Expression of the transcription factor Oct4, a marker of pluripotency, is a necessary prerequisite for development of both normal and cloned embryos. In the July 15 Current Biology, James Byrne and colleagues at the Wellcome Trust/Cancer Research UK Institute of Cancer and Developmental Biology report the expression of Oct4 during reprogramming of transferred differentiated nuclei into Xenopus oocytes. Their results indicate a repression of expression of differentiation markers and a rapid and strong induction of the Oct4 transcription factor (Current Biology, 13:1206-1213, July 15, 2003).

Byrne et al. transferred nuclei from about 100 fully differentiated mouse thymocytes into the germinal vesicles of Xenopus oocytes and monitored Oct4 expression by reverse transcription polymerase chain reaction (RT-PCR) during incubation of the oocytes. They observed fully spliced transcripts as early as 2 days after incubation at 18°C—the equivalent of 12 hours at 37°C—and also after 5.5, 7, and 9...

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