Abstract
ABSTRACTCell-cell fusion is essential for development and physiology. Actin polymerization was implicated in the Caenorhabditis elegans fusogen EFF-1 engagement in a reconstituted Drosophila cell culture system, and the actin-binding protein spectraplakin links EFF-1 to the actin cytoskeleton and promotes cell-cell fusions in C. elegans larvae. However, it remains unclear whether and how fusogens and the actin cytoskeleton are coordinated in C. elegans embryos. Here, we used live imaging analysis of GFP knock-in and RNAi embryos to study the embryonic cell-cell fusions in C. elegans. 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.
Highlights
Cell-cell fusion is involved in various developmental and physiological events, ranging from sexual reproduction, myogenesis, bone remodeling and immune responses (Chen, 2011; Chen and Olson, 2005; Podbilewicz, 2014)
In the epithelial seam and hyp7 cell-cell fusions of C. elegans larvae, EFF-1 and F-actin accumulate at the cortex of two fusing cells, and WASP-Arp2/3-dependent actin polymerization promotes this process by recruiting EFF-1 to the fusing plasma membranes (Yang et al, 2017)
WASP-Arp2/3-dependent actin polymerization promotes embryonic cell-cell fusions The largest C. elegans epithelial hyp7 syncytium contains 139 nuclei, which is formed when embryonic cell-cell fusion merges 23 cells and the remaining 116 cells fuse in larvae (Podbilewicz and White, 1994; Sulston and Horvitz, 1977)
Summary
Cell-cell fusion is involved in various developmental and physiological events, ranging from sexual reproduction, myogenesis, bone remodeling and immune responses (Chen, 2011; Chen and Olson, 2005; Podbilewicz, 2014). In the epithelial seam and hyp7 cell-cell fusions of C. elegans larvae, EFF-1 and F-actin accumulate at the cortex of two fusing cells, and WASP-Arp2/3-dependent actin polymerization promotes this process by recruiting EFF-1 to the fusing plasma membranes (Yang et al, 2017). We performed fluorescence time-lapse analysis of cell-cell fusions in RNAi-treated embryos, showing that WASP-Arp2/3-dependent actin polymerization is involved in embryonic hyp7 cell-cell fusions by recruiting EFF-1 to intracellular vesicles.
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