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.

Initiation and termination of macronuclear DNA synthesis in Paramecium: effect of variation in macronuclear DNA content

1982 ◽  
Vol 60 (10) ◽  
pp. 2501-2506 ◽  
Author(s):  
James D. Berger
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Dna Content ◽  
Relative Rate ◽  
Cell Mass ◽  
Mutant Gene ◽  
Synthesis Rate ◽  
Cycle Duration ◽  
Rate Of Increase ◽  
Wide Range

The timing of both initiation and termination of DNA synthesis was examined in Paramecium cells with an unusually wide range of DNA contents. Variation in DNA content was increased through the action of a mutant gene, tamG, which interferes with macronuclear amitosis. The major conclusions are (1) timing of initiation of DNA synthesis is unaffected by G1 macronuclear DNA content and (2) the duration of the S phase of the cell cycle increases only slightly with increasing macronuclear DNA content. Since Paramecium cells with increased DNA content do not synthesize increased amounts of DNA, the present observations imply that the absolute rate of increase in DNA content remains constant, while the relative rate of DNA synthesis (rate per unit DNA) decreases as initial DNA content increases. The implications of these conclusions for regulation of macronuclear DNA content, cell mass, and cell cycle duration are discussed.

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 MEIOTIC RECOMBINATION AND DNA SYNTHESIS IN A NEW CELL CYCLE MUTANT OF SACCHAROMYCES CEREVISIAE

Genetics ◽  
1978 ◽  
Vol 90 (1) ◽  
pp. 49-68
Author(s):  
Yona Kassir ◽  
Giora Simchen
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Nuclear Division ◽  
Temperature Shift ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Permissive Temperature ◽  
Essential Function ◽  
Normal Meiosis

ABSTRACT Vegetative cells carrying the new temperature-sensitive mutation cdc40 arrest at the restrictive temperature with a medial nuclear division phenotype. DNA replication is observed under these conditions, but most cells remain sensitive to hydroxyurea and do not complete the ongoing cell cycle if the drug is present during release from the temperature block. It is suggested that the cdc40 lesion affects an essential function in DNA synthesis. Normal meiosis is observed at the permissive temperature in cdc40 homozygotes. At the restrictive temperature, a full round of premeiotic DNA replication is observed, but neither commitment to recombination nor later meiotic events occur. Meiotic cells that are already committed to the recombination process at the permissive temperature do not complete it if transferred to the restrictive temperature before recombination is realized. These temperature shift-up experiments demonstrate that the CDC40 function is required for the completion of recombination events, as well as for the earlier stage of recombination commitment. Temperature shift-down experiments with cdc40 homozygotes suggest that meiotic segregation depends on the final events of recombination rather than on commitment to recombination.

Cell size modulation by CDC25 and RAS2 genes in Saccharomyces cerevisiae

1989 ◽  
Vol 9 (6) ◽  
pp. 2715-2723
Author(s):  
M D Baroni ◽  
E Martegani ◽  
P Monti ◽  
L Alberghina
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Culture Media ◽  
Control Cell ◽  
Cell Mass ◽  
Growth Conditions ◽  
Growth Defect ◽  
Permissive Temperature ◽  
Wild Type ◽  
Nutritional Conditions

A detailed kinetic analysis of the cell cycle of cdc25-1, RAS2Val-19, or cdc25-1/RAS2Val-19 mutants during exponential growth is presented. At the permissive temperature (24 degrees C), cdc25-1 cells show a longer G1/unbudded phase of the cell cycle and have a smaller critical cell size required for budding without changing the growth rate in comparison to an isogenic wild type. The RAS2Val-19 mutation efficiently suppresses the ts growth defect of the cdc25-1 mutant at 36 degrees C and the increase of G1 phase at 24 degrees C. Moreover, it causes a marked increase of the critical cell mass required to enter into a new cell division cycle compared with that of the wild type. Since the critical cell mass is physiologically modulated by nutritional conditions, we have also studied the behavior of these mutants in different media. The increase in cell size caused by the RAS2Val-19 mutation is evident in all tested growth conditions, while the effect of cdc25-1 is apparently more pronounced in rich culture media. CDC25 and RAS2 gene products have been showed to control cell growth by regulating the cyclic AMP metabolic pathway. Experimental evidence reported herein suggests that the modulation of the critical cell size by CDC25 and RAS2 may involve adenylate cyclase.

