Simultaneous zygotic inactivation of multiple genes in mouse through CRISPR/Cas9-mediated base editing

In vivo genetic mutation has become a powerful tool for dissecting gene function; however, multi-gene interaction and the compensatory mechanisms involved can make findings from single mutations, at best difficult to interpret, and, at worst, misleading. Hence, it is necessary to establish an efficient way to disrupt multiple genes simultaneously. CRISPR/Cas9-mediated base editing disrupts gene function by converting a protein-coding sequence into a stop codon; this is referred to as CRISPR-stop. Its application in generating zygotic mutations has not been well explored yet. Here, we first performed a proof-of-principle test by disrupting Atoh1, a gene crucial for auditory hair cell generation. Next, we individually mutated vGlut3 (Slc17a8), otoferlin (Otof) and prestin (Slc26a5), three genes needed for normal hearing function. Finally, we successfully disrupted vGlut3, Otof and prestin simultaneously. Our results show that CRISPR-stop can efficiently generate single or triple homozygous F0 mouse mutants, bypassing laborious mouse breeding. We believe that CRISPR-stop is a powerful method that will pave the way for high-throughput screening of mouse developmental and functional genes, matching the efficiency of methods available for model organisms such as Drosophila.

Characterizing a novel vGlut3-P2A-iCreER knockin mouse strain in cochlea

Precise mouse genetic studies rely on specific tools that can label specific cell types. In mouse cochlea, previous studies suggest that vesicular glutamate transporter 3 (vGlut3), also known as Slc17a8, is specifically expressed in inner hair cells (IHCs) and loss of vGlut3 causes deafness. To take advantage of its unique expression pattern, here we generate a novel vGlut3-P2A-iCreER knockin mouse strain. The P2A-iCreER cassette is precisely inserted before stop codon of vGlut3, by which the endogenous vGlut3 is intact and paired with iCreER as well. Approximately, 10.7%, 85.6% and 41.8% of IHCs are tdtomato + when tamoxifen is given to vGlut3-P2A-iCreER/+; Rosa26-LSL-tdtomato/+ reporter strain at P2/P3, P10/P11 and P30/P31, respectively. Tdtomato + OHCs are never observed. Interestingly, besides IHCs, glia cells, but not spiral ganglion neurons (SGNs), are tdtomato+, which is further evidenced by the presence of Sox10+/tdtomato+ and tdtomato+/Prox1(Gata3 or Tuj1)-negative cells in SGN region. We further independently validate vGlut3 expression in SGN region by vGlut3 in situ hybridization and antibody staining. Moreover, total number of tdtomato + glia cells decreased gradually when tamoxifen is given from P2/P3 to P30/P31. Taken together, vGlut3-P2A-iCreER is an efficient genetic tool to specifically target IHCs for gene manipulation, which is complimentary to Prestin-CreER strain exclusively labelling cochlear outer hair cells (OHCs).