Research teams from the University of Geneva (UNIGE) have found that the cytoskeleton of the malaria parasite is a rudimentary form of organelle – conoid. Scientists used to think it was an important part of the parasite’s invasion of the host.
Plasmodia are a genus of parasitic unicellular organisms, some of which cause malaria. About two hundred species are known, of which at least five species are parasitic on humans. Other species parasitize other vertebrates – monkeys, rodents, birds and reptiles.
The parasite requires two hosts – the Anopheles mosquito and a human – to complete its life cycle. It takes different forms at each stage of its life cycle. The transition from one form to another requires a 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 newly developed expansion microscopy technique. Biologists inflate cells before imaging, providing access to more structural details at the nanometer scale. During the study, scientists discovered traces of an organelle – a conoid.
The cytoskeleton or cell skeleton is made up of a network of several 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 the plasmodium – 50 times smaller than a human cell – seeing its cytoskeleton is a big technical problem. This is why we have adapted our expansion microscopy protocol. It consists in inflating a biological sample while maintaining its original shape. This is how we were able to observe plasmodia with a resolution that was not available before, ”explains Eloise Berthier and Virginia Hamel, researchers at UNIGE ..
Female scientists observed the parasite at the ookinetic stage, the form responsible for the mosquito’s midgut invasion. This is an important stage in the spread of malaria. At the tip of the parasite, biologists saw a tubulin structure. It is similar to the conoid, an organelle involved in host cell invasion in the related parasite Apicomplexa.
The discovery of this rudimentary conoid underscores the power of expansion microscopy, which can be used to view cytoskeleton structures at the nanoscale without the need for special microscopes.