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 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 Functions of the Essential Gene mraY in Cellular Morphogenesis and Development of the Filamentous Cyanobacterium Anabaena PCC 7120

2021 ◽  
Vol 12 ◽  
Author(s):  
Jing Liu ◽  
Wei-Yue Xing ◽  
Ju-Yuan Zhang ◽  
Xiaoli Zeng ◽  
Yiling Yang ◽  
...  
Keyword(s):  
Cell Division ◽  
Time Window ◽  
Essential Gene ◽  
Synthetic Activity ◽  
Filamentous Cyanobacterium ◽  
Cell Width ◽  
Cyanobacterium Anabaena ◽  
Bacterial Cell Shape ◽  
Pcc 7120 ◽  
Heterocyst Development

Bacterial cell shape is determined by the peptidoglycan (PG) layer. The cyanobacterium Anabaena sp. PCC 7120 (Anabaena) is a filamentous strain with ovoid-shaped cells connected together with incomplete cell constriction. When deprived of combined nitrogen in the growth medium, about 5–10% of the cells differentiate into heterocysts, cells devoted to nitrogen fixation. It has been shown that PG synthesis is modulated during heterocyst development and some penicillin-binding proteins (PBPs) participating in PG synthesis are required for heterocyst morphogenesis or functioning. Anabaena has multiple PBPs with functional redundancy. In this study, in order to examine the function of PG synthesis and its relationship with heterocyst development, we created a conditional mutant of mraY, a gene necessary for the synthesis of the PG precursor, lipid I. We show that mraY is required for cell and filament integrity. Furthermore, when mraY expression was being limited, persistent septal PG synthetic activity was observed, resulting in increase in cell width. Under non-permissive conditions, filaments and cells were rapidly lysed, and no sign of heterocyst development within the time window allowed was detected after nitrogen starvation. When mraY expression was being limited, a high percentage of heterocyst doublets were found. These doublets are formed likely as a consequence of delayed cell division and persistent septal PG synthesis. MraY interacts with components of both the elongasome and the divisome, in particular those directly involved in PG synthesis, including HetF, which is required for both cell division and heterocyst formation.

scholarly journals The MG1363 and IL1403 Laboratory Strains of Lactococcus lactis and Several Dairy Strains Are Diploid

2009 ◽  
Vol 192 (4) ◽  
pp. 1058-1065 ◽  
Author(s):  
Ole Michelsen ◽  
Flemming G. Hansen ◽  
Bjarne Albrechtsen ◽  
Peter Ruhdal Jensen
Keyword(s):  
Cell Cycle ◽  
Flow Cytometry ◽  
Cell Division ◽  
Dna Replication ◽  
Cell Size ◽  
Lactococcus Lactis ◽  
Uv Light ◽  
Circular Chromosome ◽  
Cellular Content ◽  
Slow Growing

ABSTRACT Bacteria are normally haploid, maintaining one copy of their genome in one circular chromosome. We have examined the cell cycle of laboratory strains of Lactococcus lactis, and, to our surprise, we found that some of these strains were born with two complete nonreplicating chromosomes. We determined the cellular content of DNA by flow cytometry and by radioactive labeling of the DNA. These strains thus fulfill the criterion of being diploid. Several dairy strains were also found to be diploid while a nondairy strain and several other dairy strains were haploid in slow-growing culture. The diploid and haploid strains differed in their sensitivity toward UV light, in their cell size, and in their D period, the period between termination of DNA replication and cell division.

scholarly journals Downward regulation of cell size in Paramecium tetraurelia: effects of increased cell size, with or without increased DNA content, on the cell cycle

1982 ◽  
Vol 57 (1) ◽  
pp. 315-329
Author(s):  
C.D. Rasmussen ◽  
J.D. Berger
Keyword(s):  
Cell Cycle ◽  
Cell Growth ◽  
Dna Synthesis ◽  
Cell Size ◽  
Dna Content ◽  
Cell Mass ◽  
Cycle Duration ◽  
Restrictive Temperature ◽  
Permissive Temperature ◽  
Rates Of Growth