The transient division block in the D9ts mutant of Tetrahymena is inducible at every cell cycle stage

1989 ◽  
Vol 92 (3) ◽  
pp. 349-352
Author(s):  
G. Cleffmann
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Specific Growth ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Permissive Temperature ◽  
Division Rate ◽  
Temperature Pulse ◽  
Controlling System ◽  
Size Controlling

The temperature-sensitive mutant D9 of Tetrahymena thermophila doubles its size at restrictive temperature. It does so by complete cessation of cell division for a limited time. After resumption of proliferation, division rate and specific growth rate are the same as at the permissive temperature, thereby maintaining the new cell size. In this study a detailed analysis of the process of controlling the new cell size is presented, by probing the temperature sensitivity of cell cycle phases. It will be shown that high temperature affects the size-controlling system immediately upon shift in temperature. Temperature pulses are effective at every stage in the cycle and are executed at the time of expected division. After return to the permissive temperature, cells gradually recover from the temperature pulse as seen by a decrease in division delay. Preparation for the next division is unaffected by the temperature pulse. It occurs at the same time as in untreated controls. The results allow us to describe some features of the division initiating system.

scholarly journals Cell size modulation by CDC25 and RAS2 genes in Saccharomyces cerevisiae.

1989 ◽  
Vol 9 (6) ◽  
pp. 2715-2723 ◽  
Author(s):  
M D Baroni ◽  
E Martegani ◽  
P Monti ◽  
L Alberghina
Keyword(s):  
Cell Cycle ◽  
Cell Size ◽  
Culture Media ◽  
Control Cell ◽  
Cell Mass ◽  
Growth Conditions ◽  
Growth Defect ◽  
Permissive Temperature ◽  
Wild Type ◽  
Nutritional Conditions

A detailed kinetic analysis of the cell cycle of cdc25-1, RAS2Val-19, or cdc25-1/RAS2Val-19 mutants during exponential growth is presented. At the permissive temperature (24 degrees C), cdc25-1 cells show a longer G1/unbudded phase of the cell cycle and have a smaller critical cell size required for budding without changing the growth rate in comparison to an isogenic wild type. The RAS2Val-19 mutation efficiently suppresses the ts growth defect of the cdc25-1 mutant at 36 degrees C and the increase of G1 phase at 24 degrees C. Moreover, it causes a marked increase of the critical cell mass required to enter into a new cell division cycle compared with that of the wild type. Since the critical cell mass is physiologically modulated by nutritional conditions, we have also studied the behavior of these mutants in different media. The increase in cell size caused by the RAS2Val-19 mutation is evident in all tested growth conditions, while the effect of cdc25-1 is apparently more pronounced in rich culture media. CDC25 and RAS2 gene products have been showed to control cell growth by regulating the cyclic AMP metabolic pathway. Experimental evidence reported herein suggests that the modulation of the critical cell size by CDC25 and RAS2 may involve adenylate cyclase.

Identification of temperature-sensitive DNA- mutants of Chinese hamster cells affected in cellular and viral DNA synthesis

1986 ◽  
Vol 6 (12) ◽  
pp. 4594-4601
Author(s):  
J J Dermody ◽  
B E Wojcik ◽  
H Du ◽  
H L Ozer
Keyword(s):  
Dna Replication ◽  
Dna Synthesis ◽  
Chinese Hamster ◽  
Human Adenovirus ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Permissive Temperature ◽  
Dependent Manner ◽  
Viral Dna ◽  
Cell Functions

We described a strategy which facilitates the identification of cell mutants which are restricted in DNA synthesis in a temperature-dependent manner. A collection of over 200 cell mutants temperature-sensitive for growth was isolated in established Chinese hamster cell lines (CHO and V79) by a variety of selective and nonselective techniques. Approximately 10% of these mutants were identified as ts DNA- based on differential inhibition of macromolecular synthesis at the restrictive temperature (39 degrees C) as assessed by incorporation of [3H]thymidine and [35S]methionine. Nine such mutants, selected for further study, demonstrated rapid shutoff of DNA replication at 39 degrees C. Infections with two classes of DNA viruses extensively dependent on host-cell functions for their replication were used to distinguish defects in DNA synthesis itself from those predominantly affecting other aspects of DNA replication. All cell mutants supported human adenovirus type 2 (Ad2) and mouse polyomavirus DNA synthesis at the permissive temperature. Five of the nine mutants (JB3-B, JB3-O, JB7-K, JB8-D, and JB11-J) restricted polyomavirus DNA replication upon transfection with viral sequences at 33 degrees C and subsequent shift to 39 degrees C either before or after the onset of viral DNA synthesis. Only one of these mutants (JB3-B) also restricted Ad2 DNA synthesis after virion infection under comparable conditions. No mutant was both restrictive for Ad2 and permissive for polyomavirus DNA synthesis at 39 degrees C. The differential effect of these cell mutants on viral DNA synthesis is expected to assist subsequent definition of the biochemical defect responsible.

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 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.

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