Sox2 controls neural stem cell self-renewal through a Fos-centered gene regulatory network

Abstract

The Sox2 transcription factor is necessary for the long-term self-renewal of neural stem cells (NSC). Its mechanism of action is still poorly defined. To identify molecules regulated by Sox2, and acting in mouse NSC maintenance, we transduced, individually or in combination, into Sox2deleted NSC, genes whose expression is strongly downregulated following Sox2 loss (Fos, Jun, Egr2). Fos alone rescued long-term proliferation, as shown by in vitro cell growth and clonal analysis. Further, Fos requirement for efficient long-term proliferation was demonstrated by the strong reduction of NSC clones capable of long-term expansion following CRISPR/Cas9-mediated Fos inactivation. Previous work showed that the Suppressor of cytokine signaling 3 (Socs3) gene is strongly downregulated following Sox2 deletion, and its reexpression by lentiviral transduction rescues long-term NSC proliferation. Fos appears to be an upstream regulator of Socs3, possibly together with Jun and Egr2; indeed, Sox2 reexpression in Sox2-deleted NSC progressively activates both Fos and Socs3 expression; in turn, Fos transduction activates Socs3 expression. Based on available SOX2 ChIPseq and ChIA-PET data, as well as results from the literature, we propose a model whereby Sox2 is a direct activator of both Socs3 and Fos, as well as possibly Jun and Egr2; in turn, Fos, Jun and Egr2 may activate Socs3. These results provide the basis for developing a model of a network of interactions, regulating critical effectors of NSC proliferation and long-term maintenance. Significance statementProliferation and maintenance of NSC are essential during normal brain development, and, postnatally, for the maintenance of hippocampal function and memory until advanced age. Little is known about the molecular mechanisms that maintain the critical aspects of NSC biology (quiescence and proliferation) in postnatal age. Our work provides a methodology, transduction of genes deregulated following Sox2 deletion, that allows to test many candidate genes for their ability to sustain NSC proliferation. In principle, this may have interesting implications for identifying targets for pharmacological manipulations.

FOS Rescues Neuronal Differentiation of Sox2-Deleted Neural Stem Cells by Genome-Wide Regulation of Common SOX2 and AP1(FOS-JUN) Target Genes

“…At the cellular level, SOX2 was found to play an essential function in the maintenance of neural stem cells (NSC) in the developing CNS and, postnatally, in both the lateral ventricle (LV) and hippocampus dentate gyrus (DG) [ 3 , 5 , 7 ]. A requirement for Sox2 in the long-term maintenance of brain-derived NSC grown in vitro was confirmed by additional studies [ 3 , 8 , 9 ]. On the other hand, the terminal differentiation of NSC into neurons was also found to require Sox2 .…”

“…Brain-derived NSC cultures were obtained from dissected telencephalon of wild-type and Sox2-deleted P0 mice [ 3 , 8 ] and grown in fresh medium (FM): DMEM-F12 with Glutamax (GIBCO, Milan, Italy), supplemented with 1/50 v/v B27 (Life Technologies, Milan, Italy), 1% of penicillin-streptomycin (Euroclone, Milan, Italy) supplemented with EGF (10 ng/mL, Tebu-bio, Milan, Italy) and bFGF (10 ng/mL, Tebu-bio, Milan, Italy) as a mitogen, as described in [ 3 , 8 , 9 , 12 ].…”

Single nucleus pituitary transcriptomic and epigenetic landscape reveals human stem cell heterogeneity with diverse regulatory mechanisms

“…WWTR1 , PITX2 , and LGR4 ; for review, see 18 ), were broadly expressed. Interestingly, expression of JUN and JUND , which were implicated in the regulation of stemness in other tissues 20, 21 , was heterogeneous, with the highest expression associated with clusters that were predominant in male samples.…”

Multiomics analysis reveals extensive epigenome remodeling during cortical development

“…To identify key transcription factors whose binding correlates with changes in chromatin accessibility, we used ChromVAR ( Figure 2C; Fornes et al, 2020;Schep et al, 2017). TFs associated with a high motif accessibility in NSC included classical neural TFs such as Sox2, Pax6 or Lhx2, as well as Tead2 and c-Fos/Jun (AP-1), which have been recently described as important in NSC (Mukhtar et al, 2020;Pagin et al, 2020). Conversely, neurogenic transcription factors such as Eomes and Neurod2 were associated with a strong increase in motif accessibility during the transition from NSC to IPC, and IPC to PN1 respectively ( Figure 2C and 2E).…”