IMMUNOELECTRON MICROSCOPIC VISUALIZATION OF INTERMEDIATE BASIC-PROTEINS HPI1 AND HPI2 IN HUMAN SPERMATIDS AND SPERMATOZOA

In humans, intermediate basic proteins HPI1 and HPI2 are considered as common precursors of the P-2 protamine family, according to data prov ided by structural studies of these proteins. The occurrence and fate of proteins HPI1 and HPI2 were investigated in nuclei of human spermat ids and spermatozoa by means of immunoelectron microscopy. A specific polyclonal antibody against a synthetic peptide overlapping the N-term inus of HPI1 and HPI2 was prepared and used to detect these proteins o n sections of testis and ejaculated sperm. A quantitative analysis of labelling density was performed on micrographs using an interactive im age analysis system. The first signs of labelling of intermediate basi c proteins appeared in spermatid nuclei at steps 4-5 of spermiogenesis , i.e. during the chromatin condensation process. The nuclear labellin g density strongly increased in elongating spermatids (steps 5 and 6) and then sharply decreased from step 6 to step 8 of spermiogenesis. Ho wever, weak labelling persisted in the nuclei of mature spermatids and ejaculated spermatozoa. The present results show that the intermediat e basic proteins HPI1 and HPI2 are synthesized in large amounts in hum an spermatids during elongation phase and disappear almost totally in mature spermatids when deposition of protamines is completed in conden sed nuclei. (C) Inra/Elsevier, Paris.