Effect of mitochondrial ATP-sensitive potassium channel opening on the translocation of protein kinase C epsilon in adult rat ventricular myocytes

This study aimed to investigate the effects of mitochondrial ATP-sensitive potassium (MitoKATP) channel opening on the translocation of protein kinase C epsilon (PKCε). In addition, we aimed to determine the relationship between PKCε translocation and the production of reactive oxygen species (ROS). PKCε protein expression in cultured adult rat ventricular myocytes was investigated by immunofluorescence and Western blotting. Diazoxide (DZ), a selective MitoKATP channel activator, caused a significant translocation to myofibrillar-like structures in cultured adult rat ventricular myocytes. N-2-Mercaptopropionylglycine, a free radical scavenger, could partially inhibit the translocation of PKCε induced by DZ. By contrast, chelerythrine, a selective PKC inhibitor, could completely block the translocation of PKCε induced by DZ. The opening of MitoKATP channels might activate and cause PKCε to translocate into myofibrillar-like structures. PKCε activation occurred downstream of the MitoKATP channel, possibly as a result of ROS production that occurred after the MitoKATP channels opened.

Manual cataract extraction via a subconjunctival limbus oblique incision for mature cataracts

Aims:

To report the technique and outcomes of sutureless manual cataract extraction via a subconjunctival limbus oblique incision for mature cataracts.

Materials and Methods:

This retrospective study comprised of 112 eyes of 83 patients with mature cataract who all had manual cataract extraction via a subconjunctival limbus oblique incision. A transconjunctival tunnel is fashioned with a 3.0 mm keratome, 0.5 mm behind the limbal vascular arcades. A limbal tunnel, with a transverse extent of 9 mm in the cornea and 7.0 mm in the limbus, is created beneath the conjunctival/Tenon's tissue using an angled bevel-up crescent blade. Outcome measures included visual acuity, intraoperative complications, surgically induced astigmatism, endothelial cell loss rate and surgery time.

Results:

Self-sealing wound was achieved in 112 eyes (98.2%). The nucleus was delivered in whole in 108 eyes (96.4%). Intraoperative complications included hyphema in 3 eyes (2.7%), iridodialysis in 2 eyes 1.8%), posterior capsular rupture and zonular dialysis in 2 eyes (1.8%). At the 3-month follow-up, 91% patients achieved a best-corrected visual acuity of 20/20 or better, the mean of surgically induced astigmatism was -0.62 ± 0.41 Diopters and endothelial cell loss was 4.2%. Average surgical time was 3.75 min per case.

Conclusion:

This subconjunctival limbus oblique incision has the potential to serve as safe and effective technique for mature cataracts.

Predicting transient particle transport in enclosed environments with the combined computational fluid dynamics and Markov chain method

To quickly obtain information about airborne infectious disease transmission in enclosed environments is critical in reducing the infection risk to the occupants. This study developed a combined computational fluid dynamics (CFD) and Markov chain method for quickly predicting transient particle transport in enclosed environments. The method first calculated a transition probability matrix using CFD simulations. Next, the Markov chain technique was applied to calculate the transient particle concentration distributions. This investigation used three cases, particle transport in an isothermal clean room, an office with an underfloor air distribution system, and the first-class cabin of an MD-82 airliner, to validate the combined CFD and Markov chain method. The general trends of the particle concentrations vs. time predicted by the Markov chain method agreed with the CFD simulations for these cases. The proposed Markov chain method can provide faster-than-real-time information about particle transport in enclosed environments. Furthermore, for a fixed airflow field, when the source location is changed, the Markov chain method can be used to avoid recalculation of the particle transport equation and thus reduce computing costs.

Design of a compact dilution sampler for stationary combustion sources

The dilution sampling method simulates the rapid cooling and dilution processes after hot flue gas have left the stack. This allows gases or vapors to nucleate both homogeneously and heterogeneously, and to condense on preexisting particles in processes analogous to those that occur in the ambient environment. Using this method the authors can collect filterable particulate matter (PM) and condensible PM, that is, primary PM, simultaneously. In order to make this method more suitable for field investigation, a compact dilution sampler was developed. The sampler enhances mixing of dilution air with the stack gas, and thus shortens the length of the mixing section. The design decreases the nominal flow rate through the aging section, and accordingly reduces the size of the residence chamber. The decreased size of the sampler is suitable for field test. Sampling gas is pressured into the residence chamber, and air pressure in the chamber is micro-positive. Uncollected redundant gas is automatically discharged through unused sampling ports, which keeps the unit stable. Performance evaluation tests demonstrate that the design is reasonable. The sampler has been applied to characterize PM emissions from various combustion sources in China.

