Abstract
Toxoplasma gondii is a polarized cell concentrating several secretory organelles at the apical pole. The secretory micronemes come in two sub-populations differentiated by dependence on the Rab5A/C in their biogenesis. Calcium-dependent exocytosis of micronemes occurs at the very apical tip and is critical for parasite egress from its host cell, adhesion and invasion of the next cell. Ferlins represent a protein family with roles in exocytosis containing multiple Ca2+-sensing C2 domains. We determined that T. gondii’s ferlin 1 (FER1) localized dynamically to the parasite’s secretory pathway. FER1 function was dissected by dominant negative overexpression strategies. We demonstrated that FER1 traffics microneme organelles along the following trajectories:1. From the trans-Golgi-endosomes network to the subpellicular cortex; 2. Along the cortex to the apical end; 3. To the apical tip for fusion with the plasma membrane; 4. Retrograde transport allowing microneme recycling from mother to daughter; 5. Differential microneme sub-population traffic. Finally, FER1 overexpression triggers a microneme exocytosis burst, supporting the notion that the radially organized micronemes at the apical tip comprise a readily-releasable microneme pool. In summary, FER1 is pivotal for dynamic microneme trafficking, acts differently on the two microneme subpopulations, and acts on the plasma membrane fusion step during microneme exocytosis.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Revisions made upon peer-review and advance experimental insights.
