The incomplete cone biopsy: a comparison of conservative and surgical management

OBJECTIVE

to determine the reliability of conservative management of cone biopsies showing apparently incomplete excision of cervical intraepithelial neoplasia (CIN) by comparing surgical and conservative management.

DESIGN

a retrospective study.

SUBJECTS

74 consecutive cone biopsies with a histology report of apparently incomplete excision of CIN 2 or CIN 3 from a series of 738 cone biopsies.

MAIN OUTCOME MEASURES

the presence of CIN at hysterectomy against the pick up rate in conservatively managed patients.

RESULTS

where excision appeared incomplete at the ectocervix this was confirmed in 1 of 6 (16.7%) of patients managed surgically and 2 of 17 (11.8%) of patients managed conservatively (P = 0.40). Where excision appeared incomplete at both endo- and ectocervix, 5 of 6 (83.3%) were confirmed to have incomplete excision in the surgical group, and 3 of 5 (60%) had further proven CIN in the conservative group (P = 0.34). Where excision appeared incomplete at the endocervix only, this was confirmed in 7 of 22 (32%) of cases managed surgically, but only 2 of 18 (11.1%) of cases managed conservatively had further proven CIN (P = 0.14). Combining all patients with incomplete excision at the endocervix irrespective of the ectocervix status revealed confirmation of residual CIN in 12 of 28 (42.9%) patients managed surgically and in 5 of 23 (21.7%) patients managed conservatively (P = 0.097).

CONCLUSIONS

management should depend on the site of the apparent incomplete excision. Where excision appears incomplete at the ectocervix only, cytological follow up should be employed. If the endocervix is involved, further excisional surgery may be more appropriate.

Medicare payment policy and recombinant erythropoietin prescribing for dialysis patients

The Medicare payment policy for recombinant human erythropoietin (rHuEPO) treatment for dialysis patients changed in January 1991 from a relatively fixed payment per treatment (allowed charge of $40 per < or = 10,000 units injected) to a more variable payment based on the amount of rHuEPO administered with each treatment (allowed charge of $11 per 1,000 units injected). This change provided an opportunity to examine how payment policy can effect the use, cost, and health outcome of a biotechnology product used in the dialysis population. In cross-sectional (n = 71,880 Medicare-entitled dialysis patients) and longitudinal (n = 29,088 Medicare-entitled dialysis patients) study designs, we used Medicare end-stage renal disease program and claims data in bivariate and multivariate analyses to examine the effect of the change in payment policy for rHuEPO on access to the biotechnology, dosing, costs, and hematocrit, including the prescribing patterns at for-profit versus not-for-profit providers. The observation period included several months before (July 1989 to December 1990) and 6 months after (January to June 1991) the change in Medicare payment policy. The mean dose per treatment during the initial and fourth month of therapy was low (2,742 [95% confidence interval, 2,703 to 2,781] units and 2,632 [95% confidence interval, 2,598 to 2,667] units, respectively, in June 1990) and increased 3.4% and 5.0%, respectively, in the next 6 months prior to the change in Medicare payment policy compared with 14.6% and 14.8%, respectively, in the 6 months following the change in payment policy. The average monthly allowed charge for rHuEPO per dialysis patient receiving rHuEPO decreased from $455 before the policy change to $349 immediately following the policy change, because the allowed charge per unit of rHuEPO was lower when payment became more dependent on the amount of rHuEPO administered with each treatment than when the payment was fixed at $40 per treatment. The average monthly allowed charge for rHuEPO increased to $375 in the sixth month following the change in payment policy as a result of the increase in dose and the new variable payment. The unadjusted and adjusted changes in mean hematocrit 6 months after the payment change were positive but clinically very small (0.3 and 0.2 percentage points, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Bovine parthenogenetic blastocysts following in vitro maturation and oocyte activation with ethanol

