Genetic mapping of a pulmonary adenoma resistance (Par1) in mouse

Disappearing Signet Ring Cell Adenocarcinoma in Gastric Cancer Patients

BACKGROUND

The incidence of diffuse-type gastric cancer is increasing steadily in the United States, Europe, and Asia. This subtype is known for aggressive clinical characteristics and transmural invasion. However, T1a diffuse-type cancers have been observed to have a better 5-year, disease-specific mortality than stage-matched intestinal tumors, supporting a clinical difference in these early-stage cancers.

METHODS

Data on all living patients with T1a gastric adenocarcinoma with a finding of signet ring cell morphology on pathology and ≥1 year of follow-up from 2013 to 2023 at Memorial Sloan Kettering Cancer Center (MSK) was collected from a prospectively maintained database. Patients with known CDH1 or CTNNA1 mutations were excluded.

RESULTS

In 7 of 30 patients, sporadic pathologically confirmed T1a signet ring cell (diffuse) cancer identified on initial biopsy was no longer detectable upon subsequent biopsy or resection with mean follow-up of 50 months.

CONCLUSIONS

These cases allude to the distinct pathways of carcinogenesis in T1a signet ring cell cancers. Potential factors that may underlie the spontaneous regression of these T1a cancers include complete removal at initial biopsy, immune clearance, and lack of survival advantage conferred by signet ring cell genetic alterations in these cases. Given their more indolent behavior at an earlier stage, we suggest that these lesions can be closely followed by endoscopy in select circumstances with thorough disease assessment and an experienced care team.

A wild-derived inbred mouse strain, MSM/Ms, provides insights into novel skin tumor susceptibility genes

Cancer is one of the most catastrophic human genetic diseases. Experimental animal cancer models are essential for gaining insights into the complex interactions of different cells and genes in tumor initiation, promotion, and progression. Mouse models have been extensively used to analyze the genetic basis of cancer susceptibility. They have led to the identification of multiple loci that confer, either alone or in specific combinations, an increased susceptibility to cancer, some of which have direct translatability to human cancer. Additionally, wild-derived inbred mouse strains are an advantageous reservoir of novel genetic polymorphisms of cancer susceptibility genes, because of the evolutionary divergence between wild and classical inbred strains. Here, we review mapped Stmm (skintumor modifier of MSM) loci using a Japanese wild-derived inbred mouse strain, MSM/Ms, and describe recent advances in our knowledge of the genes responsible for Stmm loci in the 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) two-stage skin carcinogenesis model.

Using the inbred mouse strain SPRET/EiJ to provide novel insights in inflammation and infection research

Inbred mouse strains derived from the species Mus spretus have been very informative in the study of certain gene polymorphisms in inflammation and infection. Based on our interest in sepsis, we used SPRET/EiJ mice and mapped several critical loci that are linked to sensitivity to cytokine-induced inflammation and endotoxemia. These studies were based on prominent phenotypes that have never been observed in strains derived from Mus musculus and we mapped them at a resolution that enables us to draw conclusions on the mechanisms. Now that the genome of SPRET/EiJ has been sequenced, and other tools have become available, it is time to revisit this strain and emphasize its advantages and disadvantages as a research tool and a discovery platform.

Genetic linkage analysis identifies Pas1 as the common locus modulating lung tumorigenesis and acute inflammatory response in mice

Selective breeding for the acute inflammatory response (AIR) generated two mouse lines characterized by maximum (AIRmax) and minimum (AIRmin) responses, explained by the additive effect of alleles differentially fixed in quantitative trait loci (QTLs). These mice also differ in their susceptibility to lung tumorigenesis, raising the possibility that the same loci are involved in the control of both phenotypes. To map the QTLs responsible for the different phenotypes, we carried out a genome-wide linkage analysis using single-nucleotide polymorphism arrays in a pedigree consisting of 802 mice, including 693 (AIRmax × AIRmin)F2 intercross mice treated with urethane and phenotyped for AIR and lung tumor multiplicity. We mapped five loci on chromosomes 4, 6, 7, 11 and 13 linked to AIR (logarithm of odds (LOD)=3.56, 3.52, 15.74, 7.74 and 3.34, respectively) and two loci linked to lung tumor multiplicity, on chromosomes 6 and 18 (LOD=12.18 and 4.69, respectively). The known pulmonary adenoma susceptibility 1 (Pas1) locus on chromosome 6 was the only locus linked to both phenotypes, suggesting that alleles of this locus were differentially fixed during breeding and selection of AIR mice. These results represent a step toward understanding the link between inflammation and cancer.

Differential expression of miR-1, a putative tumor suppressing microRNA, in cancer resistant and cancer susceptible mice

Mus spretus mice are highly resistant to several types of cancer compared to Mus musculus mice. To determine whether differences in microRNA (miRNA) expression account for some of the differences in observed skin cancer susceptibility between the strains, we performed miRNA expression profiling of skin RNA for over 300 miRNAs. Five miRNAs, miR-1, miR-124a-3, miR-133a, miR-134, miR-206, were differentially expressed by array and/or qPCR. miR-1 was previously shown to have tumor suppressing abilities in multiple tumor types. We found miR-1 expression to be lower in mouse cutaneous squamous cell carcinomas (cSCCs) compared to normal skin. Based on the literature and our expression data, we performed detailed studies on predicted miR-1 targets and evaluated the effect of miR-1 expression on two murine cSCC cell lines, A5 and B9. Following transfection of miR-1, we found decreased mRNA expression of three validated miR-1 targets, Met, Twf1 and Ets1 and one novel target Bag4. Decreased expression of Ets1 was confirmed by Western analysis and by 3’ reporter luciferase assays containing wildtype and mutated Ets1 3’UTR. We evaluated the effect of miR-1 on multiple tumor phenotypes including apoptosis, proliferation, cell cycle and migration. In A5 cells, expression of miR-1 led to decreased proliferation compared to a control miR. miR-1 expression also led to increased apoptosis at later time points (72 and 96 h) and to a decrease in cells in S-phase. In summary, we identified five miRNAs with differential expression between cancer resistant and cancer susceptible mice and found that miR-1, a candidate tumor suppressor, has targets with defined roles in tumorigenesis.

