SOX7 transcription factor: sequence, chromosomal localisation, expression, transactivation and interference with Wnt signalling

SOX7: from a developmental regulator to an emerging tumor suppressor

SOX7 belongs to the SOX (SRY-related HMG-box) family of transcription factors that have been shown to regulate multiple biological processes, such as hematopoiesis, vasculogenesis and cardiogenesis during embryonic development. Recent studies indicate that several SOX family members play important roles in tumorigenesis. In this review, we introduce SOX7 gene and protein structures, and discuss its expression and functional role in cancer development and progression. SOX7 is frequently downregulated in many human cancers and its reduced expression correlates with poor prognoses of several cancers. Functional studies reveal many tumor suppressive properties of SOX7 in prostate, colon, lung, and breast cancers. To date, although a few target genes of SOX7 have been identified, SOX7-mediated gene expression has not been investigated in a cancer-relevant context. Our recent studies not only for the first time demonstrate a tumor suppressive role of SOX7 in a xenograft mouse model, but also unravel that many genes regulating cell death, growth and apoptosis are affected by SOX7, strongly supporting a pivotal role of SOX7 in tumorigenesis. Thus, currently available data clearly indicate a tumor suppressive role of SOX7, but the mechanisms underlying its gene expression and tumor suppressive activity remain undetermined. The research of SOX7 in cancers remains a fertile area to be explored.

Identification of novel candidate gene loci and increased sex chromosome aneuploidy among infants with conotruncal heart defects

Congenital heart defects (CHDs) are common malformations, affecting four to eight per 1,000 total births. Conotruncal defects are an important pathogenetic subset of CHDs, comprising nearly 20% of the total. Although both environmental and genetic factors are known to contribute to the occurrence of conotruncal defects, the causes remain unknown for most. To identify novel candidate genes/loci, we used array comparative genomic hybridization to detect chromosomal microdeletions/duplications. From a population base of 974,579 total births born during 1999-2004, we screened 389 California infants born with tetralogy of Fallot or d-transposition of the great arteries. We found that 1.7% (5/288) of males with a conotruncal defect had sex chromosome aneuploidy, a sevenfold increased frequency (relative risk = 7.0; 95% confidence interval 2.9-16.9). We identified eight chromosomal microdeletions/duplications for conotruncal defects. From these duplications and deletions, we found five high priority candidate genes (GATA4, CRKL, BMPR1A, SNAI2, and ZFHX4). This is the initial report that sex chromosome aneuploidy is associated with conotruncal defects among boys. These chromosomal microduplications/deletions provide evidence that GATA4, SNAI2, and CRKL are highly dosage sensitive genes involved in outflow tract development. Genome wide screening for copy number variation can be productive for identifying novel genes/loci contributing to non-syndromic common malformations.

Impact of SOX18 expression in cancer cells and vessels on the outcome of invasive ductal breast carcinoma

PURPOSE

SOX18 is a transcription factor known to be involved in hair follicle, blood and lymphatic vessel development, as well as wound healing processes (together with SOX7 and SOX17). In addition, it has been reported that SOX18 may affect the growth of cancer cells in vitro. Until now, the exact role of SOX18 expression in invasive ductal breast carcinoma (IDC) has remained unknown.

METHODS

In this study, we have investigated SOX18 expression in cancer cells and endothelial cells in 122 IDC samples using immunohistochemistry (IHC). SOX18 expression was also determined using real-time PCR and Western blotting in a series of breast cancer-derived cell lines (i.e., MCF-7, BT-474, SK-BR-3, MDA-MB-231, BO2).

RESULTS

Using IHC, we observed SOX18 nuclear expression in cancer cells, as well as in blood and lymphatic vessels of the IDC samples tested. SOX18 expression in the IDC samples correlated with a higher malignancy grade (Grade 2 and Grade 3 versus Grade 1; p = 0.02 and p = 0.009, respectively) and VEGF-D expression (r = 0.27, p = 0.007). SOX18 expression was also associated with HER2 positivity (p = 0.02). A significantly higher SOX18 expression was found in the HER2-positive cell line BT-474, and a significantly lower expression in the triple negative cell lines MDA-MB-231 and BO2. Laser capture microdissection of IDC samples revealed significantly higher mRNA SOX7, SOX17 and SOX18 expression levels in the vessels as compared to the cancer cells (p = 0.02 and p = 0.0002, p < 0.0001, respectively). SOX18 positive intratumoral and peritumoral microvessel counts (MVC) were associated with higher malignancy grades (p = 0.04 and p = 0.02, respectively). Moreover, peritumoral SOX18 positive MVC were found to act as an independent marker for a poor prognosis (p = 0.04).

CONCLUSION

SOX18 expression may serve as a marker for a poor prognosis in IDC.

A potential relationship among beta-defensins haplotype, SOX7 duplication and cardiac defects

OBJECTIVE

To determine the pathogenesis of a patient born with congenital heart defects, who had appeared normal in prenatal screening.

METHODS

In routine prenatal screening, G-banding was performed to analyse the karyotypes of the family and fluorescence in situ hybridization was used to investigate the 22q11.2 deletion in the fetus. After birth, the child was found to be suffering from heart defects by transthoracic echocardiography. In the following study, sequencing was used to search for potential mutations in pivotal genes. SNP-array was employed for fine mapping of the aberrant region and quantitative real-time PCR was used to confirm the results. Furthermore, other patients with a similar phenotype were screened for the same genetic variations. To compare with a control, these variations were also assessed in the general population.

RESULTS

The child and his mother each had a region that was deleted in the beta-defensin repeats, which are usually duplicated in the general population. Besides, the child carried a SOX7-gene duplication. While this duplication was not detected in his mother, it was found in two other patients with cardiac defects who also had the similar deletion in the beta-defensin repeats.

CONCLUSION

The congenital heart defects of the child were probably caused by a SOX7-gene duplication, which may be a consequence of the partial haplotype of beta-defensin regions at 8p23.1. To our knowledge, this is the first congenital heart defect case found to have the haplotype of beta-defensin and the duplication of SOX7.

Mouse TU tagging: a chemical/genetic intersectional method for purifying cell type-specific nascent RNA

Transcriptional profiling is a powerful approach for understanding development and disease. Current cell type-specific RNA purification methods have limitations, including cell dissociation trauma or inability to identify all RNA species. Here, we describe "mouse thiouracil (TU) tagging," a genetic and chemical intersectional method for covalent labeling and purification of cell type-specific RNA in vivo. Cre-induced expression of uracil phosphoribosyltransferase (UPRT) provides spatial specificity; injection of 4-thiouracil (4TU) provides temporal specificity. Only UPRT(+) cells exposed to 4TU produce thio-RNA, which is then purified for RNA sequencing (RNA-seq). This method can purify transcripts from spatially complex and rare (<5%) cells, such as Tie2:Cre(+) brain endothelia/microglia (76% validated by expression pattern), or temporally dynamic transcripts, such as those acutely induced by lipopolysaccharide (LPS) injection. Moreover, generating chimeric mice via UPRT(+) bone marrow transplants identifies immune versus niche spleen RNA. TU tagging provides a novel method for identifying actively transcribed genes in specific cells at specific times within intact mice.

