Classic Experiments in Cell Cycle Regulation

Classic Experiments I: Cell Fusion (Rao & Johnson, 1970)

• Overview: Studies by Rao & Johnson in 1970 focused on the cell cycle phases of S and G2.

• Key Findings:

  • Fusion of cells in different phases discovers interactions between cell cycle stages.

  • Observations included cells in:

    • S phase - DNA synthesis

    • G1 phase - preparation for DNA synthesis

    • G2 phase - preparations for mitosis

    • M phase - actual cell division

Classic Experiments II: Discovery of Maturation Promoting Factor (MPF)

• Research by Masui (1976): Focused on Amphibian development (Xenopus oocytes).

• Key Findings:

  • MPF is a crucial regulator in driving oocytes from G2 into M phase.

  • Maturity and maturation processes through hormonal influence in cell cycle.

Classic Experiments III: Discovery of Cyclin

• Research by Hunt (1976): Investigated protein synthesis in clam oocytes.

• Key Contribution: Introduced the concept of "cyclins":

  • Proteins that are synthesized during specific stages of the cell cycle and are rapidly degraded post-division.

  • Cyclins play an essential role in regulating the cell cycle through their levels corresponding with phases: G1, S, G2, and M.

Key Concepts

Role of MPF

• What is MPF?: Maturation Promoting Factor is essential for the transition from G2 to M phase.

• Dynamics of MPF: Changes with hormonal action and fertilization stages.

Cyclins and Cell Division

• Discovery and Purpose: Cyclins are proteins that regulate the cell cycle timing and events.

• Mechanism of Action: Each cyclin's levels rise and fall in correlation with cell cycle stages, influencing MPF activity and cell division.

• Relevance in Egg Development: Cyclins are specifically crucial in the rapid division of sea urchin embryos, requiring vigilant control over synthesis and destruction.

Summary of Findings

• Importance of Protein Synthesis: Ongoing synthesis of certain proteins, specifically maternal mRNAs, is vital for sustaining rapid cleavage processes in embryos.

• Oscillation in MPF Levels: Fluctuations represent key regulatory checkpoints during early embryonic development.

Nobel Prize Recognition (2001)

• Awarded For: Research contributions to understanding key regulators of the cell cycle.

• Recipients: Paul Nurse, Tim Hunt, Lee Hartwell recognized for their pivotal role in elucidating cell cycle control mechanisms.