What happens during the disassembly of the nuclear envelope?
The nuclear envelope disintegrates during prometaphase. This disassembly allows for the sister chromatids to be released from the nucleus, which is essential for separation of genetic material into two separate cells. The breakdown of the nuclear envelope involves 3 main steps: the nuclear membranes are separated into vesicles, the nuclear pore complexes disassemble, and the nuclear lamina depolymerizes. When the nuclear membrane fragments into small vesicles, B-type lamins remain attached to these vesicles, while lamins A and C separate from the nuclear membrane and exist as free dimers in the cell’s cytosol. The disassembly of the nuclear lamina occurs due to the phosphorylation of lamins, which cause the filaments to break apart into single lamin proteins known as dimers. The Cdc2 protein kinase catalyzes the process of phosphorylation of the lamins. It has been shown that the application of Cdc2 onto isolated nuclei is able to trigger the depolymerization of the nuclear lamina.