Role of Myosin II in Motility and in Force Generation of DRG Growth Cones

Abstract

Myosin II plays a vital role in many fundamental cellular and developmental processes such as cell-cell adhesion, cell migration and cytokinesis. Using immunocytochemistry, video imaging and optical tweezers we have determined myosin II function in motility and the force exerted by lamellipodia from growth cones (GCs) of isolated Dorsal Root Ganglia (DRG) neurons. In DRG GCs the concentration of NMIIA isoform of myosin II was approximately constant from the GC center to its leading edge while NMIIB isoform of myosin II was more confined in the central region of GCs. Video imaging shows that when the activity of myosin II was inhibited by Blebbistatin lamellipodia emerging from the soma and from GCs become “filopodish” with the clear appearance of structures reminiscent of filopodia. After treatment with 20μM Blebbistatin cycles of lamellipodia protrusion/retraction slowed down and lamellipodia did not lift up axially as in control conditions and lamellipodia motion was completely abolished by 50 μM Blebbistatin. Immunocytochemical analysis of filopodia emerging from GCs treated with Blebbistatin showed the presence of tubulin, in a proportion higher than in filopodia in control conditions. In the presence of 30 μM Blebbistatin lamellipodia exerted a force 30-50 % less than in control conditions, but surprisingly the force generated by filopodia, increased by 30-50 %. These results suggest that: i - Myosin II is an essential component of motility and force generation; ii - Myosin II plays a very important role in the orchestration of GC structural stability.