Arp2/3 complex-dependent actin networks constrain myosin II function in driving retrograde actin flow

Area of Science:

• Cell Biology
• Neuroscience
• Cytoskeletal Dynamics

Background:

• The Arp2/3 complex is crucial for actin network formation at the leading edge of motile cells.
• Nonmuscle myosin II generates contractile forces essential for actin network movement.

Purpose of the Study:

• To investigate the roles of the Arp2/3 complex and myosin II in neuronal growth cone actin dynamics.
• To elucidate the interplay between Arp2/3-mediated actin assembly and myosin II-dependent contractility.

Main Methods:

• Utilized small molecule inhibitors (CK666 for Arp2/3, and myosin II inhibitors) to perturb actin dynamics in neuronal growth cones.
• Quantified changes in barbed end actin assembly site density, actin veil morphology, and retrograde actin flow rates.

Main Results:

• Arp2/3 complex inhibition reduced actin assembly sites, disrupted actin veils, and induced veil retraction.
• Arp2/3 inhibition increased retrograde actin flow, but this effect was reversed when myosin II was simultaneously inhibited.
• Myosin II inhibition prevented veil retraction and slowed retrograde flow upon Arp2/3 complex inhibition, independent of Rho kinase activity.

Conclusions:

• The Arp2/3 complex and myosin II, despite spatial segregation, interact functionally.
• Actin networks nucleated by the Arp2/3 complex can restrain myosin II-dependent contractility.
• This regulation impacts overall growth cone motility and actin dynamics.