Canonical Wnt/β-Catenin Regulation of Liver Receptor Homolog-1 Mediates Pluripotency Gene Expression  

Abstract

Delineating the signaling pathways that underlie ESC pluripotency is paramount for development of ESC applications in both the research and clinical settings. In culture pluripotency is maintained by leukemia inhibitory factor (LIF) stimulation of two separate signaling axes: Stat3/Klf4/Sox2 and PI3K/Tbx3/Nanog, which converge in the regulation of Oct4 expression. However, LIF signaling is not required in vivo for self-renewal, thus alternate signaling axes likely mediate these pathways. Additional factors that promote pluripotency gene expression have been identified, including the direct regulation of Oct4 by liver receptor homolog-1 (Lrh-1) and β-catenin regulation of Nanog. Here, we present genetic, molecular, and pharmacological studies identifying a signaling axis in which β-catenin promotes pluripotency gene expression in an Lrh-1-dependent manner. Furthermore, Lrh-1 was identified as a novel β-catenin target gene, and Lrh-1 regulation is required for maintaining proper levels of Oct4, Nanog, and Tbx3. Elucidation of this pathway provides an alternate mechanism by which the primary pluripotency axis may be regulated in vivo and may pave the way for small molecule applications to manipulate pluripotency or improve the efficiency of somatic cell reprogramming. Stem Cells 2010;28:1794–1804

Wnt Pathway Regulation of Embryonic Stem Cell Self-Renewal

“…RNAi knockdown of each Oct4, Sox2, or Nanog each caused largely overlapping effects on gene expression, consistent with each gene product regulating a common set of target genes (Loh et al 2006). Many genes regulated by Oct4, Sox2, and Nanog include factors that play a downstream, yet important role in self-renewal, including Klf4, c-myc, Esrrb, Tbx3, and Nr5a2 (Gu et al 2005;Ivanova et al 2006;Jiang et al 2008;Kim et al 2008;Hall et al 2009;Wagner et al 2010). Together, these data are consistent with Oct4, Sox2, and Nanog being the central components of a feed-forward network of transcription factors that drives self-renewal of pluripotent cells (see Fig.…”

“…Perhaps the best illustration of co-occupancy came from ChIP-seq experiments, which showed that of the 1369 known genes identified as Tcf3-bound, 1173 were also bound by Oct4, and 942 were bound by each, Tcf3, Oct4, Sox2, and Nanog (Marson et al 2008). Other studies showed Oct4 and Nanog mRNA and protein levels were increased when Tcf3 was knocked down or ablated (Pereira et al 2006;Cole et al 2008;Tam et al 2008;Salomonis et al 2010;Wagner et al 2010). Transcriptional profiling of Tcf3 2/2 ESCs showed that Tcf3 ablation caused strongly opposite effects on gene expression compared with Oct4 knockdown and Nanog knockdown (Loh et al 2006;Yi et al 2008).…”

Rapid and efficient reprogramming of somatic cells to induced pluripotent stem cells by retinoic acid receptor gamma and liver receptor homolog 1

“…This discrepancy is likely because RA signaling in reprogramming is dose-and time-dependent, which could be overshadowed by the retrovirus delivery approach. Recent evidence also suggests that Lrh-1 acts downstream of canonical Wnt signaling and regulates the Nanog and Tbx3 pluripotency signaling axis (44), which may explain the ability of expressing Lrh-1 to reliably reset EpiSCs to ground state pluripotency (45). Therefore, Lrh-1 could promote activation of other key pluripotency genes at late stages of reprogramming besides the synergic interaction with Rarg in early Oct4 activation and stabilization.…”

The evolving biology of small molecules: controlling cell fate and identity

“…Most recently, Wagner et al [21] used a combination of pharmacological and genetic methods to implicate liver receptor homolog-1 (Lrh-1) as a novel b-catenin target gene required for maintaining proper levels of Oct4 and Nanog in mESCs. They have postulated that this signalling axis might represent the in vivo counterpart of the LIF -STAT3 pathway (which is only required in vitro) [21].…”

“…They have postulated that this signalling axis might represent the in vivo counterpart of the LIF -STAT3 pathway (which is only required in vitro) [21].…”