Investigation of new cytogenetic biomarkers specific to high-LET radiation using in vivo and in vitro exposed human lymphocytes.

PURPOSE: To find detectable cytogenetic biomarkers that can offer information about the radiation quality of in vivo exposure retrospectively. MATERIALS AND METHODS: Chromosome-type aberrations of peripheral lymphocytes of uterine cancer patients that received internal gamma- and external X-ray therapy or carbon beam therapy and of victims severely exposed to neutrons and gamma-rays in a criticality accident that occurred in Tokai-mura, Japan were analysed. Data obtained from in vitro irradiation experiments using 60Co gamma-rays and 10 MeV neutrons were compared with the in vivo exposure data. RESULTS: The ratio of acentric rings to dicentric chromosomes (termed RaD ratio) and that of excess fragments to dicentrics (termed EfD ratio) showed significant (p < 0.05) differences between the two groups of cancer patients, and these ratios for accidental victims were in between the values of the two groups of cancer patients. The in vitro studies using doses equivalent to 1 - 3 Gy of gamma-rays have confirmed that the EfD ratios were increased with the high LET (linear energy transfer) and RaD ratios decreased. CONCLUSION: The present data show that the RaD and EfD ratios can be used as cytogenetic biomarkers of exposure to high-LET radiation at least within a few years of exposure.

Genetic susceptibility to thymic lymphomas and K-ras gene mutation in mice after exposure to X-rays and N-ethyl-N-nitrosourea.

PURPOSE: Ras activation is one of the major mechanisms for the development of murine thymic lymphomas by radiation and chemical carcinogens. To gain insight into the relationship between genetic susceptibility and ras gene mutation, the frequency and spectrum of ras gene mutation was examined in thymic lymphomas from susceptible and resistant mice. MATERIALS AND METHODS: K- and N-ras mutations in thymic lymphomas that arose in X-ray-irradiated and N-ethyl-N-nitrosourea (ENU)-treated mice of susceptible C57BL/6, rather resistant C3H and their hybrid B6C3F1 were analysed by polymerase chain reaction-single-strand conformation polymorphism and subsequent DNA sequencing. RESULTS: C57BL/6 exhibited a higher incidence of thymic lymphomas after exposure to X-rays and ENU than C3H, with B6C3F1 being intermediate. K-ras gene mutations occurred frequently in the pathogenesis of ENU-induced thymic lymphomas in susceptible C57BL/6 as opposed to resistant C3H. The ras mutations were more frequent in ENU-induced thymic lymphomas than X-ray-induced thymic lymphomas, and with the latter, there was no clear evidence for strain differences, suggesting that the genetic susceptibility to X-rays was independent of ras activation. The mutations of K-ras in thymic lymphomas from C57BL/6 were predominantly GGT to GAT in codon 12, whereas this mutation type was never found in those from C3H. No strain difference was observed in the nucleotide sequence or expression levels of O(6)-alkylguanine alkyltransferase, indicating that this enzyme did not account for the genetic susceptibility to ras activation. CONCLUSIONS: The results indicate that there is a clear strain and carcinogen dependency of K-ras mutation and that the frequency of ras mutation might determine the genetic susceptibility to ENU-induced lymphomagenesis, whereas pathways independent of ras activation might determine the susceptibility to X-ray-induced lymphomagenesis.

Reduced sensitivity to and ras mutation spectrum of N-ethyl-N-nitrosourea-induced thymic lymphomas in adult C.B-17 scid mice.

