Abstract
Toxoplasma gondii is an obligate intracellular parasite that invades host cells, creating a parasitophorous vacuole where it communicates with the host cell cytosol through the parasitophorous vacuole membrane. The lytic cycle of the parasite starts with its exit from the host cell followed by gliding motility, conoid extrusion, attachment, and invasion of another host cell. Here, we report that Ca(2+) oscillations occur in the cytosol of the parasite during egress, gliding, and invasion, which are critical steps of the lytic cycle. Extracellular Ca(2+) enhances each one of these processes. We used tachyzoite clonal lines expressing genetically encoded calcium indicators combined with host cells expressing transiently expressed calcium indicators of different colors, and we measured Ca(2+) changes in both parasites and host simultaneously during egress. We demonstrated a link between cytosolic Ca(2+) oscillations in the host and in the parasite. Our approach also allowed us to measure two new features of motile parasites, which were enhanced by Ca(2+) influx. This is the first study showing, in real time, Ca(2+) signals preceding egress and their direct link with motility, an essential virulence trait.
Highlights
Ca2ϩ signaling is important for the lytic cycle of T. gondii
Our experiments using T. gondii tachyzoites expressing GCaMP3 or GCaMP6f combined with host cells expressing Red-GECO or Blue-GECO (B-GECO) allowed us to directly follow changes in real time in cytosolic Ca2ϩ in the parasites, while they are inside their host cell and simultaneously in both the parasites and host cells during invasion and egress
Ca2ϩ Signaling and Egress—It has been shown that calcium ionophores and other agents induce egress of tachyzoites from their host cells
Summary
Ca2ϩ signaling is important for the lytic cycle of T. gondii. Results: Genetically encoded Ca2ϩ indicators revealed cytosolic Ca2ϩ changes in real time. Our experiments using T. gondii tachyzoites expressing GCaMP3 or GCaMP6f combined with host cells expressing Red-GECO or Blue-GECO (B-GECO) allowed us to directly follow changes in real time in cytosolic Ca2ϩ in the parasites, while they are inside their host cell and simultaneously in both the parasites and host cells during invasion and egress The use of these tools provided exciting new information about communication between the cytosolic Ca2ϩ in the host and the parasite. Our approach has allowed the measurement of two new features of motile parasites, which were enhanced by Ca2ϩ influx This is the first study to show directly that Ca2ϩ signals precede egress and to establish a direct correlation between Ca2ϩ signals and motility, an essential virulence trait, throughout the T. gondii lytic cycle
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