The appropriate in vitro bovine oocyte maturation and ethanol activation conditions for preimplantation bovine embryo parthenogenetic development to the blastocyst stage were investigated. A 7% ethanol concentration significantly enhanced (P<0.05) the proportion of activated, in vitro-matured bovine oocytes (7% ethanol, 83.4 +/- 3.2% versus 0% ethanol, 63.9 +/- 2.0%). The proportion of activated oocytes was significantly higher (P<0.05) by treatment with 7% ethanol for a minimum of 2 minutes (2 minutes, 89.8 +/- 4.0% versus 0.5 minutes 63.4 +/- 4.9%). Oocyte maturation for periods ranging from 30, 34, 38 and 44 hours resulted in a significant increase (P<0.05) in the proportion of activated oocytes, and in oocytes displaying 2 or 3 pronuclei versus oocytes matured for 26 hours. The proportion of cleaved, activated oocytes (2-cell stage), 4 -cell stage and parthenogenetic morula/blastocysts was significantly higher (P<0.05) within the 34-hour oocyte maturation treatment group. Although the 44-hour oocyte maturation treatment group displayed the highest proportion of activated oocytes with 2 pronuclei, it did not display the highest cleavage frequency, possibly due to the effects of postovulatory aging. Several morphologically normal parthenogenetic bovine blastocysts developed from oocytes that were in vitro matured for 34 hours. The ability to produce such parthenogenetic embryos will eventually facilitate investigation into the role(s) of the maternal and paternal genomes during bovine early development.

Depletion of O6-alkylguanine-DNA alkyltransferase correlates with potentiation of temozolomide and CCNU toxicity in human tumour cells

Temozolomide (8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4-(3H)-one) has shown promising activity in Phase I trials against some brain (glioma) and skin (melanoma, mycosis fungoides) cancers. Temozolomide and lomustine (CCNU) showed parallel toxicity in seven human tumour cell lines and this generally correlated (correlation coefficients 0.87 and 0.92 respectively) with the level of expression of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (ATase, EC 2.1.1.63). Pretreating cells with the ATase inhibitor, O6-benzylguanine (BG), potentiated cytotoxicity to a similar degree with both drugs, but did not sensitise a cell line (ZR-75-1) expressing very low levels of this protein. When BG pretreatment was combined with repeat doses of temozolomide a dramatic potentiation (300 fold) was seen in MAWI cells, which express high levels of ATase, but not in a cell line (U373) expressing lower levels of ATase. [14C]-labelled temozolomide uptake was similar in sensitive and resistant lines. Human ATase-cDNA transfected xeroderma pigmentosum (XP) fibroblasts were more resistant than XP control cells to temozolomide and the related chloroethylating agent mitozolomide and although BG completely suppressed ATase activity in these cells, resistance was still greater than in control cells.

Early dosing practices and effectiveness of recombinant human erythropoietin

In a national longitudinal-cohort study of 59,462 end-stage renal disease (ESRD) patients, we examined dosing and effectiveness of erythropoietin (EPO) during the first year of its use in clinical practice (July 1989 through June 1990). In unadjusted and multivariate analyses of Medicare claims data, the mean dose of EPO prescribed was: relatively small and similar for initial and maintenance therapy, 2752 (95% confidence interval 2740 to 2764) and 2668 (95% confidence interval 2654 to 2682) units, respectively; lower when initial therapy was started later (591 units lower in September 1989 and 760 units lower in November 1989 vs. July 1989, P < 0.0001); lower by 135 units during initial therapy and by 116 units during maintenance therapy for females (who weigh less) compared to males (P < 0.001); and lower by 400 units for patients treated in for-profit versus not-for-profit centers. In multivariate analysis: hematocrit response was less and mean maintenance dose was 298 units and 621 units greater for patients whose ESRD was due to multiple myeloma and sickle cell disease, respectively, compared to those with hypertension-related ESRD (P < 0.01); and hematocrit response was logarithmically related to dose [hematocrit = 0.97 ln (dose), P < 0.0001]. Forty-four percent of patients had a hematocrit > or = 30 after four months of therapy. The percent of patients transfused during three month periods before and after therapy decreased from 20% to 5%, respectively (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Bicarbonate and citrate in oral rehydration therapy: studies in a model of secretory diarrhea

