Expression of DNAJB12 or DNAJB14 causes coordinate invasion of the nucleus by membranes associated with a novel nuclear pore structure

DNAJB12 and DNAJB14 are transmembrane proteins in the endoplasmic reticulum (ER) that serve as co-chaperones for Hsc70/Hsp70 heat shock proteins. We demonstrate that over-expression of DNAJB12 or DNAJB14 causes the formation of elaborate membranous structures within cell nuclei, which we designate DJANGOS for DNAJ-associated nuclear globular structures. DJANGOS contain DNAJB12, DNAJB14, Hsc70 and markers of the ER lumen and ER and nuclear membranes. Strikingly, they are evenly distributed underneath the nuclear envelope and are of uniform size in any one nucleus. DJANGOS are composed primarily of single-walled membrane tubes and sheets that connect to the nuclear envelope via a unique configuration of membranes, in which the nuclear pore complex appears anchored exclusively to the outer nuclear membrane, allowing both the inner and outer nuclear membranes to flow past the circumference of the nuclear pore complex into the nucleus. DJANGOS break down rapidly during cell division and reform synchronously in the daughter cell nuclei, demonstrating that they are dynamic structures that undergo coordinate formation and dissolution. Genetic studies showed that the chaperone activity of DNAJ/Hsc70 is required for the formation of DJANGOS. Further analysis of these structures will provide insight into nuclear pore formation and function, activities of molecular chaperones, and mechanisms that maintain membrane identity.

Ion permeability of the nuclear pore complex and ion-induced macromolecular permeation as studied by scanning electrochemical and fluorescence microscopy

Efficient delivery of therapeutic macromolecules and nanomaterials into the nucleus is imperative for gene therapy and nanomedicine. Nucleocytoplasmic molecular transport, however, is tightly regulated by the nuclear pore complex (NPC) with the hydrophobic transport barriers based on phenylalanine and glycine repeats. Herein, we apply scanning electrochemical microscopy (SECM) to quantitatively study the permeability of the NPCs to small probe ions with a wide range of hydrophobicity as a measure of their hydrophobic interactions with the transport barriers. Amperometric detection of the redox-inactive probe ions is enabled by using the ion-selective SECM tips based on the micropipet- or nanopipet-supported interfaces between two immiscible electrolyte solutions. The remarkably high ion permeability of the NPCs is successfully measured by SECM and theoretically analyzed. This analysis demonstrates that the ion permeability of the NPCs is determined by the dimensions and density of the nanopores without a significant effect of the transport barriers on the transported ions. Importantly, the weak ion-barrier interactions become significant at sufficiently high concentrations of extremely hydrophobic ions, i.e., tetraphenylarsonium and perfluorobutylsulfonate, to permeabilize the NPCs to naturally impermeable macromolecules. Dependence of ion-induced permeabilization of the NPC on the pathway and mode of macromolecular transport is studied by using fluorescence microscopy to obtain deeper insights into the gating mechanism of the NPC as the basis of a new transport model.

The molecular architecture of the plant nuclear pore complex

The nucleus contains the cell's genetic material, which directs cellular activity via gene regulation. The physical barrier of the nuclear envelope needs to be permeable to a variety of macromolecules and signals. The most prominent gateways for the transport of macromolecules are the nuclear pore complexes (NPCs). The NPC is the largest multiprotein complex in the cell, and is composed of multiple copies of ~30 different proteins called nucleoporins. Although much progress has been made in dissecting the NPC structure in vertebrates and yeast, the molecular architecture and physiological function of nucleoporins in plants remain poorly understood. In this review, we summarize the current knowledge regarding the plant NPC proteome and address structural and functional aspects of plant nucleoporins, which support the fundamental cellular machinery.

