Functional architecture of the nuclear pore complex

UBAP2L ensures homeostasis of nuclear pore complexes at the intact nuclear envelope

Assembly of macromolecular complexes at correct cellular sites is crucial for cell function. Nuclear pore complexes (NPCs) are large cylindrical assemblies with eightfold rotational symmetry, built through hierarchical binding of nucleoporins (Nups) forming distinct subcomplexes. Here, we uncover a role of ubiquitin-associated protein 2-like (UBAP2L) in the assembly and stability of properly organized and functional NPCs at the intact nuclear envelope (NE) in human cells. UBAP2L localizes to the nuclear pores and facilitates the formation of the Y-complex, an essential scaffold component of the NPC, and its localization to the NE. UBAP2L promotes the interaction of the Y-complex with POM121 and Nup153, the critical upstream factors in a well-defined sequential order of Nups assembly onto NE during interphase. Timely localization of the cytoplasmic Nup transport factor fragile X-related protein 1 (FXR1) to the NE and its interaction with the Y-complex are likewise dependent on UBAP2L. Thus, this NPC biogenesis mechanism integrates the cytoplasmic and the nuclear NPC assembly signals and ensures efficient nuclear transport, adaptation to nutrient stress, and cellular proliferative capacity, highlighting the importance of NPC homeostasis at the intact NE.

Coronatine orchestrates ABI1-mediated stomatal opening to facilitate bacterial pathogen infection through importin β protein SAD2

Stomatal immunity plays an important role during bacterial pathogen invasion. Abscisic acid (ABA) induces plants to close their stomata and halt pathogen invasion, but many bacterial pathogens secrete phytotoxin coronatine (COR) to antagonize ABA signaling and reopen the stomata to promote infection at early stage of invasion. However, the underlining mechanism is not clear. SAD2 is an importin β family protein, and the sad2 mutant shows hypersensitivity to ABA. We discovered ABI1, which negatively regulated ABA signaling and reduced plant sensitivity to ABA, was accumulated in the plant nucleus after COR treatment. This event required SAD2 to import ABI1 to the plant nucleus. Abolition of SAD2 undermined ABI1 accumulation. Our study answers the long-standing question of how bacterial COR antagonizes ABA signaling and reopens plant stomata during pathogen invasion.

Role of the San1 ubiquitin ligase in the heat stress-induced degradation of nonnative Nup1 in the nuclear pore complex

The nuclear pore complex (NPC) mediates the selective exchange of macromolecules between the nucleus and the cytoplasm. Neurodegenerative diseases such as amyotrophic lateral sclerosis are characterized by mislocalization of nucleoporins (Nups), transport receptors, and Ras-related nuclear proteins into nucleoplasmic or cytosolic aggregates, underscoring the importance of precise assembly of the NPC. The assembly state of large protein complexes is strictly monitored by the protein quality control system. The ubiquitin-proteasome system may eliminate aberrant, misfolded, and/or orphan components; however, the involvement of the ubiquitin-proteasome system in the degradation of nonnative Nups in the NPC remains unclear. Here, we show that in Saccharomyces cerevisiae, although Nup1 (the FG-Nup component of the central core of the NPC) was stable, C-terminally green fluorescent protein-tagged Nup1, which had been incorporated into the NPC, was degraded by the proteasome especially under heat stress conditions. The degradation was dependent on the San1 ubiquitin ligase and Cdc48/p97, as well as its cofactor Doa1. We also demonstrate that San1 weakly but certainly contributes to the degradation of nontagged endogenous Nup1 in cells defective in NPC biogenesis by the deletion of NUP120. In addition, the overexpression of SAN1 exacerbated the growth defect phenotype of nup120Δ cells, which may be caused by excess degradation of defective Nups due to the deletion of NUP120. These biochemical and genetic data suggest that San1 is involved in the degradation of nonnative Nups generated by genetic mutation or when NPC biogenesis is impaired.

Malachite green: a long-buried water-soluble AIEgen with near-infrared fluorescence for living cell nucleus staining

Fluorescent imaging probes are crucial for exploring nucleus-related cellular events in live cells. Ideal probes should be photostable, small-sized, highly contrasted, and low in background. Here, we discovered that malachite green is a water-soluble near-infrared luminogen with aggregation-induced emission properties. Importantly, it can be used for living cell nucleus staining in a wash-free manner.

Nuclear localization signal-tagged systems: relevant nuclear import principles in the context of current therapeutic design

Nuclear targeting of therapeutics provides a strategy for enhancing efficacy of molecules active in the nucleus and minimizing off-target effects. 'Active' nuclear-directed transport and efficient translocations across nuclear pore complexes provide the most effective means of maximizing nuclear localization. Nuclear-targeting systems based on nuclear localization signal (NLS) motifs have progressed significantly since the beginning of the current millennium. Here, we offer a roadmap for understanding the basic mechanisms of nuclear import in the context of actionable therapeutic design for developing NLS-therapeutics with improved treatment efficacy.

Picornavirus 3C Proteins Intervene in Host Cell Processes through Proteolysis and Interactions with RNA

The Picornaviridae family comprises a large group of non-enveloped viruses with enormous impact on human and animal health. The picornaviral genome contains one open reading frame encoding a single polyprotein that can be processed by viral proteases. The picornaviral 3C proteases share similar three-dimensional structures and play a significant role in the viral life cycle and virus-host interactions. Picornaviral 3C proteins also have conserved RNA-binding activities that contribute to the assembly of the viral RNA replication complex. The 3C protease is important for regulating the host cell response through the cleavage of critical host cell proteins, acting to selectively 'hijack' host factors involved in gene expression, promoting picornavirus replication, and inactivating key factors in innate immunity signaling pathways. The protease and RNA-binding activities of 3C are involved in viral polyprotein processing and the initiation of viral RNA synthesis. Most importantly, 3C modifies critical molecules in host organelles and maintains virus infection by subtly subverting host cell death through the blocking of transcription, translation, and nucleocytoplasmic trafficking to modulate cell physiology for viral replication. Here, we discuss the molecular mechanisms through which 3C mediates physiological processes involved in promoting virus infection, replication, and release.

Nucleoporin93 (Nup93) Limits Yap Activity to Prevent Endothelial Cell Senescence

Endothelial cells (ECs) form the innermost lining of the vasculature and serve a pivotal role in preventing age-related vascular disease. Endothelial health relies on the proper nucleocytoplasmic shuttling of transcription factors via nuclear pore complexes (NPCs). Emerging studies report NPC degradation with natural aging, suggesting impaired nucleocytoplasmic transport in age-related EC dysfunction. We herein identify nucleoporin93 (Nup93), a crucial structural NPC protein, as an indispensable player for vascular protection. Endothelial Nup93 protein levels are significantly reduced in the vasculature of aged mice, paralleling observations of Nup93 loss when using in vitro models of endothelial aging. Mechanistically, we find that loss of Nup93 impairs NPC transport, leading to the nuclear accumulation of Yap and downstream inflammation. Collectively, our findings indicate maintenance of endothelial Nup93 as a key determinant of EC health, where aging targets endothelial Nup93 levels to impair NPC function as a novel mechanism for EC senescence and vascular aging.