Using mice to unveil the genetics of cancer resistance

In the UK, four in ten people will develop some form of cancer during their lifetime, with an individual's relative risk depending on many factors, including age, lifestyle and genetic make-up. Much research has gone into identifying the genes that are mutated in tumorigenesis with the overwhelming majority of genetically-modified (GM) mice in cancer research showing accelerated tumorigenesis or recapitulating key aspects of the tumorigenic process. Yet if six out of ten people will not develop some form of cancer during their lifetime, together with the fact that some cancer patients experience spontaneous regression/remission, it suggests there are ways of 'resisting' cancer. Indeed, there are wildtype, spontaneously-arising mutants and GM mice that show some form of 'resistance' to cancer. Identification of mice with increased resistance to cancer is a novel aspect of cancer research that is important in terms of providing both chemopreventative and therapeutic options. In this review we describe the different mouse lines that display a 'cancer resistance' phenotype and discuss the molecular basis of their resistance.

Most lung and colon cancer susceptibility genes are pair-wise linked in mice, humans and rats

Genetic predisposition controlled by susceptibility quantitative trait loci (QTLs) contributes to a large proportion of common cancers. Studies of genetics of cancer susceptibility, however, did not address systematically the relationship between susceptibility to cancers in different organs. We present five sets of data on genetic architecture of colon and lung cancer susceptibility in mice, humans and rats. They collectively show that the majority of genes for colon and lung cancer susceptibility are linked pair-wise and are likely identical or related. Four CcS/Dem recombinant congenic strains, each differing from strain BALB/cHeA by a different small random subset of ±12.5% of genes received from strain STS/A, suggestively show either extreme susceptibility or extreme resistance for both colon and lung tumors, which is unlikely if the two tumors were controlled by independent susceptibility genes. Indeed, susceptibility to lung cancer (Sluc) loci underlying the extreme susceptibility or resistance of such CcS/Dem strains, mapped in 226 (CcS-10×CcS-19)F2 mice, co-localize with susceptibility to colon cancer (Scc) loci. Analysis of additional Sluc loci that were mapped in OcB/Dem strains and Scc loci in CcS/Dem strains, respectively, shows their widespread pair-wise co-localization (P = 0.0036). Finally, the majority of published human and rat colon cancer susceptibility genes map to chromosomal regions homologous to mouse Sluc loci. 12/12 mouse Scc loci, 9/11 human and 5/7 rat colon cancer susceptibility loci are close to a Sluc locus or its homologous site, forming 21 clusters of lung and colon cancer susceptibility genes from one, two or three species. Our data shows that cancer susceptibility QTLs can have much broader biological effects than presently appreciated. It also demonstrates the power of mouse genetics to predict human susceptibility genes. Comparison of molecular mechanisms of susceptibility genes that are organ-specific and those with trans-organ effects can provide a new dimension in understanding individual cancer susceptibility.

Epistatic interactions govern chemically-induced lung tumor susceptibility and Kras mutation site in murine C57BL/6J-ChrA/J chromosome substitution strains

Cancer susceptibility results from interactions between sensitivity and resistance alleles. We employed murine chromosome substitution strains to study how resistance alleles affected sensitive alleles during chemically-induced lung carcinogenesis. The C57BL/6J-Chr#(A/J) strains, constructed by selectively breeding sensitive A/J and resistant C57BL/6J (B6) mice, each contain one pair of A/J chromosomes within an otherwise B6 genome. Pas1, the major locus responsible for this differential strain response to urethane carcinogenesis, resides on Chr 6, but C57BL/6J-Chr6(A/J) mice (hereafter CSS-6) developed few tumors following a single urethane injection, which demonstrates epistatic interactions with other B6 alleles. CSS6 mice developed dozens of lung tumors after chronic urethane exposure, however, indicating that these epistatic interactions could be overcome by repeated carcinogen administration. Unlike A/J, but similar to B6 mice, CSS6 mice were resistant to lung carcinogenesis induced by 3-methylcholanthrene (MCA). Tumor multiplicity increased if BHT administration followed urethane exposure, showing that a Chr 6 gene(s) regulates sensitivity to chemically-induced tumor promotion. Unlike A/J tumors (predominantly codon 61 A-->T transversions), Kras mutations in tumors induced by urethane in CSS-6 mice were similar to B6 tumors (codon 61 A-->G transitions). DNA repair genes not located on Chr 6 may determine the nature of Kras mutations. CSS-6 mice are a valuable resource for testing the ability of candidate genes to modulate lung carcinogenesis.

Systems genetics analysis of cancer susceptibility: from mouse models to humans

Genetic studies of cancer susceptibility have shown that most heritable risk cannot be explained by the main effects of common alleles. This may be due to unknown gene-gene or gene-environment interactions and the complex roles of many genes at different stages of cancer. Studies using mouse models of cancer suggest that methods that integrate genetic analysis and genomic networks with knowledge of cancer biology can help to extend our understanding of heritable cancer susceptibility.

ANALYSIS OF THEPar2MODIFIER OF PULMONARY ADENOMA FORMATION IN MICE

Inbred strains of mouse show various susceptibilities to spontaneous and chemical-induced lung tumorigenesis. Genetic analyses have revealed that lung tumor susceptibilities of inbred mouse strains are governed by quantitative trait loci (QLTs) located on multiple chromosomes. A major lung tumor resistance QLT, designated pulmonary adenoma resistance 2 (Par2), was mapped to the mouse chromosome 18 independently by several groups and accounted for up to 60% phenotype variance between susceptible A/J and more resistant BALB/c strains. The authors recently conducted studies to positionally clone the Par2 gene. This review summarizes the effort and progress towards the identification of Par2 candidates.

Thirty years of Mus spretus: a promising future

Extensive genetic polymorphisms in Mus spretus have ensured its widespread use in many areas of genetics. With the recent increase in the number of single nucleotide polymorphisms available for laboratory mouse strains, M. spretus is becoming less appealing, in particular for genetic mapping. Although M. spretus mice are aggressive and poor breeders, they have a bright future because they provide phenotypes unobserved in laboratory strains, and tools are available for modifying their genome and dissecting the genetic architecture of complex traits. Furthermore, they provide information on fundamental genetic questions, such as the details of evolution of genomes and speciation. Here, we examine the use of M. spretus from these perspectives. The impending completion of the M. spretus genome sequence will synergize these advantages.

Genetic architecture of mouse skin inflammation and tumour susceptibility

Germline polymorphisms in model organisms and humans influence susceptibility to complex trait diseases such as inflammation and cancer. Mice of the Mus spretus species are resistant to tumour development, and crosses between M. spretus and susceptible Mus musculus strains have been used to map locations of genetic variants that contribute to skin cancer susceptibility. We have integrated germline polymorphisms with gene expression in normal skin from a M. musculus x M. spretus backcross to generate a network view of the gene expression architecture of mouse skin. Here we demonstrate how this approach identifies expression motifs that contribute to tissue organization and biological functions related to inflammation, haematopoiesis, cell cycle control and tumour susceptibility. Motifs associated with inflammation, epidermal barrier function and proliferation are differentially regulated in backcross mice susceptible or resistant to tumour development. The intestinal stem cell marker Lgr5 is identified as a candidate master regulator of the hair follicle, and the vitamin D receptor (Vdr) is linked to coordinated control of epidermal barrier function, inflammation and tumour susceptibility.