Tumor suppressor SCUBE2 inhibits breast-cancer cell migration and invasion through the reversal of epithelial-mesenchymal transition

SCUBE2 (signal peptide-CUB-EGF domain-containing protein 2) belongs to a secreted and membrane-associated multi-domain SCUBE protein family. We previously demonstrated that SCUBE2 was a novel breast-tumor suppressor and could be a useful prognostic marker. However, the role of SCUBE2 in breast-cancer cell migration and invasion and how it is regulated during the epithelial-mesenchymal transition (EMT) remain undefined. In this study, we showed that ectopic SCUBE2 overexpression could enhance the formation of E-cadherin-containing adherens junctions by β-catenin/SOX-mediated induction of forkhead box A1 (a positive regulator of E-cadherin) and upregulation of E-cadherin, which in turn led to epithelial transition and inhibited migration and invasion of aggressive MDA-MB-231 breast-carcinoma cells. SCUBE2 expression was repressed together with that of E-cadherin in TGF-β-induced EMT; direct expression of SCUBE2 alone was sufficient to inhibit the TGF-β-induced EMT. Furthermore, quantitative DNA methylation, methylation-specific PCR, and chromatin immunoprecipitation analyses revealed that SCUBE2 expression was inactivated by DNA hypermethylation at the CpG islands by recruiting and binding DNA methyltransferase 1 during TGF-β-induced EMT. Together, our results suggest that SCUBE2 plays a key role in suppressing breast-carcinoma cell mobility and invasiveness by increasing the formation of the epithelial E-cadherin-containing adherens junctions to promote epithelial differentiation and drive the reversal of EMT.

Congenital diaphragmatic hernia interval on chromosome 8p23.1 characterized by genetics and protein interaction networks

Chromosome 8p23.1 is a common hotspot associated with major congenital malformations, including congenital diaphragmatic hernia (CDH) and cardiac defects. We present findings from high-resolution arrays in patients who carry a loss (n = 18) or a gain (n = 1) of sub-band 8p23.1. We confirm a region involved in both diaphragmatic and heart malformations. Results from a novel CNVConnect algorithm, prioritizing protein-protein interactions between products of genes in the 8p23.1 hotspot and products of previously known CDH causing genes, implicated GATA4, NEIL2, and SOX7 in diaphragmatic defects. Sequence analysis of these genes in 226 chromosomally normal CDH patients, as well as in a small number of deletion 8p23.1 patients, showed rare unreported variants in the coding region; these may be contributing to the diaphragmatic phenotype. We also demonstrated that two of these three genes were expressed in the E11.5-12.5 primordial mouse diaphragm, the developmental stage at which CDH is thought to occur. This combination of bioinformatics and expression studies can be applied to other chromosomal hotspots, as well as private microdeletions or microduplications, to identify causative genes and their interaction networks.

Foregut Mesenchyme Contributes Cells to Islets during Pancreatic Development in a 3-Dimensional Avian Model

Current interest in the potential use of pancreatic stem-cells in the treatment of insulin dependent diabetes mellitus has led to increased research into normal pancreatic development. Pancreatic organogenesis involves branching morphogenesis of undifferentiated epithelium within surrounding mesenchyme. Current understanding is that the pancreatic islets develop exclusively from the epithelium of the embryonic buds. However, a cellular contribution to islets by mesenchyme has not been conclusively excluded. We present evidence that the mesenchyme of both the dorsal pancreatic bud and stomach rudiment make a substantial contribution of cells to islets during development in a three-dimensional avian model. These data suggest that mesenchyme can be a source not only of signals but also of cells for the definitive epithelia, making pancreatic organogenesis more akin to that of the kidney than to other endodermal organs. This raises the possibility for the use of mesenchymal cells as stem-or progenitor-cells for islet transplantation.

Insertional translocation of 15q25-q26 into 11p13 and duplication at 8p23.1 characterized by high resolution arrays in a boy with congenital malformations and aniridia

We report on a boy presenting submucous cleft palate, hydronephrosis, ventriculoseptal defect, aniridia, and developmental delay. Additional material on 11p13 was cytogenetically visible and array analyses identified a duplicated segment on 15q25-26 chromosome region; further, array analyses revealed a small deletion (49 kb) at 11p13 region involving the ELP4 gene and a duplication at 8p23.1. Results were confirmed with both molecular and molecular cytogenetics techniques. Possibilities for etiological basis of clinical phenotype are discussed.

Decreased expression of SOX7 is correlated with poor prognosis in lung adenocarcinoma patients

Lung adenocarcinoma is the most frequently histologic subtype and the most histologically heterogeneous form of lung cancer. De-regulation of Wnt/β-catenin signaling pathway is implicated in lung carcinogenesis. SOX7, as a member of high mobility group (HMG) transcription factor family, plays a role in the modulation of the Wnt/β-catenin signaling pathway. However, the expression pattern and clinicopathological significance of SOX7 in patients with lung adenocarcinoma is still unclear. To address this problem, the SOX7 mRNA expression was detected by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Immunohistochemical studies were performed on 288 pairs of adjacent normal lung and lung adenocarcinoma tissues with complete follow-up records. Association of SOX7 protein expression with clinical outcomes was evaluated using the Kaplan-Meier method and a multivariate Cox proportional hazards regression model. SOX7 mRNA expression was significantly down-regulated in lung adenocarcinoma compared with matched adjacent normal tissues (P < 0.001). SOX7 protein was expressed in the cytoplasm of lung adenocarcinoma cells in 106/288 (36.8 %) of cases, whereas its immunoreactivities were predominantly located in the cytoplasm of the adjacent normal tissues. The reduced SOX7 expression was correlated with poor differentiation (P = 0.002), lymph node metastasis (P = 0.011) and advanced TNM stage (P = 0.006). Regarding patient survival, the overall survival and the disease-free survival rates were both significantly lower in patients with SOX7-negative tumors than in those with SOX7-positive tumors (P = 0.018 and 0.013, respectively). Multivariate analysis using a Cox proportional-hazards model demonstrated that SOX7 expression status was an independent prognostic factor predicting the overall survival and the disease-free survival of patients with lung adenocarcinoma (P = 0.021 and 0.016, respectively).Our data suggest that the decreased expression of SOX7 is an important feature of lung adenocarcinoma. The expression level of SOX protein may be a useful prognostic marker for patients with lung adenocarcinoma.

KLF4 and SOX9 transcription factors antagonize β-catenin and inhibit TCF-activity in cancer cells

The transcriptional activator β-catenin is a key mediator of the canonical Wnt signaling pathway. β-catenin itself does not bind DNA but functions via interaction with T-cell factor (TCF)/lymphoid-enhancing factor (LEF) transcription factors. Thus, in the case of active Wnt signaling, β-catenin, in cooperation with TCF/LEF proteins family, activates the expression of a wide variety of genes. To date, the list of established β-catenin interacting targets is far from complete. In this study, we aimed to establish the interaction between β-catenin and transcription factors that might affect TCF activity. We took advantage of EMSA, using TCF as a probe, to screen oligonucleotides known to bind specific transcription factors that might dislodge or antagonize β-catenin/TCF binding. We found that Sox9 and KLF4 antagonize β-catenin/TCF binding in HEK293, A549, SW480, and T47D cells. This inhibition of TCF binding was concentration-dependent and correlated to the in vitro TCF-luciferase functional assays. Overexpression of Sox9 and KLF4 transcription factors in cancer cells shows a concentration-dependent reduction of TCF-luciferase as well as the TCF-binding activities. In addition, we demonstrated that both Sox9 and KLF4 interact with β-catenin in an immunoprecipitation assay and reduce its binding to TCF4. Together, these results demonstrate that Sox9 and KLF4 transcription factors antagonize β-catenin/TCF in cancer cells.