Scaffold, mechanics and functions of nuclear lamins

Nuclear lamins are type-V intermediate filaments that are involved in many nuclear processes. In mammals, A- and B-type lamins assemble into separate physical meshwork underneath the inner nuclear membrane, the nuclear lamina, with some residual fraction localized within the nucleoplasm. Lamins are the major part of the nucleoskeleton, providing mechanical strength and flexibility to protect the genome and allow nuclear deformability, while also contributing to gene regulation via interactions with chromatin. While lamins are the evolutionary ancestors of all intermediate filament family proteins, their ultimate filamentous assembly is markedly different from their cytoplasmic counterparts. Interestingly, hundreds of genetic mutations in the lamina proteins have been causally linked with a broad range of human pathologies, termed laminopathies. These include muscular, neurological and metabolic disorders, as well as premature aging diseases. Recent technological advances have contributed to resolving the filamentous structure of lamins and the corresponding lamina organization. In this review, we revisit the multiscale lamin organization and discuss its implications on nuclear mechanics and chromatin organization within lamina-associated domains.

Natural variation in OsSEC13 HOMOLOG 1 modulates redox homeostasis to confer cold tolerance in rice

Rice (Oryza sativa L.) is a cold-sensitive species that often faces cold stress, which adversely affects yield productivity and quality. However, the genetic basis for low-temperature adaptation in rice remains unclear. Here, we demonstrate that 2 functional polymorphisms in O. sativa SEC13 Homolog 1 (OsSEH1), encoding a WD40-repeat nucleoporin, between the 2 subspecies O. sativa japonica and O. sativa indica rice, may have facilitated cold adaptation in japonica rice. We show that OsSEH1 of the japonica variety expressed in OsSEH1MSD plants (transgenic line overexpressing the OsSEH1 allele from Mangshuidao [MSD], cold-tolerant landrace) has a higher affinity for O. sativa metallothionein 2b (OsMT2b) than that of OsSEH1 of indica. This high affinity of OsSEH1MSD for OsMT2b results in inhibition of OsMT2b degradation, with decreased accumulation of reactive oxygen species and increased cold tolerance. Transcriptome analysis indicates that OsSEH1 positively regulates the expression of the genes encoding dehydration-responsive element-binding transcription factors, i.e. OsDREB1 genes, and induces the expression of multiple cold-regulated genes to enhance cold tolerance. Our findings highlight a breeding resource for improving cold tolerance in rice.

Research progress in nucleus-targeted tumor therapy

The nucleus is considered the most important organelle in the cell as it plays a central role in controlling cell reproduction, metabolism, and the cell cycle. The successful delivery of drugs into the nucleus can achieve excellent therapeutic effects, which reveals the potential of nucleus-targeted therapy in precision medicine. However, the transportation of therapeutics into the nucleus remains a significant challenge due to various biological barriers. Herein, we summarize the recent progress in the nucleus-targeted drug delivery system (NDDS). The structures of the nucleus and nuclear envelope are first described in order to understand the mechanisms by which drugs cross the nuclear envelope. Then, various drug delivery strategies based on the mechanisms and their applications are discussed. Finally, the challenges and solutions in the field of nucleus-targeted drug delivery are raised for developing a more efficient NDDS and promoting its clinical transformation.

Steroid-Resistant Nephrotic Syndrome Caused by NUP93 Pathogenic Variants

BACKGROUND

Although steroid therapy is a standard of care for nephrotic syndrome treatment, 15-20% of patients do not respond to it. Finding the genetic background is possible in >10% of steroid-resistant nephrotic syndrome (SRNS) cases. Variants in genes encoding nuclear pore complex proteins are a novel cause of paediatric steroid-resistant nephrotic syndrome (SRNS). Recent studies suggest NUP93 variants to be a significant cause of paediatric onset SRNS. The clinical data on certain variants and disease history are still very limited.

METHODS AND RESULTS

We report the SRNS case of a 12-year-old boy with two detected NUP93 variants, which are pathogenic and possibly pathogenic. The onset of the disease was early and severe. The patient was admitted to the paediatric nephrology department due to nephrotic-range proteinuria and hypoalbuminemia with a long medical history of steroid and non-steroid immunosuppressive treatment. The genetic panel targeting 50 genes, clinically relevant for nephrotic syndrome, was performed. The only gene which was found to be affected by mutations, namely c.2326C>T and c.1162C>T, respectively, was NUP93. Conclusions: NUP93 variants are rarely identified as causes of SRNS. Clinical data are of utmost importance to establish the standard of care for SRNS patients suffering from this genetic disfunction. This is the first case of a heterozygous patient with the c.2326C>T and c.1162C>T variants and confirmed clinical history of the SRNS described so far. Our data suggest the clinical relevance of the c.1162C>T variant.

Regulation of FLC nuclear import by coordinated action of the NUP62-subcomplex and importin β SAD2

Flowering locus C (FLC) is a central transcriptional repressor that controls flowering time. However, how FLC is imported into the nucleus is unknown. Here, we report that Arabidopsis nucleoporins 62 (NUP62), NUP58, and NUP54 composed NUP62-subcomplex modulates FLC nuclear import during floral transition in an importin α-independent manner, via direct interaction. NUP62 recruits FLC to the cytoplasmic filaments and imports it into the nucleus through the NUP62-subcomplex composed central channel. Importin β supersensitive to ABA and drought 2 (SAD2), a carrier protein, is critical for FLC nuclear import and flower transition, which facilitates FLC import into the nucleus mainly through the NUP62-subcomplex. Proteomics, RNA-seq, and cell biological analyses indicate that the NUP62-subcomplex mainly mediates the nuclear import of cargos with unconventional nuclear localization sequences (NLSs), such as FLC. Our findings illustrate the mechanisms of the NUP62-subcomplex and SAD2 on FLC nuclear import process and floral transition, and provide insights into the role of NUP62-subcomplex and SAD2 in protein nucleocytoplasmic transport in plants.

Unraveling the impact of disrupted nucleocytoplasmic transport systems in C9orf72-associated ALS

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two adult-onset neurodegenerative diseases that are part of a common disease spectrum due to clinical, genetic, and pathological overlap. A prominent genetic factor contributing to both diseases is a hexanucleotide repeat expansion in a non-coding region of the C9orf72 gene. This mutation in C9orf72 leads to nuclear depletion and cytoplasmic aggregation of Tar DNA-RNA binding protein 43 (TDP-43). TDP-43 pathology is characteristic of the majority of ALS cases, irrespective of disease causation, and is present in ~50% of FTD cases. Defects in nucleocytoplasmic transport involving the nuclear pore complex, the Ran-GTPase cycle, and nuclear transport factors have been linked with the mislocalization of TDP-43. Here, we will explore and discuss the implications of these system abnormalities of nucleocytoplasmic transport in C9orf72-ALS/FTD, as well as in other forms of familial and sporadic ALS.