The prognostic significance of apoptosis-related biological markers in Chinese gastric cancer patients

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Background: The prognosis varied among the patients with the same stage, therefore there was a need for new prognostic and predictive factors. The aim of this study was to evaluate the relationship of apoptosis-related biological markers such as P21, P27, P53, Bcl-2, Bax, and c-myc, and clinicopathological features and their prognostic value.

Methods: From January 1996 to December 2007, 4,426 patients had undergone gastrectomy for gastric cancer at Fudan University Shanghai Cancer Center. Among 501 patients, the expression levels of P21, P27, P53, Bcl-2, Bax, and c-myc were examined by immunohistochemistry. The prognostic value of biological markers and the correlation between biological markers and other clinicopathological factors were investigated.

Results: There were 339 males and 162 females (2.09:1) with a mean age of 57. The percentages of positive expression of P21, P27, P53, Bcl-2, Bax, and c-myc were 73%, 25%, 65%, 22%, 43%, and 58%, respectively. There was a strong correlation between P21, P53, Bax, and c-myc expression (p = 0.00). There was significant association between P27, Bcl-2, and Bax expression (p < 0.05). The P21 expression correlated with male (p = 0.00), histological grade (p = 0.00), Borrmann type (p = 0.02), tumor location (p = 0.01); the P53 expression with histological grade (p = 0.01); Bcl-2 expression with pathological stage (p = 0.01); Bax expression with male (p = 0.02), histological grade (p = 0.01), Borrmann type (p = 0.01), tumor location (p = 0.00), lymph node metastasis (p = 0.03), pathological stage (p = 0.01); c-myc expression with Borrmann type (p = 0.00). Bcl-2 expression was related with good survival in univariate analysis (p = 0.01). Multivariate analysis showed that Bcl-2 expression and pathological stage were defined as independent prognostic factors for gastric cancers. There was significant differences of overall 5-year survival rates according to Bcl-2 expression or not in stage III (p = 0.00).

Conclusions: The expressionof Bcl-2 was an independent prognostic factor for Chinese patients with gastric cancer; it might be a candidate for the gastric cancer staging system.

No significant financial relationships to disclose.

Cloning, mapping and mutation analysis of human geneGJB5 encoding gap junction protein beta-5

By homologous EST searching and nested PCR a new human geneGJB5 encoding gap junction protein beta-5 was identified.GJB5 was genetically mapped to human chromosome 1p33-p35 by FISH. RT-PCR revealed that it was expressed in skin, placenta and fetal skin. DNA sequencing ofGJB5 was carried out in 142 patients with sensorineural hearing impairment and probands of 36 families with genetic diseases, including erythrokeratodermia (5 families), Charcot-Marie-Tooth disease (13), ptosis (4), and retinitis pigmentosa and deafness (14). Two missense mutations (686A-->G, H229R; 25C-->T, L9F) were detected in two sensorineural hearing impairment families. A heterologous deletion of 18 bp within intron was found in 3 families with heredity hearing impairment, and in one of the 3 families, a missense mutation (R265P) was identified also. But the deletion and missense mutation seemed not segregating with hearing impairment in the family. No abnormal mRNA or mRNA expression was detected in deletion carriers by RT-PCR analysis in skin tissue. Mutation analysis in 199 unaffected individuals revealed that two of them were carriers with the same 18 bp deletion.

Non-viral ex vivo transduction of human hepatocyte cells to express factor VIII using a human ribosomal DNA-targeting vector

BACKGROUND

In gene therapy, one of the most important issues is the choice of the vectors. pHrneo is a human-derived vector previously constructed by our group, which can target a foreign gene into a human ribosomal DNA (hrDNA) locus.