In situ perfusion of the rat jejunum and ileum was used to study the effect of inclusion of bicarbonate or citrate on the ability of four oral rehydration solutions to promote small-intestinal absorption of water and sodium. Solutions varied in their sodium (60-90 mM) and glucose (111-140 mM) content and osmolality (281-331 mosmol/kg). They were studied before and after exclusion of base both in normal intestine and in secreting intestine after exposure to cholera toxin. All solutions promoted net water absorption in the normal intestine and reversed net water secretion to absorption in the cholera toxin-treated intestine to varying degrees. Net sodium movement was directly related to the sodium content of oral rehydration solutions. Inclusion of bicarbonate or citrate did not promote significantly greater absorption of water or sodium than did solutions without base, in normal or secreting intestine. In the secreting intestine, inclusion of bicarbonate in two solutions actually resulted in greater sodium secretion than did identical solutions from which bicarbonate was omitted. These studies suggest that the inclusion of base or base precursors in oral rehydration solutions to enhance water and sodium absorption is unjustified in both normal and secreting small intestine.

Infection with a ratborne hantavirus in US residents is consistently associated with hypertensive renal disease

A survey of 8080 subjects was conducted in Baltimore, examining the association between infection with hantaviruses and renal disease. Two groups (N = 6060) with no known risk factors were selected to establish a baseline antibody prevalence. Overall, antibody prevalence was 0.25%. Seroprevalence increased with age, without sex- or race-related differences. Patients with proteinuria showed the same patterns of infection but were more commonly seropositive (1.46%) than the reference group (OR, 3.23; P < .05). Infection among dialysis patients with end-stage renal disease was 2.76%, significantly higher than in the reference group (OR, 5.03; P < .05). In the proteinuria and the dialysis groups, hantavirus infection was consistently associated with a diagnosis of hypertensive renal disease. The association was unrelated to other chronic renal disease diagnoses. Overall, 6.5% of patients with end-stage renal disease due to hypertension were seropositive for a hantavirus. These data suggest that hantavirus infection is associated with hypertensive renal disease.

Expression of the E.coli 3-methyladenine DNA glycosylase I gene in mammalian cells reduces the toxic and mutagenic effects of methylating agents

In order to investigate the importance of 3-methyladenine in cellular sensitivity to chemical methylating agents we have constructed retroviral vectors for the integration and expression of the Escherichia coli tag gene in mammalian cells. The tag gene encodes 3-methyladenine DNA glycosylase-1 which specifically removes 3-alkyladenines from DNA. The constructs were introduced into Chinese hamster V79 cells by liposome mediated transfection or into murine haemopoietic stem cells by cocultivation with a lipofected, virus-packaging cell line. In both cases, stable transfectants were selected for resistance to the antibiotic, G418, conferred by expression of the neo gene carried by the vector. Measurements of 3-methyladenine DNA glycosylase activity in cell extracts showed an up to 10-fold increase in cell lines with stably integrated tag gene sequences. These cell lines were significantly more resistant to the cytotoxic effects of methylmethanesulfonate and N-methyl-N-nitrosourea than their parent cell lines, indicating that 3-methyladenine repair is a limiting factor in cellular resistance to these methylating agents. Furthermore, the mutation frequency induced by methylmethanesulfonate was reduced to 50% of normal by expression of 3-methyladenine I activity in the Chinese hamster cells, indicating that m3A is not only a cytotoxic but also a premutagenic lesion in mammalian cells. It is concluded that an alkylation repair gene function of a type only thought to be present in bacteria can yield a hyperresistant phenotype when transferred to mammalian cells.

