Plasmodium falciparum (Pf) is the most prevalent and deadly plasmodium species that causes malaria in humans. The parasite has a complex lifecycle in its human host, including asexual and sexual stages of development. Sexual-stage parasites (gametocytes) undergo a complex process of development known as gametogenesis, in which they transform from a spherical stage I gametocyte into an elongated, falciform-shaped stage V gametocyte [1]. The dramatic morphological changes that occur through the five stages of gametogenesis are largely mediated by alterations in the parasite’s cytoskeleton, of which microtubules represent a key component. Of note, early ultrastructural studies [2] revealed bundles of intranuclear microtubules in stage II and III gametocytes, which is an atypical observation in eukaryotic cells. Herein, we complementarily employ light and electron microscopy to elucidate the organisation of intranuclear microtubules in stage II and III Pf gametocytes.
EB1 is a plus-end tracking protein that binds to the growing ends of microtubules and regulates the dynamics of the microtubule cytoskeleton [3]. We constructed an EB1-GFP cell line to elucidate microtubule organisation and mechanics. Deconvolution fluorescence microscopy reveals EB1-GFP is associated with gametocyte nuclear microtubules via co-localisation with Tubulin Tracker™ and Hoechst™. Transmission electron tomography reveals that nuclear microtubules nucleate from a microtubule organising centre embedded within the nuclear envelope. Using fluorescence and transmission electron microscopy we identified four distinct arrangements of intranuclear microtubules that appear to drive nuclear elongation in the developing gametocyte and may play an important role in nucleating sub-pellicular microtubules and promoting cell rigidity. Increasing cell rigidity is a key component of the pathogenesis of malaria infection, in which the parasitised erythrocytes avoid splenic clearance via adhesion to the endothelium [4].
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