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Cell type-specific autoregulation of the Caudal-related homeobox gene Cdx-2/3
1Oncology Research Laboratory, The Toronto Hospital, University of Toronto, Toronto, Ontario M5G 2M1, Canada.
Abstract:
The caudal-related homeobox gene Cdx-2/3 is a critical "master" control gene in embryogenesis. Mice heterozygous for a null mutation in Cdx-2/3 exhibit multiple malfunctions including tail abnormalities, stunted growth, a homeotic shift in vertebrae, and the development of multiple intestinal adenomatous polyps, indicating that Cdx-2/3 is haplo-insufficient. In vitro studies have identified more than a half-dozen downstream target genes expressed in pancreatic and intestinal cells for this transcription factor. We have examined the transcriptional properties of the mouse Cdx-2/3 promoter. This promoter could be autoregulated in pancreatic and intestinal cells that express endogenous Cdx-2/3. In contrast, Cdx-2/3 transfection represses the Cdx-2/3 promoter in fibroblasts, which do not express endogenous Cdx-2/3. Since Cdx-2/3 activates proglucagon gene promoter in both pancreatic and intestinal cells and in fibroblasts, we suggest that some, yet to be identified, cell type-specific components are required for activating selected target gene promoters of Cdx-2/3, including the Cdx-2/3 promoter itself. Cdx-2/3 binds to the TATA box and another AT-rich motif, designated as DBS, within an evolutionarily conserved proximal element of the Cdx-2/3 promoter. The DBS motif is critical for the autoregulation, whereas the TATA box may act as an attenuating element for the autoregulatory loop. Finally, overexpression of Cdx-2/3 in a pancreatic cell line activated the expression of the endogenous Cdx-2/3. Taken together, our results indicate that the dose-dependent phenotype of Cdx-2/3 expression on its downstream targets in vivo could be regulated initially via a transcriptional network involving cell type-specific autoregulation of the Cdx-2/3 promoter.
Insights
The caudal-related homeobox gene Cdx-2/3 is essential for development. Its autoregulation in specific cells, involving the DBS motif, controls gene expression, impacting embryonic development and disease.
Area of Science:
- Developmental Biology
- Molecular Biology
- Genetics
Background:
- Caudal-related homeobox gene Cdx-2/3 is a master control gene in embryogenesis.
- Cdx-2/3 haploinsufficiency in mice causes developmental defects and polyps.
- Cdx-2/3 regulates downstream target genes in pancreatic and intestinal cells.
Purpose of the Study:
- To investigate the transcriptional properties of the mouse Cdx-2/3 promoter.
- To understand the autoregulation mechanism of the Cdx-2/3 gene.
- To identify factors involved in cell type-specific gene activation by Cdx-2/3.
Main Methods:
- Analysis of Cdx-2/3 promoter activity in different cell types (pancreatic, intestinal, fibroblasts).
- Transfection studies to examine Cdx-2/3's effect on its own promoter and other target genes.
- Identification of DNA binding sites (TATA box, DBS motif) within the Cdx-2/3 promoter.
Main Results:
- Cdx-2/3 promoter is autoregulated in pancreatic and intestinal cells but repressed in fibroblasts.
- Cdx-2/3 activates the proglucagon gene promoter in various cell types.
- The DBS motif is crucial for autoregulation, while the TATA box may attenuate it.
- Overexpression of Cdx-2/3 activates endogenous Cdx-2/3 expression in pancreatic cells.
Conclusions:
- Cell type-specific components are required for Cdx-2/3 to activate certain target promoters.
- Autoregulation of the Cdx-2/3 promoter involves specific DNA motifs and cell-specific factors.
- Transcriptional networks, including cell type-specific autoregulation, regulate Cdx-2/3's dose-dependent effects in vivo.