Geometric constrains for detecting short actin filaments by cryogenic electron tomography

Area of Science:

• Cell Biology
• Parasitology
• Microscopy

Background:

• Actin polymerization drives membrane extensions like filopodia, essential for cell motility and phagocytosis.
• Short actin filaments are implicated in the motility of apicomplexan parasites, including the malaria parasite.
• Visualizing these short filaments in intact parasite cells has been a significant challenge.

Purpose of the Study:

• To investigate the structure and visualization limits of short actin filaments in intact Plasmodium sporozoites.
• To explore the role of actin polymerization in the motility of malaria parasites using advanced imaging techniques.

Main Methods:

• Cryogenic electron tomography (cryo-ET) was employed to image Plasmodium sporozoites.
• In silico simulations were performed to assess the limitations of electron microscopy (EM) data collection and tomographic reconstruction.
• Analysis focused on identifying filamentous structures within the parasite's supra-alveolar space.

Main Results:

• Filopodia-like extensions and filamentous structures were observed beneath the plasma membrane of Plasmodium sporozoites.
• These observed filaments could not be definitively identified as actin filaments.
• Simulations revealed that filament length, concentration, and orientation significantly limit their detectability in EM data.

Conclusions:

• Cryo-ET provides insights into the ultrastructure of Plasmodium sporozoites but faces limitations in visualizing short, sparsely distributed filaments.
• The study highlights the technical challenges in resolving short actin filaments within intact malaria parasites.
• Further advancements in imaging and computational methods are needed to visualize and characterize these crucial motility structures.