Scid mice are defective in the ability to repair DNA double strand breaks and, as a consequence, their cells are radiosensitive. Further, they have been shown to be prone to develop thymic lymphomas (TLs) after small doses of ionizing radiation. Little is known, however, on the role of scid mutation in chemical carcinogenesis. To determine if scid mutation increased predisposition to chemical carcinogenesis, we examined both the susceptibility of scid mice to N-ethyl-N-nitrosourea (ENU)-induced lymphomagenesis and the involvement of ras gene activation. Adult female mice at 8 weeks of age were given ENU in their drinking water at 400 ppm for 2-10 weeks. Contrary to expectations, we observed a two to three-fold reduction in TL development in the scid mice. The highest incidence was achieved by ENU treatment for 8 weeks for scid and wild-type C.B-17 mice, of 42 and 85%, respectively (P<0.05). We investigated whether this was attributable to the usage of the ras mutation pathway. There was, however, no significant difference in the frequency and spectrum of K-ras mutation between the scid and wild-type C.B-17 mice. Most of the K-ras mutations were either GGT to GAT transition in codon 12 (11/23: 48%) or CAA to CCA transversion in codon 61 (8/23: 35%) that was independent of scid background. The incidence of N-ras mutation was very low. These results indicate that scid mice are less susceptible to ENU-induced lymphomagenesis and ras gene mutation frequently occurs in both scid and wild-type C.B-17 mice.

Characteristic association between K-ras gene mutation with loss of heterozygosity in X-ray-induced thymic lymphomas of the B6C3F1 mouse.

PURPOSE: To elucidate the characteristics of radiation carcinogenesis, the spectra of K- and N-ras oncogene mutations, loss of heterozygosity (LOH) and their association in X-ray-induced thymic lymphomas (TL) were determined by comparing with those of N-ethyl-N-nitrosourea (ENU)-induced and spontaneously occurring TL. MATERIALS AND METHODS: TL that arose in untreated, X-ray-irradiated and ENU-treated B6C3F1 mice were examined both for K- and N-ras mutations by PCR-SSCP and DNA sequencing and for LOH by PCR with polymorphic microsatellite markers. RESULTS: (1) ras gene mutations were found in a proportion of TL from X-ray-exposed (approximately 20%) and ENU-treated (30-40%) mice while no ras gene mutations were found in spontaneous TL. N-ras mutations were rare. (2) The spectrum of ras gene mutations was diverse and seemed to differ little between X-ray-induced and ENU-induced TL, even though there was a higher frequency of ras mutations in ENU-induced TL that clustered to K-ras codon 12. (3) The X-ray-induced TL showing K-ras mutation were associated with LOH on chromosome 6, while those showing no K-ras mutation were associated with high frequency of LOH on chromosomes 4, 11 and 12. CONCLUSION: These results demonstrate that, in the B6C3F1 mouse TL, X-ray-induced lymphomagenesis showed both the co-expression, yet low occurrence of allelic imbalance on chromosome 6 and K-ras mutation, and exclusive expression of frequent allelic imbalance on chromosomes 4, 11 and 12 and K-ras mutation.

Absence of linkage between radiosensitivity and the predisposing atp7b gene mutation for heritable hepatitis in the LEC rat.

The LEC rat is known to be a mutant strain that spontaneously develops heritable hepatitis due to copper accumulation, caused by mutation of the copper-transporting ATPase gene (Atp7b). Immunodeficiency and radiosensitivity have also been observed. Hayashi et al. extensively examined the radiosensitivity of the LEC rat and concluded that its hypersensitivity is controlled by a single autosomal gene. Furthermore, they suggested the possibility that it correlates to copper accumulation due to the Atp7b gene mutation, because ionizing radiation-induced hydroxyl radicals might act in concert with copper-induced hydroxyl radicals. In the present experiment, we analyzed linkage between radiosensitivity and the mutation responsible for hepatitis in F(1) animals of a cross with the F344 rat. Our results clearly demonstrated an absence of any significant association. In addition, partial dominance for radiosensitivity was observed, and radiosensitive (F(1) x LEC) backcross rats were twice as numerous as their radioresistant counterparts, suggesting the possibility of control by two or more recessive genes.

Low frequency of Ras gene mutation in spontaneous and gamma-ray-induced thymic lymphomas of scid mice.

