Timing of the phases of the cell cycle during the period of asynchronous division up to the 49-cell stage in Lymnaea

Development ◽  
1971 ◽  
Vol 26 (3) ◽  
pp. 367-391
Author(s):  
J. A. M. van den Biggelaar
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Bilateral Symmetry ◽  
Supporting Evidence ◽  
Cell Stage ◽  
Vegetative Cells ◽  
Animal Pole ◽  
Cell Cycles ◽  
Cell Embryo ◽  
In Cells

The duration of the phases of the cell cycle (M-G1–S-G2) has been determined from the 8-up to the 49-cell stage in eggs of Lymnaea, using autoradiography and cytophotometry of Feulgen-stained nuclei. Division asynchrony of corresponding cells in different quadrants is primarily caused by unequal lengthening of the G2 phases. In general it appeared that in the vegetative cells lengthening of the cell cycles is chiefly due to an extension of the G2 phases, whereas in the cells of the animal half the duration of both the S and the G2 phases are extended. DNA synthesis is not blocked in cells which stop dividing and start to differentiate. A conspicuous lengthening of the cell cycles is observed in the 16- and 24-cell embryo; this is accompanied with the reappearance of distinct nucleoli. Supporting evidence has been obtained for the assumption that bilateral symmetry at the animal pole of the embryo is induced by cells from the vegetative hemisphere, presumably by the macromere 3D, during the 24-cell stage.

Timing of the phases of the cell cycle with tritiated thymidine and Feulgen cytophotometry during the period of synchronous division in Lymnaea

Development ◽  
1971 ◽  
Vol 26 (3) ◽  
pp. 351-366
Author(s):  
J. A. M. van den Biggelaar
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Tritiated Thymidine ◽  
S Phase ◽  
Energy Requirements ◽  
G1 Phase ◽  
Cell Stage ◽  
Cell Cycles ◽  
Feulgen Cytophotometry

The duration of the phases of the cell cycle during the 1-, the 2- and the 4-cell stage of the Lymnaea egg were determined with [3H]thymidine and with Feulgen cytophotometry. The M, S and G2 phases occupy 48, 27 and 25% of the first three cell cycles. A G1 phase cannot be observed. Only from the 4-cell stage was [3H]thymidine readily incorporated into DNA. The theory that an increase in respiration during the S phase of the 4-cell stage is connected with the energy requirements of DNA synthesis is discussed.

Brief cytochalasin-induced disruption of microfilaments during a critical interval in 1-cell C. elegans embryos alters the partitioning of developmental instructions to the 2-cell embryo

Development ◽  
1990 ◽  
Vol 108 (1) ◽  
pp. 159-172 ◽  
Author(s):  
D.P. Hill ◽  
S. Strome
Keyword(s):  
Cell Cycle ◽  
Asymmetric Cell Division ◽  
Critical Time ◽  
Time Interval ◽  
Critical Interval ◽  
Cell Stage ◽  
C Elegans ◽  
Daughter Cells ◽  
Correct Pattern ◽  
Cell Embryo

We are investigating the involvement of the microfilament cytoskeleton in the development of early Caenorhabditis elegans embryos. We previously reported that several cytoplasmic movements in the zygote require that the microfilament cytoskeleton remain intact during a narrow time interval approximately three-quarters of the way through the first cell cycle. In this study, we analyze the developmental consequences of brief, cytochalasin D-induced microfilament disruption during the 1-cell stage. Our results indicate that during the first cell cycle microfilaments are important only during the critical time interval for the 2-cell embryo to undergo the correct pattern of subsequent divisions and to initiate the differentiation of at least 4 tissue types. Disruption of microfilaments during the critical interval results in aberrant division and P-granule segregation patterns, generating some embryos that we classify as ‘reverse polarity’, ‘anterior duplication’, and ‘posterior duplication’ embryos. These altered patterns suggest that microfilament disruption during the critical interval leads to the incorrect distribution of developmental instructions responsible for early pattern formation. The strict correlation between unequal division, unequal germ-granule partitioning, and the generation of daughter cells with different cell cycle periods observed in these embryos suggests that the three processes are coupled. We hypothesize that (1) an ‘asymmetry determinant’, normally located at the posterior end of the zygote, governs asymmetric cell division, germ-granule segregation, and the segregation of cell cycle timing elements during the first cell cycle, and (2) the integrity or placement of this asymmetry determinant is sensitive to microfilament disruption during the critical time interval.

scholarly journals SYNCHRONIZATION OF MITOCHONDRIAL DNA SYNTHESIS IN CHINESE HAMSTER CELLS (LINE CHO) DEPRIVED OF ISOLEUCINE

