Only one way to organize a movement?

The needs of the pore ccording to a model that has prevailed since the early 1990s, nuclear import complexes need to dock to the cytoplasmic filaments of the nuclear pore complex (NPC) before they can be translocated to the nucleus. On page 63, Walther et al. A overturn this idea, demonstrating that cytoplasmic filaments have no essential function in the nuclear import of bulk cargos. The results also provide new insights on the composition of the filaments. Using the Xenopus egg extract system, the authors analyzed two cytoplasmically oriented nucleoporins, CAN/Nup214 and RanBP2/Nup358. CAN/Nup214 was previously thought to be a component of the cytoplasmic filaments, but in the new work it appears to be located near the entrance to the translocation channel in the NPC. RanBP2/Nup358, however, is an essential component of the cytoplasmic filaments: depleting Cytoplasmic filaments (blue) are not needed for nuclear import (red). this protein causes NPCs to form without cytoplasmic filaments. Surprisingly, NPCs lacking cytoplasmic filaments show no deficiency in nuclear import, indicating that the filaments are dispensable for this function. wo reports in this issue identify a strikingly similar pattern of coordination between F-actin and microtubule dynamics, suggesting that such coordination may be a basic mechanism by which cells both direct movement and respond to environmental cues. Previous work had suggested that microtubules mimic F-actin movements in migrating cells, but technological limitations have made this idea difficult to test. On page 31, Salmon et al., studying migrating epithelial cells from newt lung, used new fluorescence speckle microscopy (FSM) imaging techniques to observe the movement of F-actin and microtubules nearly simultaneously in living cells. F-actin moves differently in four zones of the cell. Microtubules oriented parallel to the leading edge precisely mimic T Walther et al. propose that instead of being an obligatory stop on the nuclear import pathway, NPC cytoplasmic filaments of RanBP2/Nup358 may arrest import complexes to allow specific modifications before they enter the nucleus. For a nuclear pore to form, the inner and outer membranes of the nucleus must fuse. This process is thought to involve the integral membrane protein gp210, which has a short COOH-terminal tail extending into the cytoplasm. Drummond and Wilson, reporting on page 53, now provide strong evidence to support this idea and present a new model to help explain nuclear pore formation. Recombinant gp210 tail polypeptides, or antibodies against the tail, stop nuclear pore formation at an early …