Analysis of Ca2+ mediated signaling regulating Toxoplasma infectivity reveals complex relationships between key
Rebecca J Stewart1,2, Lachlan Whitehead1,2, Brunda Nijagal3
1The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.
Abstract:
Host cell invasion, exit and parasite dissemination is critical to the pathogenesis of apicomplexan parasites such as Toxoplasma gondii and Plasmodium spp. These processes are regulated by intracellular Ca2+ signaling although the temporal dynamics of Ca2+ fluxes and down-stream second messenger pathways are poorly understood. Here, we use a genetically encoded biosensor, GFP-Calmodulin-M13-6 (GCaMP6), to capture Ca2+ flux in live Toxoplasma and investigate the role of Ca2+ signaling in egress and motility. Our analysis determines how environmental cues and signal activation influence intracellular Ca2+ flux, allowing placement of effector molecules within this pathway. Importantly, we have identified key interrelationships between cGMP and Ca2+ signaling that are required for activation of egress and motility. Furthermore, we extend this analysis to show that the Ca2+ Dependent Protein Kinases-TgCDPK1 and TgCDPK3-play a role in signal quenching before egress. This work highlights the interrelationships of second messenger pathways of Toxoplasma in space and time, which is likely required for pathogenesis of all apicomplexan species.
Insights
This study reveals how calcium (Ca2+) signaling dynamics regulate Toxoplasma gondii invasion and spread. We identified crucial links between cGMP and Ca2+ pathways, and the roles of specific protein kinases in parasite egress.
Area of Science:
- Parasitology
- Cellular Biology
- Biochemistry
Background:
- Apicomplexan parasites like Toxoplasma gondii rely on host cell invasion, exit, and dissemination for pathogenesis.
- Intracellular calcium (Ca2+) signaling regulates these critical processes, but its temporal dynamics and downstream pathways remain unclear.
Purpose of the Study:
- To investigate the role of Ca2+ signaling in Toxoplasma gondii egress and motility using a live-cell biosensor.
- To elucidate the temporal dynamics of Ca2+ fluxes and their relationship with other second messenger pathways.
Main Methods:
- Utilized a genetically encoded Ca2+ biosensor (GCaMP6) to monitor intracellular Ca2+ flux in live Toxoplasma gondii.
- Analyzed environmental cue influences on Ca2+ flux and identified interrelationships with cGMP signaling.
- Investigated the function of Ca2+ Dependent Protein Kinases (TgCDPK1 and TgCDPK3) in regulating egress.
Main Results:
- Mapped the temporal dynamics of intracellular Ca2+ flux in response to environmental cues.
- Identified critical interconnections between cGMP and Ca2+ signaling pathways essential for parasite egress and motility.
- Demonstrated that TgCDPK1 and TgCDPK3 are involved in quenching Ca2+ signals prior to egress.
Conclusions:
- This research elucidates the complex interplay of second messenger pathways (cGMP and Ca2+) in Toxoplasma gondii.
- Understanding these spatiotemporal dynamics provides insights into apicomplexan parasite pathogenesis.
- Identified key regulators of Ca2+ signaling, offering potential targets for therapeutic intervention.
