Question

Explain the role of growth factors and MPFs in the cell cycle.

Answer 1

MPF does a number of things but in short it promotes the mitosis, hence it's names mitosis - promoting factor or M-phase promoting factor. It is a kinase and it acts on various substrate molecules: condensins which promote chromatin condensation, lamins which normally make up the nuclear membrane but are disrupted by phosphorylation, microtubule-associated proteins which are part of the mitotic spindle. Another target is myosin, which is part of the cell machinery of telophase where chromosomes move apart. The phosphorylation prevents myosin from working so no cytokinesis can occur before MPF activity falls in anaphase.

Growth factors provide the signal to divide for cells - this is called mitogenic signalling. Cells in culture tend to enter the cell cycle when growth factors are added and in vivo they have similar effects.