Bao Li, Mei-Zi Zhang, Fang-Zhen Sun, Wei-Guang Liu, Wei-Hong Huang, Xiaomin Cao, Shuo-Guo Li, Xiao-Wei Liang, Xiu-Ying Huang, Fengqin Xu, and Long-Long Fu
In human sperm, a fraction of its chromatin retains nucleosomes that are positioned on specific sequences containing genes and regulatory units essential for embryonic development. This nucleosome positioning (NP) feature provides an inherited epigenetic mark for sperm. However, it is not known whether there is a structural constraint for these nucleosomes and, if so, how they are localized in a three-dimensional (3D) context of the sperm nucleus. In this study, we examine the 3D organization of sperm chromatin and specifically determine its 3D localization of nucleosomes using structured illumination microscopy. A fraction of the sperm chromatin form nucleosome domains (NDs), visible as microscopic puncta ranging from 40 μm to 700 μm in diameter, and these NDs are precisely localized in the post acrosome region (PAR), outside the sperm's core chromatin. Further, NDs exist mainly in sperm from fertile men in a pilot survey with a small sample size. Together, this study uncovers a new spatially-restricted sub-nuclear structure containing NDs that are consistent with NPs of the sperm, which might represent a novel mark for healthy sperm in human., Summary: Programmed gene expression is the key to life, confirmed experimentally in this study, which shows that nucleosomes in human sperm are specifically localized in genomic regions, guiding programmed gene expression.