Biology subjects

Hossain, M. J.

Publications and source records attributed to Hossain, M. J..

17 recordsLinked to original sources

bioRxiv2026

Dosage-dependent disruption of corticofugal neuron development by Fezf2 loss

Background. Fezf2 (Forebrain Embryonic Zinc Finger 2) is a dosage-sensitive transcription factor required for the specification of corticofugal projection neurons, and rare predicted-deleterious Fezf2 variants are associated with human neurodevelopmental disorders. The cell-type-specific and temporal manner in which Fezf2 dosage shapes cortical development remains incompletely resolved at single-cell resolution. This study aims to quantify the temporal and cell-type-specific transcriptional response to progressive Fezf2 loss by re-analyzing a public single-cell atlas of mouse cortical development. Methods. We re-analyzed 20 single-cell RNA-seq samples spanning embryonic day (E) 10 to postnatal day (P) 4 across wild-type (WT), Fezf2-heterozygous (Het), and Fezf2-knockout (KO) genotypes, together with 3 wild-type single-cell ATAC-seq samples, from Di Bella et al. (2021) (GSE153164). After quality control, consensus doublet removal, and batch integration with two complementary methods (Harmony and scVI), we annotated cell types and quantified genotype effects. Because the source design includes a single library per genotype at most stages, we report effect sizes with bootstrap 95% confidence intervals and calibrate candidate dysregulation against a biological-noise null estimated from the two WT replicates at P1, rather than reporting formal inferential p-values. Results. We recovered 121,889 high-quality cells and 20,982 genes, resolving 17 transcriptionally distinct cell types. The most prominent genotype effect was a dosage-dependent depletion of subcerebral projection neurons (SCPNs) at P1 - the only timepoint at which all three genotypes were sampled: SCPNs comprised 2.21% of WT cells (mean of two replicates) but 0.18% of Het and 0.15% of KO cells, an approximately 13 -15-fold reduction. Using the WT-replicate null (99th percentile |log2 fold-change| = 0.34), we identified 947, 1,119, and 838 genes exceeding this threshold in Maturing, Corticothalamic, and Callosal projection neurons, respectively. Genes downregulated in KO projection neurons were convergently enriched for cytoplasmic translation and ribosome biogenesis (adjusted P {approx} 8.8*10^-30; in Corticothalamic Neurons). Regulon-activity analysis nominated Six4, Atf5, and Myt1 as increased and Hdac7, Rest, and Kdm5a as decreased in KO cells. Conclusions. Progressive Fezf2 loss is associated with a dosage-dependent, cell-type-specific disruption of cortical development, most notably near-elimination of the SCPN compartment by birth and a convergent downregulation of translational/maturation-associated genes across projection neurons. These associations nominate candidate downstream programs for experimental follow-up; they do not by themselves establish a mechanism.

neuroscience↗

bioRxiv2026

HIV-1 can undergo Env-independent retrotransposon-like activity

Retrovirus replication requires coordinated interplay between viral proteins and host cellular machinery, including reverse transcription of the viral RNA genome into DNA and its subsequent integration into the host genomes. SOX2-dependent retrotransposon dynamics have been reported for endogenous retrovirus HERV-K; however, whether a similar intracellular pathway exists for exogenous retroviruses remains unclear. To address whether infection-independent intracellular reverse transcription and partial integration can occur, that is, whether retrovirus can exhibit retrotransposon-like activity, we utilized HeLa and 293T cells, which express no HIV-1 entry receptors. We engineered an Env-deficient HIV-1 NL4-3-based reporter encoding a reverse-oriented, intron-disrupted nanoluciferase cassette that becomes expressible only after splicing followed by reverse transcription. We found that reporter activation depends on reverse transcriptase and protease activities. While integrase is dispensable for early expression, it is essential for long-term maintenance of the nanoluciferase signal. Integration site mapping using next-generation sequencing further confirmed that stable reporter activity requires integrase-dependent proviral insertion. Functional analysis of Gag revealed that membrane binding, multimerization, and budding are prerequisite steps for reporter activation. Concentrated virus preparations from culture supernatants failed to activate the reporter in 293T cells, ruling out a role for reinfection. Electron and confocal microscopy suggested that Gag or viral particles traffic through endosomal compartments. Furthermore, inhibition of dynamin- and clathrin-dependent endocytic pathways reduced reporter activity, indicating that these pathways contribute to efficient reporter activity. Collectively, these finding support the conclusion that HIV-1 can undergo intracellular reverse transcription and partial integration in an infection-independent manner, prompting a reconsideration of the boundary between exogenous retroviruses and endogenous retroelements. Author summaryEnv-independent, infection-independent intracellular reverse transcription and integration in HIV-1 may contribute to integration-site diversity within the same cell. More broadly, this phenomenon suggests continuity between the retroviral life cycle and retrotransposition dynamics, therefore informing our understanding of host-virus coevolution, mechanisms of long-term persistence, and the redesign of therapeutic strategies targeting pre-integration steps.

