• Candida albicans
• Fungal pathogens
• Microtubules
• Nucleolus
• Spindle pole bodies
• Ultrastructure expansion microscopy

• Microtubules/ultrastructure
• Microtubules/metabolism
• Hyphae/ultrastructure
• Hyphae/growth & development
• Candida albicans/ultrastructure
• Spindle Pole Bodies/metabolism
• Spindle Pole Bodies/ultrastructure
• Saccharomycetales/ultrastructure
• Mitochondria/ultrastructure
• Microscopy/methods
• Humans

• DBT/2020/January/58 Department of Biotechnology, India
• JCB/2020/000021 Science and Engineering Research Board, Department of Science and Technology, India
• 10212 EMBO Scientific Exchange Grant
• 101078291 ERC
• 847543 EMBL Interdisciplinary Postdoctoral Fellowship under Marie Sklodowska-Curie Actions
• JNCASR Intramural Support
• EMBL Corporate Partnership Programme Fellowship
• 10212 EMBO Scientific Exchange
• Jawaharlal Nehru Centre for Advanced Scientific Research
• JCB/2020/000021 Science and Engineering Research Board, Department of Science and Technology, Govt. of India
• European Molecular Biology Laboratory
• 101078291 European Union
• 847543 Sklodowska-Curie Actions

Mitotic exit in budding yeast is dependent on correct orientation of the mitotic spindle along the cell polarity axis. When accurate positioning of the spindle fails, a surveillance mechanism named the spindle position checkpoint (SPOC) prevents cells from exiting mitosis. Mutants with a defective SPOC become multinucleated and lose their genomic integrity. Yet, a comprehensive understanding of the SPOC mechanism is missing. In this study, we identified the type 1 protein phosphatase, Glc7, in association with its regulatory protein Bud14 as a novel checkpoint component. We further showed that Glc7-Bud14 promotes dephosphorylation of the SPOC effector protein Bfa1. Our results suggest a model in which two mechanisms act in parallel for a robust checkpoint response: first, the SPOC kinase Kin4 isolates Bfa1 away from the inhibitory kinase Cdc5, and second, Glc7-Bud14 dephosphorylates Bfa1 to fully activate the checkpoint effector.

• PP1
• S. cerevisiae
• cell biology
• cell cycle
• mitotic exit
• signalling
• spindle position checkpoint

• APC
• Wnt signalling
• actin
• cell division
• cell migration
• colorectal cancer
• cytoskeleton
• gut renewal
• microtubules
• spindle orientation
• stem cells

• Drosophila
• FlyBook
• adipocytes
• diet
• germline stem cells
• microorganisms
• oogenesis
• ovary
• physiology
• spermatogenesis
• testis

• Adult Stem Cells/cytology
• Adult Stem Cells/metabolism
• Animals
• Drosophila melanogaster/genetics
• Drosophila melanogaster/growth & development
• Gametogenesis
• Gene Expression Regulation, Developmental
• Gene-Environment Interaction
• Stem Cell Niche

• R01 GM069875 NIGMS NIH HHS
• R01 GM125121 NIGMS NIH HHS

Venkei and Yamashita summarize recent advances in our understanding of asymmetric stem cell division in tissue homeostasis.

The asymmetric cell division of stem cells, which produces one stem cell and one differentiating cell, has emerged as a mechanism to balance stem cell self-renewal and differentiation. Elaborate cellular mechanisms that orchestrate the processes required for asymmetric cell divisions are often shared between stem cells and other asymmetrically dividing cells. During asymmetric cell division, cells must establish asymmetry/polarity, which is guided by varying degrees of intrinsic versus extrinsic cues, and use intracellular machineries to divide in a desired orientation in the context of the asymmetry/polarity. Recent studies have expanded our knowledge on the mechanisms of asymmetric cell divisions, revealing the previously unappreciated complexity in setting up the cellular and/or environmental asymmetry, ensuring binary outcomes of the fate determination. In this review, we summarize recent progress in understanding the mechanisms and regulations of asymmetric stem cell division.

