Replication and transcription sites are colocalized in human cells

1994 ◽  
Vol 107 (2) ◽  
pp. 425-434 ◽  
Author(s):  
A.B. Hassan ◽  
R.J. Errington ◽  
N.S. White ◽  
D.A. Jackson ◽  
P.R. Cook
Keyword(s):  
Cell Cycle ◽  
Confocal Microscopy ◽  
Dna Synthesis ◽  
Fluorescent Probes ◽  
Hela Cells ◽  
Nuclear Architecture ◽  
Human Cells ◽  
Dynamic Nature ◽  
Nucleotide Triphosphates ◽  
Transcription Sites

HeLa cells synchronized at different stages of the cell cycle were permeabilized and incubated with analogues of nucleotide triphosphates; then sites of incorporation were immunolabeled with the appropriate fluorescent probes. Confocal microscopy showed that sites of replication and transcription were not diffusely spread throughout nuclei, reflecting the distribution of euchromatin; rather, they were concentrated in ‘foci’ where many polymerases act together. Transcription foci aggregated as cells progressed towards the G1/S boundary; later they dispersed and became more diffuse. Replication was initiated only at transcription sites; later, when heterochromatin was replicated in enlarged foci, these remained sites of transcription. This illustrates the dynamic nature of nuclear architecture and suggests that transcription may be required for the initiation of DNA synthesis.

scholarly journals Adenovirus E1B 55-Kilodalton Protein Is Required for both Regulation of mRNA Export and Efficient Entry into the Late Phase of Infection in Normal Human Fibroblasts

2006 ◽  
Vol 80 (2) ◽  
pp. 964-974 ◽  
Author(s):  
Ramon Gonzalez ◽  
Wenying Huang ◽  
Renee Finnen ◽  
Courtney Bragg ◽  
S. J. Flint
Keyword(s):  
Dna Synthesis ◽  
Hela Cells ◽  
Human Fibroblasts ◽  
Late Phase ◽  
Mrna Export ◽  
Human Cells ◽  
Insertion Mutation ◽  
Viral Dna ◽  
Normal Human ◽  
Normal Human Cells

ABSTRACT The human adenovirus type 5 (Ad5) E1B 55-kDa protein is required for selective nuclear export of viral late mRNAs from the nucleus and concomitant inhibition of export of cellular mRNAs in HeLa cells and some other human cell lines, but its contributions(s) to replication in normal human cells is not well understood. We have therefore examined the phenotypes exhibited by viruses carrying mutations in the E1B 55-kDa protein coding sequence in normal human fibroblast (HFFs). Ad5 replicated significantly more slowly in HFFs than it does in tumor cells, a difference that is the result of delayed entry into the late phase of infection. The A143 mutation, which specifically impaired export of viral late mRNAs from the nucleus in infected HeLa cells (R. A. Gonzalez and S. J. Flint, J. Virol. 76:4507-4519, 2002), induced a more severe defect in viral mRNA export in HFFs. This observation indicates that the E1B 55-kDa protein regulates mRNA export during the late phase of infection of normal human cells. Other mutants exhibited phenotypes not observed in HeLa cells. In HFFs infected by the null mutant Hr6, synthesis of viral late mRNAs and proteins was severely impaired. Such defects in late gene expression were the result of inefficient progression into the late phase of infection, for viral DNA synthesis was 10-fold less efficient in Hr6-infected HFFs than in cells infected by Ad5. Similar, but less severe, defects in viral DNA synthesis were induced by the insertion mutation H224, which has been reported to inhibit binding of the E1B 55-kDa protein to p53 (C. C. Kao, P. R. Yew, and A. J. Berk, Virology 179:806-814, 1990).

Changes in the organization of chromosomes during the cell cycle: response to ultraviolet light

1975 ◽  
Vol 17 (3) ◽  
pp. 539-565
Author(s):  
S.L. Schor ◽  
R.T. Johnson ◽  
C.A. Waldren
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Ultraviolet Light ◽  
Hela Cells ◽  
Close Correlation ◽  
Chromosome Condensation ◽  
Unscheduled Dna Synthesis ◽  
Interphase Chromosome ◽  
Interphase Cells ◽  
Chromosome Decondensation

Fusion between mitotic and interphase cells results in the premature condensation of the interphase chromosomes into a morphology related to the position in the cell cycle at the time of fusion. These prematurely condensed chromosomes (PCC) have been used in conjunction with u.v. irradiation to examine the interphase chromosome condensation cycle of HeLa cells. The following observations have been made: (I) There is a progressive decondensation of the chromosomes during G1 which is accentuated by u.v. irradiation: (2) The chromosomes become more resistant to u.v.-induced decondensation during G2 and mitosis. (3) There is a close correlation between the degree of chromosome decondensation and the amount of unscheduled DNA synthesis induced by u.v. irradiation during G1 and mitosis: (4) Hydroxyurea enhances the ability of u.v. irradiation to promote the decondensation of chromosomes during G1, G2 and mitosis. Hydroxyurea also potentiates the lethal action of u.v. irradiation during mitosis and G1. These data are discussed in relation to the suggestion that chromosomes undergo a progressive decondensation during G1 and condensation during G2.

