Therapeutic use of selected herbs

An increasing number of people in the United States are using herbs for health promotion and specific symptom management. Herbs are used to initiate healing through synergistic responses unlike the specific properties of pharmaceuticals. Anecdotal data comprise much of the popular information available about herbs. Scientific studies of the efficacy and safety of herbs, although on the rise, are less available than other drug trials. Clinicians need an appropriate knowledge base for dealing with patients who take herbal preparations as well as the ability to confidently include herbal preparations in their formulary. In this article, five common herbs are reviewed. The effects, clinical studies, side effects, and dosing regimens for aloe vera, arnica, black cohosh, evening primrose oil, and saw palmetto are described.

Calcium phosphate-containing precipitate and the carcinogenicity of sodium salts in rats

Sodium saccharin, ascorbate and other sodium salts fed at high doses to rats produce urinary bladder urothelial cytotoxicity with consequent regenerative hyperplasia. For sodium salts that have been tested, tumor activity is enhanced when administered either alone or after a brief exposure to a known genotoxic bladder carcinogen. These sodium salts alter urinary composition of rats resulting in formation of an amorphous precipitate. We examined the precipitate to ascertain its composition and further delineate the basis for its formation in rat urine. Using scanning electron microscopy with attached X-ray energy dispersive spectroscopy, the principal elements present were calcium, phosphorus, minor amounts of silicon and sulfur. Smaller elements are not detectable by this method. Infrared analyses demonstrated that calcium phosphate was in the tribasic form and silicon was most likely in the form of silica. Small amounts of saccharin were present in the precipitate from rats fed sodium saccharin (<5%), but ascorbate was not detectable in the precipitate from rats fed similar doses of sodium ascorbate. Large amounts of urea and mucopolysaccharide, apparently chondroitin sulfate, were detected in the precipitate by infrared analysis. Chemical analyses confirmed the presence of large amounts of calcium phosphate with variably small amounts of magnesium, possibly present as magnesium ammonium phosphate crystals, present in urine even in controls. Small amounts of protein, including albumin and alpha(2u)-globulin, were also detected (<5% of the precipitate). Calcium phosphate is an essential ingredient of the medium for tissue culture of epithelial cells, but when present at high concentrations (>5 mM) it precipitates and becomes cytotoxic. The nature of the precipitate reflects the unique composition of rat urine and helps to explain the basis for the species specificity of the cytotoxic and proliferative effects of high doses of these sodium salts.

Wingless gradient formation in the Drosophila wing

BACKGROUND

Secreted signaling proteins of the Wingless (Wg)/Wnt, Hedgehog and bone morphogenetic protein (BMP)/Decapentaplegic (Dpp) families function as morphogens to control growth and pattern formation during development. Although these proteins have been shown to act directly on distant cells in the developing limbs of the fruit fly Drosophila, little is known about how ligand gradients form in vivo. Wg protein is found in vesicles in Wg-responsive cells in the embryo and imaginal discs. It has been proposed that Wg may be transported by a vesicle-mediated mechanism.

RESULTS

A novel method to visualize extracellular Wg protein was used to show that Wg forms an unstable gradient on the basolateral surface of the wing imaginal disc epithelium. Wg movement did not require internalization by dynamin-mediated endocytosis. Dynamin activity was, however, required for Wg secretion. By reversibly blocking Wg secretion, we found that Wg moves rapidly to form a long-range extracellular gradient.

CONCLUSIONS

The Wg morphogen gradient forms by rapid movement of ligand through the extracellular space, and depends on continuous secretion and rapid turnover. Endocytosis is not required for Wg movement, but contributes to shaping the gradient by removing extracellular Wg. We propose that the extracellular Wg gradient forms by diffusion.

Endoneurial vasculitis and tubuloreticular inclusions in peripheral nerve biopsy

We describe 3 patients in whom nerve biopsy revealed endothelial tubuloreticular inclusions in association with peripheral nerve endoneurial vasculitis. Two of the patients had systemic lupus erythematosus (SLE), while the third was HIV-positive. Review of our biopsy material featuring the much more common finding of epineurial vasculitis failed to disclose any instances in which endothelial tubuloreticular inclusions (TRIs) were present. We conclude that TRIs and endoneurial vasculitis are closely associated. Moreover, if detected on a nerve biopsy specimen, TRIs are very suggestive of SLE or HIV infection. Finally, literature evidence is cited to suggest that an "acid-labile" alpha-interferon may be pathogenically related to the vasculitic process in these patients, perhaps through a process mediated by tumor necrosis factor.

