High-resolution genetic map of X-linked juvenile-type granulosa cell tumor susceptibility genes in mouse

SWR/Bm (SWR) female mice spontaneously develop early-onset ovarian granulosa cell (GC) tumors that can progress to metastatic carcinoma and thus provide a model system for human, juvenile-type GC tumors. In SWR mice, GC tumor susceptibility is an inherited, polygenic trait that appears at a low frequency. A dramatic increase in tumor frequency occurs when the autosomal SWR genetic complement is combined with the X-linked Gct4 allele of the mouse strain SJL/Bm (SJL). The modifier effect of the SJL Gct4 allele (Gct4(J)) also shows a strong parent-of-origin effect, occurring only when the Gct4(J) allele is paternally inherited. To genetically localize Gct4, we generated seven congenic mouse strains (SWR.SJL-X1 through -X7) that contained a defined segment of the SJL X chromosome (Chr) on the SWR autosomal strain background and mapped Gct4 to a 3 cM region. To better define the location of Gct4, we created an additional congenic strain (SWR.CAST-X) that contains most of the genetically polymorphic Chr X from the strain CAST/Ei. From crosses of the SWR.CAST-X and SWR.SJL-X congenic strains, we derived males carrying unique combinations of SJL-X and CAST-X segments. Progeny testing subsequently revealed a second SJL-derived, GC tumor frequency modifier gene, Gct6, located 6.5 cM distal to Gct4 on Chr X. In summary, we have mapped two modifier genes on the mouse Chr X that cause high-frequency, juvenile-type GC tumor development in female mice. The identity of these genes will provide a solid foundation for determination of tumor susceptibility genes in human cases of juvenile-type GC tumors.     

Gene for ovarian granulosa cell tumor susceptibility, Gct, in SWXJ recombinant inbred strains of mice revealed by dehydroepiandrosterone

Spontaneous, malignant ovarian granulosa cell (GC) tumors occur in pubertal SWR and specific SWXJ recombinant inbred strains of mice. Treatment of these mice with dehydroepiandrosterone (DHEA), an adrenal secretory steroid with anticancer actions against spontaneous and carcinogen-induced tumors of different tissues, gave unexpected results. Diet supplemented with 0.4% DHEA (a) induced significantly more GC tumors in spontaneous tumor-susceptible strains (SWR and SWXJ-1, -4, and -9), (b) induced the first GC tumors observed in five previously tumor-free strains (SWXJ-6, -7, -8, -10, and -12), and (c) failed to induce GC tumors in SJL and in the remaining six SWXJ strains (SWXJ-2, -3, -5, -11, -13, and -14). The strain distribution pattern of DHEA-induced GC tumor susceptibility versus resistance was compared with strain distribution patterns for 35 different loci known to distinguish SWR and SJL progenitor strains. A complete match of DHEA-induced GC tumors with pancreas-2 (Pan-2) on mouse chromosome 4 was found. We have named this new locus GC tumor susceptibility (Gct), with the Gcts (susceptible) allele found in SWR and the Gctr (resistant) allele found in SJL mice. The Gct locus is closely linked to pancreas-2, Pan-2, but the order of genes is not yet confirmed. In addition, data from F1 progeny of matings between SWR and selected inbred strains provide suggestive evidence for a second gene controlling GC tumor incidence that we hypothesize involves steroid metabolism. Differences in GC tumor incidence data from reciprocal F1 progeny of matings between SWR and SJL mice reveal a strong maternal effect that may represent yet a third gene. These data support a heritable basis for GC tumorigenesis in the SWR model involving a small number of genes.     

