Coordinated regulation of diverse F-actin organizations orchestrates F-actin pulses in the actomyosin network.

Pulsatile actomyosin networks emerge as a widespread mechanism driving tissue morphogenesis. Compared with myosin-II pulses, F-actin pulses are largely unexplored. By studying Drosophila oogenesis, we report that basal pulsatile actomyosin networks consist of F-actin bundle and meshwork architectures, implicating the existence of different F-actin microstructures and corresponding nucleators. Here, Rac1 and the Scar/WAVE-Arp2/3 complex (branched F-actin nucleator), exhibiting constant levels, are necessary to support F-actin pulsation, whereas pulses of Dia (unbranched F-actin nucleator) trigger F-actin pulsation. The pulsatile F-actin networks recruit the F-actin turnover regulator cofilin, thus generating cofilin pulses. Cofilin at relatively low concentration can cooperate with F-actin nucleators to amplify F-actin and enhance its pulsation, while cofilin at relatively high concentration might trigger the F-actin disassembly to attenuate its pulsation. These two different effects of cofilin on F-actin pulsation were confirmed by Zdk-cofilin optogenetics. Rac1 signaling, Dia, and cofilin are also crucial for F-actin pulses in border cell migration. Our findings thus reveal a coordinated regulation of F-actin pulses conferring actomyosin contractility in morphogenesis and cell migration.