Transcriptional regulatory networks in epiblast cells and during anterior neural plate development as modeled in epiblast stem cells

Abstract

Somatic development initiates from the epiblast in post-implantation mammalian embryos. Recent establishment of epiblast stem cell (EpiSC) lines has opened up new avenues of investigation of the mechanisms that regulate the epiblast state and initiate lineage-specific somatic development. Here, we investigated the role of cell-intrinsic core transcriptional regulation in the epiblast and during derivation of the anterior neural plate (ANP) using a mouse EpiSC model. Cells that developed from EpiSCs in one day in the absence of extrinsic signals were found to represent the ANP of ~E7.5 embryos. We focused on transcription factors that are uniformly expressed in the E6.5 epiblast but in a localized fashion within or external to the ANP at E7.5, as these are likely to regulate the epiblast state and ANP development depending on their balance. Analyses of the effects of knockdown and overexpression of these factors in EpiSCs on the levels of downstream transcription factors identified the following regulatory functions: cross-regulation among Zic, Otx2, Sox2 and Pou factors stabilizes the epiblastic state; Zic, Otx2 and Pou factors in combination repress mesodermal development; Zic and Sox2 factors repress endodermal development; and Otx2 represses posterior neural plate development. All of these factors variably activate genes responsible for neural plate development. The direct interaction of these factors with enhancers of Otx2, Hesx1 and Sox2 genes was demonstrated. Thus, a combination of regulatory processes that suppresses non-ANP lineages and promotes neural plate development determines the ANP.

Location of transient ectodermal progenitor potential in mouse development

“…Studies in mouse EpiSCs and human embryonic stem cells (ESCs) also revealed that inhibition of Nodal signaling by SB431542 (Inman et al, 2002;Laping et al, 2002) attenuates mesoderm/endoderm differentiation and promotes neural induction (Chng et al, 2010;Patani et al, 2009;Vallier et al, 2009). A recent study further revealed that cells developing from EpiSCs in the absence of extrinsic signals (including Nodal signaling) express levels of core transcription factors similar to the anterior neural plate of ~E7.5 embryos (Iwafuchi-Doi et al, 2012). We show here that Nodal inhibition is not merely an enhancer of neural fate.…”

“…Epiblast cells from Nodal −/− embryos readily differentiate into neurons in explant culture (Camus et al, 2006). Studies in mouse EpiSCs and human ESCs also revealed that inhibition of Nodal signaling promotes neural induction (Chng et al, 2010;Iwafuchi-Doi et al, 2012;Patani et al, 2009;Vallier et al, 2009).…”

Head formation: OTX2 regulates Dkk1 and Lhx1 activity in the anterior mesendoderm

“…Chimera experiments have shown that OTX2 acts cellautonomously to maintain the expression of the anterior neuronal markers Hesx1, Wnt1, Cdh4 and Efna2 in the ANE (Rhinn et al, 1999), whereas inactivating Otx2 in epiblast stem cells impairs the differentiation of anterior neural tissues (Iwafuchi-Doi et al, 2012;Acampora et al, 2013). These results highlight the intrinsic requirement of Otx2 activity in the ANE for differentiation.…”

Single Cell Analysis Reveals Concomitant Transcription of Pluripotent and Lineage Markers During the Early Steps of Differentiation of Embryonic Stem Cells

“…In mouse, neural stem cells prepared from the whole cerebrum of E14 embryos were found to express Pou5f1, although at low levels [42]. Expression of Pou5f1 was also detected by qRT-PCR in early populations of Sox1-expressing neural plate cells derived from epiblast stem cells [43]. Recently, the coexpression of pluripotent and early neuronal markers (POU5F1 and PAX6) in lineageprimed human ESCs was confirmed by single-cell qRT-PCR [11].…”