Quantitative trait locus mapping of susceptibilities to butylated hydroxytoluene-induced lung tumor promotion and pulmonary inflammation in CXB mice

We have reported previously [Bauer,A.K. et al. (2001) Exp. Lung Res., 27, 197-216] that the 13 CXB recombinant inbred mouse strains derived from BALB/cByJ and C57BL/6J progenitors vary in their responsiveness to both lung tumor promotion and pulmonary inflammation induced by chronic administration of butylated hydroxytoluene (BHT). Herein we have applied these data, along with markers known to be polymorphic among these strains, to conduct linkage analysis of these susceptibilities. This enabled us to assign provisional quantitative trait loci (QTL) that govern these strain variations in susceptibility as a genetic approach to assessing the influence of inflammation on tumorigenesis. A Chr 15 (39.1-55.6 cM) QTL regulated susceptibility to two-stage carcinogenesis, a protocol in which chronic BHT exposure followed a single urethane injection; a similar QTL on Chr 15 (46.7-61.7 cM) influenced BHT induction of cyclooxygenase-2 (COX-2) expression. A Chr 18 (37-41 cM) QTL modulated both the number of lung tumors induced by 3-methylcholanthrene (MCA) injection with subsequent treatment with BHT as well as BHT-induced ingress of macrophages into airways. Other chromosomal sites that affected either the degree of BHT-elicited macrophage infiltration, Chr 9 (48-61 cM), or COX-2 induction, Chr 10 (59-65 cM), were reported to influence susceptibility to lung tumorigenesis in other strains. The fact that common chromosomal locations regulate both inflammation and carcinogenesis suggests a pathogenic role of inflammatory mediators in tumor development that may be exploited for chemoprevention of lung cancer.     

Allele-specific Hras mutations and genetic alterations at tumor susceptibility loci in skin carcinomas from interspecific hybrid mice

We have investigated the effects of germ-line variants that influence skin tumor susceptibility loci on the patterns of somatic genetic alterations in mouse skin cancers. Using a two-stage skin carcinogenesis model, we previously identified at least 13 skin tumor susceptibility (Skts) loci in a large interspecific F1 backcross [(NIH/Ola x M. spretus) x NIH/Ola] study. In this report, we describe the analysis of allele-specific alterations at these loci in skin tumors from the same backcross animals. The mouse Hras gene, located close to Skts2 on chromosome 7, had specific activating mutations in the Mus musculus allele in 23 of 26 carcinomas. In all cases, tumors with Hras mutations also showed specific imbalance of chromosome 7 markers that favored the chromosome carrying the mutant allele. Allele-specific quantitative microsatellite analysis was also carried out, using DNA from 62 carcinomas from (NIH/Ola x M. spretus) x NIH/Ola mice. Frequent allelic imbalance was detected at five additional tumor-susceptibility loci on chromosomes 4, 6, 7, 9, and 16 (Skts7, Skts12, Skts1, Skts6, and Skts9, respectively). At all except Skts7, we found loss of the allele inherited from the resistant strain or amplification of the allele from the susceptible strain. We conclude that polymorphisms in some low-penetrance tumor modifier genes are reflected in the pattern of somatic alterations in tumors. Analysis of such allele-specific changes in tumors may facilitate the identification of functional germ-line variants that control tumor susceptibility.     

小鼠SP2/0细胞移植瘤的遗传修饰位点

BACKGROUND & OBJECTIVE: Our previous study found that BALB/c mice are highly susceptible to transplanted SP2/0 tumors, whereas C57BL/6J mice are barely susceptible. This study was to detect genetic modifier loci that would influence the size of transplanted SP2/0 tumors using these two inbred mouse strains and their F2 progenies. METHODS: A total of 5x106 SP2/0 cells were inoculated subcutaneously in the left hide legs of 208 F2 mice derived from BALB/c and C57BL/6J strains. At the 17th day since inoculation, all mice were killed, the number and weight of transplanted tumors were recorded. A whole genomic scan using 85 microsatellite markers covering all chromosomes of the mouse, and composite interval mapping analysis were conducted in 208 F2 mice. RESULTS: Eight loci, with the percent of the total variance explanation of >/= 10% and P value of 相似文献   

Genetic analyses of mouse skin tumor progression susceptibility using SENCAR inbred derived strains

