Immunocytochemical localization of nuclear protamine in boar spermatozoa during epididymal transit

Protamine was specifically demonstrated in boar spermatozoa collected from the rete testis, caput, corpus and cauda epididymidis and the ejaculate by immunoelectron microscopy, using anti-boar or anti-ram protamine antisera and an indirect post-embedding immunogold technique. Spermatozoa from all collection sites stained after incubation although with different degrees of labelling. Controls were negative. Labelling increased from the rete testis towards the epididymal corpus, where it was most intense, decreasing sharply thereafter. The weakest binding of the assayed antibodies was obtained in the ejaculated spermatozoa but it could be reversed by in-vitro induction of chromatin decondensation with sodium dodecyl sulphate and the metal-chelating EDTA. The finding of a significant decrease in the immunolabelling detected from the corpus epididymidis onwards indicates a critical point for the interaction between DNA and the protamines in boar spermatozoa during the epididymal maturation.