Nuclear envelope formation by chromatin-mediated reorganization of the endoplasmic reticulum The formation of the nuclear envelope (NE) around chromatin is a major membrane-remodelling event that occurs during cell division of metazoa. It is unclear whether the nuclear membrane reforms by the fusion of NE fragments or if it re-emerges from an intact tubular network of the endoplasmic reticulum (ER). Here, we show that NE formation and expansion requires a tubular ER network and occurs efficiently in the presence of the membrane fusion inhibitor GTPγS. Chromatin recruitment of membranes, which is initiated by tubule-end binding, followed by the formation, expansion and sealing of flat membrane sheets, is mediated by DNA-binding proteins residing in the ER. Thus, chromatin plays an active role in reshaping of the ER during NE formation. 9 10 1160-1166 1160-1166 Springer Nature 1