Two temperature-sensitive cell-cycle mutants were used to generate abnormally large cells (size estimated by protein content) with either normal or increased DNA contents. The first mutant, cc1, blocks DNA synthesis, but allows cell growth at the restrictive temperature. The cells do not progress through the cell cycle while at the restrictive temperature, but do recover and complete the cell cycle when returned to permissive conditions. The progeny have increased cell size and normal DNA content. Downward regulation of cell size occurs during the ensuing cell cycle at permissive temperature. Two processes are involved. First, the G1 period is reduced or eliminated. As initial cell size increases there is a progressive shortening of the cell cycle to 75% of normal. This limit cell-cycle duration is reached when the initial mass of the cell is equal to or greater than that of normal cells at the time of DNA synthesis initiation (0.25 of a cell cycle). Cells with the limit cell cycle begin macronuclear DNA synthesis immediately after fission. The durations of the S period and fission are normal. Second, the rate of cell growth is unaffected by the increase in cell size, and results in the partitioning of excess cell mass between the daughter cells at the next fission. The second mutant, cc2, blocks cell division, but allows DNA synthesis to occur at a reduced rate so that cells with up to about 140% of the normal initial DNA content and twice the normal cell mass can be produced. The pattern of cell-cycle shortening is the same as in ccl. The rates of growth and both the rate and amount of DNA synthesis are proportional to the initial DNA content. This suggests that the rates of growth and DNA synthesis are limited by the transcriptional activity of the macronucleus in both cc1 and cc2 cells when they begin the cell cycle with experimentally increased cell mass. Increases in both cell size and initial DNA content are required to bring about increases in the rates of growth and DNA accumulation.

scholarly journals Inhibition of Cell Division Suppresses Heterocyst Development in Anabaena sp. Strain PCC 7120

2006 ◽  
Vol 188 (4) ◽  
pp. 1396-1404 ◽  
Author(s):  
Samer Sakr ◽  
Robert Jeanjean ◽  
Cheng-Cai Zhang ◽  
Tania Arcondeguy
Keyword(s):  
Cell Division ◽  
Fluorescent Protein ◽  
Ring Structure ◽  
Molecular Evidence ◽  
Filamentous Cyanobacterium ◽  
Heterocyst Differentiation ◽  
Ftsz Ring ◽  
Pcc 7120 ◽  
Heterocyst Development

ABSTRACT When the filamentous cyanobacterium Anabaena PCC 7120 is exposed to combined nitrogen starvation, 5 to 10% of the cells along each filament at semiregular intervals differentiate into heterocysts specialized in nitrogen fixation. Heterocysts are terminally differentiated cells in which the major cell division protein FtsZ is undetectable. In this report, we provide molecular evidence indicating that cell division is necessary for heterocyst development. FtsZ, which is translationally fused to the green fluorescent protein (GFP) as a reporter, is found to form a ring structure at the mid-cell position. SulA from Escherichia coli inhibits the GTPase activity of FtsZ in vitro and prevents the formation of FtsZ rings when expressed in Anabaena PCC 7120. The expression of sulA arrests cell division and suppresses heterocyst differentiation completely. The antibiotic aztreonam, which is targeted to the FtsI protein necessary for septum formation, has similar effects on both cell division and heterocyst differentiation, although in this case, the FtsZ ring is still formed. Therefore, heterocyst differentiation is coupled to cell division but independent of the formation of the FtsZ ring. Consistently, once the inhibitory pressure of cell division is removed, cell division should take place first before heterocyst differentiation resumes at a normal frequency. The arrest of cell division does not affect the accumulation of 2-oxoglutarate, which triggers heterocyst differentiation. Consistently, a nonmetabolizable analogue of 2-oxoglutarate does not rescue the failure of heterocyst differentiation when cell division is blocked. These results suggest that the control of heterocyst differentiation by cell division is independent of the 2-oxoglutarate signal.

scholarly journals A conserved Lkb1 signaling axis modulates TORC2 signaling in budding yeast