Susceptibility to tumor development varies among individuals in the human population. This variability can also be found among different strains of mice, particularly in the mouse skin chemical carcinogenesis model. The genetic mechanisms underlying mouse skin tumor susceptibility are not fully understood. The SENCAR stock has been found to be the most sensitive mice for skin carcinogenesis studies; however, little is known about the genes underlying tumor susceptibility, particularly, those involved in tumor progression. Experiments with the SSIN/Sprd mice, an inbred strain derived from the outbred SENCAR stock, suggested that papilloma development, tumor promotion, and their conversion into squamous cell carcinomas (SCCs), progression, are regulated by different genes. In the highly sensitive SSIN/Sprd mice, papillomas rarely progress to SCC. Using crosses between the outbred SENCAR and the SSIN/Sprd mice, we previously determined that papilloma progression in the SENCAR stock could be controlled by at least one autosomal dominant gene. However, the outbred nature of the SENCAR stock precluded us from extending those findings. More recently, another inbred strain was developed from the outbred SENCAR stock, the SENCARB/Pt. These mice have similar tumor promotion sensitivity to the SSIN/Sprd but in contrast, have high papilloma progression susceptibility, similar to the outbred original stock. In the present study, we generated F(1), F(2), and backcross hybrids between the SSIN/Sprd and SENCARB/Pt mice to determine a possible model for tumor progression susceptibility and to map the putative tumor susceptibility genes. Our tumor data suggests that papilloma progression susceptibility in the SENCAR mouse skin model could be genetically determined by one susceptibility gene. Our preliminary linkage analysis failed to identify one strong susceptibility locus to confirm this but provided some evidence for at least one possible susceptibility locus in mouse chromosome 14.     

Identification of five novel modifier loci of ApcMin harbored in the BXH14 recombinant inbred strain

Every year thousands of people in the USA are diagnosed with small intestine and colorectal cancers (CRC). Although environmental factors affect disease etiology, uncovering underlying genetic factors is imperative for risk assessment and developing preventative therapies. Familial adenomatous polyposis is a heritable genetic disorder in which individuals carry germ-line mutations in the adenomatous polyposis coli (APC) gene that predisposes them to CRC. The Apc ( Min ) mouse model carries a point mutation in the Apc gene and develops polyps along the intestinal tract. Inbred strain background influences polyp phenotypes in Apc ( Min ) mice. Several Modifier of Min (Mom) loci that alter tumor phenotypes associated with the Apc ( Min ) mutation have been identified to date. We screened BXH recombinant inbred (RI) strains by crossing BXH RI females with C57BL/6J (B6) Apc ( Min ) males and quantitating tumor phenotypes in backcross progeny. We found that the BXH14 RI strain harbors five modifier loci that decrease polyp multiplicity. Furthermore, we show that resistance is determined by varying combinations of these modifier loci. Gene interaction network analysis shows that there are multiple networks with proven gene-gene interactions, which contain genes from all five modifier loci. We discuss the implications of this result for studies that define susceptibility loci, namely that multiple networks may be acting concurrently to alter tumor phenotypes. Thus, the significance of this work resides not only with the modifier loci we identified but also with the combinations of loci needed to get maximal protection against polyposis and the impact of this finding on human disease studies.     

Localization of a novel chromosome 7 locus that suppresses development of N-methyl-N-nitrosourea—induced murine thymic lymphomas

