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R Drouin

Publications and source records attributed to R Drouin.

At least 37 records · Page 2Linked to original sources
PubMed2000

In vivo protein-DNA interactions at the kinin B(1) receptor gene promoter: no modification on interleukin-1 beta or lipopolysaccharide induction.

The kinin B(1) receptor (B(1)R) gene is strongly upregulated following tissue injury and inflammation. In an attempt to define the regulatory elements that account for the control of B(1)R gene expression, we have conducted in vivo footprinting analysis of the B(1)R gene promoter region in three human cell types: embryonic lung fibroblast cells (IMR-90), embryonic kidney cells (HEK-293), and primary cultures of vascular umbilical smooth muscle cells. Initial in vitro delineation of the B(1)R gene promoter by transient transfection experiments with a reporter gene indicated that a 1.4-kb region, located just upstream of the transcription initiation site, bears all the characteristics of a core promoter with a functional TATA box and additional positive and negative control elements, as some of them could be tissue-specific. In vivo ultraviolet and dimethylsulfate footprinting analyses of the 1.4-kb region revealed no difference between the footprint patterns in the three cell types studied. We found that even in the noninduced state, the B(1)R gene promoter is possibly bound by several sequence-specific DNA binding proteins (GATA-1, PEA3, AP-1, CAAT, Sp1, Pit-1a, Oct-1, CREB). Some other footprints were detected on sequences that do not correspond to any known transcription factor binding site. No additional changes in protein-DNA complexes were observed upon treatment with interleukin-1 beta (IL-1beta) or bacterial lipopolysaccharide, shown previously to induce B(1)R gene expression. These results indicate that complex protein-DNA interactions exist at the B(1)R gene promoter prior to induction by external stimuli even in cells (HEK-293) that do not express a functional B(1)R.

Base Sequence↗
PubMed2000

Optimization of the fluorescence in situ hybridization (FISH) technique for high detection efficiency of very small proportions of target interphase nuclei.

Using commercially available fluorochrome-labeled probes specific for chromosomes X, Y, 13, 18, and 21, we optimized the technical protocols for fluorescence in situ hybridization (FISH) so that the highest sensitivity and specificity were achieved. Also, we compared the optical properties of different types of fluorescent labels in an effort to develop the most efficient FISH protocol, including the determination of which types of labels are the easiest to count accurately. The lymphocytes were purified from blood of normal male and female newborns, normal male and female adults, and a trisomy 21 male adult. Male and female lymphocytes were mixed in five different combinations. For each combination, the male lymphocytes either from newborns or from adults were diluted with female lymphocytes in seven different proportions. For each of these 35 different cell mixtures, 100,000 nuclei were analyzed and scored in a blind fashion. Among the different fluorochrome-labeled probes, the highest sensitivity and specificity were achieved when SpectrumAqua CEP-Y/SpectrumOrange CEP X probe mixture, SpectrumAqua CEP-18, SpectrumOrange LSI-13, and SpectrumOrange LSI-21 were hybridized. The hybridization sensitivity and specificity were higher than 99% for the identification of chromosomes X, Y, 13, and 18, and higher than 98% for the detection of trisomy 21. The proportion of false-positive signals was under 0.005% for XY detection and lower than 0.14% for autosome detection. With these high hybridization sensitivities and specificities, the optimized FISH protocol developed in our laboratory has the potential to detect very rare events, e.g., when the proportion of cells being sought is lower than 0.01%. In other words, our protocol allows the specific detection of one male cell sunken among 10,000 female cells.

Adult↗
PubMed2000

The efficacy of a broad-spectrum sunscreen to protect engineered human skin from tissue and DNA damage induced by solar ultraviolet exposure.

Sunscreens are known to protect against sunlight-induced erythema and sunburn, but their efficiency at protecting against skin cancer is still a matter of debate. Specifically, the capacity of sunscreens to prevent or reduce tissue and DNA damage has not been thoroughly investigated. The present study was undertaken to assess the ability of a chemical broad-spectrum sunscreen to protect human skin against tissue and DNA damage after solar UV radiation. Engineered human skin was generated and either treated or not with a broad-spectrum SPF 30 sunscreen and exposed to increasing doses of simulated sunlight (SSL). Immediately after irradiation, histological, immunohistochemical, and molecular quantitative analyses were performed. The unprotected irradiated engineered human skin showed significant epidermal disorganization accompanied by a complete absence of laminin deposition. The sunscreen prevented SSL-induced epidermal damage at low doses and allowed laminin deposition at almost all SSL doses tested. The frequencies of cyclobutane pyrimidine dimers, pyrimidine (6-4) pyrimidone photoproducts, and photooxidative lesions measured by alkaline gel electrophoresis and radioimmunoassay were significantly reduced by the sunscreen. Thus, tissue and DNA damage may provide excellent quantitative end points for assessing the photoprotective efficacy of sunscreens.

