Hyperacetylation of histone H4 in rat testis spermatids.

Acetate was incorporated efficiently into rat testis histones after an intratesticular injection of [3H]acetate. The pattern of in vivo acetylation of the testis histones was quite similar to the pattern of in vitro acetylation seen in a previous study with histones H3 and H4 acetylated to the greatest extent [13]. Acetylation of one or more of the major testis H2A variants was confirmed by analysis of these histones on high resolution polyacrylamide gels (PAGE) containing Triton X-100. Of the four variants, H2A.1 appeared to be labeled to the greatest extent. When testis cells were separated into highly enriched populations of specific cell types by centrifugal elutriation after an intratesticular injection of labeled acetate, histone H4 from all fractions of cells was acetylated, but histone H4 from the fraction of cells most enriched in elongating spermatids was hyperacetylated. Thus, the in vivo hyperacetylation of histone H4 which occurs in elongating spermatids is a physiological event which occurs during the relatively short time period when the entire complement of histones is replaced by more basic, protamine-like proteins, and therefore must be one of the key steps in this dramatic protein transition.