microbiology↗

bioRxiv2025

Hydrophobic interactions of FG-nucleoporins are required for dilating nuclear membrane pores into selective transport channels after mitosis

Nuclear envelope (NE) reformation after mitosis is essential for daughter cell viability and requires tightly coordinated nuclear pore complex (NPC) assembly and nuclear membrane reformation. To reveal how these processes are mechanistically linked, we combined acute molecule perturbations in live cells with correlative 3D electron tomography or MINFLUX super-resolution microscopy. We show that degrading Nup62 during mitosis arrests NPC assembly at an intermediate step with smaller membrane pores and removes the whole central transport channel. Molecular dynamics simulations predicted that 32 copies of the central channel subcomplex, recruited into the previously unoccupied pore center, can self-associate via hydrophobic interactions to occupy the volume required for full pore size and exert an outward pushing force; indeed, disrupting these interactions during NPC assembly blocked pore dilation. Later in mitotic exit, perturbed cells exhibited impaired nuclear import, smaller nuclei, and looser NE spacing. Acute inhibition of nuclear import recapitulated these NE defects without affecting NPC assembly. Together, our findings reveal a new, two-step molecular mechanism linking NPC assembly and NE reformation. First, hydrophobic FG-nucleoporins dilate the assembling nuclear pore to its full width by forming the central transport channel, which then allows nuclear import-driven nuclear expansion leading to tight, regular NE membrane spacing.

cell biology↗

bioRxiv2025

Lenacapavir binding to immature Gag triggers the emergence of giant HIV-1 virions

Lenacapavir (LEN), a potent capsid inhibitor, suppresses reverse transcription and nuclear import by disrupting capsid core formation in human immunodeficiency virus type 1 (HIV-1). However, its effect on the late-stage viral assembly remains unclear. Although p24 ELISA suggested that LEN inhibited HIV-1, both RT-dPCR and Vpr-HiBiT assays indicated no reduction in the viral output. This discrepancy was attributed to LEN-induced epitope masking of p24, which was reversed by altered sample processing. Furthermore, LEN induced numerous abnormal, discrete clusters of Gag at the plasma membrane. Mass photometry and transmission electron microscopy revealed heterogeneous viral-like particles (LENiVLPs; diameter >200 nm), containing both Gag and Env proteins. Although LENiVLPs retained membrane fusion capability, they were non-infectious owing to post-entry defects. Thus, LEN binds to the precursor Gag and promotes aberrant particle formation, offering novel insights that could guide the development of next-generation LEN-based therapeutics targeting the late stages of the viral life cycle.

microbiology↗

bioRxiv2025

Local trade-offs shape flower size evolution across Arabidopsis thaliana distribution.

The diversification of flowers, largely driven by mutualistic interactions with animal pollinators, has generated remarkable variation in floral form and size and is thought to have driven the evolutionary radiation of angiosperms. Here, we investigate the geographic variation in reproductive organ growth in the self-fertilizing species Arabidopsis thaliana, where the loss of pollinator dependence is predicted to favour reduced floral investment through resource reallocation. We find extensive variation in flower size underpinned by a polygenic architecture, in which derived alleles both increase and decrease petal size and show signatures of positive selection. Nevertheless, the evolutionary direction of flower size differs across regions, reflecting environmentally mediated shifts in the relationship between flower size and seed production. Strong purifying selection at the climatic margins favours smaller flowers, whereas relaxed environmental constraints in more suitable habitats allow the emergence and persistence of both small and large-flower variants. This biogeographic pattern extends to other life-history traits, highlighting how environmental heterogeneity and resource allocation constraints shape evolutionary trajectories and maintain phenotypic diversity in selfing lineages.

