Identification and Characterization of Mlp1p and Mlp2p : Molecular Components of Filaments Localized at the Interface between the Nuclear Pore Complex and Nuclear Interior

In eukaryotic cells the segregation of the genome in a closed organelle requires an efficient mechanism to ensure the constant exchange of material between the nucleus and the cytoplasm. Nuclear pore complexes (NPCs) provide the only known sites for exchange of material across the nuclear envelope (NE). A wealth of evidence has accumulated throughout the years that strongly suggest that the NPCs are structurally linked to the nuclear interior. It has long been proposed that this structural continuity is essential for the efficient exchange of material between the nuclear interior and the cytoplasm. Unfortunately, the understanding of the molecular basis of such functional and structural connections has lagged behind. This dissertation describes a combined biochemical and immunological approach aimed at the identification of novel yeast proteins that could be involved in providing such link. The first step of this approach was the development of a large scale enrichment procedure to prepare yeast nuclear envelopes (NEs). These NEs can be stripped of peripheral proteins to produce a heparin-extracted NE (H-NE) fraction highly enriched in integral membrane proteins. Extraction of H-NEs with detergents revealed previously uncharacterized ring structures associated with the NE that apparently stabilize the grommets of the nuclear pore complexes (NPCs). The high yields obtained throughout the fractionation procedure allowed balance-sheet tabulation of the subcellular distribution of various NE and non-NE associated proteins. As the second step of the approach described here, three different highly enriched NE-derived fractions were used to generate a panel of 114 monoclonal antibodies (mAbs) against NE-associated antigens. Finally, this panel of anti-NE mAbs were subjected to a novel NPC-clustering screen aimed at the identification of NE-associated antigens that were only peripherally associated with the NPC. Two mAbs were isolated using this screen (MAb148G11 and MAb215B9). Both of these mAbs were found to recognize the same -220 kD protein (p220) on immunoblots of highly enriched NE fractions. The gene encoding p220 was cloned and was found to be the previously identified gene of unknown function, MLP1. Disruptions of MLP1 and its homologue MLP2 (the uncharacterized yeast ORF, YIL149C), were found to be non lethal either separately or in combination. Though both M lplp and Mlp2p largely cofractionated with isolated NEs, neither cofractionated with isolated NPCs. Ultrastructural localization demonstrated that both Mlplp and Mlp2p are localized to filaments that appear to connect the NPC to the nuclear interior. Functional studies performed using yeast strains harboring a double deletion of MLP1 and MLP2 suggested that these proteins could be involved in facilitating nuclear import and led to the proposal of a model for the possible role of these proteins in nuclear transport

Jumping over the fence: RNA nuclear export revisited

The nuclear envelope forms a cocoon that surrounds the cellular genome keeping it out of harm\u27s way and can be utilized by the cell as a means of functionally regulating chromatin structure and gene expression. At the same time, this double-layered membrane system constitutes a formidable obstacle to the unimpeded flow of genetic information between the genome and the rest of the cell. The nuclear pore has been long considered the sole passageway between nucleus and cytoplasm. A new report challenges this view and proposes a novel mechanism by which RNA transcripts destined for localized translation in highly polarized cell types, cross both inner and outer nuclear envelope membranes and reach the cytoplasm without utilizing the nuclear pore route

Proposal for minimum information guidelines to report and reproduce results of particle tracking and motion analysis [preprint]

