Deletion Of Sox17 Research Articles

E2F1 Mediates SOX17 Deficiency-Induced Pulmonary Hypertension.

Rare genetic variants and genetic variation at loci in an enhancer in SOX17 (SRY-box transcription factor 17) are identified in patients with idiopathic pulmonary arterial hypertension (PAH) and PAH with congenital heart disease. However, the exact role of genetic variants or mutations in SOX17 in PAH pathogenesis has not been reported. SOX17 expression was evaluated in the lungs and pulmonary endothelial cells (ECs) of patients with idiopathic PAH. Mice with Tie2Cre-mediated Sox17 knockdown and EC-specific Sox17 deletion were generated to determine the role of SOX17 deficiency in the pathogenesis of PAH. Human pulmonary ECs were cultured to understand the role of SOX17 deficiency. Single-cell RNA sequencing, RNA-sequencing analysis, and luciferase assay were performed to understand the underlying molecular mechanisms of SOX17 deficiency-induced PAH. E2F1 (E2F transcription factor 1) inhibitor HLM006474 was used in EC-specific Sox17 mice. SOX17 expression was downregulated in the lung and pulmonary ECs from patients with idiopathic PAH. Mice with Tie2Cre-mediated Sox17 knockdown and EC-specific Sox17 deletion induced spontaneously mild pulmonary hypertension. Loss of endothelial Sox17 in EC exacerbated hypoxia-induced pulmonary hypertension in mice. Loss of SOX17 in lung ECs induced endothelial dysfunctions including upregulation of cell cycle programming, proliferative and antiapoptotic phenotypes, augmentation of paracrine effect on pulmonary arterial smooth muscle cells, impaired cellular junction, and BMP (bone morphogenetic protein) signaling. E2F1 signaling was shown to mediate the SOX17 deficiency-induced EC dysfunction. Pharmacological inhibition of E2F1 in Sox17 EC-deficient mice attenuated pulmonary hypertension development. Our study demonstrated that endothelial SOX17 deficiency induces pulmonary hypertension through E2F1. Thus, targeting E2F1 signaling represents a promising approach in patients with PAH.

Abstract 13304: Sox17 Deficiency Induces Pulmonary Hypertension Through E2F1/BRD4 Signaling

Introduction: Pulmonary arterial hypertension (PAH) is a disaster disease characterized by obliterative vascular remodeling and persistent increase of vascular resistance, leading to right heart failure and premature death. Understanding the cellular and molecular mechanisms will help develop novel therapeutic approaches for PAH patients. Hypothesis: Genetic SOX17 mutations are associated with PAH. We hypothesized that endothelial SOX17 mutations or loss of function contributes to endothelial dysfunction and the pathogenesis of PAH. Methods: Endothelial-specific deletion of Sox17 ( Sox17iCKO ) mice were generated. Sox17iCKO and Sox17f/f (WT) mice after tamoxifen injection were incubated without or with hypoxia (10% O 2 ) for 3 weeks to induce PH. EC proliferation, apoptosis, cell junction assay, Western blotting, QRT-PCR, RNA-sequencing analysis, and luciferase assays were performed to understand the molecular mechanisms of SOX17 deficiency and mutation in ECs. siRNA and inhibitors were used to determine the involvement of E2F1/BRD4 signaling in SOX17 deficiency ECs. Results: Sox17iCKO mice developed spontaneous mild PH and exaggerated hypoxia-induced PH evidenced by the increase of RVSP and RV hypertrophy compared to WT mice. SOX17 knockdown in human PVECs induced cell proliferation, anti-apoptosis, and impaired cell integrity. SOX17 knockdown reduced BMPR2 signaling. SOX17 knockdown and mutations at the HMG domain lost transcriptional activities and its ability to repress -catenin. RNA-seq analysis demonstrated enrichment of cell cycle pathway after the loss of SOX17 in PVECs. iRegulon analysis revealed the involvement of transcriptional factor E2F1. siRNA-mediated E2F1 knockdown normalized SOX17 deficiency-induced PVECs dysfunction. Knockdown SOX17 significantly upregulated E2F1 promoter activity, which was dependent on the binding site in the E2F1 promoter by luciferase and mutagenesis assay. E2F1 or BRD4 inhibitors attenuated SOX17 deficiency-induced PH in mice. Conclusions: Our study demonstrated that endothelial loss of SOX17 induces PH in mice. Pharmacological inhibition of E2F1/BRD4 signaling attenuated PH development in Sox17iCKO mice.

