Clocks regulating developmental processes.

@article{Pourqui1998ClocksRD,
  title={Clocks regulating developmental processes.},
  author={Olivier Pourqui{\'e}},
  journal={Current opinion in neurobiology},
  year={1998},
  volume={8 5},
  pages={665-70}
}
Developmental clocks are hypothetical embryonic time-measuring devices--some are run by oscillators, whereas others depend on rate-limiting processes. Their existence has been deduced from recent studies of the timing of the midblastula transition, the opening of the Hox cluster during organogenesis, and oligodendrocyte progenitor differentiation; however, the mechanisms underlying their function remain largely unknown.