bims-nucpor 2023-10-08 papers

Issue of 2023–10–08
nine papers selected by
Sara Mingu, Johannes Gutenberg University

FEBS Lett. 2023 Oct 03.

Evolutionary, structural and functional insights in nuclear organisation and nucleocytoplasmic transport in trypanosomes.

Norma E Padilla-Mejia, Mark C Field.

One of the remarkable features of eukaryotes is the nucleus, delimited by the nuclear envelope, a complex structure and home to the nuclear lamina and nuclear pore complex (NPC). For decades these structures were believed to be mainly architectural elements and, in the case of the NPC, simply facilitating nucleocytoplasmic trafficking. More recently the critical roles of the lamina, NPC and other nuclear envelope constituents in genome organisation, maintaining chromosomal domains and regulating gene expression have been recognised. Importantly, mutations in genes encoding lamina and NPC components lead to pathogenesis in humans, while in pathogenic protozoa disrupt the progression of normal development and expression of pathogenesis-related genes. Here we review features of the lamina and NPC across eukaryotes and discuss how these elements are structured in trypanosomes, protozoa of high medical and veterinary importance, highlighting lineage-specific and conserved aspects of nuclear organisation.

Keywords: evolutionary diversity; nuclear lamina; nuclear pore complex; nucleus; trypanosoma

DOI: https://doi.org/10.1002/1873-3468.14747

FEBS Lett. 2023 Sep 30.

The magnified view: from ancient trinkets to single nuclear pore complexes.

Boris Fichtman, Amnon Harel.

A journey from the earliest known use of lenses and magnifying glasses in ancient times, through the development of microscopes and towards modern electron microscopy techniques. The evolving technology and improved microscopes enabled the discovery of intracellular organelles, the nucleus and nuclear pore complexes (NPCs). Current advances have led to composite three-dimensional models showing NPC structure in unprecedented detail but relying on the averaging of many images. A complementary approach is field emission scanning electron microscopy providing topographic surface images that are easily and intuitively interpreted by our brain. Recent advances in this technique have made it possible to expose nuclei from human cells and to focus on individual NPCs and their architectural features.

Keywords: RanBP2/NUP358; ancient lenses; auxin-induced degron; magnifying glasses; nuclear pore complex; scanning electron microscopy

DOI: https://doi.org/10.1002/1873-3468.14746

FEBS Lett. 2023 Oct 05.

RANBP2 Evolution and Human Disease.

Sophie Desgraupes, Lucie Etienne, Nathalie J Arhel.

RANBP2/Nup358 (Ran Binding Protein 2) is a nucleoporin and a key component of the nuclear pore complex. Through its multiple functions (e.g. SUMOylation, regulation of nucleocytoplasmic transport) and subcellular localizations (e.g. at the nuclear envelope, kinetochores, annulate lamellae), it is involved in many cellular processes. RANBP2 dysregulation or mutation leads to the development of human pathologies, such as Acute Necrotizing Encephalopathy 1 (ANE1), cancer, neurodegenerative diseases and it is also involved in viral infections. The chromosomal region containing the RANBP2 gene is highly dynamic, with high structural variation and recombination events that led to the appearance of a gene family called RGPD (RANBP2 and GCC2 Protein Domains), with multiple gene loss/duplication events during ape evolution. Although RGPD homoplasy and maintenance during evolution suggest they might confer an advantage to their hosts, their functions are still unknown and understudied. In this review, we discuss the appearance and importance of RANBP2 in metazoans and its function-related pathologies, caused by an alteration of its expression levels (through promotor activity, post-transcriptional or post-translational modifications), its localization or genetic mutations.

Keywords: ANE1; NPC; RANBP2; RGPD; disease; evolution; nucleocytoplasmic transport

DOI: https://doi.org/10.1002/1873-3468.14749

New Phytol. 2023 Oct 02.

NUA positively regulates plant immunity by coordination with ESD4 to deSUMOylate TPR1 in Arabidopsis.

Bao Xie, Mingyu Luo, Qiuyi Li, Jing Shao, Desheng Chen, David E Somers, Dingzhong Tang, Hua Shi.