Toward a genetics of cancer resistance

Two of three humans never get cancer. Even the majority of heavy smokers remain cancer free. Is this a matter of chance, or are there cancer-resistant genotypes? Based on the evidence discussed, it would appear that evolution has favored a limited number of relatively common resistance genes that may nip incipient cancerous foci in the bud, i.e., to stop them at their inception. It is further suggested that resistance genes may act at the level of tissue organization in a dominant fashion.

Association of KRAS polymorphisms with risk for lung adenocarcinoma accompanied by atypical adenomatous hyperplasias

The pulmonary adenoma susceptibility 1 (Pas1) gene affects susceptibility to the development of lung adenomas in mice with a subset of the adenomas progressing to adenocarcinoma (ADC). In this study, genotype distributions for 10 polymorphisms in the human counterparts for three mouse candidate Pas1 genes, KRAS, CASC1/LAS1 and LRMP, were examined in a hospital-based case-control study consisting of 364 lung ADC cases and 253 controls. All the ADC cases were subjected to lobectomy and subsequent pathological investigation of atypical adenomatous hyperplasia (AAH), a putative precursor for peripheral lung ADC, including bronchioloalveolar carcinoma, in the resected lobes. Eighty-one (22%) of the ADC cases carried at least one AAH lesion in addition to the primary ADC and 34 (9%) of them carried multiple AAH lesions. None of the 10 polymorphisms examined showed significant associations with overall lung ADC risk (P > 0.05). However, minor allele carriers for two polymorphisms in the KRAS gene, KRAS-1 and -6, showed significantly increased odds ratios (ORs) for ADC accompanied by multiple AAHs [OR = 3.0; 95% confidence interval (CI) = 1.4-6.2, P = 0.004 and OR = 2.4; 95% CI = 1.1-4.7, P = 0.02, respectively]. Minor haplotypes including the minor allele for the KRAS-6 polymorphism showed increased ORs for ADC accompanied by multiple AAHs, and KRAS transcripts from the minor allele for this polymorphism were more abundantly detected in lung tissues than those from the major allele. Thus, KRAS polymorphisms were indicated to be involved in risk for the development of AAHs that progress to ADC by causing differential KRAS oncogene expression in the lungs.

Fine mapping and candidate gene analyses of pulmonary adenoma resistance 1, a major genetic determinant of mouse lung adenoma resistance

Pulmonary adenoma resistance 1 (Par1) is a major genetic determinant of mouse lung adenoma resistance. Although Par1 was previously mapped to mouse chromosome 11 by conventional linkage analyses, its candidate region was broad and undefined. In our present study, we generated Par1 congenic mice using two mouse strains A/J (Par1/-) and Mus spretus (Par1/+). Analyzing these congenic mice enabled us to fine map the Par1 quantitative trait loci (QTL) into a 2.0-cM (2.2 Mb) chromosomal region between genetic marker D11Mit70 and the gene Hoxb9. We then conducted systematic candidate gene screening through nucleotide polymorphism and expression analyses. Genes showing differential lung tissue expression or carrying nonsynonymous single nucleotide polymorphisms were identified and discussed. In particular, we evaluated tumor suppressor gene Tob1 for its Par1 candidacy. Our findings have narrowed the Par1 QTL region and will greatly facilitate the identification of the major genetic determinant of mouse lung adenoma resistance.

Welding fume exposure and associated inflammatory and hyperplastic changes in the lungs of tumor susceptible a/j mice

It has been suggested that welding fume (WF) exposure increases lung cancer risk in welders. Epidemiology studies have failed to conclude that WF alone causes lung cancer and animal studies are lacking. We examined the course of inflammation, damage, and repair in the lungs of A/J mice, a lung tumor susceptible strain, caused by stainless steel WF. Mice were exposed by pharyngeal aspiration to 40 mg/kg of WF, silica, or saline. Bronchoalveolar lavage (BAL) was performed 24 hours, 1 and 16 weeks to assess lung injury and inflammation and histopathology was done 1, 8, 16, 24, and 48 weeks postexposure. Both exposures increased inflammatory cells, lactate dehydrogenase and albumin at 24 hr and 1 week. At 16 weeks, these parameters remained elevated in silica-exposed but not WF-exposed mice. Histopathologic evaluation at 1 week indicated that WF induced bronchiolar epithelial hyperplasia with associated cellular atypia, alveolar bronchiolo-alveolar hyperplasia (BAH) in peribronchiolar alveoli, and peribronchiolar lymphogranulomatous inflammation. Persistent changes included foci of histiocytic inflammation, fibrosis, atypical bronchiolar epithelial cells, and bronchiolar BAH. The principle changes in silica-exposed mice were histiocytic and suppurative inflammation, fibrosis, and alveolar BAH. Our findings that WF causes persistent bronchiolar and peribronchiolar epithelial changes, suggest a need for studies of bronchiolar changes after WF exposure.

A V141L polymorphism of the human LRMP gene is associated with survival of lung cancer patients

Mouse Lrmp and Casc1 genes are candidates for the pulmonary adenoma susceptibility 1 (Pas1) locus, the major determinant of strain variation in lung tumor susceptibility. These genes contain coding and non-coding single nucleotide polymorphisms (SNPs) strongly associated with lung tumor risk in mice. Analysis of LRMP and CASC1 gene SNPs in 361 lung adenocarcinoma (ADCA) patients and 327 healthy controls revealed common SNPs in LRMP (V141L and S197C) and CASC1 (R33S and three intronic variations), and none showed a significant association with lung ADCA risk. However, in the time-dependent Cox regression model, after adjustment for age, gender, smoking history and clinical stage, the carrier status of the Leu variation (V141L) of the LRMP gene was associated with higher mortality in patients with age at tumor onset < or = 65 years [hazard ratio (HR) 2.3; 95% CI 1.4-3.7; P = 0.001]. These findings suggest that the LRMP V141L polymorphism can predict survival in lung ADCA and that the role of LRMP and CASC1 in human lung cancer risk may differ from that in mice.