The proposed Minimum Information About Particle Tracking Experiments (MIAPTE) reporting guidelines described here aim to deliver a set of rules representing the minimal information required to report and support interpretation and assessment of data arising from intracellular multiple particle tracking (MPT) experiments. Examples of such experiments are those tracking viral particles as they move from the site of entry to the site of replication within an infected cell, or those following vesicular dynamics during secretion, endocytosis, or exocytosis. By promoting development of community standards, we hope that MIAPTE will contribute to making MPT data FAIR (Findable Accessible Interoperable and Reusable). Ultimately, the goal of MIAPTE is to promote and maximize data access, discovery, preservation, re-use, and repurposing through efficient annotation, and ultimately to enable reproducibility of particle tracking experiments. This document introduces MIAPTE v0.2, which updates the version that was posted to Fairsharing.org in October 2016. MIAPTE v0.2 is presented with the specific intent of soliciting comments from the particle tracking community with the purpose of extending and improving the model. The MIAPTE guidelines are intended for different categories of users: 1) Scientists with the desire to make new results available in a way that can be interpreted unequivocally by both humans and machines. For this class of users, MIAPTE provides data descriptors to define data entry terms and the analysis workflow in a unified manner. 2) Scientists wishing to evaluate, replicate and re-analyze results published by others. For this class of users MIAPTE provides descriptors that define the analysis procedures in a manner that facilitates its reproduction. 3) Developers who want to take advantage of the schema of MIAPTE to produce MIAPTE compatible tools. MIAPTE consists of a list of controlled vocabulary (CV) terms that describe elements and properties for the minimal description of particle tracking experiments, with a focus on viral and vesicular traffic within cells. As part of this submission we provide entity relationship (ER) diagrams that show the relationship between terms. Finally, we also provide documents containing the MIAPTE-compliant XML schema describing the data model used by Open Microscopy Environment inteGrated Analysis (OMEGA), our novel particle tracking data analysis and management tool, which is reported in a separate manuscript. MIAPTE is structured in two sub-sections: 1) Section 1 contains elements, attributes and data structures describing the results of particle tracking, namely: particles, links, trajectories and trajectory segments. 2) Section 2 contains elements that provide details about the algorithmic procedure utilized to produce and analyze trajectories as well as the results of trajectory analysis. In addition MIAPTE includes those OME-XML elements that are required to capture the acquisition parameters and the structure of images to be subjected to particle tracking

Rapid isolation of functionally intact nuclei from the yeast Saccharomyces [preprint]

Most available methods for nuclear isolation entail lengthy procedures that are difficult to master and generally emphasize yield and enrichment over nuclear preservation, thus limiting their utility for further studies. Here we demonstrate a novel and robust method to rapidly isolate well-preserved yeast nuclei. The method can be easily adapted to multiple preparation scales depending on experimental need and it can readily be performed on multiple samples by a single researcher in one day. We show that the nuclei fraction is strongly enriched and that the resulting nuclei are free from contaminating endoplasmic reticulum and other cell debris. EM studies show that preservation of nuclear morphology is exquisite, making it possible to study peripheral nuclear pore components such as the cytoplasmic filaments and the basket, whose structure is generally difficult to maintain ex vivo. In addition, incubation of isolated nuclei with bulk transport substrates of different sizes and with import cargo indicates that the nuclear envelope is intact and nuclear pores retain their capacity to bind transport substrates. Our results suggest that this preparation procedure will greatly facilitate studies of the yeast nucleus which have been difficult to establish and to multiplex to date

The DHODH inhibitor PTC299 arrests SARS-CoV-2 replication and suppresses induction of inflammatory cytokines

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for therapeutics that inhibit the SARS-COV-2 virus and suppress the fulminant inflammation characteristic of advanced illness. Here, we describe the anti-COVID-19 potential of PTC299, an orally bioavailable compound that is a potent inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. In tissue culture, PTC299 manifests robust, dose-dependent, and DHODH-dependent inhibition of SARS-COV-2 replication (EC50 range, 2.0-31.6 nM) with a selectivity index \u3e 3,800. PTC299 also blocked replication of other RNA viruses, including Ebola virus. Consistent with known DHODH requirements for immunomodulatory cytokine production, PTC299 inhibited the production of interleukin (IL)-6, IL-17A (also called IL-17), IL-17 F, and vascular endothelial growth factor (VEGF) in tissue culture models. The combination of anti-SARS-CoV-2 activity, cytokine inhibitory activity, and previously established favorable pharmacokinetic and human safety profiles render PTC299 a promising therapeutic for COVID-19

