Wojtczak A, Popłońska K, Kwiatkowska M
Department of Cytophysiology, University of Łódź, Łódź, Poland.
Protoplasma. 2008 Nov;233(3-4):263-7. doi: 10.1007/s00709-008-0010-y. Epub 2008 Aug 6.
Phosphorylation of H2AX histone results not only from DNA damage (caused by ionizing radiation, UV or chemical substances, e.g. hydroxyurea), but also regularly takes place during spermiogenesis, enabling correct chromatin remodeling. Immunocytochemical analysis using antibodies against H2AX histone phosphorylated at serine 139 indirectly revealed endogenous double-stranded DNA breaks in Chara vulgaris spermatids in mid-spermiogenesis (stages V, VI and VII), when protamine-type proteins appear in the nucleus. Fluorescent foci were not observed in early (stages I-IV) and late (VIII-X) spermiogenesis, after replacement of histones by protamine-type proteins was finished. A similar phenomenon exists in animals. Determination of the localization of fluorescent foci and the ultrastructure of nuclei led to the hypothesis that DNA breaks at stage V, when condensed chromatin adheres to the nuclear envelope. This is transformed into a net-like structure during stage VI, probably allowing chromosome repositioning to specific regions in the mature spermatozoid. However, at stages VI and VII, DNA breaks are necessary for transformation of the nucleosomal structure into a fibrillar and finally the extremely condensed status of sleeping genes at stage X.
H2AX组蛋白的磷酸化不仅源于DNA损伤（由电离辐射、紫外线或化学物质如羟基脲引起），而且在精子发生过程中也会定期发生，从而实现正确的染色质重塑。使用针对丝氨酸139位点磷酸化的H2AX组蛋白的抗体进行免疫细胞化学分析间接揭示，在精子发生中期（V、VI和VII阶段），当细胞核中出现鱼精蛋白样蛋白时，普通轮藻精子细胞中存在内源性双链DNA断裂。在早期（I-IV阶段）和晚期（VIII-X阶段）精子发生过程中，鱼精蛋白样蛋白取代组蛋白完成后，未观察到荧光焦点。动物中也存在类似现象。对荧光焦点的定位和细胞核超微结构的测定得出一个假设，即在V阶段，当浓缩染色质附着于核膜时会发生DNA断裂。在VI阶段，这种结构会转变为网状结构，这可能有助于染色体重新定位到成熟精子细胞中的特定区域。然而，在VI和VII阶段，DNA断裂对于核小体结构转变为纤维状结构以及最终在X阶段将静止基因转变为极度浓缩状态是必要的。
