Further extension of mammalian GATA-6

GATA6 in pancreatic cancer initiation and progression

Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy characterized by insidious onset and lack of effective therapy. The molecular pathogenesis of PDA remains to be understood fully. Transcriptional factor GATA6 is an important transcriptional regulator in normal pancreas development, particularly in the initial specification and differentiation of the pancreas. Recent studies have linked pancreatic malignancy closely to GATA6. Increased levels of GATA6 expression enhance pancreatic cancer cell growth. GATA6 emerges as a lineage-specific oncogenic factor in PDA, augmenting the oncogenic phenotypes of PDA cells upon its overexpression. However, elevated GATA6 levels are correlated with well-differentiated tumors and a more favorable patient prognosis. Experimental evidence in genetic mouse models has revealed a tumor-suppressive role for GATA6. The circumstantial roles of GATA6 in pancreatic tumorigenesis remain to be defined. This review aims to elucidate recent advances in comprehending GATA6, emphasizing its crucial roles in both pancreas physiology and pathology. Special attention will be given to its involvement in PDA pathogenesis, exploring its potential as a novel biomarker and a promising therapeutic target for PDA.

Association between SMAD4 Mutations and GATA6 Expression in Paired Pancreatic Ductal Adenocarcinoma Tumor Specimens: Data from Two Independent Molecularly-Characterized Cohorts

Several molecular biomarkers have been identified to guide induction treatment selection for localized pancreatic ductal adenocarcinoma (PDAC). SMAD4 alterations and low GATA6 expression/modified "Moffitt" basal-like phenotype have each been associated with inferior survival uniquely for patients receiving 5-FU-based therapies. SMAD4 may directly regulate the expression of GATA6 in PDAC, pointing to a common predictive biomarker. To evaluate the relationship between SMAD4 mutations and GATA6 expression in human PDAC tumors, patients with paired SMAD4 mutation and GATA6 mRNA expression data in the TCGA and CPTAC were identified. In 321 patients (TCGA: n = 180; CPTAC: n = 141), the rate of SMAD4 alterations was 26.8%. The rate of SMAD4 alteration did not vary per tertile of normalized GATA6 expression (TCGA: p = 0.928; CPTAC: p = 0.828). In the TCGA, SMAD4 alterations and the basal-like phenotype were each associated with worse survival (log rank p = 0.077 and p = 0.080, respectively), but their combined presence did not identify a subset with uniquely inferior survival (p = 0.943). In the CPTAC, the basal-like phenotype was associated with significantly worse survival (p < 0.001), but the prognostic value was not influenced by the combined presence of SMAD4 alterations (p = 0.960). SMAD4 alterations were not associated with poor clinico-pathological features such as poor tumor grade, advanced tumor stage, positive lymphovascular invasion (LVI), or positive perineural invasion (PNI), compared with SMAD4-wildtype. Given that SMAD4 mutations were not associated with GATA6 expression or Moffitt subtype in two independent molecularly characterized PDAC cohorts, distinct biomarker-defined clinical trials are necessary.

Expression profile and prognostic values of GATA family members in kidney renal clear cell carcinoma

To investigate the possible diagnostic and prognostic biomarkers of kidney renal clear cell carcinoma (KIRC), an integrated study of accumulated data was conducted to obtain more reliable information and more feasible measures. Using the Tumor Immune Estimation Resource (TIMER), University of Alabama at Birmingham Cancer Data Analysis Portal (UALCAN), Human Protein Atlas (HPA), Kaplan-Meier plotter database, Gene Expression Profiling Interactive Analysis (GEPIA2) database, cBioPortal, and Metascape, we analyzed the expression profiles and prognoses of six members of the GATA family in patients with KIRC. Compared to normal samples, KIRC samples showed significantly lower GATA2/3/6 mRNA and protein expression levels. KIRC's pathological grades, clinical stages, and lymph node metastases were closely related to GATA2 and GATA5 levels. Patients with KIRC and high GATA2 and GATA5 expression had better overall survival (OS) and recurrence-free survival (RFS), while those with higher expression of GATA3/4/6 had worse outcomes. The role and underlying mechanisms of the GATA family in cell cycle, cell proliferation, metabolic processes, and other aspects were evaluated based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses. Furthermore, we found that infiltrating immune cells were highly correlated with GATA expression profiles. These results showed that GATA family members may serve as prognostic biomarkers and therapeutic targets for KIRC.

Distinct expression and prognostic values of GATA transcription factor family in human ovarian cancer

Accumulated studies have provided controversial evidences of expression patterns and prognostic value of the GATA family in human ovarian cancer. In the present study, we accessed the distinct expression and prognostic roles of 7 individual members of GATA family in ovarian cancer (OC) patients through Oncomine analysis, CCLE analysis, Human Protein Atlas (HPA), Kaplan–Meier plotter (KM plotter) database, cBioPortal and Metascape. Our results indicated that GATA1, GATA3, GATA4 and TRPS1 mRNA and protein expression was significantly higher in OC than normal samples. High expression of GATA1, GATA2, and GATA4 were significantly correlated with better overall survival (OS), while increased GATA3 and GATA6 expression were associated with worse prognosis in OC patients. GATA1, GATA2, GATA3 and GATA6 were closely related to the different pathological histology, pathological grade, clinical stage and TP53 mutation status of OC. The genetic variation and interaction of the GATA family may be closely related to the pathogenesis and prognosis of OC, and the regulatory network composed of GATA family genes and their neighboring genes are mainly involved in Notch signaling pathway, Th1 and Th2 cell differentiation and Hippo signaling pathway. Transcriptional GATA1/2/3/4/6 could be prognostic markers and potential therapeutic target for OC patients.

