Histone H3 trimethylation at lysine 9 marks the inactive metaphase X chromosome in the marsupial Monodelphis domestica

Abstract

In somatic cells of female marsupial and eutherian mammals, X chromosome inactivation (XCI) occurs. XCI results in the transcriptional silencing of one of the two X chromosomes and is accompanied by specific covalent histone modifications attributable to the inactive chromatin state. Because data about repressed chromatin of the inactive X chromosome (Xi) in marsupials are sparse, we examined in more detail the distribution of active and inactive chromatin markers on metaphase X chromosomes of an American marsupial, Monodelphis domestica. Consistent with data reported previously both for eutherian and marsupial mammals, we found that the Xi of M. domestica lacks active histone markers-H3K4 dimethylation and H3K9 acetylation. We did not observe on metaphase spreads enrichment of the Xi with H3K27 trimethylation which is involved in XCI in eutherians and was detected on the Xi in the interphase nuclei of mature female M. domestica in an earlier study. Moreover, we found that the Xi of M. domestica was specifically marked with H3K9 trimethylation, which is known to be a component of the Xi chromatin in eutherians and is involved in both marsupials and eutherians in meiotic sex chromosome inactivation which has been proposed as an ancestral mechanism of XCI.

The origin and evolution of vertebrate sex chromosomes and dosage compensation

“…Some modifications were completely absent from the marsupial Xi (Koina et al, 2009;Chaumeil et al, 2011), whereas others were restricted to specific windows of the cell cycle (Chaumeil et al, 2011). Of considerable surprise was the accumulation of marks on Xi that are associated with pericentromeric heterochromatin (Mahadevaiah et al, 2009;Rens et al, 2010;Chaumeil et al, 2011;Zakharova et al, 2011). Thus, it seems that the marsupial Xi bears an epigenetic signature similar to that of pericentromeric heterochromatin, and is unlike the XIST-associated facultative heterochromatin in eutherians.…”

X-inactivation and X-reactivation: epigenetic hallmarks of mammalian reproduction and pluripotent stem cells

“…Based on the accumulation of H3K27me3 on the marsupial inactive X-chromosome, it was proposed that imprinted X-inactivation may have a common mechanism with marsupials and placental mammals (Mahadevaiah et al 2009). However, subsequent studies revealed that trimethylation at H3K9 (H3K9me3) and HP1 are stable markers of marsupial inactive X-chromosomes and that H3K27me3 accumulation is transient and labile (Chaumeil et al 2011; Rens et al 2010; Zakharova et al 2011). H3K9me3 and HP1 are well-characterized markers of pericentromeric heterochromatin and are also conserved markers of mammalian PMSC in spermiogenesis (Namekawa et al 2007), supporting a notion that germline silencing is the ancestral driving force of imprinted X-inactivation in the absence of Xist RNA in marsupials.…”

Transcriptome Characteristics and X-Chromosome Inactivation Status in Cultured Rat Pluripotent Stem Cells

“…S8). This alternating pattern was previously found on the inactive X chromosome of other placental mammals and seems to reflect two different types of facultative heterochromatin acting in XCI [15,16,[38][39][40][41]. However, no H3K9me3 enrichment (excluding the centromeric region) was detected on the inactive X chromosome in the female rEFs used for the NF13 line generation.…”

“…5B-D and Supplementary Fig.S8). Using a combination of IF, RNA, and DNA FISH, we tested X chromosomes for loss of active chromatin marks and enrichment of repressive histone modifications that had been found on the inactive X chromosome in other mammals [15,16,[38][39][40][41]. In all the three cell lines, shortly after Xist RNA coating, X chromosome undergoing XCI was depleted in H3K4me2, an active chromatin marker, and enriched with H3K27me3 and ubiquitylated H2A (uH2A), repressive chromatin modifications.…”