Cell biology: nuclear dilemma resolved.

Abstract

After cell division, membranes become fused around the nucleus to encapsulate the cell's chromosomes. It emerges that this process is regulated by the ESCRT-III protein complex. See Letters p.231 & p.236 At an early stage of cell division in animal cells the nuclear envelope breaks down, and once cell division draws to a close at anaphase, the envelope must reform around the nuclei of the two daughter cells. It is known that the nuclear envelope is derived from the membranes of another organelle, the endoplasmic reticulum, and that it is sealed through a membrane fusion step, but the mechanism of fusion remains partially understood. Two groups report this week [in this issue of Nature] that this process is regulated by ESCRT-III, a protein complex best known for membrane constriction and sealing during various cellular processes. Harald Stenmark and colleagues show that ESCRT-III and two other proteins, VPS4 and spastin, cooperatively coordinate envelope fusion and spindle disassembly in a process mechanistically similar to the cytokinesis that ensures physical separation of the two daughter cells. Jeremy Carlton and colleagues find that the CHMP2A component of ESCRT-III is directed to the forming nuclear envelope where it localizes to sites of fusion through binding to CHMP4B, and with the help of UFD1 — a component of the p97 complex previously implicated in nuclear envelope fusion.