scholarly journals Cell growth dilutes the cell cycle inhibitor Rb to trigger cell division

2018 ◽  
Author(s):  
Evgeny Zatulovskiy ◽  
Daniel F. Berenson ◽  
Benjamin R. Topacio ◽  
Jan M. Skotheim
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Cell Growth ◽  
Cell Size ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Inverse Correlation ◽  
Cell Types ◽  
Similar Amount ◽  
Cell Cycle Inhibitor

Cell size is fundamental to function in different cell types across the human body because it sets the scale of organelle structures, biosynthesis, and surface transport1,2. Tiny erythrocytes squeeze through capillaries to transport oxygen, while the million-fold larger oocyte divides without growth to form the ~100 cell pre-implantation embryo. Despite the vast size range across cell types, cells of a given type are typically uniform in size likely because cells are able to accurately couple cell growth to division3–6. While some genes whose disruption in mammalian cells affects cell size have been identified, the molecular mechanisms through which cell growth drives cell division have remained elusive7–12. Here, we show that cell growth acts to dilute the cell cycle inhibitor Rb to drive cell cycle progression from G1 to S phase in human cells. In contrast, other G1/S regulators remained at nearly constant concentration. Rb is a stable protein that is synthesized during S and G2 phases in an amount that is independent of cell size. Equal partitioning to daughter cells of chromatin bound Rb then ensures that all cells at birth inherit a similar amount of Rb protein. RB overexpression increased cell size in tissue culture and a mouse cancer model, while RB deletion decreased cell size and removed the inverse correlation between cell size at birth and the duration of G1 phase. Thus, Rb-dilution by cell growth in G1 provides a long-sought cell autonomous molecular mechanism for cell size homeostasis.

scholarly journals Relationship among Several Key Cell Cycle Events in the Developmental Cyanobacterium Anabaena sp. Strain PCC 7120

2006 ◽  
Vol 188 (16) ◽  
pp. 5958-5965 ◽  
Author(s):  
Samer Sakr ◽  
Melilotus Thyssen ◽  
Michel Denis ◽  
Cheng-Cai Zhang
Keyword(s):  
Cell Cycle ◽  
Flow Cytometry ◽  
Cell Division ◽  
Cell Growth ◽  
Cell Size ◽  
Dna Content ◽  
Small Cells ◽  
Filamentous Cyanobacterium ◽  
Pcc 7120 ◽  
Heterocyst Development

ABSTRACT When grown in the absence of a source of combined nitrogen, the filamentous cyanobacterium Anabaena sp. strain PCC 7120 develops, within 24 h, a differentiated cell type called a heterocyst that is specifically involved in the fixation of N2. Cell division is required for heterocyst development, suggesting that the cell cycle could control this developmental process. In this study, we investigated several key events of the cell cycle, such as cell growth, DNA synthesis, and cell division, and explored their relationships to heterocyst development. The results of analyses by flow cytometry indicated that the DNA content increased as the cell size expanded during cell growth. The DNA content of heterocysts corresponded to the subpopulation of vegetative cells that had a big cell size, presumably those at the late stages of cell growth. Consistent with these results, most proheterocysts exhibited two nucleoids, which were resolved into a single nucleoid in most mature heterocysts. The ring structure of FtsZ, a protein required for the initiation of bacterial cell division, was present predominantly in big cells and rarely in small cells. When cell division was inhibited and consequently cells became elongated, little change in DNA content was found by measurement using flow cytometry, suggesting that inhibition of cell division may block further synthesis of DNA. The overexpression of minC, which encodes an inhibitor of FtsZ polymerization, led to the inhibition of cell division, but cells expanded in spherical form to become giant cells; structures with several cells attached together in the form of a cloverleaf could be seen frequently. These results may indicate that the relative amounts of FtsZ and MinC affect not only cell division but also the placement of the cell division planes and the cell morphology. MinC overexpression blocked heterocyst differentiation, consistent with the requirement of cell division in the control of heterocyst development.

scholarly journals Size control in mammalian cells involves modulation of both growth rate and cell cycle duration

2017 ◽  
Author(s):  
Clotilde Cadart ◽  
Sylvain Monnier ◽  
Jacopo Grilli ◽  
Rafaele Attia ◽  
Emmanuel Terriac ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Cell Division ◽  
Cell Growth ◽  
Single Cell ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Size Control ◽  
Cycle Duration ◽  
Mathematical Framework

