Reprogramming to pluripotency does not require transition through a primitive streak-like state

Abstract

Pluripotency can be induced in vitro from adult somatic mammalian cells by enforced expression of defined transcription factors regulating and initiating the pluripotency network. Despite the substantial advances over the last decade to improve the efficiency of direct reprogramming, exact mechanisms underlying the conversion into the pluripotent stem cell state are still vaguely understood. Several studies suggested that induced pluripotency follows reversed embryonic development. For somatic cells of mesodermal and endodermal origin that would require the transition through a Primitive streak-like state, which would necessarily require an Eomesodermin (Eomes) expressing intermediate. We analyzed reprogramming in human and mouse cells of mesodermal as well as ectodermal origin by thorough marker gene analyses in combination with genetic reporters, conditional loss of function and stable fate-labeling for the broad primitive streak marker Eomes. We unambiguously demonstrate that induced pluripotency is not dependent on a transient primitive streak-like stage and thus does not represent reversal of mesendodermal development in vivo.

Merging organoid and organ-on-a-chip technology to generate complex multi-layer tissue models in a human retina-on-a-chip platform

“…Total RNA isolation and gene expression analysis was performed as previously described (Raab et al, 2017). For quantification of the gene expression of the genes of interest, Taqman assays were purchased from Thermo Fisher Scientific, USA.…”

Cellular trajectories and molecular mechanisms of iPSC reprogramming

“…Thus, both mouse [30] and human [10,39] fibroblasts undergoing reprogramming transiently express regulators of later developmental stages including the primitive streak. While the functional relevance of this observation is debated [40], recent observations in a highly efficient mouse reprogramming system suggest that transient upregulation of transcription factors associated with the post-implantation epiblast coincides with acquisition of functional pluripotency as measured by the ability to give rise to entirely iPSC-derived animals [41]. The observation that intermediates of iPSC derivation express pluripotency regulators yet are prone to differentiation might reconcile studies claiming OKSM factors can trigger direct lineage conversions [42–44] with subsequent work demonstrating that such conversions – at least in mouse – entail transient acquisition of pluripotency features such as Nanog expression and X chromosome reactivation [45,46].…”

Zfp281 orchestrates interconversion of pluripotent states by engaging Ehmt1 and Zic2

“…Consistent with this possibility, a mesenchymal‐to‐epithelial transition is necessary for iPSC formation (Li et al , ; Samavarchi‐Tehrani et al , ), while the converse epithelial‐to‐mesenchymal transition is crucial for embryogenesis, e.g., during gastrulation and neural crest formation (Acloque et al , ). Although it is debated whether these observations reflect a shared developmental intermediate (Raab et al , ), they suggest that de‐differentiation and differentiation employ common mechanisms in opposite directions. Here, we systematically and functionally examine this concept using naïve pluripotent embryonic stem cells (ESCs) and primed pluripotent epiblast stem cells (EpiSCs; Smith, ).…”