Scid mice, which have a defect in the capacity to repair DNA double-strand breaks, were highly prone to the induction of thymic lymphomas after exposure to ionizing radiation; approximately 70% of mice developed lymphomas within 1 year after exposure to 1-3 Gy, whereas approximately 20% of unirradiated control mice developed lymphomas. To gain information on the possible role of Ras activation in development of thymic lymphomas in scid mice, we have examined both the frequency and the spectrum of Kras and Nras mutations in spontaneous and radiation-induced lymphomas. Neither activated Kras nor Nras genes were detected in spontaneous lymphomas, while Kras mutations increased in a dose-dependent manner in radiation-induced lymphomas. However, Kras mutations were infrequent (6% in lymphomas in mice exposed to 1 Gy, 12.5% in those exposed to 2 Gy, 16.7% in those exposed to 3 Gy), and no mutations were detected in Nras genes, suggesting that Ras mutation was not significantly involved in the development of thymic lymphomas in scid mice. Analysis of the spectrum of Kras mutations demonstrated unique mutations in both codons 13 (GGC to GAC) and 61 (CAA to CTA) in addition to the commonly identified substitution of GAT for GGT in codon 12 of Kras.

Induction of ovarian tumors by heavy ion irradiation in B6C3F1 mice.

Six-week-old B6C3F1 mice were exposed to 0.439 Gy heavy ion irradiation as a 290 MeV/u carbon-ion beam (LET 10 keV/micron) at 2 cm from the upper proximal point of a spread Bragg beam and autopsied 13.5 months after the irradiation. In males total tumor incidences, mainly liver tumors, were 37.0% in irradiated group and 25.0% in control (P>0.05). In females the total tumor incidences were 32.3%, mainly ovarian tumors, in the irradiated group and 0% in the controls. These results indicate that heavy ion irradiation induces ovarian tumors in females but does not target any organ in males.

Comparison of tumorigenesis between accelerated heavy ion and X-ray in B6C3F1 mice.

The effects of heavy ion and X-ray irradiation on tumorigenesis in B6C3F1 mice were compared. Six-week-old animals were divided into 6 groups and exposed to 0.426 Gy heavy ion irradiation of 290 MeV/u carbon-ion beam (LET 60-210 KeV/micron) at the dose rate of 0.4 +/- 0.2 Gy/min; 0.5 Gy of X-ray irradiation at 0.1 Gy/min or 5 Gy of X-ray irradiation at 1 Gy/min. The mice were killed and an autopsy performed 13.5 months after the whole body irradiation. Body weights were heaviest for both sexes in the 0.5 Gy group and lightest in the 5 Gy one. Total tumor incidences in the males were 30, 56 and 13% respectively in the heavy ion, 5 Gy and 0.5 Gy X-irradiated groups, stomach tumors, lymphomas and adrenal tumors being the most common outcome of the high dose X-rays. Liver tumor induction did not differ significantly among the groups. In the females tumorigenicity was significantly lower for heavy ion than for 0.5 Gy and 5 Gy X-ray irradiation (P < 0.05), the respective incidences, mainly ovary one, being 73%, 17% and 41%. Non-cancerous lesions, such as graying of the hair, glomerular sclerosis and amyloidosis appeared in the 5 Gy group. These findings indicate that 0.426 Gy of heavy ion irradiation induced lower carcinogenicity than 5 Gy of X-irradiation and higher carcinogenicity than that of 0.5 Gy X-irradiation in male mice.

Increased sensitivity of scid heterozygous mice to ionizing radiation.

In the present study, acute effects of ionizing radiation on animal survival, bone marrow cells and fibroblast cell lines of scid homozygous, scid heterozygous and wild-type mice with the same C.B-17 genetic background were examined. The sensitivities to ultraviolet light (UV) and various chemicals, bleomycin, mitomycin C, N-methyl-N'-nitro-N-nitrosoguanidine, methyl methanosulphonate, 5-fluorouracil, 6-mercaptopurine, 4-nitroquinoline 1-oxide and potassium bromate) were also investigated. In addition, micronucleus testing of whole-body irradiated mice was performed. Scid heterozygous mice were found to be less sensitive than the homozygotes but more sensitive to ionizing radiation than wild-type mice, not only in vivo but also for bone marrow cells in vitro, suggesting partial dominance under both conditions. In contrast, there were no differences in sensitivity to UV light and various chemicals, as compared with wild-type and scid heterozygous cell lines, either in vitro or in the micronucleus test.

