Sox7, Sox17, and Sox18 Cooperatively Regulate Vascular Development in the Mouse Retina

Abstract

Vascular development and maintenance are controlled by a complex transcriptional program, which integrates both extracellular and intracellular signals in endothelial cells. Here we study the roles of three closely related SoxF family transcription factors–Sox7, Sox17, and Sox18 –in the developing and mature mouse vasculature using targeted gene deletion on a mixed C57/129/CD1 genetic background. In the retinal vasculature, each SoxF gene exhibits a distinctive pattern of expression in different classes of blood vessels. On a mixed genetic background, vascular endothelial-specific deletion of individual SoxF genes has little or no effect on vascular architecture or differentiation, a result that can be explained by overlapping function and by reciprocal regulation of gene expression between Sox7 and Sox17. By contrast, combined deletion of Sox7, Sox17, and Sox18 at the onset of retinal angiogenesis leads to a dense capillary plexus with a nearly complete loss of radial arteries and veins, whereas the presence of a single Sox17 allele largely restores arterial identity, as determined by vascular smooth muscle cell coverage. In the developing retina, expression of all three SoxF genes is reduced in the absence of Norrin/Frizzled4-mediated canonical Wnt signaling, but SoxF gene expression is unaffected by reduced VEGF signaling in response to deletion of Neuropilin1 (Npn1). In adulthood, Sox7, Sox17, and Sox18 act in a largely redundant manner to maintain blood vessel function, as adult onset vascular endothelial-specific deletion of all three SoxF genes leads to massive edema despite nearly normal vascular architecture. These data reveal critical and partially redundant roles for Sox7, Sox17 and Sox18 in vascular growth, differentiation, and maintenance.

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

“…By contrast, SOX7 is expressed from the onset of endothelial differentiation in the yolk sac at E7.5, and is expressed in arterial and venous vasculature (Gandillet et al, 2009;Sakamoto et al, 2007;Zhou et al, 2015). In agreement with these data, we discovered that SOX7 is more broadly expressed across the yolk sac HE at E8.5 compared with SOX17.…”

“…Yolk sacs were isolated and flat mounted with DAPI, as previously described (Frame et al, 2015), before imaging. All primary antibodies have been used in previous studies (Yokomizo et al, 2013;Yzaguirre and Speck, 2016;Zhou et al, 2015). Specific labelling of primary antibodies was determined by comparison with no primary antibody-treated controls.…”

“…Other endothelial transcription factors must therefore be important for regulating HE in the yolk sac. SOX7 is a prime candidate for this role, as previous studies have demonstrated that this SOXF factor is expressed from E7.5 in the yolk sac and is widely expressed in the developing vascular network: in both arteries and veins, and in large and small blood vessels (Gandillet et al, 2009;Sakamoto et al, 2007;Zhou et al, 2015).…”

SoxF factors induce Notch1 expression via direct transcriptional regulation during early arterial development

“…The SoxF group of transcription factors (Sox7, Sox17 and Sox18) are expressed in endothelial cells from early in development (Francois et al, 2010). While each SoxF member displays a subtly different endothelial expression pattern, all three factors are expressed early in arterial development (Corada et al, 2013;François et al, 2008;Zhou et al, 2015) and share considerable functional redundancy, complicating interpretation of the consequences of gene disruption (Hosking et al, 2009;Zhou et al, 2015). Combined loss of sox7 and sox18 in zebrafish, both by morpholino-based knockdown and genetic mutation, resulted in serious arteriovenous malformations similar to those seen after Notch ablation, suggesting that SoxF factors might genetically interact with the Notch pathway in endothelial cells (Cermenati et al, 2008;Hermkens et al, 2015;Herpers et al, 2008;Lawson et al, 2001).…”

“…Combined loss of sox7 and sox18 in zebrafish, both by morpholino-based knockdown and genetic mutation, resulted in serious arteriovenous malformations similar to those seen after Notch ablation, suggesting that SoxF factors might genetically interact with the Notch pathway in endothelial cells (Cermenati et al, 2008;Hermkens et al, 2015;Herpers et al, 2008;Lawson et al, 2001). Further evidence was provided in mice, where endothelial-specific ablation of Sox17 caused arterial differentiation and remodelling defects (Corada et al, 2013), and conditional deletion of SoxF factors in the adult resulted in loss of major vessel identity in the retina (Zhou et al, 2015). Inhibition of Vegfa signalling can significantly impact SoxF expression and activity in both mouse and zebrafish models (Kim et al, 2016;Pendeville et al, 2008;Duong et al, 2014;Pennisi et al, 2000b), suggesting that members of the SoxF family lie downstream of Vegfa.…”