SoxF Transcription Factors Are Positive Feedback Regulators of VEGF Signaling.

Vascular endothelial growth factor (VEGF) signaling is a key pathway for angiogenesis and requires highly coordinated regulation. Although the Notch pathway-mediated suppression of excessive VEGF activity via negative feedback is well known, the positive feedback control for augmenting VEGF signaling remains poorly understood. Transcription factor Sox17 is indispensable for angiogenesis, but its association with VEGF signaling is largely unknown. The contribution of other Sox members to angiogenesis also remains to be determined. To reveal the genetic interaction of Sox7, another Sox member, with Sox17 in developmental angiogenesis and their functional relationship with VEGF signaling. Sox7 is expressed specifically in endothelial cells and its global and endothelial-specific deletion resulted in embryonic lethality with severely impaired angiogenesis in mice, substantially overlapping with Sox17 in both expression and function. Interestingly, compound heterozygosity for Sox7 and Sox17 phenocopied vascular defects of Sox7 or Sox17 homozygous knockout, indicating that the genetic cooperation of Sox7 and Sox17 is sensitive to their combined gene dosage. VEGF signaling upregulated both Sox7 and Sox17 expression in angiogenesis via mTOR pathway. Furthermore, Sox7 and Sox17 promoted VEGFR2 (VEGF receptor 2) expression in angiogenic vessels, suggesting a positive feedback loop between VEGF signaling and SoxF. Our findings demonstrate that SoxF transcription factors are indispensable players in developmental angiogenesis by acting as positive feedback regulators of VEGF signaling.

Kim K ，Kim IK ，Yang JM ，Lee E ，Koh BI ，Song S ，Park J ，Lee S ，Choi C ，Kim JW ，Kubota Y ，Koh GY ，Kim I ... -  《-》

Notch pathway targets proangiogenic regulator Sox17 to restrict angiogenesis.

The Notch pathway stabilizes sprouting angiogenesis by favoring stalk cells over tip cells at the vascular front. Because tip and stalk cells have different properties in morphology and function, their transcriptional regulation remains to be distinguished. Transcription factor Sox17 is specifically expressed in endothelial cells, but its expression and role at the vascular front remain largely unknown. To specify the role of Sox17 and its relationship with the Notch pathway in sprouting angiogenesis. Endothelial-specific Sox17 deletion reduces sprouting angiogenesis in mouse embryonic and postnatal vascular development, whereas Sox17 overexpression increases it. Sox17 promotes endothelial migration by destabilizing endothelial junctions and rearranging cytoskeletal structure and upregulates expression of several genes preferentially expressed in tip cells. Interestingly, Sox17 expression is suppressed in stalk cells in which Notch signaling is relatively high. Notch activation by overexpressing Notch intracellular domain reduces Sox17 expression both in primary endothelial cells and in retinal angiogenesis, whereas Notch inhibition by delta-like ligand 4 (Dll4) blockade increases it. The Notch pathway regulates Sox17 expression mainly at the post-transcriptional level. Furthermore, endothelial Sox17 ablation rescues vascular network from excessive tip cell formation and hyperbranching under Notch inhibition in developmental and tumor angiogenesis. Our findings demonstrate that the Notch pathway restricts sprouting angiogenesis by reducing the expression of proangiogenic regulator Sox17.

Lee SH ，Lee S ，Yang H ，Song S ，Kim K ，Saunders TL ，Yoon JK ，Koh GY ，Kim I ... -  《-》

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

Zhou Y ，Williams J ，Smallwood PM ，Nathans J ... -  《PLoS One》

VEGF-dependent testicular vascularisation involves MEK1/2 signalling and the essential angiogenesis factors, SOX7 and SOX17.

Abnormalities of in utero testis development are strongly associated with reproductive health conditions, including male infertility and testis cancer. In mouse testes, SOX9 and FGF9 support Sertoli cell development, while VEGF signalling is essential for the establishment of vasculature. The mitogen-activated protein kinase (MAPK) pathway is a major signalling cascade, essential for cell proliferation, differentiation and activation of Sry during primary sex-determination, but little is known about its function during fetal testis morphogenesis. We explored potential functions of MAPK signalling immediately after the establishment of testis cords in embryonic day (E)12.5 Oct4-eGFP transgenic mouse testes cultured using a MEK1/2 inhibitor. RNA sequencing in isolated gonadal somatic cells identified 116 and 114 differentially expressed genes after 24 and 72 h of MEK1/2 inhibition, respectively. Ingenuity Pathway Analysis revealed an association of MEK1/2 signalling with biological functions such as angiogenesis, vasculogenesis and cell migration. This included a failure to upregulate the master transcriptional regulators of vascular development, Sox7 and Sox17, VEGF receptor genes, the cell adhesion factor gene Cd31 and a range of other endothelial cell markers such as Cdh5 (encoding VE-cadherin) and gap junction genes Gja4 and Gja5. In contrast, only a small number of Sertoli cell enriched genes were affected. Immunofluorescent analyses of control testes revealed that the MEK1/2 downstream target, ERK1/2 was phosphorylated in endothelial cells and Sertoli cells. Inhibition of MEK1/2 eliminated pERK1/2 in fetal testes, and CD31, VE-cadherin, SOX7 and SOX17 and endothelial cells were lost. Consistent with a role for VEGF in driving endothelial cell development in the testis, inhibition of VEGFR also abrogated pERK1/2 and SOX7 and SOX17 expressing endothelial cells. Moreover, while Sertoli cell proliferation and localisation to the testis cord basement membrane was disrupted by inhibition of MEK1/2, it was unaffected by VEGFR inhibition. Instead, inhibition of FGF signalling compromised Sertoli cell proliferation and localisation to the testis cord basement membrane. Together, our data highlight an essential role for VEGF-dependent MEK1/2 signalling in promoting vasculature and indicate that FGF signalling through MEK1/2 regulates Sertoli cell organisation in the developing mouse testis.

Blücher RO ，Lim RS ，Ritchie ME ，Western PS ... -  《-》

Dll4 Blockade Promotes Angiogenesis in Nonhealing Wounds of Sox7-Deficient Mice.

Yang JM ，Ryu J ，Kim I ，Chang H ，Kim IK ... -  《-》