The Embryonic Stem Cell (ESC) Core is responsible for: Creating and providing state-of-the-art reagents for the production of targeted mutations in murine embryonic stem cells. Creating and maintaining quality-controlled embryonic stem cell lines from a variety of mouse backgrounds. Teaching the methodology of embryonic stem cell culture and manipulation. The ESC Core provides consultative services for Siteman Cancer Center members when they are designing knock-out or knock-in vectors, and it creates and distributes user-friendly plasmids that facilitate the generation of targeting vectors. By providing a comprehensive service, the ESC Core facilitates the production of gain-offunction and loss-of-function mouse models for Siteman Cancer Center faculty.