evolutionary biology↗

bioRxiv2024

Quantitative imaging of loop extruders rebuilding interphase genome architecture after mitosis

How cells establish the interphase genome organization after mitosis is incompletely understood. Using quantitative and super-resolution microscopy, we show that the transition from a Condensin to a Cohesin-based genome organization occurs dynamically over two hours. While a significant fraction of Condensins remains chromatin-bound until early Gl, Cohesin-STAGl and its boundary factor CTCF are rapidly imported into daughter nuclei in telophase, immediately bind chromosomes as individual complexes and are sufficient to build the first interphase TAD structures. By contrast, the more abundant Cohesin-STAG2 accumulates on chromosomes only gradually later in Gl, is responsible for compaction inside TAD structures and forms paired complexes upon completed nuclear import. 0ur quantitative time-resolved mapping of mitotic and interphase loop extruders in single cells reveals that the nested loop architecture formed by sequential action of two Condensins in mitosis is seamlessly replaced by a less compact, but conceptually similar hierarchically nested loop architecture driven by sequential action of two Cohesins.

cell biology↗

bioRxiv2024

A heterocyclic compound inhibits viral release by inducing cell surface BST2/Tetherin/CD317/HM1.24

The introduction of combined antiretroviral therapy (cART) has greatly improved the quality of life of human immunodeficiency virus type 1 (HIV-1)-infected individuals. Nonetheless, the ever-present desire to seek out a full remedy for HIV-1 infections makes the discovery of novel antiviral medication compelling. Owing to this, a new late-stage inhibitor, Lenacapavir/Sunlenca, an HIV multi-phase suppressor, was clinically authorized in 2022. Besides unveiling cutting-edge antivirals inhibiting late-stage proteins or processes, newer therapeutics targeting host restriction factors hold promise for the curative care of HIV-1 infections. Notwithstanding, bone marrow stromal antigen 2 (BST2)/Tetherin/CD317/HM1.24, which entraps progeny virions is an appealing HIV-1 therapeutic candidate. In this study, a novel drug screening system was established, using the Jurkat/Vpr-HiBiT T cells, to identify drugs that could obstruct HIV-1 release; the candidate compounds were selected from the Ono Pharmaceutical compound library. Jurkat T cells expressing Vpr-HiBiT were infected with NL4-3, and the amount of virus release was quantified indirectly by the amount of Vpr-HiBiT incorporated into the progeny virions. Subsequently, the candidate compounds that suppressed viral release were used to synthesize the heterocyclic compound, HT-7, which reduces HIV-1 release with less cellular toxicity. Notably, HT-7 increased cell surface BST2 coupled with HIV-1 release reduction in Jurkat cells but not Jurkat/KO-BST2 cells. Seemingly, HT-7 impeded simian immunodeficiency virus (SIV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) release. Concisely, these results suggest that the reduction in viral release, following HT-7 treatment, resulted from the modulation of cell surface expression of BST2 by HT-7. ImportanceA collection of scientific strategies has been revealed to find long-term cure for HIV-1 infection. One of these techniques, the therapeutic approach, involves harnessing late events that are not targeted by current medication. The regulator of HIV-1 assembly and release, the HIV-1 Gag protein, has emerged as a prospective inhibitor. We set up a high-efficiency, economically viable, and facile screening system for the identification of late-stage inhibitors. Herein, we discovered a heterocyclic compound that inhibits HIV-1 release. This newly high- performance testing technique can be employed in virological research for investigating HIV- 1 late-stage processes.

microbiology↗

bioRxiv2021

A quantitative map of nuclear pore assembly reveals two distinct mechanisms

Understanding how the nuclear pore complex (NPC) assembles is of fundamental importance to grasp the mechanisms behind its essential function and understand its role during evolution of eukaryotes1-4. While at least two NPC assembly pathways exist, one during exit from mitosis and one during nuclear growth in interphase, we currently lack a quantitative map of the molecular assembly events. Here, we use fluorescence correlation spectroscopy (FCS) calibrated live imaging of endogenously fluorescently-tagged nucleoporins to map the changes in composition and stoichiometry of seven major modules of the human NPC during its assembly in single dividing cells. This systematic quantitative map reveals that the two assembly pathways employ strikingly different molecular mechanisms, inverting the order of addition of two large structural components, the central ring complex and nuclear filaments. The dynamic stoichiometry data underpinned integrative spatiotemporal modeling of the NPC assembly pathway, predicting the structures of postmitotic NPC assembly intermediates.

