Abstract
Mouse embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs) represent naive and primed pluripotency states, respectively, and are maintained in vitro by specific signalling pathways. Furthermore, ESCs cultured in serum-free medium with two kinase inhibitors (2i-ESCs) are thought to be the ground naïve pluripotent state. Here, we present a comparative study of the epigenetic and transcriptional states of pericentromeric heterochromatin satellite sequences found in these pluripotent states. We show that 2i-ESCs are distinguished from other pluripotent cells by a prominent enrichment in H3K27me3 and low levels of DNA methylation at pericentromeric heterochromatin. In contrast, serum-containing ESCs exhibit higher levels of major satellite repeat transcription, which is lower in 2i-ESCs and even more repressed in primed EpiSCs. Removal of either DNA methylation or H3K9me3 at PCH in 2i-ESCs leads to enhanced deposition of H3K27me3 with few changes in satellite transcript levels. In contrast, their removal in EpiSCs does not lead to deposition of H3K27me3 but rather removes transcriptional repression. Altogether, our data show that the epigenetic state of PCH is modified during transition from naive to primed pluripotency states towards a more repressive state, which tightly represses the transcription of satellite repeats.
Highlights
Pluripotency is defined as the ability of a stem cell to generate all three embryonic lineages
We first examined the distribution of H3K9me[3], the hallmark of heterochromatin, at pericentromeric heterochromatin (PCH)/CH regions in embryonic stem cells (ESCs) in serum and 2i conditions and in epiblast stem cells (EpiSCs) by immunofluorescence
The different types of pluripotent cell lines that can be derived from embryos reflect this progression: 2i-ESCs, serum-ESCs and EpiSCs, the former being the closest to the inner cell mass (ICM) and the latter, the closest to the late epiblast
Summary
Pluripotency is defined as the ability of a stem cell to generate all three embryonic lineages. ESCs are classically maintained in serum-containing medium supplemented with LIF that activates the STAT3 signalling pathway but can be cultured in serum-free medium with only inhibitors of two differentiation pathways: MAPK/ERK (mitogen-activated protein kinases/extracellular signal-regulated kinases) and GSK3 (glycogen synthase kinase 3) pathways[5] In this 2i medium, cells are in a ground naive state, with more efficient repression of lineage commitment markers and more homogenous expression of pluripotency genes than those cultured in serum/ LIF6,7. On the other hand, reverting EpiSCs into naive cells is a long and inefficient process, eliciting the notion of epigenetic barrier to reprogramming[18] These studies all suggest that each pluripotent cell type is characterized by a specific chromatin organization and epigenome. PCH in serum-ESCs shows some plasticity, as demonstrated in mutants that lacks either H3K9me[3] (Suv39h dn knockout) or DNA methylation (Dnmt knockout), where these missing marks are replaced by the typical facultative heterochromatin mark H3K27me[322,29,30]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
