Method of establishing mouse strain

A method for producing a chimeric mouse, the method comprising the step of transferring an aggregate of a first pluripotent stem cell, a second pluripotent stem cell comprising an epigenetic modification associated with lack of or low ability to form germ cells, and an embryo into a host mouse, wherein the first pluripotent stem cell is incorporated into the germline of the embryo for the purpose of strain establishment, wherein the second pluripotent stem cell is a cell deposited with the Patent Microorganisms Depositary, National Institute of Technology and Evaluation (Japan), and identified by accession number NITE BP-973, accession number NITE BP-1135, or accession number NITE BP-1136, and wherein the host mouse is a prepared pseudopregnant mouse and the embryo in the aggregate is a chimeric embryo, and wherein, upon transfer to the uterus of the host mouse, the host mouse carries the embryo to term, thereby producing the chimeric mouse.