Cyclin E controls S phase progression and its down-regulation during Drosophila embryogenesis is required for the arrest of cell proliferation.

Most cells of the dorsal epidermis exit from the mitotic cycle after division 16 in Drosophila embryogenesis. This exit is dependent on the down-regulation of Drosophila cyclin E (DmcycE) during the final mitotic cycle. Ectopic expression of DmcycE after the final mitosis induces entry into S phase and reaccumulation of G2 cyclins and results in progression through a complete additional cell cycle. Conversely, analyses in DmcycE mutant embryos indicate that cyclin E is required for progression through S phase of the mitotic cycle. Moreover, endoreplication, which occurs in late wild-type embryos in the same pattern as DmcycE expression, is not observed in the mutant embryos. Therefore, Drosophila cyclin E, which forms a complex with the Dmcdc2c kinase, controls progression through S phase and its down-regulation limits embryonic proliferation.