c-Jun (AP-1) activates BMP-4 transcription in Xenopus embryos.
Zygotic expression of the BMP-4 gene in Xenopus embryos is regulated by an auto-regulatory loop. Since AP-1 is known as a mediator of auto-regulatory loops both in the case of the Drosophila dpp and the mammalian TGF-beta genes, we have analysed the potential of Xenopus c-Jun (AP-1) as a mediator of BMP-4 expression during Xenopus development. RNA injection experiments revealed that both heteromeric c-Fos/c-Jun and homodimeric c-Jun/c-Jun strongly activate BMP-4 transcription, whereas BMP signaling was found to activate the Xenopus c-Jun gene only at a rather low extent. In addition, the lack of zygotic c-Jun transcripts until the end of gastrulation should exclude a role of AP-1 in the activation and the early expression of BMP-4 during gastrulation in vivo. However, at later stages of Xenopus development, we find a spatial overlap of c-Jun and BMP-4 transcripts which suggests that AP-1 might serve as an additional activatory component for the auto-regulation of BMP-4. Promoter/reporter and gel mobility shift assays demonstrate multiple responsive sites for AP-1 in the 5' flanking region and two in the second intron of the BMP-4 gene. We further demonstrate that AP-1 acts independently of Xvent-2 which has recently been shown to mediate the early expression of BMP-4 in gastrula stage embryos.
Knöchel
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S
Abteilung Biochemie, Universität Ulm, Albert-Einstein-Allee 11, D-89081, Ulm, Germany.
Schuler-Metz
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A
Knöchel
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W
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000235:genetics*; D017931:DNA Primers / Q000235:genetics; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D016758:Genes, jun; D017403:In Situ Hybridization; D007438:Introns; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D018808:Transcription Factor AP-1 / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation; D014981:Xenopus / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism; D029867:Xenopus Proteins
D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D017931:DNA Primers; D018808:Transcription Factor AP-1; D029867:Xenopus Proteins; C525812:bmp4 protein, Xenopus