The differentiation of murine and human embryonic stem (ES) cells into pancreatic cell types has been shown by several methods including spontaneous differentiation, formation of multi-lineage progenitors, lineage selection or transgene expression. However, these strategies led to a mixture of cells of all three primary germ layers and only a low percentage of definitive endoderm cells giving rise to pancreas, liver, lung and intestine. To reproducibly generate functional insulin-producing cells, ES cells have to be differentiated via definitive endoderm and pancreatic endocrine progenitors recapitulating the in vivo development. Activin A, a member of the transforming growth factor beta superfamily, has been shown to induce definitive endoderm cells dependent on concentration, culture conditions and time of application. Moreover, serum components or contamination by feeder cells as well as differentiation and proliferation factors are critical for successful generation of activin A-induced ES cells into endoderm and pancreatic cells. The review presents an overview on those factors that influence activin A activity on endoderm and endocrine progenitor cells and determines the role of signaling factors in the differentiation process into the pancreatic lineage.

Expression of the mouse transcription factor EC (Tfec) is restricted to the myeloid compartment, suggesting a function for Tfec in the development or function of these cells. However, mice lacking Tfec develop normally, indicating a redundant role for Tfec in myeloid cell development. We now report that Tfec is specifically induced in bone marrow-derived macrophages upon stimulation with the Th2 cytokines, IL-4 and IL-13, or LPS. LPS induced a rapid and transient up-regulation of Tfec mRNA expression and promoter activity, which was dependent on a functional NF-κB site. IL-4, however, induced a rapid, but long-lasting, increase in Tfec mRNA, which, in contrast to LPS stimulation, also resulted in detectable levels of Tfec protein. IL-4-induced transcription of Tfec was absent in macrophages lacking Stat6, and its promoter depended on two functional Stat6-binding sites. A global comparison of IL-4-induced genes in both wild-type and Tfec mutant macrophages revealed a surprisingly mild phenotype with only a few genes affected by Tfec deficiency. These included the G-CSFR (Csf3r) gene that was strongly up-regulated by IL-4 in wild-type macrophages and, to a lesser extent, in Tfec mutant macrophages. Our study also provides a general definition of the transcriptome in alternatively activated mouse macrophages and identifies a large number of novel genes characterizing this cell type.

Background Embryonic stem (ES) cells differentiate into cardiac phenotypes representing early pacemaker-, atrial-, ventricular-, and sinus node-like cells, however, ES-derived specification into sinus nodal cells is not yet known. By using the naphthylamine derivative of urea, suramin, we were able to follow the process of cardiac specialization into sinus node-like cells. Methods Differentiating mouse ES cells were treated with suramin (500 μM) from day 5 to 7 of embryoid body formation, and cells were analysed for their differentiation potential via morphological analysis, flow cytometry, RT-PCR, immunohistochemistry and patch clamp analysis. Results Application of suramin resulted in an increased number of cardiac cells, but inhibition of neuronal, skeletal muscle and definitive endoderm differentiation. Immediately after suramin treatment, a decreased mesendoderm differentiation was found. Brachyury, FGF10, Wnt8 and Wnt3a transcript levels were significantly down-regulated, followed by a decrease in mesoderm- and cardiac progenitor-specific markers BMP2, GATA4/5, Wnt11, Isl1, Nkx2.5 and Tbx5 immediately after removal of the substance. With continued differentiation, a significant up-regulation of Brachyury, FGF10 and GATA5 transcript levels was observed, whereas Nkx2.5, Isl1, Tbx5, BMP2 and Wnt11 levels were normalized to control levels. At advanced differentiation stages, sinus node-specific HCN4, Tbx2 and Tbx3 transcript levels were significantly up-regulated. Immunofluorescence and patch-clamp analysis confirmed the increased number of sinus node-like cells, and electrophysiological analysis revealed a lower number of atrial- and ventricular-like cardiomyocytes following suramin treatment. Conclusion We conclude that the interference of suramin with the cardiac differentiation process modified mesoderm- and cardiac-specific gene expression resulting in enhanced formation of sinus node-like cells.

Embryonic stem (ES) cells offer a valuable source for generating insulin-producing cells. However, current differentiation protocols often result in heterogeneous cell populations of various developmental stages. Here we show the activin A-induced differentiation of mouse ES cells carrying a homologous dsRed-IRES-puromycin knock-in within the Sox17 locus into the endoderm lineage. Sox17-expressing cells were selected by fluorescence-assisted cell sorting (FACS) and characterized at the transcript and protein level. Treatment of ES cells with high concentrations of activin A for 10 days resulted in up to 19% Sox17-positive cells selected by FACS. Isolated Sox17-positive cells were characterized by defini- tive endoderm-specific Sox17/Cxcr4/Foxa2 transcripts, but lacked pluripotency-associated Oct4 mRNA and protein. The Sox17-expressing cells showed downregulation of extraembryonic endoderm (Sox7, Afp, Sdf1)-, mesoderm (Foxf1, Meox1)- and ectoderm (Pax6, NeuroD6)-specific transcripts. The presence of Hnf4α, Hes1 and Pdx1 mRNA demonstrated the expression of primitive gut/foregut cell-specific markers. Ngn3, Nkx6.1 and Nkx2.2 transcripts in Sox17-positive cells were determined as properties of pancreatic endocrine progenitors. Immunocytochemistry of activin A-induced Sox17-positive embryoid bodies revealed coexpression of Cxcr4 and Foxa2. Moreover, the histochemical demonstration of E-cadherin-, Cxcr4-, Sox9-, Hnf1β- and Ngn3-positive epithelial-like structures underlined the potential of Sox17-positive cells to further differentiate into the pancreatic lineage. By reducing the heterogeneity of the ES cell progeny, Sox17-expressing cells are a suitable model to evaluate the effects of growth and differentiation factors and of culture conditions to delineate the differentiation process for the generation of pancreatic cells in vitro.

The microphthalmia transcription factor (MITF) regulates different target genes in several distinct cell types, including osteoclasts. The role of the closely related factors TFE3 and TFEC in MITF action was studied. The TFE3 and TFEC proteins were expressed in osteoclast-like cells, and both could be immunoprecipitated in a complex with MITF. In transient transfection assays, TFE3 and TFEC could collaborate with MITF to superactivate the tartrate resistant acid phosphatase (TRAP) promoter, a target for MITF in osteoclasts. Although TFEC had been thought to act as a repressor, we could demonstrate that TFEC acted as a transactivator when fused to the gal4 DNA-binding domain in a yeast one-hybrid-type assay. Additionally, two mRNA isoforms of MITF, MITF-M and MITF-A, were detected in primary osteoclast-like cells by RT-PCR. In transient transfection assays, the MITF-A and MITF-M isoforms activated the promoter of the TRAP gene to the same extent, and both forms could collaborate equally well with TFE3 to activate the TRAP promoter. These results indicate that although different isoforms of MITF appear to be functionally similar, the TFE3 and TFEC proteins may collaborate with MITF to efficiently regulate expression of target genes in osteoclasts.