Dynamic stem cell states: naïve to primed pluripotency in rodents and humans

Abstract

and N.N (noa.novershtern@weizman.ac.il). PrefaceThe molecular mechanisms and signalling pathways that regulate the in vitro preservation of distinct pluripotent stem cell configurations, and their induction in somatic cells via direct reprogramming approaches, continue to constitute a highly exciting area of research. In this review, we provide an integrative synthesis on recent discoveries related to isolating unique naïve and primed pluripotent stem cell states with altered functional and molecular characteristics, and from different species. We overview pathways underlying pluripotent state transitions and interconversion in vitro and in vivo. We conclude by highlighting unresolved key questions, future directions and potential novel applications of such dynamic pluripotent cell states. IntroductionPluripotency describes cells that have the potential to give rise to cells from all three embryonic germ-layers and possibly to primordial germ cells (PGCs), but not extra-embryonic tissues 1 . While pluripotency is a transient state in vivo, pluripotent cells can be derived from different stages of early embryonic development and indefinitely maintained in an artificially induced self-renewal state in vitro, by supplementing exogenous cues 2 . Thus, it is important to stress that self-renewal is not a defining feature of pluripotency and is only transiently assembled during early development. Pluripotency is highly dynamic and evolves at different stages of pre-and post-implantation stages 3 . However, the self-renewal aspect is a highly useful in vitro artificial "engineering trick" 4 that has brought pluripotent cells to the front stage as a tool for tissue replacement, disease modelling and animal engineering technologies 5 .There are multiple pluripotent stem cell types that can be isolated from vertebrates, including rodents and human, typically annotated based on their donor cell-of-origin (Fig. 1). Embryonic stem cells (ESCs) are isolated from the inner cell mass (ICM) of developing pre-implantation mouse or human blastocysts [6][7][8] . Epiblast stem cells (EpiSCs) are isolated from mouse postimplantation epiblasts 9,10 , however equivalent derivations haven't been attempted with human embryos due to justified ethical complexities. Early rodent migrating PGCs can be converted in vitro into pluripotent ESC-like cells termed embryonic germ cells 11,12 . Mouse neonatal and adult spermatogonial stem cells can be reverted toward pluripotency and generate male germ stem cells (GSCs) [13][14][15] . The latter have the disadvantage of retaining only male imprint signature, which can increase tumorigenic potential 15 . Intriguingly, stable and validated EGs and GSCs have not been isolated from primates thus far 16,17 (Fig. 1).Somatic cell reprogramming provides alternative routes for isolating pluripotent cell types. Human and rodent somatic cells can be artificially reprogrammed into ESC-like cells following reprogramming via nuclear transfer, termed NT-ESCs [18][19][20] . Ten years ago, Yamanaka established d...

Esrrb, an estrogen‐related receptor involved in early development, pluripotency, and reprogramming

“…Among these two broad classes of activities can be distinguished: the core components, Oct4 and Sox2, display stable expression and provide the constant input that the network requires for its function; additionally, a large group of ancillary TFs —incuding Nanog, Klfs, Tbx3, Nr5a2, Dax1, Tfcp21l, and Esrrb—present expression levels that are rapidly adjusted in the cells in response to developmental cues. This confers flexibility to the pluripotency network: changes in the activity of these factors modulate the balance between maintenance and loss of pluripotency—reviewed in . This pluripotent state, defined ‘naïve’ , presents unique features in terms of transcriptional permissivity, global chromatin accessibility, and reduced dependence on the deposition of repressive chromatin modifications .…”

“…Upon implantation, Nanog and a subset of ancillary TFs—including Klfs, Tbx3, Nr5a2, Dax1, Tfcp21l, and Esrrb—are sharply downregulated . Epiblast cells transit to a ‘primed’ state , readily amenable to somatic differentiation and characterized by more conventional mechanisms of chromatin regulation . EpiSC lines mirror in culture these changes, lacking expression of preimplantation pluripotency factors, including Esrrb , and displaying random X inactivation .…”

Zfp281 Coordinates Opposing Functions of Tet1 and Tet2 in Pluripotent States

“…Notably, manipulation of key signaling pathways is sufficient to force specific cell types to undergo global transcriptional changes in order to acquire new identities, including pluripotency (Chou et al, 2008). A great interest has thus emerged to understand how these alternative pluripotent identities are regulated (Weinberger et al, 2016; Wu and Izpisua Belmonte, 2015). In mouse embryonic stem cells (ESCs), standard culture conditions containing serum and leukemia inhibitory factor (LIF) (hereafter “SL”) support the self-renewal and maintenance of a heterogeneous or metastable pluripotent state (Marks et al, 2012).…”

Stem Cells: A Renaissance in Human Biology Research

“…Despite the usefulness of primed hPSCs, whether mESC-like naive hPSCs can be captured and stabilized in culture has been a major focus of human stem cell biology in recent years (Weinberger et al, 2016). Several notable advantages associated with naive pluripotency, such as high single cell cloning efficiency, facile genome editing capability and higher developmental potential, can facilitate gene targeting, relieve researchers from tedious clump passaging, and generate more mature cells for transplantation.…”