Immunoelectron microscopic visualization of intermediate basic proteins HPI1 and HPI 2 in human spermatids and spermatozoa

In humans, intermediate basic proteins HPI I and HPL are considered as common precursors of the P 2 protamine family, according to data provided by structural studies of these proteins.The occur- rence and fate of proteins HPI, and HP1 2 were investigated in nuclei of human spermatids and sper- matozoa by means of immunoelectron microscopy.A specific polyclonal antibody against a synthetic peptide overlapping the N-terminus of HPI 1 and HPL was prepared and used to detect these proteins on sections of testis and ejaculated sperm.A quantitative analysis of labelling density was performed on micrographs using an interactive image analysis system.The first signs of labelling of intermediate basic proteins appeared in spermatid nuclei at steps 4-5 of spermiogenesis, i.e. during the chroma- tin condensation process.The nuclear labelling density strongly increased in elongating spermatids (steps 5 and 6) and then sharply decreased from step 6 to step 8 of spermiogenesis.However, weak labelling persisted in the nuclei of mature spermatids and ejaculated spermatozoa.The present results show that the intermediate basic proteins HPI! and HPL are synthesized in large amounts in human spermatids during elongation phase and disappear almost totally in mature spermatids when deposition of protamines is completed in condensed nuclei.© Inra/Elsevier, Paris intermediate basic proteins / protamines / male gamete / spermiogenesis / immunocytochemistry Résumé -Mise en évidence par immunocytochimie ultrastructurale des protéines basiques intermédiaires HPh et HP1 2 dans les spermatides et les spermatozoïdes humains.Chez l'homme, les protéines basiques intermédiaires HPI I et HPL sont considérées comme les précurseurs com- muns des protamines P 2 , selon les données fournies par les études structurales de ces protéines.La 1 mise en place et le devenir des protéines HPI I et HP1 2 ont été étudiées dans les noyaux des sperma-