cell biology↗

bioRxiv2021

Comparative genomic analysis and characterization of Staphylococcus sp. AOAB, isolated from a notoriously invasive Mnemiopsis leidyi gut revealed multiple antibiotic resistance determinants

Here, we describe the isolation and characterization of a coagulase-negative, vancomycin and oxacillin-susceptible novel bacterium of the genus Staphylococcus. Staphylococcus sp. strain AOAB was isolated from the stomodeum (gut) of the Mnemiopsis leidyi from Mobile Bay, Alabama USA. A polyphasic taxonomic approach comprised of phenotypic, chemotaxonomic and genotypic characteristics was used for analysis. The dominant respiratory quinone detected was MK-7 (100%). Major cellular fatty acids were anteiso-C15:0 (40.52%), anteiso-C17:0 (13.04 %), C-18:0 (11.53%) and C-20:0 (10.45%). The polar lipid profile consisted of glycolipid, phospholipid, phosphatidylglycerol and diphosphatidylglycerol. Although strain AOAB had a 16SrRNA gene sequence similarity of 99% with S. warneri SG1, S. pasteuri, S. devriesei KS-SP_60, S. lugdunensis HKU09-01, S. epidermidis RP62A, S. haemolyticus JCSC1435 and S. hominis DM 122, it was be distinguished from those species based on Multi-Locus Sequence Analysis (MLSA) using 6 marker genes (16S rRNA, hsp60, rpoB, dnaJ, sodA and tuf). MLSA revealed strain AOAB to be closely related to S. warneri SG1 and S. pasteuri SP1 but distinct from two hitherto known species. These results were confirmed by Average Nucleotide Identity (closest ANI of 84.93% and 84.58% identity against S. warneri SG1 and S. pasteuri SP1 respectively). In-silico DNA-DNA hybridization was <70% (33.1 % and 32.8% against S. warneri SG1 and S. pasteuri SP1 respectively), which further confirmed that the strain was a potential novel Staphylococcus species.

genomics↗

bioRxiv2020

3D super-resolution fluorescence microscopy maps the variable molecular architecture of the Nuclear Pore Complex

Nuclear pore complexes (NPCs) are large macromolecular machines that mediate the traffic between the nucleus and the cytoplasm. In vertebrates, each NPC consists of ~1000 proteins, termed nucleoporins, and has a mass of over 100 MDa. While a pseudo-atomic static model of the central scaffold of the NPC has recently been assembled by integrating data from isolated proteins and complexes, many structural components still remain elusive due to the enormous size and flexibility of the NPC. Here, we explored the power of 3D super-resolution microscopy combined with computational classification and averaging to explore the 3D structure of the NPC in single human cells. We show that this approach can build the first integrated 3D structural map containing both central as well as peripheral NPC subunits with molecular specificity and nanoscale resolution. Our unbiased classification of over ten thousand individual NPCs indicates that the nuclear ring and the nuclear basket can adopt different conformations. Our approach opens up the exciting possibility to relate different structural states of the NPC to function in situ.

cell biology↗

bioRxiv2020

Non-rodent mammalian zygotes assemble dual spindles despite the presence of paternal centrosomes

The first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded and, instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In non-rodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether non-rodent zygotes assemble a single centrosomal spindle around both genomes, or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form around the parental genomes despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in non-rodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos. SummaryThis study investigates spindle assembly during the first embryonic division in bovine zygotes that, like human, inherit centrosomes from the sperm. It shows that two independent microtubule arrays form by self-organization around parental genomes with only loosely connected centrosomes.

cell biology↗

bioRxiv2020

Genomic Diversity of Escherichia coli isolates from healthy children in rural Gambia