• Drosophila
• centriole
• centrosome
• microtubule
• microtubule-organizing center (MTOC)
• ninein
• non-centrosomal MTOC
• patronin
• γ-tubulin

• R15 GM119078 NIGMS NIH HHS
• GM119078 National Institutes of Health
• 7ZK06 Florida Department of Health

• APC
• C. elegans
• asymmetric division
• microtubule
• spindle

• Adenomatous Polyposis Coli Protein/metabolism
• Animals
• Asymmetric Cell Division
• CRISPR-Cas Systems
• Caenorhabditis elegans/cytology
• Caenorhabditis elegans Proteins/metabolism
• Cell Cycle Proteins/metabolism
• Cell Polarity
• Centrosome/metabolism
• Computer Simulation
• Cytoplasm/metabolism
• Green Fluorescent Proteins/metabolism
• Microtubules/metabolism
• Models, Theoretical
• Mutation
• RNA Interference
• Spindle Apparatus
• Stress, Mechanical
• Tubulin/metabolism
• Zygote

• P40 OD010440 NIH HHS
• R01 GM049869 NIGMS NIH HHS

Cytoplasmic microtubules (cMT) control mitotic spindle positioning in many organisms, and are therefore pivotal for successful cell division. Despite its importance, the temporal control of cMT formation remains poorly understood. Here we show that unlike the best-studied yeast Saccharomyces cerevisiae, position of pre-anaphase nucleus is not strongly biased toward bud neck in Ogataea polymorpha and the regulation of spindle positioning becomes active only shortly before anaphase. This is likely due to the unstable property of cMTs compared to those in S. cerevisiae. Furthermore, we show that cMT nucleation/anchoring is restricted at the level of recruitment of the γ-tubulin complex receptor, Spc72, to spindle pole body (SPB), which is regulated by the polo-like kinase Cdc5. Additionally, electron microscopy revealed that the cytoplasmic side of SPB is structurally different between G1 and anaphase. Thus, polo-like kinase dependent recruitment of γ-tubulin receptor to SPBs determines the timing of spindle orientation in O. polymorpha.

Before a cell divides, it needs to duplicate its genetic material to provide the new daughter cell with a full set of genetic information. To do so, the cell forms a complex of proteins called the spindle apparatus, which is made up of string-like microtubules that divide the chromosomes evenly. In many organisms, the position of the spindle determines where in the cell this separation happens.

However, in baker’s yeast, the location where the cell will divide is determined well before the spindle is formed. Unlike many other eukaryotic cells, these yeast cells divide asymmetrically and create buds that will form the new daughter cells. The position of this bud determines where the spindle should be located and where the chromosomes separate.

The spindle itself is then organised by a structure called the spindle pole body, which connects to microtubules inside the cell nucleus and microtubules in the cell plasma. Several proteins control where and how the spindle forms, including a protein called the spindle pole component 72, or Spc72 for short, and an enzyme called Cdc5. However, until now it was unclear how spindle formation is timed and controlled in other yeast species.

Now, Maekawa et al. have used fluorescent markers and time lapse microscopy to examine how the spindle forms in the yeast species Ogataea polymorpha, an important industrial yeast used to produce medicines and alcohol. The results show that in O. polymorpha, the positioning and orientation of the spindle only occurred very late in the cell cycle and the microtubules in the cell plasma remained unstable until the chromosomes were about to separate. This was linked to changes in the level of Spc72, which increased at the spindle pole body before the chromosomes separated and then dropped again. This was controlled by Cdc5.

Understanding when and where microtubules are formed is an important step in understanding how cells divide. This is the first example of a budding yeast that creates new microtubules in the cell plasma every time the cell divides. Unravelling the molecular differences between yeast species could lead to new ways to optimise the use of industrial yeasts like O. polymorpha, or to combat disease-causing ones.

