Oscillating signaling pathways during embryonic development.

Oscillatory signaling pathway activity during embryonic development was first identified in the process of vertebrate somite formation. In mouse, this process is thought to be largely controlled by a cyclic signaling network involving the Notch, FGF, and Wnt pathways. Surprisingly, several recent genetic studies reveal that the core oscillation pacemaker is unlikely to involve periodic activation by these pathways. The mechanism(s) responsible for the production of oscillatory gene activity during somite formation remains, therefore, to be discovered. Oscillatory signaling activity has recently been identified in developmental processes distinct from somite formation. Both the processes of limb development in chick embryos and the maintenance of neural progenitors in mouse embryos involve oscillatory gene activity related to the Notch pathway. These discoveries indicate that oscillatory signaling activities during embryonic development might serve a more general function than previously thought.