Mammalian Cell Fusion Assays for the Study of Cell Cycle Progression by Functional Complementation

Cell cycle progression, or its arrest upon checkpoint activation, is directed by a complex array of cellular processes dependent on the diffusion of chemical signals. These signals regulate the onset of each cell cycle phase and prevent undesired phase transitions. Functional complementation is a robust strategy to identify such signals, by which mutant phenotypes are rescued through complementation with candidate factors. Here we describe a method that reclaims a five-decade old mammalian cell-cell fusion strategy of functional complementation to study the molecular control of cell cycle progression. The generation of cell-cell fusions (heterokaryons) allows for the analysis, via immunofluorescence, of cell cycle regulator dynamics and evaluating the effective rescue of cell cycle progression in specific genetic settings.