Pre-assembled Nuclear Pores Insert into the Nuclear Envelope during Early Development
Authors: Hampoelz B, Mackmull MT, Machado P, Ronchi P, Bui KH, Schieber N, Santarella-Mellwig R, Necakov A, Andrés-Pons A, Philippe JM, Lecuit T, Schwab Y, Beck M
CellNetworks People: Beck Martin
Journal: Cell. 2016 Jul 28;166(3):664-78. doi: 10.1016/j.cell.2016.06.015

Nuclear pore complexes (NPCs) span the nuclear envelope (NE) and mediate nucleocytoplasmic transport. In metazoan oocytes and early embryos, NPCs reside not only within the NE, but also at some endoplasmic reticulum (ER) membrane sheets, termed annulate lamellae (AL). Although a role for AL as NPC storage pools has been discussed, it remains controversial whether and how they contribute to the NPC density at the NE. Here, we show that AL insert into the NE as the ER feeds rapid nuclear expansion in Drosophila blastoderm embryos. We demonstrate that NPCs within AL resemble pore scaffolds that mature only upon insertion into the NE. We delineate a topological model in which NE openings are critical for AL uptake that nevertheless occurs without compromising the permeability barrier of the NE. We finally show that this unanticipated mode of pore insertion is developmentally regulated and operates prior to gastrulation.