SummaryDespite decades of research, it remains unclear how mammalian cell growth varies with cell size and across the cell division cycle to maintain size control. Answers have been limited by the difficulty of directly measuring growth at the single cell level. Here we report direct measurement of single cell volumes over complete cell division cycles. The volume added across the cell cycle was independent of cell birth size, a size homeostasis behavior called “adder”. Single-cell growth curves revealed that the homeostatic behavior relied on adaptation of G1 duration as well as growth rate modulations. We developed a general mathematical framework that characterizes size homeostasis behaviors. Applying it on datasets ranging from bacteria to mammalian cells revealed that a near-adder is the most common type of size control, but only mammalian cells achieve it using modulation of both cell growth rate and cell-cycle progression.

scholarly journals Distinct and sequential re-replication barriers ensure precise genome duplication

2018 ◽  
Author(s):  
Yizhuo Zhou ◽  
Pedro N. Pozo ◽  
Seeun Oh ◽  
Haley M. Stone ◽  
Jeanette Gowen Cook
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Dna Replication ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Genome Duplication ◽  
Dna Helicase ◽  
Cell Division Cycle ◽  
G1 Phase ◽  
Cycle Phase

AbstractAchieving complete and precise genome duplication requires that each genomic segment be replicated only once per cell division cycle. Protecting large eukaryotic genomes from re-replication requires an overlapping set of molecular mechanisms that prevent the first DNA replication step, the DNA loading of MCM helicase complexes to license replication origins. Previous reports have defined many such origin licensing inhibition mechanisms, but the temporal relationships among them are not clear, particularly with respect to preventing re-replication in G2 and M phases. Using a combination of mutagenesis, biochemistry, and single cell analyses in human cells, we define a new mechanism that prevents re-replication through hyperphosphorylation of the essential MCM loading protein, Cdt1. We demonstrate that Cyclin A/CDK1 hyperphosphorylates Cdt1 to inhibit MCM re-loading in G2 phase. The mechanism of inhibition is to block Cdt1 binding to MCM independently of other known Cdt1 inactivation mechanisms such as Cdt1 degradation during S phase or Geminin binding. Moreover, we provide evidence that protein phosphatase 1-dependent Cdt1 dephosphorylation at the mitosis-to-G1 phase transition re-activates Cdt1. We propose that multiple distinct, non-redundant licensing inhibition mechanisms act in a series of sequential relays through each cell cycle phase to ensure precise genome duplication.Author SummaryThe initial step of DNA replication is loading the DNA helicase, MCM, onto DNA during the first phase of the cell division cycle. If MCM loading occurs inappropriately onto DNA that has already been replicated, then cells risk DNA re-replication, a source of endogenous DNA damage and genome instability. How mammalian cells prevent any sections of their very large genomes from re-replicating is still not fully understood. We found that the Cdt1 protein, one of the critical MCM loading factors, is inhibited specifically in late cell cycle stages through a mechanism involving protein phosphorylation. This phosphorylation prevents Cdt1 from binding MCM; when Cdt1 can’t be phosphorylated MCM is inappropriately re-loaded onto DNA and cells are prone to re-replication. When cells divide and transition into G1 phase, Cdt1 is then dephosphorylated to re-activate it for MCM loading. Based on these findings we assert that the different mechanisms that cooperate to avoid re-replication are not redundant, but rather distinct mechanisms are dominant in different cell cycle phases. These findings have implications for understanding how genomes are duplicated precisely once per cell cycle and shed light on how that process is perturbed by changes in Cdt1 levels or phosphorylation activity.

scholarly journals Bacterial cell proliferation: from molecules to cells

2020 ◽  
Author(s):  
Alix Meunier ◽  
François Cornet ◽  
Manuel Campos
Keyword(s):  
Cell Cycle ◽  
Cell Proliferation ◽  
Cell Division ◽  
Dna Replication ◽  
Cell Growth ◽  
Bacterial Cell ◽  
Cell Biology ◽  
Molecular Mechanisms ◽  
Cell Physiology ◽  
Precise Knowledge

ABSTRACT Bacterial cell proliferation is highly efficient, both because bacteria grow fast and multiply with a low failure rate. This efficiency is underpinned by the robustness of the cell cycle and its synchronization with cell growth and cytokinesis. Recent advances in bacterial cell biology brought about by single-cell physiology in microfluidic chambers suggest a series of simple phenomenological models at the cellular scale, coupling cell size and growth with the cell cycle. We contrast the apparent simplicity of these mechanisms based on the addition of a constant size between cell cycle events (e.g. two consecutive initiation of DNA replication or cell division) with the complexity of the underlying regulatory networks. Beyond the paradigm of cell cycle checkpoints, the coordination between the DNA and division cycles and cell growth is largely mediated by a wealth of other mechanisms. We propose our perspective on these mechanisms, through the prism of the known crosstalk between DNA replication and segregation, cell division and cell growth or size. We argue that the precise knowledge of these molecular mechanisms is critical to integrate the diverse layers of controls at different time and space scales into synthetic and verifiable models.