N-Methyl-N-nitrosourea (MNU) is a potent carcinogen that causes the development of murine thymic lymphomas. MNU-induced tumor incidence varies considerably among different inbred mouse strains. In particular, the AKR strain is highly susceptible, whereas the C57L strain is highly resistant to MNU-induced lymphoma formation. Crosses between AKR and C57L mice were established to investigate the genetic basis for the differential susceptibility of these inbred strains. A strong association between MNU-induced lymphoma development and coat color was observed in (AKR x C57)F₂ and AKR x (AKR x C57)F₁ progeny such that albino mice developed a higher tumor incidence than nonalbino animals. These data suggest that a locus on chromosome 7 influences tumor development. Analysis of four additional polymorphic loci (D7Rp2, Fes, Hbb, and Int-2) on chromosome 7 in AKR x (AKR x C57)F₁ backcross mice revealed a significant linkage between high tumor incidence and homozygous inheritance of AKR alleles at the albino (tyrosinase) and Hbb loci. Thus, inheritance of at least one C57L allele at the albino or Hbb loci was associated with protection against MNU-induced lymphoma development. There was no association between tumor incidence and genotype at the D7Rp2, Fes, or Int-2 loci. Taken together, the data suggest that whereas C57L mice contain a dominant tumor suppressor gene on chromosome 7, in the AKR strain both alleles at this locus are defective resulting in enhanced susceptibility to MNU-induced lymphomagenesis.     

Genetic analysis of three-dimensional shape of mouse lung tumors reveals eight lung tumor shape-determining (Ltsd) loci that are associated with tumor heterogeneity and symmetry

Most lung tumor linkage studies focus on identifying loci that confer susceptibility or resistance irrespective of the tumor types developed. However, different mouse strains develop different types of lung tumors. A major obstacle for genetic studies of these differences is the lack of reproducible, quantitative, and uniform assessment of tumor type. We have previously described a new variable (Rratio) that assesses the three-dimensional shape of lung tumors in a quantifiable way and showed that nonspherical tumors are correlated with tumor heterogeneity and with a tendency to asymmetrical growth (N. Tripodis and P. Demant, Exp. Lung Res., 27: 521-531, 2001). In the present study, we use the Rratio variable to search for quantitative trait loci affecting tumor phenotype. We tested the F(2) cross between the susceptible strain O20 and the recombinant congenic strain OcB-9. Both develop mixed alveolar and papillary lung tumors, and the OcB9 tumors are, on average, more elongated than the O20 ones. We mapped eight new lung tumor shape-determining loci (Ltsd1-8) involved in mutual interactions. Two of these loci, Ltsd1 and Ltsd3, seem to play a major role in tumor shape formation. The Ltsd4 locus was confirmed in a second F(2) cross between strain O20 and the recombinant congenic strain OcB-6. Genotype-phenotype associations show that nonspherical tumors are correlated with tumor heterogeneity and nonsymmetrical (focal) development of structures. Most of the new Ltsd loci map in regions where susceptibility to lung cancer (Sluc) loci have been previously mapped, raising the question of whether they are identical or closely linked loci. Based on models of tumor growth indicating that supply of nutrients and the ability to create a capillary network may be shape-determining factors (G. P. Pescarmona et al., Med. Hypoth., 53: 497-503, 1999), we suggest as likely candidates for the Ltsd loci genes involved in angiogenesis, vascularization, and capillary patterning. This is the first set of loci that affects qualitative aspects of lung tumors and may provide biologically and clinically interesting indicators of lung tumor progression.     

Genetic analyses of differences in incidence of mammary tumors and reticulum cell neoplasms with the use of recombinant inbred lines of mice.

The influence of genes, in addition to genes in the H-2 complex, that effect the genesis of mammary tumors was studied. The recombinant inbred (RI) CXB lines were chosen for this investigation, because they are well suited for the study of the genetics of a trait for which the genotype affects probability of phenotype expression and which therefore is measured as incidence. Females of seven RI lines (CXBD, CXBE, CXBG, CXBH, CXBI, CXBJ, and CXBK) and their progenitor strains C57BL/6By (B6) and BALB/cBy (BALB/c) were given ip injections of MuMTV at 3 months of age and were force bred. They were observed for mammary tumors. The B6 strain was least susceptible, and mammary tumors appeared late in life. The BALB/c strain was most susceptible, and the tumors appeared early in life. The course of tumor development in the RI lines fell between these extremes. The RI strain distribution pattern of mammary tumor incidence indicated that at least one and probably several loci in addition to those at H-2 determined the difference between the BALB/c and B6 strains. Effects of the other gene(s) appeared to be even more important than those of H-2. The locations of those loci were not made clear by this study. The spontaneous incidence of reticulum cell neoplasms was also recorded. The most frequently formed neoplasm of the reticular system was a Hodgkin's-like lesion. The data suggested an influence of the H-2 complex.     

