Plasmodium is a genus of parasitic single-celled organisms, some species of which cause malaria.
The parasite requires two hosts—a mosquitoAnopheles and man to complete their life cycle. It takes different forms at each stage of its life cycle. The transition from one form to another requires massive reorganization of the cytoskeleton. Scientists from the University of Geneva (UNIGE) have shed light on the organization of the cytoskeleton in plasmodia.
Their study, published in PLOS Biology,details the parasite's skeletal organization on an unprecedented scale by adapting a recently developed expansion microscopy technique. Biologists “inflate” cells before imaging, allowing access to more structural detail at the nanometric scale. During the study, scientists discovered traces of an organelle - conoids.
The cytoskeleton, or cell skeleton, is made up of a networkseveral types of filaments, including actin and tubulin. As the parasite goes through the developmental stages, its cytoskeleton undergoes multiple radical reorganizations. In particular, plasmodia require a very specific cytoskeleton to move and penetrate the membrane barriers of its host cells. These two processes are central to the pathogenesis of the parasites that cause malaria.
“Due to the very small size of plasmodium - 50times smaller than a human cell - seeing its cytoskeleton is a big technical problem. This is why we adapted our expansion microscopy protocol. It involves inflating a biological sample while maintaining its original shape. This is how we were able to observe plasmodia with a resolution that was not previously available,” explain Héloïse Berthier and Virginia Hamel, researchers from UNIGE.
Female scientists observed the parasite at the stageookinetes, the form responsible for invading the midgut of the mosquito. This is an important stage in the spread of malaria. At the tip of the parasite, biologists saw a structure made of tubulin. It is similar to the conoid, an organelle involved in host cell invasion, in the related Apicomplexa parasites.
Discovery of this rudimentary conoidhighlights the power of expansion microscopy that can be used to view cytoskeleton structures at nanoscale without the need for special microscopes.
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Anopheles mosquitoes - genus Dipterainsects, many species of which are carriers of human parasites - malaria plasmodia. Anopheles together with the genera Bironella and Chagasia make up the subfamily Anophelinae.
Intermediate filaments (PF, nanofilaments) -threadlike structures of special proteins, one of the three main components of the cytoskeleton of eukaryotic cells. Contained both in the cytoplasm and in the nucleus of most eukaryotic cells.
Actin is a globular protein from which microfilaments are formed - one of the main components of the cytoskeleton of eukaryotic cells.
Tubulin is the protein from whichmicrotubules. In them, as well as in the cytoplasm of cells, it is in the form of a dimer of one α-tubulin molecule and one β-tubulin molecule. As part of such a dimer, a GTP molecule is attached to each tubulin molecule. Each of these subunits has three domains.
In the method of expansion microscopy, the proteins under study are embedded in a dense network of molecules of the swelling polyelectrolyte gel, due to which the sample is physically enlarged.