• Ogataea polymorpha
• Spc72
• cell biology
• cell cycle
• cytoplasmic microtubules
• infectious disease
• microbiology
• none
• polo-like kinase
• spindle pole body

• Asymmetric Cell Division/physiology
• Cell Polarity/physiology
• Saccharomyces cerevisiae/physiology
• Saccharomyces cerevisiae Proteins
• Spindle Apparatus/physiology
• Spindle Poles/physiology

• Wellcome Trust

• Drifts
• Evolutionary leaps
• Selection
• Survival determinism

• Animals
• Asymmetric Cell Division/physiology
• Body Patterning/physiology
• Xenopus Proteins/metabolism
• Xenopus laevis/embryology
• Xenopus laevis/physiology

• Asymmetric cell division
• Cell fate determinants
• Cell polarity
• Fluorescence microscopy
• Image quantification
• Lymphocytes
• T Cells
• Thymocyte

• Animals
• Asymmetric Cell Division/immunology
• Caenorhabditis elegans/immunology
• Cytokinesis/immunology
• Drosophila melanogaster
• Microscopy, Fluorescence/methods
• T-Lymphocytes/cytology
• T-Lymphocytes/immunology

• Cdc14 phosphatase
• Hippo pathway
• MEN
• Mitosis
• Mitotic exit network

In budding yeast, if the spindle becomes mispositioned, cells prevent exit from mitosis by inhibiting the mitotic exit network (MEN). The MEN is a signaling cascade that localizes to spindle pole bodies (SPBs) and activates the phosphatase Cdc14. There are two competing models that explain MEN regulation by spindle position. In the 'zone model', exit from mitosis occurs when a MEN-bearing SPB enters the bud. The 'cMT-bud neck model' posits that cytoplasmic microtubule (cMT)-bud neck interactions prevent MEN activity. Here we find that 1) eliminating cMT– bud neck interactions does not trigger exit from mitosis and 2) loss of these interactions does not precede Cdc14 activation. Furthermore, using binucleate cells, we show that exit from mitosis occurs when one SPB enters the bud despite the presence of a mispositioned spindle. We conclude that exit from mitosis is triggered by a correctly positioned spindle rather than inhibited by improper spindle position.

DOI:http://dx.doi.org/10.7554/eLife.14036.001

Most cells duplicate their genetic material and then separate the two copies before they divide. This is true for budding yeast cells, which divide in an unusual manner. New daughter cells grow as a bud on the side of a larger mother cell and are eventually pinched off. To make healthy daughter cells, yeast must share their chromosomes between the mother cell and the bud. This involves threading the chromosomes through a small opening called the bud neck, which connects the mother cell and the bud.

A surveillance mechanism in budding yeast monitors the placement of the molecular machine (called the spindle) that separates the chromosomes before a cell divides. This mechanism stops the cell from dividing if the spindle is not positioned correctly. Two models could explain how an incorrectly positioned spindle prevents budding yeast from dividing. The first model proposes that yeast cells do not divide if protein filaments (called microtubules) touch the bud neck. This only occurs if the spindle is not properly threaded into the bud through the small opening of the bud neck. The second model proposes that specific proteins required for cell division (which are found at the ends of the spindle) are inhibited while they are inside the mother cell. This means that the cell cannot divide until one end of its spindle moves out of the mother cell and into the bud.

Now, Falk et al. report the results of experiments that aimed to distinguish between these two models. First, a laser was used to cut the spindle filaments in live yeast cells. This stopped the filaments from touching the neck between the mother cell and the bud, but did not cause the cell to divide. Therefore, these results refute the first model. Next, Falk et al. generated yeast cells that had essentially been tricked into forming two separate spindles before they started to divide. As would be predicted by the second model, these cells could divide as long as an end from at least one of the spindles entered the bud.

These findings strongly suggest that the second model provides the best explanation for how yeast cells sense spindle position to control cell division. The findings also lend further support to previous work that showed that activators of cell division are found in the bud, while inhibitors of cell division are found in the mother cell. Finally, in a related study, Gryaznova, Caydasi et al. identify a protein at the ends of the spindle that acts like a regulatory hub to coordinate cell division with spindle position. Their findings also suggest that the surveillance mechanism is switched off in the bud to allow the cell to divide.