Predisposition to efficient mammary tumor metastatic progression is linked to the breast cancer metastasis suppressor gene Brms1.

Tumor metastasis is one of the most important clinical aspects of neoplastic disease because patient mortality is frequently attributable to disseminated rather than primary tumors. However, it still is not possible to definitively distinguish those individuals at high risk for disseminated disease, who would benefit from aggressive adjuvant therapy, from the low-risk patients who might be spared the side effects of additional anticancer therapy. To identify factors that predispose toward metastatic disease, we have used a genetic approach. Using a highly metastatic model of mammary cancer, we identified previously inbred mouse strains (DBA/2J, NZB/B1NJ, and I/LnJ) that harbor genetic factors that significantly suppress metastatic efficiency. In this study, we report the results of four experiments to localize the genetic map locations of the metastasis efficiency modifier genes. One statistically significant locus was identified on proximal Chr 19 designated Mtes1. Secondary candidate intervals were detected on Chrs 6, 9, 13, and 17. Interestingly, Mtes1 colocalizes with the murine orthologue of the human breast cancer metastasis suppressor gene Brms1, suggesting that allelic variants of Brms1 might be responsible for the metastasis suppression observed.     

Comparative structure and characterization of a CDKN2 gene in a Xiphophorus fish melanoma model.

We have cloned, sequenced, and characterized the RNA expression properties of a fish CDKN2 gene from Xiphophorus helleri and X. maculatus. This gene, termed CDKN2X, shows a high degree of amino acid sequence similarity to members of the mammalian CDKN2 gene family, which includes the tumor suppressor loci CDKN2A (P16) and CDKN2B (P15). Comparative sequence analysis suggests that fish CDKN2X is similarly related to all four mammalian gene family members, and may represent a descendant of an ancestral prototypic CDKN2 gene. CDKN2X was mapped to a region on autosomal Xiphophorus linkage group V (LG V) known to contain the DIFF gene that acts as a tumor suppressor of melanoma formation in X. helleri/X. maculatus backcross hybrids. Thus, CDKN2X may be a candidate for the tumor suppressor DIFF gene. Here we have sequenced CDKN2X in both Xiphophorus species and have characterized its expression in normal and melanotic tissues within control and backcross hybrid fish. A simultaneous expressional analysis of the Xmrk-2 tyrosine kinase receptor gene, which is strongly implicated in melanomagenesis in this system, was also performed. RT - PCR analyses revealed that both genes were highly expressed in melanomas. For CDKN2X, this result contrasts numerous findings in human tumors including human melanoma in which either CDKN2A (P16) deactivation or LOH was observed.     

Propylnitrosourea-induced T-lymphomas in LEXF RI strains of rats: genetic analysis.

