Kudo Ryoma, Yoshida Ikuya, Matiz Ceron Luisa, Mizushima Shusei, Kuroki Yoko, Jogahara Takamichi, Kuroiwa Asato
Reproductive and Developmental Sciences, Biosystems Science Course, Graduate School of Life Science, Hokkaido University, Sapporo, Japan.
Division of Reproductive and Developmental Biology, Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, Japan.
Cytogenet Genome Res. 2022;162(11-12):632-643. doi: 10.1159/000531275. Epub 2023 Jun 2.
X chromosome inactivation (XCI) is an essential mechanism for gene dosage compensation between male and female cells in mammals. The Okinawa spiny rat (Tokudaia muenninki) is a native rodent in Japan with XX/XY sex chromosomes, like most mammals; however, the X chromosome has acquired a neo-X region (Xp) by fusion with an autosome. We previously reported that dosage compensation has not yet evolved in the neo-X region; however, X-inactive-specific transcript (Xist) RNA (long non-coding RNA required for the initiation of XCI) is partially localized in the region. Here, we show that the neo-X region represents an early chromosomal state in the acquisition of XCI by analyses of heterochromatin and Barr body formation. We found no evidence for heterochromatin formation in the neo-X region by R-banding by acridine orange (RBA) assays and immunostaining of H3K27me3. Double-immunostaining of H3K27me3 and HP1, a component of the Barr body, revealed that the entire ancestral X chromosome region (Xq) showed a bipartite folded structure. By contrast, HP1 was not localized to the neo-X region. However, BAC-FISH revealed that the signals of genes on the neo-X region of the inactive X chromosome were concentrated in a narrow region. These findings indicated that although the neo-X region of the inactive X chromosome does not form a complete Barr body structure (e.g., it lacks HP1), it forms a slightly condensed structure. These findings combined with the previously reported partial binding of Xist RNA suggest that the neo-X region exhibits incomplete inactivation. This may represent an early chromosomal state in the acquisition of the XCI mechanism.
X染色体失活(XCI)是哺乳动物中雄性和雌性细胞之间基因剂量补偿的重要机制。冲绳刺鼠(Tokudaia muenninki)是日本本土的啮齿动物,与大多数哺乳动物一样具有XX/XY性染色体;然而,X染色体通过与常染色体融合获得了一个新X区域(Xp)。我们之前报道过,新X区域尚未进化出剂量补偿机制;然而,X失活特异性转录本(Xist)RNA(XCI起始所需的长链非编码RNA)部分定位于该区域。在这里,我们通过对异染色质和巴氏小体形成的分析表明,新X区域代表了XCI获得过程中的一种早期染色体状态。我们通过吖啶橙R带分析(RBA)和H3K27me3免疫染色,未发现新X区域有形成异染色质的证据。H3K27me3和巴氏小体成分HP1的双重免疫染色显示,整个祖先X染色体区域(Xq)呈现出二分折叠结构。相比之下,HP1未定位于新X区域。然而,BAC-FISH显示,失活X染色体新X区域上基因的信号集中在一个狭窄区域。这些发现表明,尽管失活X染色体的新X区域没有形成完整的巴氏小体结构(例如,它缺乏HP1),但它形成了一种略微浓缩的结构。这些发现与之前报道的Xist RNA的部分结合相结合,表明新X区域表现出不完全失活。这可能代表了XCI机制获得过程中的一种早期染色体状态。