Sorting nuclear membrane proteins at mitosis

The nuclear envelope (NE) breaks down reversibly and reassembles at mitosis . Two models of mitotic nuclear membrane disassembly and reformation have e merged from studies of NE dynamics in somatic cells and egg extracts. One m odel suggests that nuclear membranes fragment reversibly by vesiculation, p roducing NE-derived vesicles separate from the endoplasmic reticulum. The s econd model proposes that nuclear membranes vanish by diffusion of their in tegral proteins through a continuous endoplasmic reticulum. Here, we discus s critically the grounds for the elaboration of these apparently mutually e xclusive views. Our conclusions favour a model in which nuclear membranes d o not vesiculate during mitosis.