Structural organization of the nuclear pore permeability barrier

The efficiency of gene therapy in non-dividing cells is particularly poor due to restricted nuclear delivery rates of exogenously applied macromolecules across the nuclear pore complexes (NPCs). Therefore, improved intranuclear delivery of transgenes requires an ability to modulate the barrier function of the NPC. Despite a large body of experimental evidence accumulated to date, the contribution of individual NPC proteins (nucleoporins) to the formation of the NPC permeability barrier as well as their structural organization within the NPC remains under debate. In the present study, we revisit the view on the spatial arrangement of the Phe-Gly rich domains (FG-domains) of a subset of nucleoporins known as FG-nucleoporins. They are generally believed to be the key constituents of the NPC permeability barrier. Comparison of the binding pattern of a transport receptor importin β fragment, that binds specifically to FG-domains, with the binding pattern of wheat germ agglutinin that binds elsewhere in the NPC, reveals that FG-domains tend to cluster in the very center of the NPC. Furthermore, a controlled sequential release of the barrier-forming nucleoporins results in a gradual breakdown of the NPC permeability barrier. The breakdown is initiated by a dissociation of Nup62 from the NPC. This is accompanied by an increased passive diffusion of small molecules across the NPC. Subsequent dissociation of Nup98 and possibly other nucleoporins results in a collapse of the barrier for larger molecules. We therefore conclude that FG-nucleoporins do not contribute equally to the maintenance of the NPC permeability barrier exclusion limit. This implies that a controlled release of nucleoporins that contribute most to the formation and maintenance of the NPC barrier can facilitate access of therapeutic macromolecules into the nucleus.

The induction of a nucleoplasmic reticulum by prelamin A accumulation requires CTP:phosphocholine cytidylyltransferase-α

Farnesylated prelamin A accumulates when the final endoproteolytic maturation of the protein fails to occur and causes a dysmorphic nuclear phenotype; however, the morphology and mechanisms of biogenesis of these changes remain unclear. We show here that acute prelamin A accumulation after reduction in the activity of the ZMPSTE24 endoprotease by short interfering RNA knockdown, results in the generation of a complex nucleoplasmic reticulum that depends for its formation on the enzyme CTP:phosphocholine-cytidylyltransferase-α (CCT-α, also known as choline-phosphate cytidylyltransferase A). This structure can form during interphase, confirming that it is independent of mitosis and therefore not a consequence of disordered nuclear envelope assembly. Serial-section dual-axis electron tomography reveals that these invaginations can take two forms: one in which the inner nuclear membrane infolds alone with an inter membrane space interior, and the other in which an invagination of both nuclear membranes occurs, enclosing a cytoplasmic core. Both types of invagination can co-exist in one nucleus and both are frequently studded with nuclear pore complexes (NPC), which reduces NPC abundance on the nuclear surface.

Nuclear transport of baculovirus: revealing the nuclear pore complex passage

Baculoviruses are one of the largest viruses that replicate in the nucleus of their host cells. During an infection the capsid, containing the DNA viral genome, is released into the cytoplasm and delivers the genome into the nucleus by a mechanism that is largely unknown. Here, we used capsids of the baculovirus Autographa californica multiple nucleopolyhedrovirus in combination with electron microscopy and discovered this capsid crosses the NPC and enters into the nucleus intact, where it releases its genome. To better illustrate the existence of this capsid through the NPC in its native conformation, we reconstructed the nuclear import event using electron tomography. In addition, using different experimental conditions, we were able to visualize the intact capsid interacting with NPC cytoplasmic filaments, as an initial docking site, and midway through the NPC. Our data suggests the NPC central channel undergoes large-scale rearrangements to allow translocation of the intact 250-nm long baculovirus capsid. We discuss our results in the light of the hypothetical models of NPC function.

