Generation and applications of MADM-based mouse genetic mosaic system

Genetic mosaics describe organisms that contain cells with distinct genotypes related to somatic transposition, mitotic recombination, or genomic aberrations. Most, if not all, human cancers are genetic mosaics because cancer cells bear mutations that are absent in normal cells within the same body. While naturally occurring mutant cells in genetic mosaic animals are difficult to track down, a genetically engineered mosaic mouse model termed MADM (Mosaic Analysis with Double Markers) enables one to perform phenotypic analysis of mutant cells at single-cell resolution in vivo. While cancer modeling is the most obvious application, MADM is also highly suitable for studying developmental biology, neuroscience, and regenerative biology problems to investigate clonal contributions. Here we describe the construction of the MADM model on a specific chromosome through ES cell-based targeting of MADM cassettes into a pair of homologous chromosomes. We also detail procedures to verify the labeling efficiency of the newly established MADM model. Finally, we explain the breeding schemes and analytical principles that enable using MADM for in vivo phenotypic analysis at single-cell resolution.