The cell biology of blastocyst development

Preimplantation development encompasses the "free"-living period of mammalian embryogenesis, which culminates in the formation of a fluid-filled structure, the blastocyst. Cavitation (blastocyst formation) is accompanied by the expression of a novel set of gene products that contribute directly to the attainment of cell polarity with the trophectoderm, which is both the first epithelium of development and the outer cell layer encircling the inner cell mass of the blastocyst. Several of these gene products have been identified and include the tight junction (ZO-1), Na/K-ATPase (alpha and beta subunits), uvomorulin, gap junction (connexin43), and growth factors such as transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF). This review will examine the role(s) of each of these gene products during the onset and progression of blastocyst formation. The trophectodermal tight junctional permeability seal regulates the leakage of blastocoel fluid and also assists in the maintenance of a polarized Na/K-ATPase distribution to the basolateral plasma membrane domain of the mural trophectoderm. The polarized distribution of the Na/K-ATPase plays an integral role in the establishment of a trans-trophectoderm Na+ gradient, which drives the osmotic accumulation of water across the epithelium into the nascent blastocoelic cavity. The cell adhesion provided by uvomorulin is necessary for the establishment of the tight junctional seal, as well as the maintenance of the polarized Na/K-ATPase distribution. Growth factors such as TGF-alpha and EGF stimulate an increase in the rate of blastocoel expansion, which could, in part, be mediated by secondary messengers that result in an increase in Na/K-ATPase activity. Insight into the mechanism of cavitation has, therefore, directly linked blastocyst formation to trophectoderm cell differentiation, which arises through fundamental cell biological processes that are directly involved in the attainment of epithelial cell polarity.

Evaluation of the nutritive value of yellow rice in rats and broiler chicks

Yellow discoloration often develops in rice kernels during post-harvest storage, due possibly to fungal activity. The present study examined the changes in nutrient composition taking place during yellowing of rice, and the effects of feeding rats and broiler chicks on a moderately yellow rice at 600 g/kg diet. Nitrogen content was found to be higher in rice grains that had become more yellow, only part of the increase being in non-protein-N; however, relative to crude protein (N x 6.25) the concentrations of lysine, methionine, cystine and arginine were lower. There were no significant differences between white and yellow rice in the food intake, weight gain and efficiency of food utilization (EFU) of rats and chicks when diets were formulated to contain similar nutrient concentrations, or the same basal ingredient composition. Diet pelleting increased food intake and weight gain in both animal species, but reduced dry matter and energy digestibility in rats; effects on nutrient retention in chicks were largely non-significant. Liver weights of rats and chicks and pancreas weights of chicks were unaffected by yellow rice; however, chicks fed on mash had a larger pancreas on average than those fed on pellets. Thus, whilst the nutrient composition of rice is altered during yellowing, a moderately yellow rice is unlikely to produce major adverse effects when fed to rats and broiler chicks.

How to make a blastocyst

Several of the new reproductive technologies have been cultivated from our current understanding of the genetic programming and cellular processes that are involved in the major morphogenetic events of mammalian preimplantation development. Research directed at characterizing the patterns of gene expression during early development has shown that the embryo is initially under maternal control and later superseded by new transcriptional activity provided by the activation of the embryonic genome. Several embryonic transcripts encoding: (i) growth factors, (ii) cell junctions, (iii) plasma membrane ion transporters, and (iv) cell adhesion molecules have been identified as contributing directly to the progression of the embryo through the preimplantation interval of development. In this brief review, we have outlined the patterns of expression and the integral roles that these gene families play in the morphogenetic events of compaction and cavitation. Research of this type has greatly facilitate our understanding of the control processes that underlie preimplantation development and represent but one area of this exciting and vigorous field of research.

Access to recombinant erythropoietin by Medicare-entitled dialysis patients in the first year after FDA approval

OBJECTIVE

Examine access to recombinant human erythropoietin (rHuEPO) by dialysis-dependent end-stage renal disease (ESRD) patients during the first year after FDA approval for use in clinical practice and Medicare coverage.

DESIGN

Longitudinal and cross-sectional claims data analyses.

SETTING

All US providers of outpatient dialysis treatment.

PATIENTS

126,201 Medicare-entitled dialysis patients (approximately 93% of all US dialysis patients).

OUTCOME MEASURES

Percentage of patients who received rHuEPO, odds of receiving rHuEPO according to patient characteristics, and cost of rHuEPO to Medicare.