CD4+ T-cell synapses involve multiple distinct stages

One very striking feature of T-cell recognition is the formation of an immunological synapse between a T cell and a cell that it is recognizing. Formation of this complex structure correlates with cytotoxicity in the case of killer (largely CD8(+)) T-cell activity, or robust cytokine release and proliferation in the case of the much longer lived synapses formed by helper (CD4(+)) T cells. Here we have used electron microscopy and 3D tomography to characterize the synapses of antigen-specific CD4(+) T cells recognizing B cells and dendritic cells at different time points. We show that there are at least four distinct stages in synapse formation, proceeding over several hours, including an initial stage involving invasive T-cell pseudopodia that penetrate deeply into the antigen-presenting cell, almost to the nuclear envelope. This must involve considerable force and may serve to widen the search for potential ligands on the surface of the cell being recognized. We also show that centrioles and the Golgi complex are always located immediately beneath the synapse and that centrioles are significantly shifted toward the late contact zone with either B lymphocytes or bone marrow-derived dendritic cells such as antigen-presenting cells, and that there are dynamic, stage-dependent changes in the organization of microtubules beneath the synapse. These data reinforce and extend previous data on cytotoxic T cells that one of the principal functions of the immunological synapse is to facilitate cytokine secretion into the synaptic cleft, as well as provide important insights into the overall dynamics of this phenomenon.

Cryo-electron tomography: gaining insight into cellular processes by structural approaches

Visualization of cellular processes at a resolution of the individual protein should involve integrative and complementary approaches that can eventually draw realistic functional and cellular landscapes. Electron tomography of vitrified but otherwise unaltered cells emerges as a central method for three-dimensional reconstruction of cellular architecture at a resolution of 2-6 nm. While a combination of correlative light-based microscopy with cryo-electron tomography (cryo-ET) provides medium-resolution insight into pivotal cellular processes, fitting high-resolution structural approaches, for example, X-ray crystallography, into reconstructed macromolecular assemblies provides unprecedented information on native protein assemblies. Thus, cryo-ET bridges the resolution gap between cellular and structural biology. In this article, we focus on the study of eukaryotic cells and macromolecular complexes in a close-to-life-state. We discuss recent developments and structural findings enabling major strides to be made in understanding complex physiological functions.

Organization of amyloid-beta protein precursor intracellular domain-associated protein-1 in the rat brain

Sustained activity-dependent synaptic modifications require protein synthesis. Although proteins can be synthesized locally in dendrites, long-term changes also require nuclear signaling. Amyloid-beta protein precursor intracellular domain-associated protein-1 (AIDA-1), an abundant component of the biochemical postsynaptic density fraction, contains a nuclear localization sequence, making it a plausible candidate for synapse-to-nucleus signaling. We used immunohistochemistry to study the regional, cellular, and subcellular distribution of AIDA-1. Immunostaining was prominent in the hippocampus, cerebral cortex, and neostriatum. Along with diffuse staining of neuropil, fluorescence microscopy revealed immunostaining of excitatory synapses throughout the forebrain, and immunoreactive puncta within and directly outside the nucleus. Presynaptic staining was conspicuous in hippocampal mossy fibers. Electron microscopic analysis of material processed for postembedding immunogold revealed AIDA-1 label within postsynaptic densities in both hippocampus and cortex. Together with previous work, these data suggest that AIDA-1 serves as a direct signaling link between synapses and the nucleus in adult rat brain.

Nuclear pores in luteal cells during pregnancy and after parturition and pup removal in the rat. A freeze-fracture study

In a previous paper we described a pronounced increase of apoptotic nuclei in rat corpus luteum of pregnancy whose programmed chromatin degeneration was induced by the progesterone antagonist mifepristone. Those observations encouraged us to study the apoptotic nuclear membrane during pregnancy and after parturition and pup removal, by using a freeze-fracture technique which allows us to observe 'en face' the nuclear envelop and also permits nuclear pore counting. This study was complemented with the TUNEL assay (TdT-mediated dUTP nick-end labelling). Changes in nuclear pores during pregnancy begin with an intense reduction in number but still showing an even distribution on the nuclear membrane, never forming aggregations sharply separated from pore-free areas, which are characteristic of other apoptotic models. Electron microscopy of thin-sections shows, coincidently with findings in the freeze-fracture replicas, a moderately irregular aggregation of marginal heterochromatin condensations. After nuclear fragmentation and micronuclear formation, pores behave in the usual manner in other apoptotic models, i.e., mainly showing migrations of nuclear pores toward the chromatin-free areas. The present results support the hypothesis that nuclear pore complexes are dynamic structures, which permit their migration toward nuclear membrane areas devoid of chromatin aggregations that might block the nucleocytoplasmic transport in such areas.