GATA6 promotes epithelial-mesenchymal transition and metastasis through MUC1/β-catenin pathway in cholangiocarcinoma

GATA6 acts as an oncogene or tumour suppressor in different cancers. Previously, we found that aberrant expression of GATA6 promoted metastasis in cholangiocarcinoma (CCA). However, the mechanism by which GATA6 promotes metastasis in CCA is unclear. In the present study, we aimed to investigate the role of GATA6 in CCA cell epithelial–mesenchymal transition (EMT). Our results showed that GATA6 expression was positively associated with N-cadherin and vimentin expression but negatively associated with E-cadherin expression in 91 CCA samples. GATA6 promoted EMT and metastasis in CCA cells in vitro and in vivo based on knockdown and overexpression analyses. ChIP-sequencing data revealed that MUC1 is a novel downstream target of GATA6. GATA6 upregulated MUC1 expression through binding to both the 1584 and 1456 GATA-motifs in the promoter region and enhancing its transcription by luciferase reporter assays and point-mutant assays. MUC1 expression was positively associated with N-cadherin and vimentin expression but negatively associated with E-cadherin expression in 91 CCA samples. In addition, MUC1 promoted EMT in CCA cells based on knockdown and overexpression analyses. Moreover, MUC1 knockdown significantly abrogated the GATA6-induced EMT in CCA cells, indicating that MUC1 promoted EMT through upregulating MUC1 in CCA cells. β-Catenin is a putative transcriptional coactivator that regulates EMT in cancers. Our data showed that MUC1 expression was positively associated with nuclear β-catenin expression in 91 CCA samples. MUC1 upregulated nuclear β-catenin expression in CCA cells. Moreover, MUC1 bound to β-catenin in CCA cells based on protein immunoprecipitation analyses. MUC1 knockdown significantly decreased the binding of MUC1 to β-catenin, and thereby decreased nuclear β-catenin protein levels in CCA cells, indicating that MUC1 bound to β-catenin and increased its nuclear expression in CCA cells. Together, our results show that GATA6 promotes EMT through MUC1/β-catenin pathway in CCA, indicating potential implications for anti-metastatic therapy.

GATA6 Exerts Potent Lung Cancer Suppressive Function by Inducing Cell Senescence

Lung cancer is the leading cause of cancer-related deaths worldwide. Tumor suppressor genes (TSGs) play a critical role in restricting tumorigenesis and impact the therapeutic effect of various treatments. However, TSGs remain to be systemically determined in lung cancer. Here, we identified GATA6 as a potent lung cancer TSG. GATA6 inhibited lung cancer cell growth in vitro and tumorigenesis in vivo. Mechanistically, GATA6 upregulated p53 and p21 mRNA while it inhibited AKT activation to stabilize p21 protein, thus inducing lung cancer cell senescence. Furthermore, we showed that ectopic expression of GATA6 led to dramatic slowdown of growth rate of established lung tumor xenograft in vivo.

GATA6 Cooperates with EOMES/SMAD2/3 to Deploy the Gene Regulatory Network Governing Human Definitive Endoderm and Pancreas Formation

Heterozygous de novo mutations in GATA6 are the most frequent cause of pancreatic agenesis in humans. In mice, however, a similar phenotype requires the biallelic loss of Gata6 and its paralog Gata4. To elaborate the human-specific requirements for GATA6, we chose to model GATA6 loss in vitro by combining both gene-edited and patient-derived pluripotent stem cells (hPSCs) and directed differentiation toward β-like cells. We find that GATA6 heterozygous hPSCs show a modest reduction in definitive endoderm (DE) formation, while GATA6-null hPSCs fail to enter the DE lineage. Consistent with these results, genome-wide studies show that GATA6 binds and cooperates with EOMES/SMAD2/3 to regulate the expression of cardinal endoderm genes. The early deficit in DE is accompanied by a significant reduction in PDX1⁺ pancreatic progenitors and C-PEPTIDE⁺ β-like cells. Taken together, our data position GATA6 as a gatekeeper to early human, but not murine, pancreatic ontogeny.

Deregulated GATA6 modulates stem cell-like properties and metabolic phenotype in hepatocellular carcinoma

Accumulating evidence illustrates the significance of cell plasticity in the molecular biology of liver cancer. Reprogramming of mature parenchymal cells to a less differentiated state by key molecular targets contributes to the pathogenesis of hepatocellular carcinoma (HCC). Hereby, we investigated the role of GATA6, a transcription factor implicated in hepatocyte lineage specification, in HCC. Our results demonstrated a lower expression of GATA6 in HCC tissues compared to the corresponding nontumoral liver tissues. Moreover, GATA6 underexpression, as observed in about 50% cases in our clinical cohort, was associated with a poorer degree of tumor cell differentiation and worse disease-free survival outcome. In vitro, silencing of GATA6 in HCC cells augmented cell migration and invasion abilities of HCC cells by activating epithelial-mesenchymal transition. Self-renewal was also enhanced in vitro. Consistently, in vivo tumorigenicity and self-renewal was promoted upon GATA6 knockdown. Notably, suppression of GATA6 converts HCC cells to a metabolic phenotype recapitulating stem-cell state. Expression of glycolytic markers was elevated in GATA6-knockdown clones accompanied by increased glucose uptake; while overexpression of GATA6 resulted in opposite effects. Further to this, we identified that GATA6 bound to the promoter region of PKM gene and regulated PKM2 transcription. Taken together, downregulation of GATA6 directs HCC cells to glycolytic metabolism and fosters tumorigenicity, self-renewal and metastasis. GATA6 is a transcriptional regulator and a genetic switch that converts the phenotypic reprogramming of HCC cells. It is a potential prognostic biomarker and therapeutic target for liver cancer.

Mutant Lef1 controls Gata6 in sebaceous gland development and cancer

Mutations in Lef1 occur in human and mouse sebaceous gland (SG) tumors, but their contribution to carcinogenesis remains unclear. Since Gata6 controls lineage identity in SG, we investigated the link between these two transcription factors. Here, we show that Gata6 is a β‐catenin‐independent transcriptional target of mutant Lef1. During epidermal development, Gata6 is expressed in a subset of Sox9‐positive Lef1‐negative hair follicle progenitors that give rise to the upper SG. Overexpression of Gata6 by in utero lentiviral injection is sufficient to induce ectopic sebaceous gland elements. In mice overexpressing mutant Lef1, Gata6 ablation increases the total number of skin tumors yet decreases the proportion of SG tumors. The increased tumor burden correlates with impaired DNA mismatch repair and decreased expression of Mlh1 and Msh2 genes, defects frequently observed in human sebaceous neoplasia. Gata6 specifically marks human SG tumors and also defines tumors with elements of sebaceous differentiation, including a subset of basal cell carcinomas. Our findings reveal that Gata6 controls sebaceous gland development and cancer.

