Models of Intracellular Transport: Contradictions and Current Understanding.

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Intracellular transport is crucial for cellular function and involves complex mechanisms.
• Existing models like vesicular transport, diffusion, and cisterna maturation struggle to fully explain experimental data.
• Understanding the secretory pathway's transport dynamics remains a significant challenge in cell biology.

Purpose of the Study:

• To analyze and compare different intracellular transport models within the secretory pathway.
• To identify the most accurate model by evaluating its ability to explain experimental observations.
• To elucidate the mechanisms governing cargo movement from the endoplasmic reticulum to the cell surface.

Main Methods:

• Comparative analysis of existing intracellular transport models (vesicular, diffusion, cisterna maturation-progression).
• Identification of experimental observations not fully explained by current models.
• Evaluation of the 'kiss-and-run' model against these observations.

Main Results:

• The 'kiss-and-run' model emerges as the most powerful explanation for intracellular transport.
• COPI-dependent vesicles are implicated at ER exit sites.
• Microtubules facilitate bolus-like transport of carriers between the Golgi and peripheral structures.
• Intra-Golgi transport relies on temporary cisternal connections and perforations.
• Cargo movement shifts from linear to exponential decay at the Golgi exit site.
• Post-Golgi carriers undergo SNARE exchange for proper plasma membrane fusion.

Conclusions:

• The 'kiss-and-run' model provides a more comprehensive framework for understanding secretory pathway transport.
• Specific mechanisms involving COPI, microtubules, cisternal dynamics, and SNAREs are essential for directional cargo movement.
• This model integrates various observations, offering a refined view of intracellular trafficking.