Amy R. Moser

Genetic identification of Mom-1, a major modifier locus affecting Min-induced intestinal neoplasia in the mouse

Mutations in the human APC gene caused various familial colon cancer syndromes. The Multiple intestinal neoplasia (Min) mouse provides an excellent model for familial colon cancer: it carries a mutant mouse Apc gene and develops many intestinal adenomas. Here, we analyze how this tumor phenotype is dramatically modified by genetic background. We report the genetic mapping of a locus that strongly modifies tumor number in Min/+ animals. This gene, Mom-1 (Modifier of Min-1), maps to distal chromosome 4 and controls about 50% of genetic variation in tumor number in two intraspecific backcrosses. The mapping is supported by a LOD score exceeding 14. Interestingly, Mom-1 lies in a region of synteny conservation with human chromosome 1p35-36, a region of frequent somatic loss of heterozygosity in a variety of human tumors, including colon tumors. These results provide evidence of a major modifier affecting expression of an inherited cancer syndrome.

ApcMin: A mouse model for intestinal and mammary tumorigenesis

Min (multiple intestinal neoplasia) is a mutant allele of the murine Apc (adenomatous polyposis coli) locus, encoding a nonsense mutation at codon 850. Like humans with germline mutations in APC, Min/+ mice are predisposed to intestinal adenoma formation. The number of adenomas is influenced by modifier loci carried by different inbred strains. One modifier locus, Mom-1 (modifier of Min-1), maps to distal chromosome 4. Intestinal tumours from both B6 (C57BL/6J) and hybrid Min/+ mice show extensive loss of the wild-type allele at Apc. B6 Min/+ female mice are predisposed to spontaneous mammary tumours. The incidence of both intestinal and mammary tumours can be increased in an age-specific manner by treatment with ethylnitrosourea (ENU). Min mice provide a good animal model for studying the role of Apc and interacting genes in the initiation and progression of intestinal and mammary tumorigenesis.

Pathway Pathology: Histological Differences Between ErbB/Ras and Wnt Pathway Transgenic Mammary Tumors

To study phenotype-genotype correlations, ErbB/Ras pathway tumors (transgenic for ErbB2, c-Neu, mutants of c-Neu, polyomavirus middle T antigene (PyV-mT), Ras, and bi-transgenic for ErbB2/Neu with ErbB3 and with progesterone receptor) from four different institutions were histopathologically compared with Wnt pathway tumors [transgenes Wnt1, Wnt10b, dominant-negative glycogen synthase kinase 3-beta, beta-Catenin, and spontaneous mutants of adenomatous polyposis coli gene (Apc)]. ErbB/Ras pathway tumors tend to form solid nodules consisting of poorly differentiated cells with abundant cytoplasm. ErbB/Ras pathway tumors also have scanty stroma and lack myoepithelial or squamous differentiation. In contrast, Wnt pathway tumors exhibit myoepithelial, acinar, or glandular differentiation, and, frequently, combinations of these. Squamous metaplasia is frequent and may include transdifferentiation to epidermal and pilar structures. Most Wnt pathway tumors form caricatures of elongated, branched ductules, and have well-developed stroma, inflammatory infiltrates, and pushing margins. Tumors transgenic for interacting genes such as protein kinase CK2alpha (casein kinase IIalpha), and the fibroblast growth factors (Fgf) Int2/Fgf3 or keratinocyte growth factor (Kgf/Fgf7) also have the Wnt pathway phenotype. Because the tumors from the ErbB/Ras and the Wnt pathway are so distinct and can be readily identified using routine hematoxylin and eosin sections, we suggest that pathway pathology is applicable in both basic and clinical cancer research.

Effects of ENU dosage on mouse strains.

Abstract. The germline supermutagen, N-ethyl-N-nitrosourea (ENU), has a variety of effects on mice. ENU is a toxin and carcinogen as well as a mutagen, and strains differ in their susceptibility to its effects. Therefore, it is necessary to determine an appropriate mutagenic, non-toxic dose of ENU for strains that are to be used in experiments. In order to provide some guidance, we have compiled data from a number of laboratories that have exposed male mice from inbred and non-inbred strains or their F1 hybrids to ENU. The results show that most F1 hybrid animals tolerate ENU well, but that inbred strains of mice vary in their longevity and in their ability to recover fertility after treatment with ENU.

Wnt Signaling Stimulates Transcriptional Outcome of the Hedgehog Pathway by Stabilizing GLI1 mRNA

Wnt and Hedgehog signaling pathways play central roles in embryogenesis, stem cell maintenance, and tumorigenesis. However, the mechanisms by which these two pathways interact are not well understood. Here, we identified a novel mechanism by which Wnt signaling pathway stimulates the transcriptional output of Hedgehog signaling. Wnt/beta-catenin signaling induces expression of an RNA-binding protein, CRD-BP, which in turn binds and stabilizes GLI1 mRNA, causing an elevation of GLI1 expression and transcriptional activity. The newly described mode of regulation of GLI1 seems to be important to several functions of Wnt, including survival and proliferation of colorectal cancer cells.

High rates of chromosome missegregation suppress tumor progression but do not inhibit tumor initiation

Expression of a truncated allele of the Apc tumor suppressor causes intestinal tumors with a low rate of chromosomal instability (CIN). Increasing the rate of CIN suppresses tumor growth without inhibiting tumor initiation in both the small intestine and colon, suggesting that increasing CIN is a useful chemotherapeutic strategy.