A SOX17-PDGFB signaling axis regulates aortic root development

Developmental etiologies causing complex congenital aortic root abnormalities are unknown. Here we show that deletion of Sox17 in aortic root endothelium in mice causes underdeveloped aortic root leading to a bicuspid aortic valve due to the absence of non-coronary leaflet and mispositioned left coronary ostium. The respective defects are associated with reduced proliferation of non-coronary leaflet mesenchyme and aortic root smooth muscle derived from the second heart field cardiomyocytes. Mechanistically, SOX17 occupies a Pdgfb transcriptional enhancer to promote its transcription and Sox17 deletion inhibits the endothelial Pdgfb transcription and PDGFB growth signaling to the non-coronary leaflet mesenchyme. Restoration of PDGFB in aortic root endothelium rescues the non-coronary leaflet and left coronary ostium defects in Sox17 nulls. These data support a SOX17-PDGFB axis underlying aortic root development that is critical for aortic valve and coronary ostium patterning, thereby informing a potential shared disease mechanism for concurrent anomalous aortic valve and coronary arteries.

Abstract 14257: Endothelial SOX17 Deficiency Induces Pulmonary Arterial Hypertension

Introduction: Pulmonary arterial hypertension (PAH) is a disaster disease characterized by obliterative vascular remodeling and persistent increase of vascular resistance, leading to right heart failure and premature death. Understanding the cellular and molecular mechanisms will help develop novel therapeutic approaches for PAH patients. Hypothesis: Human genome-wide association studies identified that SOX17 locus variants are associated with PAH. SOX17 mutation is also found in patients with PAH. We hypothesis that endothelial SOX17 deficiency contributes to the pathogenesis of PAH. Methods: Mice with EndoSCL-CreERT mediated deletion of Sox17 ( Sox17 iCKO ) were generated. Sox17 iCKO and Sox17 f/f mice after tamoxifen injection were incubated with hypoxia (10% O 2 ) for 3 weeks to induced PAH. Hemodynamics and histological examination were measured to determine the PAH phenotypes and vascular remodeling. EC proliferation and apoptosis were assessed in SiRNA-mediated SOX17 knockdown in human lung microvascular endothelial cells (hLMVECs). The RNA-sequencing analysis was performed to understand the molecular mechanisms of SOX17 deficiency in ECs. Results: Sox17 iCKO mice exhibited exaggerative PAH evident by the increase of RVSP and RV hypertrophy after hypoxia treatment compared to Sox17 f/f WT mice. SOX17 knockdown in hLMVECs induced cell proliferation and reduced starvation-induced apoptosis. RNA-seq analysis and DAVID pathway analysis demonstrated that there was dysregulation of cell proliferation-related genes, which are enriched in the pathways related to cell cycle, cell division, and mitotic cell cycle. Transcriptional factor, target, and motif discovery analysis of the dysregulated gene set revealed the involvement of transcriptional factors FOXM1 and E2F1. siRNA mediated knockdown of E2F1 but not FOXM1 normalized SOX17 deficiency-induced hLMVECs proliferation and anti-apoptosis. Conclusions: Our study demonstrated that endothelial SOX17 deficiency exaggerates hypoxia-induced PAH. Loss of SOX17 promotes EC proliferation and anti-apoptosis via the upregulation of transcription factor E2F1.

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

Objective: This study aimed to elucidate the role of the proangiogenic transcription factors Sox7 and Sox17 in the wound healing process and investigate the therapeutic potential of Dll4 blockade, which is an upstream regulator of Sox17, for the treatment of nonhealing wounds.Approach: After generating a full-thickness skin defect wound model of endothelial Sox7- and/or Sox17-deficient mice, we measured the wound healing rates and performed histological analysis. The effects of an anti-Dll4 antibody on wound angiogenesis in Sox7-deficient mice and db/db diabetic mice were assessed.Results: Sox7 and/or Sox17 deletion delayed wound healing. Moreover, the loss of Sox7 and Sox17 inhibited wound angiogenesis, without affecting the expression of the other. Of interest, after anti-Dll4 antibody treatment, Sox17 levels were increased and the suppression of angiogenesis was alleviated in Sox7-deficient mice and db/db diabetic mice. Consequently, Dll4 blockade effectively recovered the observed delay in wound healing.Innovation: The proangiogenic role of Sox7 and Sox17 in wound angiogenesis was addressed and effective treatment of nonhealing wounds by Dll4 blockade was suggested.Conclusion: This study revealed the proangiogenic role of the transcription factors Sox7 and Sox17 in wound angiogenesis. Furthermore, we suggest a novel method for treating nonhealing wounds by particularly targeting the Dll4–Sox17 axis.

