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Oct-1, silencer sequence, and GC box regulate thyroid hormone receptor beta1 promoter
T Nagasawa1, T Takeda, K Minemura
1Department of Medicine, The University of Chicago, IL 60637, USA.
Molecular and Cellular Endocrinology
|June 20, 1997
Summary
Thyroid hormone receptors (TRs) are vital for brain development. This study found that proteins binding to silencer and GC box elements in the TR beta1 promoter are more abundant in fetal brains, while Oct-1 is more abundant in adult brains, influencing TR beta1 expression.
Area of Science:
- Neuroscience
- Molecular Biology
- Endocrinology
Background:
- Thyroid hormone is essential for brain development, and its receptors (TRs) mediate its effects.
- TR alpha mRNA is present throughout development, but TR beta1 mRNA levels increase significantly from fetal to adult stages in the brain.
- Understanding the regulation of TR beta1 expression is crucial for comprehending thyroid hormone's role in brain maturation.
Purpose of the Study:
- To investigate the regulatory factors controlling TR beta1 gene expression in the mouse brain during development.
- To compare the binding of nuclear proteins to the TR beta1 promoter in fetal versus adult mouse brains.
- To elucidate the roles of specific promoter elements and transcription factors in differential TR beta1 expression.
Main Methods:
- Comparative analysis of mouse fetal and adult brain nuclear extracts using DNase I footprinting and electrophoretic gel mobility shift assays (EMSA) on the TR beta1 promoter.
- Transient transfection studies in COS 1 cells utilizing a luciferase reporter assay with wild-type and mutated TR beta1 promoter constructs.
- Overexpression studies of specific transcription factors, including Oct-1, in conjunction with promoter-reporter constructs.
Main Results:
- Fetal brain nuclear extracts showed stronger binding to silencer and GC box elements within the TR beta1 promoter region (-950 to -717) compared to adult extracts.
- Electrophoretic gel mobility shift assays revealed higher affinity binding of fetal proteins to silencer, GC box, and E box sequences.
- Adult brain extracts exhibited increased binding to the octamer binding site, primarily mediated by Oct-1, while fetal extracts showed stronger binding to other factors at this site.
Conclusions:
- The TR beta1 promoter is negatively regulated by proteins binding to silencer and GC box elements, which are more abundant in fetal brains.
- Oct-1 positively regulates TR beta1 promoter activity and is more abundant in adult brains.
- Differential expression of these regulatory factors contributes to the higher levels of TR beta1 observed in late fetal and adult brains, impacting brain development.