Identification of Gene Expression Changes Associated With Uterine Receptivity in Mice

The mouse is a widely used animal model for studying human reproduction. Although global gene expression changes associated with human uterine receptivity have been determined by independent groups, the same studies in the mouse are scarce. The extent of similarities/differences between mice and humans on uterine receptivity at the molecular level remains to be determined. In the present study, we analyzed global gene expression changes in receptive uterus on day 4 of pregnancy compared to non-receptive uterus on day 3 of pregnancy in mice. A total of 541 differentially expressed genes were identified, of which 316 genes were up-regulated and 225 genes were down-regulated in receptive uterus compared to non-receptive uterus. Gene ontology and gene network analysis highlighted the activation of inflammatory response in the receptive uterus. By analyzing the promoter sequences of differentially expressed genes, we identified 12 causal transcription factors. Through connectivity map (CMap) analysis, we revealed several compounds with potential anti-receptivity activity. Finally, we performed a cross-species comparison against human uterine receptivity from a published dataset. Our study provides a valuable resource for understanding the molecular mechanism underlying uterine receptivity in mice.

GATA6 suppresses migration and metastasis by regulating the miR-520b/CREB1 axis in gastric cancer

Transcription factors (TFs) and microRNAs (miRNAs) are tightly linked to each other in tumor development and progression, but their interactions in gastric cancer (GC) metastasis remain elusive. Here we report a novel suppressive role of GATA6 in inhibiting GC metastasis by transactivating miR-520b. We found that GATA6 expression was significantly downregulated in metastatic GC cells and tissues and that its downregulation was correlated with a poor GC prognosis. Overexpression of GATA6 suppressed GC cell migration, invasion and metastasis both in vitro and in vivo. Luciferase reporter assays and chromatin immunoprecipitation assays demonstrated that miR-520b is a direct transcriptional target of GATA6. Moreover, miR-520b expression was positively correlated with GATA6 expression in GC tissues, and ectopic expression of miR-520b inhibited the migration and invasion of GC cells. Furthermore, cAMP responsive element binding protein 1 (CREB1) was identified as a direct and functional target of miR-520b, and GATA6 could suppress GC cell migration and metastasis via miR-520b-mediated repression of CREB1. Downregulation of GATA6 and miR-520b may partly account for the overexpression of CREB1 in GC. In conclusion, our results provide novel insight into the TF-miRNA regulatory network involved in GC metastasis. Targeting the GATA6/miR-520b/CREB1 axis may be an effective approach for GC treatment.

GATA6: a new predictor for prognosis in ovarian cancer

Ovarian cancer (OC) is the main cause of gynecological cancer-associated mortality. Improving the diagnosis is important for guiding clinical treatment. The present study aimed to investigate the relationship between expression of GATA6, a stem cell factor, and its prognosis in OC. In total, 521 OC cases were included. Immunohistochemistry analysis demonstrated that GATA6 was expressed in both high-grade serous carcinoma as well as non-serous tumors. High grade serous carcinoma showed a higher percentage of GATA6 positive staining. Positive staining of GATA6 showed worse overall survival (OS) in all ovarian cancers or serous and non-serous carcinoma individually. GATA6 was revealed as an independent risk factor for prognosis by multivariate Cox analysis. In all, GATA6 may present as a novel marker for poor prognosis in OC.

Targeted sequencing identifies novel GATA6 variants in a large cohort of patients with conotruncal heart defects

Studies have highlighted the critical role of GATA6 in conotruncal heart defects (CTDs). Nevertheless, relationship between GATA6 variants and different CTDs remains largely unknown. Here GATA6 gene was screened in 542 patients with CTDs using targeted sequencing. Variant frequency was 2.0% (11/542). Three novel variants: c.86C>A (p.A29E), c.296T>A (p.V99D) and c.1254delC (p.S418fs) were identified in patients with transposition of the great arteries, double outlet right ventricle and persistent truncus arteriosus, respectively, but in none of the 400 controls. Western blot revealed that A29E and V99D mutant protein had similar expression pattern with wild-type GATA6 protein, but S418fs mutant protein appeared as a truncated doublet. Reporter gene assay demonstrated that A29E and V99D mutant protein retained the ability to activate BNP and ANF promoter, whereas S418fs mutant protein failed to transactivate both of them, compared with wild-type. Subcellular localization of wild-type, A29E and V99D mutant protein were in the nucleus, while S418fs mutant protein was expressed both in the nucleus and cytoplasm. In conclusion, GATA6 variant frequency in sporadic CTDs patients was higher than that in other congenital heart diseases. Variant c.1254delC was a pathogenic variant associated with CTDs, especially PTA, whereas c.86C>A and c.296T>A should be considered as likely pathogenic variants.

GATA6 regulates EMT and tumour dissemination, and is a marker of response to adjuvant chemotherapy in pancreatic cancer

BACKGROUND AND AIMS

The role of GATA factors in cancer has gained increasing attention recently, but the function of GATA6 in pancreatic ductal adenocarcinoma (PDAC) is controversial. GATA6 is amplified in a subset of tumours and was proposed to be oncogenic, but high GATA6 levels are found in well-differentiated tumours and are associated with better patient outcome. By contrast, a tumour-suppressive function of GATA6 was demonstrated using genetic mouse models. We aimed at clarifying GATA6 function in PDAC.

DESIGN

We combined GATA6 silencing and overexpression in PDAC cell lines with GATA6 ChIP-Seq and RNA-Seq data, in order to understand the mechanism of GATA6 functions. We then confirmed some of our observations in primary patient samples, some of which were included in the ESPAC-3 randomised clinical trial for adjuvant therapy.

RESULTS

GATA6 inhibits the epithelial-mesenchymal transition (EMT) in vitro and cell dissemination in vivo. GATA6 has a unique proepithelial and antimesenchymal function, and its transcriptional regulation is direct and implies, indirectly, the regulation of other transcription factors involved in EMT. GATA6 is lost in tumours, in association with altered differentiation and the acquisition of a basal-like molecular phenotype, consistent with an epithelial-to-epithelial (ET2) transition. Patients with basal-like GATA6low tumours have a shorter survival and have a distinctly poor response to adjuvant 5-fluorouracil (5-FU)/leucovorin. However, modulation of GATA6 expression in cultured cells does not directly regulate response to 5-FU.

CONCLUSIONS

We provide mechanistic insight into GATA6 tumour-suppressive function, its role as a regulator of canonical epithelial differentiation, and propose that loss of GATA6 expression is both prognostic and predictive of response to adjuvant therapy.