Adolescent↗
PubMed1999

Human cells compromised for p53 function exhibit defective global and transcription-coupled nucleotide excision repair, whereas cells compromised for pRb function are defective only in global repair.

After exposure to DNA-damaging agents, the p53 tumor suppressor protects against neoplastic transformation by inducing growth arrest and apoptosis. A series of investigations has also demonstrated that, in UV-exposed cells, p53 regulates the removal of DNA photoproducts from the genome overall (global nucleotide excision repair), but does not participate in an overlapping pathway that removes damage specifically from the transcribed strand of active genes (transcription-coupled nucleotide excision repair). Here, the highly sensitive ligation-mediated PCR was employed to quantify, at nucleotide resolution, the repair of UVB-induced cyclobutane pyrimidine dimers (CPDs) in genetically p53-deficient Li-Fraumeni skin fibroblasts, as well as in human lung fibroblasts expressing the human papillomavirus (HPV) E6 oncoprotein that functionally inactivates p53. Lung fibroblasts expressing the HPV E7 gene product, which similarly inactivates the retinoblastoma tumor-suppressor protein (pRb), were also investigated. pRb acts downstream of p53 to mediate G(1) arrest, but has no demonstrated role in DNA repair. Relative to normal cells, HPV E6-expressing lung fibroblasts and Li-Fraumeni skin fibroblasts each manifested defective CPD repair along both the transcribed and nontranscribed strands of the p53 and/or c-jun loci. HPV E7-expressing lung fibroblasts also exhibited reduced CPD removal, but only along the nontranscribed strand. Our results provide striking evidence that transcription-coupled repair, in addition to global repair, are p53-dependent in UV-exposed human fibroblasts. Moreover, the observed DNA-repair defect in HPV E7-expressing cells reveals a function for this oncoprotein in HPV-mediated carcinogenesis, and may suggest a role for pRb in global nucleotide excision repair.

DNA Repair↗
PubMed1999

The multilayered organization of engineered human skin does not influence the formation of sunlight-induced cyclobutane pyrimidine dimers in cellular DNA.

Solar UVB initiates skin cancer mainly by generating highly premutagenic cyclobutane pyrimidine dimers (CPDs) and subsequent mutations in critical growth control genes. It is universally presumed that the upper epidermis in human skin blocks a significant portion of the incident UVB, thereby protecting the cancer-prone basal layer from CPD formation. Using two sensitive techniques for measuring CPD in cellular DNA, we confirmed that the multilayered organization of engineered human skin efficiently shields the basal layer against 254-nm UVC (which is not present in terrestrial sunlight) but, very unexpectedly, provides virtually no protection against environmentally relevant UVB. This underscores the importance of regular sunscreen use, which, in light of our data, may constitute a considerably more important first line of defense against photocarcinogenesis than previously believed.

Biomedical Engineering↗
PubMed1999

Physiological and cytogenetic characterization of immortalized human endometriotic cells containing episomal simian virus 40 DNA.

The study of misplaced endometrial cells, which abnormally implant and grow outside the uterine cavity, is of considerable interest for the understanding of the pathophysiology of endometriosis. However, endometriotic cells, particularly epithelial cells, required for primary cell culture are not easily available. We report here the characterization of an endometriotic cell line immortalized after infection of primary endometriotic cell cultures with simian virus 40. Transformed cells express T-antigen, and blot hybridization analysis showed that the viral genome is present as an episome. Cytogenetic analysis revealed a polyploid karyotype with numerical and structural rearrangements involving mainly the same chromosomes (6, 10, 11, 15, and 17). The cell line has been maintained in culture for over 80 passages and was still proliferating without any noticeable change in the biological properties investigated. Transformed endometriotic cells expressed both progesterone and estradiol receptors and were stimulated by these ovarian hormones to secrete monocyte chemotactic protein-1, a factor that may play an important role in the recruitment and activation of peritoneal macrophages. In addition, this response was enhanced in interleukin-1-treated cells. Taken together, these findings support the view that this cell line may be an interesting tool for the study of the pathophysiology of endometriosis.

