WASP-Arp2/3-dependent actin polymerization influences fusogen localization during cell-cell fusion in embryos.

Cell-cell fusion is essential for development and physiology. Actin polymerization was implicated in the fusogen EFF-1 engagement in a reconstituted cell culture system, and the actin-binding protein spectraplakin links EFF-1 to the actin cytoskeleton and promotes cell-cell fusions in larvae. However, it remains unclear whether and how fusogens and the actin cytoskeleton are coordinated in embryos. Here, we used live imaging analysis of GFP knock-in and RNAi embryos to study the embryonic cell-cell fusions in Our results show that the inhibition of WASP-Arp2/3-dependent actin polymerization delays cell-cell fusions. EFF-1 is primarily distributed in intracellular vesicles in embryonic fusing cells, and we find that the perturbation of actin polymerization reduces the number of EFF-1-postive vesicles. Thus, the actin cytoskeleton differently promotes cell-cell fusion by regulating fusogen localization to the fusing plasma membrane in larvae or to intracellular vesicles in embryos.