Oral administration of propylnitrosourea (PNU) in drinking water induces high incidence of lympho-haemopoietic malignancies in rats. Previously we reported that F344 strain rats were highly susceptible to T-lymphomas, and LE/Stm rats, to erythro- or myeloid leukaemias. For analysis of the genetic factors determining types of diseases, we have established LEXF recombinant inbred strains of rats comprising 23 substrains, each derived from intercross between F344 and LE/Stm rats. Rats of 23 LEXF substrains were given PNU, and the development of tumours was observed. The overall incidence of haemopoietic tumours ranged from 100% to 66.7%, and the fractions of T-lymphomas, from 100% to 4%, showing a continuous spectrum. Based on the genetic profile published as a strain distribution pattern table for the LEXF, we screened the potential quantitative trait loci involved in determination of the types of disease and length of the latency period. Statistical calculation was performed using the Map Manager QT software developed by Manly. Four loci, on chromosome 4, 7, 10 and 18, were suggested to associate with the T-lymphoma susceptibility and three loci, on chromosome 1, 5 and 16, with the length of the latency period. These putative loci were further examined in backcross (F344 x LE)F1 x LE. Among seven loci suggested by the recombinant inbred study, three loci, on chromosome 5, 7 and 10, were significantly associated with T-lymphomas and another locus on chromosome 1, just weakly. These observations indicate that PNU-induced lymphomagenesis is a multifactorial genetic process involving a number of loci linked with susceptibility and resistance.     

Evidence for complex multigenic inheritance of radiation AML susceptibility in mice revealed using a surrogate phenotypic assay

The mapping of genes which affect individual cancer risk is an important but complex challenge. A surrogate assay of susceptibility to radiation-induced acute myeloid leukaemia (AML) in the mouse based on chromosomal radiosensitivity has been developed and validated. This assay was applied to the mapping of radiation-induced AML risk modifier loci by association with microsatellite markers. A region on chromosome (chr) 18 with strong association is identified and confirmed by backcross analysis. Additional loci on chrs 8 and 13 show significant association. A key candidate gene Rbbp8 on chr18 is identified. Rbbp8 is shown to be upregulated in response to X-irradiation in the AML sensitive CBA strain but not AML resistant C57BL/6 strain. This study demonstrates the strength of utilizing surrogate endpoints of cancer susceptibility in the mapping of mouse loci and identifies additional loci that may affect radiation cancer risk.     

Allelotype analysis of chemically induced squamous cell carcinomas in F(1) hybrids of two inbred mouse strains with different susceptibility to tumor progression

Loss of heterozygosity (LOH) at specific chromosomal loci is generally considered indirect evidence for the presence of putative suppressor genes. Allelotyping of tumors using polymorphic markers distributed throughout the entire genome allows the analysis of specific allelic losses. In the field of chemical carcinogenesis, the outbred SENCAR mouse has been commonly used to analyze the multistage nature of skin tumor development. In the study reported here we generated F(1) hybrids between two inbred strains (SENCARB/Pt and SSIN/Sprd) derived from the SENCAR stock that differ in their susceptibility to tumor progression. We typed 24 7, 12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate-induced squamous cell carcinomas for LOH using 56 microsatellite markers distributed among all autosomal chromosomes. The highest percentage of LOH, 78%, was found on chromosome 7, but there was no preferential loss of one particular allele, indicating that the putative suppressor genes found in this area are not involved in genetic susceptibility. High levels of LOH were also found on chromosomes 16 (39%), 6 (29%), 4 (25%), 9 (25%), 14 (22%), 10 (20%) and 19 (20%), but with no preferential loss of the alleles of one strain. The chromosomal regions with LOH on mouse chromosomes 4, 6, 7, 9, 10, 14, 16 and 19 correspond to regions in the human genome where LOH has been reported and have been suggested to harbor tumor suppressor genes.     

Hepatocellular carcinoma in Txnip-deficient mice

The molecular pathogenesis and the genetic aberrations that lead to the progression of hepatocellular carcinoma (HCC) are largely unknown. Here, we demonstrate that the thioredoxin interacting protein (Txnip) gene is a candidate tumor suppressor gene in vivo. We previously showed that the recombinant inbred congenic strain HcB-19 has a spontaneous mutation of the Txnip gene, and we now show that the strain has dramatically increased incidence of HCC, and that the HCC cosegregates with the Txnip mutation. Approximately 40% of the Txnip-deficient mice developed hepatic tumors with an increased prevalence in male mice. Visible tumors develop as early as 8 months of age. Histological analysis confirmed the morphology of HCC in the Txnip-deficient mice. Molecular markers of HCC, alpha-fetoprotein and p53, were increased in tumors of Txnip-deficient mice. The upregulation of p53 preceded tumor development; however, bromodeoxyuridine (BrdU) labeling of normal hepatic tissue of Txnip-deficient mice did not reveal increased cell proliferation. Finally, microarray analyses of tumor, non-tumor adjacent, and normal tissue of Txnip-deficient mice highlighted the genetic differences leading to the predisposition and onset of HCC. Our findings suggest that Txnip deficiency is sufficient to initiate HCC and suggest novel mechanisms in hepatocarcinogenesis.     