Unique and redundant roles of SOX2 and SOX17 in regulating the germ cell tumor fate.

Embryonal carcinomas (ECs) and seminomas are testicular germ cell tumors. ECs display expression of SOX2, while seminomas display expression of SOX17. In somatic differentiation, SOX17 drives endodermal cell fate. However, seminomas lack expression of endoderm markers, but show features of pluripotency. Here, we use chromatin immunoprecipitation sequencing to report and compare the binding pattern of SOX17 in seminoma-like TCam-2 cells to SOX17 in somatic cells and SOX2 in EC-like 2102EP cells. In seminoma-like cells, SOX17 was detected at canonical (SOX2/OCT4), compressed (SOX17/OCT4) and noncomposite SOX motifs. SOX17 regulates TFAP2C, PRDM1 and PRDM14, thereby maintaining latent pluripotency and suppressing somatic differentiation. In contrast, in somatic cells canonical motifs are rarely bound by SOX17. In sum, only 12% of SOX17-binding sites overlap in seminoma-like and somatic cells. This illustrates that binding site choice is highly dynamic and cell type specific. Deletion of SOX17 in seminoma-like cells resulted in loss of pluripotency, marked by a reduction of OCT4 protein level and loss of alkaline phosphatase activity. Furthermore, we found that in EC-like cells SOX2 regulates pluripotency-associated genes, most likely by partnering with OCT4. In conclusion, SOX17 (in seminomas) functionally replaces SOX2 (in ECs) to maintain expression of the pluripotency cluster.

Endocardium differentiation through Sox17 expression in endocardium precursor cells regulates heart development in mice

The endocardium is the endothelial component of the vertebrate heart and plays a key role in heart development. Where, when, and how the endocardium segregates during embryogenesis have remained largely unknown, however. We now show that Nkx2-5+ cardiac progenitor cells (CPCs) that express the Sry-type HMG box gene Sox17 from embryonic day (E) 7.5 to E8.5 specifically differentiate into the endocardium in mouse embryos. Although Sox17 is not essential or sufficient for endocardium fate, it can bias the fate of CPCs toward the endocardium. On the other hand, Sox17 expression in the endocardium is required for heart development. Deletion of Sox17 specifically in the mesoderm markedly impaired endocardium development with regard to cell proliferation and behavior. The proliferation of cardiomyocytes, ventricular trabeculation, and myocardium thickening were also impaired in a non-cell-autonomous manner in the Sox17 mutant, likely as a consequence of down-regulation of NOTCH signaling. An unknown signal, regulated by Sox17 and required for nurturing of the myocardium, is responsible for the reduction in NOTCH-related genes in the mutant embryos. Our results thus provide insight into differentiation of the endocardium and its role in heart development.

RUNX1 AND GROUP F SOX GENES ARE REQUIRED AT DISTINCT STAGES FOR HUMAN HAEMATOPOIETIC DEVELOPMENT

Detailed understanding of the genetic regulation of haematopoiesis is essential for blood cell therapies and to faithfully model haematologic disease. Unlike in the mouse, this knowledge is lacking in humans. To address this, we followed endothelial (SOX17) and haematopoietic (RUNX1C) development using in vitro differentiation of human pluripotent stem cells (hPSCs). Mimicking yolk sac haematopoiesis, we identified SOX17-CD34+CD43- endothelial-like cells as the major source of haematopoietic progeny while SOX17+CD34+CD43- cells mostly formed endothelium. Deletion of RUNX1 permitted a single wave of GFI1/1B-dependent yolk sac-like primitive erythropoiesis, but no yolk sac myelopoiesis or aorta-gonad-mesonephros (AGM)-like haematopoiesis. Deletion of SOX17 or all GROUP F SOX genes (SOX7, SOX17, SOX18) did not influence yolk sac-like haematopoiesis, but severely perturbed the development of AGM-like vessels and reduced their haemogenic capacity. This phenotype was largely mediated by reduced NOTCH signaling and recapitulated by inhibiting γ-secretase. Our data extend mouse studies, identifying unique and distinct requirements for RUNX1 and SOX genes during human haematopoiesis.

