Multiple Myeloma Plasma Cell Kinetics: Rapid and Reliable Evaluation using 5-Bromo-2-Deoxyuridine (BrdUrd) DNA Incorporation Detected by an Anti-BrdUrd Monoclonal Antibody

In 19 patients with monoclonal gammopathy, plasma cell proliferative activity was evaluated using 5-bromo-2-deoxyuridine (BrdUrd) incorporation, as revealed by an anti-BrdUrd monoclonal antibody. A simultaneous standard labelled thymidine incorporation was carried out in all patients as reference test. The BrdUrd method was confirmed as a reliable test and is recommended for routine clinical application in monoclonal gammopathies.

Most anti-BrdU antibodies react with 2'-deoxy-5-ethynyluridine -- the method for the effective suppression of this cross-reactivity

5-Bromo-2'-deoxyuridine (BrdU) and 2'-deoxy-5-ethynyluridine (EdU) are widely used as markers of replicated DNA. While BrdU is detected using antibodies, the click reaction typically with fluorescent azido-dyes is used for EdU localisation. We have performed an analysis of ten samples of antibodies against BrdU with respect to their reactivity with EdU. Except for one sample all the others evinced reactivity with EdU. A high level of EdU persists in nuclear DNA even after the reaction of EdU with fluorescent azido-dyes if the common concentration of dye is used. Although a ten-time increase of azido-dye concentration resulted in a decrease of the signal provided by anti-BrdU antibodies, it also resulted in a substantial increase of the non-specific signal. We have shown that this unwanted reactivity is effectively suppressed by non-fluorescent azido molecules. In this respect, we have tested two protocols of the simultaneous localisation of incorporated BrdU and EdU. They differ in the mechanism of the revelation of incorporated BrdU for the reaction with antibodies. The first one was based on the use of hydrochloric acid, the second one on the incubation of samples with copper(I) ions. The use of hydrochloric acid resulted in a significant increase of the non-specific signal. In the case of the second method, no such effect was observed.

Combined bromodeoxyuridine immunocapture and terminal-restriction fragment length polymorphism analysis highlights differences in the active soil bacterial metagenome due to Glomus mosseae inoculation or plant species

High numbers of bacteria are associated with arbuscular mycorrhizal (AM) fungi, but their functions and in situ activities are largely unknown and most have never been characterized. The aim of the present study was to study the impact of Glomus mosseae inoculation and plant type on the active bacterial communities in soil by using a molecular approach, bromodeoxyuridine (BrdU) immunocapture in combination with terminal-restriction fragment length polymorphism (T-RFLP). This approach combined with sequence information from clone libraries, enabled the identification of actively growing populations, within the total bacterial community. Distinct differences in active bacterial community compositions were found according to G. mosseae inoculation, treatment with an antifungal compound (Benomyl) and plant type. The putative identities of the dominant bacterial species that were activated as a result of G. mosseae inoculation were found to be mostly uncultured bacteria and Paenibacillus species. These populations may represent novel bacterial groups that are able to influence the AM relationship and its subsequent effect on plant growth.

Maintenance of long-term tumour-specific T-cell memory by residual dormant tumour cells

LacZ (Gal)-reactive immune cells were transferred into athymic nu/nu mice inoculated with Gal-expressing syngeneic tumour cells (ESbL-Gal) in order to study tumour-protective T-cell memory. This transfer prevented tumour outgrowth in recipients and resulted in the persistence of a high frequency of Gal-specific CD8(+) T cells in the bone marrow and spleen. In contrast, such Ag-specific memory CD8(+) T cells were not detectable by peptide-major histocompatibility complex (MHC) multimer staining in animals that had not previously received an antigenic challenge. Even though CD44(hi) memory T cells from the bone marrow showed a significantly higher turnover rate, as judged by bromodeoxyuridine (BrdU) incorporation, than respective cells from spleen or lymph nodes, as well as in comparison to CD44(lo) naïve T cells, these findings suggest that tumour-associated antigen (TAA) from residual dormant tumour cells are implicated in maintaining high frequencies of long-term surviving Gal-specific memory CD8(+) T cells. Memory T cells could be recruited to the peritoneal cavity by tumour vaccination of immunoprotected nu/nu mice and exhibited ex vivo antitumour reactivity. Long-term immune memory and tumour protection could be maintained over four successive transfers between tumour-inoculated recipients, which involved periodic antigenic restimulation in vivo prior to reisolating the cells for adoptive transfer. Using a cell line (ESbL-Gal-BM) that was established from dormant tumour cells isolated from the bone marrow of immunoprotected animals, it could be demonstrated that the tumour cells had up-regulated the expression of MHC class I molecules and down-regulated the expression of several adhesion molecules during the in vivo passage. Our results suggest that the bone marrow microenvironment has special features that are of importance for the maintenance of tumour dormancy and immunological T-cell memory, and that a low level of persisting antigen favours the maintenance of Ag-specific memory T cells over irrelevant memory T cells.

Low doses of bromo- and iododeoxyuridine produce near-saturation labeling of adult proliferative populations in the dentate gyrus

Cell proliferation can be detected by the incorporation of tritiated thymidine (3H-dT) or halopyrimidines during DNA synthesis in progenitor cells. Administration of two thymidine analogues at different times can further determine the cell-cycle kinetics of proliferating cells. Traditionally, this was done by combining bromodeoxyuridine (BrdU) immunocytochemistry and 3H-dT autoradiography, or by BrdU and iododeoxyuridine (IdU) double-labeling using two mouse antibodies. However, these methods either require lengthy exposure time or involve complicated histological procedures for differentiating between two antibodies of the same species. Here we report a simple and reliable method of distinguishing BrdU- and IdU-labeled cells by immunofluorescence. This method uses a mouse monoclonal antibody that recognizes both BrdU and IdU and a rat anti-BrdU antibody that has no cross-reactivity with IdU. When combined with species-specific secondary antibodies that are conjugated to different fluorophores, this method identifies BrdU- and IdU-incorporation as doubly and singly labeled cells, respectively. This method has broad applications. First, we demonstrate that this method can distinguish mouse cortical neurons generated on different embryonic days. Second, by administering IdU and BrdU at varying intervals, we used this method to calculate that the length of S-phase of neural progenitor cells in the adult mouse dentate gyrus is approximately 6 h. Finally, we show that a six-fold higher concentration of IdU detects only 10% more cells than the standard dose of BrdU (50 mg/kg) using the double-labeling method. These results suggest that the standard dose of BrdU is sufficient to label the majority of proliferative populations in the S-phase in pulse labeling experiments.

Marrow Stromal Cell Transplantation after Traumatic Brain Injury Promotes Cellular Proliferation within the Brain

OBJECTIVE

This study was designed to investigate the effects of intracerebral as well as intravenous administration of bone marrow stromal cells (MSCs) on endogenous cellular proliferation after traumatic brain injury (TBI).

METHODS

Two experimental groups of Wistar rats were studied. One group received MSCs intracerebrally, and the other group received MSCs intravenously after injury by controlled cortical impact. MSCs were harvested from the bone marrow of male Wistar rats. For the intracerebral study, 24 male rats were divided into three groups (eight rats per group): rats injected with MSCs (1 x 10(6)) intracerebrally 1 day after TBI; 2) rats injected with phosphate-buffered saline intracerebrally 1 day after TBI; and 3) sham group not subjected to injury and not administered treatment. For the intravenous study, 10 female Wistar rats were injected 1 day after TBI with either MSCs (2 x 10(6)) (n = 5) or phosphate-buffered saline (n = 5) via the tail vein. Neurological function of the rats was evaluated with modified neurological severity scores and rotarod motor test. All rats were injected with bromodeoxyuridine intraperitoneally, to label the newly generating cells. Rats were killed 15 days after TBI, and coronal brain sections were stained immunohistochemically with diaminobenzidine to identify newly generating bromodeoxyuridine-positive cells. To study the differentiation of newly generating cells into neurons, sections were also double-stained for neuronal markers (Tuj1, doublecortin, NeuN) with fluorescein isothiocyanate.

