Question

Relate the role of the mitotic promoting factor (cyclin-cdk complex) to the breakdown of nuclear envelope.

Answer 1

The nuclear envelope breaks down at the onset of mitosis. This process is mainly controlled by the cyclin-cdk complexes that phosphorylates inner nuclear membrane proteins to disrupt their association with chromatin and to disintegrate the nuclear lamina. Upon nuclear envelope break down, the nuclear membrane and integral nuclear membrane proteins retract into the ER, whereas other peripheral nuclear membrane proteins and some components of the nuclear pore complex become disperse in the cytosol.

At late anaphase, inactivation of the cyclin-cdk complexes and dephosphorylation of INM proteins allow these proteins to bind the chromatin and brings the ER membrane to the chromatin surface to initiate nuclear envelop assembly around the compact chromosome Mass. The nuclear envelope disassembly and assembly are thus coordinated with the segregation of sister chromatids in each cell division cycle to maintain genome stability. Nuclear envelope breakdown is essential for sister chromatid segregation.