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doi: 10.1242/10.1242/dev.00150

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ß-Catenin/Tcf-regulated transcription prior to the midblastula transition

¹ Department of Medicine (Hematology — Oncology) and Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
² Department of Cell Biology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA

^* Author for correspondence (e-mail: pklein{at}mail.med.upenn.edu)

Accepted 4 September 2002

Following fertilization, the zygotic genome in many organisms is quiescent until the midblastula transition (MBT), when large-scale transcription begins. In Xenopus embryos, for example, transcription is believed to be repressed until the twelfth cell division. Thus, although dorsal-ventral patterning begins during the first cell cycle, little attention has been given to transcriptional regulation in pre-MBT development. We present evidence that regulated transcription begins during early cleavage stages and that the ß-catenin—Tcf complex is required for the transcription of the Xenopus nodal genes Xnr5 and Xnr6 as early as the 256-cell stage. Moreover, inhibition of ß-catenin/Tcf function can block dorsal development, but only if the inhibition begins early and is maintained throughout pre-MBT stages. Dorsal development can be rescued in ventralized embryos if Tcf-dependent transcription is activated prior to MBT, but activation of Tcf after MBT cannot rescue ventralized embryos, suggesting that ß-catenin/Tcf-dependent transcription is required prior to MBT for dorsal-ventral patterning in Xenopus.

Key words: Wnt, ß-catenin, Tcf, LEF, Midblastula transition, transcription, Xenopus embryo, Lithium

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