Quantitative Trait Loci Associated with Susceptibility to Bladder and Kidney Infections Induced by Escherichia coli in Female C3H/HeJMice

BACKGROUND The C3H/HeJ mouse strain develops severe bladder and kidney infections after receiving intravesical inoculation with uropathogenic Escherichia coli. This susceptibility is genetically determined, but the specific genes involved have not been completely defined. The objective of the present study was to use quantitative trait locus (QTL) mapping to identify chromosomal sites associated with susceptibility to infection in C3H/HeJ mice. METHODS Female mice from a backcross of C3H/HeJ and (BALB/cxC3H/HeJ)F1 mice were inoculated with E. coli, and the number of E. coli colony-forming units present in the bladder and kidneys was quantified 10 days later. Genomic DNA was scanned using microsatellite markers to localize chromosomal segments derived from parental strains. Statistical analyses associated infection phenotypes with chromosomal sites. RESULTS A highly significant QTL for susceptibility to bladder infection was identified on chromosome 4, and C3H/HeJ alleles at this locus interacted with BALB/c alleles on chromosome 19 to increase the severity of infection. A significant QTL on chromosome 6 was associated with severe kidney infections. CONCLUSIONS Increased susceptibility to E. coli bladder and kidney infections in female C3H/HeJ mice is associated with specific chromosomal sites located near genes contributing to host resistance to infection. The results demonstrate the multigenic nature of susceptibility to urinary tract infections.

Identification of Novel Modifier Loci of ApcMin Affecting Mammary Tumor Development

Genetic background affects the susceptibility to mammary tumor development in Apc(Min/+) mice. Here we report the identification of four novel modifier loci that influence different aspects of mammary tumor development in Apc(Min/+) mice. Analysis of tumor development in a backcross of (FVBB6 Apc(Min/+)) x B6 Apc(Min/+) mice has identified a modifier on chromosome 9 that significantly affects tumor multiplicity, and a modifier on chromosome 4 that significantly affects tumor latency and affects tumor number with suggestive significance. This modifier was also identified in a backcross involving 129X1/SvJ and B6 Apc(Min/+) mice. A modifier on chromosome 18 specifically affects tumor latency but not tumor number. Kaplan-Meier analysis suggests there is at least an additive interaction affecting tumor latency between the loci on chromosomes 4 and 18. We also identified a modifier locus on chromosome 6 that interacts with the loci on chromosome 4 and chromosome 9 to affect tumor number. These results suggest that multiple genetic loci control different aspects of mammary tumor development. None of these modifiers is associated with intestinal tumor susceptibility, which indicates that these modifiers act on tumor development in a tissue-specific manner.

ROSA26 mice carry a modifier of Min-induced mammary and intestinal tumor development.

Abstract. B6.129S7-Gtrosa26 (B6.R26) mice carry a LacZ-neoR insertion on Chromosome (Chr) 6, made by promoter trapping with 129 ES cells. Female C57BL/6J ApcMin/+ (B6Min/+) mice are highly susceptible to intestinal tumors and to the induction of mammary tumors after treatment with ethylnitrosourea (ENU). However, B6.R26/+Min/+ females develop fewer mammary and intestinal tumors after ENU treatment than do B6 Min/+ mice. B6.R26/+ mice from two independently derived congenic lines show this modifier effect. Each of these congenic lines carries approximately 20 cM of 129-derived DNA flanking the insertion, raising the possibility that the resistance is due to a linked modifier locus. To further map the modifier locus, we have generated several lines of mice carrying different regions of the congenic interval. We have found that resistance to mammary and intestinal tumors in ENU-treated Min/+ mice maps to a minimum 4-cM interval that includes the ROSA26 LacZ-neoR insertion. Therefore, the resistance to tumor development is due to either the ROSA26 insertion or a very tightly linked modifier locus.

The ROSA26 LacZ-neo(R) insertion confers resistance to mammary tumors in Apc(Min/+) mice.

B6.129S7-Gtrosa26 (ROSA26) mice carry a LacZ-neoR insertion on Chromosome (Chr) 6, made by promoter trapping with AB1 129 ES cells. Female C57BL/6J ApcMin/+ (B6 Min/+) mice are very susceptible to the induction of mammary tumors after treatment with ethylnitrosourea (ENU). However, ENU-treated B6 mice carrying both ApcMin and ROSA26 are resistant to mammary tumor formation. Thus, ROSA26 mice carry a modifier of Min-induced mammary tumor susceptibility. We have previously mapped the modifier to a 4-cM interval of 129-derived DNA that also contains the ROSA26 insertion. Here we report additional evidence for the effect of the ROSA26 insertion on mammary tumor formation. To test the hypothesis that the resistance was due to a linked modifier locus, we utilized two approaches. We have derived and tested two lines of mice that are congenic for 129-derived DNA within the minimal modifier interval and show that they are as susceptible to mammary tumors as are B6 mice. Additionally, we analyzed a backcross population segregating for the insertion and show that mice carrying the insertion are more resistant to mammary tumor development than are mice not carrying the insertion. Thus, the resistance is not due to a 129-derived modifier allele, but must be due to the ROSA26 insertion. In addition, the effect of the ROSA26 insertion can be detected in a backcross population segregating for other mammary modifiers.