Poly (ADP-ribosyl)ation as one of the molecular events that accompany mammalian spermatogenesis

It is known that mammalian spermatogenesis is a synchronous process of cellular differentiation during which morphological changes occur, concomitantly with alterations in the complement of constituent proteins, that reflect differences in the mRNA populations coding for stage-specif ic proteins. Moreover, the most dramatic changes in chromatin structure observed in eukaryotes, take place during spermiogenesis, and the main nuclear processes occur in well-defined cell stages. Rat test is has been used as experimental model in a research project carried out at various levels , represented by rat germinal cel ls (primary and secondary spermatocytes, round spermatids), chromatin fractions (transcriptionally active chromatin, nuclear matrix, MARs) and purified nuclear proteins (histone and non-histone proteins). Specific experiments have been carried out in order to determine the poly(ADPR)polymerase content at different stages of germ-cell differentiation, the poly(ADP-ribose) amount, length and complexity inside the nucleus, and the poly(ADP-ribose) acceptors among tissueand stage-specific nuclear proteins. The results indicate that regulation of the poly(ADPribosyl)ation system accompanies the earlier phases of the germinal cell differentiation. Indeed, poly(ADPribose)polymerase is particularly active in primary spermatocytes, being possibly implicated in the recombination events that characterize the pachytene phase of the meiot ic divis ion. Different c lasses of poly(ADPribose) modify different chromatin fractions (DNase I-sensitive, DNase I-resistant chromatin, and nuclear matrix) implicated in DNA replication, repair and transcription. Moreover, the H1 variant H1t, specifically expressed in pachytene spermatocytes, represents the main poly(ADPribose) acceptor, together with poly(ADPR)polymerase itself , in rat germ-cells . Its modification can amplify the role of histone H1 variants as modulators of chromatin structure.