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Our research program focuses on biology and phylogeny of early emerging apicomplexans
Phylum Apicomplexa represents one of the most successful groups of eukaryotic unicellular parasites consisting entirely of parasitic genera that infect a wide spectrum of vertebrates and invertebrates. They exhibit specific adaptations for invading and surviving within their hosts, which have evolved under distinct evolutionary pressures, resulting in diverse attachment strategies and host-parasite interactions. Apicomplexans restricted to invertebrates are usually considered of no economic or medical significance and thus, despite their enormous diversity, they generally remain poorly understood.It is generally accepted that ancestral apicomplexans parasitized marine annelids, and their radiation and adaptation to the parasitic life style took place before the era of vertebrates. First they spread to other marine invertebrates (crustaceans, turbellaria, echinoderms, etc.), then to freshwater and terrestrial invertebrates, and finally to vertebrates. There might be several early dispersed apicomplexan branches, e.g. blastogregarines, archigregarines, eu- and neogregarines, agamococcidians, protococcidians, and cryptosporidia.
They exhibit an enormous diversity in cell architecture and dimensions, depending on their parasitic strategy and surrounding environment, and seem to be a perfect example of a coevolution between a group of parasites and their hosts.
These organisms obviously differ from other apicomplexans in that their trophozoites and gamonts stage are often motile at least to some degree, and their locomotion usually differs from the substrate-dependent, actiomyosin-based gliding motility observed in motile apicomplexan zoite stages (the so called ‘glideosome’ concept). They seem to use several mechanisms of cell motility that correlate with various modifications of their cell cortex (epicyte), usually consisting of the plasma membrane and the closely apposed inner membrane complex that is associated with a number of cytoskeletal elements.
Different modes of motility, such as bending, rolling, coiling or nematode-like motility, gliding, metaboly or peristalsis, could represent specific adaptation of basal apicomplexans to parasitism in different environment within the host.
In contrast, apicomplexans parasitizing vertebrates comprise numerous etiologic agents of globally significant human diseases (e.g. malaria, toxoplasmosis, cryptosporidiosis) and thus are intensively studied. Strategies to control these pathogens are usually hampered by their localization and strategies to evade host immune responses and chemotherapeutics. In addition, apicomplexans possess a complex life cycle with several stages exhibiting different infective and metabolic properties within one species, and this makes prevention and therapy more difficult when compared to the common viral or bacterial diseases.
Recent phylogenetic and morphological analyses have pointed out close affinity of gregarines and cryptosporidia, and speculation that the genus Cryptosporidium represents a ‘missing link’ between the gregarines and coccidians is frequently discussed.