Dazlin' pluripotent stem cells

Abstract

Pluripotent embryonic stem cells (ESCs) can be isolated from the inner cell mass (ICM) of blastocyst embryos and differentiate into all three germ layers in vitro. However, despite their similar origin, mouse embryonic stem cells represent a more naïve ICM-like pluripotent state whereas human embryonic stem cells exist in a post-implantation epiblast-like primed pluripotent state. Developing germ cells represent an in vivo cell population that is closely related to pluripotent stem cells. Indeed, ESCs can differentiate into functional primordial germ cells (PGCs) in vitro and a hallmark of naïve pluripotency is the expression of several germ cell markers. During my PhD research I investigated the significance of a germ cell signature, and particularly the role of Dazl, for the nature of pluripotency in ESCs. Insight in the mechanisms underlying pluripotency could also provide a better understanding of the interconvertability of different pluripotent states. Dazl is a germ cell specific RNA-binding protein and is essential for developing primordial germ cells (PGCs). We investigated the role of Dazl during in vitro and in vivo PGC development in mice as well as in ESCs using a Dazl-GFP reporter. Studying molecular markers of subpopulations within PGCs or ESCs provides insight in the balance between maintenance of pluripotency and differentiation in these cells. Our research has led to important insights on how Dazl controls pluripotency during germ cell development and provides a protective mechanism against pluripotent conversion and teratoma formation. We also found that Dazl is expressed and plays a role in naïve pluripotency and DNA demethylation in mESCs, and potentially also during the transition of primed to naïve human ESCs. These observations, combined with the indispensability of Dazl for the establishment of PGCs, suggest that by determining the precise mechanism of action of Dazl, we can shed unique light on the regulation of pluripotency and the epigenome across different mammalian species. Furthermore, we have explored the signaling pathways that govern the transition of pluripotent epiblast stem cells (EpiSCs) into ESCs. We have found that rapid and complete EpiSC reprogramming is triggered by simultaneous inhibition of EpiSC self-renewal and differentiation pathways, in combination with lipid activation of the orphan nuclear receptor, Nr5a2. This concept provides insight required modulation of the extracellular signaling networks that is needed to drive changes in cell identity and improves our understanding of reprogramming.