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.

scholarly journals Differential response of cycling and noncycling cells to inducers of DNA synthesis and mitosis

1981 ◽  
Vol 88 (3) ◽  
pp. 649-653 ◽  
Author(s):  
PN Rao ◽  
ML Smith
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Uv Irradiation ◽  
Hela Cells ◽  
Cell Cycle Progression ◽  
Sendai Virus ◽  
Nonhistone Proteins ◽  
Interesting Observation ◽  
Human Diploid Fibroblasts ◽  
Kinetics Of

The objective of this study was to determine whether cells in G(0) phase are functionally distinct from those in G(1) with regard to their ability to respond to the inducers of DNA synthesis and to retard the cell cycle traverse of the G(2) component after fusion. Synchronized populations of HeLa cells in G(1) and human diploid fibroblasts in G(1) and G(0) phases were separately fused using UV-inactivated Sendai virus with HeLa cells prelabeled with [(3)H]ThdR and synchronized in S or G(2) phases. The kinetics of initiation of DNA synthesis in the nuclei of G(0) and G(1) cells residing in G(0)/S and G(1)/S dikaryons, respectively, were studied as a function of time after fusion. In the G(0)/G(2) and G(1)/G(2) fusions, the rate of entry into mitosis of the heterophasic binucleate cells was monitored in the presence of Colcemid. The effects of protein synthesis inhibition in the G(1) cells, and the UV irradiation of G(0) cells before fusion, on the rate of entry of the G(2) component into mitosis were also studied. The results of this study indicate that DNA synthesis can be induced in G(0)nuclei after fusion between G(0)- and S-phase cells, but G(0) nuclei are much slower than G(1) nuclei in responding to the inducers of DNA synthesis because the chromatin of G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells differ from G(1) cells with regard to their effects on the cell cycle progression of the G(2) nucleus into mitosis. This difference between G(0) and G(1) cells appears to depend on certain factors, probably nonhistone proteins, present in G(1) cells but absent in G(0) cells. These factors can be induced in G(0) cells by UV irradiation and inhibited in G(1) cells by cycloheximide treatment.

scholarly journals Transcription Sites Are Not Correlated with Chromosome Territories in Wheat Nuclei

1998 ◽  
Vol 143 (1) ◽  
pp. 5-12 ◽  
Author(s):  
Rita Abranches ◽  
Alison F. Beven ◽  
Luis Aragón-Alcaide ◽  
Peter J. Shaw
Keyword(s):  
Confocal Microscopy ◽  
Three Dimensional ◽  
Nuclear Architecture ◽  
Chromosome Territories ◽  
Addition Lines ◽  
Wheat Roots ◽  
Tissue Sections ◽  
Genomic Probe ◽  
Transcription Sites ◽  
The Relationship

We have determined the relationship between overall nuclear architecture, chromosome territories, and transcription sites within the nucleus, using three-dimensional confocal microscopy of well preserved tissue sections of wheat roots. Chromosome territories were visualized by GISH using rye genomic probe in wheat/rye translocation and addition lines. The chromosomes appeared as elongated regions and showed a clear centromere–telomere polarization, with the two visualized chromosomes lying approximately parallel to one another across the nucleus. Labeling with probes to telomeres and centromeres confirmed a striking Rabl configuration in all cells, with a clear clustering of the centromeres, and cell files often maintained a common polarity through several division cycles. Transcription sites were detected by BrUTP incorporation in unfixed tissue sections and revealed a pattern of numerous foci uniformly distributed throughout the nucleoplasm, as well as more intensely labeled foci in the nucleoli. It has been suggested that the gene-rich regions in wheat chromosomes are clustered towards the telomeres. However, we found no indication of a difference in concentration of transcription sites between telomere and centromere poles of the nucleus. Neither could we detect any evidence that the transcription sites were preferentially localized with respect to the chromosome territorial boundaries.

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