Endothelial Sox17 promotes allergic airway inflammation

IL-33, levels of which are known to be increased in patients with eosinophilic asthma and which is suggested as a therapeutic target for it, activates endothelial cells in which Sry-related high-mobility-group box (Sox) 17, an endothelium-specific transcription factor, was upregulated. We investigated the relationship between Sox17 and IL-33 and the possible role of Sox17 in the pathogenesis of asthma using a mouse model of airway inflammation. We used ovalbumin (OVA) to induce airway inflammation in endothelium-specific Sox17 null mutant mice and used IL-33 neutralizing antibody to evaluate the interplay between IL-33 and Sox17. We evaluated airway inflammation and measured levels of various cytokines, chemokines, and adhesion molecules. We also carried out loss- or gain-of-function experiments for Sox17 in human endothelial cells. Levels of IL-33 and Sox17 were significantly increased in the lungs of OVA-challenged mice. Anti-IL-33 neutralizing antibody treatment attenuated not only OVA-induced airway inflammation but also Sox17 expression in pulmonary endothelial cells. Importantly, endothelium-specific deletion of Sox17 resulted in significant alleviation of various clinical features of asthma, including airway inflammation, immune cell infiltration, cytokine/chemokine production, and airway hyperresponsiveness. Sox17 deletion also resulted in decreased densities of Ly6chigh monocytes and inflammatory dendritic cells in the lungs. In IL-33-stimulated human endothelial cells, Sox17 showed positive correlation with CCL2 and intercellular adhesion molecule 1 levels. Lastly, Sox17 promoted monocyte adhesion to endothelial cells and upregulated the extracellular signal-regulated kinase-signal transducer and activator of transcription 3 pathway. Sox17 was regulated by IL-33, and its genetic ablation in endothelial cells resulted in alleviation of asthma-related pathophysiologic features. Sox17 might be a potential target for asthma management.

Abstract WP333: Endothelium-Specific Sox17 Deletion Ameliorates ALK1-mediated Arteriovenous Malformation (AVM)

Introduction: Sox17 promotes endothelial migration by destabilizing endothelial adherens junctions, rearranging cytoskeletal structure and upregulates expression of a number of genes preferentially expressed in angiogenic tip cells. However, the deletion of Sox17 stabilizes endothelial junctions and decreased proliferation, vice versa. The AVM after endothelial Alk1 deletion shows uncontrolled endothelial proliferation and cytoskeletal misarrangement. Therefore, we hypothesized that deletion of Sox17 in endothelial cells are sufficient to ameliorate brain AVM via Notch pathway modulation. Methods: Alk1 2f/2f Sox17 2f/2f double transgenic mice (Alk1 exons 4-6 flanked by loxP sites) were bred with VEcad-iCreER T2 mice that express tamoxifen-inducible cre re-combinase (iCreER) in EC. EC-Alk1 and Sox17 deletion was induced by intraperitoneal injection of tamoxifen (25mg/kg, Sigma-Aldrich) with interval of 3 days. The spatiotemporal changes of blood vessel were investigated in Alk1 deletion alone and Alk1-Sox17 co-deletion mice. Vascular morphology was analyzed 9 days after tamoxifen administration. The transcripts (mRNA) and protein expression of target molecules of Notch pathway (Dll4, Hey1, Hey2, NIICD) were also evaluated. Results: The dysplastic blood vessel index of solitary Alk1 2f/2f deletion mice was higher than Alk1 2f/2f -Sox17 2f/2f double transgenic mice (P<0.001) and was similar to human AVM. Dysplasia in Alk1 2f/2f mice was partially rescued by Sox17 co-deletion in morphologically. In addition, target molecules of Notch pathway, Dll4, Hey1, Hey2, Jag1 was increased in Alk1-Sox17 co-deletion mice rather than solitary Alk1 deletion mice. Conclusions: Collectively, our findings demonstrate that the modulation of Sox17 could restrict the Alk1-induced AVM by upregulation of Notch pathway. This work establishes the Notch-Sox17 axis as a novel regulatory mechanism underlying Notch-mediated vascular stabilization in brain AVM.

