Abstract
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 beta-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 beta-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 beta-catenin/Tcf-dependent transcription is required prior to MBT for dorsal-ventral patterning in Xenopus.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Blastula / metabolism
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Cell Division
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Cytoskeletal Proteins / metabolism
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Cytoskeletal Proteins / physiology*
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Embryo, Nonmammalian / physiology*
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Gene Expression Regulation, Developmental*
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Genes, Dominant
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HMGB Proteins / metabolism
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HMGB Proteins / physiology*
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Lithium / pharmacology
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Luciferases / metabolism
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Nodal Signaling Ligands
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Phenotype
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Plasmids / metabolism
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Protein Biosynthesis
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction
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TCF Transcription Factors
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Time Factors
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Trans-Activators / metabolism
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Trans-Activators / physiology*
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Transcription Factor 7-Like 1 Protein
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Transcription Factors / metabolism
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Transcription Factors / physiology*
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Transcription, Genetic
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Transcriptional Activation
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Xenopus / embryology*
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Xenopus Proteins*
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beta Catenin
Substances
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CTNNB1 protein, Xenopus
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Cytoskeletal Proteins
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HMGB Proteins
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Nodal Signaling Ligands
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TCF Transcription Factors
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Trans-Activators
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Transcription Factor 7-Like 1 Protein
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Transcription Factors
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Xenopus Proteins
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beta Catenin
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nodal5 protein, Xenopus
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nodal6 protein, Xenopus
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Lithium
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Luciferases