Ultrastructure Expansion Microscopy (U-ExM) of the Fission Yeast Schizosaccharomyces pombe.

Among widely used super-resolution microscopy techniques, including stimulated emission depletion (STED), photoactivated localization microscopy (PALM), and stochastic optical reconstruction microscopy (STORM), expansion microscopy (ExM) is unique in achieving increased resolution through a physical manipulation of the actual sample rather than optics or postprocessing. Originally developed for applications in neuroscience, ExM now has a solid foothold across many fields and model systems, and has been adapted to work for organisms with cell walls, including budding and fission yeasts, through the inclusion of a pre-expansion enzymatic digestion step. A variant of the ExM technique optimized for preserving the architecture of protein complexes, ultrastructure expansion microscopy (U-ExM), enables super-resolution imaging of full 3D volumes at increased throughput using conventional microscopes and can be readily combined with commonly used antibodies, dyes, and stains.

Origin and evolution of microvilli.

Background Information: Microvilli are finger-like, straight, and stable cellular protrusions that are filled with F-actin and present a stereotypical length. They are present in a broad range of cell types across the animal tree of life and mediate several fundamental functions, including nutrient absorption, photosensation, and mechanosensation. Therefore, understanding the origin and evolution of microvilli is key to reconstructing the evolution of animal cellular form and function.

Spindle architecture constrains karyotype evolution.

The eukaryotic cell division machinery must rapidly and reproducibly duplicate and partition the cell's chromosomes in a carefully coordinated process. However, chromosome numbers vary dramatically between genomes, even on short evolutionary timescales. We sought to understand how the mitotic machinery senses and responds to karyotypic changes by using a series of budding yeast strains in which the native chromosomes have been successively fused.

Expansion microscopy reveals characteristic ultrastructural features of pathogenic budding yeast species.

Candida albicans is the most prevalent fungal pathogen associated with candidemia. Similar to other fungi, the complex life cycle of C. albicans has been challenging to study with high-resolution microscopy due to its small size.

Life-cycle-coupled evolution of mitosis in close relatives of animals.

Eukaryotes have evolved towards one of two extremes along a spectrum of strategies for remodelling the nuclear envelope during cell division: disassembling the nuclear envelope in an open mitosis or constructing an intranuclear spindle in a closed mitosis. Both classes of mitotic remodelling involve key differences in the core division machinery but the evolutionary reasons for adopting a specific mechanism are unclear. Here we use an integrated comparative genomics and ultrastructural imaging approach to investigate mitotic strategies in Ichthyosporea, close relatives of animals and fungi.

Spindle architecture constrains karyotype in budding yeast.

The eukaryotic cell division machinery must rapidly and reproducibly duplicate and partition the cell's chromosomes in a carefully coordinated process. However, chromosome number varies dramatically between genomes, even on short evolutionary timescales. We sought to understand how the mitotic machinery senses and responds to karyotypic changes by using a series of budding yeast strains in which the native chromosomes have been successively fused.

Experimental evolution for cell biology.

Evolutionary cell biology explores the origins, principles, and core functions of cellular features and regulatory networks through the lens of evolution. This emerging field relies heavily on comparative experiments and genomic analyses that focus exclusively on extant diversity and historical events, providing limited opportunities for experimental validation. In this opinion article, we explore the potential for experimental laboratory evolution to augment the evolutionary cell biology toolbox, drawing inspiration from recent studies that combine laboratory evolution with cell biological assays.

Microtubule-mitochondrial attachment facilitates cell division symmetry and mitochondrial partitioning in fission yeast.

Association with microtubules inhibits the fission of mitochondria in Schizosaccharomyces pombe. Here, we show that this attachment of mitochondria to microtubules is an important cell-intrinsic factor in determining cell division symmetry. By comparing mutant cells that exhibited enhanced attachment and no attachment of mitochondria to microtubules (Dnm1Δ and Mmb1Δ, respectively), we show that microtubules in these mutants displayed aberrant dynamics compared to wild-type cells, which resulted in errors in nuclear positioning.

Ultrastructure expansion microscopy reveals the cellular architecture of budding and fission yeast.

The budding and fission yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe have served as invaluable model organisms to study conserved fundamental cellular processes. Although super-resolution microscopy has in recent years paved the way to a better understanding of the spatial organization of molecules in cells, its wide use in yeasts has remained limited due to the specific know-how and instrumentation required, contrasted with the relative ease of endogenous tagging and live-cell fluorescence microscopy. To facilitate super-resolution microscopy in yeasts, we have extended the ultrastructure expansion microscopy (U-ExM) method to both S.

A quantitative and spatial analysis of cell cycle regulators during the fission yeast cycle.

We have carried out a systems-level analysis of the spatial and temporal dynamics of cell cycle regulators in the fission yeast . In a comprehensive single-cell analysis, we have precisely quantified the levels of 38 proteins previously identified as regulators of the G2 to mitosis transition and of 7 proteins acting at the G1- to S-phase transition. Only 2 of the 38 mitotic regulators exhibit changes in concentration at the whole-cell level: the mitotic B-type cyclin Cdc13, which accumulates continually throughout the cell cycle, and the regulatory phosphatase Cdc25, which exhibits a complex cell cycle pattern.

Tracking changes between preprint posting and journal publication during a pandemic.