RESULTS

The data demonstrate that newly generating cells were mainly present in the subventricular zone, hippocampal formation, and boundary zone of contusion of both treated and control animals. Intracerebral MSC treatment significantly increased the progenitor cell proliferation in the subventricular zone and boundary zone compared with the controls, whereas intravenous MSC treatment enhanced this endogenous proliferation in subventricular zone, hippocampus, and boundary zone. In both groups, some of the new cells revealed positive staining for neuronal markers. A statistically significant functional improvement was observed in both the intracerebrally as well as intravenously treated groups.

CONCLUSION

Intracerebral and intravenous MSC administration promotes endogenous cellular proliferation after TBI in rats. This may contribute to the functional improvement observed in these rats.

Autoantibodies to REG, a beta-cell regeneration factor, in diabetic patients

BACKGROUND

Regenerating gene (Reg) product, Reg, acts as an autocrine/paracrine growth factor for beta-cell regeneration. The presence of autoimmunity against REG may affect the operative of the regenerative mechanisms in beta cells of Type 1 and Type 2 diabetes patients. We screened sera from Type 1 and Type 2 diabetes subjects for anti-REG autoantibodies, searched for correlations in the general characteristics of the subjects with the presence of anti-REG autoimmunity, and tested the attenuation of REG-induced beta-cell proliferation by the autoanitibodies.

MATERIAL AND METHODS

We examined the occurrence of anti-REG autoantibodies in patients' sera (265 Type 1, 368 Type 2 diabetes patients, and 75 unrelated control subjects) by Western blot analysis, and evaluated inhibitory effects of the sera on REG-stimulated beta-cell proliferation by a 5'-Bromo-2'-deoxyuridine (BrdU) incorporation assay in vitro.

RESULTS

Anti-REG autoantibodies were found in 24.9% of Type 1, 14.9% of Type 2 and 2.7% of control subjects (P = 0.0004). There were significant differences between the autoantibody positive and negative groups in the duration of disease in the Type 1 subjects (P = 0.0035), and the age of onset in the Type 2 subjects (P = 0.0274). The patient sera containing anti-REG autoantibodies significantly attenuated the BrdU incorporation by REG (35.6 +/- 4.06% of the control), whereas the nondiabetic sera without anti-REG autoantibodies scarcely reduced the incorporation (88.8 +/- 5.10%).

CONCLUSION

Anti-REG autoantibodies, which retard beta-cell proliferation in vitro, are found in some diabetic patients. Thus, autoimmunity to REG may be associated with the development/acceleration of diabetes in at least some patients.

Rapid development of Th2 activity during T cell priming

The paradigm of T helper-1 (Th-1) and Th-2 cells developing from non-committed naïve precursors is firmly established. Th1 cells are characterized by IFN production and, in mice, the selective switching to IgG2a. Conversely IL-4 production and selective switching to IgG1 and IgE characterize Th2 cells. Analysis of Th2 induction in vitro indicates that this polarization develops gradually in T cells activated by anti-CD3 in the presence of IL-4; conversely anti-CD3 and IFN induce Th1 cells. In this report, we explore evidence that indicates that the T helper cell polarization in vivo cannot solely be explained by the cytokine environment. This is provided by studying the early acquisition of Th1 and Th2 activities during responses to a mixture of Th1 and Th2-inducing antigens. It is shown that these divergent forms of T cell help can rapidly develop in cells within a single lymph node. It is argued that early polarization to show Th-1 or Th-2 behavior can be induced by signals delivered during cognate interaction between virgin T cells and dendritic cells, in the absence of type 1 or type 2 cytokines. This contrasts with the critical role of the cytokines in reinforcing the Th-phenotype and selectively expanding T helper clones.

Neuropeptide Y promotes beta-cell replication via extracellular signal-regulated kinase activation

AIMS/HYPOTHESIS

Previous studies have shown that neuropeptide Y (NPY) gene expression and release are increased in hyperphagic ob/ob mice and diabetic rats. Therefore, we hypothesized that orexigenic agent, NPY, has the effect on the obesity and diabetes. To elucidate the relationship, we have studied the regulatory role of NPY on islet cells.

METHODS

Isolated islets were incubated with NPY or NPY Y1 receptor specific antagonist, BIBP3226. Proliferation, apoptosis, and Y1 receptor expression were identified by immunohistochemistry. We studied that ERK1/2 mediates the NPY pathway with PD98059 (MAP kinase inhibitor), wortmannin (phosphatidylinositol 3-kinase inhibitor), and BIM-1 (protein kinase C inhibitor). After NPY-treated islets were exposed to high glucose, insulin levels were detected.

RESULTS

beta-Cell replication was enhanced in a dose-dependent manner, but without any changes on the other cells in islet. NPY Y1 receptors were expressed on islet and NPY induced phosphorylation of ERK1/2 rapidly and transiently. PD98059 (MAPK kinase inhibitor) and BIM-1 (protein kinase C inhibitor) inhibited activation of ERK1/2 by NPY, but wortmannin (phosphatidylinositol 3-kinase inhibitor) did not. Exposure of NPY-treated islets to high glucose showed the decreasing trend of insulin secretion.

CONCLUSION/INTERPRETATION

Our data suggest that NPY promotes beta-cell replication via extracellular signal-regulated kinase activation and inhibits glucose-stimulated insulin secretion.

Immunocytochemical identification of neoplastic cell clone in phase S of cell cycle in transplantable rat tumors

Wistar and Buffalo rats of both sexes, aged 4 months, were divided into three groups: I which was given an intramuscular injection of 3 x 10(6) cells of Morris hepatoma (Buffalo males), II--subcutaneous injection of 3 x 10(4) cells of mammary gland carcinoma (Wistar females), III--intraperitoneal injection of 3 x 10(4) cells of Yoshid sarcoma (Wistar males). The animals were killed: in group I--19, group II--13 and in group III--6 days after tumor transplantation. Twenty four hours before euthanasia the rats were given 5-brome-2'-deoxyuridine (BRd-U) at a dose of 50 mg/kg body mass. The control group consisted of animals with tumour. They were not treated with BRd-U. Immunocytochemical reaction was performed on the sections of tumors, using monoclonal anti-BRd-U clone BU-33, Sigma. Computer measurements of tumor cells were carried out. There was a high similarity in morphological parameters between two kinds of cancer, and clear differences between them and Yoshid sarcoma. The main difference was noted in a twofold increase in the quantity of synthesised DNA in the nuclei of sarcoma cells. Immunocytochemical identification of tumor cells in phase S of the cell cycle with the use of monoclonal anti-BRd-U antibody is a precise and quick method of estimation of their proliferative potential.

Use of bromodeoxyuridine immunocapture to identify active bacteria associated with arbuscular mycorrhizal hyphae

Arbuscular mycorrhizae are beneficial for crops grown under low-till management systems. Increasingly, it is becoming apparent that bacteria associated with mycorrhizae can enhance the beneficial relationship between mycorrhizae and plants. However, it has been difficult to study these relationships by conventional techniques. In this study actively growing bacteria were identified in soil from an undisturbed fallow field known to contain arbuscular mycorrhizae by using molecular tools to eliminate the need for cultivation. A thymidine analog, bromodeoxyuridine (BrdU), was added to the soil and incubated for 2 days. DNA was extracted, and the newly synthesized DNA was isolated by immunocapture of the BrdU-containing DNA. The active bacteria in the community were identified by 16S rRNA gene PCR amplification and DNA sequence analysis. Based on 16S rRNA gene sequence information, a selective medium was chosen to isolate the corresponding active bacteria. Bacillus cereus strain VA1, one of the bacteria identified by the BrdU method, was isolated from the soil and tagged with green fluorescent protein. By using confocal microscopy, this bacterium was shown to clearly attach to arbuscular mycorrhizal hyphae. This study was the first to use this combination of molecular and traditional approaches to isolate, identify, and visualize a specific bacterium that is active in fallow soil and associates with arbuscular mycorrhizal hyphae.

