James A. Byrne ^{1, 2}, Stina Simonsson ^{1, 2}, Patrick S. Western ^{1, 3}, and John B. Gurdon ^{1, 2}

¹ Wellcome Trust/Cancer Research UK Institute, Tennis Court Road, University of Cambridge, Cambridge CB2 1QR, United Kingdom
² Department of Zoology, University of Cambridge, Cambridge CB2 1QR, United Kingdom
³ Department of Physiology, University of Cambridge, Cambridge CB2 1QR, United Kingdom

Correspondence:   John B. Gurdon:     j.gurdon@welc.cam.ac.uk

Nuclear reprogramming by the transplantation of somatic cell nuclei to eggs (in second meiotic metaphase) is
always followed by a phase of chromosome replication and cell division before new gene expression is seen. To
help understand the mechanism of nuclear reprogramming, we have asked whether the nuclei of normal,
nontransformed, nondividing, and terminally differentiated mammalian cells can be directly reprogrammed,
without DNA replication, by Xenopus oocytes. We find that nuclei of adult mouse thymocytes and of adult
human blood lymphocytes, injected into Xenopus oocytes, are induced to extinguish a differentiation marker
and to strongly express oct-4, the most diagnostic mammalian stem cell/pluripotency marker. In the course of 2
days at 18°C, the mammalian oct-4 transcripts are spliced to mature mRNA. We conclude that normal
mammalian nuclei can be directly reprogrammed by the nucleus (germinal vesicle) of amphibian oocytes to
express oct-4 at a rate comparable to that of oct-4 in mouse ES cells. To our knowledge, this is the first
demonstration of a stem cell marker being induced in a differentiated adult human cell nucleus. This is an early step toward the long-term aim of developing a procedure for reprogramming readily accessible human adult
cells for cell replacement therapy.

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