Myosin switching during amoebo-plasmodial differentiation of slime mold, Physarum polycephalum

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Myosins from amoebal and plasmodial stages of Physarum polycephalum exhibit distinct heavy chain structures and phosphorylatable light chains.
• Calcium-binding light chains (14,000 Mr) are conserved across both amoebal and plasmodial myosin forms.
• Apogamic differentiation in Physarum polycephalum involves a transition from amoebae to multinucleate plasmodia via intermediate cells.

Purpose of the Study:

• To investigate the changes in myosin heavy and light chain expression during the differentiation of Physarum polycephalum.
• To determine the temporal relationship between myosin subunit switching and the synthesis of other cytoskeletal proteins, such as HMWP.

Main Methods:

• Immunofluorescence microscopy was employed to visualize the localization of specific myosin heavy and light chains in differentiating Physarum polycephalum cultures.
• Antibodies were generated against plasmodial myosin heavy chain (PMHC), plasmodial myosin light chain 18 kDa (PMLC18), and amoebal myosin heavy chain (AMHC).
• Antibody against high molecular weight actin-binding protein (HMWP), a plasmodium-specific protein, was also used.

Main Results:

• Antibodies against PMHC and PMLC18 stained intermediate cells and young plasmodia, but not typical amoebae.
• Antibodies against AMHC stained typical amoebae and intermediate cells, but not young plasmodia.
• Intermediate cells showed positive staining for both AMHC and PMHC, as well as for HMWP.

Conclusions:

• Myosin subunit synthesis switches from the amoebal type to the plasmodial type in mononucleate intermediate cells with swollen nuclei.
• This myosin switching event is closely associated with the initiation of HMWP synthesis during Physarum polycephalum differentiation.