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First published online 22 February 2005
doi: 10.1242/jcs.01706
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Research Article |
1 Department of Biological Science, The University of Tulsa, 600 S College Ave., Tulsa, OK 74104-3189, USA
2 Department of Pediatrics and Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
3 Department of Anatomy and Cell Biology, University of Iowa College of Medicine, Iowa City, IA 52242, USA
* Author for correspondence (e-mail: bamendt{at}ibt.tamhsc.edu)
Accepted 6 January 2005
PITX2, ß-catenin and lymphoid enhancer factor (LEF-1) are required for the inductive formation of several epithelial-derived organs, including teeth. Lef-1 is expressed in the dental epithelium after Pitx2, and both factors have overlapping expression patterns in the tooth bud and cap stages. Our analysis of Pitx2–/– mutant mice showed reduced Lef-1 expression in facial tissues by RT-PCR and quantitative RT-PCR. Consistent with these results we show that the human 2.5 kb LEF-1 promoter is activated by PITX2. Furthermore, the LEF-1 promoter is differentially activated by PITX2 isoforms, which are co-expressed in dental epithelium. The 2.5 kb LEF-1 promoter contains two regions that act to inhibit its transcription in concert with PITX2. The proximal region contains a Wnt-responsive element (WRE) that attenuates PITX2 activation. LEF-1 cannot autoregulate LEF-1 expression; however co-transfection of PITX2 and LEF-1 result in a synergistic activation of the 2.5 kb LEF-1 promoter. LEF-1 specifically interacts with the PITX2 C-terminal tail. Deletion of a distal 800 bp segment of the LEF-1 promoter resulted in enhanced PITX2 activation, and increased synergistic activation in the presence of LEF-1. Furthermore, ß-catenin in combination with PITX2 synergistically activates the LEF-1 promoter and this activation is independent of the Wnt-responsive element. ß-catenin directly interacts with PITX2 to synergistically regulate LEF-1 expression. We show a new mechanism where LEF-1 expression is regulated through PITX2, LEF-1 and ß-catenin direct physical interactions. LEF-1 and ß-catenin interactions with PITX2 provide new mechanisms for the regulation of PITX2 transcriptional activity.
Key words: LEF-1, ß-catenin, PITX2, Gene expression, Transcription
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