The Dynamic Nature of the Nuclear Envelope.

Eukaryotes characteristically organize their genome in a separate compartment, the nucleus, which is surrounded by the nuclear envelope as a barrier. Ruptures of the nuclear envelope and exposure of chromatin threaten cell viability and cause genome instability. Despite its essential boundary function, the nuclear envelope undergoes remarkable morphological changes, most noticeable during mitosis. Here we summarize our current understanding of nuclear envelope dynamics and its mutable relationship to the endoplasmic reticulum. We discuss how the nuclear envelope is remodeled to insert nuclear pore complexes, the transport gates of the nucleus, into its double membrane structure. Recent 3D electron microscopy time courses of assembling nuclear pore complexes show that these structures integrate into the nuclear envelope during interphase and mitosis following different pathways. Both pathways ensure that pores are formed in the nuclear envelope connecting cytoplasm and nucleoplasm.