Roles of GATA6 during Gonadal Development in Japanese Flounder: Gonadogenesis, Regulation of Gender-Related Genes, Estrogen Formation and Gonadal Function Maintenance

GATA-binding protein 6 (GATA6), a highly-conserved transcription factor of the GATA family plays an important role in gonadal cell proliferation, differentiation and endoderm development. In this study, the full-length cDNA of GATA6 of Paralichthys olivaceus (Japanese flounder) was obtained. Phylogenetic, gene structure and synteny analyses demonstrated that GATA6 of P. olivaceus is homologous to that of teleosts and tetrapods. The P. olivaceus GATA6 transcript showed higher expression in testis than in ovary, demonstrating a sexually dimorphic gene expression. During embryonic development, the expression of P. olivaceus GATA6 increased at the blastula stage, demonstrating that GATA6 is involved in morphogenesis. Results of in situ hybridization showed that GATA6 signals were detected in Sertoli cells, oogonia and oocytes. Moreover, 17α methyl testosterone, a male hormone, could moderately upregulate P. olivaceus GATA6 and downregulate P. olivaceus aromatase CYP19A1 in testis cells. These results suggest that GATA6 may play an important role in gonadal development in P. olivaceus. This study provides valuable information on the function of P. olivaceus GATA6, laying the foundation for further development of breeding techniques in this species.

Gata6 promotes hair follicle progenitor cell renewal by genome maintenance during proliferation

Cell proliferation is essential to rapid tissue growth and repair, but can result in replication-associated genome damage. Here, we implicate the transcription factor Gata6 in adult mouse hair follicle regeneration where it controls the renewal of rapidly proliferating epithelial (matrix) progenitors and hence the extent of production of terminally differentiated lineages. We find that Gata6 protects against DNA damage associated with proliferation, thus preventing cell cycle arrest and apoptosis. Furthermore, we show that in vivo Gata6 stimulates EDA-receptor signaling adaptor Edaradd level and NF-κB pathway activation, known to be important for DNA damage repair and stress response in general and for hair follicle growth in particular. In cultured keratinocytes, Edaradd rescues DNA damage, cell survival, and proliferation of Gata6 knockout cells and restores MCM10 expression. Our data add to recent evidence in embryonic stem and neural progenitor cells, suggesting a model whereby developmentally regulated transcription factors protect from DNA damage associated with proliferation at key stages of rapid tissue growth. Our data may add to understanding why Gata6 is a frequent target of amplification in cancers.

Anisomycin-induced GATA-6 degradation accompanying a decrease of proliferation of colorectal cancer cell

Transcription factor GATA-6 plays a key role in normal cell differentiation of the mesoderm and endoderm. On the other hand, GATA-6 is abnormally overexpressed in many clinical gastrointestinal cancer tissue samples, and accelerates cell proliferation or an anti-apoptotic response in cancerous tissues. We previously showed that activation of the JNK signaling cascade causes proteolysis of GATA-6. In this study, we demonstrated that anisomycin, a JNK activator, stimulates nuclear export of GATA-6 in a colorectal cancer cell line, DLD-1. Concomitantly, anisomycin remarkably inhibits the proliferation of DLD-1 cells via G2/M arrest in a plate culture. However, it did not induce apoptosis under growth arrest conditions. Furthermore, the growth of DLD-1 cells in a spheroid culture was suppressed by anisomycin. Although 5-FU showed only a slight inhibitory effect on 3D spheroid cultures, the same concentration of 5-FU together with a low concentration of anisomycin exhibited strong growth inhibition. These results suggest that the induction of GATA-6 dysfunction may be more effective for chemotherapy for colorectal cancer, although the mechanism underlying the synergistic effect of 5-FU and anisomycin remains unknown.

The acinar regulator Gata6 suppresses KrasG12V-driven pancreatic tumorigenesis in mice

BACKGROUND AND AIMS

Gata6 is required to complete and maintain acinar differentiation in the mouse pancreas. Pancreas-specific Gata6 ablation during development causes extensive and persistent acinar-ductal metaplasia, which is considered an initial step of mutant KRas-driven carcinogenesis. Therefore, the Gata6-null pancreas might represent a tumour-prone environment. We investigated whether Gata6 plays a role during pancreatic tumorigenesis.

DESIGN

We analysed genetically engineered mouse models and human pancreatic ductal adenocarcinoma (PDAC) cell lines, using a combination of histopathological studies, genome-wide expression and chromatin immunoprecipitation experiments to understand the role of Gata6 in the initiation and progression of KRas(G12V)-driven tumours

RESULTS

We show that Gata6 maintains the acinar differentiation programme, both directly and indirectly, and it concomitantly suppresses ectopic programmes in the pancreas. Gata6 ablation renders acinar cells more sensitive to KRas(G12V), thereby accelerating tumour development. Gata6 expression is spontaneously lost in a mouse model of KRas(G12V)-driven PDAC, in association with altered cell differentiation. Using a combination of ChIP-Seq and RNA-Seq, we show that Gata6 exerts its tumour-suppressive effect through the promotion of cell differentiation, the suppression of inflammatory pathways, and the direct repression of cancer-related pathways. Among them is the epidermal growth factor receptor (EGFR) pathway, the activity of which is upregulated in the normal and preneoplastic Gata6-null pancreas. Accordingly, GATA6-silencing in human PDAC cells leads to an upregulation of EGFR.

CONCLUSIONS

We propose that, in the pancreas, Gata6 acts as a tumour suppressor by enforcing acinar cell differentiation, by directly and indirectly repressing ectopic differentiation programmes, and by regulating crucial cancer-related gene expression pathways.

A loss-of-function and H2B-Venus transcriptional reporter allele for Gata6 in mice

Background

The GATA-binding factor 6 (Gata6) gene encodes a zinc finger transcription factor that often functions as a key regulator of lineage specification during development. It is the earliest known marker of the primitive endoderm lineage in the mammalian blastocyst. During gastrulation, GATA6 is expressed in early cardiac mesoderm and definitive endoderm progenitors, and is necessary for development of specific mesoderm and endoderm-derived organs including the heart, liver, and pancreas. Furthermore, reactivation or silencing of the Gata6 locus has been associated with certain types of cancer affecting endodermal organs.

Results

We have generated a Gata6^H2B-Venus knock-in reporter mouse allele for the purpose of labeling GATA6-expressing cells with a bright nuclear-localized fluorescent marker that is suitable for live imaging at single-cell resolution.

