Sorting out the nuclear envelope from the endoplasmic reticulum

Although the interphase nuclear envelope is continuous with the endoplasmic reticulum, it is distinct from the endoplasmic reticulum in both form and composition. In metazoans, the nuclear envelope breaks down during mitosis and is thought to be completely reabsorbed by the endoplasmic reticulum. How these near neighbours are sorted out at the end of mitosis is an interesting mystery.