During cell-cell fusion, two cells' plasma membranes merge, allowing the cytoplasms to mix and form a syncytium. Little is known about the mechanisms of cell fusion. Here, we asked whether eff-1, shown previously to be essential for fusion in Caenorhabditis elegans, acts directly in the fusion machinery. We show that expression of EFF-1 transmembrane protein drives fusion of heterologous cells into multinucleate syncytia. We obtained evidence that EFF-1-mediated fusion involves a hemifusion intermediate characterized by membrane mixing without cytoplasm mixing. Furthermore, syncytiogenesis requires EFF-1 in both fusing cells. To test whether this mechanism also applies in vivo, we conducted genetic mosaic analysis of C. elegans and found that homotypic epidermal fusion requires EFF-1 in both cells. Thus, although EFF-1-mediated fusion shares characteristics with viral and intracellular fusion, including an apparent hemifusion step, it differs from these reactions in the homotypic organization of the fusion machinery.
Bibliographical noteFunding Information:
We thank Y. Kohara and W. Mohler for cDNAs, the C. elegans knockout consortium for the eff-1(ok1021) deletion allele, T. Stiernagle and the Caenorhabditis Genetics Center for nematode strains, and P. Blank for advice on microscopy. We also thank J. Zimmerberg for discussions and support, and O. Beja, D. Cassel, M. Krause, K. Melikov, J.M. White, and K. Brunschwig for critically reading the manuscript. This research was supported by grants from Israel Science Foundation, Fund for the Promotion of Research at the Technion, and Human Frontier Science Program (B.P.), and by the Intramural Research Program of the National Institute of Child Health and Human Development, National Institutes of Health (B.P. and L.V.C.). E.L. and A.S. contributed equally to this work. E.L. and B.P. performed cell fusion assays. A.S. did the molecular work. E.L., C.V., and B.P. did biochemical experiments. M.S. and G.S. performed the genetic mosaic analyses. L.V.C. and B.P. designed and analyzed the experiments and wrote the paper. All authors discussed the results and commented on the manuscript.
ASJC Scopus subject areas
- Molecular Biology
- Biochemistry, Genetics and Molecular Biology (all)
- Developmental Biology
- Cell Biology