Nuclear pore complex (NPC) is composed of multiple nucleoporins (Nups). A plethora of studies have highlighted the significance of NPC in plant immunity. However, the specific roles of individual Nups are poorly understood. NUCLEAR PORE ANCHOR (NUA) is a component of NPC. Loss of NUA leads to an increase in SUMO conjugates and pleiotropic developmental defects in Arabidopsis thaliana. Herein, we revealed that NUA is required for plant defense against multiple pathogens. NUCLEAR PORE ANCHOR associates with the transcriptional corepressor TOPLESS-RELATED1 (TPR1) and contributes to TPR1 deSUMOylation. Significantly, NUA-interacting protein EARLY IN SHORT DAYS 4 (ESD4), a SUMO protease, specifically deSUMOylates TPR1. It has been previously established that the SUMO E3 ligase SAP AND MIZ1 DOMAIN-CONTAINING LIGASE 1 (SIZ1)-mediated SUMOylation of TPR1 represses the immune-related function of TPR1. Consistent with this notion, the hyper-SUMOylated TPR1 in nua-3 leads to upregulated expression of TPR1 target genes and compromised TPR1-mediated disease resistance. Taken together, our work uncovers a mechanism by which NUA positively regulates plant defense responses by coordination with ESD4 to deSUMOylate TPR1. Our findings, together with previous studies, reveal a regulatory module in which SIZ1 and NUA/ESD4 control the homeostasis of TPR1 SUMOylation to maintain proper immune output.

Keywords: Arabidopsis; ESD4; NUA; TPR1; deSUMOylation; nuclear pore complex; plant immunity

DOI: https://doi.org/10.1111/nph.19287

Anal Chem. 2023 Oct 02.

Mapping the Direction of Nucleocytoplasmic Transport of Glucocorticoid Receptor (GR) in Live Cells Using Two-Foci Cross-Correlation in Massively Parallel Fluorescence Correlation Spectroscopy (mpFCS).

Stanko N Nikolić, Sho Oasa, Aleksandar J Krmpot, Lars Terenius, Milivoj R Belić, Rudolf Rigler, Vladana Vukojević.

Nucleocytoplasmic transport of transcription factors is vital for normal cellular function, and its breakdown is a major contributing factor in many diseases. The glucocorticoid receptor (GR) is an evolutionarily conserved, ligand-dependent transcription factor that regulates homeostasis and response to stress and is an important target for therapeutics in inflammation and cancer. In unstimulated cells, the GR resides in the cytoplasm bound to other molecules in a large multiprotein complex. Upon stimulation with endogenous or synthetic ligands, GR translocation to the cell nucleus occurs, where the GR regulates the transcription of numerous genes by direct binding to glucocorticoid response elements or by physically associating with other transcription factors. While much is known about molecular mechanisms underlying GR function, the spatial organization of directionality of GR nucleocytoplasmic transport remains less well characterized, and it is not well understood how the bidirectional nucleocytoplasmic flow of GR is coordinated in stimulated cells. Here, we use two-foci cross-correlation in a massively parallel fluorescence correlation spectroscopy (mpFCS) system to map in live cells the directionality of GR translocation at different positions along the nuclear envelope. We show theoretically and experimentally that cross-correlation of signals from two nearby observation volume elements (OVEs) in an mpFCS setup presents a sharp peak when the OVEs are positioned along the trajectory of molecular motion and that the time position of the peak corresponds to the average time of flight of the molecule between the two OVEs. Hence, the direction and velocity of nucleocytoplasmic transport can be determined simultaneously at several locations along the nuclear envelope. We reveal that under ligand-induced GR translocation, nucleocytoplasmic import/export of GR proceeds simultaneously but at different locations in the cell nucleus. Our data show that mpFCS can characterize in detail the heterogeneity of directional nucleocytoplasmic transport in a live cell and may be invaluable for studies aiming to understand how the bidirectional flow of macromolecules through the nuclear pore complex (NPC) is coordinated to avoid intranuclear transcription factor accretion/abatement.

DOI: https://doi.org/10.1021/acs.analchem.3c01427

Nat Cell Biol. 2023 Oct 02.

An ESCRT grommet cooperates with a diffusion barrier to maintain nuclear integrity.

Nicholas R Ader, Linda Chen, Ivan V Surovtsev, William L Chadwick, Elisa C Rodriguez, Megan C King, C Patrick Lusk.

The molecular mechanisms by which the endosomal sorting complexes required for transport (ESCRT) proteins contribute to the integrity of the nuclear envelope (NE) barrier are not fully defined. We leveraged the single NE hole generated by mitotic extrusion of the Schizosaccharomyces pombe spindle pole body to reveal two modes of ESCRT function executed by distinct complements of ESCRT-III proteins, both dependent on CHMP7/Cmp7. A grommet-like function is required to restrict the NE hole in anaphase B, whereas replacement of Cmp7 by a sealing module ultimately closes the NE in interphase. Without Cmp7, nucleocytoplasmic compartmentalization remains intact despite NE discontinuities of up to 540 nm, suggesting mechanisms to limit diffusion through these holes. We implicate spindle pole body proteins as key components of a diffusion barrier acting with Cmp7 in anaphase B. Thus, NE remodelling mechanisms cooperate with proteinaceous diffusion barriers beyond nuclear pore complexes to maintain the nuclear compartment.

DOI: https://doi.org/10.1038/s41556-023-01235-4