Conclusions

Expression of the Venus reporter was characterized starting from embryonic stem (ES) cells, through mouse embryos and adult animals. The Venus reporter was not expressed in ES cells, but was activated upon endoderm differentiation. Gata6^{H2B-Venus/H2B-Venus} homozygous embryos did not express GATA6 protein and failed to specify the primitive endoderm in the blastocyst. However, null blastocysts continued to express high levels of Venus in the absence of GATA6 protein, suggesting that early Gata6 transcription is independent of GATA6 protein expression. At early post-implantation stages of embryonic development, there was a strong correlation of Venus with endogenous GATA6 protein in endoderm and mesoderm progenitors, then later in the heart, midgut, and hindgut. However, there were discrepancies in reporter versus endogenous protein expression in certain cells, such as the body wall and endocardium. During organogenesis, detection of Venus in specific organs recapitulated known sites of endogenous GATA6 expression, such as in the lung bud epithelium, liver, pancreas, gall bladder, stomach epithelium, and vascular endothelium. In adults, Venus was observed in the lungs, pancreas, liver, gall bladder, ovaries, uterus, bladder, skin, adrenal glands, small intestine and corpus region of the stomach. Overall, Venus fluorescent protein under regulatory control of the Gata6 locus was expressed at levels that were easily visualized directly and could endure live and time-lapse imaging techniques. Venus is co-expressed with endogenous GATA6 throughout development to adulthood, and should provide an invaluable tool for examining the status of the Gata6 locus during development, as well as its silencing or reactivation in cancer or other disease states.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0086-5) contains supplementary material, which is available to authorized users.

REG4 is a transcriptional target of GATA6 and is essential for colorectal tumorigenesis

The transcription factor GATA6 is a critical regulator of cell proliferation and development in the gastrointestinal tract. We have recently reported that GATA6 induces the expression of the intestinal stem cell marker LGR5 and enhances the clonogenicity and tumorigenicity of colon cancer cells, but not the growth of these cells cultured under adherent conditions. Here we show that REG4, a member of the regenerating islet-derived (REG) family, is also a target of GATA6. We further demonstrate that REG4 is downregulated by overexpression of miR-363, which suppresses GATA6 expression. Moreover, we show that GATA6-mediated activation of REG4 enhances the growth of colon cancer cells under adherent conditions and is required for their tumorigenicity. Taken together, our findings demonstrate that GATA6 simultaneously induces the expression of genes essential for the growth of colon cancer cells under adherent conditions (REG4) and genes required for their clonogenicity (LGR5), and that the miR-363-GATA6-REG4/LGR5 signaling cascade promotes the tumorigenicity of colon cancer cells.

Amino-terminal extension of 146 residues of L-type GATA-6 is required for transcriptional activation but not for self-association

Transcription factor GATA-6 plays essential roles in developmental processes and tissue specific functions through regulation of gene expression. GATA-6 mRNA utilizes two Met-codons in frame as translational initiation codons. Deletion of the nucleotide sequence encoding the PEST sequence (Glu(31)-Cys(46)) between the two initiation codons unusually reduced the protein molecular size on SDS-polyacrylamide gel-electrophoresis, and re-introduction of this sequence reversed this change. The long-type (L-type) GATA-6 containing this PEST sequence self-associated similarly to the short-type (S-type) GATA-6, as determined on co-immunoprecipitation of Myc-tagged GATA-6 with HA-tagged GATA-6. The L-type and S-type GATA-6 also interacted mutually. The L-type GATA-6 without the PEST sequence also self-associated and interacted with the S-type GATA-6. The transcriptional activation potential of L-type GATA-6 is higher than that of S-type GATA-6. When the PEST sequence (Glu(31)-Cys(46)) was inserted into the L-type GATA-6 without Arg(13)-Gly(101), the resultant recombinant protein showed significantly higher transcriptional activity, while the construct with an unrelated sequence exhibited lower activity. These results suggest that the Glu(31)-Cys(46) segment plays an important role in the transcriptional activation, although it does not participate in the self-association.

Alternative transcription initiation and the AUG context configuration control dual-organellar targeting and functional competence of Arabidopsis Lon1 protease

Cellular homeostasis relies on components of protein quality control including chaperones and proteases. In bacteria and eukaryotic organelles, Lon proteases play a critical role in removing irreparably damaged proteins and thereby preventing the accumulation of deleterious degradation-resistant aggregates. Gene expression, live-cell imaging, immunobiochemical, and functional complementation approaches provide conclusive evidence for Lon1 dual-targeting to chloroplasts and mitochondria. Dual-organellar deposition of Lon1 isoforms depends on both transcriptional regulation and alternative translation initiation via leaky ribosome scanning from the first AUG sequence context that deviates extensively from the optimum Kozak consensus. Organelle-specific Lon1 targeting results in partial complementation of Arabidopsis lon1-1 mutants, whereas full complementation is solely accomplished by dual-organellar targeting. Both the optimal and non-optimal AUG sequence contexts are functional in yeast and facilitate leaky ribosome scanning complementing the pim1 phenotype when the mitochondrial presequence is used. Bioinformatic search identified a limited number of Arabidopsis genes with Lon1-type dual-targeting sequence organization. Lon4, the paralog of Lon1, has an ambiguous presequence likely evolved from the twin presequences of an ancestral Lon1-like gene, generating a single dual-targeted protein isoform. We postulate that Lon1 and its subfunctional paralog Lon4 evolved complementary subsets of transcriptional and posttranscriptional regulatory components responsive to environmental cues for dual-organellar targeting.

