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DNA binding and transactivating properties of the paired and homeobox protein Pax4
A Kalousová1, V Benes, J Paces
1Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Prague, Czech Republic. Anna@biomed.cas.cz
Abstract:
Transcription factors Pax-4 and Pax-6 are known to be key regulators of pancreatic cell differentiation and development. We report on the cloning of a mouse Pax-4 gene, which contains 10 exons, spanning a 4. 7-kbp region. The gene-targeting experiments revealed that Pax-4 and Pax-6 cannot substitute for each other in tissue with overlapping expression of both genes. We identified DNA-binding specificities of Pax-4 paired domain and paired-type homeodomain. Despite the different Pax-4 amino acid residues in positions responsible for Pax-6 paired-domain specificity, the DNA-binding specificities of Pax-4 and Pax-6 are similar. The Pax-4 homeodomain was shown to preferentially dimerize on DNA sequences consisting of an inverted TAAT motif, separated by 4-nucleotide spacing. The Pax-4 transactivation domain was localized within its C-terminal region, which transactivated GAL-based reporter 2.5-fold less than the C-terminal region of Pax-6. We believe that Pax-4 can act as a Pax-6 "repressor," due to the competition for binding sites and lower transactivation potential of Pax-4.
Insights
Transcription factors Pax-4 and Pax-6 regulate pancreatic development. Gene targeting shows they are not interchangeable, with Pax-4 potentially acting as a Pax-6 repressor due to binding competition and lower activity.
Area of Science:
- Developmental Biology
- Molecular Genetics
Background:
- Transcription factors Pax-4 (Paired box 4) and Pax-6 (Paired box 6) are crucial for pancreatic cell differentiation.
- Understanding their specific roles and interactions is key to comprehending pancreatic development.
Purpose of the Study:
- To clone and characterize the mouse Pax-4 gene.
- To investigate the functional relationship and DNA-binding specificities of Pax-4 and Pax-6.
- To determine the transactivation potential of Pax-4 compared to Pax-6.
Main Methods:
- Gene cloning and sequencing of the mouse Pax-4 gene.
- Gene-targeting experiments to assess functional redundancy.
- Electrophoretic mobility shift assays (EMSAs) to identify DNA-binding specificities.
- Reporter gene assays to measure transactivation potential.
Main Results:
- The mouse Pax-4 gene comprises 10 exons over a 4.7-kbp region.
- Pax-4 and Pax-6 are not functionally redundant in tissues where both are expressed.
- Identified DNA-binding specificities for Pax-4 paired domain and homeodomain, noting similarities with Pax-6 despite amino acid differences.
- Pax-4 homeodomain preferentially dimerizes on specific inverted TAAT motifs.
- Pax-4's transactivation domain exhibits lower activity than Pax-6's.
Conclusions:
- Pax-4 and Pax-6 have distinct, non-interchangeable roles in pancreatic development.
- Pax-4's lower transactivation potential and competitive binding suggest it may act as a repressor of Pax-6 activity.
- These findings provide insights into the regulatory mechanisms governing pancreatic cell differentiation.