Hybrid Embryonic Stem Cell-Derived Tetraploid Mice Show Apparently Normal Morphological, Physiological, and Neurological Characteristics Frieder Schwenk,1 Branko Zevnik,1 Jens Bru¨ning,2 MathiasRo¨hl,2Antje Willuweit,1 Anja Rode,1 Thomas Hennek,1 Gunther Kauselmann,1RudolfJaenisch,3 and Ralf Ku¨hn1* Artemis Pharmaceuticals GmbH1 and Klinik II und Poliklinikfu¨rInnere Medizin der Universita¨t Ko¨ln and Center of Molecular Medicine,2 Cologne, Germany, andWhiteheadInstitute for Biomedical Research and Department of Biology, Massachusetts Institute ofTechnology,Cambridge, Massachusetts3 胚胎聚集針 胚胎聚集針