Histone H1(0) mRNA and protein accumulate early during retinoic acid induced differentiation of synchronized embryonal carcinoma cells

Histone H1(o) expression in the developing cat retina

Histone H1(o) is a subtype of the non-core H1 histones located in the linker region of DNA between nucleosome cores and postulated to be involved in the regulation of gene expression. Studies in both the mouse retina and rat brain have correlated the terminal differentiation of cell types in these tissues to the expression of H1(o)a The expression of H1(o) in mouse retina occurs after light exposure suggesting that light may trigger the expression of H1(o). The aims of the present research were to: (1) describe the relationship of the appearance of H1(o) protein immunoreactivity to the formation of cell types and layers in the cat retina; and (2) determine whether H1(o) may be dependent on exposure to light or on other postnatal developmental events. We find the nuclei of ganglion, amacrine, and prospective bipolar cells contain H1(o) immunoreactivity before birth, prior to the terminal differentiation of these cells. In the cat retina, expression of H1(o) occurs prior to light exposure. These results show that the expression of H1 degrees protein is not required for the terminal differentiation of retinal cell types in the cat. Additionally, we find no requirement for light exposure prior to H1(o) expression. These findings are at variance with the findings in the mouse retina and are inconsistent with any cross species requirement for the expression of this histone in the terminal differentiation of cell types in the retina.

Thyroid hormone receptors bind to the promoter of the mouse histone H10 gene and modulate its transcription

It has been shown that the mouse histone H10 promoter contains a DNA element, composed of a direct repeat of the sequence GGTGACC separated by 7 nt, which is able to bind retinoic acid receptors and to modulate transcription of reporter genes following treatment with retinoic acid. We have now investigated whether this DNA motif is also responsive to thyroid hormone. We co-transfected CV-1 monkey kidney cells with chloramphenicol acetyltransferase (CAT) expression plasmids containing either 740 bp of the H10 wild-type promoter or five copies of the repeat element cloned in front of the thymidine kinase promoter and expression vectors for human thyroid hormone receptors (TRs) alpha or beta and retinoid X receptor alpha (RXR alpha). Treatment of transfected cells with triiodothyronine led to a dose-dependent increase in CAT activity. Transfection experiments with increasing amounts of expression vectors for either TR alpha or RXR alpha resulted in up to 6-fold enhancement of CAT transcription. Furthermore, point mutations within the half-sites of the response element of the H10 promoter, as well as deletions within the interspace region, lowered CAT activity to 60-80% of that of the wild-type control. Electrophoretic mobility shift assays showed that the repeat element was able to form retarded complexes with TR alpha homodimers, as well as with TR alpha-RXR alpha heterodimers. Our results suggest that thyroid hormone receptors are involved in the regulation of mouse histone H10 expression.