Deviated overexpression of TCR-beta, TCR-gamma, CD4, and CD8 on thymic lymphomas induced by 1-propyl-1-nitrosourea: destruction of the allelic exclusion of TCR-beta and expression of functional TCR-betagamma heterodimer on a lymphoma, cFTL53.

Thymic lymphomas (FTLs) induced by the chemical carcinogen 1-propyl-1-nitrosourea (PNU) in F344 rats showed deviated overexpression of TCR-beta, TCR-gamma, CD4, and CD8. Even though most FTLs were in the CD4+ CD8+ stage, all FTLs expressed TCR-beta mRNA with TCR-gamma mRNA, but without TCR-alpha mRNA or TCR-delta mRNA. One of the FTLs, cFTL53, expressed two kinds of TCR-beta mRNA and two kinds of TCR-gamma mRNA, but did not express any mRNA of TCR-alpha or TCR-delta. Both alleles of TCR-beta loci were rearranged on cFTL53. cDNA cloning and sequencing analysis showed that one TCR-gamma mRNA, Vgamma4-Jgamma1-Cgamma1, and both TCR-beta mRNA, Vbeta2-Dbeta2-Jbeta2.1 and Vbeta19-Dbeta2-Jbeta2.1-Cbeta2, on cFTL53 were in the productive form, while the other TCR-gamma mRNA, Vgamma1-Jgamma4-Cgamma4L, was not. Both TCR beta-chains and a TCR gamma-chain were expressed on cFTL53, making a novel set of TCR-betagamma heterodimer. Cross-linking of TCR-betagamma heterodimer on cFTL53 resulted in a calcium flux, indicating that TCR-betagamma works as a signal transduction receptor. Thus, there are four strange phenomena on FTLs; CD4 and CD8 are expressed without TCR-alphabeta or TCR-gammadelta, TCR-beta mRNA and TCR-gamma mRNA were expressed simultaneously without TCR-alpha and TCR-delta mRNA on FTLs, the allelic exclusion of TCR-beta was destroyed in cFTL53, and a novel set of functional TCR-betagamma heterodimer was expressed on cFTL53.

A statistical analysis of the internal organ weights of normal Japanese people.

Correlation of weights of various organs with age, body weight, and/or body height was statistically analyzed using data on the Japanese physique collected by the Medico-Legal Society from Universities and Research Institutes in almost all areas of Japan. After exclusion of unsuitable individual data for statistical analysis, findings for 4,667 Japanese, aged 0-95 y, including 3,023 males and 1,644 females were used in the present study. Analyses of age-dependent changes in weights of the brain, heart, lung, kidney, spleen, pancreas, thymus, thyroid gland and adrenal gland and also of correlations between organ weights and body height, weight, or surface area were carried out. It was concluded that organ weights in the growing generation (under 19 y) generally increased with a coefficient expressed as (body height x body weight0.5). Because clear age-dependent changes were not observed in adults over 20 y, they were classified into 4 physical types, thin, standard, plump and obese, and the relations of organ weights with these physical types were assessed. Some organs were relatively heavier in fat groups and light in thin individuals, or vice versa.

Comparison of dose-dependent enhancing effects of gamma-ray irradiation on urethan-induced lung tumorigenesis in athymic nude (nu/nu) mice ac (nu/+) littermates.

