Abstract
BackgroundCharacterization of the structural morphology of virus particles in electron micrographs is a complex task, but desirable in connection with investigation of the maturation process and detection of changes in viral particle morphology in response to the effect of a mutation or antiviral drugs being applied. Therefore, we have here developed a procedure for describing and classifying virus particle forms in electron micrographs, based on determination of the invariant characteristics of the projection of a given virus structure. The template for the virus particle is created on the basis of information obtained from a small training set of electron micrographs and is then employed to classify and quantify similar structures of interest in an unlimited number of electron micrographs by a process of correlation.ResultsPractical application of the method is demonstrated by the ability to locate three diverse classes of virus particles in transmission electron micrographs of fibroblasts infected with human cytomegalovirus. These results show that fast screening of the total number of viral structures at different stages of maturation in a large set of electron micrographs, a task that is otherwise both time-consuming and tedious for the expert, can be accomplished rapidly and reliably with our automated procedure. Using linear deformation analysis, this novel algorithm described here can handle capsid variations such as ellipticity and furthermore allows evaluation of properties such as the size and orientation of a virus particle.ConclusionOur methodological procedure represents a promising objective tool for comparative studies of the intracellular assembly processes of virus particles using electron microscopy in combination with our digitized image analysis tool. An automated method for sorting and classifying virus particles at different stages of maturation will enable us to quantify virus production in all stages of the virus maturation process, not only count the number of infectious particles released from un infected cell.
Highlights
Characterization of the structural morphology of virus particles in electron micrographs is a complex task, but desirable in connection with investigation of the maturation process and detection of changes in viral particle morphology in response to the effect of a mutation or antiviral drugs being applied
The fact that the level of significance of H0 was 0.92 according to Student's t-test indicates that there was a fair probability that there was no systematic difference between these two approaches in mean. These results show that fast screening of the total number of viral structures at different stages of maturation in a large set of electron micrographs, a task that is otherwise both time-consuming and tedious for the expert, can be accomplished rapidly and reliably with our automated procedure
When investigating the process of virus assembly information concerning the structural topology in relationship to the stage of maturation is usually not available or vaguely defined
Summary
Characterization of the structural morphology of virus particles in electron micrographs is a complex task, but desirable in connection with investigation of the maturation process and detection of changes in viral particle morphology in response to the effect of a mutation or antiviral drugs being applied. Viruses utilize a host cell to produce their progeny virus particles by undergoing a complex process of maturation and intracellular transport. This process can be monitored at high magnification and resolution utilizing electron microscopy, which allows visual identification of different types of virus particles in different cellular compartments. Structural aspects of the virus maturation are generally hard to address visualisation techniques such as tomography and cryo-Electron Microscopy (cryoEM) have contributed tremendously to the vast information on virus structures. Image analysis tools to characterize and quantify virus particle maturation and intracellular transport would facilitate objective studies of different virus assembly states employing electron microscopy. Extraction of data from images by image analysis will be a valuable tool in virus assembly studies
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