Annulate Lamellae Play Only a Minor Role in the Storage of Excess Nucleoporins in Drosophila Embryos (original) (raw)
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Nuclear Pores Assemble from Nucleoporin Condensates During Oogenesis
Cell, 2019
The molecular events that direct nuclear pore complex (NPC) assembly toward nuclear envelopes have been conceptualized in two pathways that occur during mitosis or interphase, respectively. In gametes and embryonic cells, NPCs also occur within stacked cytoplasmic membrane sheets, termed annulate lamellae (AL), which serve as NPC storage for early development. The mechanism of NPC biogenesis at cytoplasmic membranes remains unknown. Here, we show that during Drosophila oogenesis, Nucleoporins condense into different precursor granules that interact and progress into NPCs. Nup358 is a key player that condenses into NPC assembly platforms while its mRNA localizes to their surface in a translation-dependent manner. In concert, Microtubule-dependent transport, the small GTPase Ran and nuclear transport receptors regulate NPC biogenesis in oocytes. We delineate a non-canonical NPC assembly mechanism that relies on Nucleoporin condensates and occurs away from the nucleus under conditions of cell cycle arrest.
2020
Figure 1-1: Nuclear pore complex architecture and nucleoporin arrangement (A) Electron density map of the Homo sapiens (H.s.) NPC core scaffold, determined by cryo electron tomography [23]. Individual rings are pseudo-colored based on their corresponding sub-complexes. The cytoplasmic and nuclear rings consist of two concentric rings of Y-complexes each (light green and dark green) and are arranged in a head-to-tail orientation and dimerized with a rotational shift. The inner ring is composed of a total of four inner ring (IR) subcomplex modules that are oligomerized in a head-to-tail fashion, dimerized with a rotational shift, and mirrored across the membrane plane. Peripheral subcomplexes such as the cytoplasmic filaments, nuclear basket and transmembrane Nups remain unresolved and are thus absent from the depicted electron density map. The NPC is arranged on top of the double layered nuclear membrane depicted in light blue. (B) Drosophila melanogaster (D.m.) nucleoporins and their assumed arrangement across the NPC. Nucleoporins are divided into sub-complexes including cytoplasmic filament Nups (orange), nuclear basket Nups (blue), central channel nucleoporins (light yellow), transmembrane nucleoporins (purple), as well as scaffold Nups including Y-complex members (green) and IRcomplex members (dark yellow). Certain nucleoporins act as linker Nups, connecting several subunits including Nup98, Nup93 and Nup35, and others serve as members of several complexes, such as Nup62 (member of central channel Nups and cytoplasmic filaments). ELYS is considered to be part of the Y-complex but only to be present at the nucleoplasmic side. Visualization is based on [EMDB: 3103] [23] and inventory of D.m. nucleoporins is based on [Flybase.org: FBgg0000146]. Scaffold nucleoporins The large scale architecture of the NPC described above is largely constructed of scaffold nucleoporins. Amongst them, another layer of the aforementioned modularity is reflected in the clear recycling of a set of structurally related protein domains. The repeated usage
Pre-assembled Nuclear Pores Insert into the Nuclear Envelope during Early Development
Cell, 2016
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.
Journal of Cell Biology, 1984
Annulate lamellae are cytoplasmic organelles composed of stacked sheets of membrane containing pores that are structurally indistinguishable from nuclear pores. The functions of annulate lamellae are not well understood. Although they may be found in virtually any eucaryotic cell, they occur most commonly in transformed and embryonic tissues. In Drosophila, annulate lamellae are found in the syncytial blastoderm embryo as it is cleaved to form the cellular blastoderm. The cytological events of the cellularization process are well documented, and may be used as temporal landmarks when studying changes in annulate lamellae. By using morphometric techniques to analyze electron micrographs of embryos, we are able to calculate the number of pores per nucleus in nuclear envelopes and annulate lamellae during progressive stages of cellularization. We find that annulate lamellae pores remain at a low level while nuclear envelopes are expanding and acquiring pores in early interphase. Once n...
Development, 2011
The nuclear pore complex (NPC) mediates the transport of macromolecules between the nucleus and cytoplasm. Recent evidence indicates that structural nucleoporins, the building blocks of the NPC, have a variety of unanticipated cellular functions. Here, we report an unexpected tissue-specific requirement for the structural nucleoporin Seh1 during Drosophila oogenesis. Seh1 is a component of the Nup107-160 complex, the major structural subcomplex of the NPC. We demonstrate that Seh1 associates with the product of the missing oocyte (mio) gene. In Drosophila, mio regulates nuclear architecture and meiotic progression in early ovarian cysts. Like mio, seh1 has a crucial germline function during oogenesis. In both mio and seh1 mutant ovaries, a fraction of oocytes fail to maintain the meiotic cycle and develop as pseudo-nurse cells. Moreover, the accumulation of Mio protein is greatly diminished in the seh1 mutant background. Surprisingly, our characterization of a seh1 null allele indic...
In Vivo Dynamics of Drosophila Nuclear Envelope Components
Molecular Biology of The Cell, 2008
Nuclear pore complexes (NPCs) are multisubunit protein entities embedded into the nuclear envelope (NE). Here, we examine the in vivo dynamics of the essential Drosophila nucleoporin Nup107 and several other NE-associated proteins during NE and NPCs disassembly and reassembly that take place within each mitosis. During both the rapid mitosis of syncytial embryos and the more conventional mitosis of larval neuroblasts, Nup107 is gradually released from the NE, but it remains partially confined to the nuclear (spindle) region up to late prometaphase, in contrast to nucleoporins detected by wheat germ agglutinin and lamins. We provide evidence that in all Drosophila cells, a structure derived from the NE persists throughout metaphase and early anaphase. Finally, we examined the dynamics of the spindle checkpoint proteins Mad2 and Mad1. During mitotic exit, Mad2 and Mad1 are actively imported back from the cytoplasm into the nucleus after the NE and NPCs have reformed, but they reassociate with the NE only later in G1, concomitantly with the recruitment of the basket nucleoporin Mtor (the Drosophila orthologue of vertebrate Tpr). Surprisingly, Drosophila Nup107 shows no evidence of localization to kinetochores, despite the demonstrated importance of this association in mammalian cells.
Molecular Cell, 2005
et al., 1990; Finlay and Forbes, 1990; Macaulay et al., 1995) and are recruited from the cytosol during assembly, but two integral membrane proteins have been identified in the NPC of vertebrates, gp210 (Gerace et al., 1982; Wozniak et al., 1989) and pom121 (Hallberg et al., ). These proteins are proposed to have a role in Germany anchoring the NPC to the pore-associated membrane and in nucleating NPC assembly (Gerace et al., 1982; Wozniak et al., 1989