Mouse model reveals the role of SOX7 in the development of congenital diaphragmatic hernia associated with recurrent deletions of 8p23.1

Recurrent microdeletions of 8p23.1 that include GATA4 and SOX7 confer a high risk of both congenital diaphragmatic hernia (CDH) and cardiac defects. Although GATA4-deficient mice have both CDH and cardiac defects, no humans with cardiac defects attributed to GATA4 mutations have been reported to have CDH. We were also unable to identify deleterious GATA4 sequence changes in a CDH cohort. This suggested that haploinsufficiency of another 8p23.1 gene may contribute, along with GATA4, to the development of CDH. To determine if haploinsufficiency of SOX7-another transcription factor encoding gene-contributes to the development of CDH, we generated mice with a deletion of the second exon of Sox7. A portion of these Sox7(Δex2/+) mice developed retrosternal diaphragmatic hernias located in the anterior muscular portion of the diaphragm. Anterior CDH is also seen in Gata4(+/-) mice and has been described in association with 8p23.1 deletions in humans. Immunohistochemistry revealed that SOX7 is expressed in the vascular endothelial cells of the developing diaphragm and may be weakly expressed in some diaphragmatic muscle cells. Sox7(Δex2/Δex2) embryos die prior to diaphragm development with dilated pericardial sacs and failure of yolk sac remodeling suggestive of cardiovascular failure. Similar to our experience screening GATA4, no clearly deleterious SOX7 sequence changes were identified in our CDH cohort. We conclude that haploinsufficiency of Sox7 or Gata4 is sufficient to produce anterior CDH in mice and that haploinsufficiency of SOX7 and GATA4 may each contribute to the development of CDH in individuals with 8p23.1 deletions.

SOX7 regulates the expression of VE-cadherin in the haemogenic endothelium at the onset of haematopoietic development

At early stages of vertebrate ontogeny, blood and endothelial cells develop from a common mesodermal progenitor, the haemangioblast. Upon haematopoietic commitment, the haemangioblast generates blood precursors through populations of endothelial cells with haemogenic properties. Although several transcription factors have been implicated in haemangioblast differentiation, the precise mechanisms governing cell fate decisions towards the generation of haemogenic endothelium precursors remain largely unknown. Under defined conditions, embryonic stem (ES) cells can be differentiated into haemangioblast-like progenitors that faithfully recapitulate early embryonic haematopoiesis. Here, we made use of mouse ES cells as a model system to understand the role of SOX7, a member of a large family of transcription factors involved in a wide range of developmental processes. During haemangioblast differentiation, SOX7 is expressed in haemogenic endothelium cells and is downregulated in nascent blood precursors. Gain-of-function assays revealed that the enforced expression of Sox7 in haemangioblast-derived blast colonies blocks further differentiation and sustains the expression of endothelial markers. Thus, to explore the transcriptional activity of SOX7, we focused on the endothelial-specific adhesion molecule VE-cadherin. Similar to SOX7, VE-cadherin is expressed in haemogenic endothelium and is downregulated during blood cell formation. We show that SOX7 binds and activates the promoter of VE-cadherin, demonstrating that this gene is a novel downstream transcriptional target of SOX7. Altogether, our findings suggest that SOX7 is involved in the transcriptional regulation of genes expressed in the haemogenic endothelium and provide new clues to decipher the molecular pathways that drive early embryonic haematopoiesis.

Genome-wide analysis of HMGA2 transcription factor binding sites by ChIP on chip in gastric carcinoma cells

High mobility group protein A2 (HMGA2) is an architectural transcription factor that plays an important role in development and progression of malignant neoplasias. Recently, some studies reported that HMGA2 is also implicated in epithelial-mesenchymal transitions (EMT) and cancer stem cells. But the underlying mechanisms of these conditions are poorly understood. Therefore, we established an EMT model of gastric carcinoma cells by overexpressing HMGA2 in vitro, then global mapping of HMGA2 potential transcription factor binding sites was identified by promoter microarray in these cells, and the date obtained from the microarrays were validated via chromatin immunoprecipitation-PCR (ChIP-PCR) and real-time PCR. HMGA2 potential target genes were classified in KEGG database and Gene Ontology (GO) analyses. To our knowledge, this is the first report on the genome-wide analysis of HMGA2 downstream direct targets, and these findings will be valuable in understanding the roles of HMGA2 in EMT.

The 14q22.2 colorectal cancer variant rs4444235 shows cis-acting regulation of BMP4

Common genetic variation at human 14q22.2 tagged by rs4444235 is significantly associated with colorectal cancer (CRC) risk. Re-sequencing was used to comprehensively annotate the 17kb region of strong linkage disequilibrium encompassing rs4444235. Through bioinformatic analyses using H3K4Me1, H3K4Me3, and DNase-I hypersensitivity chromatin signatures and evolutionary conservation we identified seven candidate disease-causing single-nucleotide polymorphisms mapping to six regions within the 17-kb region predicted to have regulatory potential. Reporter gene studies of these regions demonstrated that the element to which rs4444235 maps acts as an allele-specific transcriptional enhancer. Allele-specific expression studies in CRC cell lines heterozygous for rs4444235 showed significantly increased expression of bone morphogenetic protein-4 (BMP4) associated with the risk allele (P<0.001). These data provide evidence for a functional basis for the non-coding risk variant rs4444235 at 14q22.2 and emphasizes the importance of genetic variation in the BMP pathway genes as determinants of CRC risk.

SRY-box containing gene 17 regulates the Wnt/β-catenin signaling pathway in oligodendrocyte progenitor cells

The SRY-box (Sox) transcription factors regulate oligodendrocyte differentiation, but their signaling targets are largely unknown. We have identified a major signal transduction pathway regulated by Sox containing gene 17 (Sox17) in the oligodendrocyte lineage. Microarray analysis in oligodendrocyte progenitor cells (OPCs) after Sox17 attenuation revealed upregulated genes associated with cell cycle control and activation of the Wingless and integration site (Wnt)/β-catenin pathway. Sox17 knockdown also increases the levels of cyclin D1, Axin2, and activated β-catenin. In OPCs, the expression pattern of Sox17, cyclin D1, and secreted Frizzled-related protein-1 in the presence of platelet-derived growth factor (PDGF) was coordinately accelerated by addition of thyroid hormone, indicating differentiation-induced regulation of Sox17 targets. In developing white matter, decreased total β-catenin, activated β-catenin, and cyclin D1 levels coincided with the peak of Sox17 expression, and immunoprecipitates showed a developmentally regulated interaction among Sox17, T-cell transcription factor 4, and β-catenin proteins. In OPCs, PDGF stimulated phosphorylation of glycogen synthase 3β and the Wnt coreceptor LRP6, and enhanced β-catenin-dependent gene expression. Sox17 overexpression inhibited PDGF-induced TOPFLASH and cyclin D1 promoter activity, and decreased endogenous cyclin D1, activated β-catenin, as well as total β-catenin levels. Recombinant Sox17 prevented Wnt3a from repressing myelin protein expression, and inhibition of Sox17-mediated proteasomal degradation of β-catenin blocked myelin protein induction. These results indicate that Sox17 suppresses cyclin D1 expression and cell proliferation by directly antagonizing β-catenin, whose activity in OPCs is stimulated not only by Wnt3a, but also by PDGF. Our identification of downstream targets of Sox17 thus defines signaling pathways and molecular mechanisms in OPCs that are regulated by Sox17 during cell cycle exit and the onset of differentiation in oligodendrocyte development.

SOX4 interacts with plakoglobin in a Wnt3a-dependent manner in prostate cancer cells

Background

SOX4 is a developmental transcription factor that is required for differentiation and proliferation in multiple tissues. SOX4 is overexpressed in many human malignancies, but the precise role of SOX4 in cancer progression is still not well understood. Thus, the identification of additional SOX4 binding partners is essential for elucidating the mechanism of SOX4-mediated effects in cancer progression.

