show Abstracthide AbstractCell competition is a short-range intercellular communication in which cells with relatively lower fitness are eliminated as a loser by winner cells, i.e. the cells with relatively higher fitness. For the aim of identification of novel genes involved in cell competitin in mouse, we performed genome-wide screening using mouse NIH3T3 cells. Using a genome-wide gRNA lentiviral libraries of CRISPR/Cas9 (Koike-Yusa et al. Nature Biotechnology 32, 267-273, 2014, or GeCKOv2 mouse sgRNA library, Nature Methods 11, 783-784, 2014), we generated mutant NIH3T3 cell library. If the mutant cell library is cultured, the mutant cells that have mutations in genes involved in cell competition are expected to be either eliminated as losers or increased as winners through cell competition with normal cells. We sequenced the gRNA region of the original lentiviral library and genome DNAs of the mutant cell library cultured for 4 days and 10 days. By comparing the relative read numbers of each gRNA from different samples, we will be able to identify the gRNAs that show differential abundance ratio among samples. The genes targeted by such gRNAs are candidate genes involved in cell competition.