Hepatocarcinogenesis in BXH recombinant inbred strains of mice: Analysis of diverse phenotypic effects of the hepatocarcinogen sensitivity loci

The hepatocarcinogen sensitivity (Hcs) loci were originally identified as determinants of the approximately 50-fold higher susceptibility of male C3H/HeJ (C3H) mice to perinatally induced hepatocarcinogenesis relative to male C57BL/6J (B6) mice. These two inbred strains also differ in other phenotypes related to hepatocarcinogenesis, including their incidences of spontaneous liver tumors and the properties of neoplastic hepatic lesions. To test the hypothesis that the Hcs loci also influence these phenotypes, we characterized male mice from B6, C3H, and nine BXH recombinant inbred (a) strains for spontaneous liver tumor development, the frequency of activating mutations in tumors, and the presence of cytoplasmic inclusions in preneoplastic lesions. By comparing these results to the relative susceptibilities of the parental and Rl strains to N, N-diethylnitrosamine (a) -and N-ethyl-N-nitrosourea-induced hepatocarcinogenesis in preweanling male mice, we concluded that the C3H alleles of the Hcs loci also positively influence the spontaneous development of liver tumors in male animals. While strain-dependent differences in the frequency of Ha-ras-1 activation in DEN-initiated liver tumors were observed, this phenotype was not correlated with susceptibility to liver tumor induction. The formation of eosinophilic intracytoplasmic inclusion bodies observed specifically in B6 liver tumors, which has been suggested to be associated with the resistance of this strain to hepatocarcinogenesis, also segregated independently of the Hcs loci. © 1995 Wiley- Liss, Inc.     

Ethylnitrosourea-induced development of malignant schwannomas in the rat: two distinct loci on chromosome of 10 involved in tumor susceptibility and oncogenesis

Inbred rodent strains with differing sensitivity to experimental tumor induction provide model systems for the detection of genes that either are responsible for cancer predisposition or modify the process of carcinogenesis. Rats of the inbred BD strains differ in their susceptibility to the induction of neural tumors by N-ethyl-N-nitrosourea (EtNU). Newborn BDIX rats that are exposed to EtNU (80 microg/g body weight; injected s.c.) develop malignant schwannomas predominantly of the trigeminal nerves with an incidence >85%, whereas BDIV rats are entirely resistant. A T:A-->A:T transversion mutation at nucleotide 2012 of the neu (erbB-2) gene on chromosome 10, presumably the initial event in EtNU-induced schwannoma development, is later followed by loss of the wild-type neu allele. Genetic crosses between BDIX and BDIV rats served: (a) to investigate the inheritance of susceptibility; (b) to obtain animals informative for the mapping of losses of heterozygosity (LOH) in tumors with polymorphic simple sequence length polymorphisms (SSLPs); and (c) to localize genes associated with schwannoma susceptibility by linkage analysis with SSLPs. Schwannoma development was strongly suppressed in F1 animals (20% incidence). All of the F1 schwannomas displayed LOH on chromosome 10, with a consensus region on the telomeric tip encompassing D10Rat3, D10Mgh16 and D10Rat2 but excluding neu. A strong bias toward losing the BDIV alleles suggests the involvement of a BDIV-specific tumor suppressor gene(s). Targeted linkage analysis with chromosome 10 SSLPs in F2 intercross and backcross animals localized schwannoma susceptibility to a region around D10Wox23, 30 cM centromeric to the tip. Ninety-four % of F1 tumors exhibited additional LOH at this region. Two distinct loci on chromosome 10 may thus be connected with susceptibility to the induction and development of schwannomas in rats exposed to EtNU.     