Proliferating cells in the rat anterior pituitary during the postnatal period: immunoelectron microscopic observations using monoclonal anti-bromodeoxyuridine antibody

Proliferating cells in the male rat anterior pituitary at 1, 3, 5, and 8 weeks of age were labeled with bromodeoxyuridine (BrdU) and studied by light and electron microscopic immunocytochemistry using anti-BrdU. They decreased in number from 402+/-31/mm(2) at 1 week to 50+/-1.5/mm(2) at 8 weeks, while their cell area increased by about twofold during this period. They had a slightly higher nucleus/whole cell (N/C) ratio than non-proliferating cells. According to their ultrastructure we classified them into granular and agranular cells. The percentage of granular cells ranged from 73% to 82% of all the proliferating cells during the period studied. They had many granules of various sizes and shapes, and some contained growth hormone and prolactin. Agranular cells, constituting 18-27% of proliferating cells, were small and had a high N/C ratio, indicating their immaturity. Moreover, they showed several features of folliculo-stellate (FS) cells: they showed no secretory granules in the cytoplasm, extended thin cytoplasmic processes, and sometimes they constructed a follicle among them. These results suggest: (1) the majority of proliferating cells were mature cells producing anterior pituitary hormone(s) and (2) most of the agranular proliferating cells maybe FS cells. The possibility of the latter is discussed.

Temporal and spacial changes of BrdU immunoreactivity in amygdala kindling development

To investigate the proliferation of neural stem cells (NSC) in epileptic brain, spaciotemporal expression of immunoreactive bromodeoxyuridine (BrdU) was examined in kindling development of rat. Amygdaloid kindling in partial seizure (PS) was effective in proliferation of NSC detected with BrdU-labeling in subventricular zone (SVZ), but not in dentate gyrus (DG). In SVZ, however, the BrdU-labeling cells decreased at stage generalized seizure (GS). These facts indicate that proliferation of NSC increased with PS and decreased with more severe seizures of GS in SVZ, that such a proliferation did not occur in DG with PS or GS. Thus, the proliferation of NSC was spacially and temporally different between brain regions depending on different kindling stages.

Complex relationships between 5-aza-dC induced DNA demethylation and chromosome compaction at mitosis

A variety of treatments with 5-azadeoxycytidine (5-aza-dC) were applied to cultured human lymphocytes during one to four cell cycles. The effect of 5-aza-dC on DNA methylation was studied by using an antibody against 5-methylcytosine on mitotic chromosomes. 5-Azadeoxycytidine is known to induce strong and permanent demethylation of DNA. Unexpectedly complex relationships were observed between DNA methylation status and chromatid/chromosome compaction. The most dramatic alteration of compaction at mitosis was observed when pre-replicative chromosomes had unifilarly demethylated DNA. The compaction of chromosomes was found to depend only partially on the methylation of their DNA at the time of mitosis. Our results suggest that alteration of DNA methylation prevents the synchronization of chromatin compaction, inducing premature (or delayed) chromosome condensation, and that a crucial step is the DNA methylation status of the pre-replicative chromosome.

Immunohistochemical detection of cell growth fraction in formalin-fixed and paraffin-embedded murine tissue

Monoclonal antibody MIB-1 is a reliable tool for determining proliferating cells in human tissues, but does not react with the homologous mouse antigen and is therefore useless in experimental pathology using mice as model systems. Standard method for assessment of cellular proliferation in formalin-fixed, paraffin-embedded murine tissues is immunohistochemical detection of DNA synthesis using antibodies against exogenously injected 5-bromodeoxyuridine (BrdU), which is a tedious procedure and not useful for routine investigations. We tested monoclonal antibody MIB-5 and monoclonal and polyclonal anti-MCM3 antibodies as immunohistochemical proliferation markers for paraffin-embedded nonneoplastic and neoplastic tissues of wild-type and transgenic mice, compared to anti-BrdU immunostaining. Percentage of proliferating cells was determined with continuously decreasing antibody dilutions. Percentages of MIB-5 and anti-BrdU immunostained cells correlated strongly, as well as percentage of MIB-5-decorated cells and frequency of mitotic figures. Anti-MCM3 antibodies labeled significantly higher percentages of cells than anti-BrdU or MIB-5, and showed a linear decrease with increasing antibody dilutions. We conclude that MIB-5 detects reliably the cell growth fraction in formalin fixed, paraffin-embedded murine tissues, bypassing methodological drawbacks of BrdU. Anti-MCM3 antibodies are less useful for determination of proliferating cells although they might detect the fraction of cells remaining competent for proliferation.

Proliferative Activity of Epidermal Basal Cells after Wounding

Quantitative changes in nucleolus organizer regions (NORs) are known markers of proliferation that can be demonstrated by a specific silver staining technique on paraffin-embedded sections. Wounding of skin induces proliferation of basal epidermal cells at the wound margin. The degree of proliferation depends on the survival time and can be measured by morphometric assessment of argyrophilic NORs (AgNORs). Following incision wounding of the pinnae, rats were allowed to survive for different intervals (7 rats per interval) up to 120 hours. Before each sacrifice, biopsies were taken and incubated in a bromodeoxyuridine (BrdU) solution, embedded in paraffin, and stained with an antibody against BrdU. At the same time morphometric analysis of AgNOR counts was performed on sections made from the same material. BrdU incorporating nuclei were assessed by simple counting, whereas morphometric analysis of AgNOR counts was computer aided. Both methods revealed an increase in the number of proliferating cells, a plateau phase being reached after about 36 hours, followed by a decline after about 70 hours. Both methods thus allowed a reliable temporal classification of the skin injury according to survival time. The molecular background of the AgNOR changes in relation to the proliferation of cellular elements is discussed in detail.

Hoechst fluorescence intensity can be used to separate viable bromodeoxyuridine-labeled cells from viable non-bromodeoxyuridine-labeled cells

BACKGROUND

5-Bromo-2'-deoxyuridine (BrdU) is a powerful compound to study the mitotic activity of a cell. Most techniques that identify BrdU-labeled cells require conditions that kill the cells. However, the fluorescence intensity of the membrane-permeable Hoechst dyes is reduced by the incorporation of BrdU into DNA, allowing the separation of viable BrdU positive (BrdU+) cells from viable BrdU negative (BrdU-) cells.

METHODS

Cultures of proliferating cells were supplemented with BrdU for 48 h and other cultures of proliferating cells were maintained without BrdU. Mixtures of viable BrdU+ and viable BrdU- cells from the two proliferating cultures were stained with Hoechst 33342. The viable BrdU+ and BrdU- cells were sorted into different fractions from a mixture of BrdU+ and BrdU- cells based on Hoechst fluorescence intensity and the ability to exclude the vital dye, propidium iodide. Subsequently, samples from the original mixture, the sorted BrdU+ cell population, and the sorted BrdU- cell population were immunostained using an anti-BrdU monoclonal antibody and evaluated using flow cytometry.