METHODS AND RESULTS

In this study, we inserted an expression cassette of reconstructive hFVIII (hFVIII-BDDAK39) to pHrneo to construct a targeting vector: pHrneo-BDDAK39. Through electroporation of pHrneo-BDDAK39 into HL7702 cells (human hepatocyte), we identified the homologous recombinants using polymerase chain reaction, and tested the expression of hFVIII-BDDAK39 located at the hrDNA locus. The hFVIII-BDDAK39 was successfully targeted into the hrDNA locus of HL7702 by pHrneo-BDDAK39, and the efficiency of site-specific integration was 1.1 x 10(-5). The hFVIII-BDDAK39 at the hrDNA locus of HL7702 was found to be able to express efficiently (4.3 +/- 0.9 ng 10(-6) cells 24 h(-1)).

CONCLUSION

It has been indicated that the targeting vector pHrneo-BDDAK39 can be used in gene therapy for hemophilia A.

[Effects of vitamin A and iron supplementation on the improvement of iron status and immunological function in preschool children]

OBJECTIVE

In order to understand the changes in immunological function in rural preschool children with lower levels of vitamin A and iron, and the effect of vitamin A and iron supplementation on the improvement of iron status and immunological function.

METHODS

Serum vitamin A concentration and hemoglobin (Hb), serum iron (SI), transferrin saturation (TS), serum ferritin (SF) were determined in 270 rural preschool children aged 3-7 years in Beijing, and the subjects were divided into four groups based on their determinations: control, lower serum vitamin A, lower iron, and both lower iron and serum vitamin A. Forty subjects were selected from each group, and serum IgA, IgG, IgM and interleukin-2 (IL-2) were determined for them. Forty-one subjects who had lower iron and lower serum vitamin A (< 1.12 mumol/L) were divided into two groups: one of them supplemented with 30 mg iron element (ferrous sulfate 0.15 g) once a day for 8 weeks, and the other group supplemented with iron and 12,500 IU vitamin A twice a week for 8 weeks. After supplementation of vitamin A and iron, their serum vitamin A, hematological iron index and serum immunological index were determined again for the two groups.

RESULTS

Serum IgM were (1,260 +/- 310) mg/L in both lower iron and serum vitamin A groups, significantly higher than that in normal group (1,070 +/- 170) mg/L (P < 0.05). But there were no significant differences in serum levels of IgG, IgA and IL-2. After supplementation of iron and vitamin A, their serum TS increased to (26.5 +/- 8.6)%, significantly higher than that before supplementation and that supplemented with iron only (22.3 +/- 3.8)%. And, their serum IL-2 were (278.9 +/- 117.7) ng/L after supplementation, significantly higher than that before supplementation (161.6 +/- 90.3) ng/L and that in those supplemented with iron only (189.5 +/- 89.3) ng/L. There was no significant difference in other biochemical indices of iron and immunological indices.

CONCLUSIONS

Supplementation with vitamin A and iron was helpful to improve body iron nutritional status and immunological function obviously in preschool children with iron-deficiency and sub-clinical deficiency of vitamin A.

Determination of D- and L-aspartate in cell culturing medium, within cells of MPT1 cell line and in rat blood by a column-switching high-performance liquid chromatogrpahic method

HPLC fluorometric methods have been used to analyze trace amounts of D-amino acids in biological samples. In this study, we established an expedient column-switching fluorometric HPLC system that would improve the analysis of D-amino acids, in particular D-aspartate (Asp). Our system consists of the fluorogenic derivatization of amino acids with NBD-F and two chromatographic steps, one that separates individual amino acids in reverse phase mode and another that separates the chiral forms of each amino acid in normal-phase mode. The two separation steps are linked through a trapping column by an automated column-switching system. In addition, sample preparation is simplified and improved, where trichloroacetic acid is used for deproteinization, and borate buffer, pH 9.5 is employed for the fluorescent derivatization. The detection limit for D-Asp in culturing medium is 5 nM. The resulting peak heights correlated well with concentrations that ranged from 12.5 to 250 nM for both D- and L-Asp. The present method was applied to determine D- and L-Asp levels in cell culturing medium, and within cells of MPT1 cell line. The detected cellular levels of D- and L-Asp agree with those detected by our previous method. In addition, this method was used to measure D- and L-Asp levels in rat blood samples, and the results are consistent with the reported values.

[Changes of serum transferrin receptor in children with iron deficiency and its response to iron supplementation]

OBJECTIVES

To study the level of serum transferrin receptor (sTfR) in children with different stages of iron deficiency, as well as in the normal children, to observe its response to iron supplementation, and to explore the role of sTfR in surveillance of iron status and assessment of iron supplementation in population.