scholarly journals A G1 sizer mechanism coordinates growth and division in the mouse epidermis

2019 ◽  
Author(s):  
Shicong Xie ◽  
Jan M. Skotheim
Keyword(s):  
Cell Cycle ◽  
Cell Growth ◽  
Cell Size ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Single Cells ◽  
Mouse Skin ◽  
Mouse Epidermis ◽  
Cycle Progression

SummaryCell size homeostasis is often achieved by coupling cell cycle progression to cell growth. Studies of cell size homeostasis in single-celled bacteria and yeast have observed several distinct phenomena. Growth can be coupled to division through a range of mechanisms, including a ‘sizer’, wherein cells of varying birth size divide at similar final sizes [1–3], and an ‘adder’, wherein cells increase in size a fixed amount per cell cycle [4–6]. Importantly, intermediate control mechanisms are observed, and even the same organism can exhibit distinct control phenomena depending on growth conditions [2,7,8]. While studying unicellular organisms in laboratory conditions may give insight into their growth control in the wild, this is less apparent for studies of mammalian cells growing outside the organism. Sizer, adder, and intermediate mechanisms have been observed in vitro [9–12], but it is unclear how these diverse size homeostasis phenomena relate to mammalian cell proliferation in vivo. To address this gap, we analyzed time-lapse images of the mouse epidermis taken over one week during normal tissue turnover [13]. We quantified the 3D volume growth and cell cycle progression of single cells within the mouse skin. In dividing epidermal stem cells, we found that cell growth is coupled to division through a sizer mechanism operating largely in the G1 phase. Thus, while the majority of tissue culture studies to-date identified adder mechanisms, our analysis demonstrates that sizer mechanisms are important in vivo and highlights the need to determine their underlying molecular origin.

scholarly journals Exploring the Intracrine Functions of VEGF-A

Biomolecules ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 128
Author(s):  
Sophie Wiszniak ◽  
Quenten Schwarz
Keyword(s):  
Cell Growth ◽  
Molecular Mechanisms ◽  
Direct Action ◽  
Cancer Therapeutics ◽  
Cell Types ◽  
Vascular Endothelial ◽  
Signalling Molecule ◽  
Endothelial Growth Factor ◽  
Important Signalling Molecule ◽  
Vegf Signalling

Vascular endothelial growth factor A (VEGF-A or VEGF) is a highly conserved secreted signalling protein best known for its roles in vascular development and angiogenesis. Many non-endothelial roles for VEGF are now established, with the discovery that VEGF and its receptors VEGFR1 and VEGFR2 are expressed in many non-vascular cell-types, as well as various cancers. In addition to secreted VEGF binding to its receptors in the extracellular space at the cell membrane (i.e., in a paracrine or autocrine mode), intracellularly localised VEGF is emerging as an important signalling molecule regulating cell growth, survival, and metabolism. This intracellular mode of signalling has been termed “intracrine”, and refers to the direct action of a signalling molecule within the cell without being secreted. In this review, we describe examples of intracrine VEGF signalling in regulating cell growth, differentiation and survival, both in normal cell homeostasis and development, as well as in cancer. We further discuss emerging evidence for the molecular mechanisms underpinning VEGF intracrine function, as well as the implications this intracellular mode of VEGF signalling may have for use and design of anti-VEGF cancer therapeutics.

Overexpression Phenotypes of Plk1 and Ndrg2 in Schizosaccharomyces Pombe: Fission Yeast System for Mammalian Gene Study

2005 ◽  
Vol 277-279 ◽  
pp. 1-6 ◽  
Author(s):  
Young Joo Jang ◽  
Young Sook Kil ◽  
Jee Hee Ahn ◽  
Jae Hoon Ji ◽  
Jong Seok Lim ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Schizosaccharomyces Pombe ◽  
Fission Yeast ◽  
Rna Splicing ◽  
Mammalian Cells ◽  
Protein Modification ◽  
Genetic System ◽  
Functional Study ◽  
Mammalian Genes