The Mouse Tumor Biology Database: integrated access to mouse cancer biology data

Mice have long been used as models for the study of human cancer. The National Cancer Institute has included among its research areas of extraordinary opportunity the development of new mouse genetic models of human cancer and the exploration of cancer imaging as a research tool. Because of the volume and interconnectedness of relevant data, the creation and maintenance of bioinformatics resources of mouse tumor biology is necessary to facilitate current and future cancer research. The Mouse Tumor Biology (MTB) Database provides electronic access to data generated through the study of spontaneous and induced tumors in genetically defined mice (inbred, hybrid, spontaneous and induced mutant, and genetically engineered strains of mice).

Smoking-gene interaction and disease development: relevance to pancreatic cancer and atherosclerosis

There is little doubt that cigarette smoking remains a major environmental health risk that humans are facing in the twenty-first century. Cigarette smokers are more likely to develop many forms of diseases than nonsmokers, including cancers and vascular diseases. With the availability of the human genome sequence, we become more aware of the genetic contributions to these common diseases, especially the interactive relations between environmental factors (e.g., smoking) and genes on disease susceptibility, development, and prognosis. Although smoking is responsible for up to 30% of pancreatic cancers and about 10% of cases are ascribed to genetic reasons, some genetic variants do not predispose carriers to disease development unless they are exposed to a specific adverse environment such as smoking. This smoke-gene interaction could potentially be responsible for most of the cases. Certain polymorphisms in genes such as CYP1A1 have been shown particularly sensitive to smoking-induced pathogenesis, including pancreatic cancer and atherosclerosis. We found that individuals with CYP1A1 CC genotype had a more than three fold increase in risk for severe coronary atherosclerosis when they smoked. Patients with endothelial nitric oxide synthase (eNOS) intron 4 27 repeat homozygotes were more likely to develop severe coronary stenosis when they smoked. On the other hand, DNA variants at the eNOS gene also dictate how smoking affects the expression of eNOS. We showed that GSTM1 deficiency was not involved in smoking-induced vascular diseases, but p53 polymorphisms tended to modify the disease severity in smokers. We are still at an early stage of defining the pairs and mechanisms of smoke-gene interaction, and this etiologic mechanism may hold great potential for risk assessment, treatment strategy, and prognostic predictions.

Breaking the species barrier: derivation of germline-competent embryonic stem cells from Mus spretus x C57BL/6 hybrids

Embryonic stem (ES) cells, which can differentiate into almost all types of cells, have been derived from the house mouse Mus musculus, rat, rabbit, humans, and other species. Transmission of the genotype to the offspring of chimeras has been achieved only with M. musculus ES cells, limiting targeted mutagenesis using ES cells to this species. Mus spretus, which exhibits many genetic polymorphisms with M. musculus, displays dominant resistance to cancer and inflammation, making derived inbred strains very useful in positional cloning and interspecies mapping. We show here for the first time the derivation of ES cells from hybrid blastocysts, obtained by the mating of two different species, namely Mus musculus and Mus spretus, and their use for the generation of chimeric mice that transmit the Mus spretus genotype and phenotype to the offspring. These hybrid ES cells allow the genetic manipulation of Mus spretus, as an alternative to Mus musculus.

Susceptibility to neoplastic and non-neoplastic pulmonary diseases in mice: genetic similarities

Chronic inflammation predisposes toward many types of cancer. Chronic bronchitis and asthma, for example, heighten the risk of lung cancer. Exactly which inflammatory mediators (e.g., oxidant species and growth factors) and lung wound repair processes (e.g., proangiogenic factors) enhance pulmonary neoplastic development is not clear. One approach to uncover the most relevant biochemical and physiological pathways is to identify genes underlying susceptibilities to inflammation and to cancer development at the same anatomic site. Mice develop lung adenocarcinomas similar in histology, molecular characteristics, and histogenesis to this most common human lung cancer subtype. Over two dozen loci, called Pas or pulmonary adenoma susceptibility, Par or pulmonary adenoma resistance, and Sluc or susceptibility to lung cancer genes, regulate differential lung tumor susceptibility among inbred mouse strains as assigned by QTL (quantitative trait locus) mapping. Chromosomal sites that determine responsiveness to proinflammatory pneumotoxicants such as ozone (O3), particulates, and hyperoxia have also been mapped in mice. For example, susceptibility QTLs have been identified on chromosomes 17 and 11 for O3-induced inflammation (Inf1, Inf2), O3-induced acute lung injury (Aliq3, Aliq1), and sulfate-associated particulates. Sites within the human and mouse genomes for asthma and COPD phenotypes have also been delineated. It is of great interest that several susceptibility loci for mouse lung neoplasia also contain susceptibility genes for toxicant-induced lung injury and inflammation and are homologous to several human asthma loci. These QTLs are described herein, candidate genes are suggested within these sites, and experimental evidence that inflammation enhances lung tumor development is provided.

Pas1 haplotype-dependent genetic predisposition to lung tumorigenesis in rodents: a meta-analysis

Rodent species and strains show wide variations in susceptibility to lung tumorigenesis. In mice, hierarchical clustering of 29 inbred laboratory strains by pulmonary adenoma susceptibility 1 (Pas1) locus polymorphisms separated the strains into either an A/J- or a C57BL/6J-type Pas1 haplotype. A pooled analysis (including >8500 mice) of studies on spontaneous and chemically induced lung tumorigenesis in these strains revealed a significantly higher risk of spontaneous lung tumors [odds ratio (OR) 12.17; 95% confidence interval (CI) 9.00-16.45] as well as of chemically induced lung tumors (OR 15.14; 95% CI 12.51-18.31) in the A/J-type haplotype. Strain differences were observed with six different carcinogens, suggesting that Pas1 locus activity is carcinogen-independent. Thus, the present meta-analysis indicates a link between the genetic control of spontaneous and chemically induced lung tumor susceptibility in mice. The Pas1 susceptibility allele is frequent in the population of inbred mouse strains, whereas a counterpart appears to be absent or rare in rat and hamster strains. These findings might help in the interpretation of results of rodent carcinogenicity bioassays and assessing the risk of lung carcinogenesis from chemicals.