RESULTS

Two mixtures consisting of approximately 55% and 69% BrdU+ cells were sorted into fractions consisting of greater than 93% BrdU+ cells and 92% BrdU- cells. The separated cell populations were maintained in vitro after sorting to demonstrate their viability.

CONCLUSIONS

Hoechst fluorescence intensity in combination with cell sorting is an effective tool to separate viable BrdU+ from viable BrdU- cells for further study. The separated cell populations were maintained in vitro after sorting to demonstrate their viability.

A detailed analysis of cyclin A accumulation at the G(1)/S border in normal and transformed cells

The temporal relationship between cyclin A accumulation and the onset of DNA replication was analyzed in detail. Five untransformed and nine transformed asynchronously growing cell cultures were investigated using a triple immunofluorescence staining protocol combined with computerized evaluation of staining intensities in individual cells. The simultaneous staining of BrdU, cyclin A, and cyclin E made it possible to determine the cell cycle position of each cell investigated. Cells at the G(1)/S border were identified on the basis of cyclin E content and were further analyzed with respect to cyclin A and BrdU content. A method was developed to calculate objective thresholds defining the highest staining intensity found in the negative cells in the population. Using the thresholds we could distinguish cells with minute amounts of cyclin A and BrdU from truly negative cells. We show that the onset of cyclin A accumulation and the start of DNA replication occurs at the same time, or deviating by a few minutes at the most. We also show that cyclin A accumulates continuously during S. This study clearly demonstrates that nuclear cyclin A can be used as a reliable marker for the S and G(2) phases in both normal and transformed interphase cells.

The organization of replicon clusters is not affected by polyamine depletion

Earlier investigations have shown that polyamine depletion affects DNA replication negatively. DNA is synthesized in replicons which are gathered in replicon clusters. DNA replication is initiated simultaneously in every replicon of a replicon cluster. By pulse labeling cells with the thymidine analog bromodeoxyuridine and then detecting bromodeoxyuridine in situ with immunofluorescence, replicon clusters can be studied. We have used this method to investigate the effects of 2-difluoromethylornithine (DFMO)- and 4-amidinoindan-1-one 2'-amidinohydrazone (CGP 48664)-mediated polyamine depletion on the organization of replicon clusters. The cells were studied by fluorescence microscopy and confocal laser scanning microscopy. Our studies give at hand that neither the number nor the distribution of replicon clusters were affected even after 4 days of treatment with 5 mM DFMO or 20 microM CGP 48664, indicating that polyamine depletion did not affect the organization of replicon clusters. However, the fluorescence intensity of the replicon clusters was much lower in inhibitor-treated cells. The results indicate that the impaired DNA replication observed in polyamine-depleted cells is not due to an effect on the initiation step of DNA replication, but rather on the elongation process. To confirm that it is possible to observe changes in the organization of replicon clusters using bromodeoxyuridine, we treated the cells with various drugs that affect DNA replication. Aphidicolin, which inhibits DNA elongation, gave results similar to those of DFMO and CGP 48664.

Effect of fixation and epitope retrieval on BrdU indices in mammary carcinomas

Studies in which 5-bromo-2'-deoxyuridine (BrdU) is used to quantify rates of cell proliferation are conducted prospectively. Therefore, the opportunity exists to select conditions that optimize detection of the BrdU epitope. The objective of this study was to quantify the extent to which the BrdU epitope was masked by formalin vs methacarn fixation in the assessment of cell proliferation. Mammary carcinomas from animals pulse-labeled with BrdU were trisected. A portion was frozen and the remaining two portions were fixed in 10% neutral buffered formalin or methacarn for 24 hr, processed, embedded in paraffin, and sections stained for incorporated BrdU using a peroxidase immunohistochemical staining technique. Antigen retrieval techniques also were applied to formalin-fixed sections. Fixation in methacarn gave the highest labeling index (16.4%), which was comparable to that observed in unfixed frozen sections (17.5%). Formalin fixation alone dramatically suppressed the labeling index (0.3%), which was only partially recovered using various antigen retrieval techniques (2.1-8.1%). Methacarn fixation is recommended for prospective studies in which BrdU detection is planned because of the quantitative recovery of epitope and the simplicity of the approach.

Glial cell proliferation in the spinal cord after dorsal rhizotomy or sciatic nerve transection in the adult rat

Proliferation of glial cells is one of the hallmarks of CNS responses to neural injury. These responses are likely to play important roles in neuronal survival and functional recovery after central or peripheral injury. The boundary between the peripheral nervous system (PNS) and CNS in the dorsal roots, the dorsal root transitional zone (DRTZ), marks a distinct barrier for growth by injured dorsal root axons. Regeneration occurs successfully in the PNS environment, but ceases at the PNS-CNS junction. In order to understand the role of different glial cells in this process, we analysed the proliferation pattern of glial cells in central (CNS) and peripheral (PNS) parts of the dorsal root and the segmental white and grey spinal cord matter after dorsal rhizotomy or sciatic nerve transection in adult rats 1-7 days after injury. Monoclonal antibody MIB-5 or antibodies to bromodeoxyuridine were used to identify proliferating cells. Polyclonal antibodies to laminin were used to distinguish the PNS and CNS compartments of the dorsal root. Dorsal root lesion induced glial cell proliferation in the CNS as well as PNS beginning at 1 day, with peaks from 2 to 4 days postoperatively. After sciatic nerve injury, cell proliferation occurred only in the CNS, was minimal at 1 day, and peaked from 2 to 4 days postoperatively. Double immunostaining with specific glial cell markers showed that after dorsal root transection 60% of the proliferating cells throughout the postoperative period examined were microglia, 30% astrocytes and 10% unidentified in the CNS, while in the PNS 40% were Schwann cells, 40% macrophages and 20% unidentified. After sciatic nerve injury virtually all proliferating cells were microglia. These findings indicate that non-neuronal cells in the CNS and PNS are extremely sensitive to the initial changes which occur in the degenerating dorsal root axons, and that extensive axonal degeneration is a prerequisite for astroglial and Schwann cell, but not microglial cell, proliferation.

Olfactory epithelium consisting of supporting cells and horizontal basal cells in the posterior nasal cavity of mice

The olfactory epithelium of mice generally consists of olfactory cells, progenitors of olfactory cells (globose basal cells), supporting cells, and horizontal basal cells. However, in the dorsal fossa (the roof) of the posterior nasal cavity of mice, we found seven epithelial patches consisting of only non-neuronal cell types, i.e., supporting cells and horizontal basal cells, among the normal olfactory epithelium. The supporting cells occupied three or four layers in the apical to middle regions; in the basal region, horizontal basal cells were localized in a single row adjacent to the basement membrane. Bowman's gland ducts were also present in the epithelium. Neuronal cells (olfactory cells and globose basal cells) were totally absent. The ultrastructure of the supporting cells, horizontal basal cells, and Bowman's glands was essentially similar to that in the normal olfactory epithelium. In the early postnatal period (P1-P7), cell types in the epithelium were the same as those in the normal olfactory epithelium. From P10 to P21, olfactory cells and globose basal cells had disappeared from the olfactory epithelium. At this period, the number of TUNEL-positive cells was significantly higher than that in the surrounding olfactory epithelium; ultrastructurally, many apoptotic figures were observed. This suggests that the epithelium consisting of supporting cells and horizontal basal cells is generated by the apoptotic death of olfactory cells and globose basal cells during postnatal development.