Transcription factors GATA-4 and GATA-6: molecular characterization, expression patterns and possible functions during goose (Anser cygnoides) follicle development

The transcription factors GATA-4 and GATA-6, members of the GATA family, play an important role in ovarian cell proliferation, differentiation and apoptosis. In this study, the full-length coding sequences of goose GATA-4 and GATA-6 were cloned and characterized. GATA-4 and GATA-6 consist of 1236 and 1104 nucleotides encoding proteins with 411 and 367 amino acids, respectively. The deduced amino acid sequences of both proteins include two adjacent zinc finger domains with the distinctive form (CVNC-X17-CNAC)-X29-(CANC-X17-CNAC) and share 84.76% identity within this domain. In silico prediction together with matching of the high affinity RRXS(T)Y motif revealed that the GATA-4 protein might be phosphorylated predominantly at S(233), but no phosphorylation site was found in the GATA-6 protein. Real-time quantitative PCR analysis showed that GATA-4 and GATA-6 mRNAs were co-expressed in goose follicles, moderately expressed in granulosa cells and weakly expressed in theca cells. The expression level of GATA-4 mRNA in healthy follicles was significantly higher than in atretic follicles or postovulatory follicles (P<0.01), and the expression level of GATA-6 mRNA in healthy follicles was significantly lower than in atretic follicles or postovulatory follicles (P<0.01). The expression level of GATA-4 mRNA in granulosa cells was downregulated during follicle development; the peak of expression occurred in the 8-10 mm follicles, and the lowest expression was in the F1 follicles. GATA-6 was upregulated and reached its peak expression in the F1 follicles. These results indicate that the molecular structural differences in goose GATA-4 and GATA-6 may be related to their different roles during follicle development.

GATA6 is a crucial regulator of Shh in the limb bud

In the limb bud, patterning along the anterior-posterior (A-P) axis is controlled by Sonic Hedgehog (Shh), a signaling molecule secreted by the “Zone of Polarizing Activity”, an organizer tissue located in the posterior margin of the limb bud. We have found that the transcription factors GATA4 and GATA6, which are key regulators of cell identity, are expressed in an anterior to posterior gradient in the early limb bud, raising the possibility that GATA transcription factors may play an additional role in patterning this tissue. While both GATA4 and GATA6 are expressed in an A-P gradient in the forelimb buds, the hindlimb buds principally express GATA6 in an A-P gradient. Thus, to specifically examine the role of GATA6 in limb patterning we generated Prx1-Cre; GATA6^fl/fl mice, which conditionally delete GATA6 from their developing limb buds. We found that these animals display ectopic expression of both Shh and its transcriptional targets specifically in the anterior mesenchyme of the hindlimb buds. Loss of GATA6 in the developing limbs results in the formation of preaxial polydactyly in the hindlimbs. Conversely, forced expression of GATA6 throughout the limb bud represses expression of Shh and results in hypomorphic limbs. We have found that GATA6 can bind to chromatin (isolated from limb buds) encoding either Shh or Gli1 regulatory elements that drive expression of these genes in this tissue, and demonstrated that GATA6 works synergistically with FOG co-factors to repress expression of luciferase reporters driven by these sequences. Most significantly, we have found that conditional loss of Shh in limb buds lacking GATA6 prevents development of hindlimb polydactyly in these compound mutant embryos, indicating that GATA6 expression in the anterior region of the limb bud blocks hindlimb polydactyly by repressing ectopic expression of Shh.

Sonic Hedgehog (Shh) is a crucial regulator of the growth and anterior-posterior patterning of the developing limb bud, and is produced in the “Zone of Polarizing Activity” in the posterior of the limb bud. Here, we demonstrate that GATA4 and GATA6 (members of the GATA family of transcription factors) are expressed in the anterior mesenchyme of mouse limb buds and that limb bud-specific deletion of GATA6 results in ectopic expression of Shh and its target genes (such as Gli1) in the anterior limb bud mesenchyme, resulting in preaxial polydactyly. Conversely, over-expression of GATA6 in limb buds causes down-regulation of Shh and its target genes, resulting in a decreased number of digits. We also show that GATA6 binds to the sequences that regulate expression of either Shh or Gli1, and that simultaneous deletion of both GATA6 and Shh genes in developing limb buds rescues the polydactylous hindlimb phenotype of GATA6 mutants. Our findings indicate that GATA6 is necessary to repress ectopic expression of both Shh and hedgehog transcriptional targets in the anterior region of the mouse hindlimb bud, and thus demonstrate that GATA transcription factors, in addition to being regulators of cell identity, are important negative regulators of ectopic Shh expression in the limb bud.

Gata6 is required for complete acinar differentiation and maintenance of the exocrine pancreas in adult mice

OBJECTIVES

Previous studies have suggested an important role of the transcription factor Gata6 in endocrine pancreas, while GATA6 haploinsufficient inactivating mutations cause pancreatic agenesis in humans. We aimed to analyse the effects of Gata6 inactivation on pancreas development and function.

DESIGN

We deleted Gata6 in all epithelial cells in the murine pancreas at the onset of its development. Acinar proliferation, apoptosis, differentiation and exocrine functions were assessed using reverse transcriptase quantitative PCR (RT-qPCR), chromatin immunoprecipitation, immunohistochemistry and enzyme assays. Adipocyte transdifferentiation was assessed using electron microscopy and genetic lineage tracing.

RESULTS

Gata6 is expressed in all epithelial cells in the adult mouse pancreas but it is only essential for exocrine pancreas homeostasis: while dispensable for pancreatic development after e10.5, it is required for complete acinar differentiation, for establishment of polarity and for the maintenance of acinar cells in the adult. Gata6 regulates directly the promoter of genes coding for digestive enzymes and the transcription factors Rbpjl and Mist1. Upon pancreas-selective Gata6 inactivation, massive loss of acinar cells and fat replacement take place. This is accompanied by increased acinar apoptosis and proliferation, acinar-to-ductal metaplasia and adipocyte transdifferentiation. By contrast, the endocrine pancreas is spared.

CONCLUSIONS

Our data show that Gata6 is required for the complete differentiation of acinar cells through multiple transcriptional regulatory mechanisms. In addition, it is required for the maintenance of the adult acinar cell compartment. Our studies suggest that GATA6 alterations may contribute to diseases of the human adult exocrine pancreas.

Silencing of GATA6 suppresses SW1990 pancreatic cancer cell growth in vitro and up-regulates reactive oxygen species

BACKGROUND/AIMS

Pancreatic cancer has the worst prognosis of any gastrointestinal cancer with a mortality rate approaching its incidence. Previous studies have indicated that GATA6 plays a key role in organ development and function, and that abnormal expression of GATA6 may induce tumorigenesis. Meanwhile, it has been reported that generation of reactive oxygen species contributes to carcinogenesis. In this study, we set out to study the role of GATA6 expression on proliferation and apoptosis of pancreatic cancer cells and the role of reactive oxygen species.