Classification of proliferative pulmonary lesions of the mouse: recommendations of the mouse models of human cancers consortium

Rapid advances in generating new mouse genetic models for lung neoplasia provide a continuous challenge for pathologists and investigators. Frequently, phenotypes of new models either have no precedents or are arbitrarily attributed according to incongruent human and mouse classifications. Thus, comparative characterization and validation of novel models can be difficult. To address these issues, a series of discussions was initiated by a panel of human, veterinary, and experimental pathologists during the Mouse Models of Human Cancers Consortium (NIH/National Cancer Institute) workshop on mouse models of lung cancer held in Boston on June 20-22, 2001. The panel performed a comparative evaluation of 78 cases of mouse and human lung proliferative lesions, and recommended development of a new practical classification scheme that would (a) allow easier comparison between human and mouse lung neoplasms, (b) accommodate newly emerging mouse neoplasms, and (c) address the interpretation of benign and preinvasive lesions of the mouse lung. Subsequent discussions with additional experts in pulmonary pathology resulted in the current proposal of a new classification. It is anticipated that this classification, as well as the complementary digital atlas of virtual histological slides, will help investigators and pathologists in their characterization of new mouse models, as well as stimulate further research aimed at a better understanding of proliferative lesions of the lung.

A chemically induced model for squamous cell carcinoma of the lung in mice: histopathology and strain susceptibility

Lung cancer, primarily associated with tobacco use, is the leading cause of cancer morbidity and mortality in the United States. Squamous cell carcinoma (SCC) is one of the four major histological types of lung cancer. Although there are several established models for lung adenoma and adenocarcinomas, there is no well-established mouse model for lung SCC. We treated eight different inbred strains of mice with N-nitroso-tris-chloroethylurea by skin painting and found that this regimen induced lung SCCs in five strains of mouse (SWR/J, NIH Swiss, A/J, BALB/cJ, and FVB/J) but not in the others (AKR/J, 129/svJ, and C57BL/6J). Mouse lung SCCs have similar histopathological features and keratin staining to human SCC. Moreover, a wide spectrum of abnormal lung squamous phenotypes including hyperplasia, metaplasia, carcinoma in situ, and invasive carcinoma, were observed. There are strain-specific differences in susceptibility to Lscc induction by N-nitroso-tris-chloroethylurea with NIH Swiss, A/J, and SWR/J mice developing scores of SCCs whereas the resistant strains AKR/J, 129/svJ, and C57BL/6J failed to develop any SCCs. FVB/J and BALB/cJ mice had an intermediate response. We conducted whole-genome linkage disequilibrium analysis in seven strains of mice, divided into three phenotype categories of susceptibility, using Fisher's exact test applied to 6,128 markers in publically available databases. Three markers were found significantly associated with susceptibility to SCC with the P < 0.05. They were D1Mit169, D3Mit178, and D18Mit91. Interestingly, none of these sites overlap with the major susceptibility loci associated with lung adenoma/adenocarcinoma development in mice. The mouse SCC described here is highly significant for preclinical studies of lung cancer chemopreventive agents because most human trials have been conducted against precancerous lesions for SCC. Furthermore, this model can be used in determining genetic modifiers that contribute to susceptibility or resistance to lung SCC development.

Cancer susceptibility in the mouse: genetics, biology and implications for human cancer

Growing evidence that a large proportion of apparently non-hereditary sporadic cancers occur in genetically predisposed individuals has emphasized the need to identify the underlying susceptibility genes. Increasingly, it seems that the best approach to define the numerous genes that have small but cumulative effects is to first identify and map them in mice, and subsequently to study the role of their homologues in humans. Development of new gene-mapping resources and strategies in mice has, for the first time, allowed some of these genes to be identified. In future, this unique approach is likely to provide important insights into the pathways of tumour development and might ultimately lead to more effective individually targeted cancer-prevention strategies.

Genetic influence on cigarette-induced cardiovascular disease

Cigarette smoking as an addictive habit has accompanied human beings for more than 4 centuries. It is also one of the most potent and prevalent environmental health risks human beings are exposed to, and it is responsible for more than 1000 deaths each day in the United States. With recent research progress, it becomes clear that cigarette smoking can cause almost all major diseases prevalent today, such as cancer or heart disease. These detrimental effects are not only present in active smokers who choose the risk, but also to innocent bystanders, as passive smokers, who are exposed to cigarettes not-by-choice. While the cigarette-induced harm to human health is indiscriminate and severe, the degree of damage also varies from individual to individual. This intersubject variability in cigarette-induced pathologies is partly mediated by genetic variants of genes that may participate in detoxification process, eg, cytochrome P450 (CYP), cellular susceptibility to toxins, such as p53, or disease development. Through population studies, we have learned that certain CYP1A1 variants, such as Mspl polymorphism, may render the carriers more susceptible to cigarette-induced lung cancer or severe coronary atherosclerosis. The endothelial nitric oxide synthase intron 4 rare allele homozygotes are more likely to have myocardial infarction if they also smoke. In vitro experimental approach has further demonstrated that cigarettes may specifically regulate these genes in genotype-dependent fashion. While we still know little about genetic basis and molecular pathways for cigarette-induced pathological changes, understanding these mechanisms will be of great value in designing strategies to further reduce smoking in targeted populations, and to implement more effective measures in prevention and treatment of cigarette-induced diseases.

Pulmonary adenoma susceptibility 1 (Pas1) locus affects inflammatory response

Two outbred mouse lines, phenotypically selected for differential subcutaneous (s.c.) acute inflammatory response (AIR), were analysed for urethane-induced lung inflammatory response and susceptibility to lung tumorigenesis. AIR(min) mice, which show a low response to s.c. acute inflammation, developed a persistent subacute lung inflammatory response and a 40-fold higher lung tumor multiplicity than did AIR(max) mice, which are selected for high response to s.c. acute inflammation and showed a transient lung inflammatory response. A highly significant linkage disequilibrium pattern was observed in AIR(max) and AIR(min) mice at marker alleles located within a 452-kb pulmonary adenoma susceptibility 1 (Pas1) locus region, thus defining the location of gene candidacy for inflammatory response and for the biological effects of Pas1 in this region. AIR(min) and AIR(max) mice segregated by descent the Pas1(s) and Pas1(r) alleles, respectively, providing evidence for the involvement of the Pas1 locus in the inflammatory response. The 452-kb region contains Kras2 and four additional genes, including the lymphoid-restricted membrane protein (Lrmp) gene, whose Pro-->Leu nonconservative variation was linked with inflammatory response and Pas1 allelotype. These results provide a model to explore the mechanism underlying inherited predisposition to lung cancer in the context of a link to inflammation.

