| Description |
Apicomplexans belong to the most monitored group of Protista, comprising exclusively parasites of vertebrates and invertebrates. Phylum Apicomplexa is characterised by typical apical complex and a complicated cell cortex consisting of inner membrane complex (IMC) underlying the plasma membrane. The IMC is connected with numerous cytoskeletal elements such as actomyosin complex, microtubules and a network of intermediate filaments. Numerous studies report that the motile apicomplexan invasive stages, the so-called zoites, use a unique mechanism of substrate dependent gliding motility facilitated by a conserved form of actomyosin motor (the so called “glideosome” concept). This concept was first time described in Toxoplasma gondii. The gliding motility relies on dynamic turnover of actin. Similarly apicomplexan myosins are considered unconventional and form a new class (XIV). This actomyosin motor is localized in between the parasite plasma membrane and IMC, and the gliding motility is based on the locomotion of myosin along actin filaments together with the transport of adhesins to the parasite’s posterior end. This machinery is based and limited by a formation of transient actin filaments and their fixation to the IMC, and requires a stabile subpellicular network of microtubules. Nevertheless, there exist early emerging groups of Apicomplexa, comprising gregarines, in which the exact mechanism of motility still remains unknown. These organisms seem to use several mechanisms of motility that correlate with various modifications of their cell cortex (epicyte). Different modes of motility, such as bending, rolling, coiling or waving, gliding, metaboly or peristalsis, could represent specific adaptations to parasitism in different environment. Deeper understanding of cell motility in basal lineages of Apicomplexa could help to explore new practical possibilities, such as treatment for diseases caused by them. Here we present our preliminary data on Siedleckia nematoides (blastogregarine), which is intestinal parasite of polychaete Scoloplos (Scoloplos) armiger. The elongated, flattened individuals of S. nematoides perform wavy movement and are covered by a pellicle, consisting of the plasma membrane and IMC. Their surface appears smooth lacking any grooves or folds. Interestingly, subpellicular microtubules are organized in several layers. Drugs proved to influence polymerization of cytoskeletal proteins, actin and tubulin, were used to evaluate the presumptive involvement of specific subcellular components in gregarine motility. For monitoring the subpellicular microtubules, incubation of living parasites in oryzalin (a drug causing the disruption of the microtubules) was performed. To verify the essential role actin microfilaments in motility of S. nematoides, drugs with contradictory effect, i.e. JAS (induce polymerization of actin) and cytochalasin D (inhibits polymerization of actin) were applied. Incubation in all mentioned drugs resulted in partial or complete blocking of parasites’ motility, but their motility recovered after returning them to the seawater. The application of oryzalin for prolonged period completely blocked the parasites’ motility, and the putatively unpolymerized alfa-tubulin seemed to be more dispersed throughout the cytoplasm (forming rosette-like structures) in contrast to control parasites incubated in the seawater (visualized using specific fluorescent labelling and CLSM). Similarly, changes in presence and distribution of F-actin were observed using the TRIC-phalloidin staining for CLSM; i.e. prolonged incubation of parasites in high doses of JAS caused significant increase of fluorescent signal, while their incubation in cytochalasin D resulted in its obvious decrease. Results of this study proved that the actin and tubulin polymerized forms play essential role in the movement of S. nematoides and the motility mechanism is comparable to the “glideosome” concept in apicomplexan zoites.
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