Results

Here, we have adapted a one-step affinity purification method that enables rapid purification of SOX4 complexes via intracellular biotinylation of the amino-terminus of SOX4 to perform large-scale proteomics analysis. We have discovered that junction plakoglobin (JUP) interacts with SOX4 in both the cytosol and the nucleus and the interaction between SOX4 and plakoglobin is significantly increased when prostate and breast cancer cells are stimulated with WNT3A. Interactions between SOX4 and plakoglobin were further enhanced by the nuclear export inhibitor leptomycin B (LMB), suggesting that plakoglobin promotes nuclear export of SOX4. The SOX4-plakoglobin complex affected the expression of Wnt pathway target genes and SOX4 downstream targets, such as AXIN2, DICER1, and DHX9. In addition, SOX4 DNA binding activity to the promoters of DICER1, AXIN2, DHX9 and SOX4 itself was reduced by conditions that promote SOX4-plakoglobin complex formation. Conditions that enhanced SOX4-plakoglobin interactions resulted in reduced transcriptional activity of β-catenin luciferase reporters.

Conclusions

These data suggest that this newly identified interaction between SOX4 and plakoglobin is inhibitory and provides new insights into the role of SOX4 in key pathways in cell proliferation, development, and cancer progression.

Culture of mouse embryonic stem cells with serum but without exogenous growth factors is sufficient to generate functional hepatocyte-like cells

Mouse embryonic stem cells (mESC) have been used to study lineage specification in vitro, including towards a hepatocyte-like fate, and such investigations guided lineage differentiation protocols for human (h)ESC. We recently described a four-step protocol to induce hepatocyte-like cells from hESC which also induced hepatocyte-like cell differentiation of mouse induced pluripotent stem cells. As ESC also spontaneously generate hepatocyte-like cells, we here tested whether the growth factors and serum used in this protocol are required to commit mESC and hESC to hepatocyte-like cells. Culture of mESC from two different mouse strains in the absence of serum and growth factors did not induce primitive streak/definitive endoderm genes but induced default differentiation to neuroectoderm on day 6. Although Activin-A and Wnt3 induced primitive streak/definitive endoderm transcripts most robustly in mESC, simple addition of serum also induced these transcripts. Expression of hepatoblast genes occurred earlier when growth factors were used for mESC differentiation. However, further maturation towards functional hepatocyte-like cells was similar in mESC progeny from cultures with serum, irrespective of the addition of growth factors, and irrespective of the mouse strain. This is in contrast to hESC, where growth factors are required for specification towards functional hepatocyte-like cells. Culture of mESC with serum but without growth factors did not induce preferential differentiation towards primitive endoderm or neuroectoderm. Thus, although induction of primitive streak/definitive endoderm specific genes and proteins is more robust when mESC are exposed to a combination of serum and exogenous growth factors, ultimate generation of hepatocyte-like cells from mESC occurs equally well in the presence or absence of exogenous growth factors. The latter is in contrast to what we observed for hESC. These results suggest that differences exist between lineage specific differentiation potential of mESC and hESC, requiring optimization of different protocols for ESC from either species.

Inhibition of SRY-calmodulin complex formation induces ectopic expression of ovarian cell markers in developing XY gonads

The transcription factor sex-determining region of the Y chromosome (SRY) plays a key role in human sex determination, because mutations in SRY cause disorders of sex development in XY individuals. During gonadal development, Sry in pre-Sertoli cells activates Sox9 gene transcription, committing the fate of the bipotential gonad to become a testis rather than an ovary. The high-mobility group domain of human SRY contains two independent nuclear localization signals, one bound by calmodulin (CaM) and the other by importin-β. Although XY females carry SRY mutations in these nuclear localization signals that affect SRY nuclear import in transfected cells, it is not known whether these transport mechanisms are essential for gonadal development and sex determination. Here, we show that mouse Sry protein binds CaM and that a CaM antagonist reduces CaM binding, nuclear accumulation, and transcriptional activity of Sry in transfected cells. CaM antagonist treatment of cultured, sexually indifferent XY mouse fetal gonads led to reduced expression of the Sry target gene Sox9, defects in testicular cord formation, and ectopic expression of the ovarian markers Rspondin1 and forkhead box L2. These results indicate the importance of CaM for SRY nuclear import, transcriptional activity, testis differentiation, and sex determination.

Human embryonic and rat adult stem cells with primitive endoderm-like phenotype can be fated to definitive endoderm, and finally hepatocyte-like cells

Stem cell-derived hepatocytes may be an alternative cell source to treat liver diseases or to be used for pharmacological purposes. We developed a protocol that mimics mammalian liver development, to differentiate cells with pluripotent characteristics to hepatocyte-like cells. The protocol supports the stepwise differentiation of human embryonic stem cells (ESC) to cells with characteristics of primitive streak (PS)/mesendoderm (ME)/definitive endoderm (DE), hepatoblasts, and finally cells with phenotypic and functional characteristics of hepatocytes. Remarkably, the same protocol can also differentiate rat multipotent adult progenitor cells (rMAPCs) to hepatocyte-like cells, even though rMAPC are isolated clonally from cultured rat bone marrow (BM) and have characteristics of primitive endoderm cells. A fraction of rMAPCs can be fated to cells expressing genes consistent with a PS/ME/DE phenotype, preceding the acquisition of phenotypic and functional characteristics of hepatocytes. Although the hepatocyte-like progeny derived from both cell types is mixed, between 10-20% of cells are developmentally consistent with late fetal hepatocytes that have attained synthetic, storage and detoxifying functions near those of adult hepatocytes. This differentiation protocol will be useful for generating hepatocyte-like cells from rodent and human stem cells, and to gain insight into the early stages of liver development.

Alterations in the developing testis transcriptome following embryonic vinclozolin exposure

The current study investigates the direct effects of in utero vinclozolin exposure on the developing F1 generation rat testis transcriptome. Previous studies have demonstrated that exposure to vinclozolin during embryonic gonadal sex determination induces epigenetic modifications of the germ line and transgenerational adult onset disease states. Microarray analyses were performed to compare control and vinclozolin treated testis transcriptomes at embryonic days 13, 14 and 16. A total of 576 differentially expressed genes were identified and the major cellular functions and pathways associated with these altered transcripts were examined. The sets of regulated genes at the different development periods were found to be transiently altered and distinct. Categorization by major known functions of altered genes was performed. Specific cellular process and pathway analyses suggest the involvement of Wnt and calcium signaling, vascular development and epigenetic mechanisms as potential mediators of the direct F1 generation actions of vinclozolin.

Interactions between SOX factors and Wnt/beta-catenin signaling in development and disease

The SOX family of transcription factors have emerged as modulators of canonical Wnt/beta-catenin signaling in diverse development and disease contexts. There are over 20 SOX proteins encoded in the vertebrate genome and recent evidence suggests that many of these can physically interact with beta-catenin and modulate the transcription of Wnt-target genes. The precise mechanisms by which SOX proteins regulate beta-catenin/TCF activity are still being resolved and there is evidence to support a number of models including: protein-protein interactions, the binding of SOX factors to Wnt-target gene promoters, the recruitment of co-repressors or co-activators, modulation of protein stability, and nuclear translocation. In some contexts, Wnt signaling also regulates SOX expression resulting in feedback regulatory loops that fine-tune cellular responses to beta-catenin/TCF activity. In this review, we summarize the examples of Sox-Wnt interactions and examine the underlying mechanisms of this potentially widespread and underappreciated mode of Wnt-regulation.