1973 ◽  
Vol 58 (2) ◽  
pp. 340-345 ◽  
Author(s):  
Kenneth D. Ley ◽  
Marilyn M. Murphy
Keyword(s):  
Cell Cycle ◽  
Mitochondrial Dna ◽  
Dna Synthesis ◽  
Cell Cycle Progression ◽  
Time Course ◽  
Nuclear Dna ◽  
Tritiated Thymidine ◽  
Chinese Hamster ◽  
Chinese Hamster Cells ◽  
In Cells

Mitochondrial DNA (mit-DNA) synthesis was compared in suspension cultures of Chinese hamster cells (line CHO) whose cell cycle events had been synchronized by isoleucine deprivation or mitotic selection. At hourly intervals during cell cycle progression, synchronized cells were exposed to tritiated thymidine ([3H]TdR), homogenized, and nuclei and mitochondria isolated by differential centrifugation. Mit-DNA and nuclear DNA were isolated and incorporation of radioisotope measured as counts per minute ([3H]TdR) per microgram DNA. Mit-DNA synthesis in cells synchronized by mitotic selection began after 4 h and continued for approximately 9 h. This time-course pattern resembled that of nuclear DNA synthesis. In contrast, mit-DNA synthesis in cells synchronized by isoleucine deprivation did not begin until 9–12 h after addition of isoleucine and virtually all [3H]TdR was incorporated during a 3-h interval. We have concluded from these results that mit-DNA synthesis is inhibited in CHO cells which are arrested in G1 because of isoleucine deprivation and that addition of isoleucine stimulates synchronous synthesis of mit-DNA. We believe this method of synchronizing mit-DNA synthesis may be of value in studies of factors which regulate synthesis of mit-DNA.

scholarly journals Identification of an Arginine-Rich Motif in Human Papillomavirus Type 1 E1^E4 Protein Necessary for E4-Mediated Inhibition of Cellular DNA Synthesis In Vitro and in Cells

2008 ◽  
Vol 82 (18) ◽  
pp. 9056-9064 ◽  
Author(s):  
Sally Roberts ◽  
Sarah R. Kingsbury ◽  
Kai Stoeber ◽  
Gillian L. Knight ◽  
Phillip H. Gallimore ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Host Cell ◽  
S Phase ◽  
Human Papillomaviruses ◽  
Soluble Form ◽  
Cellular Dna ◽  
In Cells

ABSTRACT Productive infections by human papillomaviruses (HPVs) are restricted to nondividing, differentiated keratinocytes. HPV early proteins E6 and E7 deregulate cell cycle progression and activate the host cell DNA replication machinery in these cells, changes essential for virus synthesis. Productive virus replication is accompanied by abundant expression of the HPV E4 protein. Expression of HPV1 E4 in cells is known to activate cell cycle checkpoints, inhibiting G2-to-M transition of the cell cycle and also suppressing entry of cells into S phase. We report here that the HPV1 E4 protein, in the presence of a soluble form of the replication-licensing factor (RLF) Cdc6, inhibits initiation of cellular DNA replication in a mammalian cell-free DNA replication system. Chromatin-binding studies show that E4 blocks replication initiation in vitro by preventing loading of the RLFs Mcm2 and Mcm7 onto chromatin. HPV1 E4-mediated replication inhibition in vitro and suppression of entry of HPV1 E4-expressing cells into S phase are both abrogated upon alanine replacement of arginine 45 in the full-length E4 protein (E1^E4), implying that these two HPV1 E4 functions are linked. We hypothesize that HPV1 E4 inhibits competing host cell DNA synthesis in replication-activated suprabasal keratinocytes by suppressing licensing of cellular replication origins, thus modifying the phenotype of the infected cell in favor of viral genome amplification.

scholarly journals Cell Cycle regulations: The timing of pronuclear formation, DNA synthesis and cleavage in the human 1-cell embryo

1996 ◽  
Vol 2 (5) ◽  
pp. 299-306 ◽  
Author(s):  
Gemma Capmany ◽  
Alison Taylor ◽  
Peter R. Braude ◽  
Virginia N. Bolton
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Cell Embryo ◽  
Pronuclear Formation

Memoirs: The Direct Development of a New Zealand Ophiuroid

1941 ◽  
Vol s2-82 (327) ◽  
pp. 377-440
Author(s):  
H. BARRACLOUGH FELL
Keyword(s):  
Bilateral Symmetry ◽  
Ventral Surface ◽  
Radial Symmetry ◽  
Early Ontogeny ◽  
Body Cavity ◽  
Cell Stage ◽  
Animal Pole ◽  
Early Stages ◽  
Vegetal Pole ◽  
Primitive Structure