The fission yeast, Schizosaccharomyces pombe is a single-celled free-living fungus that shares many features with cells of more complicated eukaryotes. Many of the genes required for the cell-cycle control, proteolysis, protein modification, and RNA splicing are highly conserved with those of higher eukaryotes. Moreover, fission yeast has the merit of genetics and its genetic system is already well characterized. As such, the current study evaluated the use of a fission yeast system as a tool for the functional study of mammalian genes and attempted to set up an assay system for novel genes. Since the phenotypes of a deletion mutant and the overexpression of a gene are generally analyzed for a functional study of specific genes in yeast, the present study used overexpression phenotypes to study the functions of mammalian genes. Therefore, based on using a thiamine-repressive promoter, two mammalian genes were expressed in fission yeast, and their overexpressed phenotypes compared with those in mammalian cells. The phenotypes resulting from overexpression were analyzed using a FACS, which analyzes the DNA contents, and a microscope. One of the selected genes was the mammalian Polo-like kinase 1 (Plk1), which is activated and plays a role in the mitotic phase of the cell division cycle. The overexpression of various constructs of Plk1 in the HeLa cells caused cell cycle defects, suggesting that the ectopic Plk1s blocked the endogenous Plk1 in the cells. As expected, when the constructs were overexpressed in the fission yeast system, the cells were arrested in mitosis and defected at the end of mitosis. As such, this data suggests that the Plk1-overexpressed phenotypes were similar in the mammalian cells and the fission yeast, thereby enabling the mammalian Plk1 functions to be approximated in the fission yeast. The other selected gene was the N-Myc downstream-regulated gene 2 (ndrg2), which is upregulated during cell differentiation, yet still not well characterized. When the ndrg2 gene was overexpressed in the fission yeast, the cells contained multi-septa. The septa were positioned well, yet their number increased per cell. Therefore, this gene was speculated to block cell division in the last stage of the cell cycle, making the phenotype potentially useful for explaining cell growth and differentiation in mammalian cells. Accordingly, fission yeast is demonstrated to be an appropriate species for the functional study of mammalian genes.

The structural mechanics of cell division in Trypanosoma brucei

2008 ◽  
Vol 36 (3) ◽  
pp. 421-424 ◽  
Author(s):  
Sue Vaughan ◽  
Keith Gull
Keyword(s):  
Cell Division ◽  
Trypanosoma Brucei ◽  
Mammalian Cells ◽  
Reverse Genetics ◽  
Protozoan Parasite ◽  
Cell Types ◽  
Single Copy ◽  
Structural Mechanics ◽  
Sub Saharan Africa ◽  
Mammalian Host

Undoubtedly, there are fundamental processes driving the structural mechanics of cell division in eukaryotic organisms that have been conserved throughout evolution and are being revealed by studies on organisms such as yeast and mammalian cells. Precision of structural mechanics of cytokinesis is however probably no better illustrated than in the protozoa. A dramatic example of this is the protozoan parasite Trypanosoma brucei, a unicellular flagellated parasite that causes a devastating disease (African sleeping sickness) across Sub-Saharan Africa in both man and animals. As trypanosomes migrate between and within a mammalian host and the tsetse vector, there are periods of cell proliferation and cell differentiation involving at least five morphologically distinct cell types. Much of the existing cytoskeleton remains intact during these processes, necessitating a very precise temporal and spatial duplication and segregation of the many single-copy organelles. This structural precision is aiding progress in understanding these processes as we apply the excellent reverse genetics and post-genomic technologies available in this system. Here we outline our current understanding of some of the structural aspects of cell division in this fascinating organism.

scholarly journals Generation of asymmetry during development. Segregation of type-specific proteins in Caulobacter.

1979 ◽  
Vol 81 (1) ◽  
pp. 123-136 ◽  
Author(s):  
N Agabian ◽  
M Evinger ◽  
G Parker
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Messenger Rna ◽  
Cell Types ◽  
Specific Protein ◽  
Soluble Proteins ◽  
Specific Cell ◽  
Daughter Cells ◽  
Specific Proteins ◽  
Entire Cell

An essential event in developmental processes is the introduction of asymmetry into an otherwise undifferentiated cell population. Cell division in Caulobacter is asymmetric; the progeny cells are structurally different and follow different sequences of development, thus providing a useful model system for the study of differentiation. Because the progeny cells are different from one another, there must be a segregation of morphogenetic and informational components at some time in the cell cycle. We have examined the pattern of specific protein segregation between Caulobacter stalked and swarmer daughter cells, with the rationale that such a progeny analysis would identify both structurally and developmentally important proteins. To complement the study, we have also examined the pattern of protein synthesis during synchronous growth and in various cellular fractions. We show here, for the first time, that the association of proteins with a specific cell type may result not only from their periodicity of synthesis, but also from their pattern of distribution at the time of cell division. Several membrane-associated and soluble proteins are segregated asymmetrically between progeny stalked and swarmer cells. The data further show that a subclass of soluble proteins becomes associated with the membrane of the progeny stalked cells. Therefore, although the principal differentiated cell types possess different synthetic capabilities and characteristic proteins, the asymmetry between progeny stalked and swarmer cells is generated primarily by the preferential association of specific soluble proteins with the membrane of only one daughter cell. The majority of the proteins which exhibit this segregation behavior are synthesized during the entire cell cycle and exhibit relatively long, functional messenger RNA half-lives.

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