Nucleoporin Nup358 Downregulation Tunes the Neuronal Excitability in Mouse Cortical Neurons

Nucleoporins (NUPs) are proteins that comprise the nuclear pore complexes (NPCs). The NPC spans the nuclear envelope of a cell and provides a channel through which RNA and proteins move between the nucleus and the cytoplasm and vice versa. NUP and NPC disruptions have a great impact on the pathophysiology of neurodegenerative diseases (NDDs). Although the downregulation of Nup358 leads to a reduction in the scaffold protein ankyrin-G at the axon initial segment (AIS) of mature neurons, the function of Nup358 in the cytoplasm of neurons remains elusive. To investigate whether Nup358 plays any role in neuronal activity, we downregulated Nup358 in non-pathological mouse cortical neurons and measured their active and passive bioelectrical properties. We identified that Nup358 downregulation is able to produce significant modifications of cell-membrane excitability via voltage-gated sodium channel kinetics. Our findings suggest that Nup358 contributes to neuronal excitability through a functional stabilization of the electrical properties of the neuronal membrane. Hypotheses will be discussed regarding the alteration of this active regulation as putatively occurring in the pathophysiology of NDDs.

[Structural and mechanical plasticity of the nuclear pore]

The nuclear pore, which can be seen as the gateway to the cell nucleus, is central to many processes including gene regulation. It is a complex and dynamic structure composed of more than 30 proteins present in multiple copies that allows the selective and directional transport of RNA and proteins. As shown by recent studies, it is able to adapt its overall structure to the state of the cell. These results suggest that the structural and mechanical plasticity of the nuclear pore is important for its function but also in the development of cancer or viral infections.

An Analysis Regarding the Association Between the Nuclear Pore Complex (NPC) and Hepatocellular Carcinoma (HCC)

Background

The nuclear pore complex (NPC) is the main mediator of nuclear and cytoplasmic communication, and delaying or blocking nuclear RNA export and protein shuttling can inhibit cell proliferation and induce apoptosis. Although NPC is a research hotspot in structural biology, relevant studies in hepatocellular carcinoma are scarce, especially in terms of translation into clinical practice.

Methods

This study used a bioinformatics approach combining validation experiments to investigate the biological mechanisms that may be related with NPC. A series of experiments performed to explore the function of the Targeting protein for Xenopus kinesin-like protein 2 (TPX2) in HCC.

Results

Patients with HCC can be divided into two NPC clusters. Patients with high NPC levels (C1) had a shorter survival time than those with low NPC levels (C2) and are characterised by high levels of proliferative signals. We demonstrated that TPX2 regulates HCC growth and inhibits apoptosis in an NPC-dependent manner and contributes to the maintenance of HCC stemness. We developed the NPCScore to predict the prognosis and degree of differentiation in HCC patients.

Conclusion

NPC plays an important role in the malignant proliferation of HCC. Assessing NPC expression patterns could help enhance our understanding of tumor cell proliferation and could guide more effective chemotherapeutic strategies.

Identification of nuclear pore complexes (NPCs) and revealed outer-ring component BnHOS1 related to cold tolerance in B. napus

Nuclear pore complexes (NPCs) consist of ~30 different nucleoporins (Nups), are the unique channels that govern development, hormonal response, and roles in both biotic and abiotic responses, as well as the transport and information exchange of biomacromolecules between nucleoplasms. Here, we report the comprehensive identification of 77 BnNups throughout the zhongshuang11 (ZS11) genome, which were classified into 29 distinct categories based on their evolutionary connections. We compared and contrasted different BnNups by analyzing at their gene structures, protein domains, putative three-dimensional (3D) models and expression patterns. Additional examples of genome-wide duplication events and cross-species synteny are provided to demonstrate the proliferation and evolutionary conservation of BnNups. When BnHOS1 was modified using CRISPR/Cas9 technology, the resulting L10 and L28 lines exhibited substantial freezing resistance. This not only demonstrated the negative regulatory impact of BnHOS1 on cold stress, but also offered a promising candidate gene for cold tolerance breeding and augmented the available B. napus material. These findings not only help us learn more about the composition and function of BnNPCs in B. napus, but they also provide light on how NPCs in other eukaryotic organism functions.

Spelling out the roles of individual nucleoporins in nuclear export of mRNA

The Nuclear Pore Complex (NPC) represents a critical passage through the nuclear envelope for nuclear import and export that impacts nearly every cellular process at some level. Recent technological advances in the form of Auxin Inducible Degron (AID) strategies and Single-Point Edge-Excitation sub-Diffraction (SPEED) microscopy have enabled us to provide new insight into the distinct functions and roles of nuclear basket nucleoporins (Nups) upon nuclear docking and export for mRNAs. In this paper, we provide a review of our recent findings as well as an assessment of new techniques, updated models, and future perspectives in the studies of mRNA's nuclear export.

Mechanisms of UV-B light-induced photoreceptor UVR8 nuclear localization dynamics

Light regulates the subcellular localization of plant photoreceptors, a key step in light signaling. Ultraviolet-B radiation (UV-B) induces the plant photoreceptor UV RESISTANCE LOCUS 8 (UVR8) nuclear accumulation, where it regulates photomorphogenesis. However, the molecular mechanism for the UV-B-regulated UVR8 nuclear localization dynamics is unknown. With fluorescence recovery after photobleaching (FRAP), cell fractionation followed by immunoblotting and co-immunoprecipitation (Co-IP) assays we tested the function of UVR8-interacting proteins including CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 in the regulation of UVR8 nuclear dynamics in Arabidopsis thaliana. We showed that UV-B-induced rapid UVR8 nuclear translocation is independent of COP1, which previously was shown to be required for UV-B-induced UVR8 nuclear accumulation. Instead, we provide evidence that the UV-B-induced UVR8 homodimer-to-monomer photo-switch and the concurrent size reduction of UVR8 enables its monomer nuclear translocation, most likely via free diffusion. Nuclear COP1 interacts with UV-B-activated UVR8 monomer, thereby promoting UVR8 nuclear retention. Conversely, RUP1and RUP2, whose expressions are induced by UV-B, inhibit UVR8 nuclear retention via attenuating the UVR8-COP1 interaction, allowing UVR8 to exit the nucleus. Collectively, our data suggest that UV-B-induced monomerization of UVR8 promotes its nuclear translocation via free diffusion. In the nucleus, COP1 binding promotes UVR8 monomer nuclear retention, which is counterbalanced by the major negative regulators RUP1 and RUP2.

Insights into the role of Nup62 and Nup93 in assembling cytoplasmic ring and central transport channel of the nuclear pore complex

The nuclear pore complex (NPC) is a highly modular assembly of 34 distinct nucleoporins (Nups) to form a versatile transport channel between the nucleus and the cytoplasm. Among them, Nup62 is known as an essential component for nuclear transport, Nup93 for proper nuclear envelope assembly. These Nups constitute various NPC subcomplexes such as the central transport channel (CTC), the cytoplasmic ring (CR), and the inner ring (IR). However, how they play their roles in NPC assembly and transport activity is not clear. Here we delineated the interacting regions and conducted biochemical reconstitution and structural characterization of the mammalian CR complex to reveal its intrinsic dynamic behavior and a distinct "4"-shaped architecture resembling the CTC complex. Our in vitro reconstitution data demonstrate that the Nup62 coiled-coil domain is critical to form both Nup62^322-525 •Nup88^517-742 and Nup62^322-525•Nup88^517-742•Nup214^693-926 heterotrimers and both can bind to Nup93^1-150. We therefore propose that Nup93 acts as a "sensor" to bind to Nup62 shared heterotrimers including the Nup62•Nup54 heterotrimer of the CTC, which was not shown previously to be an interacting partner. Altogether, our biochemical study suggests that Nup62 via its coiled-coil domain is central to form compositionally distinct yet structurally similar heterotrimers and Nup93 binds these diverse heterotrimers nonselectively.

