ABSTRACT: The generation of induced pluripotent stem cells (iPSCs) by the forced expression of defined transcription factors in somatic cells holds great promise for the future of regenerative medicine. However, due to a poor understanding of the initial reprogramming mechanism, it is difficult to control the efficiency and quality of the iPSCs. Here we show that Zscan4, expressed transiently in 2-cell embryos and embryonic stem cells (ESCs), efficiently produces iPSCs from mouse embryo fibroblasts when coexpressed with Klf4, Oct4, and Sox2. Unlike other factors, Zscan4 is required only for the first few days of iPSC formation. Microarray analysis revealed transient and early induction of preimplantation-specific genes in a Zscan4-dependent manner. Our work indicates that Zscan4 is a previously unidentified potent natural factor that facilitates the reprogramming process through the recapitulation of the early embryonic program. V6.5 ES cells derived from an F1 hybrid strain (C57BL/6 x 129/Sv) were purchased from Thermo Scientific Open Biosystems. ES cells were cultured at 37C in 5% CO2 in a complete ES medium: DMEM, 15% FBS, 1000 U/ml LIF (ESGRO, Chemicon), 1 mM sodium pyruvate, 0.1 mM non-essential amino acids, 2 mM GlutaMAX, 0.1 mM -mercaptoethanol, penicillin, and streptomycin. V6.5 ES cells (5x105 cells) in suspension were cotransfected with 2 g of a linearized pCAG-Zscan4-ERT2 vector and 0.4 g of a PL452 vector (Liu et al., 2003) (a neomycin-resistant gene driven by a PGK promoter) using the Effectene (QIAGEN) according to the manufacturer s protocol, and plated in 100 mm cell culture dishes. After selecting with G418 for 8 days, resulting ES cell colonies were picked, expanded, and frozen. Subsequently, an ES-ZERT cell clone was selected based on the results of genotyping, qPCR, and puromycin-resistance. ES-ZERT cells (10-15 cells) were injected into 2N blastocysts and then transferred to E2.5 recipient females. After genotyping the pups, ZERT chimeric mice carrying pCAG-Zscan4-ERT2 DNA were established.