RESULTS

One year after FDA approval, 52% of all dialysis and 60% of in-center hemodialysis patients who regularly had Medicare-paid dialysis services received rHuEPO at a monthly cost to Medicare of $19 million (18% of Medicare ESRD outpatient expenditures and 6% of all ESRD program expenditures). Blacks were less likely than whites to receive rHuEPO (odds ratio, 0.88; 95% confidence interval, 0.86 to 0.91). Home peritoneal and hemodialysis patients were less likely than in-center hemodialysis patients to receive rHuEPO (odds ratios, 0.17 and 0.22, respectively; 95% confidence intervals, 0.16 to 0.17 and 0.20 to 0.24, respectively). Use of rHuEPO varied across geographic regions. The odds of receiving rHuEPO were lower for patients of male vs female sex, of ages 35 through 64 years vs less than 35 years and greater than 65 years, with a longer history of ESRD, with polycystic kidney disease vs other causes of ESRD, and receiving care in nonprofit vs for-profit facilities. First-month hematocrits were slightly higher (1.2 percentage points) for patients starting rHuEPO in the 12th month than in the first month after FDA approval.

CONCLUSIONS

With prompt insurance coverage, the majority of Medicare-entitled dialysis patients received rHuEPO following widespread availability. Factors that may not be related to clinical need (race, setting of care, and geography) possibly influenced early patient access. More attention should be paid to monitoring the appropriate use of high-cost biotechnologic therapy.

Expression of bovine trophoblast interferon in conceptuses derived by in vitro techniques

Expression of the trophoblast interferon, bovine trophoblast protein-1 (bTP-1), has been studied in embryos produced by in vitro maturation-in vitro fertilization (IVM-IVF). No bTP-1 production was noted until after embryos had reached the expanded blastocyst stage and had begun to hatch (Days 8-9 post-fertilization). Single blastocysts comprising 115 +/- 22 cells released 1.0 +/- 0.1 units of interferon activity/24 h. Amplification of conceptus mRNA by reverse transcription-polymerase chain reaction procedure with bTP-1-specific oligonucleotides confirmed that bTP-1 transcripts were present in blastocysts but were not detectable at earlier stages. Although cultured blastocysts produced by IVM-IVF procedures continued to secrete bTP-1 for a few days, they failed to attach to the substratum and form outgrowths, and soon lost structural integrity. However, when Day 8 blastocysts/morulae were transferred to the uteri of synchronized cows, recovered 4 days later, and placed into individual cultures, they attached and formed outgrowths that produced large amounts of bTP-1 (greater than 2000 units/culture/24 h after 14 days). Embryos thus first expressed bTP-1 when a functional trophectoderm was first formed, and induction did not require a period of in vivo development. However, continued viability of the blastocyst and bTP-1 production were not sustained in vitro and may require some exposure to the uterine environment.

Sequence and expression of a membrane-associated C-type lectin that exhibits CD4-independent binding of human immunodeficiency virus envelope glycoprotein gp120

The binding of the human immunodeficiency virus (HIV) envelope glycoprotein gp120 to the cell surface receptor CD4 has been considered a primary determinant of viral tropism. A number of cell types, however, can be infected by the virus, or bind gp120, in the absence of CD4 expression. Human placenta was identified as a tissue that binds gp120 in a CD4-independent manner. A placental cDNA library was screened by expression cloning and a cDNA (clone 11) encoding a gp120-binding protein unrelated to CD4 was isolated. The 1.3-kilobase cDNA predicts a protein of 404 amino acids with a calculated M(r) of 45,775 and organized into three domains: an N-terminal cytoplasmic and hydrophobic region, a set of seven complete and one incomplete tandem repeat, and a C-terminal domain with homology to C-type (calcium-dependent) lectins. A type II membrane orientation (N-terminal cytoplasmic) is predicted both by the cDNA sequence and by the reactivity of C-terminal peptide-specific antiserum with the surface of clone 11 transfected cells. Native and recombinant gp120 and whole virus bind transfected cells. gp120 binding is high affinity (kd, 1.3-1.6 nM) and inhibited by mannan, D-mannose, and L-fucose; once bound, gp120 is internalized rapidly. Collectively, these data demonstrate that the gp120-binding protein is a membrane-associated mannose-binding lectin. Proteins of this type may play an important role in the CD4-independent association of HIV with cells.