DOI:http://dx.doi.org/10.7554/eLife.14036.002

• CDC14
• Cdc14 early anaphase release network
• KIN4
• S. cerevisiae
• cell biology
• mitotic exit network
• spindle position checkpoint
• zone model

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes (platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells (GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug. In both, moths and the milkweed bug, GSCs form finger-like projections toward the niche, the apical cells (homologs of the hub cells in Drosophila). Whereas in the milkweed bug the projection terminals remain at the surface of the niche cells, in the gipsy moth they protrude deeply into the singular niche cell. In both cases, the projections undergo serial retrograde fragmentation with progressing signs of autophagy. In the gipsy moth, the autotomized vesicles are phagocytized and digested by the niche cell. In the milkweed bug the autotomized vesicles accumulate at the niche surface and disintegrate. Autotomy and sprouting of new projections appears to occur continuously. The significance of the GSC-niche interactions, however, remains enigmatic. Our concept on the signaling relationship between stem cell-niche in general and GSC and niche (hub cells and cyst stem cells) in particular has been greatly shaped by Drosophila melanogaster. In comparing the interactions of GSCs with their niche in Drosophila with those in species exhibiting GSC autotomy it is obvious that additional or alternative modes of stem cell-niche communication exist. Thus, essential signaling pathways, including niche-stem cell adhesion (E-cadherin) and the direction of asymmetrical GSC division - as they were found in Drosophila - can hardly be translated into the systems where GSC autotomy was reported. It is shown here that the serial autotomy of GSC projections shows remarkable similarities with Wallerian axonal destruction, developmental axon pruning and dying-back degeneration in neurodegenerative diseases. Especially the hypothesis of an existing evolutionary conserved “autodestruction program” in axons that might also be active in GSC projections appears attractive. Investigations on the underlying signaling pathways have to be carried out. There are two other well known cases of programmed cell autotomy: the enucleation of erythroblasts in the process of erythrocyte maturation and the segregation of thousands of thrombocytes (platelets) from one megakaryocyte. Both progenitor cell types - erythroblasts and megakaryocytes - are associated with a niche in the bone marrow, erythroblasts with a macrophage, which they surround, and the megakaryocytes with the endothelial cells of sinusoids and their extracellular matrix. Although the regulatory mechanisms may be specific in each case, there is one aspect that connects all described processes of programmed cell autotomy and neuronal autodestruction: apoptotic pathways play always a prominent role. Studies on the role of male GSC autotomy in stem cell-niche interaction have just started but are expected to reveal hitherto unknown ways of signal exchange. Spermatogenesis in mammals advance our understanding of insect spermatogenesis. Mammal and insect spermatogenesis share some broad principles, but a comparison of the signaling pathways is difficult. We have intimate knowledge from Drosophila, but of almost no other insect, and we have only limited knowledge from mammals. The discovery of stem cell autotomy as part of the interaction with the niche promises new general insights into the complicated stem cell-niche interdependence.

• Stem cell-niche interaction
• Male germline stem cells
• Spermatogenesis
• Erythropoiesis
• Stem cell autotomy
• Thrombopoiesis

A strong correlation between centrosome age and fate has been reported in some stem cells and progenitors that divide asymmetrically. In some cases, such stereotyped centrosome behaviour is essential to endow stemness to only one of the two daughters, whereas in other cases causality is still uncertain. Here, we present the different cell types in which correlated centrosome age and fate has been documented, review current knowledge on the underlying molecular mechanisms and discuss possible functional implications of this process.

• asymmetric cell division
• centriole
• centrosome
• stem cell

• D. melanogaster
• Drosophila
• asymmetric division
• cell biology
• centrosome
• developmental biology
• niche
• stem cell
• stem cells

• Asymmetric cell division
• Centrosome
• Checkpoint
• Drosophila
• Spindle orientation
• Stem cells

The Saccharomyces cerevisiae lysine deacetylase Hos3 is asymmetrically targeted to the daughter side of the neck, dependent on the morphogenesis checkpoint member Hsl7, and to the daughter spindle pole body (SPB). In the presence of spindle misalignment, Hos3 at the SPBs functions as a brake component to inhibit mitotic exit.