METHODS

By determining iron status index, 1,006 children aged 6-14 years in Fangshan District, Beijing were divided into four groups, control group, iron depletion (ID) group, iron deficiency erythropoiesis (IDE) group and iron deficiency anemia (IDA) group, and 239 of them were measured for sTfR with Quintikine enzyme immunoassay (R&D system, Minneapolis, MN) and sTfR/logserum ferratin (SF) was estimated. Iron supplementation (NaFeEDTA capsules, containing 60 mg iron element per capsule) was administered for the children with ID and IDE per capsule once weekly and for the children with IDA per capsule thrice weekly for nine weeks. Iron status index and sTfR were measured before and after iron supplementation.

RESULTS

The levels of sTfR and sTfR/log SF in children with ID, IDE and IDA were (20.03 +/- 2.33) nmol/L, (24.52 +/- 1.07) nmol/L, (33.28 +/- 6.09) nmol/L and (18.15 +/- 5.31), (20.98 +/- 8.88), (29.08 +/- 8.57), respectively, significantly higher than those in the control group [sTfR(18.74 +/- 3.06) nmol/L and sTfR/log SF(9.89 +/- 1.74)]. Statistical analysis showed that sTfR correlated to free erythrocyte protoporphyrin and hemoglobin. sTfR levels in normal children was (12.5-23.5) nmol/L. After iron supplementation, sTfR levels in children with ID was (16.37 +/- 3.10) nmol/L, significantly decreased than those before iron supplementation, but no change in sTfR was observed in children with IDE and IDA. sTfR/log SF were decreased significantly in all children with ID group(11.42 +/- 3.12), IDE (16.54 +/- 4.70) and IDA (23.59 +/- 9.93).

CONCLUSION

sTfR is a specific indicator for identifying IDE and IDA, and sTfR/log SF is a sensitive index for assessing the effects of iron supplementation.

[Effects of cactus, alove veral, momorcica charantia on reducing the blood glucose of diabetic mice]

The effects of cactus, alove veral and momorcica charantia on reducing the blood glucose level of mice were observed. The diabetic model with no symptom in mice was established by injection of streptozotocin(STZ) 80 mg/kg BW into abdominal cavity for 11 days. The diabetic mice were randomly divided into 8 groups: STZ diabetic model, diet A, diet B, cactus, alove veral, momordica charantia and glyburide groups. Cactus (60 g/kg BW), alove veral (60 g/kg BW), and momordica charantia (30 g/kg BW) were administrated orally each day to the diabetic mice for another 21 days. Serum glucose of mice fasting for 12 hours and 2 hours after meal was determined with the method of glucose-oxidase at the 21th day of the experiment. The results showed that serum glucose levels of diabetic mice were significantly higher than the normal control group (P < 0.01). After giving diet A, cactus, alove veral and momorcica charantia juice for 21 days, the serum glucose concentration of these diabetic mice were significantly lower than STZ diabetic model group (P < 0.01) but still higher than the normal control group.

Occurrence of D-Amino Acids and a pyridoxal 5'-phosphate-dependent aspartate racemase in the acidothermophilic archaeon, Thermoplasma acidophilum

Free D-amino acid content in some archaea was investigated and D-forms of several amino acids were found in them. In the acidothermophilic archaeon, Thermoplasma acidophilum, the proportion of D-aspartate (D-Asp) to total Asp was as high as 39.7%. Crude extracts of Thermoplasma acidophilum had Asp-specific racemase activity that was pyridoxal 5'-phosphate (PLP)-dependent. The relative insensitivity to a SH-modifying reagent distinguished this activity from those of the PLP-independent Asp racemases found in other hyperthermophilic archaea (Matsumoto, M., et al., J. Bacteriol. 181, 6560-6563 1999). Thus, high levels of d-Asp should be produced by a new type(s) of Asp-specific racemase in Thermoplasma acidophilum, although the function of d-Asp in this archaeon remains unknown.