METHODS

Four target miRNA sequences against GATA6 mRNA were synthesized and used to transfect SW1990 cells. Then, GATA6 expression in SW1990 cells was examined by western blot and quantative real-time polymerase chain reaction. Cell proliferation was examined by WST-8 and colony formation assay. Cell cycle progression and apoptosis were measured by flow cytometry. We also measured the generation of reactive oxygen species by immunofluorescence and flow cytometry.

RESULTS

RNA interference against GATA6 successfully inhibited mRNA and protein expression of GATA6 in the SW1990 pancreatic cancer cell line. Silencing of GATA6 by RNA interference inhibited cell proliferation and increased apoptosis of SW1990, and enhanced the expression of reactive oxygen species.

CONCLUSIONS

These results suggest that the RNA interference approach against GATA6 may be an effective therapeutic approach for treatment of pancreatic cancer.

Aberrant expression of GATA binding protein 6 correlates with poor prognosis and promotes metastasis in cholangiocarcinoma

AIM

GATA6, a zinc-finger transcription factor, functions as a tumour promoter or suppresser according to different tumour origins. We investigated the clinical significance of GATA6 and its role in invasion and metastasis in cholangiocarcinoma (CCA).

METHODS

Expression of GATA6 in 87 cancerous, 24 paracancerous, 32 lymph-node metastatic and 8 liver metastatic samples from 87 CCA patients undergoing surgical resection was detected by immunohistochemistry. Impact of GATA6 on invasion, metastasis and 67kDa laminin receptor expression (67LR) was evaluated in CCA cells by shRNA lentivirus or expressed-plasmid transfection.

RESULTS

Aberrant expression of GATA6 in CCAs was significantly associated with lymph-node metastasis. GATA6 expression was higher in lymph-node and liver metastatic tissues compared with primary cancerous tissues. Kaplan-Meier analysis showed GATA6 expression correlated with poor overall survival and early recurrence in CCAs. Cox analysis suggested GATA6 was an independent prognostic marker for overall survival and recurrence-free survival. CCA cell invasion and migration were decreased by GATA6 knockdown and enhanced by GATA6 overexpression in vitro. Knockdown of GATA6 reduced CCA cell metastasis by xenotransplantation into nude mice. 67LR, which is overexpressed in CCAs and promotes invasion and metastasis through several pathways, positively correlated with GATA6 expression in 87 CCAs. Both mRNA and protein levels of 67LR were regulated by GATA6 in CCA cells. Moreover, ChIP analysis showed GATA6 bound to 67LR gene promoter in CCA cells.

CONCLUSION

Aberrant expression of GATA6 correlates with poor prognosis and promotes invasion and metastasis in CCA.

cAMP-dependent proteolysis of GATA-6 is linked to JNK-signaling pathway

A JNK inhibitor SP600125 inhibited cAMP-dependent proteolysis of GATA-6 by proteasomes around its IC50. We further examined the effects of SP600125 on the degradation of GATA-6 in detail, since an activator of JNK (anisomycin) is available. Interestingly, anisomycin immediately stimulated the export of nuclear GATA-6 into the cytoplasm, and then the cytoplasmic content of GATA-6 decreased slowly through degradation by proteasomes. Such an effect of anisomycin was inhibited by SP600125, indicating that the observed phenomenon might be linked to the JNK signaling pathway. The inhibitory effect of SP600125 could not be ascribed to the inhibition of PKA, since phosphorylation of CREB occurred in the presence of dbcAMP and SP600125. The nuclear export of GATA-6 was inhibited by leptomycin B, suggesting that CRM1-mediated export could be activated by anisomycin. Furthermore, it seems likely that the JNK activated by anisomycin may stimulate not only the nuclear export of GATA-6 through CRM1 but also the degradation of GATA-6 by cytoplasmic proteasomes. In contrast, A-kinase might activate only the latter process through JNK.

GATA6 activates Wnt signaling in pancreatic cancer by negatively regulating the Wnt antagonist Dickkopf-1

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal disease characterized by late diagnosis and treatment resistance. Recurrent genetic alterations in defined genes in association with perturbations of developmental cell signaling pathways have been associated with PDAC development and progression. Here, we show that GATA6 contributes to pancreatic carcinogenesis during the temporal progression of pancreatic intraepithelial neoplasia by virtue of Wnt pathway activation. GATA6 is recurrently amplified by both quantitative-PCR and fluorescent in-situ hybridization in human pancreatic intraepithelial neoplasia and in PDAC tissues, and GATA6 copy number is significantly correlated with overall patient survival. Forced overexpression of GATA6 in cancer cell lines enhanced cell proliferation and colony formation in soft agar in vitro and growth in vivo, as well as increased Wnt signaling. By contrast siRNA mediated knockdown of GATA6 led to corresponding decreases in these same parameters. The effects of GATA6 were found to be due to its ability to bind DNA, as forced overexpression of a DNA-binding mutant of GATA6 had no effects on cell growth in vitro or in vivo, nor did they affect Wnt signaling levels in these same cells. A microarray analysis revealed the Wnt antagonist Dickopf-1 (DKK1) as a dysregulated gene in association with GATA6 knockdown, and direct binding of GATA6 to the DKK1 promoter was confirmed by chromatin immunoprecipitation and electrophoretic mobility shift assays. Transient transfection of GATA6, but not mutant GATA6, into cancer cell lines led to decreased DKK1 mRNA expression and secretion of DKK1 protein into culture media. Forced overexpression of DKK1 antagonized the effects of GATA6 on Wnt signaling in pancreatic cancer cells. These findings illustrate that one mechanism by which GATA6 promotes pancreatic carcinogenesis is by virtue of its activation of canonical Wnt signaling via regulation of DKK1.

Critical role for GATA3 in mediating Tie2 expression and function in large vessel endothelial cells

Endothelial phenotypes are highly regulated in space and time by both transcriptional and post-transcriptional mechanisms. There is increasing evidence that the GATA family of transcription factors function as signal transducers, coupling changes in the extracellular environment to changes in downstream target gene expression. Here we show that human primary endothelial cells derived from large blood vessels express GATA2, -3, and -6. Of these factors, GATA3 was expressed at the highest levels. In DNA microarrays of human umbilical vein endothelial cells (HUVEC), small interfering RNA-mediated knockdown of GATA3 resulted in reduced expression of genes associated with angiogenesis, including Tie2. At a functional level, GATA3 knockdown inhibited angiopoietin (Ang)-1-mediated but not vascular endothelial cell growth factor (VEGF)-mediated AKT signaling, cell migration, survival, and tube formation. In electrophoretic gel mobility shift assays and chromatin immunoprecipitation, GATA3 was shown to bind to regulatory regions within the 5'-untranslated region of the Tie2 gene. In co-immunoprecipitation and co-transfection assays, GATA3 and the Ets transcription factor, ELF1, physically interacted and synergized to transactivate the Tie2 promoter. GATA3 knockdown blocked the ability of Ang-1 to attenuate vascular endothelial cell growth factor stimulation of vascular cell adhesion molecule-1 expression and monocytic cell adhesion. Moreover, exposure of human umbilical vein endothelial cells to tumor necrosis factor-alpha resulted in marked down-regulation of GATA3 expression and reduction in Tie2 expression. Together, these findings suggest that GATA3 is indispensable for Ang-1-Tie2-mediated signaling in large vessel endothelial cells.