Adult↗
PubMed1999

Treatment of human cells with N-Nitroso(acetoxymethyl)methylamine: distribution patterns of piperidine-sensitive DNA damage at the nucleotide level of resolution are related to the sequence context.

The nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) present in tobacco smoke is a major carcinogen involved in tobacco-induced lung cancer. Its complex bioactivation along two pathways, which leads to methylation and pyridyloxobutylation of DNA, makes the study of NNK-induced DNA damage difficult. We selected two nitroso compounds, N-methyl-N-nitrosourea (MNU) and N-nitroso(acetoxymethyl)methylamine (NDMAOAc), with which to map NNK-induced DNA methylation frequency at every nucleotide position. We address the issue of how sequence context and complex chromatin structures, present in living cells, regulate the formation of modified purines through methylation generated by MNU and NDMAOAc. For comparison purposes, purified DNA was treated with dimethyl sulfate (DMS). We used ligation-mediated polymerase chain reaction to map and conduct a high-resolution footprinting analysis of the DNA damage along the p53 gene (exons 5-8), the ras gene family (exons 1 and 2 of H-, K-, and N-ras genes), and the c-jun promoter in living cells. The distribution of piperidine-sensitive DNA damage induced in cellular DNA and purified DNA by MNU or NDMAOAc was identical. MNU and NDMAOAc methylate more frequently the central guanines in a run of guanines, suggesting a regioselective mechanism for DNA methylation. In contrast, DMS methylates more frequently guanines at the 5'-end of a guanine run; this frequency decreased from the 5'- to the 3'-end. While the presence of adenines in a guanine run does not affect the distribution pattern, the presence of pyrimidines does change said pattern. Our data lead us to suggest that NNK would also methylate DNA sequences in a way similar to that of MNU or NDMAOAc. Footprinted areas of DNA methylated with MNU or NDMAOAc correspond to a consensus sequence for transcription factors AP-1, NF-Jun, CCAAT box, SP-1, and RSRF, as observed in c-jun promoters. Our results are in line with the fact that NNK metabolites, generated through the alpha-hydroxylation pathways, could potentially be mutagenic, since these activated metabolites can methylate guanines. In p53 and ras genes, the frequency of methylation of guanines parallels the frequency of mutations of those same guanines in lung cancer.

Base Sequence↗
PubMed1998

ABC50, a novel human ATP-binding cassette protein found in tumor necrosis factor-alpha-stimulated synoviocytes.

We have used the recently developed technique of differential display polymerase chain reaction to seek for new genes modulated by tumor necrosis factor-alpha (TNF-alpha) in cultured synoviocytes. One PCR fragment was shown to correspond to a new gene that was mapped by high-resolution fluorescence in situ hybridization to band 6p21.33. The cDNA of this gene was cloned, and the deduced amino acid sequence revealed consensus motifs for the nucleotide binding folds of the ATP-binding cassette (ABC) family of proteins. However, a hydropathy curve showed that the polypeptide does not contain the transmembrane domains that are typical of the subfamily of ABC transporters and are associated with transporter/channel functions. The new gene, called ABC50, is the first human and mammalian ABC protein found to lack transmembrane domains. Homology with some yeast ABC proteins suggests that ABC50 codes for a new human ribosomal protein involved in translation of mRNA. It could therefore play a role in the enhancement of protein synthesis that follows TNF-alpha treatment of synoviocytes and thus participate in the inflammatory processes mediated by this cytokine. Furthermore, since TNF-alpha also modulates the expression of MHC class I genes, and these genes are known to map to 6p21.33, it is hypothesized that ABC50 and MHC class I are part of the same chromatin expression domain.

ATP-Binding Cassette Transporters↗
PubMed1998

Increased hepatic glucose production response to glucagon in trained subjects.