Sox7 promotes high-grade glioma by increasing VEGFR2-mediated vascular abnormality

High-grade glioma (HGG) is highly angiogenic, but antiangiogenic therapy has transient clinical benefit in only a fraction of patients. Vascular regulators of these heterogeneous responses remain undetermined. We found up-regulation of Sox7 and down-regulation of Sox17 in tumor endothelial cells (tECs) in mouse HGG. Sox7 deletion suppressed VEGFR2 expression, vascular abnormality, hypoxia-driven invasion, regulatory T cell infiltration, and tumor growth. Conversely, Sox17 deletion exacerbated these phenotypes by up-regulating Sox7 in tECs. Anti-VEGFR2 antibody treatment delayed tumor growth by normalizing Sox17-deficient abnormal vessels with high Sox7 levels but promoted it by regressing Sox7-deficient vessels, recapitulating variable therapeutic responses to antiangiogenic therapy in HGG patients. Our findings establish that Sox7 promotes tumor growth via vessel abnormalization, and its level determines the therapeutic outcome of VEGFR2 inhibition in HGG. In 189 HGG patients, Sox7 expression was heterogeneous in tumor vessels, and high Sox7 levels correlated with poor survival, early recurrence, and impaired vascular function, emphasizing the clinical relevance of Sox7 in HGG.

Abstract WP435: Endothelium-Specific Sox17 Deletion Ameliorates ALK1-mediated Cerebral Arteriovenous Malformation

Background and Purpose: The deletion of Sox17 stabilizes endothelial junctions and decreased proliferation, vice versa. The AVM after endothelial Alk1 deletion shows uncontrolled endothelial proliferation and cytoskeletal misarrangement. The vascular phenomena by endothelial specific deletion of Sox17 and Alk1 are diametrical. Coincidentally, these two antidotal genes act via Notch signaling pathway. Therefore, we hypothesized that deletion of Sox17 in endothelial cells are sufficient to ameliorate brain AVM via Notch pathway modulation. Methods: Alk1 2f/2f Sox17 2f/2f double transgenic mice were bred with VEcad-iCreER T2 mice that express tamoxifen-inducible cre re-combinase in EC. EC-Alk1 and Sox17 deletion was induced by intraperitoneal injection of tamoxifen (25mg/kg) with interval of 3 days. The spatiotemporal changes of blood vessel were investigated in Alk1 deletion alone and Alk1-Sox17 co-deletion mice. Vascular morphology was analyzed using real-time multiphoton microscopy and immunostaining. EC proliferation and dysplasia index were quantified. The transcripts and protein expression of target molecules of Notch pathway (Dll4, Hey1, Hey2, NIICD) were also evaluated. Results: The dysplastic blood vessel index of solitary Alk1 2f/2f deletion mice was higher than Alk1 2f/2f -Sox17 2f/2f double transgenic mice (P<0.001). Dysplasia in Alk1 2f/2f mice was partially rescued by Sox17 co-deletion in morphologically. In addition, target molecules of Notch pathway, Dll4, Hey1, Hey2, Jag1 was increased in Alk1-Sox17 co-deletion mice rather than solitary Alk1 deletion mice. Conclusions: Collectively, our findings demonstrate that the modulation of Sox17 could restrict the Alk1-induced AVM by upregulation of Notch pathway. This work establishes the Notch-Sox17 axis as a novel regulatory mechanism underlying Notch-mediated vascular stabilization in brain AVM.

Embryonic cholecystitis and defective gallbladder contraction in the Sox17-haploinsufficient mouse model of biliary atresia.