An increasing number of cellular activities can be regulated by reversible lysine acetylation. Targeting the enzymes responsible for such posttranslational modifications is instrumental in defining their substrates and functions in vivo. Here we show that a Saccharomyces cerevisiae lysine deacetylase, Hos3, is asymmetrically targeted to the daughter side of the bud neck and to the daughter spindle pole body (SPB). The morphogenesis checkpoint member Hsl7 recruits Hos3 to the neck region. Cells with a defect in spindle orientation trigger Hos3 to load onto both SPBs. When associated symmetrically with both SPBs, Hos3 functions as a spindle position checkpoint (SPOC) component to inhibit mitotic exit. Neck localization of Hos3 is essential for its symmetric association with SPBs in cells with misaligned spindles. Our data suggest that Hos3 facilitates cross-talk between the morphogenesis checkpoint and the SPOC as a component of the intricate monitoring of spindle orientation after mitotic entry and before commitment to mitotic exit.

• Cell Cycle/genetics
• Cell Cycle Checkpoints/genetics
• Cell Cycle Proteins/genetics
• Checkpoint Kinase 2/genetics
• Cytoskeletal Proteins/genetics
• DNA Damage/genetics
• G2 Phase Cell Cycle Checkpoints/genetics
• Mitosis
• Phosphorylation/genetics
• Saccharomyces cerevisiae
• Saccharomyces cerevisiae Proteins/genetics
• Spindle Apparatus/genetics
• Telomere/genetics

• Actins/metabolism
• Bridged Bicyclo Compounds, Heterocyclic/pharmacology
• Cell Nucleus/drug effects
• Cell Nucleus/metabolism
• Cell Polarity/drug effects
• Cytoplasm/drug effects
• Cytoplasm/metabolism
• Diffusion
• Green Fluorescent Proteins/metabolism
• Inheritance Patterns
• Luminescent Proteins/metabolism
• Mitochondria/drug effects
• Mitochondria/metabolism
• Mitochondrial Dynamics/drug effects
• Mutation/genetics
• Polymerization/drug effects
• Polyribosomes/drug effects
• Polyribosomes/metabolism
• Prions/metabolism
• Saccharomyces cerevisiae/cytology
• Saccharomyces cerevisiae/drug effects
• Saccharomyces cerevisiae/growth & development
• Saccharomyces cerevisiae/metabolism
• Septins/metabolism
• Solubility
• Thiazolidines/pharmacology
• Time Factors
• Zygote/drug effects
• Zygote/metabolism

• P30 CA043703 NCI NIH HHS
• R01 GM089872 NIGMS NIH HHS
• P30 CA43703-12 NCI NIH HHS
• R01GM089872 NIGMS NIH HHS

• Bacteria/cytology
• Bacteria/genetics
• Bacteria/growth & development
• Bacterial Proteins/genetics
• Bacterial Proteins/physiology
• Cell Division
• Computational Biology/methods
• Genome, Bacterial
• Signal Transduction

• Animals
• Biological Evolution
• Cell Polarity
• Centrioles/physiology
• Centrioles/ultrastructure
• Centrosome/physiology
• Centrosome/ultrastructure
• Cilia/physiology
• Cilia/ultrastructure
• Embryonic Development/physiology
• Humans
• Microtubules/physiology
• Models, Biological
• Phylogeny
• Planarians/physiology
• Planarians/ultrastructure
• Regeneration/physiology
• Species Specificity

• jak-stat signaling
• dedifferentiation
• differentiation
• germline stem cell
• niche
• spermatogonia

• R01 HD040307 NICHD NIH HHS
• R01 HD052937 NICHD NIH HHS
• S10 RR024550 NCRR NIH HHS