The role of immunological surveillance in carcinogenesis is still controversial. In our previous experiments, urethan-induced lung tumorigenesis in athymic (nu/nu) mice and euthymic (nu/+) littermates was examined, and it was concluded that immunosurveillance mediated by T cells could not be demonstrated. However, the reported enhancement of development of various tumors following ionizing radiation might be achieved through modulating the host immunological conditions. In the present experiment, nu/nu and littermate nu/+ mice were treated with 1-4 Gy gamma-rays alone at 6 weeks of age or treated with urethan at 0.5 mg/g body weight when aged 14 days followed by 1-4 GY gamma-rays 4 weeks later. Lung tumors were assessed at 6.5 months of age. Ionizing radiation itself caused a very low incidence of these lesions. On the other hand, multiplicities and incidences of lung tumors after urethan treatment at 0.5 mg/g body weight were similar between the two phenotypically different groups of mice (1.66 and 1.84 tumors/mouse, 73% and 80% incidences, for nu/nu and nu/+ cases respectively). This urethan-induced lung tumorigenesis was significantly enhanced by gamma-rays in both nu/nu and nu/+ mice, and the magnitude of tumor enhancement was somewhat higher in nu/+ mice than in nu/nu mice, especially with a 2-Gy dose. In conclusion, it may be said that lung tumorigenicity of gamma-ray irradiation itself and the enhancing effect of radiation on urethan-induced tumorigenesis are scarcely influenced by immunosurveillance mechanisms mediated by T cells.

Reduced fidelity of DNA synthesis in cell extracts from chemically induced primary thymic lymphomas of mice.

To examine whether the fidelity of DNA synthesis is reduced in tumor cells, M13 mp2-based fidelity assays were carried out using 15 samples of whole-cell extracts from primary mouse thymic lymphomas induced by alkylating agents. We found that DNA synthesis activities of thymic lymphomas, detected as incorporation of [3H]TTP into acid-insoluble materials, were 2- to 10-fold higher compared to those of normal thymus. Furthermore, mutant frequencies in the forward mutation assay of DNA synthesis were increased 2- to 7-fold in cell extracts from thymic lymphomas compared to those from normal thymus. As the DNA polymerase beta (pol beta) activity was extremely high in the thymic lymphomas, we screened mutations in the pol beta gene to examine the possibility of involvement of mutated pol beta in reduction of the fidelity of DNA synthesis. Of 20 lymphomas, one case of point mutation (T to A) was found by reverse transcription-PCR single-strand conformation polymorphism analysis. These results suggest that the mutagenic DNA synthesis is involved in murine thymic lymphoma genesis, although mutation of the pol beta gene is not a major causal event.

Genetic regulation of development of thymic lymphomas induced by N-propyl-N-nitrosourea in the rat.

To clarify the linkage between Hbb and Tls-1 (thymic lymphoma susceptible-1) loci and to investigate other loci concerned in thymic lymphomagenesis, the BUF/Mna rat, which is highly sensitive to the lymphomagenic activity of N-propyl-N-nitrosourea (PNU), the WKY/NCrj rat, reported to be resistant, and their cross offspring were subjected to genetic analysis. F1 hybrid and backcross generations were raised from the 2 strains, and 6 genetic markers including Hbb were analyzed in individuals of the backcross generation. However, no linkage between Hbb and Tls-1 loci could be demonstrated since WKY rats also developed a high incidence of thymic lymphomas in response to PNU. Nevertheless, thymic lymphomas developed more rapidly and reached a larger size in the BUF rats. F1 rats expressed a rather rapid and large tumor growth phenotype, while the [(WKY X BUF) X WKY] backcross generation consisted of rats with either rapidly growing or slowly growing tumors. It was thus concluded that rapid development of thymic lymphomas is determined by a gene, provisionally designated Tls-3. Analysis of the relationship between 6 genetic markers and development of thymic lymphoma in the backcross generation demonstrated that the Tls-3 locus is loosely linked to the Gc locus, suggesting a possible location on rat chromosome 14. Tls-3 may not be identical with Tls-1 and other genes known to be relevant to thymic tumors, but its relationship with Tls-2 remains obscure.

Age-dependent induction of thymic lymphomas by N-propyl-N-nitrosourea in the F344/DuCrj rat.

