Designing Genetically Engineered Mouse Models (GEMMs) Using CRISPR Mediated Genome Editing.

Genetically engineered mouse models (GEMMs) are very powerful tools to study lineage hierarchy and cellular dynamics of stem cells in vivo. Stem cell behavior in various contexts such as development, normal homeostasis and diseases have been investigated using GEMMs. The strategies to generate GEMMs have drastically changed in the last decade with the development of the CRISPR/Cas9 system for manipulation of the mammalian genome. The advantages of the CRISPR/Cas9 are its simplicity and efficiency. The bioinformatics tools available now allow us to quickly identify appropriate guide RNAs and design experimental conditions to generate the targeted mutation. In addition, the genome can be manipulated directly in the zygote which reduces the time to modify target genes compared to other technologies such as Embryonic Stem (ES) cells. Equally important is that we can manipulate the genome of any mouse background with the CRISPR/Cas9 system which omits time-consuming backcrossing processes, accelerates research and increases flexibility. Here, we will summarize basic allelic types and our standard strategies of how to generate them.