Localization, Transport, and Uptake of -Aspartate in the Rat Adrenal and Pituitary Glands

Large amounts of D-aspartate (D-Asp) are present in the rat adrenal and pituitary glands. D-Asp is thought to be synthesized in the mammalian body and also accumulates in various tissues following intraperitoneal or intravenous administration. This report examines the origins of D-Asp in the adrenal and pituitary glands. We administered D-Asp to male rats intraperitoneally and immunolocalized this exogenous D-Asp in adrenal and pituitary tissue, using an anti-D-Asp antiserum which was previously developed in our laboratory. D-Asp levels in the rat adrenal gland have been shown to undergo a transient increase at 3 weeks of age and to decrease rapidly thereafter. We found that in the adrenal gland, exogenous D-Asp administered intraperitoneally was incorporated into the same region of the adrenal cortex in which endogenous D-Asp was present. By Northern and Western blot analysis and immunohistochemistry of glutamate (Glu) transporter, we also found that expression of the Glu transporter (GLAST), which has an affinity for D-Asp, transiently increased at 3 weeks of age and that localization patterns of the Glu transporter within the tissue were almost coincident with those of endogenous D-Asp. These observations suggest that D-Asp in the adrenal cortex of 3-week-old male rats is primarily acquired by uptake from the vascular system. We have previously shown that D-Asp is specifically localized in prolactin (PRL)-containing cells in the anterior lobe of the adult rat pituitary gland. Here we report that in the pituitary gland, exogenous D-Asp accumulated in endothelial cells, but not in PRL-containing cells. Northern and Western blot analysis and immunohistochemistry of Glu transporter revealed that developmental changes in the Glu transporter (GLAST) expression did not correlate with tissue levels of D-Asp and that the Glu transporter was not expressed in PRL-containing cells. These observations suggest that, in contrast to the adrenal gland, most of the D-Asp in the pituitary gland of adult male rats originates inside the gland itself.

Antiretroviral agents inhibit infection of human cells by porcine endogenous retroviruses

The efficacy of antiretroviral drugs against porcine endogenous retroviruses (PERV) that may be harbored in pig organs intended for transplantation was examined in human cells in vitro. The nucleoside analogs zidovudine and dideoxyinosine were found to effectively inhibit PERV replication.

d-Aspartate in a prolactin-secreting clonal strain of rat pituitary tumor cells (GH(3))

d-Aspartate (d-Asp) is found in prolactin (PRL)-containing cells of the rat anterior pituitary gland [Lee et al., Brain Res. 838, 193-199, 1999]. In order to determine whether d-Asp is actually produced by the anterior pituitary gland and whether it plays a physiological role in PRL function, a PRL-secreting clonal strain of rat pituitary tumor cells (GH(3)) was employed in this study. HPLC analysis and immunocytochemical staining detected the presence and synthesis of d-Asp in the cytoplasm of these cells. In addition, thyrotropin-releasing hormone-stimulated PRL secretion was increased in a dose-dependent fashion by d-Asp from these cells. These results suggest that the anterior pituitary gland synthesizes d-Asp and that d-Asp acts as a messenger in this gland.

Infection by porcine endogenous retrovirus after islet xenotransplantation in SCID mice

Animal donors such as pigs could provide an alternative source of organs for transplantation. However, the promise of xenotransplantation is offset by the possible public health risk of a cross-species infection. All pigs contain several copies of porcine endogenous retroviruses (PERV), and at least three variants of PERV can infect human cell lines in vitro in co-culture, infectivity and pseudotyping experiments. Thus, if xenotransplantation of pig tissues results in PERV viral replication, there is a risk of spreading and adaptation of this retrovirus to the human host. C-type retroviruses related to PERV are associated with malignancies of haematopoietic lineage cells in their natural hosts. Here we show that pig pancreatic islets produce PERV and can infect human cells in culture. After transplantation into NOD/SCID (non-obese diabetic, severe combined immunodeficiency) mice, we detect ongoing viral expression and several tissue compartments become infected. This is the first evidence that PERV is transcriptionally active and infectious cross-species in vivo after transplantation of pig tissues. These results show that a concern for PERV infection risk associated with pig islet xenotransplantation in immunosuppressed human patients may be justified.

[A clinicopathological study of mediastinal lymph node metastasis of lung cancer]

BACKGROUND

To investigate the characteristics of mediastinal lymph node metastasis of lung cancer from a view of pathology.

METHODS

Radical pulmonectomy or lobectomy combined with extensive dissection of mediastinal lymph node was carrived out in 398 patients with lung cancr. N2 disease was diagnozed in 160 cases, and total 352 groups of mediastinal lymph node invaded were analyzed.

