Depletion in nuclear spermine during human spermatogenesis, a natural process of cell differentiation

Polyamines (PA), polycations present in all mammalian cells, are essential for cell proliferation and differentiation. In vitro, PA are known to bind to DNA with a high affinity. In vivo, the intimate association of endogenous PA with highly condensed chromatin has been reported. During spermatogenesis, when processes of cell proliferation and differentiation take place, the potential role of polyamines has not been studied in depth. We report here the PA levels measured in human spermatogenic cell nuclei at different stages of differentiation. Cell populations (spermatocytes and round, elongating, or elongated spermatids) were obtained after submitting human testes to a trypsin-deoxyribonuclease digestion, then to a centrifugal elutriation and Percoll gradient centrifugation. A significant and progressive nuclear spermine level decrease was observed from primary spermatocytes to elongated spermatids. This release of spermine from nuclei was concomitant with three major events in mammalian spermiogenesis: the reduction of DNA transcription activity, the replacement of histone proteins by protamines, and the compaction of chromatin. This is the first report arguing a release of nuclear spermine during an in vivo physiological cell differentiation process.