Visualizing cellular processes at the molecular level by cryo-electron tomography

The cellular landscape rapidly changes throughout the biological processes that transpire within a cell. For example, the cytoskeleton is remodeled within fractions of a second. Therefore, reliable structural analysis of the cell requires approaches that allow for instantaneous arrest of functional states of a given process while offering the best possible preservation of the delicate cellular structure. Electron tomography of vitrified but otherwise unaltered cells (cryo-ET) has proven to be the method of choice for three-dimensional (3D) reconstruction of cellular architecture at a resolution of 4-6 nm. Through the use of cryo-ET, the 3D organization of macromolecular complexes and organelles can be studied in their native environment in the cell. In this Commentary, we focus on the application of cryo-ET to study eukaryotic cells - in particular, the cytoskeletal-driven processes that are involved in cell movements, filopodia protrusion and viral entry. Finally, we demonstrate the potential of cryo-ET to determine structures of macromolecular complexes in situ, such as the nuclear pore complex.

Adding pieces to the puzzling plant nuclear envelope

The nuclear envelope (NE) and the nuclear pores are important structures that both separate and selectively connect the nucleoplasm and the cytoplasm. NE and nuclear pore research in plants have recently seen an elevated level of interest. This is based both on new findings demonstrating the importance of nucleocytoplasmic trafficking for several signal transduction events, and on increasing evidence that NE and nuclear pore components play important roles during plant cell division. Here, we review the most recent reports in the field and compare them to the more advanced knowledge about yeast and animal model systems. They deal with the refined ultrastructure of the NE and NPC, with the discovery of novel NE components, and, importantly, with novel roles and fates of NE-associated and NPC-associated proteins during plant mitosis and cytokinesis.

Adding pieces to the puzzling plant nuclear envelope

The nuclear envelope (NE) and the nuclear pores are important structures that both separate and selectively connect the nucleoplasm and the cytoplasm. NE and nuclear pore research in plants have recently seen an elevated level of interest. This is based both on new findings demonstrating the importance of nucleocytoplasmic trafficking for several signal transduction events, and on increasing evidence that NE and nuclear pore components play important roles during plant cell division. Here, we review the most recent reports in the field and compare them to the more advanced knowledge about yeast and animal model systems. They deal with the refined ultrastructure of the NE and NPC, with the discovery of novel NE components, and, importantly, with novel roles and fates of NE-associated and NPC-associated proteins during plant mitosis and cytokinesis.

Structural analysis of a metazoan nuclear pore complex reveals a fused concentric ring architecture

The sole gateway for molecular exchange between the cytoplasm and the nucleus is the nuclear pore complex (NPC). This large supramolecular assembly mediates transport of cargo into and out of the nucleus and fuse the inner and outer nuclear membranes to form an aqueous translocation channel. The NPC is composed of eight proteinaceous asymmetric units forming a pseudo-8-fold symmetric passage. Due to its shear size, complexity, and plastic nature, dissecting the high-resolution three-dimensional structure of the NPC in its hydrated state is a formidable challenge. Toward this goal, we applied cryo-electron tomography to spread nuclear envelopes from Xenopus oocytes. To compensate for perturbations of the 8-fold symmetry of individual NPCs, we performed symmetry-independent asymmetric unit averaging of three-dimensional tomographic NPC volumes to eventually yield a refined model at 6.4 nm resolution. This approach revealed novel structural features, particularly in the spoke-ring complex and luminal domains. Fused concentric ring architecture of the spoke-ring complex was found along the translocation channel. Additionally, a comparison of the refined Xenopus model to that of its Dictyostelium homologue yielded similar pore diameters at the level of the three canonical rings, although the Xenopus NPC was found to be 30% taller than the Dictyostelium pore. This discrepancy is attributed primarily to the relatively low homology and different organization of some nucleoporins in the Dictyostelium genome as compared to that of vertebrates. Nevertheless, the experimental conditions impose a preferred axial orientation of the NPCs within spread Xenopus oocyte nuclear envelopes. This may at least in part explain the increased height of the reconstructed vertebrate NPCs compared to those obtained from tomographic reconstruction of intact Dictyostelium nuclei.

