Interplay between SOX7 and RUNX1 regulates hemogenic endothelial fate in the yolk sac

Abstract

Endothelial to hematopoietic transition (EHT) is a dynamic process involving the shutting down of endothelial gene expression and switching on of hematopoietic gene transcription. Although the factors regulating EHT in hemogenic endothelium (HE) of the dorsal aorta have been relatively well studied, the molecular regulation of yolk sac HE remains poorly understood. Here, we show that SOX7 inhibits the expression of RUNX1 target genes in HE, while having no effect on RUNX1 expression itself. We establish that SOX7 directly interacts with RUNX1 and inhibits its transcriptional activity. Through this interaction we demonstrate that SOX7 hinders RUNX1 DNA binding as well as the interaction between RUNX1 and its co-factor CBFβ. Finally, we show by single-cell expression profiling and immunofluorescence that SOX7 is broadly expressed across the RUNX1 + yolk sac HE population compared with SOX17. Collectively, these data demonstrate for the first time how direct protein-protein interactions between endothelial and hematopoietic transcription factors regulate contrasting transcriptional programs during HE differentiation and EHT.

SOX7 expression is critically required in FLK1-expressing cells for vasculogenesis and angiogenesis during mouse embryonic development

“…In addition to its expression in endothelial progenitors, Sox7 has been previously detected in primitive endoderm (Futaki et al, 2004, Murakami et al, 2004), in the earliest specified hematopoietic progenitors (Gandillet et al, 2009) and in emerging hematopoietic clusters in the dorsal aorta (Lilly et al, 2016, Nobuhisa et al, 2014). To define a possible role and requirement for Sox7 in specific compartments, we generated a Sox7 conditional allele in which the exon 2 of Sox7 is flanked by LoxP sequences and can be excised upon CRE expression.…”

“…Finally, we analysed the consequence of the specific deletion of Sox7 in the hematopoietic compartment given the observed expression of SOX7 at all sites of hematopoietic emergence during embryogenesis (Lilly et al, 2016). Indeed, this was further confirmed by the co-expression of SOX7 with RUNX and cKIT, both marking emerging blood cells in the ventral aspect of the dorsal aorta in wild type embryos at E10.5 (Fig.…”

RUNX transcription factors: orchestrators of development

“…1B) (Rennert et al, 2003). The RHD is essential for (1) binding to the DNA at the consensus RUNX motif 'PyGPyGGTPy' (Kamachi et al, 1990;Wang and Speck, 1992), (2) protein-protein interactions (Lilly et al, 2016;Nagata et al, 1999) and (3) the nuclear localization of the RUNX factors (Michaud et al, 2002;Telfer et al, 2004). The C terminus is less conserved and contains an activation domain, an inhibitory domain and a five amino acid C-terminal motif (VWRPY in most cases), known as the recruitment signal for the Groucho/ TLE (transducin-like enhancer of split) family of co-repressors (Levanon et al, 1998;Seo et al, 2012b;Yarmus et al, 2006).…”

Transcriptional control of blood cell emergence

“…Similarly, SOX7 was shown to mark HE and upon enforced expression to block the transition from endothelium-to-haematopoiesis and to promote HE proliferation [96,97]. Further insight into the molecular mechanism underlying this block revealed that SOX7 physically interacts with RUNX1 in HE and prevents RUNX1 from switching on the blood program and switching off the endothelium program [98]. This is thought to create a meta-stable HE state, poised to give rise to haematopoietic cells upon disruption of the SOX7/RUNX1 interaction.…”

“…SOX17 was shown to mark HE [93] as well as newly formed HSCs [94] and, upon enforced expression, to maintain HSCs undifferentiated over several passages in vitro [95]. Further insight into the molecular mechanism underlying this block revealed that SOX7 physically interacts with RUNX1 in HE and prevents RUNX1 from switching on the blood program and switching off the endothelium program [98]. Further insight into the molecular mechanism underlying this block revealed that SOX7 physically interacts with RUNX1 in HE and prevents RUNX1 from switching on the blood program and switching off the endothelium program [98].…”