Sox17-2A-iCre: a knock-in mouse line expressing Cre recombinase in endoderm and vascular endothelial cells

Sox17 encodes an SRY-related high-mobility group (HMG) box transcription factor that is essential for endoderm formation and fetal hematopoietic stem cell maintenance. In the mouse, expression of Sox17 is first observed in the extraembryonic endoderm and is subsequently seen in the definitive endoderm as well as in blood and the endothelial cells of the developing vasculature. To conditionally inactivate genes in these domains, we have targeted the Sox17 locus to generate a bicistronic mRNA linking Sox17 to a codon improved Cre recombinase (iCre) via a viral 2A sequence. Here we report a new Cre knock-in mouse line, Sox17-2A-iCre, with activity in the developing endoderm, the vascular endothelial cells of the cardiovascular system and the hematopoietic system. Our results indicate that the Sox17-2A-iCre is active in an early endoderm progenitor and recombination of the Rosa26 reporter was observed in all previously reported expression domains of Sox17. The Sox17-2A-iCre line will be an excellent tool to conditionally inactivate genes in the definitive endoderm as well as in the vasculature and hematopoietic system.

Induction and down-regulation of Sox17 and its possible roles during the course of gastrointestinal tumorigenesis

BACKGROUND & AIMS

The activation of Wnt/beta-catenin signaling causes the development of gastric and colon cancers. Sox17 represses Wnt/beta-catenin signaling and is down-regulated in colon cancer. This study was designed to elucidate the role of Sox17 during the course of gastrointestinal tumorigenesis.

METHODS

Sox17 expression was examined in gastrointestinal tumors of mouse models and humans. The roles of Sox17 in gastric tumorigenesis were examined by cell culture experiments and by construction of Sox17 transgenic mice.

RESULTS

Sox17 was induced in K19-Wnt1/C2mE mouse gastric tumors and K19-Wnt1 preneoplastic lesions, where Wnt/beta-catenin signaling was activated. Consistently, Wnt activation induced Sox17 expression in gastric cancer cells. In contrast, Sox17 was rarely detected by immunohistochemistry in gastric and colon cancers, whereas strong nuclear staining of Sox17 was found in >70% of benign gastric and intestinal tumors. Treatment with a demethylating agent induced Sox17 expression in gastric cancer cells, thus indicating the down-regulation of Sox17 by methylation. Moreover, transfection of Sox17 in gastric cancer cells suppressed both the Wnt activity and colony formation efficiency. Finally, transgenic expression of Sox17 suppressed dysplastic tumor development in K19-Wnt1/C2mE mouse stomach.

CONCLUSIONS

Sox17 plays a tumor suppressor role through suppression of Wnt signaling. However, Sox17 is induced by Wnt activation in the early stage of gastrointestinal tumorigenesis, and Sox17 is down-regulated by methylation during malignant progression. It is therefore conceivable that Sox17 protects benign tumors from malignant progression at an early stage of tumorigenesis, and down-regulation of Sox17 contributes to malignant progression through promotion of Wnt activity.

Chromosome 8p23.1 deletions as a cause of complex congenital heart defects and diaphragmatic hernia

Recurrent interstitial deletion of a region of 8p23.1 flanked by the low copy repeats 8p-OR-REPD and 8p-OR-REPP is associated with a spectrum of anomalies that can include congenital heart malformations and congenital diaphragmatic hernia (CDH). Haploinsufficiency of GATA4 is thought to play a critical role in the development of these birth defects. We describe two individuals and a monozygotic twin pair discordant for anterior CDH all of whom have complex congenital heart defects caused by this recurrent interstitial deletion as demonstrated by array comparative genomic hybridization. To better define the genotype/phenotype relationships associated with alterations of genes on 8p23.1, we review the spectrum of congenital heart and diaphragmatic defects that have been reported in individuals with isolated GATA4 mutations and interstitial, terminal, and complex chromosomal rearrangements involving the 8p23.1 region. Our findings allow us to clearly define the CDH minimal deleted region on chromosome 8p23.1 and suggest that haploinsufficiency of other genes, in addition to GATA4, may play a role in the severe cardiac and diaphragmatic defects associated with 8p23.1 deletions. These findings also underscore the importance of conducting a careful cytogenetic/molecular analysis of the 8p23.1 region in all prenatal and postnatal cases involving congenital defects of the heart and/or diaphragm.

Cell-intrinsic and vector-related properties cooperate to determine the incidence and consequences of insertional mutagenesis

In gene therapeutic approaches targeting hematopoietic cells, insertional mutagenesis may provoke clonal dominance with potential progress to overt leukemia. To investigate the contribution of cell-intrinsic features and determine the frequency of insertional proto-oncogene activation, we sorted hematopoietic subpopulations before transduction with replication-deficient gamma-retroviral vectors and studied the clonal repertoire in transplanted C57BL/6J mice. Progressive clonal dominance only developed in the progeny of populations with intrinsic stem cell potential, where expanding clones with insertional upregulation of proto-oncogenes such as Evi1 were retrieved with a frequency of approximately 10(-4). Longitudinal studies by high-throughput sequencing and locus-specific quantitative PCR showed clones with >50-fold expansion between weeks 5 and 31 after transplantation. In contrast, insertional events in proto-oncogenes did not endow the progeny of multipotent or myeloid-restricted progenitors with the potential for clonal dominance (risk <10(-6)). Transducing sorted hematopoietic stem cells (HSCs) with self-inactivating (SIN) lentiviral vectors in short-term cultures improved chimerism, and although clonal dominance developed, there was no evidence for insertional events in the vicinity of proto-oncogenes as the underlying cause. We conclude that cell-intrinsic properties cooperate with vector-related features to determine the incidence and consequences of insertional mutagenesis. Furthermore, our study offers perspectives for refinement of animal experiments in the assessment of vector-related genotoxicity.

Sox17 promotes cell cycle progression and inhibits TGF-beta/Smad3 signaling to initiate progenitor cell behavior in the respiratory epithelium

The Sry-related high mobility group box transcription factor Sox17 is required for diverse developmental processes including endoderm formation, vascular development, and fetal hematopoietic stem cell maintenance. Expression of Sox17 in mature respiratory epithelial cells causes proliferation and lineage respecification, suggesting that Sox17 can alter adult lung progenitor cell fate. In this paper, we identify mechanisms by which Sox17 influences lung epithelial progenitor cell behavior and reprograms cell fate in the mature respiratory epithelium. Conditional expression of Sox17 in epithelial cells of the adult mouse lung demonstrated that cell cluster formation and respecification of alveolar progenitor cells toward proximal airway lineages were rapidly reversible processes. Prolonged expression of Sox17 caused the ectopic formation of bronchiolar-like structures with diverse respiratory epithelial cell characteristics in alveolar regions of lung. During initiation of progenitor cell behavior, Sox17 induced proliferation and increased the expression of the progenitor cell marker Sca-1 and genes involved in cell cycle progression. Notably, Sox17 enhanced cyclin D1 expression in vivo and activated cyclin D1 promoter activity in vitro. Sox17 decreased the expression of transforming growth factor-beta (TGF-beta)-responsive cell cycle inhibitors in the adult mouse lung, including p15, p21, and p57, and inhibited TGF-beta1-mediated transcriptional responses in vitro. Further, Sox17 interacted with Smad3 and blocked Smad3 DNA binding and transcriptional activity. Together, these data show that a subset of mature respiratory epithelial cells retains remarkable phenotypic plasticity and that Sox17, a gene required for early endoderm formation, activates the cell cycle and reinitiates multipotent progenitor cell behavior in mature lung cells.

