Lamin A is one of the intermediate filament proteins that weave together to form a shell called the nuclear lamina which lines the inner surface of the nucleus of every eukaryotic cell. Lamin A and its closely related variant, Lamin C, are both derived from the same gene by Alternative splicing of a shared pre-mRNA transcript.
Early in mitosis, MPF phospohrylates specific serine residues in all three nuclear lamins, causing depolymerization of the lamin intermediate filaments. The phosphorylated lamin A and lamin B dimers remain associated with the nuclear embrane via their isoprenyl anchor. Depolymerization of the nuclear lamins leads to disintergration of the nuclear envelope. Transfection experiments demonstrate that phosphorylation of human lamin A is required for lamin depolymerization, and thus for disassembly of the nuclear envelope, which normally occurs early in mitosis.