Nanog safeguards early embryogenesis against global activation of maternal β-catenin activity by interfering with TCF factors

Abstract

Maternal β-catenin activity is essential and critical for dorsal induction and its dorsal activation has been thoroughly studied. However, how the maternal β-catenin activity is suppressed in the nondorsal cells remains poorly understood. Nanog is known to play a central role for maintenance of the pluripotency and maternal-zygotic transition (MZT). Here, we reveal a novel role of Nanog as a strong repressor of maternal β-catenin signaling to safeguard the embryo against hyperactivation of maternal β-catenin activity and hyperdorsalization. In zebrafish, knockdown of nanog at different levels led to either posteriorization or dorsalization, mimicking zygotic or maternal activation of Wnt/β-catenin activities, and the maternal zygotic mutant of nanog (MZnanog) showed strong activation of maternal β-catenin activity and hyperdorsalization. Although a constitutive activator-type Nanog (Vp16-Nanog, lacking the N terminal) perfectly rescued the MZT defects of MZnanog, it did not rescue the phenotypes resulting from β-catenin signaling activation. Mechanistically, the N terminal of Nanog directly interacts with T-cell factor (TCF) and interferes with the binding of βcatenin to TCF, thereby attenuating the transcriptional activity of β-catenin. Therefore, our study establishes a novel role for Nanog in repressing maternal β-catenin activity and demonstrates a transcriptional switch between β-catenin/TCF and Nanog/TCF complexes, which safeguards the embryo from global activation of maternal β-catenin activity.

Vertebrate Cell Differentiation, Evolution, and Diseases: The Vertebrate-Specific Developmental Potential Guardians VENTX/NANOG and POU5/OCT4 Enter the Stage

“…ScRNA sequencing (scRNA-seq) of zebrafish, Xenopus , primates (i.e., human and marmoset) embryos highlights the importance of vsDPGs as part of the refractory/naïve pluripotency gene regulatory network (GRN) [ 24 , 25 , 37 , 38 , 39 , 53 ]. It also confirms functional analyses in vivo and in vitro showing that vsDPGs have crucial functions in maintaining pluripotency and counteracting spontaneous and precocious PSCs differentiation [ 14 , 16 , 17 , 21 , 22 , 26 , 27 , 28 , 33 , 34 , 35 , 36 , 54 , 55 ].…”

“…Biochemical and molecular studies in vivo demonstrated that VENTX-POU5 and NANOG-POU5 proteins physically interact as a heterodimer to control transcription of genes required for germ layer commitment, patterning and morphogenesis ( Figure 2 A) [ 16 , 26 , 27 , 28 , 33 , 34 , 35 , 36 , 54 ]. VsDPGs heterodimer physically interact also with SMADs proteins (effectors of the TGFβ NODAL/ACTIVIN and BMPs signaling pathways), as well as with CTNNB1 (β-CATENIN)-TCF/TLE proteins (effectors of the WNT signaling pathway) [ 21 , 26 , 27 , 33 , 34 , 35 , 36 , 54 ].…”

“…Biochemical and molecular studies in vivo demonstrated that VENTX-POU5 and NANOG-POU5 proteins physically interact as a heterodimer to control transcription of genes required for germ layer commitment, patterning and morphogenesis ( Figure 2 A) [ 16 , 26 , 27 , 28 , 33 , 34 , 35 , 36 , 54 ]. VsDPGs heterodimer physically interact also with SMADs proteins (effectors of the TGFβ NODAL/ACTIVIN and BMPs signaling pathways), as well as with CTNNB1 (β-CATENIN)-TCF/TLE proteins (effectors of the WNT signaling pathway) [ 21 , 26 , 27 , 33 , 34 , 35 , 36 , 54 ]. In conjunction with genomic analyses (genome-wide chromatin immunoprecipitation ChIP; gene expression microarrays, RNA-sequencing), these results shed light on the role of vsDPGs as modulators of PSCs competence and actors in the activation of the transcriptional program(s) involved in lineage commitment (e.g., SOX3 , GSC , HHEX , EOMES , SOX17 ) [ 21 , 22 , 26 , 27 , 28 , 33 , 34 , 35 , 36 , 49 , 54 , 55 , 56 , 57 , 58 ].…”

“…The molecular mechanisms governing such a continuum are relevant to understanding canalization in vivo, and to translational approaches targeting the obtention of a given cell type. Human orthologs of VENTX and NANOG ( VENTX / NANOG family) and POU5 ( POU5 / OCT4 family) transcription factors (TF) control such pluripotency continuum in vertebrate embryos [ 14 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. The conserved ability of these factors to participate in nuclear reprogramming of somatic cells into induced PSCs (iPSCs) further confirm the relevance of these TF in conferring unrestricted cell’s developmental potential [ 18 , 19 , 20 , 29 , 30 , 31 , 32 ].…”

“…The conserved ability of these factors to participate in nuclear reprogramming of somatic cells into induced PSCs (iPSCs) further confirm the relevance of these TF in conferring unrestricted cell’s developmental potential [ 18 , 19 , 20 , 29 , 30 , 31 , 32 ]. Vertebrate models were crucial in shedding light on the activity of these TF in blastula/epiblast PSCs and during cell commitment to the three germ layers [ 14 , 16 , 17 , 26 , 27 , 28 , 33 , 34 , 35 , 36 ]. Expression and function of VENTX / NANOG and POU5 / OCT4 functional homologs is often associated with the maintenance of pluripotency of blastula/epiblast cells, as described in zebrafish, Xenopus , and chickens [ 4 , 14 , 16 , 17 , 21 , 22 , 37 , 38 , 39 ] and in germ line (GL) development [ 4 , 40 , 41 , 42 , 43 , 44 ], though they are reactivated later in a restricted group of undifferentiated embryonic somatic cells (e.g., neural crest cells, NCCs; posterior neural-mesodermal progenitors, NMPs) [ 15 , 45 , 46 , 47 , 48 ] ( Figure 1 C).…”