Dynamic Equilibrium and Heterogeneity of Mouse Pluripotent Stem Cells with Distinct Functional and Epigenetic States

Abstract

SUMMARY Embryonic stem cells (ESC) are apparently homogeneous self-renewing cells, but Stella, a marker of preimplantation embryos and germ cells showed heterogeneous expression in ESCs. Here we show that the Stella-positive ESCs were like the inner cell mass (ICM) while the Stella-negative cells were like the epiblast cells, although these populations exhibited interchangeability that reflected an adherence to an inherent program. Thus, ESCs are in a metastable state since they shift between the ICM- and epiblast-like phenotypes, which provides an insight into their instability, plasticity and pluripotency. This equilibrium was skewed reversibly by environmental and epigenetic cues; for example, the absence of signals from feeder cells caused a shift towards an epiblast-like state while trichostatin A, an inhibitor of histone deactelylase, restored Stella-positive population. Consistently, the two populations showed different histone modifications but with hypomethylated DNA in stella locus, as well as functional differences when induced to undergo differentiation. The Stella-negative cells were apparently more like the post-implantation epiblast-derived stem cells (EpiSCs), except that the stella locus was hypermethylated and repressed in the latter, which denotes a robust boundary between ESCs and EpiSCs.