This study was designed to characterize the impact of endurance training on the hepatic response to glucagon. We measured the effect of glucagon on hepatic glucose production (HGP) in resting trained (n = 8) and untrained (n = 8) healthy male subjects (maximal rate of O2 consumption: 65.9 +/- 1.6 vs. 46.8 +/- 0.6 ml O2.kg-1.min-1, respectively, P < 0.001). Endogenous insulin and glucagon were suppressed by somatostatin (somatotropin release-inhibiting hormone) infusion (450 micrograms/h) over 4 h. Insulin (0.15 mU.kg-1.min-1) was infused throughout the study, and glucagon (1.5 ng.kg-1.min-1) was infused over the last 2 h. During the latter period, plasma glucagon and insulin remained constant at 138.2 +/- 3.1 vs. 145.3 +/- 2.1 ng/l and at 95.5 +/- 4.5 vs. 96.2 +/- 1.9 pmol/l in trained and untrained subjects, respectively. Plasma glucose increased and peaked at 11.4 +/- 1.1 mmol/l in trained subjects and at 8.9 +/- 0.8 mmol/l in untrained subjects (P < 0.001). During glucagon stimulation, the mean increase in HGP area under the curve was 15.8 +/- 2.8 mol.kg-1.min-1 in trained subjects compared with 7.4 +/- 1.6 mol.kg-1.min-1 in untrained subjects (P < 0.01) over the first hour and declined to 6.8 +/- 2.8 and 4.9 +/- 1.4 mol.kg-1.min-1 during the second hour. In conclusion, these observations indicate that endurance training is associated with an increase in HGP in response to physiological levels of glucagon, thus suggesting an increase in hepatic glucagon sensitivity.

Adult↗
PubMed1998

Increased expression of monocyte chemotactic protein-1 in the endometrium of women with endometriosis.

The pathogenesis of endometriosis, a disease widely believed to arise from an aberrant growth of endometrial tissue outside the uterus, is still unclear. We have previously observed that cytokine-stimulated endometrial cells of women with endometriosis secrete in vitro increased amounts of monocyte chemotactic protein-1 (MCP-1). This factor may be important in the recruitment and activation of peritoneal macrophages observed in endometriosis patients. The present study reports that, in the presence of the disease, such an up-regulation of MCP-1 expression arises in vivo and can be encountered in situ in the intrauterine endometrium. In women with endometriosis, MCP-1 expression was elevated in endometrial glands, both at the level of the protein (immunohistochemistry) and the mRNA (in situ hybridization). This was observed throughout the menstrual cycle and varied according to the stage of the disease. These findings strongly argue in favor of the presence of pathophysiological changes in the eutopic endometrium of patients with endometriosis and make plausible MCP-1 as a key effector cell mediator involved in the pathogenesis of the disease.

Adult↗
PubMed1997

A hot spot for hydrogen peroxide-induced damage in the human hypoxia-inducible factor 1 binding site of the PGK 1 gene.

Using ligation-mediated polymerase chain reaction to separately map the distribution of induced oxidized bases and strand breaks along the human PGK1 promoter at nucleotide resolution, we previously described the pattern of oxidative DNA damage induced in vitro by Cu(II)/ascorbate/H2O2 [J. Biol. Chem. 270, 17633-17640 (1995)]. Here we report that the pattern of in vivo base damage caused by H2O2 is almost identical to that of the previously used in vitro system with the exception of transcription factor-associated footprints. An unusually strong positive footprint for both strand breaks and oxidized bases is associated with binding of the hypoxia-inducible transcription factor-1. Base damage at this footprint was 52-91% repaired in 24 h, which was similar to the global base damage repair rate. However, strand breaks at this footprint were only 39-55% repaired in 24 h or approximately 100-fold slower than the global strand break repair rate.

Ascorbic Acid↗
PubMed1997

Chemical inactivators as sterilization agents for bovine collagen materials.

The use of collagen as a biomedical implant raises safety issues with regard to viruses and prions. Specific chemical agents that inactivate prion infectivity could be applied to collagen implants. The physicochemical changes and the in vitro and in vivo biocompatibility of collagen treated by formic acid (FA), trifluoroacetic acid (TFA), tetrafluorethanol (TFE), and hexafluoroisopropanol (HFIP) were investigated. In addition, the effects of these treatments on nucleic acids incorporated in collagen were analyzed. The molecules of FA and, more important, of TFA remained within collagen. FA, TFA, and HFIP treatments modify the secondary structure of collagen, as shown by Fourier transform infrared spectroscopy, while TFE does not. Differential scanning calorimetry measurements showed a decrease in the denaturation temperature compared to untreated collagen. However, resistance to collagenase was modified only after HFIP treatment. In vitro, cell growth was not impaired; in vivo, implants induced a temporary inflammatory reaction that was prolonged with TFA and HFIP treatments. TFE and FA-treated collagen were thoroughly infiltrated by fibroblasts. On the other hand, FA and TFA resulted in extensive depurination of nucleic acids while HFIP and TFE did so to a lesser degree. Among the investigated chemical scrapie inactivators, FA treatment could offer a safe and biocompatible collagen-derived material for biomedical use.

