Transició de proteïnes nuclears i condensació de la cromatina espermiogènica : proposta d'un model ancestral de l'espermiogènesi nuclear

We study the correlation between: i) nuclear protein exchange in spermiogenic nuclei,
ii) the chromatin condensation pattern, and iii) the acetylation of histones. The study is
applied to four species which demonstrate an increasing complexity in nuclear protein
transitions. In Sparus aurata histones remain in sperm nuclei. In Dicentrarchus labrax and
Monodonta turbinata the histones are substituted by a much more basic molecules. In spermiogenesis
of Sepia officinalis histones are replaced by a precursor protamine, which is
transformed into the protamine in the last phases of spermiogenesis. The results indicate
that in the first phase of spermiogenesis of all four species an identical process is involved,
in which: i) the chromatin looses typical somatic structure and ends up organized
into granules measuring 20 nm in diameter, and ii) the histones undergo a moderate acetylation.