2018 ◽  
Author(s):  
Maria Alcaide-Gavilán ◽  
Rafael Lucena ◽  
Katherine Schubert ◽  
Karen Artiles ◽  
Jessica Zapata ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Cell Growth ◽  
Carbon Source ◽  
Cell Size ◽  
Nutrient Availability ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Small Cells ◽  
Cycle Progression

ABSTRACTNutrient availability, growth rate and cell size are closely linked. For example, in budding yeast, the rate of cell growth is proportional to nutrient availability, cell size is proportional to growth rate, and growth rate is proportional to cell size. Thus, cells grow slowly in poor nutrients and are nearly half the size of cells growing in rich nutrients. Moreover, large cells grow faster than small cells. A signaling network that surrounds Tor kinase complex 2 (TORC2) plays an important role in enforcing these proportional relationships. Cells that lack components of the TORC2 network fail to modulate their growth rate or size in response to changes in nutrient availability. Here, we show that budding yeast homologs of the Lkb1 tumor suppressor kinase are required for normal modulation of TORC2 signaling and in response to changes in carbon source. Lkb1 kinases activate Snf1/AMPK to initiate transcription of genes required for utilization of poor carbon sources. However, Lkb1 influences TORC2 signaling via a novel pathway that is independent of Snf1/AMPK. Of the three Lkb1 homologs in budding yeast, Elm1 plays the most important role in modulating TORC2. Elm1 activates a pair of related kinases called Gin4 and Hsl1. Previous work found that loss of Gin4 and Hsl1 causes cells to undergo unrestrained growth during a prolonged mitotic arrest, which suggests that play a role in linking cell cycle progression to cell growth. We found that Gin4 and Hsl1 also control the TORC2 network. In addition, Gin4 and Hsl1 are themselves influenced by signals from the TORC2 network, consistent with previous work showing that the TORC2 network constitutes a feedback loop. Together, the data suggest a model in which the TORC2 network sets growth rate in response to carbon source, while also relaying signals via Gin4 and Hsl1 that set the critical amount of growth required for cell cycle progression. This kind of close linkage between control of cell growth and size would suggest a simple mechanistic explanation for the proportional relationship between cell size and growth rate.

scholarly journals Large cells activate global protein degradation to maintain cell size homeostasis

2021 ◽  
Author(s):  
Shixuan Liu ◽  
Ceryl Tan ◽  
Chloe Melo-Gavin ◽  
Kevin G. Mark ◽  
Miriam Bracha Ginzberg ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Cell Size ◽  
Cell Cycle Progression ◽  
Mapk Pathway ◽  
Cellular Growth ◽  
Small Cells ◽  
Animal Cells ◽  
Size Dependent

Proliferating animal cells maintain a stable size distribution over generations despite fluctuations in cell growth and division size. This tight control of cell size involves both cell size checkpoints (e.g., delaying cell cycle progression for small cells) and size-dependent compensation in rates of mass accumulation (e.g., slowdown of cellular growth in large cells). We previously identified that the mammalian cell size checkpoint is mediated by a selective activation of the p38 MAPK pathway in small cells. However, mechanisms underlying the size-dependent compensation of cellular growth remain unknown. In this study, we quantified global rates of protein synthesis and degradation in naturally large and small cells, as well as in conditions that trigger a size-dependent compensation in cellular growth. Rates of protein synthesis increase proportionally with cell size in both perturbed and unperturbed conditions, as well as across cell cycle stages. Additionally, large cells exhibit elevated rates of global protein degradation and increased levels of activated proteasomes. Conditions that trigger a large-size-induced slowdown of cellular growth also promote proteasome-mediated global protein degradation, which initiates only after growth rate compensation occurs. Interestingly, the elevated rates of global protein degradation in large cells were disproportionately higher than the increase in size, suggesting activation of protein degradation pathways. Large cells at the G1/S transition show hyperactivated levels of protein degradation, even higher than similarly sized or larger cells in S or G2, coinciding with the timing of the most stringent size control in animal cells. Together, these findings suggest that large cells maintain cell size homeostasis by activating global protein degradation to induce a compensatory slowdown of growth.

