Toxoplasma Actin Is Required for Efficient Host Cell Invasion.

Area of Science:

• Cell biology
• Parasitology
• Molecular biology

Background:

• Apicomplexan parasites invade host cells via an actin-dependent myosin motor.
• Inducible knockout of actin (ACT1) in Toxoplasma gondii partially inhibits invasion, suggesting alternative pathways.
• Residual protein levels can complicate interpretation of inducible knockout phenotypes.

Purpose of the Study:

• To investigate the mechanism behind residual invasion ability in ACT1-deleted T. gondii.
• To determine if alternative invasion pathways exist or if residual actin explains the phenotype.
• To clarify the role of parasite actin in host cell invasion.

Main Methods:

• Inducible knockout of the ACT1 gene in Toxoplasma gondii.
• Quantification of residual ACT1 protein over time post-deletion.
• Assessment of parasite invasion efficiency and attachment.
• Use of the actin polymerization inhibitor cytochalasin D.

Main Results:

• Residual ACT1 protein was detected in inducible knockout parasites for up to 5 days after deletion.
• Invasion defects worsened with longer propagation times after ACT1 deletion.
• Parasite invasion remained sensitive to cytochalasin D.
• No significant defects in attachment or moving junction formation were observed, but delayed host cell entry occurred.

Conclusions:

• Residual ACT1 protein, not alternative pathways, accounts for the limited invasion ability of inducible knockout parasites.
• Parasite actin is essential for efficient host cell penetration.
• Careful consideration of residual protein is necessary when interpreting inducible knockout phenotypes in Cre-Lox systems.