Peering through the Pore Mythili Suntharalingam, Susan R Wente  Developmental Cell  Volume 4, Issue 6, Pages 775-789 (June 2003) DOI: 10.1016/S1534-5807(03)00162-X

Figure 1 Schematic Diagram of NPC Substructures The structure has an apparent 8-fold rotational symmetry perpendicular to the plane of the nuclear membrane; however, certain facing portions are removed in this diagram to reveal the architecture of the central region. Labels for all the structures found in vertebrate NPCs are included, with the cytoplasmic face on top. Adapted from the model in Rout and Wente, 1994. Developmental Cell 2003 4, 775-789DOI: (10.1016/S1534-5807(03)00162-X)

Figure 2 Peering through the NPC Electron micrograph of NPC structures in cytoplasmic annulate lamellae. The image was generously provided by Dr. John Heuser, Washington University School of Medicine. Samples from Dictyostelium were frozen, etched, and rotary shadowed with platinum (Heuser, 2000). The NPCs are oriented randomly, with some showing a view from the nuclear basket face (as in the schematic on the lower left) and some a view from the cytoplasmic filaments (as in the lower right). Developmental Cell 2003 4, 775-789DOI: (10.1016/S1534-5807(03)00162-X)

Figure 3 Nup Subcomplexes in Both Yeast S. cerevisiae and Vertebrate NPCs (A) Biochemical and molecular characterization studies have defined a network of Nup-Nup subcomplexes. The boxes on the left show the reported budding yeast Nup subcomplexes. On the right, the vertebrate subcomplexes are shown. Defined Nup-Nup interactions are indicated by the dashes, whereas commas indicate the association network is not fully known. Their relative surface-accessible localizations are indicated: red or blue box: asymmetric, only on the designated side; green box: symmetric with two sets, one on each side. Complexes containing dynamic Nups are indicated by an asterisk. Based on data in references: (1) Grandi et al., 1995a; Hurwitz et al., 1998; Bailer et al., 1998, 2000; Belgareh et al., 1998; Ho et al., 1998; (2) Marelli et al., 1998; (3) Grandi et al., 1993, 1995a; Schlaich et al., 1997; (4) Nehrbass et al., 1996; Zabel et al., 1996; Kosova et al., 1999; (5) Siniossoglou et al., 1996, 2000; Lutzmann et al., 2002; (6) Denning et al., 2001; Dilworth et al., 2001; (7) Macaulay et al., 1995; Bastos et al., 1997; Fornerod et al., 1997; (8) Finlay et al., 1991; Kita et al., 1993; Hu et al., 1996; (9) Belgareh et al., 2001; Vasu et al., 2001; Harel et al., 2003; (10) Grandi et al., 1997; Miller et al., 2000; (11) Pritchard et al., 1999; Blevins et al., 2003. (B) The self-assembly of the yeast Nup84 complex yields a Y-shaped structure (reproduced with permission from Lutzmann et al., 2002). Developmental Cell 2003 4, 775-789DOI: (10.1016/S1534-5807(03)00162-X)

Figure 4 A Model for the Nuclear Envelope and NPC Assembly Pathway The entire postmitotic assembly pathway is outlined (upper left) as well as interphase assembly (upper right). The model is based on the hypothesis of Macaulay and Forbes (1996) that mitotic assembly involves insertion into an intact nuclear envelope by a similar mechanism as assembly during interphase. (A) For nuclear envelope reformation, fusion of chromatin-bound vesicles requires the RanGTPase and the p97 ATPase complex (Hetzer et al., 2000, 2001; Zhang and Clarke, 2000). (B) Before the nuclear envelope is fully closed, a subset of Nups associates with the chromatin (Chaudhary and Courvalin, 1993; Bodoor et al., 1999; Haraguchi et al., 2000; Belgareh et al., 2001; Harel et al., 2003; Walther et al., 2003). (C) In interphase metazoan cells, or budding yeast at all phases of the cell cycle, Nups may be localized to the nuclear side by import through existing NPCs (Lusk et al., 2002). (D) At the closed nuclear envelope (inset), the RanGTPase cycle regulates a vesicle-mediated step (Ryan et al., 2003). The vesicles contain specific integral membrane proteins and Nups. (E) When the vesicles fuse with the outer nuclear membrane, a localized Nup/Pom concentration may result. (F) Pore formation may be triggered by association of the outer and inner membrane complexes in the lumen. (G) Poms are thought to sequentially mediate the close apposition of the two membranes, fusion for pore formation and dilation to the mature pore (Drummond and Wilson, 2002). Further Nup subcomplexes will then be inserted, resulting in the complete NPC. Developmental Cell 2003 4, 775-789DOI: (10.1016/S1534-5807(03)00162-X)

Figure 5 Intermediates in the NPC Assembly Pathway Recent studies have provided striking images of assembly blocked at different steps. Top row: in budding yeast, perturbation of the RanGTPase cycle results in the accumulation of cytoplasmic Nup-containing vesicles. Cryo-immunolabeling in wild-type cells (left) shows Nups only at the nuclear envelope pore (arrow, gold label), and absent from the cytoplasm. In mutant cells with a defective Ran guanine nucleotide exchange factor (RanGEF, prp20-G282S), the arrowheads indicate label on cytoplasmic membranes/vesicles. (Reproduced with permission from Ryan et al., 2003). Labels denote nucleus (n), nuclear envelope (ne), mitochondria (m), vacuole (v), and plasma membrane (pm). Bottom row: in Xenopus egg extracts, wild-type NPCs are assembled in vitro (left). The addition of antibodies against the cytoplasmic gp210 tail domain inhibits the assembly and results in membranes without any detectable NPCs (right). (Reproduced with permission from Drummond and Wilson, 2002). Developmental Cell 2003 4, 775-789DOI: (10.1016/S1534-5807(03)00162-X)

Figure 6 Models for NPC Translocation (A) The salient points for karyopherin (Kap)-dependent transport pathways are outlined. In the cytoplasm (upper), the importing Kap (blue) binds the NLS cargo, docks at the NPC, and moves to the nuclear compartment where RanGTP binding triggers NLS cargo release. In the opposite direction, the exporting Kap (green) binds the NES cargo in a RanGTP-dependent manner, docks at the NPC, and moves to the cytoplasm where GTP hydrolysis on Ran results in NES cargo release. The putative docking sites and translocation machinery are shown in purple. On the right, enlarged views of key points for different translocation models are shown. (B) The FG Nups may form a filamentous network that excludes macromolecules that do not directly interact. The interactions may facilitate random movement through the network and the NPC (Denning et al., 2003). (C) The FG Nups may weakly interact to form a hydrophobic partition (inset). The FG binding sites on the shuttling receptors allow selective passage through the hydrophobic environment (Ribbeck and Gorlich, 2001). (D) The FG Nups may also provide a series of sequential binding sites of increasing affinity for the translocating macromolecules (Ben-Efraim and Gerace, 2001). Not specifically shown is the possibility that FG binding sites at the NPC faces create a high concentration of transport complexes and increases the probability that the complex will move through the NPC by random diffusion (Rout et al., 2000). Developmental Cell 2003 4, 775-789DOI: (10.1016/S1534-5807(03)00162-X)