Figure 2.

Types and origin of syncytia. (A) Syncytium derived from the fusion of identical cells is called homotypic syncytium. Homotypic fusion of cell cytoplasms creates homotypic heterokaryotic syncytium with multiple nuclei. Homotypic fusion of cell cytoplasms and nuclei creates homotypic synkaryotic syncytium. Syncytium derived from the fusion of different cell types is called heterotypic syncytium. Heterotypic fusion of only cell cytoplasms creates heterotypic heterokaryotic syncytium with multiple nuclei of different origins. Heterotypic fusion of cell cytoplasms and nuclei creates heterotypic synkaryotic syncytium. (B) Origin of syncytia during development. In some instances, progenitor cell divides multiple times with partial cytokinesis forming a group (called nest or cyst) of descendant cells connected by cytoplasmic bridges. Eventually, these cells either separate into individual cells (for example, in frog or mammalian oogenesis) or fuse to form multinuclear syncytium (for example, nurse cell syncytium in insect telotrophic ovary). In other instances, for example, during early embryogenesis in Drosophila, the nucleus of the progenitor cell divides multiple times, creating a multinuclear cell (syncytium), which eventually cellularizes into individual cells.