Vascular defects in a mouse model of hypotrichosis-lymphedema-telangiectasia syndrome indicate a role for SOX18 in blood vessel maturation

Mutations in the transcription factor gene SOX18 cause vascular, lymphatic and hair follicle defects in humans with dominant and recessive forms of hypotrichosis-lymphedema-telangiectasia (HLT) syndrome. Here, we clarify the role of SOX18 in the vascular dysfunction in HLT by ultrastructural, immunofluorescence, molecular and functional analysis of vascular anomalies in embryos of the naturally occurring Sox18-mutant mouse strain ragged-opossum (Ra(Op)). Early genesis and patterning of vasculature was unimpaired in Ra(Op) embryos, but surface capillaries became enlarged from 12.5 dpc and embryos developed massive surface hemorrhage by 14.5 dpc. Large focal breaches in the endothelial barrier were observed, in addition to endothelial hyperplasia associated with impaired pericyte recruitment to the microvasculature. Expression of the genes encoding the endothelial factors MMP7, IL7R and N-cadherin was reduced in Ra(Op) embryos, suggesting that these are downstream targets of SOX18. Together, our results indicate that vascular anomalies in HLT arise from defects in regulation of genes required for the acquisition of structural integrity during microvascular maturation.

Genome-wide analysis of genetic alterations in Barrett's adenocarcinoma using single nucleotide polymorphism arrays

We performed genome-wide analysis of copy-number changes and loss of heterozygosity (LOH) in Barrett's esophageal adenocarcinoma by single nucleotide polymorphism (SNP) microarrays to identify associated genomic alterations. DNA from 27 esophageal adenocarcinomas and 14 matching normal tissues was subjected to SNP microarrays. The data were analyzed using dChipSNP software. Copy-number changes occurring in at least 25% of the cases and LOH occurring in at least 19% were regarded as relevant changes. As a validation, fluorescence in situ hybridization (FISH) of 8q24.21 (CMYC) and 8p23.1 (SOX7) was performed. Previously described genomic alterations in esophageal adenocarcinomas could be confirmed by SNP microarrays, such as amplification on 8q (CMYC, confirmed by FISH) and 20q13 or deletion/LOH on 3p (FHIT) and 9p (CDKN2A). Moreover, frequent gains were detected on 2p23.3, 7q11.22, 13q31.1, 14q32.31, 17q23.2 and 20q13.2 harboring several novel candidate genes. The highest copy numbers were seen on 8p23.1, the location of SOX7, which could be demonstrated to be involved in amplification by FISH. A nuclear overexpression of the transcription factor SOX7 could be detected by immunohistochemistry in two amplified tumors. Copy-number losses were seen on 18q21.32 and 20p11.21, harboring interesting candidate genes, such as CDH20 and CST4. Finally, a novel LOH region could be identified on 6p in at least 19% of the cases. In conclusion, SNP microarrays are a valuable tool to detect DNA copy-number changes and LOH at a high resolution. Using this technique, we identified several novel genes and DNA regions associated with esophageal adenocarcinoma.

Lineage specification of Flk-1+ progenitors is associated with divergent Sox7 expression in cardiopoiesis

Embryonic stem cell differentiation recapitulates the diverse phenotypes of a developing embryo, traceable according to markers of lineage specification. At gastrulation, the vascular endothelial growth factor (VEGF) receptor, Flk-1 (KDR), identifies a mesoderm-restricted potential of embryonic stem cells. The multi-lineage propensity of Flk-1(+) progenitors mandates the mapping of fate-modifying co-factors in order to stratify differentiating cytotypes and predict lineage competency. Here, Flk-1-based selection of early embryonic stem cell progeny separated a population depleted of pluripotent (Oct4, Sox2) and endoderm (Sox17) markers. The gene expression profile of the Flk-1(+) population was notable for a significant upregulation in the vasculogenic Sox7 transcription factor, which overlapped with the emergence of primordial cardiac transcription factors GATA-4, Myocardin and Nkx2.5. Sorting the parental Flk-1(+) pool with the chemokine receptor CXCR4 to enrich the cardiopoietic subpopulation uncovered divergent Sox7 expression, with a 7-fold induction in non-cardiac compared to cardiac progenitors. Bioinformatic resolution sequestered a framework of gene expression relationship between Sox transcription factor family members and the Flk-1/CXCR4 axes with significant integration of beta-catenin signaling. Thus, differential Sox7 gene expression presents a novel biomarker profile, and possible regulatory switch, to distinguish cardiovascular pedigrees within Flk-1(+) multi-lineage progenitors.

Sox7 Is an independent checkpoint for beta-catenin function in prostate and colon epithelial cells

The presence of somatic beta-catenin mutations in some prostate cancers implies that aberrant WNT signaling is involved in the cancer development. Although beta-catenin stability is regulated by a multicomponent destruction complex, mutational alterations of beta-catenin or other components of the destruction complexes are rare in prostate tumors. Therefore, beta-catenin may be regulated by another protein in the prostate. In fact, recent linkage and somatic deletion analyses in prostate cancers reveal a 1.4-Mb candidate tumor suppressor locus on 8p23.1, which includes the Sox7 gene. Here we show that Sox7 protein expression was indeed down-regulated in 47% (15 of 32) of prostate adenocarcinomas. In addition, Sox7 mRNA was down-regulated in 60% of snap-frozen tumors. This down-regulation was found to be due to tumor-specific promoter hypermethylation, which was present in 48% (10 of 21) of primary prostate tumors and 44% (11 of 25) of prostate cancer cell lines/xenografts. We discovered that Sox7 protein physically interacts with beta-catenin and suppresses beta-catenin-mediated transcription by depleting active beta-catenin. Furthermore, in HCT116 colorectal cancer cell lines with Sox7 inactivation, ectopic Sox7 expression suppressed cell proliferation and inhibited transcription that was activated by an endogenous mutant beta-catenin. Although nearly all colorectal cancers contain mutations in beta-catenin or adenomatous polyposis coli/axin, epigenetic silencing of Sox7 was still observed. These data suggest that Sox7 is a tumor suppressor that functions as an independent checkpoint for beta-catenin transcriptional activity. Inactivation of Sox7 could promote the development of a majority of colorectal tumors and approximately half of prostate tumors.

Ectopic expression of mouse Sry interferes with Wnt/beta-catenin signaling in mouse embryonal carcinoma cell lines

In mammals, Sry is the master regulator of male sex determination, although how it functions is still unclear. By contrast, female sex determination depends on the action of Rspo1 and Wnt4, the regulators of Wnt/beta-catenin signaling. To seek a possible interaction between male and female sex determination mechanisms, we examined whether Sry affects Wnt/beta-catenin signaling. Using the TOPFLASH reporter system to measure Lef/Tcf-dependent transcriptional activity, we showed that ectopic expression of mouse Sry strongly suppressed Wnt/beta-catenin signaling in mouse embryonal carcinoma and human embryonic kidney cell lines. This inhibition occurred downstream of beta-catenin but upstream of Lef/Tcf, and depended on both the HMG-box and the C-terminal transcriptional activation domain. By contrast, TOPFLASH was not inhibited by human SRY, which apparently lacks a transcriptional activation domain. However, a fusion construct consisting of human SRY attached to the C-terminal domain of mouse Sry was able to inhibit TOPFLASH effectively. Furthermore, Sry constructs carrying point mutations equivalent to those in human sex reversal mutations were less effective in inhibiting Wnt/beta-catenin signaling. Also, we showed that the action of Sry as a transcriptional activator was both necessary and sufficient to inhibit Wnt/beta-catenin signaling, suggesting that the transcriptional targets of Sry are responsible for the inhibition of signaling. Sox9 is a potential transcriptional target of Sry, although quantitative RT-PCR analysis indicates that the expression of Sox9 was not up-regulated by the ectopic expression of mouse Sry in mouse embryonal carcinoma cells. While the present study demonstrates an impact of mouse Sry on Wnt/beta-catenin signaling at an in vitro level, it requires further investigations to assess whether such action also takes place in vivo to regulate male sex determination.