Bromodeoxyuridine labelling as an alternative method to identify 6-thioguanine-resistant mutant lymphocytes in humans

6-Thioguanine-resistant (TGR) mutant lymphocytes in human blood are usually enumerated by the cloning assay which allows the molecular characterisation of the HPRT mutations to be detected. A "short-term" alternative approach is provided by the anti-bromodeoxyuridine (anti-BrdU) technique in which TGR lymphocytes are identified immunocytochemically by their ability to synthesise DNA in the presence of 6-thioguanine (TG). We have evaluated the influence of various experimental factors that could affect the frequency of TGR lymphocytes. A standard protocol is proposed, based on 24-h cold storage of isolated lymphocytes at 4 degrees C and 40-h culture with and without TG, the last 16 h with BrdU. The harvested cells are treated with hypotonic (0.075 M) KCl, fixed with methanol:acetic acid (3:1) and put on microscopic slides. For the TG cultures, all cells are prepared on the slides, while slides from the control cultures are made by a 1/50 dilution. DNA is denatured by formamide, and the BrdU label is identified by anti-BrdU antibody detected by immunoperoxidase staining using a peroxidase-conjugated secondary antibody with diaminobenzidine as substrate. In 10 donors, the frequency of TGR lymphocytes (variant frequency, Vf) detected by this protocol ranged from 69.65 x 10(-6) to 83.45 x 10(-6), and split measurements showed a relatively small intra-assay variation in Vf values of each donor. BrdU in DNA was also detected by immunofluorescence using a fluorescein-conjugated anti-BrdU monoclonal antibody. This method, facilitating easy identification of positive cells and rapid microscopic scoring, may serve as a basis for an automated analysis of TGR lymphocytes. Vf values detected by the anti-BrdU assay are higher than mutant frequencies obtained by the cloning assay, which has been assigned to the presence of non-mutant phenocopies considered to represent spontaneously cycling lymphocytes. Although the anti-BrdU assay is rapid and easy and has been shown to respond to genotoxic exposures, its true value could be evaluated only when it can be ascertained that phenocopies do not significantly contribute to the Vf values obtained.

Normal human telomeres are not late replicating

Telomeres in yeast are late replicating. Genes placed next to telomeres in yeast can be repressed (telomere positional effects), leading to the hypothesis that telomeres may be heterochromatic and may control the expression of subtelomeric genes. In addition, yeast telomeres are processed to have a transient long overhang at the end of S phase. The applicability of the yeast data to human biology was examined by determining the timing of telomere replication and processing in normal human diploid fibroblasts. Telomeres were purified from synchronized cells that had been labeled with 5-bromodeoxyuridine (BrdU) at hourly intervals, and the fraction of labeled telomeres was analyzed by retrieval with anti-BrdU antibodies. We determined that normal human telomeres replicate throughout S phase rather than being very late replicating. Furthermore, the overall timing of replication was unaffected by telomere length in young versus old cells or cells whose telomeres had been elongated following transfection with the catalytic subunit of telomerase. Finally, the asymmetry in the length of the G-rich overhang in daughter telomeres produced by leading versus lagging strand synthesis was shown to be established within 1 h of telomere replication, indicating there is no significant delay between synthesis and the processing events that contribute to the establishment of asymmetric overhangs. Therefore, the timings of replication and processing of human telomeres are very different from those of yeast.

Mitotic sympathetic neuroblasts initiate axonal pathfinding in vivo

Neuronal precursor proliferation and axodendritic outgrowth have been traditionally regarded as discrete and sequential developmental stages. However, we recently found that sympathetic neuroblasts in vitro often elaborate long neuritic processes before dividing. Furthermore, these "paramitotic" neurites were maintained during cell division and neuritic morphology was consistently preserved by daughter cells after mitosis. This inheritance of neuritic morphology in vitro raised the possibility that proliferating neuroblasts engage in axodendritic outgrowth. To determine whether mitotic superior cervical ganglion (SCG) neuroblasts are engaged in pathfinding in vivo, we have combined retrograde axonal tracing of efferent nerve trunks with bromodeoxyuridine (BrdU) labeling of cells in S-phase. In fact, about 13% of BrdU(+) cells were retrogradely labeled, indicating that mitotic neuroblasts often have extraganglionic axonal projections. Moreover, the presence of axons during S-phase was observed at two developmental ages (E15.5 and E16. 5), implicating an ongoing function of paramitotic axons during neuronal ontogeny. Using a calculation to account for experimental limitations, we estimate that virtually all mitotic SCG neuroblasts have direct access to extraganglionic signals during development. We conclude that mitotic neuronal precursors in vivo engage in pathfinding, raising the possibility that interaction of proliferating populations with distant signals actively coordinates cell division and neural connectivity.

Improved immunodetection of nuclear antigens after sodium dodecyl sulfate treatment of formaldehyde-fixed cells

Immunostaining techniques are commonly employed to determine the temporal and spatial patterns of cellular components in in situ preparations of cells and tissues. Usually, cells are formalin-fixed, permeabilized with nonionic detergents, and probed with specific antibodies. The incorporation of a sodium dodecyl sulfate (SDS) treatment after chemical crosslinking has been shown to improve the immunodetection of some cytosolic and cell surface antigens. By incorporating an SDS treatment after crosslinking, we report a significant improvement in the detection of two nuclear antigens (i.e.) the DNA binding proteins apurinic/apyrimidinic endonuclease and DNA polymerase-beta) and bromodeoxyuridine-tagged DNA by indirect immunofluorescence of whole cells. In bromodeoxyuridine-tagged DNA, the improvement in detection after an SDS treatment was observed only after long incorporation protocols (>48 hr) and, interestingly, it was more pronounced in cultured human foreskin keratinocytes than in bovine aorta endothelial cells. In addition, the SDS treatment proved in these studies to be superior to the standard Triton X-100 permeabilization. SDS thus provides a potential means to visualize previously undetectable or poorly detectable nuclear antigens.

DNA repair of pyrimidine dimers and 6-4 photoproducts in the ribosomal DNA

The nucleolus is a unique structural component of interphase nuclei where the ribosomal genes, trans-cribed by RNA polymerase I (RNA pol I), are organized. In the present study, the repair of UV-induced photolesions was investigated in the ribosomal DNA (rDNA) in relation to RNA pol I transcription. We used hamster cells because their repair phenotype permits the separate analysis of the major photo-products induced by UV light. Immunofluorescent labeling of UV-induced DNA repair and transcription sites showed that the nucleolar regions were defic-ient in DNA repair despite the presence of abundant RNA pol I transcription foci. Immunological staining indicated that various NER proteins, including TFIIH (subunits p62 and p89), p53, Gadd 45 and prolifer-ating cell nuclear antigen are all enriched in the nuclei but distinctly absent in nucleoli. This lack of enrichment of NER factors in the nucleolus may be responsible for the inefficient repair of photo-products in the rDNA. UV irradiation generates two major photoproducts, the cyclobutane pyrimidine dimers (CPDs) and the 6-4 photoproducts (6-4 PPs). The repair kinetics of these two lesions were assessed simultaneously by the immunological isolation of bromodeoxyuridine (BudR) containing excision repair patches using an antibody to BudR. We found that the repair of the photolesions was less efficient in the rDNA compared to that of the endo-genous housekeeping gene, dihydrofolate reductase (DHFR). Gene specific repair of each of these two photoproducts was then measured separately in the rDNA and in the DHFR gene, which is transcribed by RNA pol II. The removal of CPDs was deficient in the rDNA as compared to the DHFR gene. On the contrary, 6-4 PPs were removed efficiently from the rDNA although somewhat slower than from the DHFR gene. The relatively efficient repair of 6-4 PPs in the rDNA is consistent with the notion that the 6-4 PPs are repaired efficiently in different genomic regions by the global genome repair pathway.