NUCLEAR PORE ANCHOR and EARLY IN SHORT DAYS 4 negatively regulate abscisic acid signaling by inhibiting Snf1-related protein kinase2 activity and stability in Arabidopsis

Abscisic acid (ABA) is a key regulator of plant responses to abiotic stresses, such as drought. Abscisic acid receptors and coreceptors perceive ABA to activate Snf1-related protein kinase2s (SnRK2s) that phosphorylate downstream effectors, thereby activating ABA signaling and the stress response. As stress responses come with fitness penalties for plants, it is crucial to tightly control SnRK2 kinase activity to restrict ABA signaling. However, how SnRK2 kinases are inactivated remains elusive. Here, we show that NUCLEAR PORE ANCHOR (NUA), a nuclear pore complex (NPC) component, negatively regulates ABA-mediated inhibition of seed germination and post-germination growth, and drought tolerance in Arabidopsis thaliana. The role of NUA in response to ABA depends on SnRK2.2 and SnRK2.3 for seed germination and on SnRK2.6 for drought. NUA does not directly inhibit the phosphorylation of these SnRK2s or affects their abundance. However, the NUA-interacting protein EARLY IN SHORT DAYS 4 (ESD4), a SUMO protease, negatively regulates ABA signaling by directly interacting with and inhibiting SnRK2 phosphorylation and protein levels. More importantly, we demonstrated that SnRK2.6 can be SUMOylated in vitro, and ESD4 inhibits its SUMOylation. Taken together, we identified NUA and ESD4 as SnRK2 kinase inhibitors that block SnRK2 activity, and reveal a mechanism whereby NUA and ESD4 negatively regulate plant responses to ABA and drought stress possibly through SUMOylation-dependent regulation of SnRK2s.

NLR we there yet? Nucleocytoplasmic coordination of NLR-mediated immunity

Plant intracellular nucleotide-binding leucine-rich repeat immune receptors (NLRs) perceive the activity of pathogen-secreted effector molecules that, when undetected, promote colonisation of hosts. Signalling from activated NLRs converges with and potentiates downstream responses from activated pattern recognition receptors (PRRs) that sense microbial signatures at the cell surface. Efficient signalling of both receptor branches relies on the host cell nucleus as an integration point for transcriptional reprogramming, and on the macromolecular transport processes that mediate the communication between cytoplasm and nucleoplasm. Studies on nuclear pore complexes (NPCs), the nucleoporin proteins (NUPs) that compose NPCs, and nuclear transport machinery constituents that control nucleocytoplasmic transport, have revealed that they play important roles in regulating plant immune responses. Here, we discuss the contributions of nucleoporins and nuclear transport receptor (NTR)-mediated signal transduction in plant immunity with an emphasis on NLR immune signalling across the nuclear compartment boundary and within the nucleus. We also highlight and discuss cytoplasmic and nuclear functions of NLRs and their signalling partners and further consider the potential implications of NLR activation and resistosome formation in both cellular compartments for mediating plant pathogen resistance and programmed host cell death.

Phase separation of low-complexity domains in cellular function and disease

In this review, we discuss the ways in which recent studies of low-complexity (LC) domains have challenged our understanding of the mechanisms underlying cellular organization. LC sequences, long believed to function in the absence of a molecular structure, are abundant in the proteomes of all eukaryotic organisms. Over the past decade, the phase separation of LC domains has emerged as a fundamental mechanism driving dynamic multivalent interactions of many cellular processes. We review the key evidence showing the role of phase separation of individual proteins in organizing cellular assemblies and facilitating biological function while implicating the dynamics of phase separation as a key to biological validity and functional utility. We also highlight the evidence showing that pathogenic LC proteins alter various phase separation-dependent interactions to elicit debilitating human diseases, including cancer and neurodegenerative diseases. Progress in understanding the biology of phase separation may offer useful hints toward possible therapeutic interventions to combat the toxicity of pathogenic proteins.

TurboID Identification of Evolutionarily Divergent Components of the Nuclear Pore Complex in the Malaria Model Plasmodium berghei

Twenty years since the publication of the Plasmodium falciparum and P. berghei genomes one-third of their protein-coding genes still lack functional annotation. In the absence of sequence and structural homology, protein-protein interactions can facilitate functional prediction of such orphan genes by mapping protein complexes in their natural cellular environment. The Plasmodium nuclear pore complex (NPC) is a case in point: it remains poorly defined; its constituents lack conservation with the 30+ proteins described in the NPC of many opisthokonts, a clade of eukaryotes that includes fungi and animals, but not Plasmodium. Here, we developed a labeling methodology based on TurboID fusion proteins, which allows visualization of the P. berghei NPC and facilitates the identification of its components. Following affinity purification and mass spectrometry, we identified 4 known nucleoporins (Nups) (138, 205, 221, and the bait 313), and verify interaction with the putative phenylalanine-glycine (FG) Nup637; we assigned 5 proteins lacking annotation (and therefore meaningful homology with proteins outside the genus) to the NPC, which is confirmed by green fluorescent protein (GFP) tagging. Based on gene deletion attempts, all new Nups — Nup176, 269, 335, 390, and 434 — are essential to parasite survival. They lack primary sequence homology with proteins outside the Plasmodium genus; albeit 2 incorporate short domains with structural homology to human Nup155 and yeast Nup157, and the condensin SMC (Structural Maintenance Of Chromosomes 4). The protocols developed here showcase the power of proximity labeling for elucidating protein complex composition and annotation of taxonomically restricted genes in Plasmodium. It opens the door to exploring the function of the Plasmodium NPC and understanding its evolutionary position.

Trafficking and/or division: Distinct roles of nucleoporins based on their location within the nuclear pore complex

The nuclear pore complex (NPC) facilitates the trafficking of proteins and RNA between the nucleus and cytoplasm. The role of nucleoporins (Nups) in transport in the context of the NPC is well established, yet their function in tRNA export has not been fully explored. We selected several nucleoporins from different parts of the NPC to investigate their potential role in tRNA trafficking in Trypanosoma brucei. We show that while all of the nucleoporins studied are essential for cell viability, only TbNup62 and TbNup53a function in tRNA export. In contrast to homologs in yeast TbNup144 and TbNup158, which are part of the inner and outer ring of the NPC, have no role in nuclear tRNA trafficking. Instead, TbNup144 plays a critical role in nuclear division, highlighting the role of nucleoporins beyond nucleocytoplasmic transport. These results suggest that the location of nucleoporins within the NPC is crucial to maintaining various cellular processes.

