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Xiao J, Turner JJ, Kõivomägi M, Skotheim JM. Whi5 hypo- and hyper-phosphorylation dynamics control cell-cycle entry and progression. Curr Biol 2024; 34:2434-2447.e5. [PMID: 38749424 DOI: 10.1016/j.cub.2024.04.052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Revised: 03/18/2024] [Accepted: 04/23/2024] [Indexed: 05/28/2024]
Abstract
Progression through the cell cycle depends on the phosphorylation of key substrates by cyclin-dependent kinases. In budding yeast, these substrates include the transcriptional inhibitor Whi5 that regulates G1/S transition. In early G1 phase, Whi5 is hypo-phosphorylated and inhibits the Swi4/Swi6 (SBF) complex that promotes transcription of the cyclins CLN1 and CLN2. In late G1, Whi5 is rapidly hyper-phosphorylated by Cln1 and Cln2 in complex with the cyclin-dependent kinase Cdk1. This hyper-phosphorylation inactivates Whi5 and excludes it from the nucleus. Here, we set out to determine the molecular mechanisms responsible for Whi5's multi-site phosphorylation and how they regulate the cell cycle. To do this, we first identified the 19 Whi5 sites that are appreciably phosphorylated and then determined which of these sites are responsible for G1 hypo-phosphorylation. Mutation of 7 sites removed G1 hypo-phosphorylation, increased cell size, and delayed the G1/S transition. Moreover, the rapidity of Whi5 hyper-phosphorylation in late G1 depends on "priming" sites that dock the Cks1 subunit of Cln1,2-Cdk1 complexes. Hyper-phosphorylation is crucial for Whi5 nuclear export, normal cell size, full expression of SBF target genes, and timely progression through both the G1/S transition and S/G2/M phases. Thus, our work shows how Whi5 phosphorylation regulates the G1/S transition and how it is required for timely progression through S/G2/M phases and not only G1 as previously thought.
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Affiliation(s)
- Jordan Xiao
- Department of Biology, Stanford University, 327 Campus Dr., Stanford, CA 94305, USA
| | - Jonathan J Turner
- Department of Biology, Stanford University, 327 Campus Dr., Stanford, CA 94305, USA
| | - Mardo Kõivomägi
- Department of Biology, Stanford University, 327 Campus Dr., Stanford, CA 94305, USA; Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, 37 Convent Dr., Bethesda, MD 20892, USA.
| | - Jan M Skotheim
- Department of Biology, Stanford University, 327 Campus Dr., Stanford, CA 94305, USA; Chan Zuckerberg Biohub, 499 Illinois St., San Francisco, CA 94158, USA.
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Ramakanth S, Kennedy T, Yalcinkaya B, Neupane S, Tadic N, Buchler NE, Argüello-Miranda O. Deep learning-driven imaging of cell division and cell growth across an entire eukaryotic life cycle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.25.591211. [PMID: 38712227 PMCID: PMC11071524 DOI: 10.1101/2024.04.25.591211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2024]
Abstract
The life cycle of biomedical and agriculturally relevant eukaryotic microorganisms involves complex transitions between proliferative and non-proliferative states such as dormancy, mating, meiosis, and cell division. New drugs, pesticides, and vaccines can be created by targeting specific life cycle stages of parasites and pathogens. However, defining the structure of a microbial life cycle often relies on partial observations that are theoretically assembled in an ideal life cycle path. To create a more quantitative approach to studying complete eukaryotic life cycles, we generated a deep learning-driven imaging framework to track microorganisms across sexually reproducing generations. Our approach combines microfluidic culturing, life cycle stage-specific segmentation of microscopy images using convolutional neural networks, and a novel cell tracking algorithm, FIEST, based on enhancing the overlap of single cell masks in consecutive images through deep learning video frame interpolation. As proof of principle, we used this approach to quantitatively image and compare cell growth and cell cycle regulation across the sexual life cycle of Saccharomyces cerevisiae . We developed a fluorescent reporter system based on a fluorescently labeled Whi5 protein, the yeast analog of mammalian Rb, and a new High-Cdk1 activity sensor, LiCHI, designed to report during DNA replication, mitosis, meiotic homologous recombination, meiosis I, and meiosis II. We found that cell growth preceded the exit from non-proliferative states such as mitotic G1, pre-meiotic G1, and the G0 spore state during germination. A decrease in the total cell concentration of Whi5 characterized the exit from non-proliferative states, which is consistent with a Whi5 dilution model. The nuclear accumulation of Whi5 was developmentally regulated, being at its highest during meiotic exit and spore formation. The temporal coordination of cell division and growth was not significantly different across three sexually reproducing generations. Our framework could be used to quantitatively characterize other single-cell eukaryotic life cycles that remain incompletely described. An off-the-shelf user interface Yeastvision provides free access to our image processing and single-cell tracking algorithms.