Functionalization of a nanopore: the nuclear pore complex paradigm

Biological cells maintain a myriad of nanopores which, although relying on the same basic small-hole principle, serve a large variety of functions. Here we consider how the nuclear pore complex (NPC), a large nanopore mediating the traffic between genetic material and protein synthesizing apparatus, is functionalized to carry out a set of transport functions. A major parameter of NPC functionalization is a lining of it external and internal surfaces with so-called phenylalanine glycine (FG) proteins. FG proteins integrate a multitude of transport factor binding sites into intrinsically disordered domains. This surprising finding has given rise to a number of transport models assigning direct gating functions to FG proteins. However, recent data suggest that the properties of FG proteins cannot be properly assessed by considering only the purified, transport-factor-stripped NPC. At physiological conditions transport factors may shape FG proteins in a way allotting an essential role to surface diffusion, reconciling tight binding with efficient transport. Thus, NPC studies are revealing both general traits and novel aspects of nanopore functionalization. In addition, they inspire artificial molecule sorters for proteomic and pharmaceutical applications.

Nuclear envelope and nuclear pore complex structure and organization in tobacco BY-2 cells

The nuclear envelope (NE) is a fundamental structure of eukaryotic cells with a dual role: it separates two distinct compartments, and enables communication between them via nuclear pore complexes (NPCs). Little is known about NPCs and NE structural organization in plants. We investigated the structure of NPCs from both sides of the NE in tobacco BY-2 cells. We detected structural differences between the NPCs of dividing and quiescent nuclei. Importantly, we also traced the organizational pattern of the NPCs, and observed non-random NPC distribution over the nuclear surface. Lastly, we observed an organized filamentous protein structure that underlies the inner nuclear membrane, and interconnects NPCs. The results are discussed within the context of the current understanding of NE structure and function in higher eukaryotes.

Exploring the nuclear envelope of herpes simplex virus 1-infected cells by high-resolution microscopy

Herpesviruses are composed of capsid, tegument, and envelope. Capsids assemble in the nucleus and exit the nucleus by budding at the inner nuclear membrane, acquiring tegument and the envelope. This study focuses on the changes of the nuclear envelope during herpes simplex virus 1 (HSV-1) infection in HeLa and Vero cells by employing preparation techniques at ambient and low temperatures for high-resolution scanning and transmission electron microscopy and confocal laser scanning microscopy. Cryo-field emission scanning electron microscopy of freeze-fractured cells showed for the first time budding of capsids at the nuclear envelope at the third dimension with high activity at 10 h and low activity at 15 h of incubation. The mean number of pores was significantly lower, and the mean interpore distance and the mean interpore area were significantly larger than those for mock-infected cells 15 h after inoculation. Forty-five percent of nuclear pores in HSV-1-infected cells were dilated to more than 140 nm. Nuclear material containing capsids protrude through them into the cytoplasm. Examination of in situ preparations after dry fracturing revealed significant enlargements of the nuclear pore diameter and of the nuclear pore central channel in HSV-1-infected cells compared to mock-infected cells. The demonstration of nucleoporins by confocal microscopy also revealed fewer pores but focal enhancement of fluorescence signals in HSV-1-infected cells, whereas Western blots showed no loss of nucleoporins from cells. The data suggest that infection with HSV-1 alters the number, size, and architecture of nuclear pores without a loss of nucleoporins from altered nuclear pore complexes.