Amid the Coronavirus Disease 2019 (COVID-19) pandemic, preprints in the biomedical sciences are being posted and accessed at unprecedented rates, drawing widespread attention from the general public, press, and policymakers for the first time. This phenomenon has sharpened long-standing questions about the reliability of information shared prior to journal peer review. Does the information shared in preprints typically withstand the scrutiny of peer review, or are conclusions likely to change in the version of record? We assessed preprints from bioRxiv and medRxiv that had been posted and subsequently published in a journal through April 30, 2020, representing the initial phase of the pandemic response.

Nuclear size and shape control.

The nucleus displays a wide range of sizes and shapes in different species and cell types, yet its size scaling and many of the key structural constituents that determine its shape are highly conserved. In this review, we discuss the cellular properties and processes that contribute to nuclear size and shape control, drawing examples from across eukaryotes and highlighting conserved themes and pathways. We then outline physiological roles that have been uncovered for specific nuclear morphologies and disease pathologies associated with aberrant nuclear morphology.

The evolving role of preprints in the dissemination of COVID-19 research and their impact on the science communication landscape.

The world continues to face a life-threatening viral pandemic. The virus underlying the Coronavirus Disease 2019 (COVID-19), Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has caused over 98 million confirmed cases and 2.2 million deaths since January 2020.

Nuclear envelope remodelling during mitosis.

The defining feature of the eukaryotic cell, the nucleus, is bounded by a double envelope. This envelope and the nuclear pores within it play a critical role in separating the genome from the cytoplasm. It also presents cells with a challenge.

Moving simply: Naegleria crawls and feeds using an ancient Arp2/3-dependent mechanism.

Arp2/3-nucleated actin filaments drive crawling motility and phagocytosis in animal cells and slime molds. In this issue, Velle and Fritz-Laylin (2020. J.

Closed mitosis requires local disassembly of the nuclear envelope.

At the end of mitosis, eukaryotic cells must segregate the two copies of their replicated genome into two new nuclear compartments. They do this either by first dismantling and later reassembling the nuclear envelope in an 'open mitosis' or by reshaping an intact nucleus and then dividing it into two in a 'closed mitosis'. Mitosis has been studied in a wide variety of eukaryotes for more than a century, but how the double membrane of the nuclear envelope is split into two at the end of a closed mitosis without compromising the impermeability of the nuclear compartment remains unknown.

Science during lockdown - from virtual seminars to sustainable online communities.

The COVID-19 pandemic has disrupted traditional modes of scientific communication. In-person conferences and seminars have been cancelled and most scientists around the world have been confined to their homes. Although challenging, this situation has presented an opportunity to adopt new ways to communicate science and build scientific relationships within a digital environment, thereby reducing the environmental impact and increasing the inclusivity of scientific events.

The proteasome controls ESCRT-III-mediated cell division in an archaeon.

is the closest experimentally tractable archaeal relative of eukaryotes and, despite lacking obvious cyclin-dependent kinase and cyclin homologs, has an ordered eukaryote-like cell cycle with distinct phases of DNA replication and division. Here, in exploring the mechanism of cell division in , we identify a role for the archaeal proteasome in regulating the transition from the end of one cell cycle to the beginning of the next. Further, we identify the archaeal ESCRT-III homolog, CdvB, as a key target of the proteasome and show that its degradation triggers division by allowing constriction of the CdvB1:CdvB2 ESCRT-III division ring.

Live Imaging of a Hyperthermophilic Archaeon Reveals Distinct Roles for Two ESCRT-III Homologs in Ensuring a Robust and Symmetric Division.

Live-cell imaging has revolutionized our understanding of dynamic cellular processes in bacteria and eukaryotes. Although similar techniques have been applied to the study of halophilic archaea [1-5], our ability to explore the cell biology of thermophilic archaea has been limited by the technical challenges of imaging at high temperatures. Sulfolobus are the most intensively studied members of TACK archaea and have well-established molecular genetics [6-9].

The lysosomal GPCR-like protein GPR137B regulates Rag and mTORC1 localization and activity.

Cell growth is controlled by a lysosomal signalling complex containing Rag small GTPases and mammalian target of rapamycin complex 1 (mTORC1) kinase. Here, we carried out a microscopy-based genome-wide human short interfering RNA screen and discovered a lysosome-localized G protein-coupled receptor (GPCR)-like protein, GPR137B, that interacts with Rag GTPases, increases Rag localization and activity, and thereby regulates mTORC1 translocation and activity. High GPR137B expression can recruit and activate mTORC1 in the absence of amino acids.

Correction: Population Distribution Analyses Reveal a Hierarchy of Molecular Players Underlying Parallel Endocytic Pathways.

[This corrects the article DOI: 10.1371/journal.pone.

On the Archaeal Origins of Eukaryotes and the Challenges of Inferring Phenotype from Genotype.

If eukaryotes arose through a merger between archaea and bacteria, what did the first true eukaryotic cell look like? A major step toward an answer came with the discovery of Lokiarchaeum, an archaeon whose genome encodes small GTPases related to those used by eukaryotes to regulate membrane traffic. Although 'Loki' cells have yet to be seen, their existence has prompted the suggestion that the archaeal ancestor of eukaryotes engulfed the future mitochondrion by phagocytosis. We propose instead that the archaeal ancestor was a relatively simple cell, and that eukaryotic cellular organization arose as the result of a gradual transfer of bacterial genes and membranes driven by an ever-closer symbiotic partnership between a bacterium and an archaeon.