RESULTS

N2 disease appeared as single group, multi-groups and jumping-form groups, comprising 41.2%,58.8% and 29.3% respectively. The highest metastatic site of lymph node was group 7 mediastinal lymph node, the followings were group 4, 3 and 5 lymph nodes, comprising 45.6%, 31.3% and 25.6% respectively. The N2 metastasis was highly correlated with the site, size, histological classification and cell differentiation of the cancer. An another characteristic of N2 metastasis was that the metastatic lymph node could invaded into the bronchial wall, especially in adenocarcinoma.

CONCLUSIONS

It is necessary to dissect the lymph nodes of the hilar and upper and lower mediastinum at the homolateral thoracic cavity extensively and completely. Attention should be paid to the bronchial wall invasion by the metastatic lymph nodes, too.

Occurrence of free D-amino acids and aspartate racemases in hyperthermophilic archaea

The occurrence of free D-amino acids and aspartate racemases in several hyperthermophilic archaea was investigated. Aspartic acid in all the hyperthermophilic archaea was highly racemized. The ratio of D-aspartic acid to total aspartic acid was in the range of 43.0 to 49.1%. The crude extracts of the hyperthermophiles exhibited aspartate racemase activity at 70 degrees C, and aspartate racemase homologous genes in them were identified by PCR. D-Enantiomers of other amino acids (alanine, leucine, phenylalanine, and lysine) in Thermococcus strains were also detected. Some of them might be by-products of aspartate racemase. It is proven that D-amino acids are produced in some hyperthermophilic archaea, although their function is unknown.

A phase 1-2 clinical trial of gene therapy for recurrent glioblastoma multiforme by tumor transduction with the herpes simplex thymidine kinase gene followed by ganciclovir. GLI328 European-Canadian Study Group

This study has investigated the effects of herpes simplex thymidine kinase gene (HSV-tk) transfer followed by ganciclovir treatment as adjuvant gene therapy to surgical resection in patients with recurrent glioblastoma multiforme (GBM). The study was open and single-arm, and aimed at assessing the feasibility and safety of the technique and indications of antitumor activity. In 48 patients a suspension of retroviral vector-producing cells (VPCs) was administered by intracerebral injection immediately after tumor resection. Intravenous ganciclovir was infused daily 14 to 27 days after surgery. Patients were monitored for adverse events and for life by regular biosafety assaying. Tumor changes were monitored by magnetic resonance imaging (MRI). Reflux during injection was a frequent occurrence but serious adverse events during the treatment period (days 1-27) were few and of a nature not unexpected in this population. One patient experienced transient neurological disorders associated with postganciclovir MRI enhancement. There was no evidence of replication-competent retrovirus in peripheral blood leukocytes or in tissue samples of reresection or autopsy. Vector DNA was shown in the leukocytes of some patients but not in autopsy gonadal samples. The median survival time was 8.6 months, and the 12-month survival rate was 13 of 48 (27%). On MRI studies, tumor recurrence was absent in seven patients for at least 6 months and for at least 12 months in two patients, one of whom remains recurrence free at more than 24 months. Treatment-characteristic images of injection tracks and intracavity hemoglobin were apparent. In conclusion, the gene therapy is feasible and appears to be satisfactorily safe as an adjuvant to the surgical resection of recurrent GBM, but any benefit appears to be marginal. Investigation of the precise effectiveness of this gene therapy requires prospective, controlled studies.

In vitro analysis of transformation potential associated with retroviral vector insertions

While replication-defective retroviral vectors provide excellent vehicles for the long-term expression of therapeutic genes, they also harbor the potential to induce undesired genetic changes by random insertions into the host genome. The rate of insertional mutagenesis for retroviral vectors has been determined in several different assay systems; however, the rate at which such events induce cellular transformation has not been directly determined. Such measurements are critical to determining the actual risk of carcinogenesis resulting from retroviral gene therapy. In this study, the ability of a replication-defective retroviral vector, GlnBgSvNa, to induce cellular transformation in the BALB/c-3T3 in vitro transformation assay was assessed. The transformation frequency observed in vector-transduced BALB/c-3T3 cells, which contained one to six copies of integrated provirus, was not significantly different from that of untreated control cells. The finding that GlnBgSvNa was nontransforming in this assay indicates that the rate of transformation induced by retroviral insertions is less than the spontaneous rate of cellular transformation by BALB/c-3T3 cells, or less than 1.1 x 10(-5). These results are the first to define an upper limit for the rate of transformation induced by retroviral vectors.