Liquid-liquid phase separation as an organizing principle of intracellular space: overview of the evolution of the cell compartmentalization concept

At the turn of the twenty-first century, fundamental changes took place in the understanding of the structure and function of proteins and then in the appreciation of the intracellular space organization. A rather mechanistic model of the organization of living matter, where the function of proteins is determined by their rigid globular structure, and the intracellular processes occur in rigidly determined compartments, was replaced by an idea that highly dynamic and multifunctional "soft matter" lies at the heart of all living things. According this "new view", the most important role in the spatio-temporal organization of the intracellular space is played by liquid-liquid phase transitions of biopolymers. These self-organizing cellular compartments are open dynamic systems existing at the edge of chaos. They are characterized by the exceptional structural and compositional dynamics, and their multicomponent nature and polyfunctionality provide means for the finely tuned regulation of various intracellular processes. Changes in the external conditions can cause a disruption of the biogenesis of these cellular bodies leading to the irreversible aggregation of their constituent proteins, followed by the transition to a gel-like state and the emergence of amyloid fibrils. This work represents a historical overview of changes in our understanding of the intracellular space compartmentalization. It also reflects methodological breakthroughs that led to a change in paradigms in this area of science and discusses modern ideas about the organization of the intracellular space. It is emphasized here that the membrane-less organelles have to combine a certain resistance to the changes in their environment and, at the same time, show high sensitivity to the external signals, which ensures the normal functioning of the cell.

Function of Nuclear Pore Complexes in Regulation of Plant Defense Signaling

In eukaryotes, the nucleus is the regulatory center of cytogenetics and metabolism, and it is critical for fundamental biological processes, including DNA replication and transcription, protein synthesis, and biological macromolecule transportation. The eukaryotic nucleus is surrounded by a lipid bilayer called the nuclear envelope (NE), which creates a microenvironment for sophisticated cellular processes. The NE is perforated by the nuclear pore complex (NPC), which is the channel for biological macromolecule bi-directional transport between the nucleus and cytoplasm. It is well known that NPC is the spatial designer of the genome and the manager of genomic function. Moreover, the NPC is considered to be a platform for the continual adaptation and evolution of eukaryotes. So far, a number of nucleoporins required for plant-defense processes have been identified. Here, we first provide an overview of NPC organization in plants, and then discuss recent findings in the plant NPC to elaborate on and dissect the distinct defensive functions of different NPC subcomponents in plant immune defense, growth and development, hormone signaling, and temperature response. Nucleoporins located in different components of NPC have their unique functions, and the link between the NPC and nucleocytoplasmic trafficking promotes crosstalk of different defense signals in plants. It is necessary to explore appropriate components of the NPC as potential targets for the breeding of high-quality and broad spectrum resistance crop varieties.

Flavonoid deficiency disrupts redox homeostasis and terpenoid biosynthesis in glandular trichomes of tomato

Glandular trichomes (GTs) are epidermal structures that provide the first line of chemical defense against arthropod herbivores and other biotic threats. The most conspicuous structure on leaves of cultivated tomato (Solanum lycopersicum) is the type-VI GT (tVI-GT), which accumulates both flavonoids and volatile terpenoids. Although these classes of specialized metabolites are derived from distinct metabolic pathways, previous studies with a chalcone isomerase 1 (CHI1)-deficient mutant called anthocyanin free (af) showed that flavonoids are required for terpenoid accumulation in tVI-GTs. Here, we combined global transcriptomic and proteomic analyses of isolated trichomes as a starting point to show that the lack of CHI1 is associated with reduced levels of terpenoid biosynthetic transcripts and enzymes. The flavonoid deficiency in af trichomes also resulted in the upregulation of abiotic stress-responsive genes associated with DNA damage and repair. Several lines of biochemical and genetic evidence indicate that the terpenoid defect in af mutants is specific for the tVI-GT and is associated with the absence of bulk flavonoids rather than loss of CHI1 per se. A newly developed genome-scale model of metabolism in tomato tVI-GTs helped identify metabolic imbalances caused by the loss of flavonoid production. We provide evidence that flavonoid deficiency in this cell type leads to increased production of reactive oxygen species (ROS), which may impair terpenoid biosynthesis. Collectively, our findings support a role for flavonoids as ROS-scavenging antioxidants in GTs.

Cryo-EM structure of the nuclear ring from Xenopus laevis nuclear pore complex

Nuclear pore complex (NPC) shuttles cargo across the nuclear envelope. Here we present single-particle cryo-EM structure of the nuclear ring (NR) subunit from Xenopus laevis NPC at an average resolution of 5.6 Å. The NR subunit comprises two 10-membered Y complexes, each with the nucleoporin ELYS closely associating with Nup160 and Nup37 of the long arm. Unlike the cytoplasmic ring (CR) or inner ring (IR), the NR subunit contains only one molecule each of Nup205 and Nup93. Nup205 binds both arms of the Y complexes and interacts with the stem of inner Y complex from the neighboring subunit. Nup93 connects the stems of inner and outer Y complexes within the same NR subunit, and places its N-terminal extended helix into the axial groove of Nup205 from the neighboring subunit. Together with other structural information, we have generated a composite atomic model of the central ring scaffold that includes the NR, IR, and CR. The IR is connected to the two outer rings mainly through Nup155. This model facilitates functional understanding of vertebrate NPC.

Super-resolved 3D tracking of cargo transport through nuclear pore complexes

Nuclear pore complexes (NPCs) embedded within the nuclear envelope (NE) mediate rapid, selective, and bidirectional traffic between the cytoplasm and the nucleoplasm. Deciphering the mechanism and dynamics of this process is challenged by the need for high spatial and temporal precision. We report here a multi-color imaging approach that enables direct 3D visualization of cargo transport trajectories relative to a super-resolved octagonal double-ring structure of the NPC scaffold. The success of this approach is enabled by the high positional stability of NPCs within permeabilized cells, as verified by a combined experimental and simulation analysis. Hourglass-shaped translocation conduits for two cargo complexes representing different nuclear transport receptor (NTR) pathways indicates rapid migration through the permeability barrier on or near the NPC scaffold. Binding sites for cargo complexes extend over 100 nm from the pore openings, consistent with a wide distribution of the FG-polypeptides that bind NTRs.

In Pursuit of Distinctiveness: Transmembrane Nucleoporins and Their Disease Associations

The bi-directional nucleocytoplasmic shuttling of macromolecules like molecular signals, transcription factors, regulatory proteins, and RNAs occurs exclusively through Nuclear Pore Complex (NPC) residing in the nuclear membrane. This magnanimous complex is essentially a congregation of ~32 conserved proteins termed Nucleoporins (Nups) present in multiple copies and mostly arranged as subcomplexes to constitute a functional NPC. Nups participate in ancillary functions such as chromatin organization, transcription regulation, DNA damage repair, genome stabilization, and cell cycle control, apart from their central role as nucleocytoplasmic conduits. Thus, Nups exert a role in the maintenance of cellular homeostasis. In mammals, precisely three nucleoporins traverse the nuclear membrane, are called transmembrane Nups (TM-Nups), and are involved in multiple cellular functions. Owing to their vital roles in cellular processes and homeostasis, dysregulation of nucleoporin function is implicated in various diseases. The deregulated functioning of TM-Nups can thus act as an opportune window for the development of diseases. Indeed, mounting evidence exhibits a strong association of TM-Nups in cancer and numerous other physiological disorders. These findings have provided much-needed insights into the novel mechanisms of disease progression. While nucleoporin’s functions have often been summarized in the disease context, a focus on TM-Nups has always lacked. This review emphasizes the elucidation of distinct canonical and non-canonical functions of mammalian TM-Nups and the underlying mechanisms of their disease association.

