Abstract
Cellular motility is essential for microscopic parasites, it is used to reach the host, migrate through tissues, or evade host immune reactions. Many cells employ an evolutionary conserved motor protein– actin, to crawl or glide along a substrate. We describe the peculiar movement of Sphaerospora molnari, a myxozoan parasite with proliferating blood stages in its host, common carp. Myxozoa are highly adapted parasitic cnidarians alternately infecting vertebrates and invertebrates. S. molnari blood stages (SMBS) have developed a unique “dancing” behaviour, using the external membrane as a motility effector to rotate and move the cell. SMBS movement is exceptionally fast compared to other myxozoans, non-directional and constant. The movement is based on two cytoplasmic actins that are highly divergent from those of other metazoans. We produced a specific polyclonal actin antibody for the staining and immunolabelling of S. molnari’s microfilaments since we found that neither commercial antibodies nor phalloidin recognised the protein or microfilaments. We show the in situ localization of this actin in the parasite and discuss the importance of this motility for evasion from the cellular host immune response in vitro. This new type of motility holds key insights into the evolution of cellular motility and associated proteins.
Highlights
Motility is a basic requirement for all cells; one of the main driving forces is acto-myosin contraction which is highly conserved between divergent taxa
In Sphaerospora molnari blood stages ( S. molnari blood stages (SMBS)), the speed of motility is reduced by increased viscosity of the surrounding medium (1.5% methylcellulose) or by lower temperatures e.g. 5 °C and 10 °C, but neither viscosity increase nor temperature drop hindered fold formation
The shape of the primary cell of SMBS is extremely plastic, it alters with the production of small to large folds in the membrane in addition to the membrane shifting as a whole
Summary
Motility is a basic requirement for all cells; one of the main driving forces is acto-myosin contraction which is highly conserved between divergent taxa. The innovative nature of their gene evolution could be linked to the highly plastic and variable cnidarian biology in which life strategies range from free living to semi-parasitic and completely parasitic, some with larval stages, some as active migraters etc.[8] The conquest of these diverse biological niches has led to a high variety of cnidarian orthologues and proteins. Myxozoan blood stages were first reported in carp in 1976 as “unidentified blood objects”[17] and the movement described as “dancing”; only recently SSU rDNA sequencing identified the cells as S. molnari[16]. Their dancing movement has been described as “twitching”[18], and is extremely fast, non-directional and produced without tubulin-based cell appendages such as cilia or flagella. This adaptation of conserved proteins into new kinds of motility has evolutionary significance for all metazoan cellular movement
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