Little is known about the genomic diversity of Escherichia coli in healthy children from sub-Saharan Africa, even though this is pertinent to understanding bacterial evolution and ecology and their role in infection. We isolated and whole-genome sequenced up to five colonies of faecal E. coli from 66 asymptomatic children aged three-to-five years in rural Gambia (n=88 isolates from 21 positive stools). We identified 56 genotypes, with an average of 2.7 genotypes per host. These were spread over 37 seven-allele sequence types and the E. coli phylogroups A, B1, B2, C, D, E, F and Escherichia cryptic clade I. Immigration events accounted for three-quarters of the diversity within our study population, while one-quarter of variants appeared to have arisen from within-host evolution. Several study strains were closely related to isolates that caused disease in humans or originated from livestock. Our results suggest that within-host evolution plays a minor role in the generation of diversity than independent immigration and the establishment of strains among our study population. Also, this study adds significantly to the number of commensal E. coli genomes, a group that has been traditionally underrepresented in the sequencing of this species.

ecology↗

bioRxiv2018

A quantitative map of human Condensins provides new insights into mitotic chromosome architecture

The two Condensin complexes in human cells are essential for mitotic chromosome structure. We used homozygous genome editing to fluorescently tag Condensin I and II subunits and mapped their absolute abundance, spacing and dynamic localization during mitosis by fluorescence correlation spectroscopy-calibrated live cell imaging and super-resolution microscopy. While [~]35,000 Condensin II complexes are stably bound to chromosomes throughout mitosis, [~]195,000 Condensin I complexes dynamically bind in two steps, in prometaphase and early anaphase. The two Condensins rarely co-localize at the chromatid axis, where Condensin II is centrally confined but Condensin I reaches [~]50% of the chromatid diameter from its center. Based on our comprehensive quantitative data, we propose a three-step hierarchical loop model of mitotic chromosome compaction: Condensin II initially fixes loops of a maximum size of [~]450 kb at the chromatid axis whose size is then reduced by Condensin I binding to [~]90 kb in prometaphase and [~]70 kb in anaphase, achieving maximum chromosome compaction upon sister chromatid segregation.

cell biology↗

bioRxiv2017

An experimental and computational framework to build a dynamic protein atlas of human cell division

Essential biological functions, such as mitosis, require tight coordination of hundreds of proteins in space and time. Localization, timing of interactions and changes in cellular structure are all crucial to ensure correct assembly, function and regulation of protein complexes1-4. Live cell imaging can reveal protein distributions and dynamics but experimental and theoretical challenges prevented its use to produce quantitative data and a model of mitosis that comprehensively integrates information and enables analysis of the dynamic interactions between the molecular parts of the mitotic machinery within changing cellular boundaries.\n\nTo address this, we generated a 4D image data-driven, canonical model of the morphological changes during mitotic progression of human cells. We used this model to integrate dynamic 3D concentration data of many fluorescently knocked-in mitotic proteins, imaged by fluorescence correlation spectroscopy-calibrated microscopy5. The approach taken here in the context of the MitoSys consortium to generate a dynamic protein atlas of human cell division is generic. It can be applied to systematically map and mine dynamic protein localization networks that drive cell division in different cell types and can be conceptually transferred to other cellular functions.

systems biology↗

bioRxiv2017

Disruption of dual zygotic spindle assembly shows epigenetic asymmetry to be chromosome intrinsic

At the beginning of mammalian life the genetic material from each parent meets when the fertilized egg divides. It was previously thought that a single microtubule spindle is responsible to spatially combine the two genomes and then segregate them to create the two-cell embryo. Utilizing light-sheet microscopy, we showed that two bipolar spindles form in the zygote, that independently congress the maternal and paternal genomes. These two spindles aligned their poles prior to anaphase but kept the parental genomes apart during the first cleavage. This spindle assembly mechanism provides a rationale for erroneous divisions into more than two blastomeric nuclei observed in mammalian zygotes and reveals the mechanism behind the observation that parental genomes occupy separate nuclear compartments in the two-cell embryo.\n\nOne Sentence Summary: After fertilization, two spindles form around pro-nuclei in mammalian zygotes and keep the parental genomes apart during the first division.

cell biology↗

bioRxiv2017

Quantitative mapping of fluorescently tagged cellular proteins using FCS-calibrated four dimensional imaging