Lessons learned in applying the U.S. EPA proposed cancer guidelines to specific compounds

An expert panel was convened to evaluate the U.S. Environmental Protection Agency's "Proposed Guidelines for Carcinogen Risk Assessment" through their application to data sets for chloroform (CHCl3) and dichloroacetic acid (DCA). The panel also commented on perceived strengths and limitations encountered in applying the guidelines to these specific compounds. This latter aspect of the panel's activities is the focus of this perspective. The panel was very enthusiastic about the evolution of these proposed guidelines, which represent a major step forward from earlier EPA guidance on cancer-risk assessment. These new guidelines provide the latitude to consider diverse scientific data and allow considerable flexibility in dose-response assessments, depending on the chemical's mode of action. They serve as a very useful template for incorporating state-of-the-art science into carcinogen risk assessments. In addition, the new guidelines promote harmonization of methodologies for cancer- and noncancer-risk assessments. While new guidance on the qualitative decisions ensuing from the determination of mode of action is relatively straightforward, the description of the quantitative implementation of various risk-assessment options requires additional development. Specific areas needing clarification include: (1) the decision criteria for judging the adequacy of the weight of evidence for any particular mode of action; (2) the role of mode of action in guiding development of toxicokinetic, biologically based or case-specific models; (3) the manner in which mode of action and other technical considerations provide guidance on margin-of-exposure calculations; (4) the relative roles of the risk manager versus the risk assessor in evaluating the margin of exposure; and (5 ) the influence of mode of action in harmonizing cancer and noncancer risk assessment methodologies. These points are elaborated as recommendations for improvements to any revisions. In general, the incorporation of examples of quantitative assessments for specific chemicals would strengthen the guidelines. Clearly, any revisions should retain the emphasis present in these draft guidelines on flexibility in the use of scientific information with individual compounds, while simultaneously improving the description of the processes by which these mode-of-action data are organized and interpreted.

Transdifferentiation of somatotrophs to thyrotrophs in the pituitary of patients with protracted primary hypothyroidism

In patients with protracted primary hypothyroidism, the pituitary is enlarged due to the lack of feedback inhibition by thyroid hormone. In the present work, adenohypophysial biopsies from three women with protracted primary hypothyroidism were investigated by routine histology, immunocytochemistry, double immunostaining, immunoelectron microscopy, and combined immunocytochemistry - in situ hybridization. These methods confirmed the presence of massive thyrotroph hyperplasia and the formation of "thyroidectomy" or "thyroid deficiency" cells. A number of thyroidectomy cells were found to be immunoreactive for growth hormone (GH). Double immunostaining and immunoelectron microscopy revealed the presence of bihormonal cells containing both GH and thyroid stimulating hormone (TSH). Immunostaining combined with in situ hybridization revealed GH immunoreactive cells expressing TSH mRNA as well as TSH immunopositive cells expressing GH mRNA. Our findings provide conclusive evidence that somatotrophs may transform to thyrotrophs. Thus, in addition to multiplication of thyrotrophs, transdifferentiation of GH cells to thyrotrophs contributes to the increase of TSH-producing cells. The presence of such bihormonal cells best termed "thyrosomatotrophs" supports the concept that adenohypophysial cells are not irreversibly committed to the production of one single hormone and that their phenotype can change in response to functional demand.

Notch signaling is not sufficient to define the affinity boundary between dorsal and ventral compartments

The developing limbs of Drosophila are subdivided into distinct cells populations known as compartments. Short-range interaction between cells in adjacent compartments induces expression of signaling molecules at the compartment boundaries. In addition to serving as the sources of long-range signals, compartment boundaries prevent mixing of the adjacent cell populations. One model for boundary formation proposes that affinity differences between compartments are defined autonomously as one aspect of compartment-specific cell identity. An alternative is that the affinity boundary depends on signaling between compartments. Here, we present evidence that the dorsal selector gene apterous plays a role in establishing the dorsoventral affinity boundary that is independent of Notch-mediated signaling between dorsal and ventral cells.