scholarly journals The Ethanologenic Bacterium Zymomonas mobilis Divides Asymmetrically and Exhibits Heterogeneity in DNA Content

2021 ◽  
Vol 87 (6) ◽  
Author(s):  
Katsuya Fuchino ◽  
Helena Chan ◽  
Ling Chin Hwang ◽  
Per Bruheim
Keyword(s):  
Cell Growth ◽  
Single Cell ◽  
Cell Size ◽  
Dna Content ◽  
Bacterial Cell ◽  
Zymomonas Mobilis ◽  
Biofuel Production ◽  
Public Attention ◽  
Content Type ◽  
Cell Organization

ABSTRACT The alphaproteobacterium Zymomonas mobilis exhibits extreme ethanologenic physiology, making this species a promising biofuel producer. Numerous studies have investigated its biology relevant to industrial applications and mostly at the population level. However, the organization of single cells in this industrially important polyploid species has been largely uncharacterized. In the present study, we characterized basic cellular behavior of Z. mobilis strain Zm6 under anaerobic conditions at the single-cell level. We observed that growing Z. mobilis cells often divided at a nonmidcell position, which contributed to variant cell size at birth. However, the cell size variance was regulated by a modulation of cell cycle span, mediated by a correlation of bacterial tubulin homologue FtsZ ring accumulation with cell growth. The Z. mobilis culture also exhibited heterogeneous cellular DNA content among individual cells, which might have been caused by asynchronous replication of chromosome that was not coordinated with cell growth. Furthermore, slightly angled divisions might have resulted in temporary curvatures of attached Z. mobilis cells. Overall, the present study uncovers a novel bacterial cell organization in Z. mobilis. IMPORTANCE With increasing environmental concerns about the use of fossil fuels, development of a sustainable biofuel production platform has been attracting significant public attention. Ethanologenic Z. mobilis species are endowed with an efficient ethanol fermentation capacity that surpasses, in several respects, that of baker’s yeast (Saccharomyces cerevisiae), the most-used microorganism for ethanol production. For development of a Z. mobilis culture-based biorefinery, an investigation of its uncharacterized cell biology is important, because bacterial cellular organization and metabolism are closely associated with each other in a single cell compartment. In addition, the current work demonstrates that the polyploid bacterium Z. mobilis exhibits a distinctive mode of bacterial cell organization, likely reflecting its unique metabolism that does not prioritize incorporation of nutrients for cell growth. Thus, another significant result of this work is to advance our general understanding in the diversity of bacterial cell architecture.

scholarly journals Size uniformity of animal cells is actively maintained by a p38 MAPK-dependent regulation of G1-length

2017 ◽  
Author(s):  
Shixuan Liu ◽  
Miriam B. Ginzberg ◽  
Nish Patel ◽  
Marc Hild ◽  
Bosco Leung ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
P38 Mapk ◽  
Cell Cycle Progression ◽  
Molecular Mechanisms ◽  
Mapk Pathway ◽  
Small Cells ◽  
Animal Cells ◽  
Cycle Progression ◽  
Size Uniformity

AbstractAnimal cells within a tissue typically display a striking regularity in their size. To date, the molecular mechanisms that control this uniformity are still unknown. We have previously shown that size uniformity in animal cells is promoted, in part, by size-dependent regulation of G1 length. To identify the molecular mechanisms underlying this process, we performed a large-scale small molecule screen and found that the p38 MAPK pathway is involved in coordinating cell size and cell cycle progression. Small cells display higher p38 activity and spend more time in G1 than larger cells. Inhibition of p38 MAPK leads to loss of the compensatory G1 length extension in small cells, resulting in faster proliferation, smaller cell size and increased size heterogeneity. We propose a model wherein the p38 pathway responds to changes in cell size and regulates G1 exit accordingly, to increase cell size uniformity.One-sentence summaryThe p38 MAP kinase pathway coordinates cell growth and cell cycle progression by lengthening G1 in small cells, allowing them more time to grow before their next division.

Sign in / Sign up

Export Citation Format

Share Document