Multivalent Interactions with Intrinsically Disordered Proteins Probed by Surface Plasmon Resonance

Multivalent interactions underpin associations between intrinsically disordered proteins (IDPs) and their binding partners. This is a subject of considerable interest and governs how nuclear transport receptors (NTRs) orchestrate the nucleocytoplasmic transport (NCT) of signal-specific cargoes through nuclear pore complexes (NPCs) in eukaryotic cells. Specifically, IDPs termed phenylalanine-glycine nucleoporins (FG Nups) exert multivalent interactions with NTRs to facilitate their transport selectivity and speed through the NPC. Here, we document the use of surface plasmon resonance (SPR) to quantify the affinity and kinetics of NTR-FG Nup binding as a function of FG Nup surface density. Moreover, we describe an in situ method that measures conformational height changes that occur in a FG Nup layer following NTR-binding. Protocols by which the as-obtained SPR results are treated with respect to mass transport limitations are further described. Overall, the SPR methodology described here can be applied to studying multivalent interactions and the role of avidity in diverse biological and biointerfacial systems.

Nonequilibrium self-assembly of multiple stored targets in a dimer-based system

Nonequilibrium self-assembly can be found in various biological processes where chemical potential gradients are exploited to steer the system to a desired organized structure with a particular function. Microtubules, for example, are composed of two globular protein subunits, α-tubulin and β-tubulin, which bind together to form polar dimers that self-assemble a hollow cylinder structure in a process driven by GTPase activity. Inspired by this process, we define a generic self-assembly lattice model containing particles of two subunits, which is driven out-of-equilibrium by a dimer-favoring local driving force. Using Monte Carlo simulations, we characterize the ability of this system to restore pre-encoded target structures as a function of the initial seed size, interaction energy, chemical potential, number of target structures, and strength of the nonequilibrium drive. We demonstrate some intriguing consequences of the drive, such as a smaller critical seed and an improved target assembly stability, compared to the equilibrium scenario. Our results can expand the theoretical basis of nonequilibrium self-assembly and provide deeper understanding of how nonequilibrium driving can overcome equilibrium constraints.

LC-MS Based Draft Map of the Arabidopsis thaliana Nuclear Proteome and Protein Import in Pattern Triggered Immunity

Despite its central role as the ark of genetic information and gene expression the plant nucleus is surprisingly understudied. We isolated nuclei from the Arabidopsis thaliana dark grown cell culture left untreated and treated with flg22 and nlp20, two elicitors of pattern triggered immunity (PTI) in plants, respectively. An liquid chromatography mass spectrometry (LC-MS) based discovery proteomics approach was used to measure the nuclear proteome fractions. An enrichment score based on the relative abundance of cytoplasmic, mitochondrial and Golgi markers in the nuclear protein fraction allowed us to curate the nuclear proteome producing high quality catalogs of around 3,000 nuclear proteins under untreated and both PTI conditions. The measurements also covered low abundant proteins including more than 100 transcription factors and transcriptional co-activators. We disclose a list of several hundred potentially dual targeted proteins including proteins not yet found before for further study. Protein import into the nucleus in plant immunity is known. Here we sought to gain a broader impression of this phenomenon employing our proteomics data and found 157 and 73 proteins to possibly be imported into the nucleus upon stimulus with flg22 and nlp20, respectively. Furthermore, the abundance of 93 proteins changed significantly in the nucleus following elicitation of immunity. These results suggest promiscuous ribosome assembly and a role of prohibitins and cytochrome C in the nucleus in PTI.

The Role of Emerin in Cancer Progression and Metastasis

It is commonly recognized in the field that cancer cells exhibit changes in the size and shape of their nuclei. These features often serve as important biomarkers in the diagnosis and prognosis of cancer patients. Nuclear size can significantly impact cell migration due to its incredibly large size. Nuclear structural changes are predicted to regulate cancer cell migration. Nuclear abnormalities are common across a vast spectrum of cancer types, regardless of tissue source, mutational spectrum, and signaling dependencies. The pervasiveness of nuclear alterations suggests that changes in nuclear structure may be crucially linked to the transformation process. The factors driving these nuclear abnormalities, and the functional consequences, are not completely understood. Nuclear envelope proteins play an important role in regulating nuclear size and structure in cancer. Altered expression of nuclear lamina proteins, including emerin, is found in many cancers and this expression is correlated with better clinical outcomes. A model is emerging whereby emerin, as well as other nuclear lamina proteins, binding to the nucleoskeleton regulates the nuclear structure to impact metastasis. In this model, emerin and lamins play a central role in metastatic transformation, since decreased emerin expression during transformation causes the nuclear structural defects required for increased cell migration, intravasation, and extravasation. Herein, we discuss the cellular functions of nuclear lamina proteins, with a particular focus on emerin, and how these functions impact cancer progression and metastasis.

Tpr Deficiency Disrupts Erythroid Maturation With Impaired Chromatin Condensation in Zebrafish Embryogenesis

Vertebrate erythropoiesis involves nuclear and chromatin condensation at the early stages of terminal differentiation, which is a unique process to distinguish mature erythrocytes from erythroblasts. However, the underlying mechanisms of chromatin condensation during erythrocyte maturation remain elusive. Here, we reported a novel zebrafish mutant cas7 with erythroid maturation deficiency. Positional cloning showed that a single base mutation in tprb gene, which encodes nucleoporin translocated promoter region (Tpr), is responsible for the disrupted erythroid maturation and upregulation of erythroid genes, including ae1-globin and be1-globin. Further investigation revealed that deficient erythropoiesis in tprb cas7 mutant was independent on HIF signaling pathway. The proportion of euchromatin was significantly increased, whereas the percentage of heterochromatin was markedly decreased in tprb cas7 mutant. In addition, TPR knockdown in human K562 cells also disrupted erythroid differentiation and dramatically elevated the expression of globin genes, which suggests that the functions of TPR in erythropoiesis are highly conserved in vertebrates. Taken together, this study revealed that Tpr played vital roles in chromatin condensation and gene regulation during erythroid maturation in vertebrates.

Post-Translational Modification and Subcellular Compartmentalization: Emerging Concepts on the Regulation and Physiopathological Relevance of RhoGTPases

Cells and tissues are continuously exposed to both chemical and physical stimuli and dynamically adapt and respond to this variety of external cues to ensure cellular homeostasis, regulated development and tissue-specific differentiation. Alterations of these pathways promote disease progression-a prominent example being cancer. Rho GTPases are key regulators of the remodeling of cytoskeleton and cell membranes and their coordination and integration with different biological processes, including cell polarization and motility, as well as other signaling networks such as growth signaling and proliferation. Apart from the control of GTP-GDP cycling, Rho GTPase activity is spatially and temporally regulated by post-translation modifications (PTMs) and their assembly onto specific protein complexes, which determine their controlled activity at distinct cellular compartments. Although Rho GTPases were traditionally conceived as targeted from the cytosol to the plasma membrane to exert their activity, recent research demonstrates that active pools of different Rho GTPases also localize to endomembranes and the nucleus. In this review, we discuss how PTM-driven modulation of Rho GTPases provides a versatile mechanism for their compartmentalization and functional regulation. Understanding how the subcellular sorting of active small GTPase pools occurs and what its functional significance is could reveal novel therapeutic opportunities.