Assay of apical membrane enzymes based on fluorogenic substrates

A series of enzymatic rate assays are described. The assays are based on coumarin derivatives that are fluorogenic substrates for the enzymes dipeptidase IV, aminopeptidase N, alkaline phosphatase, and gamma-glutamyltransferase. These simple assays are rapid and offer improved sensitivity over established colorimetric methods. The substrates have apparent affinities for the enzymes of 5-250 microM. L-Glutamic acid gamma-(7-amido-4-methylcoumarin) is characterized as a substrate of gamma-glutamyltransferase on the basis of inhibition of enzymatic cleavage when the glycylglycine acceptor molecule is omitted and inhibition of the enzymatic reaction by addition of glycine. Assay conditions for the four enzymes are established such that less than 0.6% of the substrate is consumed, fluorescence is proportional to enzymatic product, and results may be directly compared to established colorimetric assays. Intestinal epithelial cells are used both to establish appropriate assay conditions and to demonstrate the utility of the assays.

Inhibition of HIV infection of resting peripheral blood lymphocytes by nucleosides

T cells in the peripheral blood are largely in the resting state and represent a significant pool of potential targets for HIV infection. The protection of these cells from infection is an important goal of nucleoside therapy. Resting PBL may not be protected effectively by such nucleosides as azidothymidine (AZT) since anabolic phosphorylation of thymidine nucleosides is reported to be limited in these cells. In this study we used DNA amplification procedures to follow HIV proviral DNA formation in resting T cells and to determine the ability of azidodeoxythymidine (AZT), dideoxyinosine (ddI), and dideoxycytosine (ddC) to inhibit this process. Experiments confirm that resting PBL synthesize HIV proviral DNA sequences. Drug titrations showed that this synthesis could be inhibited by nucleosides. ddC was the most potent drug, inhibiting transcription at the U5 region. ddI and AZT at similar concentrations (10 microM) did not inhibit. ddI in the concentration range of 10-100 microM was able to inhibit production of transcripts containing U3 and env sequences in resting cells. Similar inhibition levels were accomplished by AZT at 10-100-fold lower drug concentrations. These results demonstrate that resting T cells can be protected from HIV infection by nucleosides and that thymidine nucleosides are effective inhibitors despite the limited potential for anabolic phosphorylation.

A controlled trial of prednisolone treatment in primary biliary cirrhosis. Three-year results

The results of a 3-year, placebo-controlled trial of prednisolone treatment in primary biliary cirrhosis (PBC) are presented. The active (n = 19) and placebo (n = 17) arms were initially well matched for age, menopausal status and disease severity. At 3 years hepatic symptoms were relatively improved in the prednisolone group. Hepatic mortality was 3/19 (prednisolone), 5/17 (placebo) (p = n.s.). For all liver blood tests the trend favoured prednisolone treatment, though the differences were only significant for alkaline phosphatase and protein. All immunoglobulins fell significantly. Quantitative ELISA determination of antimitochondrial antibody showed a significant fall in the prednisolone group compared with placebo (p less than 0.001 at 1 year, p less than 0.05 at 3 years). Deterioration in histology (appearance of cirrhosis) was more common in the placebo group. Overall hepatic function (hepatic mortality, doubling in bilirubin, 6 milligrams fall in albumin, de novo appearance of cirrhosis or symptoms of portal hypertension) was significantly worse in the placebo group (p less than 0.01). After 3 years no significant differences could be detected in bone mineral content (single photon absorptiometry of radius and femur) between the two groups or in comparison with other PBC patients. Thus, after 3 years, prednisolone treatment was associated with a better overall hepatic outcome and little evidence of increased bone loss.

