Abutbul, Inbal, Sapir, Amir, Avinoam, Ori, Valansi, Clari, Danino, Dganit, White, Judith, Grunewald, Kay, Podbilewicz, Benjamin, Fridman, Karen, Zeev-Ben-Mordehai, Tzviya, Maurer, Ulrike
[
International Worm Meeting,
2011]
Cell-cell fusion is a fundamental process that occurs during development of most eukaryotes. In C. elegans cell-cell fusion is necessary for fertilization and organogenesis of the hypodermis, pharynx, vulva, uterus, glands, and male tail. Moreover, cell fusion has been implicated in myogenesis, bone formation, placentation, neuronal function, stem-cell reprogramming and carcinogenesis. Despite the relative abundance of cell fusion events during development, the molecular mechanism of cell-fusion is unknown. The first family of proteins that mediate membrane fusion (i.e fusogens) was identified in C. elegans. Its first members, AFF-1 and EFF-1 (CeFFs) are essential for cell fusion and their expression is sufficient to fuse cells that normally do not fuse both in vivo and in cell-culture. Furthermore, CeFFs are required on both membranes in order for them to fuse. We have shown that FFs are functionally conserved within and beyond the nematode phylum and that divergent members from the nematode T. spiralis and the chordate B. floridae can mediate fusion of mammalian cells. We use CeFFs as prototypic fusogens to understand the principles of cell-cell fusion machineries. In order to study the molecular mechanism of FF proteins we generated pseudotyped Vesicular Stomatitis viruses that express CeFFs on the viral membrane, in place of the endogenous fusogenic glycoprotein. We found that CeFFs are able to rescue the infectious activity of the virus and mediate viral infection via virus-cell fusion. In addition, the viral mode of fusion and infection became dependent on the expression of FFs on the virus as well as on the target cell membrane. We investigated the structure of AFF-1 at nano-resolution using electron microscopy and tomography and found that it formed distinct supercomplexes resembling pentameric and hexameric flowers on pseudoviruses. Thus, the evolution, structure and function of FFs begin to unravel as they converge with glycoproteins of enveloped viruses as minimal fusogenic machineries capable of fusing membranes independently of other cellular co-factors.