Crosstalk between nucleocytoplasmic trafficking and the innate immune response to viral infection

The nuclear pore complex is the sole gateway connecting the nucleoplasm and cytoplasm. In humans, the nuclear pore complex is one of the largest multiprotein assemblies in the cell, with a molecular mass of ∼110 MDa and consisting of 8 to 64 copies of about 34 different nuclear pore proteins, termed nucleoporins, for a total of 1000 subunits per pore. Trafficking events across the nuclear pore are mediated by nuclear transport receptors and are highly regulated. The nuclear pore complex is also used by several RNA viruses and almost all DNA viruses to access the host cell nucleoplasm for replication. Viruses hijack the nuclear pore complex, and nuclear transport receptors, to access the nucleoplasm where they replicate. In addition, the nuclear pore complex is used by the cell innate immune system, a network of signal transduction pathways that coordinates the first response to foreign invaders, including viruses and other pathogens. Several branches of this response depend on dynamic signaling events that involve the nuclear translocation of downstream signal transducers. Mounting evidence has shown that these signaling cascades, especially those steps that involve nucleocytoplasmic trafficking events, are targeted by viruses so that they can evade the innate immune system. This review summarizes how nuclear pore proteins and nuclear transport receptors contribute to the innate immune response and highlights how viruses manipulate this cellular machinery to favor infection. A comprehensive understanding of nuclear pore proteins in antiviral innate immunity will likely contribute to the development of new antiviral therapeutic strategies.

Proteomic Analysis of Generative and Vegetative Nuclei Reveals Molecular Characteristics of Pollen Cell Differentiation in Lily

In plants, the cell fates of a vegetative cell (VC) and generative cell (GC) are determined after the asymmetric division of the haploid microspore. The VC exits the cell cycle and grows a pollen tube, while the GC undergoes further mitosis to produce two sperm cells for double fertilization. However, our understanding of the mechanisms underlying their fate differentiation remains limited. One major advantage of the nuclear proteome analysis is that it is the only method currently able to uncover the systemic differences between VC and GC due to GC being engulfed within the cytoplasm of VC, limiting the use of transcriptome. Here, we obtained pure preparations of the vegetative cell nuclei (VNs) and generative cell nuclei (GNs) from germinating lily pollens. Utilizing these high-purity VNs and GNs, we compared the differential nucleoproteins between them using state-of-the-art quantitative proteomic techniques. We identified 720 different amount proteins (DAPs) and grouped the results in 11 fate differentiation categories. Among them, we identified 29 transcription factors (TFs) and 10 cell fate determinants. Significant differences were found in the molecular activities of vegetative and reproductive nuclei. The TFs in VN mainly participate in pollen tube development. In comparison, the TFs in GN are mainly involved in cell differentiation and male gametogenesis. The identified novel TFs may play an important role in cell fate differentiation. Our data also indicate differences in nuclear pore complexes and epigenetic modifications: more nucleoporins synthesized in VN; more histone variants and chaperones; and structural maintenance of chromosome (SMC) proteins, chromatin remodelers, and DNA methylation-related proteins expressed in GN. The VC has active macromolecular metabolism and mRNA processing, while GC has active nucleic acid metabolism and translation. Moreover, the members of unfolded protein response (UPR) and programmed cell death accumulate in VN, and DNA damage repair is active in GN. Differences in the stress response of DAPs in VN vs. GN were also found. This study provides a further understanding of pollen cell differentiation mechanisms and also a sound basis for future studies of the molecular mechanisms behind cell fate differentiation.

Application of SNAP-Tag in Expansion Super-Resolution Microscopy Using DNA Oligostrands

Expansion super-resolution technology is a new technology developed in recent years. It anchors the dye on the hydrogel and the dye expands with the expansion of the hydrogel so that a super-resolution map can be obtained under an ordinary microscope. However, by labeling the target protein with a first antibody and secondary antibody, the distance between the fluorescent group and the actual target protein is greatly increased. Although fluorescent proteins can also be used for expansion super-resolution to reduce this effect, the fluorescent protein is often destroyed during sample preparation. To solve this problem, we developed a novel label system for expansion microscopy, based on a DNA oligostrand linked with a fluorescent dye, acrylamide group (linker), and benzoylguanine (BG, a small substrate molecule for SNAP-tag). This protocol greatly reduced the error between the position of fluorescent group and the actual target protein, and also reduced loss of the fluorescent group during sample preparation.

Functional requirement of the Arabidopsis importin-α nuclear transport receptor family in autoimmunity mediated by the NLR protein SNC1

IMPORTIN-α3/MOS6 (MODIFIER OF SNC1, 6) is one of nine importin-α isoforms in Arabidopsis that recruit nuclear localization signal-containing cargo proteins to the nuclear import machinery. IMP-α3/MOS6 is required genetically for full autoimmunity of the nucleotide-binding leucine-rich repeat immune receptor mutant snc1 (suppressor of npr1-1, constitutive 1) and MOS6 also contributes to basal disease resistance. Here, we investigated the contribution of the other importin-α genes to both types of immune responses, and we analyzed potential interactions of all importin-α isoforms with SNC1. By using reverse-genetic analyses in Arabidopsis and protein-protein interaction assays in Nicotiana benthamiana, we provide evidence that among the nine α-importins in Arabidopsis, IMP-α3/MOS6 is the main nuclear transport receptor of SNC1, and that IMP-α3/MOS6 is required selectively for autoimmunity of snc1 and basal resistance to mildly virulent Pseudomonas syringae in Arabidopsis.

Regulation and Physiological Significance of the Nuclear Shape in Plants

The shape of plant nuclei varies among different species, tissues, and cell types. In Arabidopsis thaliana seedlings, nuclei in meristems and guard cells are nearly spherical, whereas those of epidermal cells in differentiated tissues are elongated spindle-shaped. The vegetative nuclei in pollen grains are irregularly shaped in angiosperms. In the past few decades, it has been revealed that several nuclear envelope (NE) proteins play the main role in the regulation of the nuclear shape in plants. Some plant NE proteins that regulate nuclear shape are also involved in nuclear or cellular functions, such as nuclear migration, maintenance of chromatin structure, gene expression, calcium and reactive oxygen species signaling, plant growth, reproduction, and plant immunity. The shape of the nucleus has been assessed both by labeling internal components (for instance chromatin) and by labeling membranes, including the NE or endoplasmic reticulum in interphase cells and viral-infected cells of plants. Changes in NE are correlated with the formation of invaginations of the NE, collectively called the nucleoplasmic reticulum. In this review, what is known and what is unknown about nuclear shape determination are presented, and the physiological significance of the control of the nuclear shape in plants is discussed.

The cellular environment shapes the nuclear pore complex architecture

Nuclear pore complexes (NPCs) create large conduits for cargo transport between the nucleus and cytoplasm across the nuclear envelope (NE)^1-3. These multi-megadalton structures are composed of about thirty different nucleoporins that are distributed in three main substructures (the inner, cytoplasmic and nucleoplasmic rings) around the central transport channel^4-6. Here we use cryo-electron tomography on DLD-1 cells that were prepared using cryo-focused-ion-beam milling to generate a structural model for the human NPC in its native environment. We show that-compared with previous human NPC models obtained from purified NEs-the inner ring in our model is substantially wider; the volume of the central channel is increased by 75% and the nucleoplasmic and cytoplasmic rings are reorganized. Moreover, the NPC membrane exhibits asymmetry around the inner-ring complex. Using targeted degradation of Nup96, a scaffold nucleoporin of the cytoplasmic and nucleoplasmic rings, we observe the interdependence of each ring in modulating the central channel and maintaining membrane asymmetry. Our findings highlight the inherent flexibility of the NPC and suggest that the cellular environment has a considerable influence on NPC dimensions and architecture.

