Translational control and the cytoskeleton in Physarum polycephalum

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The slime mold Physarum polycephalum transitions from an active plasmodial state to a dormant sclerotial state during starvation.
• Protein synthesis is suppressed at the initiation level in sclerotia, despite the presence of functional mRNA and ribosomes.

Purpose of the Study:

• To investigate the role of cytoskeletal alterations in regulating protein synthesis during the transition from plasmodia to sclerotia.
• To determine the distribution of polysomes and actin mRNA in cytoskeletal (CSK) and soluble (SOL) fractions of Physarum polycephalum.

Main Methods:

• Extraction of cytoskeletal (CSK) and soluble (SOL) fractions from Physarum polycephalum plasmodia and sclerotia using Triton X-100.
• Analysis of polysome and actin mRNA distribution within these fractions.
• Treatment with cycloheximide, an elongation inhibitor, to assess polysome dynamics.

Main Results:

• In plasmodia, most polysomes and actin mRNA reside in the CSK, while in sclerotia, they are primarily in the SOL.
• Starvation induces a shift of translational components from CSK to SOL, correlating with suppressed protein synthesis.
• Cycloheximide treatment causes polysome accumulation in the SOL of plasmodia, indicating limited CSK binding capacity.
• Cycloheximide treatment causes polysome and mRNA accumulation in the CSK of sclerotia, demonstrating its capacity to bind translational components.

Conclusions:

• Alterations in the Physarum polycephalum cytoskeleton are not the primary mechanism for translational control during starvation-induced dormancy.
• The shift of ribosomes and mRNA from the cytoskeleton to the soluble fraction is associated with, but not the cause of, suppressed protein synthesis.