The gallbladder excretes cytotoxic bile acids into the duodenum through the cystic duct and common bile duct system. Sox17 haploinsufficiency causes biliary atresia-like phenotypes and hepatitis in late organogenesis mouse embryos, but the molecular and cellular mechanisms underlying this remain unclear. In this study, transcriptomic analyses revealed the early onset of cholecystitis in Sox17+/- embryos, together with the appearance of ectopic cystic duct-like epithelia in their gallbladders. The embryonic hepatitis showed positive correlations with the severity of cholecystitis in individual Sox17+/- embryos. Embryonic hepatitis could be induced by conditional deletion of Sox17 in the primordial gallbladder epithelia but not in fetal liver hepatoblasts. The Sox17+/- gallbladder also showed a drastic reduction in sonic hedgehog expression, leading to aberrant smooth muscle formation and defective contraction of the fetal gallbladder. The defective gallbladder contraction positively correlated with the severity of embryonic hepatitis in Sox17+/- embryos, suggesting a potential contribution of embryonic cholecystitis and fetal gallbladder contraction in the early pathogenesis of congenital biliary atresia.

Conditional deletion of Sox17 reveals complex effects on uterine adenogenesis and function

The importance of canonical Wnt signaling to murine uterine development is well established. Mouse models in which uterine-specific Wnt ligands, β-catenin, or Lef1 are disrupted result in failure of postnatal endometrial gland development. Sox17 is a transcription factor characterized in numerous tissues as an antagonist of Wnt signaling. Thus, we hypothesized that conditional ablation of Sox17 would lead to hyperproliferation of endometrial glands in mice. Contrary to our prediction, disruption of Sox17 in epithelial and stromal compartments led to inhibition of endometrial adenogenesis and a loss of reproductive capacity. Epithelium-specific Sox17 disruption resulted in normal adenogenesis although reproductive capacity remained impaired. These findings suggest that non-epithelial, Sox17-positive cells are necessary for adenogenesis and that glands require Sox17 to properly function. To our knowledge, these findings are the first to implicate Sox17 in endometrial gland formation and reproductive success. The data presented herein underscore the importance of studying Sox17 in uterine homeostasis and function.

Circulation : Clinical Summaries

<i>Circulation</i> : Clinical Summaries

Sox17 is required for normal pulmonary vascular morphogenesis

The SRY-box containing transcription factor Sox17 is required for endoderm formation and vascular morphogenesis during embryonic development. In the lung, Sox17 is expressed in mesenchymal progenitors of the embryonic pulmonary vasculature and is restricted to vascular endothelial cells in the mature lung. Conditional deletion of Sox17 in splanchnic mesenchyme-derivatives using Dermo1-Cre resulted in substantial loss of Sox17 from developing pulmonary vascular endothelial cells and caused pulmonary vascular abnormalities before birth, including pulmonary vein varices, enlarged arteries, and decreased perfusion of the microvasculature. While survival of Dermo1-Cre;Sox17Δ/Δ mice (herein termed Sox17Δ/Δ) was unaffected at E18.5, most Sox17Δ/Δ mice died by 3 weeks of age. After birth, the density of the pulmonary microvasculature was decreased in association with alveolar simplification, biventricular cardiac hypertrophy, and valvular regurgitation. The severity of the postnatal cardiac phenotype was correlated with the severity of pulmonary vasculature abnormalities. Sox17 is required for normal formation of the pulmonary vasculature and postnatal cardiovascular homeostasis.

Sox17 promotes tumor angiogenesis and destabilizes tumor vessels in mice

Little is known about the transcriptional regulation of tumor angiogenesis, and tumor ECs (tECs) remain poorly characterized. Here, we studied the expression pattern of the transcription factor Sox17 in the vasculature of murine and human tumors and investigated the function of Sox17 during tumor angiogenesis using Sox17 genetic mouse models. Sox17 was specifically expressed in tECs in a heterogeneous pattern; in particular, strong Sox17 expression distinguished tECs with high VEGFR2 expression. Whereas overexpression of Sox17 in tECs promoted tumor angiogenesis and vascular abnormalities, Sox17 deletion in tECs reduced tumor angiogenesis and normalized tumor vessels, inhibiting tumor growth. Tumor vessel normalization by Sox17 deletion was long lasting, improved anticancer drug delivery into tumors, and inhibited tumor metastasis. Sox17 promoted endothelial sprouting behavior and upregulated VEGFR2 expression in a cell-intrinsic manner. Moreover, Sox17 increased the percentage of tumor-associated CD11b+Gr-1+ myeloid cells within tumors. The vascular effects of Sox17 persisted throughout tumor growth. Interestingly, Sox17 expression specific to tECs was also observed in highly vascularized human glioblastoma samples. Our findings establish Sox17 as a key regulator of tumor angiogenesis and tumor progression.