Apoptosis leads to a degradation of vital components of active nuclear transport and a dissociation of the nuclear lamina

Apoptosis, a physiologically critical process, is characterized by a destruction of the cell after sequential degradation of key cellular components. Here, we set out to explore the fate of the physiologically indispensable nuclear envelope (NE) in this process. The NE mediates the critical nucleocytoplasmic transport through nuclear pore complexes (NPCs). In addition, the NE is involved in gene expression and contributes significantly to the overall structure and mechanical stability of the cell nucleus through the nuclear lamina, which underlies the entire nucleoplasmic face of the NE and thereby interconnects the NPCs, the NE, and the genomic material. Using the nano-imaging and mechanical probing approach atomic force microscopy (AFM) and biochemical methods, we unveiled the fate of the NE during apoptosis. The doomed NE sustains a degradation of both the mediators of the critical selective nucleocytoplasmic transport, namely NPC cytoplasmic filaments and basket, and the nuclear lamina. These observations are paralleled by marked softening and destabilization of the NE and the detection of vesicle-like nuclear fragments. We conclude that destruction of the cell nucleus during apoptosis proceeds in a strategic fashion. Degradation of NPC cytoplasmic filaments and basket shuts down the critical selective nucleocytoplasmic cross-talk. Degradation of the nuclear lamina disrupts the pivotal connection between the NE and the chromatin, breaks up the overall nuclear architecture, and softens the NE, thereby enabling the formation of nuclear fragments at later stages of apoptosis.

Intramolecular cohesion of coils mediated by phenylalanine--glycine motifs in the natively unfolded domain of a nucleoporin

The nuclear pore complex (NPC) provides the sole aqueous conduit for macromolecular exchange between the nucleus and the cytoplasm of cells. Its diffusion conduit contains a size-selective gate formed by a family of NPC proteins that feature large, natively unfolded domains with phenylalanine–glycine repeats (FG domains). These domains of nucleoporins play key roles in establishing the NPC permeability barrier, but little is known about their dynamic structure. Here we used molecular modeling and biophysical techniques to characterize the dynamic ensemble of structures of a representative FG domain from the yeast nucleoporin Nup116. The results showed that its FG motifs function as intramolecular cohesion elements that impart order to the FG domain and compact its ensemble of structures into native premolten globular configurations. At the NPC, the FG motifs of nucleoporins may exert this cohesive effect intermolecularly as well as intramolecularly to form a malleable yet cohesive quaternary structure composed of highly flexible polypeptide chains. Dynamic shifts in the equilibrium or competition between intra- and intermolecular FG motif interactions could facilitate the rapid and reversible structural transitions at the NPC conduit needed to accommodate passing karyopherin–cargo complexes of various shapes and sizes while simultaneously maintaining a size-selective gate against protein diffusion.

The nuclear pore complex is a molecular filter that gates macromolecular exchange between the cytoplasm and the nucleoplasm of cells. It contains a size-selective diffusion barrier at its center composed of proteins named FG nucleoporins. These nucleoporins feature large, structurally disordered domains that are highly decorated with phenylalanine–glycine (FG) sequence motifs. The dynamic structure of these disordered FG domains excludes them from classical structural biology analyses such as X-ray crystallography; thus, new approaches are needed to characterize their shape. Here computational and biophysical approaches were used to elucidate the ensemble of structures adopted by the FG domain of a nucleoporin. The analyses showed that the FG motifs function as intramolecular cohesion elements that compact the shape of the FG domain, forcing it to adopt loosely knit globular configurations that are constantly reconfiguring. Within the nuclear pore complex, dozens of these nucleoporin FG domains may stack as loosely knit globules forming a porous sieve that gates molecular diffusion by size exclusion.

On the octagonal structure of the nuclear pore complex: insights from coarse-grained models

The basic structure of the nuclear pore complex (NPC), conserved across almost all organisms from yeast to humans, persists in featuring an octagonal symmetry involving the nucleoporins that constitute the NPC ring. In this article, we seek to understand and evaluate the potential biomechanical reasons for this eightfold symmetry. Our analytical investigation shows that the eightfold symmetry maximizes the bending stiffness of each of the eight NPC spokes while our computational analyses identify the most likely deformation modes, frequencies, and associated kinetic energies of the NPC. These modes have energies close to other published findings using membrane analysis of the nuclear membrane pore opening, and deformation states in agreement with experimental observations. A better understanding of NPC mechanics is essential for characterizing the nucleocytoplasmic transport, which has a central importance in cell biology.

