Ultrastructural immunolocalisation of histones (H2B, H3, H4), transition protein (TP1) and protamine in rabbit spermatids and spermatozoa nuclei. Relation to condensation of the chromatin.

The histones H2B, H3 and H4, the transition protein TP1 and protamine were localised using ultrastructural immunocytochemistry in nuclei of rabbit spermatids and spermatozoa. Histones are present in round spermatid nuclei and are lost during the elongation of nuclei. TP1 and protamine appear simultaneously in all nuclei during this period. TP1 is located at the periphery of chromatin cords, while protamine seems to be located at random in the same cords. TP1 is lost in most elongated spermatids during step 13 of spermiogenesis, and the protamine stays in all sperm nuclei. TP1 remains present in some old spermatids and ejaculated spermatozoa. In the rabbit, 3-6% of sperm nuclei decondense spontaneously. Most are characterised by a retention of TP1. Respective roles of TP1 and the protamine in spermatid nuclear condensation are discussed.