Genetically engineered mice serve as a powerful tool for studying the molecular genetic basis of human cancer and for testing new cancer therapies. The main purpose of the Transgenic and Gene Targeted Mouse Shared Resource (TGTMSR) is to generate genetically altered mice for all Mayo Clinic investigators. The TGTMSR provides two main services, the generation of gene-targeted mice and the production of transgenic animals. The gene targeting service was established in 1999, while the transgenic service is a new service established in 2006 and included in this application for support. Services are very comprehensive allowing investigators with little or no prior experience in generating transgenics or knockouts to implement genetically altered mice into their research programs. We design and purify transgenic DNA constructs and inject these into fertilized eggs. We generate transgenic founders from these eggs and cross these mice to wildtype mice to transmit the transgene through the germline. Furthermore, we design gene targeting vectors (to generate classical or conditional knockouts, hypomorphic alleles or to introduce point mutations in endogenous genes), electroporate these into ES cells and screen for clones carrying the desired alteration by southern blotting. Correctly targeted clones are karyotyped and injected into host blastocysts. Chimeric males are bred to wildtype females to establish germline transmission of the targeted mutation. Our success rate of generating transgenics is thus far 100%, while that of gene targeting is >95%. All users over the current funding period have been Mayo Clinic Cancer Center (MCCC) members. Studies using mouse models generated by the TGTMSR have led to a series of scientific publications over the past 5 years, several of which were in outstanding scientific journals. A total of 27 grant applications supported by the TGTMSR were funded, 13 of which were from the NCI.