Animals↗
PubMed1997

DNA replication asynchrony between the paternal and maternal alleles of imprinted genes does not straddle the R/G transition.

Imprinted autosomal loci apparently reside in very large chromosomal domains that exhibit asynchrony in replication of homologous alleles during the DNA synthesis phase. Replication asynchrony can be cytogenetically visualized by a replication-banding discordance between homologous bands of a given pair of chromosomal homologs. The replication time of a chromosomal band at high resolution can be determined by blocking DNA synthesis at the R/G-band transition and using replication banding. The R/G transition reflects the transition from early (R-) to late (G- and C-) band DNA replication. We studied discordance between two groups of homologous chromosomal bands: (a) four bands, 6q26-27, 11p13, 11p15.5 and 15q11.2-12, each containing at least one imprinted gene; and (b) nine bands containing no known imprinted genes. Fifty pairs of chromosomes were analyzed at high resolution after R/G transition blocking and late 5-bromo-2'-deoxyuridine incorporation. The rate of discordance was the same for bands containing imprinted genes and for control bands. Both homologous bands of a pair replicate either before or after the R/G transition and do not straddle the R/G transition. Repression associated with imprinting does not appear to involve late replication at the band level of resolution. Tissue-specific inactivation is associated with DNA methylation and late replication, whereas allele-specific inactivation is associated with DNA methylation but not with delayed or late replication.

Adult↗
PubMed1997

Structural and functional characterization of the human FMR1 promoter reveals similarities with the hnRNP-A2 promoter region.

Fragile X mental retardation syndrome is associated with an expansion of a CGG repeat within the 5'UTR of the first exon of the FMR1 gene, abnormal methylation of the CpG island in the promoter region, and a transcriptional silencing of this gene. We studied transcriptional regulation of the FMR1 gene using protein footprint analysis of the active and inactive gene in vivo . We identified four footprints within the FMR1 promoter region which correspond to consensus binding sites of known transcription factors, alpha-PAL/NRF1, Sp1, H4TF1/Sp1-like and c-myc. These footprints were present in normal cells with a transcriptionally active FMR1 gene. The same footprints were present in different cell types: primary fibroblasts, lymphoblastoid cells and peripheral lymphocytes. However, for the 1.1 kb region analyzed, no footprints were detected in a variety of cell types derived from patients with fragile X syndrome which have a transcriptionally inactive FMR1 gene. A BLAST nucleotide search identified sequence similarities between the region of the FMR1 gene containing the footprints and an analogous region within the promoter region of the gene for the heterogeneous nuclear ribonucleoprotein (hnRNP) A2, a member of a family of ribonucleoproteins implicated in mRNA processing and nuclear-cytoplasm transport. The nucleotide sequences identified in the hnRNP-A2 promoter region correspond to the same consensus binding sites showing DNA-protein interactions in the FMR1 gene. Our previous functional studies and the studies of others demonstrate that FMR proteins, like hnRNP-A2, are also ribonucleoproteins which appear to be involved in mRNA transport. The results from our footprint studies suggest that the expression of the FMR1 gene is regulated by the binding of specific transcription factors to sequence elements in the 5' region of the gene and that this expression may be regulated by elements in common with the hnRNP-A2 gene. Common regulation of these two genes might play an important role in the cooperative processing and transport of mRNA from the nucleus to the translation machinery.

Female↗
PubMed1997

UVB-induced cyclobutane pyrimidine dimer frequency correlates with skin cancer mutational hotspots in p53.