ABC of colorectal diseases. Diarrhoea

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Mechanism of action of a repressor of dioxin-dependent induction of Cyp1a1 gene transcription

A dominant mutant of Hepa-1 cells, c31, expresses a repressor that prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-dependent stimulation of Cyp1a1 transcription. The repressor acts via the xenobiotic-responsive elements (XREs), which are the DNA-binding sites for the aryl hydrocarbon (Ah) receptor-TCDD complex during transcriptional activation of the gene. High-salt nuclear extracts prepared from c31 cells grown with TCDD contained normal levels of the Ah receptor which bound the XRE with normal affinity, as judged by in vitro gel mobility shift assays. Furthermore, extracts prepared from these cells, grown either with or without TCDD, contained no novel XRE-binding proteins compared with extracts from wild-type Hepa-1 cells. However, in vivo genomic footprinting demonstrated that TCDD treatment leads to binding of the Ah receptor to the XREs in Hepa-1 but not mutant cells. This finding suggests that the repressor associates with the Ah receptor to prevent its binding to the XREs and that high-salt treatment either causes dissociation of the receptor/repressor complex or fails to extract the repressor from nuclei. The results underscore the importance of using both in vivo and in vitro assays for analyzing DNA-protein interactions.

Isolation and partial characterisation of a Chinese hamster O6-alkylguanine-DNA alkyltransferase cDNA

The cDNA encoding Chinese hamster O6-alkylguanine-DNA-alkyltransferase (ATase) has been isolated from a library prepared from RNA isolated from V79 lung fibroblasts which had an upregulated level of this repair activity following stepwise selection with a chloroethylating agent (1, 2). Expression of the cDNA in E. coli produced functionally active ATase at levels of 2.5% of total cellular protein as determined by in vitro assay. The recombinant hamster protein has a molecular weight of 28 kDa as estimated by SDS-PAGE and fluorography and this was identical to that in the upregulated cells. The characteristic PCHRV pentapeptide of the alkyl acceptor site has been identified and there is a 68 amino acid residue region which is 90% conserved across all the mammalian proteins so far analysed: in contrast, the N- and C-terminal domains diverge by as much as 50% between species. Polyclonal antibodies to the human and rat ATases hybridised to the hamster protein on western analysis suggesting at least one common epitope shared across species. However, in antibody inhibition experiments neither of the antisera cross reacted with the hamster ATase in a way which interfered with functional activity whereas the anti-human antibodies inhibited the human ATase and the anti-rat antibodies inhibited the rat and mouse ATases. There may therefore be significant tertiary structural differences between the hamster protein and the other mammalian ATases.

Dioxin- and Ah receptor-dependent protein binding to xenobiotic responsive elements and G-rich DNA studied by in vivo footprinting

DNA-protein interactions before and after transcriptional activation of the carcinogen- and dioxin-inducible enhancer of the murine CYP1A1 gene were detected in vivo by treatment with dimethyl sulfate followed by ligation-mediated, polymerase chain reaction-aided genomic sequencing. Following 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment of mouse Hepa-1 hepatoma cells, evidence of protein binding was detected at the sequence 5' CACGCNA/T 3' within two previously defined xenobiotic response elements (XREs). The observed XRE footprint was similar to that previously identified by in vitro methylation protection footprints and attributed to the binding protein for 2,3,7,8-tetrachlorodibenzo-p-dioxin the Ah receptor. No XRE footprinting was observed in Hepa-1 mutant cells possessing a defective Ah receptor. Unexpectedly, evidence of protein binding was also detected at a G-rich DNA sequence immediately adjacent to one of the XREs. Footprinting of the G-rich sequence element, like that of XRE1 and XRE2, was dependent on the presence of a functional Ah receptor. The Ah receptor is therefore able to bind to its own DNA target sites in vivo and is also required for the binding of a second factor to the G-rich element.

