Immunocytochemical localization of ubiquitin and proteasomes in spermatids during spermiogenesis of Chara vulgaris (Charophyceae)

Immunocytochemistry with anti-ubiquitin and anti-proteasome antibodies revealed antigenic signals in spermatids of Chara vulgaris in all ten spermiogenesis phases defined on the basis of morphological features. The strongest antigenic signals, indicating the presence of both ubiquitin and proteasome, were observed mainly in the cytoplasm in early and mid-spermiogenesis (phases II-V). During the transition of histone into protamine-type proteins, stronger anti-ubiquitin and anti-proteasome antigenic signals were present in the nucleus than in the cytoplasm (phases VII - VIII). In late spermiogenesis both types of signals were very scarce. We hypothesiZe that the roles of the proteasome/ubiquitin system may be: (1) participation in the degradation of shortlived proteins that appear temporarily after gene expression is triggered and initiates the programme of major ultrastructural changes in spermatids in early spermiogenesis; and (2) participation in the transition of histones into protamine-type proteins during late spermiogenesis, and in the remodelling of chromatin into extremely compact forms characteristic of generative cells.