Genetic screening of key genes regulating hair cell (HC) differentiation is of particular importance in gene therapy toward HC restoration in deaf patients in clinic. 

There is a high degree of similarity regarding the developmental process and functions of auditory system between mice and human beings, especially in sound receptor cells, HCs. While transcriptomic profiles of HCs at multiple postnatal ages are currently available, it remains poorly understood in terms of which genes are essential in regulating HC differentiation and maturation because generating mutant Founder 0 (F0) mice, germ-line transmission and subsequent inter-breeding are time-consuming and laborious. 

Previous work of Dr. LIU’s group has established a protocol which is able to inactivate three non-lethal genes simultaneously in F0 mice ready for immediate phenotype analysis. However, there are 25% of mammalian genes whose homozygous mutants will lead to embryonic or neonatal lethality, thus the strategy is not suitable for those lethal or essential genes. The typical solution is to use conditional knock out strategy, but it is very time consuming.  

Is there an alternative approach to rapidly screen those essential genes? This study provides a novel genetic strategy named ‘mosaic CRISPR-stop’ to generate F0 mice with homozygous but mosaic mutations. By injecting base editor components and gene specific sgRNAs into one of the two blastomeres, offspring cells with or without gene editing are distributed randomly throughout various organs. 

This study highlights that mosaic CRISPR-stop is a reliable method and will pave the way for genetic screening of developmentally essential genes in the mouse inner ear and other organs.