Loss of heterozygosity analysis of mouse pulmonary adenomas induced by coal tar

Manufactured gas plant (MGP) residues, commonly known as coal tars, were generated several decades ago as a byproduct of residential and industrial gas production from the distillation of coal. Previous short-term exposure studies have shown MGP residues to be tumorigenic in mouse liver and lung. In order to gain further insight into carcinogenesis by complex mixtures of environmental chemicals containing known carcinogenic polycyclic aromatic hydrocarbons, we investigated mouse pulmonary tumors for loss of heterozygosity (LOH) as a result of multiple exposure to MGP residues. Twenty mouse lung adenomas produced in (C57BL/6 x C3H)F1 hybrid mice and manually microdissected were selected to examine genome-wide allelic losses at 58 microsatellite loci. Regions of chromosomes 1, 4, 5, 8, and 11 were affected in 30-40% of tumors. The elevated rates of allelic imbalance in these chromosomes may indicate the location of unknown tumor suppressor genes significant to neoplastic transformation in mouse lung tissues. Laser capture microdissection-based LOH analysis of pulmonary adenomas showed that contamination of nonneoplastic tissues was not masking the allelic losses in the manually microdissected tumor analysis. The low frequency of chromosome instability in these tumors, measured by means of inter-simple sequence repeat PCR, suggests the presence of discrete regions of LOH instead of extensive structural rearrangements.

A new locus for resistance to gamma-radiation-induced thymic lymphoma identified using inter-specific consomic and inter-specific recombinant congenic strains of mice

Mice of the C57BL/6J inbred strain develop thymic lymphomas at very high frequency after acute gamma-irradiation, while mice of several inbred strains derived from the wild progenitor of the Mus spretus species and their F1 hybrids with C57BL/6J appear extremely resistant. Analysis of the genetic determinism of the gamma-radiation-induced thymic lymphoma (RITL) resistance with the help of inter-specific consomic strains (ICS), which carry a single introgressed Mus spretus chromosome on a C57BL/6J genetic background, provide significant evidence for the existence of a thymic lymphoma resistance (Tlyr1) locus on chromosome 19. The subsequent analysis of the backcross progeny resulting from a cross between consomic mice heterozygous for the Mus spretus chromosome 19 and C57BL/6J mice, together with the study of inter-specific recombinant congenic strains (IRCS), suggest that this Tlyr1 locus maps within the D19Mit60-D19Mit40 chromosome interval. In addition to the discovery of a new locus controlling RITL development, our study emphasizes the value of ICS and IRCS for the genetic analysis of cancer predisposition.

Identification of candidate lung cancer susceptibility genes in mouse using oligonucleotide arrays

We applied microarray gene expression profiling to lungs from mouse strains having variable susceptibility to lung tumour development as a means to identify, within known quantitative trait loci (QTLs), candidate genes responsible for susceptibility or resistance to lung cancer. At least eight chromosomal regions of mice have been mapped and verified to be linked with lung tumour susceptibility or resistance. In this study, high density oligonucleotide arrays were used to measure the relative expression levels of >36 000 genes and ESTs in lung tissues of A/J, BALB/cJ, SM/J, C3H/HeJ, and C57BL/6J mice. A number of differentially expressed genes were found in each of the lung cancer susceptibility QTLs. Bioinformatic analysis of the differentially expressed genes located within QTLs produced 28 susceptibility candidates and 22 resistance candidates. These candidates may be extremely helpful in the ultimate identification of the precise genes responsible for lung tumour susceptibility or resistance in mice and, through follow up, humans. Complete data sets are available at http://thinker.med.ohio-state.edu.

Cancer modifier alleles inhibiting lung tumorigenesis are common in inbred mouse strains

Lung tumor susceptibility in inbred mouse strains is caused by the susceptibility allele at the pulmonary adenoma susceptibility 1 (Pas1(s)) locus. However, after urethane treatment, most strains carrying the Pas1(s) allele show an intermediate (1-4 tumors/mouse) instead of a highly susceptible (15-30 tumors/mouse) lung tumor phenotype. To test the hypothesis that strains displaying the intermediate lung tumor phenotype carry dominant or codominant resistance alleles at pulmonary adenoma resistance (Par) loci, we crossed mice of intermediate susceptibility or resistance to lung tumorigenesis with the highly susceptible A/J strain. Eleven F(1) hybrids were treated with urethane to induce lung tumorigenesis. The A/J strain developed 35.3 tumors/mouse, while its F(1) hybrid with C57BL/6J mice (null allele at Par loci) developed 22.8 tumors/mouse due to the Pas1 allele dosage effect. F(1) hybrids of strains 129/SvJ, CBA/J, ST/J and LP/J (Pas1(s)) and of SPW, DBA/2J and C57L/J (Pas1(r)) mice showed significant reduction in lung tumor multiplicity (i.e., 0.3-12.8 tumors/mouse) compared to A/J and (A/J x C57BL/6J)F(1) mice. These results indicate that resistance alleles at Par loci are common in inbred mouse strains and account for the lung tumorigenesis intermediate phenotype of strains carrying the Pas1(s) allele.

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.

Inhibition of both skin and lung tumorigenesis by Car-R mouse-derived cancer modifier loci

The Car-R outbred mouse line was phenotypically selected for high resistance to two-stage skin tumorigenesis. In the present study we tested the hypothesis that a subset of genetic loci responsible for resistance to skin tumorigenesis of Car-R mice might also inhibit lung tumorigenesis. Skin and lung tumorigenesis were induced in groups of Car-R, SWR/J, (SWR/JxCar-R)F1 and SWR/Jx(SWR/JxCar-R) backcross mice by i.p. urethane initiation and skin TPA promotion. Car-R mice showed a much lower susceptibility to both skin and lung tumorigenesis as compared to SWR/J mice, which are susceptible to both lung and skin tumorigenesis. The Car-R-inherited genome significantly inhibited both skin and lung cancer development in the F1 progeny of Car-R with SWR/J mice. In the backcross population, skin and lung tumor phenotypes showed a statistically significant correlation, indicating that a subset of the cancer resistance alleles, which segregated in the Car-R line during selection for resistance to skin carcinogenesis, provides resistance to both skin and lung tumorigenesis.

Complexity of lung cancer modifiers: mapping of thirty genes and twenty-five interactions in half of the mouse genome

BACKGROUND

Numerous low-penetrance genes control susceptibility to cancer in experimental animals, but the overall genetic information on this group of genes (i.e., number of loci and their mutual interactions) is missing. We performed a systematic search, scanning roughly half of the mouse genome for lung cancer susceptibility (Sluc) genes affecting tumor size or number by using mouse recombinant congenic (RC) strains. In each RC strain (OcB), approximately 12.5% of the genome is derived from the lung cancer-resistant strain B10.O20, whereas the rest is derived from the lung cancer-susceptible strain O20.