EDITORIAL SUMMARYThis protocol describes how to estimate and spatially resolve the concentration and copy number of fluorescently tagged proteins in live cells using fluorescence imaging and fluorescence correlation spectroscopy (FCS).\n\nTWEETDetermining protein concentrations and copy numbers in live cells using fluorescence correlation spectroscopy (FCS)-calibrated imaging.\n\nCOVER TEASER Map protein concentrations with FCS-calibrated imagingUp to four primary research articles where the protocol has been used and/or developed:\n\nO_LIWalther, N., Hossain, M. J., Politi, A. Z., Koch, B., Kueblbeck, M., Oedegaard-Fougner, O., Lampe, M. and J. Ellenberg (2018). A quantitative map of human Condensins provides new insights into mitotic chromosome architecture. bioRxiv, 237834. https://doi.org/10.1101/2378342.\nC_LIO_LICai, Y., Hossain, M. J., Heriche, J.-K., Politi, A. Z., Walther, N., Koch, B., Wachsmuth, M., Nijmeijer, B., Kueblbeck, M., Martinic, M., Ladurner, R., Peters, J.M. and J. Ellenberg (2017). An experimental and computational framework to build a dynamic protein atlas of human cell division. bioRxiv, 227751 https://doi.org/10.1101/227751\nC_LIO_LIGermier, T., Kocanova, S., Walther, N., Bancaud, A., Shaban, H.A., Sellou, H., Politi, A.Z., Ellenberg, J., Gallardo, F. and K. Bystricky (2017). Real-Time Imaging of a Single Gene Reveals Transcription-Initiated Local Confinement. Biophysical Journal, 113(7), 1383-1394, https://doi.org/10.1016/j.bpj.2017.08.014.\nC_LIO_LICuylen, S., Blaukopf, C., Politi, A. Z., Muller-Reichert, T., Neumann, B., Poser, I., Ellenberg, J., Hyman, A.A., and D.W. Gerlich (2016). Ki-67 acts as a biological surfactant to disperse mitotic chromosomes. Nature, 535(7611), 308-312. http://doi.org/10.1038/nature18610.\nC_LI\n\nAbstractThe ability to tag a protein at its endogenous locus with a fluorescent protein (FP) enables the quantitative understanding of protein dynamics at the physiological level. Genome editing technology has now made this powerful approach routinely applicable to mammalian cells and many other model systems, opening up the possibility to systematically and quantitatively map the cellular proteome in four dimensions. 3D time-lapse confocal microscopy (4D imaging) is an essential tool to investigate spatial and temporal protein dynamics, however it lacks the required quantitative power to make absolute and comparable measurements required for systems analysis. Fluorescence correlation spectroscopy (FCS) on the other hand provides quantitative proteomic and biophysical parameters such as protein concentration, hydrodynamic radius and oligomerization but lacks the ability for high-throughput application in 4D spatial and temporal imaging. Here, we present an automated experimental and computational workflow that integrates both methods and delivers quantitative 4D imaging data in high-throughput. These data is processed to yield a calibration curve relating the fluorescence intensities of image voxels to absolute protein abundance. The calibration curve allows the conversion of the arbitrary fluorescence intensities to protein amounts for all voxels of 4D imaging stacks. With our workflow the users can acquire and analyze hundreds of FCS-calibrated image series to map their proteins of interest in four dimensions. Compared to other protocols, the current protocol does not require additional calibration standards and provides an automated acquisition pipeline for FCS and imaging data. The protocol can be completed in 1 day.

molecular biology↗

bioRxiv2017

Postmitotic Nuclear Pore Assembly Proceeds By Radial Dilation Of Small ER Membrane Openings

The nuclear envelope has to be reformed after mitosis to create viable daughter cells with closed nuclei. How membrane sealing of DNA and assembly of nuclear pore complexes (NPCs) are achieved and coordinated is poorly understood. Here, we reconstructed nuclear membrane topology and structure of assembling NPCs in a correlative three dimensional electron microscopy time-course of dividing human cells. Our quantitative ultrastructural analysis shows that nuclear membranes form from highly fenestrated ER sheets, whose shrinking holes are stabilized and then dilated into NPCs during inner ring complex assembly, forming thousands of transport channels within minutes. This mechanism is fundamentally different from interphase NPC assembly and explains how mitotic cells can rapidly establish a closed nuclear compartment while making it transport-competent at the same time.

cell biology↗