Epigenetic modifications in sex heterochromatin of vole rodents

Abstract

The genome of some vole rodents contains large blocks of heterochromatin coupled to the sex chromosomes. While the DNA content of these heterochromatic blocks has been extensively analyzed, little is known about the epigenetic modifications controlling their structure and dynamics. To better understand its organization and functions within the nucleus, we have compared the distribution pattern of several epigenetic marks in cells from two species, Microtus agrestis and Microtus cabrerae. We first could show that the heterochromatic blocks are identifiable within the nuclei due to their AT enrichment detectable by DAPI staining. By immunostaining analyses, we demonstrated that enrichment in H3K9me3 and HP1, depletion of DNA methylation as well as H4K8ac and H3K4me2, are major conserved epigenetic features of this heterochromatin in both sex chromosomes. Furthermore, we provide evidence of transcriptional activity for some repeated DNAs in cultivated cells. These transcripts are partially polyadenylated and their levels are not altered during mitotic arrest. In summary, we show here that enrichment in H3K9me3 and HP1, DNA demethylation, and transcriptional activity are major epigenetic features of sex heterochromatin in vole rodents.

DNA replication dynamics of vole genome and its epigenetic regulation

“…Furthermore, we also investigated several euchromatic marks such as H3K4 dimethylation (H3K4me2), H4K8 acetylation (H4K8ac), H3K9 acetylation (H3K9ac), as well as the level of DNA methylation (Additional file 1A). As shown before for male vole cells [23], the heterochromatic blocks from the X chromosomes of female Microtus cabrerae cells were depleted of euchromatic marks and their DNA was hypomethylated. In a previous study in male cells from voles, these repeats were shown to be transcribed [23].…”

“…As shown before for male vole cells [23], the heterochromatic blocks from the X chromosomes of female Microtus cabrerae cells were depleted of euchromatic marks and their DNA was hypomethylated. In a previous study in male cells from voles, these repeats were shown to be transcribed [23]. Hence, we performed transcription run-on analysis and measured the relative amount of nucleotide incorporation within the differently marked heterochromatic blocks.…”

“…In a previous study, we showed that in cell lines derived from male voles of two Microtus species ( M. agrestis and M. cabrerae ), the heterochromatic blocks from the sex chromosomes are often visible during interphase as bright dense regions of DAPI-stained chromatin [23]. Here, we have made use of this feature to investigate the epigenetic composition of the heterochromatic block coupled to the X chromosomes of female Microtus cabrerae cells.…”

“…Female Microtus cabrerae cells [45] as well as male Microtus cabrerae cells [23] were cultured in Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% fetal calf serum and 1 µM gentamicin in 5% CO 2 atmosphere at 37 °C. As positive control for 5mC staining, the mouse embryonal fibroblast W8 line [46] was used and cultured under standard conditions as described above with the addition of 1% non-essential amino acids.…”

Karyotypic diversity within the genus Makalata (Echimyidae: Echimyinae) of Brazilian Amazon: Chromosomal evidence for multiple species

“…The Y chromosome is morphologically similar between the two species, but the one in karyotype K is almost entirely heterochromatic, whereas that in karyotype L does not have evident CH (Fig 4C). This difference may reflect CH addition/deletion events or epigenetic mechanisms leading to the formation of heterochromatin [23][24][25]. The difference between the diploid numbers can be attributed to fusion-and/or fission-based chromosomal rearrangements, pericentric inversions and/or centromeric transpositions [26].…”