1. The first cleavage may be either equal, or markedly unequal; when it is equal the next segmentation affects both blastomeres; when it is unequal the larger blastomere is believed to give rise to three cells, and the smaller remains undivided till the next cleavage. 2. At the eight-cell stage there are two quartets of blastomeres. The upper quartet, micromeres, occupy the animal pole. The lower quartet, macromeres, occupy the vegetal pole. 3. The blastula comprises micromeres and macromeres, and the blastocoel is small and becomes eccentric. No cilia are developed. 4. The gastrula is formed by the shallow imagination of the macromeres, accompanied by an extensive process of epiboly affecting the micromeres. More marked epiboly of cells on two sides of the blastomere produces in the early stages two crests which later disappear. These may indicate a trace of bilateral symmetry. Epiblast comes to lie on solid mes-hypoblast. The archenteron is transient, and gives rise to no structures. The blastopore occupies the position of the definitive mouth. 5. No larva ever forms, nor is there any vestige of a larval stage. 6. The solid gastrula is converted into the adult by assuming a radial symmetry directly, with no intermediate bilaterally symmetrical form, unless the two epibolic crests are regarded as vestiges of larval symmetry. 7. The podia appear as solid outgrowths, in which the hydrocoelic cavity develops by splitting. 8. The definitive enteron appears as a split extending upward from the ventral surface through the solid hypoblast. 9. The young ophiuroid leaves the egg before the appearance of the general body cavity, and moves about, but does not at first take food. 10. The general coelomic body cavity and the perihaemal cavity develop by splitting in a mass of mesenchyme derived from the outer layers of mes-hypoblast. 11. The formation of the skeletal system is delayed till the stage of between two and three arm-segments. 12. The development of the skeleton follows closely that described for Amphiura squamata. 13. The tooth is shown to originate independently of the torus angularis; its rudiments comprise nine symmetrically disposed spicules. 14. The terminal plate arises later than the radials, and has a distinctive ‘primitive structure’. 15. The spine is shown to have a different development to that of the tooth, and therefore would seem to have no connexion with the latter in phylogeny or ontogeny. 16. It is suggested that the aberrant early stages are to be correlated with the retarding effect of the yolk mass present in the egg during ontogeny. The aberrant features may have had a different origin in phylogeny. 17. It is suggested that the simultaneous appearance in ontogeny of homologous organs situated at equal radial distances from the centre is to be explained in terms of hormonic activity. 18. It is concluded that evolution has considerably affected the early ontogeny without leaving its mark on phylogeny. The adult thus conforms to its class, the young form does not.

The induction of DNA synthesis in the chick red cell nucleus in heterokaryons during the first cell cycle after fusion with HeLa cells

1975 ◽  
Vol 18 (3) ◽  
pp. 455-490
Author(s):  
R.T. Johnson ◽  
A.M. Mullinger
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Hela Cells ◽  
S Phase ◽  
Red Cells ◽  
Red Cell ◽  
Embryonic Chick ◽  
Cell Cycles ◽  
Phase Protein ◽  
Different Parts

Induction of DNA synthesis in embryonic chick red cells has been examined during the first and second cell cycles after fusion with HeLa cells synchronized in different parts of G1 and S-phase. The data indicate that: (i) the younger the embryonic blood the more rapidly the red cells are induced into DNA synthesis; (ii) the greater the ratio of HeLa to chick nuclei in the heterokaryon, the more rapidly the induction occurs; (iii) DNA synthesis in the chick nucleus can continue after the HeLa nucleus has left S-phase and entered either G2 or mitosis; (iv) the induction potential of late S-phase HeLa is somewhat lower than that of early or mid S-phase cells; (v) less than 10% of the chick DNA is replicated during the first cycle after fusion and only a small proportion (15%) of the chick nuclei approach the 4C value of DNA during the second cycle after fusion; (vi) the newly synthesized DNA is associated either with the condensed regions of the nucleus or with the boundaries between condensed and non-condensed regions; (vii) the chick chromosomes at the first and second mitosis after fusion are in the form of PCC prematurely condensed chromosomes); they are never fully replicated and are often fragmentary; (viii) DNA synthesis in the chick nuclei is accompanied by an influx of protein (both G1 and S-phase protein) from the HeLa component of the heterokaryon.

Inhibition of Cell Division by High External NaCl Concentrations in Synchronized Cultures of Chlorella emersonii

1982 ◽  
Vol 9 (2) ◽  
pp. 179 ◽  
Author(s):  
T.L Setter ◽  
H Greenway ◽  
J Kuo
Keyword(s):  
Electron Microscopy ◽  
Cell Division ◽  
Dna Synthesis ◽  
Dna Content ◽  
Cell Cycles ◽  
Daughter Cells ◽  
Specific Effects ◽  
Rna And Dna ◽  
Synchronized Cultures ◽  
In Cells