N-Propyl-N-nitrosourea (PNU) is one of the most potent thymic-lymphomagenic agents in rats. Our previous experiments strongly suggested that leukemogenic viruses were not the cause of thymic lymphomas in rats and that target cells of PNU exist in the thymus but not in the bone marrow. On the other hand, the role of retrovirus in lymphomagenesis is undeniable in mice. Therefore, chemically induced rat thymic lymphoma provides a good model to analyse lymphomagenesis without viral implications. In the present experiment 1, we investigated the relationship between the age of animal at commencement of PNU treatment and the incidence of thymic lymphomas. Incidences of thymic lymphomas were 100, 100, 80 and 18, and average latent periods were 15.1, 18.7, 25.4 and 27.3 weeks after the start of PNU-treatment, in 5-, 10-, 20- and 40-week-old groups, respectively. In experiment 2, rats were sacrificed postnatally at 5, 10, 20, 30 and 40 weeks each, and thymus weight, number of thymocytes in the thymus, frequency of mitosis, and percentage of OX-7 (Thy 1.1), OX-8 (CD8), or W3/25 (CD4) positive cells, were examined cytologically. Thymus weight, number of cells in the thymus and mitotic index were maximum at 10 weeks old, and thereafter decreased gradually. No marked changes were observed in the ratio of each cell-surface marker positive cell. These results indicate that induction of thymic lymphomas by PNU is very closely related with the total number of mitotic cells in the thymus. Thus, chemical induction of rat thymic lymphoma reflects an age-dependent function of the thymus.

Comparative genetics of host response to N-methyl 1-N'-nitro-N-nitrosoguanidine. I. A lack of tumor production in the glandular stomach of Swiss mouse.

The present study investigated the effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) drink and 3 maintenance diets on both the survival and the glandular stomach morphology in a total of 480 Swiss/ICR mice. The MNNG conditioning was practised in one half of the mice for the first 8 months. The maintenance of mice on the standard (MF) diet, the rice-rich (R) diet or the rice- and salt-rich (RS) diet was continued for 12 months. The results obtained are as follows: 1) Many mice in the MNNG-conditioned groups experienced fatal bleeding into the small intestine before the termination of the feeding experiment. There was no sign of tumor formation in their digestive canals. The bleeding deaths took place more often in the MF- and RS- diet groups than in the R-diet groups, and started to appear earlier in males than in females within the MF-diet groups. 2) The tendency to gastric atophy, as assessed in terms of the wet weight of mouse glandular stomach as well as the quantitation of histological changes of the same organ in the one-year survivors, progressed in the order of the MF-diet groups, the R-diet groups and the RS-diet groups. 3) The effect of MNNG drink on the mouse glandular stomach morphology was bidirectional: it increased the incidence of advanced atrophy (and/or decreased the incidence of advanced hyperplasia) in the MF- and R-diet groups, and rather reduced the atrophy-oriented effect of the diet on stomach morphology in the RS-diet groups. 4) The above-mentioned effects of 3 maintenance diets and MNNG drink were more prominent in males than in females. 5) No neoplastic change was detected in the glandular stomachs of the one-year survivors with and without MNNG conditioning. 6) Evidence was presented to indicate that MNNG behaved as a quasi-antiandrogen in inducing the morphological changes of mouse glandular stomach.

DNA strand breaks and death of thymocytes induced by N-methyl-N-nitrosourea.