The premature removal of tissue expanders in breast reconstruction

The role of tissue expanders in breast reconstruction is well established. Little information exists, however, regarding the incidence and etiology of premature removal of the tissue expander before planned exchange to a permanent breast implant. The purpose of this study was to review our 10-year experience with tissue expander breast reconstruction and identify factors relating to the premature removal of the tissue expander. This study is a retrospective review of 770 consecutive patients who underwent breast reconstruction with tissue expanders over the past 10 years. Breast reconstruction was immediate in 90 percent of patients. Patients were expanded weekly, and adjuvant chemotherapy was begun during the expansion process when required. Factors potentially affecting premature expander removal (chemotherapy, diabetes, obesity, radiation therapy, and smoking) were evaluated. Fourteen patients (1.8 percent) with a mean age of 47 years (range, 38 to 62 years) required premature removal of their tissue expander. Expanders were removed a mean of 3.2 months (0.1 to 8 months) after insertion. Causes for premature removal of the tissue expander included infection (7 patients), exposure (2), skin necrosis (2), patient dissatisfaction (2), and persistent breast cancer (1). Positive wound cultures were obtained in four of the seven infected patients (57 percent), requiring expander removal for infection. Tissue expanders were removed in 11 patients for complications directly related to the expander. Among these, six (55 percent) were receiving adjuvant chemotherapy, and one was a smoker. Diabetes, obesity, other concomitant medical illnesses, and prior mantle irradiation were not associated with expander removal. Premature removal of the tissue expander was required in only 1.8 percent of the patients in this series. Infection was the most common complication necessitating an unplanned surgical procedure to remove the expander. This study demonstrates that the use of tissue expanders in breast reconstruction is reliable, with the vast majority of patients completing the expansion process.

Comparison of uroplakin expression during urothelial carcinogenesis induced by N-butyl-N-(4-hydroxybutyl)nitrosamine in rats and mice

The expression of uroplakins, the tissue-specific and differentiation-dependent membrane proteins of the urothelium, was analyzed immunohistochemically in N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-treated rats and mice during bladder carcinogenesis. Male Fischer 344 rats were treated with 0.05% BBN in the drinking water for 10 wk and were euthanatized at week 20 of the experiment. BBN was administered to male B6D2F, mice; it was either provided at a rate of 0.05% in the drinking water (for 26 wk) or 5 mg BBN was administered by intragastric gavage twice weekly for 10 wk, followed by 20 wk without treatment. In rats, BBN-induced, noninvasive, low-grade, papillary, transitional cell carcinoma (TCC) showed decreased uroplakin-staining of cells lining the lumen but showed increased expression in some nonluminal cells. In mice, nonpapillary, high-grade dysplasia, carcinoma in situ, and invasive carcinoma were induced. There was a marked decrease in the number of uroplakin-positive cells lining the lumen and in nonluminal cells. This occurred in normal-appearing urothelium in BBN-treated mice and in dysplasic urothelium, in carcinoma in situ, and in invasive TCC. The percentage of uroplakin-positive nonluminal cells was higher in control mice than in rats, but it was lower in the mouse than in the rat after BBN treatment. Uroplakin expression was disorderly and focal in BBN-treated urothelium in both species. These results indicate that BBN treatment changed the expression of uroplakins during bladder carcinogenesis, with differences in rats and mice being related to degree of tumor differentiation.

Effects of dietary dimethylarsinic acid on the urine and urothelium of rats

Dimethylarsinic acid (DMA), fed to rats for 2 years, produced bladder hyperplasia and tumors at doses of 40 and 100 p.p.m., more in females than males. No urothelial proliferation was seen in mice. Our objectives were to investigate the mode of action of bladder tumor formation, evaluate the dose-response and the role of diet and to determine if the urothelial effects were reversible. The study included groups of female F344 rats fed DMA in Purina 5002 diet at doses of 0, 2, 10, 40 or 100 p.p.m. for 10 weeks; two groups of females fed DMA (0 and 100 p.p.m.) in Altromin 1321 for 10 weeks; two groups of males fed DMA (0 and 100 p.p.m.) in Purina 5002 for 10 weeks; a female high-dose recovery group (100 p.p.m. in Purina 5002 diet for 10 weeks followed by control diet for 10 weeks); and two female groups (0 and 100 p.p.m.) in Purina diet for 20 weeks. Urothelial toxicity and hyperplasia were detected by light and scanning electron microscopy (SEM), and the bromodeoxyuridine labeling index was increased in the female 40 and 100 p.p.m. groups. The effects were less in males, but were similar in females fed DMA in Altromin 1321. SEM detected no abnormal urinary solids related to treatment in any group. Urinary calcium was increased in the females fed 40 and 100 p.p.m. in Purina diet, despite overall urinary dilution. Calcification was increased in kidneys of female rats fed Purina diet. The urothelial effects of DMA were reversible. The findings support a non-DNA reactive mechanism for DMA rat bladder carcinogenicity related to urothelial toxicity and regeneration. The toxicity is probably not due to urinary solids. The toxicity and regeneration are produced in a dose-responsive manner in female rats, are greater in female than in male rats, and are reversible.