Sox17 Regulates Organ Lineage Segregation of Ventral Foregut Progenitor Cells

The ventral pancreas, biliary system, and liver arise from the posterior ventral foregut, but the cell-intrinsic pathway by which these organ lineages are separated is not known. Here we show that the extrahepatobiliary system shares a common origin with the ventral pancreas and not the liver, as previously thought. These pancreatobiliary progenitor cells coexpress the transcription factors PDX1 and SOX17 at E8.5 and their segregation into a PDX1+ ventral pancreas and a SOX17+ biliary primordium is Sox17-dependent. Deletion of Sox17 at E8.5 results in the loss of biliary structures and ectopic pancreatic tissue in the liver bud and common duct, while Sox17 overexpression suppresses pancreas development and promotes ectopic biliary-like tissue throughout the PDX1+ domain. Restricting SOX17+ biliary progenitor cells to the ventral region of the gut requires the notch effector Hes1. Our results highlight the role of Sox17 and Hes1 in patterning and morphogenetic segregation of ventral foregut lineages.

The regulation of stem cell self‐renewal

The mechanisms that regulate stem cell self‐renewal are fundamental to the formation and maintenance of normal hematopoiesis as well as hematopoietic malignancies. Fetal stem cells differ phenotypically and functionally from adult stem cells in diverse tissues. However, little is known about how these differences are regulated. To address this we compared the gene expression profiles of fetal versus adult hematopoietic stem cells (HSCs) and discovered that the Sox17 transcription factor is specifically and preferentially expressed in fetal and neonatal but not adult HSCs (Cell 130:470). Germline deletion of Sox17 led to severe fetal hematopoietic defects, including a lack of detectable definitive HSCs. Conditional deletion of Sox17 led to the loss of fetal and neonatal but not adult HSCs. Sox17 expression by HSCs was extinguished three to four weeks after birth as HSCs acquired adult properties. During this transition, loss of Sox17 expression by individual cells correlated with slower proliferation and the acquisition of an adult phenotype. Sox17 thus distinguishes the transcriptional regulation of fetal and neonatal HSCs from that of adult HSCs.As HSCs enter the postnatal period, they become dependent upon the polycomb family transcriptional repressor, Bmi‐1. Bmi‐1 is required for the postnatal maintenance of every type of stem cell yet examined including HSCs (Nature 423:302, 2003) and neural stem cells (Nature 425:962, 2003). Bmi‐1‐deficient mice die by early adulthood with stem cell depletion, growth retardation, ataxia, and seizures. These phenotypes correlate with increased expression of the cyclin‐dependent kinase inhibitor p16Ink4a and the p53 agonist p19Arf, which promote cellular senescence. Deletion of Ink4a and/or Arf from Bmi‐1−/− mice partially rescues stem cell self‐renewal and stem cell frequency (G&amp;D 19:1432, 2005). Despite ongoing Bmi‐1 expression, Ink4a expression increases with age, reducing stem cell frequency and function (Nature 443:448). The regulation of stem cell self‐renewal throughout life by networks of proto‐oncogenes and tumor suppressors emphasizes the mechanistic links between stem cell self‐renewal and cancer cell proliferation.

Sox17 Dependence Distinguishes the Transcriptional Regulation of Fetal from Adult Hematopoietic Stem Cells

Fetal stem cells differ phenotypically and functionally from adult stem cells in diverse tissues. However, little is known about how these differences are regulated. To address this we compared the gene expression profiles of fetal versus adult hematopoietic stem cells (HSCs) and discovered that the Sox17 transcriptional regulator is specifically expressed in fetal and neonatal but not adult HSCs. Germline deletion of Sox17 led to severe fetal hematopoietic defects, including a lack of detectable definitive HSCs. Conditional deletion of Sox17 from hematopoietic cells led to the loss of fetal and neonatal but not adult HSCs. HSCs stopped expressing Sox17 approximately 4 weeks after birth. During this transition, loss of Sox17 expression correlated with slower proliferation and the acquisition of an adult phenotype by individual HSCs. Sox17 is thus required for the maintenance of fetal and neonatal HSCs and distinguishes their transcriptional regulation from adult HSCs.