Human SRY inhibits beta-catenin-mediated transcription

In most mammals, sex is determined by the presence or absence of the SRY gene. SRY encodes a DNA-binding HMG-box transcription factor which, during embryogenesis, is the initial trigger of testis differentiation from the bipotential gonad, yet its precise mode of function remains unclear. In ovarian development, R-spondin1 and Wnt4 act through the Wnt/beta-catenin-signaling pathway to regulate TCF-dependent expression of unknown target genes and repress testis development. Conversely, SRY may be necessary to prevent the development of ovaries by inhibiting the action of ovarian-determining genes. We hypothesize that SRY prevents Wnt/beta-catenin signaling, thereby inhibiting ovarian development. In HEK293T cells, SRY repressed beta-catenin-mediated TCF-dependent gene activation in the presence of a specific GSK3beta inhibitor or an activated beta-catenin mutant, suggesting that SRY inhibits Wnt signaling at the level of beta-catenin. Three SRY mutant proteins with nuclear localization defects, encoded by XY male-to-female patients, failed to inhibit beta-catenin; surprisingly four SRY sex reversed mutants with defective DNA-binding activity showed near wild-type SRY inhibitory activity. Moreover the potent transactivator SRY-VP16 fusion protein also showed wild-type SRY inhibitory activity. Thus SRY inhibition of beta-catenin involves neither DNA-binding nor transactivation functions of SRY. beta-Catenin and SRY interact in vitro and SRY expression triggered beta-catenin localization into specific nuclear bodies in NT2/D1 and Hela cells. We conclude that SRY inhibits beta-catenin-mediated Wnt signaling by a novel nuclear function of SRY that could be important in sex determination.

Epigenetic inactivation of the canonical Wnt antagonist SRY-box containing gene 17 in colorectal cancer

SRY-box containing gene 17 (Sox17) is a member of the high mobility group (HMG) transcription factor superfamily, which plays critical roles in the regulation of development and stem/precursor cell function, at least partly through repression of Wnt pathway activity. Modulators controlling aberrant Wnt signaling activation are frequently disrupted in human cancers through complementary effects of epigenetic and genetic changes. Our recent global analysis of CpG island hypermethylation and gene expression in colorectal cancer (CRC) cell lines revealed that SOX17 gene silencing is associated with DNA hypermethylation of a CpG island in the promoter region. Here, we report that CpG island methylation-dependent silencing of SOX17 occurs in 100% of CRC cell lines, 86% of colorectal adenomas, 100% of stage I and II CRC, 89% of stage III CRC, 89% of primary esophageal cancer, and 50% of non-small cell lung cancer. Overexpression of SOX17 in HCT116 CRC cells inhibits colony growth and beta-catenin/T-cell factor-dependent transcription. Structure-based deletion analysis further shows the presence of a Wnt signaling repression domain in the SOX17 HMG box. Together, our studies suggest that SOX17 is a negative modulator of canonical Wnt signaling, and that SOX17 silencing due to promoter hypermethylation is an early event during tumorigenesis and may contribute to aberrant activation of Wnt signaling in CRC.

The molecular mechanism governing the oncogenic potential of SOX2 in breast cancer

SOX genes encode a family of high-mobility group transcription factors that play critical roles in organogenesis. The functional specificity of different SOX proteins and the tissue specificity of a particular SOX factor are largely determined by the differential partnership of SOX transcription factors with other transcription regulators, many of which have not yet been discovered. Virtually all members of the SOX family have been found to be deregulated in a wide variety of tumors. However, little is known about the cellular and molecular behaviors involved in the oncogenic potential of SOX proteins. Using cell culture experiments, tissue analysis, molecular profiling, and animal studies, we report here that SOX2 promotes cell proliferation and tumorigenesis by facilitating the G(1)/S transition and through its transcription regulation of the CCND1 gene in breast cancer cells. In addition, we identified beta-catenin as the transcription partner for SOX2 and demonstrated that SOX2 and beta-catenin act in synergy in the transcription regulation of CCND1 in breast cancer cells. Our experiments not only determined a role for SOX2 in mammary tumorigenesis but also revealed another activity of the multifunctional protein, beta-catenin.

A functional screen for genes involved in Xenopus pronephros development

In Xenopus, the pronephros is the functional larval kidney and consists of two identifiable components; the glomus, the pronephric tubules, which can be divided into four separate segments, based on marker gene expression. The simplicity of this organ, coupled with the fact that it displays the same basic organization and function as more complex mesonephros and metanephros, makes this an attractive model to study vertebrate kidney formation. In this study, we have performed a functional screen specifically to identify genes involved in pronephros development in Xenopus. Gain-of-function screens are performed by injecting mRNA pools made from a non-redundant X. tropicalis full-length plasmid cDNA library into X. laevis eggs, followed by sib-selection to identify the single clone that caused abnormal phenotypes in the pronephros. Out of 768 egg and gastrula stage cDNA clones, 31 genes, approximately 4% of the screened clones, affected pronephric marker expression examined by whole mount in situ hybridization or antibody staining. Most of the positive clones had clear expression patterns in pronephros and predicted/established functions highly likely to be involved in developmental processes. In order to carry out a more detailed study, we selected Sox7, Cpeb3, P53csv, Mecr and Dnajc15, which had highly specific expression patterns in the pronephric region. The over-expression of these five selected clones indicated that they caused pronephric abnormalities with different temporal and spatial effects. These results suggest that our strategy to identify novel genes involved in pronephros development was highly successful, and that this strategy is effective for the identification of novel genes involved in late developmental events.

Sox18 and Sox7 play redundant roles in vascular development

Mutations in SOX18 cause the human hypotrichosis-lymphedema-telangiectasia (HLT) syndrome. Their murine counterparts are the spontaneous ragged mutants, showing combined defects in hair follicle, blood vessel, and lymphatic vessel development. Mice null for Sox18 display only mild coat defects, suggesting a dominant-negative effect of Sox18/ragged mutations and functional redundancy between Sox18 and other Sox-F proteins. We addressed this point in zebrafish. The zebrafish homologs of Sox18 and of Sox7 are expressed in angioblasts and in the endothelial component of nascent blood vessels in embryos. Knockdown of either gene, using moderate doses of specific morpholinos, had minimal effects on vessels. In contrast, simultaneous knockdown of both genes resulted in multiple fusions between the major axial vessels. With combined use of transgenic lines and molecular markers, we could show that endothelial cells are specified, but fail to acquire a correct arteriovenous identity. Venous endothelial cell differentiation was more severely affected than arterial. Thus, sox7 and sox18 play redundant but collectively essential roles in the establishment of proper arteriovenous identity in zebrafish. Our data suggest that a defect in arteriovenous identity could be responsible for the formation of telangiectases in patients with HLT.

Zebrafish Sox7 and Sox18 function together to control arterial-venous identity

Sox7 and Sox18 are members of the F-subgroup of Sox transcription factors family and are mostly expressed in endothelial compartments. In humans, dominant mutations in Sox18 are the underlying cause of the severe hypotrichosis-lymphedema-telangiectasia disorder characterized by vascular defects. However little is known about which vasculogenic processes Sox7 and Sox18 regulate in vivo. We cloned the orthologs of Sox7 and Sox18 in zebrafish, analysed their expression pattern and performed functional analyses. Both genes are expressed in the lateral plate mesoderm during somitogenesis. At later stages, Sox18 is expressed in all axial vessels whereas Sox7 expression is mainly restricted to the dorsal aorta. Knockdown of Sox7 or Sox18 alone failed to reveal any phenotype. In contrast, blocking the two genes simultaneously led to embryos displaying dysmorphogenesis of the proximal aorta and arteriovenous shunts, all of which can account for the lack of circulation observed in the trunk and tail. Gene expression analyses performed with general endothelial markers on double morphants revealed that Sox7 and Sox18 are dispensable for the initial specification and positioning of the major trunk vessels. However, morphants display ectopic expression of the venous Flt4 marker in the dorsal aorta and a concomitant reduction of the artery-specific markers EphrinB2a and Gridlock. The striking similarities between the phenotype of Sox7/Sox18 morphants and Gridlock mutants strongly suggest that Sox7 and Sox18 control arterial-venous identity by regulating Gridlock expression.