Colorimetric capture assay for human-immunodeficiency-virus-I reverse transcriptase activity

The development of a colorimetric capture assay for HIV-1 reverse transcriptase (RT) activity is described. This assay consisted of three basic steps: enzyme purification, RT reaction and product detection, which were all performed in the same microtitre plate. Mouse monoclonal anti-RT antibodies of subclass G2a were bound by polyclonal goat anti-(mouse IgG2a) immobilized in the wells of a microtitre plate. The monoclonal antibodies (mAbs) were selected for their ability to bind HIV-1 RT without hampering the polymerase activity. The assay system first involved the RT's adherence to the immobilized mAbs. Non-specific enzymes and other impurities were removed by a simple wash, after which an RT reaction mixture containing BrdUTP as nucleotide substrate was added. After the RT reaction substrate and product had been separated by washing of the plate, the amount of BrdUMP-DNA in the wells was finally detected with alkaline-phosphatase-conjugated mouse anti-BrdU antibodies of subclass IgG1. The background signal in this system was similar to the signals obtained with control wells coated with BSA only. A detection limit of 1.2 micro-units of RT activity, corresponding to 0.3 pg of RT protein, was obtained for the capture assay when applying colorimetric product detection. The assay detected RTs from HIV-1 subtypes A and B and one of the two D type isolates tested. None of the five non-HIV-1 RTs tested was found positive. At least 50 microl of human serum or plasma per sample could be included in the capture assay without adverse effects on the recovery of the RT activity.

Developmental neurotoxicity of phenytoin on granule cells and Purkinje cells in mouse cerebellum

Phenytoin (PHT) is a primary antiepileptic drug. Cerebellar malformations in human neonates have been described following intrauterine exposure to PHT. The neonatal period of development in the cerebellum in mice corresponds to the last trimester in humans. To examine the neurotoxic effects of PHT in the developing cerebellum, we administered PHT orally to newborn mice once a day during postnatal days 2-4. We observed many apoptotic cells in the external granular layer (EGL) on postnatal day 5, labeled cells in the EGL still remaining 72 h after labeling with 5-bromo-2'-deoxyuridine, and EGL thicker than that in the control on postnatal day 14. These results showed that PHT induced cell death of external granule cells and inhibited migration of granule cells in cerebella. In specimens immunostained with antibody against inositol 1,4,5-trisphosphate receptor type 1, Purkinje cells in the treated group had poor and immature arbors, and partially showed an irregular arrangement. The motor performance of the treated mice in a rotating rod test was impaired, although there were no changes in muscular strength or in walking pattern at the period of maturity. These findings indicate that PHT induces neurotoxic damage to granule cells and Purkinje cells in the developing cerebellum and impairs selected aspects of motor coordination ability.

Immunochemical detection and isolation of DNA from metabolically active bacteria

Most techniques used to assay the growth of microbes in natural communities provide no information on the relationship between microbial productivity and community structure. To identify actively growing bacteria, we adapted a technique from immunocytochemistry to detect and selectively isolate DNA from bacteria incorporating bromodeoxyuridine (BrdU), a thymidine analog. In addition, we developed an immunocytochemical protocol to visualize BrdU-labeled microbial cells. Cultured bacteria and natural populations of aquatic bacterioplankton were pulse-labeled with exogenously supplied BrdU. Incorporation of BrdU into microbial DNA was demonstrated in DNA dot blots probed with anti-BrdU monoclonal antibodies and either peroxidase- or Texas red-conjugated secondary antibodies. BrdU-containing DNA was physically separated from unlabeled DNA by using antibody-coated paramagnetic beads, and the identities of bacteria contributing to both purified, BrdU-containing fractions and unfractionated, starting-material DNAs were determined by length heterogeneity PCR (LH-PCR) analysis. BrdU-containing DNA purified from a mixture of DNAs from labeled and unlabeled cultures showed >90-fold enrichment for the labeled bacterial taxon. The LH-PCR profile for BrdU-containing DNA from a labeled, natural microbial community differed from the profile for the community as a whole, demonstrating that BrdU was incorporated by a taxonomic subset of the community. Immunocytochemical detection of cells with BrdU-labeled DNA was accomplished by in situ probing with anti-BrdU monoclonal antibodies and Texas red-labeled secondary antibodies. Using this suite of techniques, microbial cells incorporating BrdU into their newly synthesized DNA can be quantified and the identities of these actively growing cells can be compared to the composition of the microbial community as a whole. Since not all strains tested could incorporate BrdU, these methods may be most useful when used to gain an understanding of the activities of specific species in the context of their microbial community.

Novel formula for cell kinetics in xenograft model of hepatocellular carcinoma using histologically calculable parameters

The growth rate of tumors should be assessed in terms of both tumor cell proliferation and death. The former is considered to be determined by growth fraction and cell-cycle time, whereas the latter is mainly determined by apoptosis, especially in tumors with a low level of necrosis. While most hepatocellular carcinomas (HCCs) in a relatively early stage contain only a small amount of necrosis, the growth rate supposedly depends mainly on growth fraction, cell-cycle time, and apoptosis. However, their quantitative relationship remains unknown. We have derived a novel theoretical formula for determining this relationship in nonnecrotic HCC, using Ki-67-positive index, apoptotic score, and a correction factor, all calculable by histological assessment without injecting labeling agents. Furthermore, we confirmed the reliability of this formula, using a xenograft model of human HCC with less than 15% necrosis. In this model the values of cell-cycle time calculated from the formula were very close to those estimated by a conventional double-labeling method and showed high correlations. Since our novel formula can clarify the cell kinetics without cumbersome labeling procedures, it is expected to be clinically applicable to HCC with a small portion of necrosis, using the radiographically measured growth rate and the histologically assessed cell kinetic parameters.

Energy transfer between fluorescein isothiocyanate and propidium iodide--a problem in the estimation of Tpot with the bromodeoxyuridine-DNA flow cytometry technique?

Energy transfer in flow cytometry can occur when two fluorochromes are bound in close proximity (generally within 100 A) and the emission spectrum of one fluorochrome overlaps significantly with the excitation spectrum of the other. The latter criterium is fulfilled for the fluorochromes fluorescein isothiocyanate and propidium iodide and also the former when they, e.g., are used in bromodeoxyuridine - DNA flow cytometry methods. In the present growth kinetic study using this method, we show that energy transfer does take place between fluorescein isothiocyanate and propidium iodide which results in a detected increase in DNA content with 2-3%. Despite the erroneous increase in the obtained DNA content values, this does not seem to have any influence on the calculation of DNA synthesis time and potential doubling time where the DNA content, based on the relative movement principle of the labelled cells, is used.

An in vitro technique for tracing neuronal connections in the teleost brain

The availability of neuronal tract-tracing techniques has been fundamental to the development of the neurosciences. While most of the previously described methods are performed in vivo, in the present paper, detailed protocols are reported for tracing neuronal connections in an in vitro preparation. This technique, tested in various neural systems of the teleost brain, allows precise application of tracer substance(s) under visual control. After the isolation of the brain, the tissue is kept alive by superfusion with oxygenated artificial cerebrospinal fluid in a slice chamber. Neuronal connections are traced by the application of crystals of biocytin or dextran-tetramethylrhodamine to the region of interest. Following intracellular transport over 8-18 h, the tissue is fixed and processed histochemically for visualization of structures filled with the tracer substance. This method can readily be modified for double labelling. Step-by-step procedures are outlined for (a) the simultaneous detection of two tracer substances in the same tissue sample, (b) the combination of tract tracing with the immunohistochemical identification of various biochemical markers such as 'classical' transmitters and neuropeptides, and (c) the visualization of both traced structures and mitotically active cells labelled with the thymidine analogue 5-bromo-2'-deoxyuridine. By exhibiting a high degree of efficiency, the described in vitro tract-tracing technique represents also a significant contribution towards a reduction of living animals in neurobiological experimentation.

