IMMUNOEXPRESSION OF TESTIS-SPECIFIC HISTONE 2B IN HUMAN SPERMATOZOA AND TESTIS TISSUE

During mammalian spermatogenesis, the chromatin of the spermatogenic c ells is profoundly reorganized. Somatic histones are partly replaced b y testis-specific histones. These histones are then replaced by transi tion proteins and finally by protamines. This series of nucleoprotein rearrangements results in a highly condensed sperm cell nucleus. In co ntrast to spermatozoa from other species, human spermatozoa still cont ain a significant amount of histones, including testis-specific histon e 2B (TH2B). In the present study it is shown that an antibody targeti ng tyrosine hydroxylase, which has been found previously to cross-reac t with rat TH2B, also specifically immunoreacts with human TH2B on Wes tern blots, in immunohistochemistry of human testis tissue, and in imm unocytochemistry of decondensed human spermatozoa. In human testis tis sue, TH2B immunostaining first apparent in spermatogonia, shows marked variation, especially at the pachytene spermatocyte stage, and then r eaches an intense signal in round spermatids. Shortly before spermatid elongation, a portion of the spermatid nucleus, corresponding to the acrosomal region, loses its immunoreactivity. During condensation of t he spermatid nucleus, the immunodetectability of TH2B disappears gradu ally, from the anterior region of the nucleus onwards. At the final st ages of spermiogenesis, the immunostaining is completely absent. Immun ocytochemical staining of spermatozoa revealed no TH2B immunosignal, b ut immunostaining was observed when spermatozoa obtained from semen we re decondensed to make nuclear proteins accessible to the antibody. Th ere was, however, a striking intercellular variability in the intensit y of staining of spermatozoa within an ejaculate. In a population of 3 5 men attending our Andrology Clinic, we observed interindividual diff erences in total sperm TH2B content, which showed a significant, altho ugh not very pronounced, negative correlation with normal morphology ( P = 0.05).