Pluripotent embryonic stem cells (ESCs) may be generated by reprogramming somatic cells through transplantation of the somatic cell nucleus into an enucleated donor oocyte, a method referred to as somatic cell nuclear transplant (SCNT). Although this method has been successful in generating nuclear transfer-ESCs (NT-ESCs) in a variety of mammalian species, early embryonic arrest (prior to formation of the blastocyst) has prevented derivation of stable human NT-ESCs. Through systematic evaluation of the SCNT protocol, Tachibana et al. identified key factors limiting its success (i.e., early exit of the oocyte from meiosis and inadequate cytoplast activation posttransplant) and optimized the approach to successfully derive the first human NT-ESCs.
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