Two types of brain chondroitin sulfate proteoglycan: their distribution and possible functions in the rat embryo

The distribution of neurocan-like and 6B4 proteoglycan-like immunoreactivities in the rat embryo was investigated from gestational days 10.5-15.5 with monoclonal antibody 1G2 or 6B4 that immunoreacted with neurocan and 6B4 proteoglycan, respectively. In the brain region, the leptomeningeal layer in the myelencephalon, metencephalon, diencephalon or telencephalon was first stained with monoclonal antibody 1G2 at embryonic day 12.5. In the spinal cord, monoclonal antibody 1G2 stained the regions corresponding to the boundary caps (designated the boundary caps) after embryonic day 11.5 and the roof plate after embryonic day 12.5. The intensity of staining in the boundary caps reached a maximum at embryonic day 13.5, at around the time when the axons from the dorsal root ganglia reach this region. However, the points of contact of the axons with the boundary caps were hardly stained. By contrast, the roof plate was most strongly and widely stained at embryonic day 14.5, at around the time when the axons enter the spinal cord. Western blotting of preparations from the spinal cord that included the boundary caps revealed the presence of neurocan in this region. Thus, it is likely that neurocan serves as a barrier molecule to regulate the direction of axonal growth from the dorsal root ganglia. By contrast, in addition to staining of the future brain and spinal cord, monoclonal antibody 6B4 stained the trigeminal and sympathetic ganglia in the rat embryo on and after embryonic day 12.5, as well as the vestibular, facial and dorsal root ganglia after embryonic day 12.5. In studies in tissue culture, monoclonal antibody 6B4 prevented the inhibitory effects of 6B4 proteoglycan on the proliferation of PC12D cells. No immunostaining with monoclonal antibody 6B4 was observed in cells that had incorporated bromodeoxyuridine in vivo. Possible functions of 6B4 proteoglycan in the rat embryo are discussed.

Bulbectomy of neonatal mice induces migration of basal cells from the olfactory epithelium

Bulbectomy of neonatal mice induced cell migration from the olfactory epithelium in the nasal septum. We examined cell types of migrating clusters by immunohistochemistry using anti-keratin and anti-BrdU antibodies, and by electron microscopy. At 1-2 days after unilateral bulbectomy of P1 mice, cells migrated from the olfactory epithelium to the lamina propria of the septal olfactory mucosa. Horizontal basal cells that reacted specifically with anti-keratin antibody, and globose basal cells characterized by a round shape and poor content of organellae in their cytoplasm, were contained in the cluster. At 1 week, migrated clusters that contained keratin-positive horizontal basal cells were observed in both the lamina propria and olfactory bulb on the unoperated side. At 1 month, not only basal cells but also olfactory cells and presumed supporting cells were involved in the clusters in the lamina propria and olfactory bulb, suggesting that migrated cells do not transform to other phenotypes.

Inducible repair of thymine glycol detected by an ultrasensitive assay for DNA damage

An ultrasensitive assay for measuring DNA base damage is described that couples immunochemical recognition with capillary electrophoresis and laser-induced fluorescence detection. The method provides a detection limit of 3 x 10(-21) moles, an improvement of four to five orders of magnitude over current methods. Induction and repair of thymine glycols were studied in irradiated A549 cells (a human lung carcinoma cell line). Exposure of these cells to a low dose of radiation (0.25 Gray) 4 hours before a clinically relevant dose (2 Gray) enhanced removal of thymine glycols after the higher dose. These data provide evidence for an inducible repair response for radiation-induced damage to DNA bases.

Radiosensitivity and repair of the inactive X-chromosome. Insights from FISH and immunocytogenetics

The inactive X-chromosome provides a unique opportunity to study the role of transcriptional activity and chromatin condensation in the repair of chromosome damage. We induced chromosome breakage in human lymphocytes with X-rays (1 or 2 Gy) in either G0 and G1 phase of the cell cycle, and in the presence or absence of an inhibitor of double strand break repair, adenine 9-beta-D-arabinofuranoside (Ara-A). Chromosomal aberrations involving the X-chromosome were detected by means of fluorescence in situ hybridization with an X-chromosome specific red painting probe. The activation status of the X-chromosomes involved in the chromosomal aberrations was determined by simultaneous immunocytogenetics with FITC-conjugated antibodies against BrdUrd incorporated at late S-phase to distinguish the late replicating inactive X-chromosome in green-yellow. This multicolor approach allowed us to study and compare breakage and the extent of repair in the active and inactive X-chromosome. Our data indicate that both chromosomes responded with a similar radiosensitivity. This observation was consistent at both X-ray doses and at the two stages of the cell cycle analyzed. However, the number of chromosomal aberrations involving the inactive X-chromosome was increased after repair inhibition with Ara-A. The differential sensitivity to repair inhibition was observed in G0 after 1 Gy and in G1 after 2 Gy. Thus, the activation status of the X-chromosome might be a source of heterogeneity in breakage and repair. These observations suggest that there is heterogeneous repair when the active and the inactive X-chromosomes are compared and that the observed fragility is the result of a compromise between the actual number of breaks induced in each chromosome and their differential processing.

In situ visualization of DNA double-strand break repair in human fibroblasts

A method was developed to examine DNA repair within the intact cell. Ultrasoft x-rays were used to induce DNA double-strand breaks (DSBs) in defined subnuclear volumes of human fibroblasts and DNA repair was visualized at those sites. The DSBs remained in a fixed position during the initial stages of DNA repair, and the DSB repair protein hMre11 migrated to the sites of damage within 30 minutes. In contrast, hRad51, a human RecA homolog, did not localize at sites of DNA damage, a finding consistent with the distinct roles of these proteins in DNA repair.

Potassium chloride inhibits proliferation of cerebellar granule neuron progenitors

CNS neurogenesis involves a critical transition where neuronal progenitors exit the cell cycle and initiate terminal differentiation. Recent experiments have suggested that depolarization inhibits DNA synthesis in cortical progenitors. Depolarization of proliferating neuronal progenitors may thus activate mechanisms that prevent proliferation and allow the initiation of terminal differentiation. We present evidence that depolarizing concentrations of KCl (25-50 mM) reduce proliferation of developing postnatal cerebellar granule cells in culture. These studies show that KCl antagonizes the mitogenic response of granule cells to insulin-like growth factor-I (IGF-I) and that this reduction in proliferating cells is not the result of a selective cell death. We also examined the differentiation of granule cell cultures using Brn-5 expression as an early differentiation marker. In vivo Brn-5 expression occurs soon after developing granule cells exit the cell cycle and begin their final differentiation. In control cultures and cultures treated with high concentrations of KCl Brn-5 expression increased over 24-48 h of culture. Our results suggest depolarizing concentrations of KCl antagonize proliferation of cerebellar granule neuron progenitors however allow their continued differentiation.

Quantitative polymerase chain reaction assay for DNA repair within defined genomic regions

We have developed a quantitative assay to determine repair of structurally different DNA lesions at defined genomic sites. This assay depends on the fact that many different types of damage are repaired by the same nucleotide excision repair (NER) pathway which includes synthesis of short DNA fragments at the sites of damage. After exposure to damaging agents, cells are treated with 5-bromodeoxyuridine (BrdUrd) to label the regions undergoing repair with the presumption that regions that have been more efficiently repaired would incorporate more BrdUrd than regions that were less effectively repaired. Thus, the abundance of the different sequences in the BrdUrd-containing DNA would be a direct and quantitative measure for the repair rates of the corresponding regions. The BrdUrd-containing, repaired DNA was isolated by CsCl gradient centrifugation and immunoprecipitation with anti-BrdUrd antibody and was used as template in quantitative PCR in which the amount of the product was directly proportional to the amount of template. This approach was used to address the question whether DNA repair after UV-irradiation occurs in an uniform, random manner or with preferences for certain regions. We found out that there was a higher repair efficiency at the 5'-end of the mouse gamma-globin domain in Ehrlich ascites tumor cells.

