Getting mRNA-Containing Ribonucleoprotein Granules Out of a Nuclear Back Door  Anup Parchure, Mary Munson, Vivian Budnik  Neuron  Volume 96, Issue 3, Pages 604-615 (November 2017) DOI: 10.1016/j.neuron.2017.10.020 Copyright © 2017 Terms and Conditions

Figure 1 Hv Egress via NE Budding (A) Electron micrographs showing different stages on NE budding during the nuclear egress of HSV. Panels 1–11 show progressive stages of primary envelopment; panels 12–19 show progressive stages of de-envelopment; panel 20 shows a naked virion in the cytoplasm, in close proximity to the ONM. N, nucleoplasm; C, cytoplasm. Arrows point to the INM and ONM as indicated. Adapted from Mettenleiter et al. (2013). (B) Diagrammatic representation of NE budding during Hv egress. Capsid subcomplexes are imported into the host cell nucleus to assemble the capsid and to encapsidate the viral genome. INM-bound pUL34 viral protein recruits pUL31 to the INM, forming the nuclear egress complex (NEC). The NEC then recruits viral pUS3 kinase and cellular PKCs, which disrupt the nuclear lamina enabling the access of newly assembled capsids to the INM and its docking at this site. Membrane anchored NEC oligomerize, inwardly curving the INM around the capsid and inducing membrane scission through an increase in membrane tension. The primary enveloped capsid resides transiently at the perinuclear space until the primary envelope fuses with the ONM, releasing a naked virion to the cytoplasm for maturation. (C) Proposed model of NE budding of megaRNPs in Drosophila. DFz2C fragments enter the nucleus through NPCs and associate with megaRNPs. Atypical PKC disrupts the lamina through phosphorylation, which presumably allows interactions between the megaRNP and the INM. MegaRNPs bud into the perinuclear space by a yet-to-be-identified mechanism, and the neck of the bud is pinched off by a protein complex that includes Torsin. The INM enfolding the megaRNP within the perinuclear space presumably fuses with the ONM releasing a naked granule. Neuron 2017 96, 604-615DOI: (10.1016/j.neuron.2017.10.020) Copyright © 2017 Terms and Conditions

Figure 2 Ultrastructural Visualization of megaRNP Budding in Flies, Mammals, and Yeast in Wild-Type and Mutant Conditions Micrographs show megaRNPs granules in the nucleus of: (A) S2 cells from Jokhi et al. (2013); (B) Wild-type Drosophila nurse cell in the ovary (T. Thomson and V.B., unpublished data); (C and D) Wild-type larval body wall muscles from Jokhi et al. (2013) and Speese et al. (2012); (E) P6 wild-type mouse neuron (B. Ding, Y. Li, J. Ashley, A.P., and V.B., unpublished data); (F) Wild-type yeast. Note an NPC in cross-section (left white arrowhead in F1) and three others in a tangential section (right white arrowhead in F1 and arrowhead in F2). F2 is a high-magnification view of a region of the micrograph shown in F1 (B. Ding, A.M. Mirza, V.B., and M.M., unpublished data). Note that while in (A)–(C) granules are present in an invagination of the INM and in (D)–(F), they are located in an outpouching of the ONM. (G) Drosophila larval body wall muscles, in which Torsin-RNAi was specifically expressed in muscles from Jokhi et al. (2013); (H) Drosophila nurse cells when Torsin-RNAi was expressed in ovaries (T. Thomson, V. Jokhi, and V.B., unpublished data); (I and K) Yeast cell containing a deletion of Nup116 and incubated for 3 hr at 37°C (B. Ding, A.M. Mirza, V.B., and M.M., unpublished data); (J) Drosophila body wall muscles in animals expressing the dominant-negative mutation LamC-E174K, modeled after a PS-causing LMNA mutation from Li et al. (2016). Note the highly thickened lamina (black arrows), particularly at the neck of the budding granule. Asterisks, megaRNPs; white arrowheads, NPCs; white arrow, density at the neck of INM tethered megaRNP; Nu, nucloplasm; Cy, cytoplasm; ER, endoplasmic reticulum; INM, inner nuclear membrane; Lam, lamina; ONM, outer nuclear membrane; ribo, ribosome. Neuron 2017 96, 604-615DOI: (10.1016/j.neuron.2017.10.020) Copyright © 2017 Terms and Conditions

Figure 3 Proposed Model for the Defect in nup116Δ Mutants at 37°C Top: the NE and NPC appears normal in nup116Δ at 25°C. Bottom: at 37°C, the NPC is perturbed in nup116Δ mutant following the proposed stages (A)–(C). Adapted from Wente and Blobel (1993). Neuron 2017 96, 604-615DOI: (10.1016/j.neuron.2017.10.020) Copyright © 2017 Terms and Conditions