Placental blood flow measured by simultaneous multigate spectral Doppler imaging in pregnancies complicated by placental vascular abnormalities

OBJECTIVE

To evaluate the role of placental blood flow measurements by simultaneous multigate spectral Doppler imaging in pregnancies complicated by intrauterine growth restriction (IUGR), and for early detection of placental vascular abnormalities in high- and low-risk pregnancies.

METHODS

To assess the sensitivity and specificity of abnormal placental blood flow in detecting IUGR, we followed 22 women whose pregnancies were complicated by IUGR at 28-34 weeks' gestation, and compared the findings with those obtained in 22 matched controls. We defined placental blood flow impedance as abnormal when 10% of placental pulsatility index (PI) measurements were greater than, or equal to, the mean umbilical artery PI (placental PI/umbilical PI > or = 1). To determine the predictive value of abnormal placental blood flow measurement for identifying developing uteroplacental insufficiency, we examined an unselected group of 100 low- and high-risk patients at 20-22 weeks' gestation. We correlated the Doppler findings with the development of pre-eclampsia, IUGR, placental abruption, oligohydramnios and the presence of persistent late decelerations during labor.

RESULTS

Placental blood flow determination was more sensitive than umbilical artery blood flow in detecting abnormal umbilical-placental flow impedances as manifested by the presence of IUGR. Of the 100 mixed high- and low-risk patients examined at 20-22 weeks, 32 had abnormal placental blood flow. Of these, 19 (59.4%) subsequently developed pathologies associated with placental vascular disease. Of the 68 patients with normal placental blood flow, only six (8.8%) developed such pathologies. The sensitivity was 76% (19/25), with positive predictive value 59.4% (19/32); the specificity was 82.7% (62/75), with negative predictive value 91.2% (62/68).

CONCLUSIONS

Abnormal intraplacental blood flow at 28-34 weeks' gestation is strongly associated with IUGR. In addition, it has moderate positive and negative predictive values for identifying subsequent development of uteroplacental vascular abnormalities.

Simultaneous multigate spectral Doppler imaging of the umbilical artery and placental vessels: novel ultrasound technology

OBJECTIVE

To establish gestational age-specific nomograms of pulsatility indices in the umbilical artery and chorionic and intraplacental vessels, using novel ultrasound technology.

STUDY DESIGN

A prospective, cross-sectional study of 160 healthy singleton pregnancies between 18 and 33 weeks of gestation.

MEASUREMENTS

Using simultaneous multigate spectral Doppler imaging specialized hardware and software, we measured the flow velocity waveforms of the umbilical artery, chorionic and intraplacental vessels. Computerized automatic mapping calculated the pulsatility indices in regions of interest.

RESULTS

Data were adequately obtained for 160 fetuses. The pulsatility index values in the three sites measured decreased with advancing gestational age; the correlation coefficients r = -0.74, r = -0.67 and r = -0.68 for the umbilical artery, chorionic and intraplacental vessels, respectively, were found to be highly statistically significant (p < 0.0001).

CONCLUSION

Simultaneous multigate spectral Doppler imaging provides simultaneous measurements of the velocity waveforms in the umbilical artery, chorionic and intraplacental vessels, and is a feasible and reproducible method of obtaining these data. The normal data presented may facilitate early detection of flow disturbances in the fetoplacental circulation.

New growth factors for imaginal discs

Several families of peptide growth factors are implicated in regulating cell growth and proliferation of vertebrate cells in culture. Genetic studies in Drosophila implicate some of these factors in growth control in vivo. A recent report identifies a new family of growth factors, related to chitinase enzymes, required by Drosophila imaginal disc cells in culture. It will be of interest to determine how such factors relate to size regulation during development.

