The Mouse Breeding/Transgenic Core will maintain and breed inbred (C3H/HeN, BALB/c, C57BL/6), congenic and various transgenic and knockout strains to be used by all three projects. The core will also generate any new transgenic mice needed by the projects and be responsible for all transgenic screening. The core will provide milk from MMTV-infected mice to Core C (Virus Vector Core) for the isolation of MMTV. The health of the mice with regard to the development of mammary gland tumors or lymphomas will also be monitored by the Core. The core will also provide help to the projects with virus injections. The Core Leader, Dr. Glen Gaulton, will oversee the technician, Barbara Shields. Barbara Shields will make bi-monthly reports to the Executive Committee about the status of the core and will inform all members of the Program at scientific meetings about new technologies that might be used.