Post-translational modification of Ngn2 differentially affects transcription of distinct targets to regulate the balance between progenitor maintenance and differentiation

Abstract

SUMMARYNeurogenin 2 (Ngn2) controls neuronal differentiation cell-autonomously by transcriptional activation of targets such as NeuroD, while simultaneously controlling progenitor maintenance non-cell-autonomously by upregulating Delta expression and Notch signalling. Reduction in Cdk-dependent multisite phosphorylation of Ngn2 enhances its promoter binding affinity. This leads specifically to an increase in neuronal differentiation without an apparent increase in progenitor maintenance via Delta-Notch signalling, although the mechanism underlying this imbalance remains unclear. Here we show in Xenopus embryos and mouse P19 cells that the NeuroD promoter is substantially more sensitive to the phosphorylation status of Ngn2 than the Delta promoter, and that this can be attributed to differences in the ease of promoter activation. In addition, we also show that the phosphorylation status of Ngn2 regulates sensitivity to Notch signalling. These observations explain how Ngn2 post-translational modification in response to changes in the cell cycle kinase environment results in enhanced neuronal differentiation upon cell cycle lengthening.

Precommitment low-level Neurog3 expression defines a long-lived mitotic endocrine-biased progenitor pool that drives production of endocrine-committed cells

“…In cycling progenitors, high Cdk activity and low Cdk inhibitor (Cdki) activity during G2-S-M phases keep Neurog2 in an unstable multiphosphorylated state subject to ubiquitylation-mediated degradation (Vosper et al 2009;Ali et al 2011). The low-level phospho-Neurog2 is unable to activate neural specification target genes but activates progenitor-associated targets (Ali et al 2011;Hindley et al 2012). In our case, the Sox9 + Neurog3…”

“…Speculations on mechanisms regulating endocrine commitment vs. progenitor maintenance in Neurog3 TA.LO progenitors Several studies show that the length of the G1 phase of the cell cycle can dictate the choice of progenitor maintenance versus lineage specification (Hindley et al 2012;Pauklin and Vallier 2013;Hardwick et al 2015). For Neurog2 in neural progenitors, the low Cdk/high Cdki activity and lengthened G1 keep Neurog2 nonphosphorylated/ underphosphorylated and stable enough to activate neuronal differentiation targets (Ali et al 2011).…”

A computational model for the coordination of neural progenitor self-renewal and differentiation through Hes1 dynamics

“…Here, emphasis is laid on the Notch effector Hes1, which is known to repress the transcription of many cell cycle and differentiation regulatory genes, including cyclin D1 and E2, Ngn2, Dll1 and Hes1 (Kageyama et al, 2007). By competing with Ngn2 for binding to E-box DNA, Hes1 further promotes Ngn2 destabilization, thus preventing Ngn2-mediated transcriptional activation of proneural factors (Hindley et al, 2012). Hes1 expression is assumed to be regulated at two main levels: through the regulation of Hes1 mRNA stability by microRNA 9 (miR9), which in turn is transcriptionally repressed by Hes1 (Bonev et al, 2012;Tan et al, 2012); and, importantly, through Dll1-ligand-induced trans-activation and cis-inhibition of Notch signaling (Kageyama et al, 2007;Wang et al, 2011).…”

RAS/ERK Signaling Controls Proneural Genetic Programs in Cortical Development and Gliomagenesis

“…While oncogenic RAS activates several downstream pathways, including ERK, AKT, and Ral (Repasky et al, 2004), ERK is considered the key effector in tumorigenesis, as BRAF activating mutations are observed in pilocytic astrocytoma (PA), ganglioglioma (GG), pleomorphic xanthoastrocytoma, and glioblastoma variants (Knobbe et al, 2004;Jones et al, 2008;Pfister et al, 2008;DiasSantagata et al, 2011;Schindler et al, 2011;KleinschmidtDeMasters et al, 2013). Moreover, constitutively activate BRAF is sufficient to induce PA in mice (Gronych et al, 2011).…”

“…DIG-labeled probes were generated using a 10ϫ labeling mix per manufacturer's instructions (Roche). Probe templates included Neurog2 (Gradwohl et al, 1996), Ascl1 (Guillemot and Joyner, 1993), Dlx1 (Anderson et al, 1997b), Olig2 (Q. Zhou et al, 2000), Olig1 (Q.…”