Identification of genes that exhibit changes in expression on the 8p chromosomal arm by the Systematic Multiplex RT-PCR (SM RT-PCR) and DNA microarray hybridization methods

Losses of the p-arm of chromosome 8 are frequently observed in breast, prostate, and other types of cancers. Using the Systematic Multiplex RT-PCR (SM RT-PCR) method and the DNA microarray hybridization method, we examined the expression of 273 genes located on the p-arm of chromosome 8 in five breast and three prostate human cancer cell lines. We observed frequent decreases in expression of two dozen genes and increases in expression of several genes on this chromosomal arm. These changes in gene expression of the cell lines were later confirmed by real-time qRT-PCR. Additionally and more importantly, we found that a number of these variations were also observed in the majority of clinical cases of breast cancer we examined. These included downregulation of the MYOM2, NP_859074, NP_001034551, NRG1, PHYIP (PHYHIP), Q7Z2R7, SFRP1, and SOX7 genes, and upregulation of the ESCO2, NP_115712 (GINS4), Q6P464, and TOPK (PBK) genes.

Back to basics: Sox genes

Sox genes are indispensable for multiple aspects of development. This primer briefly describes shared properties of the Sox gene family, and five well-characterized examples of vertebrate developmental mechanisms governed by Sox gene subgroups: testis development, central nervous system neurogenesis, oligodendrocyte development, chondrogenesis, and neural crest cell development. Also featured is an interview about current issues in the field with experts Jonas Muhr, Ph.D. and Robert Kelsh, Ph.D.

Sox17 and Sox4 differentially regulate beta-catenin/T-cell factor activity and proliferation of colon carcinoma cells

The canonical Wnt pathway is necessary for gut epithelial cell proliferation, and aberrant activation of this pathway causes intestinal neoplasia. We report a novel mechanism by which the Sox family of transcription factors regulate the canonical Wnt signaling pathway. We found that some Sox proteins antagonize while others enhance beta-catenin/T-cell factor (TCF) activity. Sox17, which is expressed in the normal gut epithelium but exhibits reduced expression in intestinal neoplasia, is antagonistic to Wnt signaling. When overexpressed in SW480 colon carcinoma cells, Sox17 represses beta-catenin/TCF activity in a dose-dependent manner and inhibits proliferation. Sox17 and Sox4 are expressed in mutually exclusive domains in normal and neoplastic gut tissues, and gain- and loss-of-function studies demonstrate that Sox4 enhances beta-catenin/TCF activity and the proliferation of SW480 cells. In addition to binding beta-catenin, both Sox17 and Sox4 physically interact with TCF/lymphoid enhancer factor (LEF) family members via their respective high-mobility-group box domains. Results from gain- and loss-of-function experiments suggest that the interaction of Sox proteins with beta-catenin and TCF/LEF proteins regulates the stability of beta-catenin and TCF/LEF. In particular, Sox17 promotes the degradation of both beta-catenin and TCF proteins via a noncanonical, glycogen synthase kinase 3beta-independent mechanism that can be blocked by proteasome inhibitors. In contrast, Sox4 may function to stabilize beta-catenin protein. These findings indicate that Sox proteins can act as both antagonists and agonists of beta-catenin/TCF activity, and this mechanism may regulate Wnt signaling responses in many developmental and disease contexts.

Signaling pathways and preimplantation development of mammalian embryos

The mammalian preimplantation embryo is a critical and unique stage in embryonic development. This stage includes a series of crucial events: the transition from oocyte to embryo, the first cell divisions, and the establishment of cellular contacts. These events are regulated by multiple signal-transduction pathways. In this article we describe patterns of stage-specific expression in several signal-transduction pathways and try to give a profile of the signaling transduction network in preimplantation development of mammalian embryo.

Redundant roles of Sox17 and Sox18 in early cardiovascular development of mouse embryos

Sox7, -17 and -18 constitute the Sox subgroup F (SoxF) of HMG box transcription factor genes, which all are co-expressed in developing vascular endothelial cells in mice. Here we characterized cardiovascular phenotypes of Sox17/Sox18-double and Sox17-single null embryos during early-somite stages. Whole-mount PECAM staining demonstrated the aberrant heart looping, enlarged cardinal vein and mild defects in anterior dorsal aorta formation in Sox17 single-null embryos. The Sox17/Sox18 double-null embryos showed more severe defects in formation of anterior dorsal aorta and head/cervical microvasculature, and in some cases, aberrant differentiation of endocardial cells and defective fusion of the endocardial tube. However, the posterior dorsal aorta and allantoic microvasculature was properly formed in all of the Sox17/Sox18 double-null embryos. The anomalies in both anterior dorsal aorta and head/cervical vasculature corresponded with the weak Sox7 expression sites. This suggests the region-specific redundant activities of three SoxF members along the anteroposterior axis of embryonic vascular network.

Control of cell fate and differentiation by Sry-related high-mobility-group box (Sox) transcription factors

Maintain stemness, commit to a specific lineage, differentiate, proliferate, or die. These are essential decisions that every cell is constantly challenged to make in multi-cellular organisms to ensure proper development, adult maintenance, and adaptability. SRY-related high-mobility-group box (Sox) transcription factors have emerged in the animal kingdom to help cells effect such decisions. They are encoded by 20 genes in humans and mice. They share a highly conserved high-mobility-group box domain that was originally identified in SRY, the sex-determining gene on the Y chromosome, and that has derived from a canonical high-mobility-group domain characteristic of chromatin-associated proteins. The high-mobility-group box domain binds DNA in the minor groove and increases its DNA binding affinity and specificity by interacting with many types of transcription factors. It also bends DNA and may thereby confer on Sox proteins a unique and critical role in the assembly of transcriptional enhanceosomes. Sox proteins fall into eight groups. Most feature a transactivation or transrepression domain and thereby also act as typical transcription factors. Each gene has distinct expression pattern and molecular properties, often redundant with those in the same group and overlapping with those in other groups. As a whole the Sox family controls cell fate and differentiation in a multitude of processes, such as male differentiation, stemness, neurogenesis, and skeletogenesis. We review their specific molecular properties and in vivo roles, stress recent advances in the field, and suggest directions for future investigations.

Development of the hemangioblast defines the onset of hematopoiesis in human ES cell differentiation cultures

The onset of hematopoiesis in the mouse embryo and in the embryonic stem (ES) cell differentiation model is defined by the emergence of the hemangioblast, a progenitor with both hematopoietic and vascular potential. While there is evidence for the existence of a hemangioblast in the mouse, it is unclear if this progenitor develops during the establishment of the human hematopoietic system. In this report, we have mapped hematopoietic development in human ES cell (hESC) differentiation cultures and demonstrated that a comparable hemangioblast population exists. The human hemangioblasts were identified by their capacity to generate blast colonies that display both hematopoietic and vascular potential. These colony-forming cells express the receptor tyrosine kinase KDR (VEGF receptor 2) and represent a transient population that develops in BMP-4-stimulated embryoid bodies (EBs) between 72 and 96 hours of differentiation, prior to the onset of the primitive erythroid program. Two distinct types of hemangioblasts were identified, those that give rise to primitive erythroid cells, macrophages, and endothelial cells and those that generate only the primitive erythroid population and endothelial cells. These findings demonstrate for the first time the existence of the human hemangioblast and in doing so identify the earliest stage of hematopoietic commitment.