Epistatic interactions between skin tumor modifier loci in interspecific (spretus/musculus) backcross mice

The development of cancer is influenced both by exposure to environmental carcinogens and by the host genetic background. Epistatic interactions between genes are important in determining phenotype in plant and animal systems and are likely to be major contributors to cancer susceptibility in humans. Several tumor modifier loci have been identified from studies of mouse models of human cancer, and genetic interactions between modifier loci have been detected by genome scanning using recombinant congenic strains of mice (R. Fijneman et al., Nat. Genet., 14: 465-467, 1996; T. van Wezel et al., Nat. Genet., 14: 468-470, 1996; W. N. Frankel et al., Nat. Genet., 14, 371-373, 1996). We demonstrate here that strong genetic interactions between skin tumor modifier loci can be detected by hierarchical whole genome scanning of a complete interspecific backcross [outbred Mus spretus X Mus musculus (NIH/Ola)]. A locus on chromosome 7 (Skts1) showed a highly significant interaction with Skts5 on chromosome 12 (P < 10(-16)), whereas additional significant interactions were detected between loci on chromosomes 4 and 5, and 16 and 15. Some of these quantitative trait loci and their interactions, in particular the Skts1-Skts5 interaction, were confirmed in two completely independent backcrosses using inbred spretus strains (SEG/Pas and SPRET/Ei) and NIH/Ola. These results, therefore, illustrate the general use of interspecific crosses between Mus musculus and Mus spretus for the detection of strong genetic interactions between tumor modifier genes.     

Induction of ovarian granulosa cell tumors in SWXJ-9 mice with dehydroepiandrosterone

Spontaneous ovarian granulosa cell (GC) tumors develop in SWXJ-9 inbred mice at approximately the time of puberty. The effect of dehydroepiandrosterone (DHEA), a steroid secreted by the adrenals and reported to have antitumor actions, was examined in this ovarian tumor model. In contrast with expectations, administration of diet supplemented with 0.4% DHEA or Silastic capsules containing 10 mg DHEA resulted in a significant multifold increase in GC tumor incidence. Similar studies with metabolites of DHEA, i.e., testosterone (TESTO), dihydrotestosterone (DHT), and 17 beta-estradiol (E2), revealed that TESTO was as effective as DHEA in increasing GC tumor incidence. DHT was without effect, and E2 suppressed GC tumor incidence. Serum steroid levels and steroid target tissue responses were assessed to determine if a correlation between a change in level or response to specific steroids and GC tumorigenesis existed. In both tumor-free and GC tumor host mice, dietary or capsular treatment with DHEA, TESTO, or DHT resulted in substantial alteration in one or more of serum steroids, DHEA, androstenedione, TESTO, and DHT, in addition to the administered steroid. No consistent correlation was observed between changes in a single steroid or pattern of steroids and GC tumorigenesis. Although significant increases in serum estrogens could be detected in GC tumor hosts treated with DHEA but not TESTO, estrogens did not induce these tumors. Treatment with E2 increased only serum E2 levels. In tumor-free mice, DHEA and E2 treatments were associated with vaginal cytological evidence of estrogen action, whereas the androgens induced a leukocytic pattern. Eighty-eight % of GC tumor host mice, regardless of steroid treatment, showed a vaginal cytology pattern that included cornified cells. The evidence presented in this report leads us to hypothesize that (a) spontaneous and steroid-induced GC tumorigenesis in these mice have the same mechanism, and (b) subtle increases in DHEA or a closely related metabolite during the peripubertal period may initiate GC tumors in these genetically susceptible mice. The mechanism whereby these steroids initiate GC tumorigenesis remains to be determined.