Regulation of myelin basic protein (MBP) gene expression by thyroid hormone has been investigated in rodent brain. Quantitation of the 4 major alternatively spliced transcripts by RNase protection assay showed that the individual mRNAs, corresponding to MBP isoforms 21.5, 18.5, 17, and 14 kDa, were decreased from 2- to 17-fold at all ages studied (4-60 days) in hypothyroid animals when compared to euthyroid, but the timing of onset of expression was not altered. MBP mRNA was also reduced in young adult rats thyroidectomized at the age of 5-6 weeks and was restored to normal by thyroxine administration. Nuclear run-off assays showed that the rate of MBP gene transcription is dependent on thyroid state. Co-transfection of MBP (-256/+1)-chloramphenicol acetyltransferase chimeric gene with a plasmid expressing thyroid hormone receptor α, and in the presence of 3,5,3′-triiodothyronine, into NIH3T3 or NG108-15, increased chloramphenicol acetyltransferase expression 4-fold. Using a footprinting technique and Spodoptera frugiperda 9 (Sf9) nuclear extract infected with baculovirus expressing TRα, we have identified a single DNA-binding site (-186/-163) for the receptor. A part of this region contains the AGGACA sequence found in thyroid hormone-responsive elements of other 3,5,3′-triiodothyronine-regulated genes. Our finding of a specific hormone-receptor interaction with the MBP promoter region is the first direct demonstration of a thyroid hormone-responsive element in a brain-specific gene.
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - Dec 5 1991|
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