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Pelet S. Adapting to ever-changing conditions. eLife 2024; 13:e91717. [PMID: 38416131 PMCID: PMC10901503 DOI: 10.7554/elife.91717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/29/2024] Open
Abstract
Experiments involving periodic stimuli shed light on the interplay between hyper-osmotic stress and glucose starvation in yeast cells.
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Affiliation(s)
- Serge Pelet
- Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland
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Ros-Carrero C, Spiridon-Bodi M, Igual JC, Gomar-Alba M. The CDK Pho85 inhibits Whi7 Start repressor to promote cell cycle entry in budding yeast. EMBO Rep 2024; 25:745-769. [PMID: 38233717 PMCID: PMC10897450 DOI: 10.1038/s44319-023-00049-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Revised: 12/15/2023] [Accepted: 12/19/2023] [Indexed: 01/19/2024] Open
Abstract
Pho85 is a multifunctional CDK that signals to the cell when environmental conditions are favorable. It has been connected to cell cycle control, mainly in Start where it promotes the G1/S transition. Here we describe that the Start repressor Whi7 is a key target of Pho85 in the regulation of cell cycle entry. The phosphorylation of Whi7 by Pho85 inhibits the repressor and explains most of the contribution of the CDK in the activation of Start. Mechanistically, Pho85 downregulates Whi7 protein levels through the control of Whi7 protein stability and WHI7 gene transcription. Whi7 phosphorylation by Pho85 also restrains the intrinsic ability of Whi7 to associate with promoters. Furthermore, although Whi5 is the main Start repressor in normal cycling cells, in the absence of Pho85, Whi7 becomes the major repressor leading to G1 arrest. Overall, our results reveal a novel mechanism by which Pho85 promotes Start through the regulation of the Whi7 repressor at multiple levels, which may confer to Whi7 a functional specialization to connect the response to adverse conditions with the cell cycle control.
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Affiliation(s)
- Cristina Ros-Carrero
- Institut de Biotecnologia i Biomedicina (BIOTECMED) and Departament de Bioquímica i Biologia Molecular, Universitat de València, 46100, Burjassot, Spain
| | - Mihai Spiridon-Bodi
- Institut de Biotecnologia i Biomedicina (BIOTECMED) and Departament de Bioquímica i Biologia Molecular, Universitat de València, 46100, Burjassot, Spain
| | - J Carlos Igual
- Institut de Biotecnologia i Biomedicina (BIOTECMED) and Departament de Bioquímica i Biologia Molecular, Universitat de València, 46100, Burjassot, Spain.
| | - Mercè Gomar-Alba
- Institut de Biotecnologia i Biomedicina (BIOTECMED) and Departament de Bioquímica i Biologia Molecular, Universitat de València, 46100, Burjassot, Spain.
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Schwarz LV, Sandri FK, Scariot F, Delamare APL, Valera MJ, Carrau F, Echeverrigaray S. High nitrogen concentration causes G2/M arrest in Hanseniaspora vineae. Yeast 2023; 40:640-650. [PMID: 37997429 DOI: 10.1002/yea.3911] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Revised: 10/26/2023] [Accepted: 11/09/2023] [Indexed: 11/25/2023] Open
Abstract
Yeasts have been widely used as a model to better understand cell cycle mechanisms and how nutritional and genetic factors can impact cell cycle progression. While nitrogen scarcity is well known to modulate cell cycle progression, the relevance of nitrogen excess for microorganisms has been overlooked. In our previous work, we observed an absence of proper entry into the quiescent state in Hanseniaspora vineae and identified a potential link between this behavior and nitrogen availability. Furthermore, the Hanseniaspora genus has gained attention due to a significant loss of genes associated with DNA repair and cell cycle. Thus, the aim of our study was to investigate the effects of varying nitrogen concentrations on H. vineae's cell cycle progression. Our findings demonstrated that nitrogen excess, regardless of the source, disrupts cell cycle progression and induces G2/M arrest in H. vineae after reaching the stationary phase. Additionally, we observed a viability decline in H. vineae cells in an ammonium-dependent manner, accompanied by increased production of reactive oxygen species, mitochondrial hyperpolarization, intracellular acidification, and DNA fragmentation. Overall, our study highlights the events of the cell cycle arrest in H. vineae induced by nitrogen excess and attempts to elucidate the possible mechanism triggering this absence of proper entry into the quiescent state.