Lineage-tracing cells born in different domains along the PD axis of the developing Drosophila leg

Patterning of the developing limbs by the secreted signaling proteins Wingless, Hedgehog and Dpp takes place while the imaginal discs are growing rapidly. Cells born in regions of high ligand concentration may be displaced through growth to regions of lower ligand concentration. We have used a novel lineage-tagging method to address the reversibility of cell fate specification by morphogen gradients. We find that responses to Hedgehog and Dpp in the wing disc are readily reversible. In the leg, we find that cells readily adopt more distal fates, but do not normally shift from distal to proximal fate. However, they can do so if given a growth advantage. These results indicate that cell fate specification by morphogen gradients remains largely reversible while the imaginal discs grow. In other systems, where growth and patterning are uncoupled, nonreversible specification events or ‘ratchet’ effects may be of functional significance.

Regulation of LIM homeodomain activity in vivo: a tetramer of dLDB and apterous confers activity and capacity for regulation by dLMO

Dorsal-ventral axis formation in the Drosophila wing depends on the activity of the LIM homeodomain transcription factor Apterous and its cofactor, dLDB/Chip. We present evidence that Apterous activity depends on the formation of a LIM homeodomain dimer bridged by a dimer of cofactor. We show that Apterous activity levels are regulated in vivo by dLMO, an antagonist of homodimer formation. Making use of a constitutively active form of Apterous and dominant-negative forms of Apterous and dLDB/Chip, we show that the normal function of dLMO is to downregulate Apterous activity and that the dLMO mutant phenotype is due to excess Apterous activity. These findings may point to a general mechanism for regulation of LIM homeodomain protein activity.

The nomenclature of cell death: recommendations of an ad hoc Committee of the Society of Toxicologic Pathologists

The last several years have seen considerable confusion regarding the terms "apoptosis" and "necrosis" in pathology. This situation prompted the Society of Toxicologic Pathologists to charter the Committee on the Nomenclature of Cell Death, which was charged with making recommendations about the use of the terms "apoptosis" and "necrosis" in toxicity studies. The Committee recommends use of the term "necrosis" to describe findings comprising dead cells in histological sections, regardless of the pathway by which the cells died. The modifiers "apoptotic" and "oncotic" or "mixed apoptotic and oncotic" are recommended to specify the predominant morphological cell death pathway or pathways, when appropriate. Other standard modifiers, indicating the lesion distribution and severity, may also be used in conjunction with these. "Individual cell necrosis" (also known as "single cell necrosis") may be either of the apoptotic, oncotic, or mixed types. In many cases, more traditional terms such as "coagulation necrosis" may be used to convey a meaning similar to oncotic necrosis. It is important that pathologists use terms that accurately and concisely convey the level of information appropriate to the study's needs. Furthermore, toxicologic pathologists should actively help to disseminate these recommendations to other biologists and to regulatory authorities.

Formation of morphogen gradients in the Drosophila wing

Patterning of multicellular fields requires mechanisms to coordinate developmental decisions made by populations of cells. Evidence is accumulating that the necessary information is provided by localized sources of secreted signalling proteins which act as morphogens. We review evidence that Wingless, Dpp and Hedgehog proteins act as morphogens in the developing wing of Drosophila and discuss recent work illustrating that signalling helps to shape their activity gradients by regulating ligand distribution and by modulating the responsiveness of target cells. These studies suggest that there is more to being a morphogen than formation of a ligand gradient by passive diffusion.

Localization of vascular endothelial growth factor in nontumorous human pituitaries

Vascular endothelial growth factor (VEGF) is a key mediator of endothelial cell proliferation, angiogenesis, and vascular permeability. Our aim was to investigate whether VEGF is expressed in various cell types of the human pituitary. Eight nontumorous pituitaries were investigated by histology, immunocytochemistry, double immunostaining, and immunoelectron microscopy.Immunocytochemistry, including double immunostaining, showed VEGF immunoreactive cells to be distributed throughout the adenohypophysis. Immunopositivity was evident in all adenohypophysial cell types, but was colocalized mainly with somatotroph and stellate cell antigen (i.e., growth hormone and S-100 protein). Weak to moderate VEGF immunoreactivity was also noted in posterior lobe pituicytes as well as in most endothelial and perivascular smooth muscle cells.In situ hybridization confirmed these findings in demonstrating a strong signal in corticotrophs, somatotrophs, and stellate cells. Immunoelectron microscopy showed VEGF to be present mainly within secretory granules where it colocalized with the full spectrum of adenohypophysial hormones. The subcellular distribution of VEGF suggests that hypothalamic factors play a role in its release from adenohypophysial cells. Further studies are required to examine the possible role of VEGF in affecting both the pituitary's vasculature and endocrine activity.