Effects of high external NaCl concentrations on growth were examined in the unicellular freshwater alga Cldorella emevsonii during different phases of cell development, using synchronized cultures obtained by alternating light-dark cycles. Growth of cultures synchronized at 1 mM NaCl [external osmotic pressure (next=) 0.08 MPa] was compared with (i) cultures synchronized at 200 mM NaCl (n,,, = 1.01 MPa) and (ii) cultures synchronized at 1 mM NaCl from which the daughter cells were suddenly transferred to 100, 150 or 200 mM NaCl. The effects of these two treatments on synthesis of protein, RNA and DNA during cell cycles were similar, and are attributed to the high nexta nd not to specific effects of Na+ and C1-. Growth inhibitions in cells at 200 mM NaCl relative to 1 mM NaCl occurred mainly via effects on cell division; this was confirmed by electron microscopy. There was a lag before net DNA synthesis commenced, and there were reductions in rates of net DNA synthesis in cells at 200 mM NaCl relative to 1 mM NaC1. Rates of increase in cell volume and in protein and RNA content per cell were little affected by high external NaCl concentrations. Consequently, daughter cells at 200 mM NaCl were approximately twice the volume and contained twice as much protein and RNA as daughter cells at 1 mM NaCl, while DNA content was equal in daughter cells at 1 and 200 mM NaCl.

The vegetal determinants required for the Spemann organizer move equatorially during the first cell cycle

Development ◽  
1996 ◽  
Vol 122 (7) ◽  
pp. 2207-2214 ◽  
Author(s):  
M. Sakai
Keyword(s):  
Cell Cycle ◽  
Formation Process ◽  
Lithium Treatment ◽  
Axis Formation ◽  
Cell Stage ◽  
Spemann Organizer ◽  
Dorsal Axis ◽  
Vegetal Pole ◽  
Organizing Center ◽  
Cell Embryo

Embryos with no dorsal axis were obtained when more than 15% of the egg surface was deleted from the vegetal pole of the early 1-cell embryo of Xenopus laevis. The timing of the deletion in the first cell cycle was critical: dorsal-deficient embryos were obtained when the deletion began before time 0.5 (50% of the first cell cycle) whereas normal dorsal axis usually formed when the deletion was done later than time 0.8. The axis deficiency could be restored by lithium treatment and the injection of vegetal but not animal cytoplasm. Bisection of the embryo at the 2-cell stage, which is known to restore the dorsal structures in the UV-ventralized embryos, had no effect on the vegetal-deleted embryos. These results show clearly that, in Xenopus, (1) the dorsal determinants (DDs) localized in the vegetal pole region at the onset of development are necessary for dorsal axis development and (2) the DDs move from the vegetal pole to a subequatorial region where they are incorporated into gastrulating cells to form the future organizing center. A model for the early axis formation process in Xenopus is proposed.

scholarly journals Chromosome Methylation and Measurement of Faithful, Once and Only Once per Cell Cycle Chromosome Replication inCaulobacter crescentus

1999 ◽  
Vol 181 (7) ◽  
pp. 1984-1993 ◽  
Author(s):  
Gregory T. Marczynski
Keyword(s):  
Cell Cycle ◽  
Dna Methylation ◽  
Cell Division ◽  
Dna Synthesis ◽  
Replication Origin ◽  
Asymmetric Cell Division ◽  
Caulobacter Crescentus ◽  
Chromosome Replication ◽  
Cell Stage ◽  
Swarmer Cell

ABSTRACT Caulobacter crescentus exhibits cell-type-specific control of chromosome replication and DNA methylation. Asymmetric cell division yields a replicating stalked cell and a nonreplicating swarmer cell. The motile swarmer cell must differentiate into a sessile stalked cell in order to replicate and execute asymmetric cell division. This program of cell division implies that chromosome replication initiates in the stalked cell only once per cell cycle. DNA methylation is restricted to the predivisional cell stage, and since DNA synthesis produces an unmethylated nascent strand, late DNA methylation also implies that DNA near the replication origin remains hemimethylated longer than DNA located further away. In this report, both assumptions are tested with an engineered Tn5-based transposon, Tn5Ω-MP. This allows a sensitive Southern blot assay that measures fully methylated, hemimethylated, and unmethylated DNA duplexes. Tn5Ω-MP was placed at 11 sites around the chromosome and it was clearly demonstrated that Tn5Ω-MP DNA near the replication origin remained hemimethylated longer than DNA located further away. One Tn5Ω-MP placed near the replication origin revealed small but detectable amounts of unmethylated duplex DNA in replicating stalked cells. Extra DNA synthesis produces a second unmethylated nascent strand. Therefore, measurement of unmethylated DNA is a critical test of the “once and only once per cell cycle” rule of chromosome replication inC. crescentus. Fewer than 1 in 1,000 stalked cells prematurely initiate a second round of chromosome replication. The implications for very precise negative control of chromosome replication are discussed with respect to the bacterial cell cycle.

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