: MedlinePlus