Analysis of cell kinetics after gamma-ray irradiation using an anti-BrdU monoclonal antibody

The cell cycle was analyzed using double staining with an anti-bromodeoxyuridine (BrdU) monoclonal antibody and propidium iodide (PI). Changes in cell kinetics after irradiation were compared with those seen by the conventional PI-based DNA histogram method. The effect of irradiation on cell kinetics has been studied primarily by counting G2-arrested cells. By the present BrdU method, a rapid transition from G1 to S-phase was observed within 2 h of irradiation, followed by G1 block. Cells in the S-phase progressed to G2+M where they arrested, resulting in a decreased percentage of S cells (<5%). Release of G1 block occurred after 8 h, and G2+M cells returned to G1 after >18 h. The initial G1 arrest induced by irradiation was confirmed for the first time by the present BrdU-PI double staining.

Simultaneous detection of DNA synthesis and cytokine production in staphylococcal enterotoxin B activated CD4+ T lymphocytes by flow cytometry

Assessment of T cell activation has traditionally been performed by measuring proliferation as a function of 3[H]-thymidine incorporation, or secretion of cytokines from activated peripheral blood mononuclear cells (PBMC) in culture. An alternative method for detection of proliferation at the single cell level utilizes incorporation of bromodeoxyuridine (BrdU), an analog of thymidine, into cellular DNA. After appropriate fixation and permeabilization of the cells, a monoclonal antibody (mAb) against BrdU conjugated with a fluorescent dye is employed to measure by flow cytometry the incorporated BrdU. Here, we report a flow cytometric procedure which can be used for the simultaneous detection of BrdU incorporation, activation markers such as CD69 and CD25, and intracellular cytokines in T cell subsets from activated PBMC. Our observations are consistent with the proposal that cytokine synthesis and cell proliferation occur sequentially in CD4+ T cells stimulated with the superantigen staphylococcal enterotoxin B (SEB). The majority of cells expressing the cytokines IFN-gamma and IL-2 at 48 h appear to have undergone DNA synthesis, however all proliferating cells do not express IFN-gamma or IL-2. The methods presented in this report offer a unique approach for studying simultaneous expression of key cellular activation events in phenotypically resolved lymphocyte populations.

Assessment of cell proliferation in regenerating bone during distraction osteogenesis at different distraction rates

An experimental model of lengthening of the lower limb was used to study the morphology and cellular proliferation of regenerating bone tissue after 20% lengthening at four rates of distraction. Groups of rabbits were killed at different times 1-8 weeks after surgery. The regenerated area was divided into three zones: fibrous, primary mineralization front, and new bone. As the rate of distraction increased, the size of the fibrous zone increased and that of the new bone zone decreased. Necrosis, formation of cysts, and cartilage were found in the regenerated area at the higher distraction rates. Cell proliferation was assessed by in vivo labelling with bromodeoxyuridine, and the positive staining index for anti-bromodeoxyuridine antibody was calculated in the zones of the regenerated tissue. The index values for the fibrous zones and the new bone zones did not differ significantly in any of the groups. The value increased significantly (p < 0.05) in the primary mineralization front as the rate of distraction increased from 0.3 to 0.7 mm/day, but there was no further significant increase at higher distraction rates. In conclusion, cell proliferation was increased at all of the higher rates (more than 0.3 mm/day) of distraction studied. Higher rates of distraction caused tissue damage. A distraction rate of 0.7 mm/day appeared optimal for cell proliferation and histological characteristics.

Protease antigen recovery decreases the specificity of bromodeoxyuridine detection in formalin-fixed tissue

Incorporation of halogenated nucleotide analogues is often used to assess DNA synthesis and to quantitate cellular proliferation. Multiple antibodies have been developed to bromodeoxyuridine (BrdUrd) and it is the most frequently utilized substrate. Because the immunodetection of incorporated BrdUrd requires DNA denaturation or nuclease digestion, most of these antibodies are not reactive in tissues or cells fixed with crosslinking agents. Antigen retrieval techniques utilizing protease digestion restore BrdUrd antigenicity and permit the detection of BrdUrd in formalin-fixed tissue. However, during the development of a double label immunohistochemical protocol to quantitate proliferating alveolar Type II cells, we noted nucleus-specific staining in lung sections from animals that had not received BrdUrd. Therefore, we systematically analyzed the specificity of the immunohistochemical detection of incorporated BrdUrd in formalin-fixed tissue after protease digestion. Enzymatic antigen recovery diminished the specificity of the BrdUrd reaction product and caused false-positive staining with the BU-1, B44, and BR3 monoclonal antibodies. Staining was less prominent with Bu20a but was more specific. Protease antigen recovery may decrease the specificity of BrdUrd immunodetection. Appropriate controls are required when enzymatic digestion is used to detect incorporated BrdUrd in formalin-fixed tissue. The type and duration of fixation, antibody to BrdUrd, protease, and tissue may affect the specificity of the staining pattern.

In vitro induction of micronuclei in lymphocytes: the use of bromodeoxyuridine as a proliferation marker

A simple method to determine the induction of micronuclei in cultured lymphocytes is described as an alternative to the cytochalasin-B method. It is proposed for use in the evaluation of the genotoxic potential of agents in vitro. It allows the recording of events only in the proliferating population of cells and at the same time it eliminates the possibility of recording combined effects with a cytokinesis-blocking agent. 16 microM bromodeoxyuridine (BrdU) was used to label proliferating cells that were treated with colcemid or mitomycin C at different concentrations. A monoclonal antibody against BrdU incorporated in the DNA and a peroxidase-diaminobenzidine brown stain were used to identify those cycling cells in a slide. To obtain the maximum yield of micronuclei, the best time for the addition of bromodeoxyuridine was found to be at 40 h from the initiation of cultures, 8 h before treating cells with the chemicals. Identification of micronuclei was easy, fast and unequivocal. In addition, the formation of structures similar to micronuclei, but that still are part of the nucleus could be observed. It is not clear if these structures are an intermediate stage in the formation of MN, but this methodology provides the possibility of observing and studying them.

Auditory epithelial migration. III: An immunohistologic study using anti-BrdU antibody on tympanic membrane in mouse

A localization pattern of epidermal cells on the tympanic membrane (TM) and their migratory patterns were studied in mice, by means of immunohistologic technique using an anti-bromodeoxyuridine (BrdU) antibody. The BrdU was instilled intraperitoneally and the animals were painlessly sacrificed between 1 hour and 10 days after the injection. An immunostaining technique using anti-BrdU antibodies was applied on whole mount TM tissues. One hour after injection, BrdU-labeled cells were found in the handle of the malleus (HM) region and in the annular region of the pars tensa of the TM. Some labeled cells were observed in the intermediate region of the upper half of the superior quadrant, but no labeled cells were found in the remaining part of the intermediate region. Labeled cells were also evident in the pars flaccida without any particular pattern of distribution. As time elapsed after the injection, the labeled cells first appearing in the HM region had migrated laterally and inferiorly from the HM toward the annulus, while those in the annular region had considerably decreased in number. Results of the present study are the following: 1) the proliferation center of epidermal cells in the pars tensa is located in two different areas, i.e., the HM region and annular region, 2) newly generated cells in the HM region migrated from the HM region toward the annular region, whereas those in the annular region migrate from the the annular region to the external auditory canal, and 3) no specific generation center is located in the pars flaccida. On the basis of these results, we discuss the relationship between the site of the proliferation center of epidermal cells and their migratory patterns.