The temporal control of cell cycle and cell fate in Caenorhabditis elegans.

The nematode Caenorhabditis elegans develops through two major phases: the first phase, embryogenesis, consists of a rapid series of cleavage cell divisions leading to morphogenesis of a first stage larva. The second phase is postembryonic development, which consists of developmentally regulated cell cycles that occur during the four larval stages leading to the adult. Precursor cells set aside during embryogenesis divide through stereotypical cell lineage patterns during the four larval stages to generate larval and adult structures. The precise timing of the postembryonic cell divisions is under strict control, in most cases with a developmentally regulated G1. In certain postembryonic cell lineages, various aspects of the cell division cycle, including cell cycle exit, or G1/S progression, are controlled by temporal regulatory genes of the heterochronic gene pathway. Heterochronic genes also control the timing of numerous other developmental events, indicating that this pathway functions to coordinate the schedule of cell division and cellular differentiation throughout the animal. Some choices of cell fate that occur in response to inductive or lateral signals are linked to cell cycle progression, suggesting that cell cycle phase can confer a critical period for developmental potential in certain cells.