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Affiliation(s)
- Luisa Vivian Schwarz
- Institute of Biotechnology, University of Caxias do Sul (UCS), Caxias do Sul, Rio Grande do Sul, Brazil
| | - Fernanda Knaach Sandri
- Institute of Biotechnology, University of Caxias do Sul (UCS), Caxias do Sul, Rio Grande do Sul, Brazil
| | - Fernando Scariot
- Institute of Biotechnology, University of Caxias do Sul (UCS), Caxias do Sul, Rio Grande do Sul, Brazil
| | | | - Maria Jose Valera
- Enology and Fermentation Biotechnology Area, Departamento Ciencia y Tecnología Alimentos, Facultad de Química, Universidad de la Republica, Montevideo, Uruguay
| | - Francisco Carrau
- Enology and Fermentation Biotechnology Area, Departamento Ciencia y Tecnología Alimentos, Facultad de Química, Universidad de la Republica, Montevideo, Uruguay
| | - Sergio Echeverrigaray
- Institute of Biotechnology, University of Caxias do Sul (UCS), Caxias do Sul, Rio Grande do Sul, Brazil
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Enkhbaatar T, Skoneczny M, Stępień K, Mołoń M, Skoneczna A. Live while the DNA lasts. The role of autophagy in DNA loss and survival of diploid yeast cells during chronological aging. Aging (Albany NY) 2023; 15:9965-9983. [PMID: 37815879 PMCID: PMC10599738 DOI: 10.18632/aging.205102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 09/06/2023] [Indexed: 10/12/2023]
Abstract
Aging is inevitable and affects all cell types, thus yeast cells are often used as a model in aging studies. There are two approaches to studying aging in yeast: replicative aging, which describes the proliferative potential of cells, and chronological aging, which is used for studying post-mitotic cells. While analyzing the chronological lifespan (CLS) of diploid Saccharomyces cerevisiae cells, we discovered a remarkable phenomenon: ploidy reduction during aging progression. To uncover the mechanism behind this unusual process we used yeast strains undergoing a CLS assay, looking for various aging parameters. Cell mortality, regrowth ability, autophagy induction and cellular DNA content measurements indicated that during the CLS assay, dying cells lost their DNA, and only diploids survived. We demonstrated that autophagy was responsible for the gradual loss of DNA. The nucleophagy marker activation at the start of the CLS experiment correlated with the significant drop in cell viability. The activation of piecemeal microautophagy of nucleus (PMN) markers appeared to accompany the chronological aging process until the end. Our findings emphasize the significance of maintaining at least one intact copy of the genome for the survival of post-mitotic diploid cells. During chronological aging, cellular components, including DNA, are exposed to increasing stress, leading to DNA damage and fragmentation in aging cells. We propose that PMN-dependent clearance of damaged DNA from the nucleus helps prevent genome rearrangements. However, as long as one copy of the genome can be rebuilt, cells can still survive.
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Affiliation(s)
- Tuguldur Enkhbaatar
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Marek Skoneczny
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Karolina Stępień
- Institute of Medical Sciences, Rzeszów University, Rzeszów 35-959, Poland
| | - Mateusz Mołoń
- Institute of Biology, Rzeszów University, Rzeszów 35-601, Poland
| | - Adrianna Skoneczna
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw 02-106, Poland
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Opalek M, Tutaj H, Pirog A, Smug BJ, Rutkowska J, Wloch-Salamon D. A Systematic Review on Quiescent State Research Approaches in S. cerevisiae. Cells 2023; 12:1608. [PMID: 37371078 DOI: 10.3390/cells12121608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2023] [Revised: 06/02/2023] [Accepted: 06/09/2023] [Indexed: 06/29/2023] Open
Abstract
Quiescence, the temporary and reversible arrest of cell growth, is a fundamental biological process. However, the lack of standardization in terms of reporting the experimental details of quiescent cells and populations can cause confusion and hinder knowledge transfer. We employ the systematic review methodology to comprehensively analyze the diversity of approaches used to study the quiescent state, focusing on all published research addressing the budding yeast Saccharomyces cerevisiae. We group research articles into those that consider all cells comprising the stationary-phase (SP) population as quiescent and those that recognize heterogeneity within the SP by distinguishing phenotypically distinct subpopulations. Furthermore, we investigate the chronological age of the quiescent populations under study and the methods used to induce the quiescent state, such as gradual starvation or abrupt environmental change. We also assess whether the strains used in research are prototrophic or auxotrophic. By combining the above features, we identify 48 possible experimental setups that can be used to study quiescence, which can be misleading when drawing general conclusions. We therefore summarize our review by proposing guidelines and recommendations pertaining to the information included in research articles. We believe that more rigorous reporting on the features of quiescent populations will facilitate knowledge transfer within and between disciplines, thereby stimulating valuable scientific discussion.
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Affiliation(s)
- Monika Opalek
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, 30-387 Krakow, Poland
| | - Hanna Tutaj
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, 30-387 Krakow, Poland
| | - Adrian Pirog
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, 30-387 Krakow, Poland
| | - Bogna J Smug
- Malopolska Centre of Biotechnology, Jagiellonian University, 30-387 Krakow, Poland
| | - Joanna Rutkowska
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, 30-387 Krakow, Poland
| | - Dominika Wloch-Salamon
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, 30-387 Krakow, Poland
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