U2 small nuclear RNA localization and expression during bovine preimplantation development

This study describes the localization of the U2 small nuclear RNA (snRNA) and the major U snRNA group ribonucleoproteins (snRNPs) during bovine preimplantation development. In vitro maturation, fertilization, and oviductal epithelial cell coculture methods were employed to produce several developmental series totalling over 2,000 preimplantation-stage bovine oocytes and embryos. These oocytes and preimplantation embryos were processed for in situ hybridization, immunofluorescence and Northern blotting methods. The U2 snRNA and the major U group snRNPS were localized initially over the germinal vesicle (GV) of preovulatory oocytes but following GV breakdown were released throughout the ooplasm. They subsequently reassociated with both pronuclei during fertilization. From the two-cell to the blastocyst stages, the U2 snRNA and U snRNPs were localized to the interphase nucleus of each blastomere. The levels of U2 snRNA throughout bovine preimplantation development were determined by probing a Northern blot containing total RNA isolated from the following preimplantation bovine embryo stages: one to two cell, eight to 16 cell, early morula (greater than 32 cell), and late morula/early blastocysts. The levels of U2 snRNA remained constant between the one-cell and eight- to 16-cell bovine embryo stages but increased 4.4-fold between the eight- to 16-cell stage and the late morula/early blastocyst stages. The results suggest that a maternal pool of snRNAs is maintained in mammalian preimplantation embryos regardless of the duration of maternal control of development.

Upregulation of O6-alkylguanine-DNA-alkyltransferase expression and the presence of double minute chromosomes in alkylating agent selected Chinese hamster cells

Chinese hamster V79 lung fibroblasts are sensitive to the toxic effects of chloroethylating agents such as mitozolomide (Mz) and express very low levels (less than 2 fmol/mg) of the DNA repair enzyme O6-alkylguanine-DNA-alkyltransferase (ATase). These cells were subjected to selection by treatment with serially increasing doses of Mz. After each dose, the surviving population was expanded and ATase activity was determined in cell extracts. ATase specific activity increased stepwise and in cells surviving selection at 120 micrograms/ml Mz had reached 430 fmol/mg protein: polyacrylamide gel electrophoresis and fluorography showed the size of the ATase as 25 kDa. Cytological examination of these cells showed the presence of double minute (DM) chromosomes (mean approximately 3/cell) but no obvious homogeneously staining regions. In cells grown in continuous culture without further selection no marked decrease in ATase activity or DM frequency was observed. Karyotype analysis and DNA profiling confirmed that the parent and selected cells were of the same origin with, in the latter case, the probable loss or gain of a single restriction endonuclease site. No major differences were seen in the intensity of hybridization signals following Southern analyses of DNA from control and Mz selected cells using the human ATase cDNA as a probe. These results indicate that the ATase gene is not amplified in the Mz selected cells and suggest that increased ATase activity is a consequence only of increased transcription or translation of the ATase gene.

Expression of growth factor ligand and receptor genes in the preimplantation bovine embryo

The sensitive technique of mRNA phenotyping with the reverse transcription-polymerase chain reaction was employed to determine the patterns of gene expression for several growth factor ligand and receptor genes during bovine preimplantation development. Several thousand bovine embryos encompassing a developmental series from one-cell zygotes to hatched blastocysts were produced by the application of in vitro maturation, fertilization, and oviductal epithelial cell embryo coculture methods. Transcripts for transforming growth factor (TGF-alpha) and platelet-derived growth factor (PDGF-A) are detectable in all preimplantation bovine stages as observed in the mouse. Transcripts for TGF-beta 2 and insulin-like growth factor (IGF-II) and the receptors for PDGF-alpha, insulin, IGF-I, and IGF-II are also detectable throughout bovine preimplantation development, suggesting that these mRNAs are products of both the maternal and the embryonic genomes in the cow, whereas in the mouse they are present only following the activation of the embryonic genome at the two-cell stage. In contrast to the mouse embryo, IGF-I mRNA was detected within preimplantation bovine embryos. Basic fibroblast growth factor (bFGF) is a maternal message in the bovine embryo, since it is only detectable up until the eight-cell embryo stage. Bovine trophoblast protein (bTP) mRNA was detectable within day 8 bovine blastocysts. As was observed in the mouse, the transcripts for insulin, epidermal growth factor (EGF), or nerve growth factor (NGF) were not detectable in any bovine embryo stage. Analyses of this type should aid the development of a completely defined culture medium for the more efficient production of preimplantation bovine embryos.