N-Methyl-N-nitrosourea (MNU) is a potent carcinogen in various sites of experimental animals and induces thymic lymphoma in rats, which has long been hard to induce by any carcinogen. To analyze the action of MNU on thymocytes, DNA strand breaking in thymocytes from the MNU-treated rat and that in MNU-treated cultured thymocytes were assayed. Fluorometric analysis of DNA unwinding (FADU assay), first reported by Birnboim and Jevcak to detect X-ray-induced DNA damage, was modified and applied to detect DNA damage in thymocytes treated with MNU in vitro or in vivo. In the present modified method, cell lysate was admixed with 0.15 M sodium hydroxide, and DNA unwinding was processed at pH 12.0 for up to 2 h at 0 degree C in iced water. Double-stranded DNA remaining after alkaline reaction was detected by binding ethidium bromide and measuring its fluorescence. The severity of DNA damage, both in vivo and in vitro, depended on the MNU concentration. In addition, the sequential survival rate and cell-size distribution of thymocytes treated with MNU in vitro were investigated. A close relationship between the severity of DNA damage and cell death was demonstrated in MNU-treated thymocytes, and DNA damage by a non-cell-killing dose of MNU was detected with this FADU assay. MNU-induced cell death is not programmed as in apoptosis, which is caused in thymocytes physiologically, immunologically and by X-ray irradiation or corticoids.

Investigation into the effect of DHEA on renal carcinogenesis induced in the rat by a single dose of DMN.

Because long-term oral administration of the adrenal steroid dehydroepiandrosterone (DHEA) has previously been shown to inhibit the development of spontaneous breast cancer and chemically induced lung, colon, skin, and liver tumors in various mouse and rat strains, the effect of DHEA on the development of rat kidney tumors by a single dose of 30 mg/kg dimethylnitrosamine (DMN) was tested. DHEA was administered in the diet for a 26-week period commencing 2 weeks after DMN treatment. DHEA administration caused a reduction in body weight gain in accordance with its known antiobesity activity. However, it did not exert any inhibitory effect on either renal mesenchymal or cortical epithelial tumor induction by DMN, nor did it alter the average survival time. There was a statistically significant increase in the incidence of renal adenocarcinomas in the DHEA-treated group but not of renal adenomas. The results were discussed in relation to the mesodermal origin of kidney and the potency of single-dose systems of experimental cancer induction.

Genetic regulation of the development of glomerular sclerotic lesions in the BUF/Mna rat.

BUF/Mna strain rats spontaneously develop renal glomerular sclerotic lesions (RSL) at a nearly 100% incidence, diagnosed by hyperalbuminuria (greater than 500 mg/dl) and glomerular lesions morphologically resembling one type of human focal glomerular sclerosis (FGS). Genetic segregation of RSL development was studied by crossing the BUF/Mna strain with two other rat strains, WKY/NCrj and ACI/NMs, which were free of RSL. Two autosomal recessive genes in the BUF/Mna rats were found to determine the susceptibility to RSL in both combinations of crosses.

Thymic lymphomas induced by N-propyl-N-nitrosourea (PNU) in the BUF/Mna rat, an inbred strain with a high incidence of spontaneous thymoma.

N-Propyl-N-nitrosourea (PNU) is known to be a strong leukemogen, inducing myelogenous leukemia or thymic lymphoma in some strains of rat. The thymic lymphomagenic effect of PNU has been demonstrated in F344 rats. On the other hand, the BUF/Mna rat has been established as an inbred strain that develops spontaneous thymomas after one year of age. In the present experiment, PNU was continuously administered in drinking water to male and female BUF/Mna rats starting at 5 weeks of age. Thymic lymphomas were induced in all PNU-treated rats with an average latent period as short as 14 experimental weeks. These results show the high susceptibility of the BUF/Mna rat to the lymphomagenic activity of PNU. The BUF/Mna rat is an ideal strain for studies on epithelial cell-lymphocyte interaction, not only in the development of thymic lymphomas but also in that of spontaneous thymoma. Karyotypes of twelve primary thymic lymphomas induced by PNU were analyzed for chromosomal abnormalities. Chromosomal abnormalities were often found in chromosomes 11 and 2. In some types of abnormality, dup (11q) and del(2q) were most frequently observed. In addition, trisomy of chromosome 7, on which the c-myc gene is mapped, was observed in five lymphomas, and monosomy of chromosomes 20 and X in six and five cases, respectively, though these changes were generally observed in a minor cell population in each case.