Laboratory of Cellular Biochemistry, Department of Animal Resource Sciences/Veterinary Medical Sciences, The University of Tokyo, Tokyo, Japan.
Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan.
Sci Rep. 2018 Apr 11;8(1):5811. doi: 10.1038/s41598-018-23832-2.
Trophoblast giant cells (TGCs) are one of the cell types that form the placenta and play multiple essential roles in maintaining pregnancy in rodents. TGCs have large, polyploid nuclei resulting from endoreduplication. While previous studies have shown distinct gene expression profiles of TGCs, their chromatin structure remains largely unknown. An appropriate combination of canonical and non-canonical histones, also known as histone variants, allows each cell to exert its cell type-specific functions. Here, we aimed to reveal the dynamics of histone usage and chromatin structure during the differentiation of trophoblast stem cells (TSCs) into TGCs. Although the expression of most genes encoding canonical histones was downregulated, the expression of a few genes encoding histone variants such as H2AX, H2AZ, and H3.3 was maintained at a relatively high level in TGCs. Both the micrococcal nuclease digestion assay and nucleosome stability assay using a microfluidic device indicated that chromatin became increasingly loose as TSCs differentiated. Combinatorial experiments involving H3.3-knockdown and -overexpression demonstrated that variant H3.3 resulted in the formation of loose nucleosomes in TGCs. In conclusion, our study revealed that TGCs possessed loose nucleosomes owing to alterations in their histone composition during differentiation.
滋养层巨细胞（TGCs）是形成胎盘的细胞类型之一，在维持啮齿动物妊娠中发挥多种重要作用。TGCs 具有大的、多倍体核，这是由于内复制产生的。虽然先前的研究表明 TGCs 具有明显不同的基因表达谱，但它们的染色质结构在很大程度上仍然未知。适当的经典和非经典组蛋白（也称为组蛋白变体）组合允许每个细胞发挥其特定的细胞类型功能。在这里，我们旨在揭示滋养层干细胞（TSCs）分化为 TGCs 过程中组蛋白使用和染色质结构的动态变化。尽管大多数编码经典组蛋白的基因表达下调，但少数编码组蛋白变体（如 H2AX、H2AZ 和 H3.3）的基因在 TGCs 中仍保持相对高水平表达。微球菌核酸酶消化实验和使用微流控装置的核小体稳定性实验均表明，随着 TSCs 的分化，染色质变得越来越松散。涉及 H3.3 敲低和过表达的组合实验表明，变体 H3.3 导致 TGCs 中形成松散的核小体。总之，我们的研究表明，TGCs 在分化过程中由于其组蛋白组成的改变而具有松散的核小体。