The hippo kinase STK38 ensures functionality of XPO1

The proper segregation of basic elements such as the compartmentalization of the genome and the shuttling of macromolecules between the nucleus and the cytoplasm is a crucial mechanism for homeostasis maintenance in eukaryotic cells. XPO1 (Exportin 1) is the major nuclear export receptor and is required for the export of proteins and RNAs out of the nucleus. STK38 (also known as NDR1) is a Hippo pathway serine/threonine kinase with multifarious functions in normal and cancer cells. In this review, we summarize the history of the discovery of the nucleo/cytoplasmic shuttling of proteins and focus on the major actor of nuclear export: XPO1. After describing the molecular events required for XPO1-mediated nuclear export of proteins, we introduce the Hippo pathway STK38 kinase, synthetize its regulation mechanisms as well as its biological functions in both normal and cancer cells, and finally its intersection with XPO1 biology. We discuss the recently identified mechanism of XPO1 activation by phosphorylation of XPO1_S1055 by STK38 and contextualize this finding according to the biological functions previously reported for both XPO1 and STK38, including the second identity of STK38 as an autophagy regulator. Finally, we phrase this newly identified activation mechanism into the general nuclear export machinery and examine the possible outcomes of nuclear export inhibition in cancer treatment.

Self-reactive antibodies associated with bronchiolitis obliterans syndrome subtype of chronic lung allograft dysfunction

BACKGROUND

Chronic Lung Allograft Dysfunction (CLAD) remains the major limitation in long term survival after lung transplantation. Our objective is to evaluate for the presence of autoantibodies to self-antigens, which is a pathway along with complex interplay with immune as well as non-immune mechanisms that leads to a fibroproliferative process resulting in CLAD.

METHODS

Serum profiles of IgG autoantibodies were evaluated using customized proteomic microarray with 124 antigens. Output from microarray analyzed as antibody scores is correlated with bronchiolitis obliterans (BOS) subtype of CLAD using Mann-Whitney U test or Fisher exact test. Autoantibodies were evaluated for their predictive value for progressive BOS using a Cox proportional hazard model. BOS free survival and overall survival was analyzed using Kaplan-Meier survival analysis.

RESULTS

Forty- two patients included in the study are grouped into "stable BOS" and "progressive BOS" for comparisons. Pulmonary fibrosis is the major indication for lung transplantation in our cohort. Progressive BOS group had significantly worse survival (p < 0.005). Sixteen IgG autoantibodies are significantly elevated at baseline in progressive BOS group. Six among them correlated with worse BOS free survival (p < 0.05). In addition, these six IgG autoantibodies remain elevated at three months and one year after lung transplantation.

CONCLUSION

Pre-existing IgG autoantibodies correlate with progressive BOS and survival in a single center, small cohort of lung transplant recipients. Further validation with larger sample size, external cohort and confirmation with additional tissue, bronchoalveolar lavage samples are necessary to confirm the preliminary findings in our study.

Transient Destabilization of Biological Membranes Contributes to the Superior Performance of Star-Shaped PDMAEMA in Delivering pDNA

Nonviral DNA vectors are promising alternatives to viral ones. Their use in DNA medicine is limited by an inability to transfect, for example, nondividing or suspension cells. In recent years, star-shaped synthetic polycationic vectors, so called "Nanostars", have shown some promise in this regard, at least when compared to the "gold standard" in nonviral vectors, namely, linear poly(ethyleneimine) (l-PEI). It has been hypothesized that an ability to transiently destabilize cellular membranes is partially responsible for the phenomenon. This hypothesis is investigated here, taking human leukemia suspension cells (Jurkat cells) as an example. Contrary to l-PEI, the Nanostars promote the cellular uptake of small, normally membrane-impermeant molecules (trypan blue and propidium iodide) as well as that of fluorescent polystyrene beads (average diameter 100 nm). Since Nanostars, but not l-PEI, are apparently able to deliver DNA to nuclei of nondividing cells, nuclear uptake is, in addition, investigated with isolated cell nuclei. Our results provide evidence that Nanostars are more efficient than l-PEI in increasing the nuclear membrane association/permeability, allowing accumulation of their cargo on/in the nucleus.

A Method to Quantify Molecular Diffusion within Thin Solvated Polymer Films: A Case Study on Films of Natively Unfolded Nucleoporins

We present a method to probe molecular and nanoparticle diffusion within thin, solvated polymer coatings. The device exploits the confinement with well-defined geometry that forms at the interface between a planar and a hemispherical surface (of which at least one is coated with polymers) in close contact and uses this confinement to analyze diffusion processes without interference of exchange with and diffusion in the bulk solution. With this method, which we call plane-sphere confinement microscopy (PSCM), information regarding the partitioning of molecules between the polymer coating and the bulk liquid is also obtained. Thanks to the shape of the confined geometry, diffusion and partitioning can be mapped as a function of compression and concentration of the coating in a single experiment. The method is versatile and can be integrated with conventional optical microscopes; thus it should find widespread use in the many application areas exploiting functional polymer coatings. We demonstrate the use of PSCM using brushes of natively unfolded nucleoporin domains rich in phenylalanine-glycine repeats (FG domains). A meshwork of FG domains is known to be responsible for the selective transport of nuclear transport receptors (NTRs) and their macromolecular cargos across the nuclear envelope that separates the cytosol and the nucleus of living cells. We find that the selectivity of NTR uptake by FG domain films depends sensitively on FG domain concentration and that the interaction of NTRs with FG domains obstructs NTR movement only moderately. These observations contribute important information to better understand the mechanisms of selective NTR transport.

Spatial control of nucleoporin condensation by fragile X-related proteins

Nucleoporins (Nups) build highly organized nuclear pore complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve‐like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here, we show that fragile X‐related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule‐dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granule‐containing cells show defects in protein export, nuclear morphology and cell cycle progression. Our results reveal an unexpected role for the FXR protein family in the spatial regulation of nucleoporin condensation.

Nuclear pore complex-mediated gene expression in Arabidopsis thaliana

Nuclear pore complexes (NPCs) are large multi-protein complexes that control bidirectional trafficking of macromolecules between the nucleus and cytoplasm. This trafficking is highly regulated and participates in a considerably broader range of cellular activities, including defense responses against pathogens in plants. Recently, NPC is emerging as a platform to physically associate the underlying chromatin with the nuclear periphery, thus regulating chromatin structure and gene expression. For instance, NPC components have been shown to promote the formation of specific genomics loops, which is linked to transcriptional memory for rapid reactivation of genes. With newly developed techniques and tools, our insight in this area has been substantially advanced. This review summarizes recent works on the molecular function of NPC machinery as hubs for transcriptional regulation and compares systems between plant and non-plant organisms.