Genetic studies of candidate metastasis modifier genes on mouse chromosome 19.

Abstract

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The ability of a tumour to metastasize is the major determinant of cancer-patient mortality. Therefore elucidation of the metastasis pathway is an important priority for cancer biology. Studies have demonstrated that tumour progression from normal epithelium to metastastic cell is a complex process with many different barriers for a tumor to successfully colonize a distant site. To further explore the molecular and genetic events required for tumor dissemination, our laboratory has used the highly metastatic MMTVPyMT transgenic mouse mammary tumor model, and combined medium-resolution haplotype mapping with multiple experimental crosses to reduce the number of potential candidate genes in a complex-trait candidate interval on mouse chromosome 19. Coincident mapping of a modifier gene in multiple experimental crosses using different inbred strains is consistent with the common inheritance of a modifier allele. A haplotype map was developed in four inbred strains of mice, has been used in our complex-trait mapping crosses across the proximal 10 cM of proximal chromosome 19 to identify haplotype blocks that segregate appropriately. Only ∼23 out of >400 genes met this criteria. This strategy coupled with tissue and expression arrays, as well as our recently described common pathway analysis was used to further reduce the number of high-priority candidates to two. Subsequent analysis using both publicly available databases and direct sequencing of a set of the inbred mouse strains, has revealed multiple silent polymorphisms in both genes, Sipa1 and Map3k11, as well as a single missense mutation in a protein-binding domain of Sipa1 as well as the presence of a polymorphic VNTR in the promoter region of Map3k11. Current experiments have been investigating the role of these polymorphisms on gene function and metastatic progression by a variety of molecular strategies, including quantitative PCR, western blot analysis, mammalian gene expression, and siRNA technologies. This combination of methodologies, which we refer to as trans-omic analysis, may therefore provide a rapid, efficient method to identify and prioritize complex-trait candidate genes without requiring construction of congenic mouse strains.