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Here, we report inducible mosaic animal for perturbation (iMAP), a transgenic platform enabling in situ CRISPR targeting of at least 100 genes in parallel throughout the mouse body. iMAP combines Cre-loxP and CRISPR-Cas9 technologies and utilizes a germline-transmitted transgene carrying a large array of individually floxed, tandemly linked gRNA-coding units. Cre-mediated recombination triggers expression of all the gRNAs in the array but only one of them per cell, converting the mice to mosaic organisms suitable for phenotypic characterization and also for high-throughput derivation of conventional single-gene perturbation lines via breeding. Using gRNA representation as a readout, we mapped a miniature Perturb-Atlas cataloging the perturbations of 90 genes across 39 tissues, which yields rich insights into context-dependent gene functions and provides a glimpse of the potential of iMAP in genome decoding. [Display omitted] • Inducible mosaic animal for perturbation (iMAP) combines Cre-LoxP and CRISPR-Cas • iMAP enables large-scale in situ multiplexed mosaic gene targeting and Perturb-Atlas mapping • iMAP enables rapid derivation of single-gene perturbation mouse lines via breeding • iMAP lines are permanent resources just as conventional transgenic lines iMAP is a multiplexed mosaic in situ gene-perturbation platform, which enables large-scale mapping of the Perturb-Atlases profiling genome function across the whole body and high-throughput derivation of single-gene perturbation mouse lines. [ABSTRACT FROM AUTHOR]

RNA base editors should ideally be free of immunogenicity, compact, efficient, and specific, which has not been achieved for C > U editing. Here we first describe a compact C > U editor entirely of human origin, created by fusing the human C > U editing enzyme RESCUE-S to Cas inspired RNA targeting system (CIRTS), a tiny, human-originated programmable RNA-binding domain. This editor, CIRTS-RESCUEv1 (V1), was inefficient. Remarkably, a short histidine-rich domain (HRD), which is derived from the internal disordered region (IDR) in the human CYCT1, a protein capable of liquid-liquid phase separation (LLPS), enhanced V1 editing at on-targets as well as off-targets, the latter effect being minor. The V1-HRD fusion protein formed puncta characteristic of LLPS, and various other IDRs (but not an LLPS-impaired mutant) could replace HRD to effectively induce puncta and potentiate V1, suggesting that the diverse domains acted via a common, LLPS-based mechanism. Importantly, the HRD fusion strategy was applicable to various other types of C > U RNA editors. Our study expands the RNA editing toolbox and showcases a general method for stimulating C > U RNA base editors., Competing Interests: B.C.D. has a patent filed for the CIRTS technology. B.C.D. is a founder and holds equity in Tornado Bio, Inc., a company developing RNA-programmable therapies., (© 2024 The Author(s).)