Proximodistal axis formation in the Drosophila leg: subdivision into proximal and distal domains by Homothorax and Distal-less

The developing legs of Drosophila are subdivided into proximal and distal domains by the activity of the homeodomain proteins Homothorax (Hth) and Distal-less (Dll). The expression domains of Dll and Hth are initially reciprocal. Wingless and Dpp define both domains by activating Dll and by repressing Hth in the distal region of the disc. Wg and Dpp do not act through Dll to repress Hth. Hth functions to reduce the sensitivity of proximal cells to Wg and Dpp. This serves to limit the effective range of these signals in regulating later-acting genes such as Dac. We present evidence that proximal and distal cells tend to sort-out from one another. Cells forced to express Hth are unable to mix with distal cells. Likewise, cells forced to express Dll are unable to mix with proximal cells. Clones of cells unable to express Dll in the distal region sort-out from the disc. Clones of cells unable to express Hth lose the specialized population of cells at the interface between proximal and distal territories and cause fusion between body wall and leg segments. These observations suggest that sorting-out behavior of Hth- and Dll-expressing cells contributes to subdivision of the leg into proximal and distal domains.

Notchless encodes a novel WD40-repeat-containing protein that modulates Notch signaling activity

Signaling by Notch family receptors is involved in many cell-fate decisions during development. Several modifiers of Notch activity have been identified, suggesting that regulation of Notch signaling is complex. In a genetic screen for modifiers of Notch activity, we identified a gene encoding a novel WD40-repeat protein. The gene is called Notchless, because loss-of-function mutant alleles dominantly suppress the wing notching caused by certain Notch alleles. Reducing Notchless activity increases Notch activity. Overexpression of Notchless in Xenopus or Drosophila appears to have a dominant-negative effect in that it also increases Notch activity. Biochemical studies show that Notchless binds to the cytoplasmic domain of Notch, suggesting that it serves as a direct regulator of Notch signaling activity.

Dpp receptor levels contribute to shaping the Dpp morphogen gradient in the Drosophila wing imaginal disc

Axis formation in the Drosophila wing depends on the localized expression of the secreted signaling molecule Decapentaplegic (Dpp). Dpp acts directly at a distance to specify discrete spatial domains, suggesting that it functions as a morphogen. Expression levels of the Dpp receptor thick veins (tkv) are not uniform along the anterior-posterior axis of the wing imaginal disc. Receptor levels are low where Dpp induces its targets Spalt and Omb in the wing pouch. Receptor levels increase in cells farther from the source of Dpp in the lateral regions of the disc. We present evidence that Dpp signaling negatively regulates tkv expression and that the level of receptor influences the effective range of the Dpp gradient. High levels of tkv sensitize cells to low levels of Dpp and also appear to limit the movement of Dpp outside the wing pouch. Thus receptor levels help to shape the Dpp gradient.

Identification of chromosomal bands replicating early in the S phase of normal human fibroblasts

Normal human fibroblasts (NHF1) were released from confluence arrest (G0) and replated in medium containing bromodeoxyuridine (BrdU) and aphidicolin. Despite severe reduction in the rate of DNA synthesis by aphidicolin, cells reentering the cell cycle incorporated BrdU at regions of the human genome that replicated very early in S phase. After removal of aphidicolin and BrdU from the tissue culture medium, cells were collected in mitosis. Q-banding with 4', 6-diamidino-2-phenylindole/actinomycin D was used to identify metaphase chromosomes. A monoclonal anti-BrdU antibody and a fluorescein isothiocyanate (FITC)-conjugated goat anti-mouse antibody were used to identify the BrdU-labeled sites. The criterion for scoring DNA replication sites was the detection of FITC fluorescence at homologous regions of both sister chromatids. Early replicating regions mapped within R-bands, but not all R-bands incorporated BrdU. Chromosomal bands 1p36.1, 8q24.1, 12q13, 15q15, 15q22, and 22q13 were labeled in 53% or more of the copies of these chromosomes in the data set, suggesting that these sites replicated very early in S phase. Chromosomal band 15q22 was the most frequently labeled site (64%), which indicates that it contains some of the earliest replicating sequences in normal human fibroblasts.