Slide 7 of 79
Notes:
They called it MPF or Mitosis Promoting Factor. MPF extracted from frog eggs and injected into other types of cells (including human cells) caused them to enter mitosis also. This indicated the same regulatory system was intrinsic to all cells.
The frog ovary contains many immature oocytes, which have grown to a large size but are arrested in interphase before meiosis I so they are not ready to be fertilized. Exposure to progesterone induces the activation of MPF causing an immature oocyte to complete the first meiotic division and enter the second where it arrests in metaphase of meiosis II. After fertilization the egg completes meioses II and begins the spontaneous oscillations of the early embryonic cell cycle. Even though they're relatively simple in their behavior, you can see how these early embryonic cells would be very interesting from a dynamical point of view. They display three different dynamical states: two arrested or steady states and spontaneous limit cycle oscillations.
