New insights into the mechanisms and roles of cell-cell fusion.

Many types of eukaryotic cells can fuse together as part of their normal developmental program or life cycle. This review describes a diverse set of examples of such cell types and focuses attention on several molecules that appear intimately involved in the process of plasma membrane merger that lies at the crux of every cell-fusion event. Some of these examples come from experimental systems where the discovery of molecules essential for cell fusion is sped by the approachability of the experimental organism itself. In other cases, especially in the many fusing human cell types, the molecular players in cell-cell membrane fusion are still to be discovered.