Ultraviolet light has been identified as the major carcinogen in skin cancer and the p53 tumor suppressor gene is a major target for UV-induced mutations. The mutations are probably caused by unrepaired UV-induced cyclobutane pyrimidine dimers (CPD) and possibly by the less frequent pyrimidine (6-4) pyrimidone photoproducts. While hot spots for p53 mutations in human nonmelanoma skin tumors correspond quite well to slow spots for CPD repair in cultured cells irradiated with the model mutagen 254 nm UVC (which is not present in terrestrial sunlight), they do not all coincide with sequences that are initially frequently damaged by 254 nm UVC. Using LMPCR (ligation-mediated polymerase chain reaction), we show that environmentally relevant UVB light induces CPD at CC and Pyr(m)C positions much more frequently than does UVC light, and that all eight skin cancer hot spots in p53 are also hot spots for UVB-induced CPD. Our results show that methylation of dipyrimidine sites (Pyr(m)CpG) is associated with an increase rate of CPD formation upon UVB irradiation. Consequently, DNA methylation may increase the mutagenic potential of UVB and explains that several p53 mutation hot spots are found at Pyr(m)CpG. The distribution patterns of CPD formation and the photofootprint patterns found along exons 5 and 6 of p53 gene are suggestive of DNA folding into nucleosomes.

Base Sequence↗
PubMed1996

Cupric ion/ascorbate/hydrogen peroxide-induced DNA damage: DNA-bound copper ion primarily induces base modifications.

The kinetics of frank DNA strand breaks and DNA base modifications produced by Cu(II)/ascorbate/H2O2 were simultaneously determined in purified human genomic DNA in vitro. Modified bases were determined by cleavage with Escherichia coli enzymes Nth protein (modified pyrimidines) and Fpg protein (modified purines). Single-stranded lesion frequency before (frank strand breaks) and after (modified bases) Nth or Fpg protein digestion was quantified by neutral glyoxal gel electrophoresis. Dialysis of EDTA-treated genomic DNA purified by standard proteinase K digestion/phenol extraction was necessary to remove low molecular weight species, probably transition metal ions and metal ion chelators, which supported frank strand breaks in the presence of ascorbate + H2O2 without supplemental copper ions. We then established a kinetic model of the DNA-damaging reactions caused by Cu(II) + ascorbate + H2O2. The principal new assumption in our model was that DNA base modifications were caused exclusively by DNA-bound Cu(I) and frank strand breaks by non-DNA-bound Cu(I). The model was simulated by computer using published rate constants. The computer simulation quantitatively predicted: (1) the rate of H2O2 degradation, which was measured using an H2O2-sensitive electrode, (2) the linearity of accumulation of DNA strand breaks and modified bases over the reaction period, (3) the rate of modified base accumulation, and (4) the dependence of modified base and frank strand production on initial Cu(II) concentration. The simulation significantly overestimated the rate of frank strand break accumulation, suggesting either that the ultimate oxidizing species that attacks the sugar-phosphate backbone is a less-reactive species than the hydroxyl radical used in the model and/or an unidentified hydroxyl radical-scavenging species was present in the reactions. Our experimental data are consistent with a model of copper ion-DNA interaction in which DNA-bound Cu(I) primarily mediates DNA base modifications and nonbound Cu(I) primarily mediates frank strand break production.

Ascorbic Acid↗
PubMed1996

Complementary replication R- and G-band patterns induced by cell blocking at the R-band/G-band transition, a possible regulatory checkpoint within the S phase of the cell cycle.

The characteristic band patterns of replication banding (dynamic banding) were analyzed. High-resolution (550-1,250 bands per haploid genome) G- and R-band patterns were obtained after 5-bromo-2'-deoxyuridine (BrdU) incorporation during early or late S phase. Thymidine-BrdU permutation culture methods, which arrest DNA synthesis at the R-band/G-band transition, allow complementary BrdU substitution. The RBI (R bands by BrdU using immunological staining) and GBI (G bands by BrdU using immunological staining) band patterns were complementary for all chromosomes. There was no overlapping, and every part of each chromosome was positively stained by one of the two banding procedures. Comparative analysis of RBG (R bands by BrdU using Giemsa staining) and RBI band patterns, as well as GBG (G bands by BrdU using Giemsa staining) and GBI band patterns, showed good congruency, displaying a very good band-for-band match. The congruency and complementarity found for these band patterns show that high concentrations of both thymidine and BrdU blocked S-phase progression near the R-band to G-band replication transition within the S phase. They also prove that BrdU incorporation is complementary and, therefore, demonstrate the existence of the R/G transition: a possible regulatory checkpoint within the S phase of the cell cycle.

Adult↗