Micro-Meta App: an interactive tool for collecting microscopy metadata based on community specifications

For quality, interpretation, reproducibility and sharing value, microscopy images should be accompanied by detailed descriptions of the conditions that were used to produce them. Micro-Meta App is an intuitive, highly interoperable, open-source software tool that was developed in the context of the 4D Nucleome (4DN) consortium and is designed to facilitate the extraction and collection of relevant microscopy metadata as specified by the recent 4DN-BINA-OME tiered-system of Microscopy Metadata specifications. In addition to substantially lowering the burden of quality assurance, the visual nature of Micro-Meta App makes it particularly suited for training purposes

Evidence for biphasic uncoating during HIV-1 infection from a novel imaging assay

BACKGROUND: Uncoating of the HIV-1 core plays a critical role during early post-fusion stages of infection but is poorly understood. Microscopy-based assays are unable to easily distinguish between intact and partially uncoated viral cores. RESULTS: In this study, we used 5-ethynyl uridine (EU) to label viral-associated RNA during HIV production. At early time points after infection with EU-labeled virions, the viral-associated RNA was stained with an EU-specific dye and was detected by confocal microscopy together with viral proteins. We observed that detection of the viral-associated RNA was specific for EU-labeled virions, was detected only after viral fusion with target cells, and occurred after an initial opening of the core. In vitro staining of cores showed that the opening of the core allowed the small molecule dye, but not RNase A or antibodies, inside. Also, staining of the viral-associated RNA, which is co-localized with nucleocapsid, decays over time after viral infection. The decay rate of RNA staining is dependent on capsid (CA) stability, which was altered by CA mutations or a small molecule inducer of HIV-1 uncoating. While the staining of EU-labeled RNA was not affected by inhibition of reverse transcription, the kinetics of core opening of different CA mutants correlated with initiation of reverse transcription. Analysis of the E45A CA mutant suggests that initial core opening is independent of complete capsid disassembly. CONCLUSIONS: Taken together, our results establish a novel RNA accessibility-based assay that detects an early event in HIV-1 uncoating and can be used to further define this process

OMEGA: a software tool for the management, analysis, and dissemination of intracellular trafficking data that incorporates motion type classification and quality control [preprint]

MOTIVATION: Particle tracking coupled with time-lapse microscopy is critical for understanding the dynamics of intracellular processes of clinical importance. Spurred on by advances in the spatiotemporal resolution of microscopy and automated computational methods, this field is increasingly amenable to multi-dimensional high-throughput data collection schemes (Snijder et al, 2012). Typically, complex particle tracking datasets generated by individual laboratories are produced with incompatible methodologies that preclude comparison to each other. There is therefore an unmet need for data management systems that facilitate data standardization, meta-analysis, and structured data dissemination. The integration of analysis, visualization, and quality control capabilities into such systems would eliminate the need for manual transfer of data to diverse downstream analysis tools. At the same time, it would lay the foundation for shared trajectory data, particle tracking, and motion analysis standards. RESULTS: Here, we present Open Microscopy Environment inteGrated Analysis (OMEGA), a cross-platform data management, analysis, and visualization system, for particle tracking data, with particular emphasis on results from viral and vesicular trafficking experiments. OMEGA provides easy to use graphical interfaces to implement integrated particle tracking and motion analysis workflows while keeping track of error propagation and data provenance. Specifically, OMEGA: 1) imports image data and metadata from data management tools such as Open Microscopy Environment Remote Objects (OMERO; Allan et al., 2012); 2) tracks intracellular particles moving across time series of image planes; 3) facilitates parameter optimization and trajectory results inspection and validation; 4) performs downstream trajectory analysis and motion type classification; 5) estimates the uncertainty associated with motion analysis; and, 6) facilitates storage and dissemination of analysis results, and analysis definition metadata, on the basis of our newly proposed Minimum Information About Particle Tracking Experiments (MIAPTE; Rigano & Strambio-De-Castillia, 2016; 2017) guidelines in combination with the OME-XML data model (Goldberg et al, 2005)