Nuclear pore complex proteins mark the implantation window in human endometrium

Nucleolar channel systems (NCSs) are membranous organelles appearing transiently in the epithelial cell nuclei of postovulatory human endometrium. Their characterization and use as markers for a healthy receptive endometrium have been limited because they are only identifiable by electron microscopy. Here we describe the light microscopic detection of NCSs using immunofluorescence. Specifically, the monoclonal nuclear pore complex antibody 414 shows that NCSs are present in about half of all human endometrial epithelial cells but not in any other cell type, tissue or species. Most nuclei contain only a single NCS of uniform 1 microm diameter indicating a tightly controlled organelle. The composition of NCSs is as unique as their structure; they contain only a subset each of the proteins of nuclear pore complexes, inner nuclear membrane, nuclear lamina and endoplasmic reticulum. Validation of our robust NCS detection method on 95 endometrial biopsies defines a 6-day window, days 19-24 (+/-1) of an idealized 28 day cycle, wherein NCSs occur. Therefore, NCSs precede and overlap with the implantation window and serve as potential markers of uterine receptivity. The immunodetection assay, combined with the hitherto underappreciated prevalence of NCSs, now enables simple screening and further molecular and functional dissection.

[Dynamics of the annulate lamellae in Drosophila syncytial embryos]

In eukaryotic cells, mitotic events are controlled by evolutionarily conserved cyclin-dependent kinases (cdk): these kinases phosphorylate cell proteins, which causes structural reorganization of the entire cell. Our recent studies of Drosophila syncytial embryos have demonstrated that cdk1 activity is a key factor that controls nuclear pore complex assembly/disassembly and affects the structure of cytoplasmic pores in the annulate. In this paper, we report a comparative analysis of these cytoplasmic organelles throughout the cell-cycle and throughout the development of Drosophila syncytial embryos. Based on the results obtained, it was presupposed that distribution of annulate lamellae containing cytoplasmic pores could reflect the inactivation of the mitotic kinase cdk1 in Drosophila syncytial embryos.

Ultrastructural studies on Icerya Seychellarum seychellarum (Westwood) ovaries (Hemipotera: Margarodidae)

The paired ovaries of the scale insect Icerya seychellarum are composed of Large number of telotrophic ovarioles that are devoid of terminal filaments. Each ovariole is subdivided into an apical tropharium (= trophic chamber) and the vitellarium. The tropharium contains 7 trophocytes, while a single oocyte develops in the vitellarium. The tubular paired accessory glands are also been distinguished. This investigation clearly points out the cytotogical features of the ovaries as well as the accessory glands.

A nuclear envelope protein linking nuclear pore basket assembly, SUMO protease regulation, and mRNA surveillance

The nuclear pore complex (NPC) is both the major conduit for nucleocytoplasmic trafficking and a platform for organizing macromolecules at the nuclear envelope. We report that yeast Esc1, a non-NPC nuclear envelope protein, is required both for proper assembly of the nuclear basket, a structure extending into the nucleus from the NPC, and for normal NPC localization of the Ulp1 SUMO protease. In esc1Delta cells, Ulp1 and nuclear basket components Nup60 and Mlp1 no longer distribute broadly around the nuclear periphery, but co-localize in a small number of dense-staining perinuclear foci. Loss of Esc1 (or Nup60) alters SUMO conjugate accumulation and enhances ulp1 mutant defects. Similar to previous findings with Mlp1, both Esc1 and Ulp1 help retain unspliced pre-mRNAs in the nucleus. Therefore, these proteins are essential for proper nuclear basket function, which includes mRNA surveillance and regulation of SUMO protein dynamics. The results raise the possibility that NPC-localized protein desumoylation may be a key regulatory event preventing inappropriate pre-mRNA export.