METHODS

A total of 730 F2 hybrids from five (OcB x O20) crosses were tested. Pregnant mice were treated on day 18 of gestation with a single dose of N-ethyl-N-nitrosourea. When offspring were 16 weeks old, whole lungs were removed and sectioned semiserially, and the size of all lung tumors (n = 2658) was determined. Analysis of variance was used for detection of linkage, and models (including main effect and two-way interactions) were tested with a statistical program.

RESULTS

We detected a total of 30 Sluc loci (16 new plus 14 previously reported) and 25 two-way interactions. Some of these interactions are counteracting (e.g., Sluc17 and Sluc20), resulting in the partial or total masking of the individual independent effect (main effect) of each involved locus. Seven loci (Sluc1, Sluc5, Sluc12, Sluc16, Sluc18, Sluc20, and Sluc26) and two interactions (Sluc5 x Sluc12 and Sluc5 x Sluc26) were detected in more than one RC strain.

CONCLUSIONS

The extrapolation of our results to the whole genome suggests approximately 60 Sluc loci (90% confidence intervals = 42 to 78). Despite the genetic complexity of lung cancer, use of appropriate mapping strategies can identify a large number of responsible loci and can reveal their interactions. This study provides an insight into the genetic control of lung tumorigenesis and may serve as a paradigm for investigating the genetics of other cancer types.

Evaluating mutant mice: anatomic pathology

As the human and mouse genome projects approach their goals, initiatives in functional genomics are advancing. When the nucleotide sequences are available, identification of gene functions will assume even greater importance. Determination of gene products and their proximal biochemical functions provide a part of the picture, but determination of their functions in the context of the whole organism is the ultimate goal. The manipulated mouse genome has become accepted as a model for understanding the genetic basis of human conditions and diseases. Consequently, biomedical research institutions have seen significant increases in the use of mice since the early 1980s, and these increases are largely attributable to the use of genetically modified mice. The role of comparative pathology in research on mutant mouse models of disease is increasing in response to these trends. Evaluation and phenotypic characterization of mutant mice, via clinical and anatomic pathology techniques, will be an important component of functional genomics initiatives.

Predisposition to lung tumorigenesis

Mouse inbred strains with inherited predisposition and resistance to lung cancer provide an essential tool for the dissection of the genetics of this complex disease. We have previously mapped a major locus (Pulmonary adenoma susceptibility 1, Pas1) affecting inherited predisposition to lung cancer in mice on chromosome 6, near Kras2. Appropriate crosses that include susceptible mice (Pas1(s)) provide a model system for identifying loci that can modify the lung cancer predisposition phenotype caused by Pas1. Using this approach we have mapped the Pulmonary adenoma resistance 1 (Par1) locus that behaves like a modifier locus of Pas1. More recently, we mapped additional lung tumor resistance loci (Par2, and Par4), and a locus specifically involved with lung tumor progression (Papg1). The mapping of Pas1 in mice stimulated us to test the possible association of genetic markers located in the homologous human region (12p12) with risk and prognosis of lung adenocarcinomas in man. In the Italian population, we carried out an association study by genotyping lung adenocarcinoma patients and healthy controls for genetic markers located in the putative region of interest. Homozygosity of the A2 allele at a Kras2/RsaI polymorphism, and allele 2 at a VNTR polymorphism in the PTHLH gene showed borderline statistically significant associations with lung cancer risk. Furthermore, the same alleles were significantly associated with tumor prognosis. Studies on association were then performed in the Japanese and in European populations. In the Japanese population, the KRAS2/RsaI marker was significantly associated with prognosis of lung adenocarcinoma, whereas the European study did not confirm this association. Our results may provide evidence for the existence of the human PAS1 locus, suggesting that the mouse model of inherited predisposition to lung tumorigenesis is predictive of a human genetic mechanism of susceptibility to lung cancer.

Modeling human lung cancer in mice: similarities and shortcomings

Lung cancer kills more Americans yearly than any other neoplastic process. Mortality rates have changed little over the past several decades, despite improvements in surgical techniques, radiation therapy and chemotherapy. The identification of mutations in oncogenes and tumor suppressor genes in human lung tumor specimens, including K-ras, p53, p16INK4a and Rb, offers molecular explanations for tumor development and resistance to therapy. Mouse models of human lung cancer may advance our understanding of this disease. The examination of mice which develop lung cancer either spontaneously or due to carcinogen exposure, and the creation of mouse strains harboring the specific genetic mutations found in human lung cancer are among strategies being pursued.

Genetic mapping of cancer susceptibility/resistance loci in the mouse

Genetic linkage experiments using crosses between mouse inbred strains with an inherited predisposition and resistance to lung cancer make it possible to investigate the genetics of the complex inheritance of susceptibility and resistance to lung cancer. We have previously mapped a major locus (pulmonary adenoma susceptibility 1, Pas1) affecting inherited predisposition to lung cancer in mice onto chromosome 6, near Kras2. Appropriate crosses that include Pas1/+ mice provide a model system for identifying loci that can modify the lung cancer predisposition phenotype caused by Pas1. Using this approach, we mapped the pulmonary adenoma resistance 1 (Par1) locus on to mouse chromosome 11; this locus selectively inhibits lung tumor development in Pas1/+ animals and therefore behaves like a modulator gene of Pas1. More recently, we have mapped lung tumor modifier loci specifically affecting the initiation and progression of lung cancer. Thus experimental models provide an essential tool for the mapping of lung cancer susceptibility/resistance genes and for the subsequent cloning of candidate genes.

Genetic dissection of murine susceptibilities to liver and lung tumors based on the two-stage concept of carcinogenesis

Inbred mouse strains exhibit strain-specific susceptibilities to spontaneous and induced tumors, indicating that the individual risks for neoplastic development are largely under genetic control. Recent advances in linkage analysis have made it routine to chromosomally map the mouse genes responsible for the strain variations in tumor susceptibility using segregating crosses. It is also possible to characterize their biological functions using the positional information. These types of studies are still severely hampered for human cases due to the remarkable genetic heterogeneity and impossibility of experimental crosses. In this article, previous work on genetic susceptibility to mouse liver and lung tumors is reviewed in view of the classical two-stage concept of carcinogenesis. According to this central concept, the tumor susceptibility genes should affect either the first stage, 'initiation', or the second stage, 'promotion', or both. At least some genes seem to be specifically involved in initiation or promotion, in line with the fact that initiation and promotion are due, to a certain extent, to independent mechanisms. This notion should be also applicable to human carcinogenesis and may provide important clues for prevention of initiation and promotion in populations with a genetic predisposition for cancer development.

