PROJECT SUMMARY/ABSTRACT – GENETICALLY ENGINEERED MOUSE MODELS SHARED RESOURCE The Genetically Engineered Mouse Models Shared Resource (GEMMSR), formerly the Transgenic Gene Knockout Shared Resource, provides St. Jude Comprehensive Cancer Center (SJCCC) members with convenient and economic access to generating genetically engineered mouse models (GEMMs). This includes the production of transgenic, knock-out, conditional knock-out, deletion, and knock-in mouse lines. These models are critical tools for advancing science at the SJCCC by elucidating the role of genetic changes in the initiation and progression of cancer and deciphering the mechanisms through which therapeutic targets operate in anticancer treatment. The GEMMSR is directed by Youngwook Ahn, PhD, who has over 18 years of transgenic and GEMM creation experience and is supported by three full-time, highly experienced staff members. The GEMMSR provides a range of services, including consultation, classic transgenics, CRISPR editing via pronuclear injection, CRISPR editing via electroporation, and extended genotyping. The CRISPR editing with electroporation of zygotes and extended genotyping services were newly introduced during the project period. With this additional method for creating mouse lines, the GEMMSR increased the live birth rates of all GEMMs from ~6% to ~25% and reduced the number of zygotes required. During the project period, several additional changes were made. The GEMMSR retired the mouse embryonic stem cell arm of the facility due to decreased demand, allowing for a greater focus on CRISPR-based animal model creation. Additionally, the GEMMSR decided to stop maintaining an in-house C57BL/6 donor colony, opting instead to purchase these mice from an external vendor. This change reduced the overall number of animals and cages maintained and contributed to an increase in live birth rates. Due to these changes and increases in efficiency, GEMMSR staffing was reduced by two staff members, whil