Developmental modification of the Drosophila cell cycle.

The cell cycle is subject to extrinsic regulation that coordinates cell division with developmental events. This important area at the interface of developmental biology and research into the cell cycle has yielded recent exciting advances. Developmental modification of the cell cycle is exemplified during Drosophila embryogenesis. Early in embryogenesis, regulation of the cell cycle becomes progressively more complex as a simple S-M cycle is altered to include gap phases. Later in embryogenesis, the cycle alters again, to include only an S and a gap phase. These developmental alterations are partly effected by regulating the expression of genes that control key transitions in the cell cycle. Certain controls that are unique to the variant cell cycles have also been defined. The field is now poised for the identification of the intervening steps between the developmental signals and their ultimate effects on known cell cycle regulators.