Wnt6 induces the specification and epithelialization of F9 embryonal carcinoma cells to primitive endoderm

Epithelial-to-mesenchymal transitions (EMTs) play key roles in the normal development of an organism as well as its demise following the metastasis of a malignant tumour. An EMT during early mouse development results in the differentiation of primitive endoderm into the parietal endoderm that forms part of the parietal yolk sac. In the embryo, primitive endoderm develops from cells in the inner cell mass, but the signals that instruct these cells to become specified and adopt an epithelial fate are poorly understood. The mouse F9 teratocarcinoma cell line, a model that can recapitulate the in vivo primitive to parietal endoderm EMT, has been used extensively to elucidate the signalling cascades involved in extraembryonic endoderm differentiation. Here, we identified Wnt6 as a gene up-regulated in F9 cells in response to RA and show that Wnt6 expressing cells or cells exposed to Wnt6 conditioned media form primitive endoderm. Wnt6 induction of primitive endoderm is accompanied by beta-catenin and Snail1 translocation to the nucleus and the appearance of cytokeratin intermediate filaments. Attenuating glycogen synthase kinase 3 activity using LiCl gave similar results, but the fact that cells de-differentiate when LiCl is removed reveals that other signalling pathways are required to maintain cells as primitive endoderm. Finally, Wnt6-induced primitive endodermal cells were tested to determine their competency to complete the EMT and differentiate into parietal endoderm. Towards that end, results show that up-regulating protein kinase A activity is sufficient to induce markers of parietal endoderm. Together, these findings indicate that undifferentiated F9 cells are responsive to canonical Wnt signalling, which negatively regulates glycogen synthase kinase 3 activity leading to the epithelialization and specification of primitive endoderm competent to receive additional signals required for EMT. Considering the ability of F9 cells to mimic an in vivo EMT, the identification of this Wnt6-beta-catenin-Snail signalling cascade has broad implications for understanding EMT mechanisms in embryogenesis and metastasis.

Ubiquitous expression of the rtTA2S-M2 inducible system in transgenic mice driven by the human hnRNPA2B1/CBX3 CpG island

Background

A sensitive, ubiquitously expressed tetracycline inducible system would be a valuable tool in mouse transgenesis. However, this has been difficult to obtain due to position effects observed at different chromosomal sites of transgene integration, which negatively affect expression in many tissues. The aim of this study was to test the utility of a mammalian methylation-free CpG island to drive ubiquitous expression of the sensitive doxycycline (Dox) inducible rtTA2S-M2 Tet-transactivator in transgenic mice.

Results

An 8 kb genomic fragment from the methylation-free CpG island of the human hnRNPA2B1-CBX3 housekeeping gene locus was tested. In a number of transgenic mouse lines obtained, rtTA2S-M2 expression was detected in many tissues examined. Characterisation of the highest expressing rtTA2S-M2 transgenic mouse line demonstrated Dox-inducible GFP transgene expression in many tissues. Using this line we also show highly sensitive quantitative induction with low doses of Dox of an assayable plasma protein transgene under the control of a Tet Responsive Element (TRE). The utility of this rtTA2S-M2 line for inducible expression in mouse embryos was also demonstrated using a GATA-6 Tet-inducible transgene to show specific phenotypes in the embryonic lung, as well as broader effects resulting from the inducible widespread overexpression of the transgene.

Conclusion

The ubiquitously expressing rtTA2S-M2 transgenic mouse line described here provides a very useful tool for studying the effects of the widespread, inducible overexpression of genes during embryonic development and in adult mice.

Distinct activities of stromal cells involved in the organogenesis of lymph nodes and Peyer's patches

It is now well established that the interaction between "inducer" cells of hemopoietic origin and "organizer" cells of mesenchymal lineage is involved in the organogenesis of lymph node (LN) and Peyer's patch (PP). Organizer cells are defined by the expression of VCAM-1 and ICAM-1 and the production of homeostatic chemokines. However, several studies suggested the presence of a diversity among these cells from different lymphoid tissues. Thus, we attempted to define the difference of organizer cells of LN and PP in terms of gene expression profile. Microarray analyses of organizer cells revealed that these cells isolated from embryonic mesenteric LN expressed higher levels of genes that are related to inflammation, tissue remodeling, and development of mesenchymal lineage compared with those from PP. Several transcription factors related to epithelial-mesenchymal interactions were also up-regulated in organizer cells from LN. These results indicate that organizer cells in LN and PP are indeed distinct and suggest that the organizer cells in LN are at a more activated stage than those in PP.

Xenopus cDNA microarray identification of genes with endodermal organ expression

The endoderm is classically defined as the innermost layer of three Metazoan germ layers. During organogenesis, the endoderm gives rise to the digestive and respiratory tracts as well as associated organs such as the liver, pancreas, and lung. At present, however, how the endoderm forms the variety of cell types of digestive and respiratory tracts as well as the budding organs is not well understood. In order to investigate the molecular basis and mechanism of organogenesis and to identify the endodermal organ-related marker genes, we carried out microarray analysis using Xenopus cDNA chips. To achieve this goal, we isolated the Xenopus gut endoderm from three different stages of Xenopus organogenesis, and separated each stage of gut endoderm into anterior and posterior regions. Competitive hybridization of cDNA between the anterior and posterior endoderm regions, to screen genes that specifically expressed in the major organs, revealed 915 candidates. We then selected 104 clones for in situ hybridization analysis. Here, we report the identification and expression patterns of the 104 Xenopus endodermal genes, which would serve as useful markers for studying endodermal organ development.