Apicomplexa are unicellular eukaryotes that parasitise a wide spectrum of invertebrates and vertebrates, including humans. In their hosts, they occupy a variety of niches, from extracellular cavities (intestine, coelom) to epicellular and intracellular locations, depending on the species and/or developmental stages. During their evolution, Apicomplexa thus developed an exceptionally wide range of unique features to reach these diversified parasitic niches and to survive there, at least long enough to ensure their own transmission or that of their progeny. This review summarises the current state of knowledge on the attachment/invasive and nutrient uptake strategies displayed by apicomplexan parasites, focusing on trophozoite stages of their so far poorly studied basal representatives, which mostly parasitise invertebrate hosts. We describe their most important morphofunctional features, and where applicable, discuss existing major similarities and/or differences in the corresponding mechanisms, incomparably better described at the molecular level in the more advanced Apicomplexa species, of medical and veterinary significance, which mainly occupy intracellular niches in vertebrate hosts.

• Keywords
• apical complex, attachment, epimerite, feeder organelle, mucron, myzocytosis, nutrition, parasitophorous vacuole/sac, pores, trophozoite,
• Publication type
• Journal Article MeSH
• Review MeSH

Representatives of Apicomplexa perform various kinds of movements that are linked to the different stages of their life cycle. Ancestral apicomplexan lineages, including gregarines, represent organisms suitable for research into the evolution and diversification of motility within the group. The vermiform trophozoites and gamonts of the archigregarine Selenidium pygospionis perform a very active type of bending motility. Experimental assays and subsequent light, electron, and confocal microscopic analyses demonstrated the fundamental role of the cytoskeletal proteins actin and tubulin in S. pygospionis motility and allowed us to compare the mechanism of its movement to the gliding machinery (the so-called glideosome concept) described in apicomplexan zoites. Actin-modifying drugs caused a reduction in the movement speed (cytochalasin D) or stopped the motility of archigregarines completely (jasplakinolide). Microtubule-disrupting drugs (oryzalin and colchicine) had an even more noticeable effect on archigregarine motility. The fading and disappearance of microtubules were documented in ultrathin sections, along with the formation of α-tubulin clusters visible after the immunofluorescent labelling of drug-treated archigregarines. The obtained data indicate that subpellicular microtubules most likely constitute the main motor structure involved in S. pygospionis bending motility, while actin has rather a supportive function.

• Keywords
• Actin, Cytoskeletal drugs, Microtubules, Motility, Ultrastructure, α-Tubulin,
• MeSH
• Actins metabolism   MeSH
• Apicomplexa growth & development   physiology   ultrastructure   MeSH
• Cytoskeleton metabolism   ultrastructure   MeSH
• Microtubules metabolism   MeSH
• Parasites MeSH
• Protozoan Proteins metabolism   MeSH
• Electron Microscope Tomography MeSH
• Trophozoites growth & development   metabolism   ultrastructure   MeSH
• Tubulin metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Actins MeSH
• Protozoan Proteins MeSH
• Tubulin MeSH