A post-lysosomal compartment in Dictyostelium discoideum

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Endocytosis is a fundamental cellular process for nutrient uptake and waste removal.
• Lysosomes are key organelles involved in degrading internalized material through acidification.
• The fate of undigested cargo and the mechanisms of exocytosis in Dictyostelium discoideum require further elucidation.

Purpose of the Study:

• To investigate the intracellular trafficking and processing of endocytic cargo in Dictyostelium discoideum.
• To characterize the properties of post-lysosomal compartments involved in cargo egestion.
• To determine the temporal dynamics of cargo degradation, accumulation, and excretion.

Main Methods:

• Fed Dictyostelium discoideum with membrane-impermeable, pH-sensitive fluorophores (FITC-dextran and pyranine).
• Monitored fluorophore localization, vacuole acidity (pH), and vacuole characteristics over time using microscopy and biochemical assays.
• Assessed in vitro vacuole acidification capacity and sedimentation properties.

Main Results:

• Fluorophores initially entered neutral endocytic compartments, reaching maximal acidity (pH ~5) in lysosomes around 15 minutes.
• By 30 minutes, probes accumulated in large (up to 3 microns), nearly neutral vacuoles that sedimented rapidly.
• These late vacuoles resisted in vitro acidification and egestion of FITC-dextran began after a ~45-minute lag.

Conclusions:

• Dictyostelium discoideum utilizes a distinct post-lysosomal compartment of large, neutral vacuoles for accumulating undigested cargo.
• This compartment facilitates the return of cargo to the cell surface for egestion.
• Further research is needed to understand the role of this pathway in recycling internalized plasma membrane components.