Mutational mechanisms underlying mouse mosaicism

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A genome is often called a blueprint, but this image of a single plan fails to capture the continuous change occurring in both the structure and the sequence of a genome within an organism over a lifespan. Recent evidence in mutation research reveals that de novo mutations occur at higher rates and with greater impact on the genome landscape than thought previously. Development is a critical period of mutagenesis during which individual tissues and cells are affected at different times and to different degrees. My research team seeks to understand the origins and mechanisms of mutation characteristic of normal development by investigating the load of de novo mutations in tissues and cells of the adult mouse. Mice provide an excellent model of the mutational mechanisms in mammalian genomes and enable study of any tissue in the context of well studied genetic backgrounds. My students and I have expertise using a genomic platform to examine point mutations at 493,290 polymorphic sites in the mouse genome and to detect deletions and duplications through assay of copy number at 915,519 sites distributed across the genome. We used this genomics platform to detect single nucleotide variants and copy number variants genome wide in an evolutionary study of extensive genetic diversity in Mus musculus. We now propose to examine the load of new mutations in a panel of tissues in individuals (parents and three sons) of three families of C57BL/6J (B6) inbred mice, a reference genetic background. We selected somatic tissues with different developmental histories and we included analysis of male germ cells at two points in sperm development. We propose to repeat our study for three families of hybrid B6D2 mice predicted to have higher rates of mutation associated with heterozygosity. Since our genetics platform is biased in analyzing point mutations in nongenic regions of the genome, we propose whole exome sequencing to detect de novo mutations in protein coding regions of the genome. Our research will document the number and nature of new mutations in individual tissues of adult mice with specific examination of the influences of genomic heterozygosity, developmental history and coding sequence. Our data provide a baseline of the degree and nature of somatic mosaicism arising with normal mouse development that will be used in biomonitoring studies for understanding mutational mechanisms associated with environmental mutagens and in comparisons with mouse genetic backgrounds with compromised genome integrity to understand mechanisms of genome maintenance. Our research is fundamental to understanding mechanisms contributing to the normal genetic diversity that arises within an individual. Graduate and undergraduate students will gain technical and computational expertise in analysis of mouse genome variation valuable to research in academic institutions, research institutes and government agencies.