POSTTRANSCRIPTIONAL REGULATION OF H1-DEGREES AND H3.3B HISTONE GENES IN DIFFERENTIATING RAT CORTICAL-NEURONS

Accumulation of mRNAs encoding H1 degrees and H3.3, two histone replac ement variants, was studied in differentiating cortical neurons, cultu red in a serum-free medium, with or without triiodothyronine (T3) supp lementation We found that the levels of both H1 degrees and H3.3B mRNA s decrease in isolated neurons between the 2nd and 5th day of culture to the same extent as in vivo. At the same time, an active synthesis o f the corresponding proteins was evidenced. The effects of transcripti on inhibition by actinomycin D and the results of nuclear run-on exper iments suggest that H1 degrees and H3.3 expression is regulated mainly at the posttranscriptional level. Concerning T3, only marginal effect s were noticed, apart from up-regulation of both histone mRNAs at 2 da ys in culture. We propose one model for posttranscriptional regulation of the analyzed genes and discuss potential relationships to remodell ing of chromatin.