At least four loci and gender are associated with susceptibility to the chemical induction of lung adenomas in A/J x BALB/c mice

Four putative quantitative trait loci (QTLs) that influence susceptibility to the induction of lung adenomas by urethane in an F2 cross between A/J and BALB/cOlaHsd have been mapped. Following microsatellite typing of mice with resistant and susceptible phenotypes at 97 microsatellite marker loci, a major locus was identified on chromosome 18 with a lod score of 15. This was responsible for an 8- to 10-fold increase in tumor multiplicity in males and females, respectively, having the AA and CC genotypes at the D18Mit188 marker locus. It mapped close to Dcc (deleted in colorectal cancer). A locus on chromosome 4 (lod score 6.5) had the resistant allele in strain A/J and the susceptible allele in BALB/c, with a 14-fold difference in tumor multiplicity between mice of the AA and CC genotypes. This mapped close to the Cdkn2a (cyclin-dependent kinase inhibitor 2A) locus, which is commonly deleted in mouse lung tumors. Two loci with smaller effects (lod scores 3.03 and 3.25) were identified on chromosomes 1 and 11. There was also significant sexual dimorphism in tumor multiplicity both among 151 F2 hybrids and among 52 mice resulting from a backcross to strain A/J, with males having higher tumor counts than females.

Genetics of quantitative and qualitative aspects of lung tumorigenesis in the mouse: multiple interacting Susceptibility to lung cancer (Sluc) genes with large effects

Inbred strains of mice exhibit large differences in their susceptibility to various complex quantitative genetic traits, among which is the susceptibility to lung cancer. These differences are caused by the combined effects of multiple quantitative trait loci (QTLs). Due to their multiplicity, it is relatively difficult and laborious to study the effects of individual QTLs. To dissect complex genetic traits the authors make use of recombinant congenic strains (RCS), a system of mouse inbred strains in which the genetic complexity is reduced. The susceptibility to lung cancer is studied by using the series of O20-congenic-B10.O20 (OcB) RC strains. They are derived from the parental background strain O20 and the parental donor strain B10.O20, two mouse inbred strains that differ from each other in both quantitative and qualitative aspects of lung tumorigenesis. This study describes the segregation of lung tumor number, size, and histology among the OcB RC strains, and indicates that these traits are influenced by multiple interacting QTLs with considerable individual effects. The results suggest that some of the susceptibility loci to lung cancer affect the susceptibility to other types of cancer as well, possibly by functioning systematically.

Use of quantitative trait loci to map murine lung tumor susceptibility genes

During the last decade new methods for mapping quantitative trait loci (QTLs) have helped geneticists uncover disease-associated genes. Genetic dissection of complex multigenic diseases such as cancer is being accomplished in part by mapping QTLs in experimental crosses of mice [1]. With the recent construction of dense genetic linkage maps for the mouse, mapping of quantitative trait loci has become practical [2]. Over 6000 polymorphic simple sequence length repeat markers (microsatellite markers) have been mapped in the mouse genome [3], and new analytical approaches to linkage analysis have made QTL mapping a powerful technique for identifying cancer genes [4-7]. In this overview we discuss the design of QTL mapping studies and some of the findings from studies on the mapping of murine lung tumor susceptibility loci.

Identification, characterization, and genetic mapping of Rad51d, a new mouse and human RAD51/RecA-related gene

Homologous DNA recombination occurs in all organisms and is important for repair of DNA damage during mitosis. One of the critical genes for DNA repair and meiotic recombination in yeast is RAD51, and homologs of RAD51 have been identified in several species, including mouse and human. Here we describe a new RAD51-related mammalian gene, named Rad51d, identified by searching the EST database with the yeast RAD55 and human RAD51B/REC2 genes. A full-length 1.5-kb mouse cDNA clone that encodes a predicted 329-amino-acid protein was isolated. Rad51d mRNA was present in every mouse tissue examined. Four different transcript sizes were detected, one of which was specific to testis. Human cDNA clones that predicted 71% amino acid identity to the mouse protein were also isolated. Interestingly, the sequences of these human clones and of RT-PCR-derived products provided evidence for alternative splicing. These mRNAs are predicted to encode proteins that are truncated relative to the mouse and lack the ATP-binding motif characteristic of RecA-related proteins. Using an interspecific backcross mapping panel, Rad51d was mapped to mouse Chromosome 11, 48.5 cM from the centromere. By radiation hybrid mapping, the human ortholog RAD51D was mapped to chromosome 17q11, which is a region syntenic to mouse Chromosome 11. Due to its expression pattern and sequence similarity to other RAD51 family members, it is likely that Rad51d is part of a complex of proteins required for DNA repair and meiotic recombination.

Complex traits and polygenic inheritance in the mouse

Polygenic inheritance has recently become an increasingly active field of research due to the availability of techniques allowing in-depth screening of genetic markers across the entire genome. The mouse is being used both in its own right and as a model system for certain human traits. The advantages and disadvantages of the mouse for such studies are outlined and in this context, the adequacy of the mouse as a model for polygenic traits in humans is discussed. A detailed overview of the approaches and methods used in the analysis of polygenic inheritance in the mouse is presented.

Experimental strategies for the genetic dissection of complex traits in animal models

Current success in detecting complex trait loci in general, and quantitative trait loci (QTLs) using model organisms in particular, has attracted major biological and biomedical interest. The potential ability to identify genes and their function provides opportunities for new diagnostics and treatments of complex genetic diseases. Despite the success in gene mapping, however, cloning of complex trait loci or QTLs is not straightforward. A major obstacle lies in achieving fine mapping resolution for the detected loci. Compared to the rapid development of sophisticated statistical and molecular tools, development and analysis of experimental designs for various stages in QTL mapping experiments have barely been considered. In this study, novel and existing experimental strategies for QTL analysis are presented and evaluated.

[Evaluation of cancer risk through genetic analysis?]

BACKGROUND

The recent literature of familial cancer, specifically related to germline mutations of RB1, p53, NF1, ATM, BRCA1, Mismatch repair genes and APC is reviewed.

RESULTS AND CONCLUSIONS

Germline mutations do not relate to an increased tumor risk of any single tissue, but instead to spectra of neoplastic diseases. The genetic background plays a major role in modifying the cancer risk. Therefore, mass screening for mutations of single genes seems to be without practical value. Only in combination with an adequate and informative family history can molecular genetic analysis significantly support the care for the individual. Comparison of the data of patients inheriting germline mutations and the experience from the corresponding "knockout" mouse demonstrate that only the p53 and APC knockout mice are useful models of human disease.