Mesodermal Transcription Factors Research Articles

Early neural specification of stem cells is mediated by a set of SOX2-dependent neural-associated enhancers

SOX2 is a transcription factor involved in the regulatory network maintaining the pluripotency of embryonic stem cells in culture as well as in early embryos. In addition, SOX2 plays a pivotal role in neural stem cell formation and neurogenesis. How SOX2 can serve both processes has remained elusive. Here, we identified a set of SOX2-dependent neural-associated enhancers required for neural lineage priming. They form a distinct subgroup (1,898) among 8,531 OCT4/SOX2/NANOG-bound enhancers characterized by enhanced SOX2 binding and chromatin accessibility. Activation of these enhancers is triggered by neural induction of wild-type cells or by default in Smad4-ablated cells resistant to mesoderm induction and is antagonized by mesodermal transcription factors via Sox2 repression. Our data provide mechanistic insight into the transition from the pluripotency state to the early neural fate and into the regulation of early neural versus mesodermal specification in embryonic stem cells and embryos.

Neuromesodermal specification during head-to-tail body axis formation.

The anterior-to-posterior (head-to-tail) body axis is extraordinarily diverse among vertebrates but conserved within species. Body axis development requires a population of axial progenitors that resides at the posterior of the embryo to sustain elongation and is then eliminated once axis extension is complete. These progenitors occupy distinct domains in the posterior (tail-end) of the embryo and contribute to various lineages along the body axis. The subset of axial progenitors with neuromesodermal competency will generate both the neural tube (the precursor of the spinal cord), and the trunk and tail somites (producing the musculoskeleton) during embryo development. These axial progenitors are called Neuromesodermal Competent cells (NMCs) and Neuromesodermal Progenitors (NMPs). NMCs/NMPs have recently attracted interest beyond the field of developmental biology due to their clinical potential. In the mouse, the maintenance of neuromesodermal competency relies on a fine balance between a trio of known signals: Wnt/β-catenin, FGF signalling activity and suppression of retinoic acid signalling. These signals regulate the relative expression levels of the mesodermal transcription factor Brachyury and the neural transcription factor Sox2, permitting the maintenance of progenitor identity when co-expressed, and either mesoderm or neural lineage commitment when the balance is tilted towards either Brachyury or Sox2, respectively. Despite important advances in understanding key genes and cellular behaviours involved in these fate decisions, how the balance between mesodermal and neural fates is achieved remains largely unknown. In this chapter, we provide an overview of signalling and gene regulatory networksin NMCs/NMPs. We discuss mutant phenotypes associated with axial defects, hinting at the potential significant role of lesser studied proteins in the maintenance and differentiation of the progenitors that fuel axial elongation.

Single-cell Bayesian deconvolution

Individual cells exhibit substantial heterogeneity in protein abundance and activity, which is frequently reflected in broad distributions of fluorescently labeled reporters. Since all cellular components are intrinsically fluorescent to some extent, the observed distributions contain background noise that masks the natural heterogeneity of cellular populations. This limits our ability to characterize cell-fate decision processes that are key for development, immune response, tissue homeostasis, and many other biological functions. It is therefore important to separate the contributions from signal and noise in single-cell measurements. Addressing this issue rigorously requires deconvolving the noise distribution from the signal, but approaches in that direction are still limited. Here, we present a non-parametric Bayesian formalism that performs such a deconvolution efficiently on multidimensional measurements, providing unbiased estimates of the resulting confidence intervals. We use this approach to study the expression of the mesodermal transcription factor Brachyury in mouse embryonic stem cells undergoing differentiation.

A Mesp1-dependent developmental breakpoint in transcriptional and epigenomic specification of early cardiac precursors.

Transcriptional networks governing cardiac precursor cell (CPC) specification are incompletely understood owing, in part, to limitations in distinguishing CPCs from non-cardiac mesoderm in early gastrulation. We leveraged detection of early cardiac lineage transgenes within a granular single-cell transcriptomic time course of mouse embryos to identify emerging CPCs and describe their transcriptional profiles. Mesp1, a transiently expressed mesodermal transcription factor, is canonically described as an early regulator of cardiac specification. However, we observed perdurance of CPC transgene-expressing cells in Mesp1 mutants, albeit mislocalized, prompting us to investigate the scope of the role of Mesp1 in CPC emergence and differentiation. Mesp1 mutant CPCs failed to robustly activate markers of cardiomyocyte maturity and crucial cardiac transcription factors, yet they exhibited transcriptional profiles resembling cardiac mesoderm progressing towards cardiomyocyte fates. Single-cell chromatin accessibility analysis defined a Mesp1-dependent developmental breakpoint in cardiac lineage progression at a shift from mesendoderm transcriptional networks to those necessary for cardiac patterning and morphogenesis. These results reveal Mesp1-independent aspects of early CPC specification and underscore a Mesp1-dependent regulatory landscape required for progression through cardiogenesis.

Abstract 13139: Single Gene Cardiopoiesis Induced in Human Pluripotent Source

Introduction: The process of engaging stem cells towards a cardiopoietic (CP) state was established using a protein-based cocktail consisting of multiple growth factors. Although this regenerative enhancement protocol has been successfully tested in advanced clinical trials, it remains resource-intensive. Recent efforts have focused on streamlining cardiopoiesis through a protein-independent alternative that leverages a transfection-based mRNA approach. Microencapsulated modified messenger RNA (M3RNA) was utilized to deliver brachyury (T), an early mesodermal transcription factor to provoke early lineage specification in pluripotent cells. Hypothesis: Transfection of a human pluripotent stem cell source with T induces early expression of CP transcription factors to accelerate cardiac differentiation. Methods: Human pluripotent stem cells were transfected with T and maintained for 14 days. Expression of the cardiopoietic markers MEF2C, GATA4, and Nkx2.5 was analyzed using RT-qPCR, in tandem with MYH6 at days 10 and 20. Differentiation proficiency was independently corroborated by assessing Mef2c and Nkx2.5 expression by IF. Results: Following transfection with T, Nkx2.5, MEF2C and GATA4 were significantly induced at 72h (60-, 20- and 40-fold, respectively, p<0.01 for all 3 markers vs baseline), reflecting timing of differentiation initiation. At 5 days post differentiation, expression of the cardiac-specific Nkx2.5 increased by 5 fold vs control and the cell cycle regulator CHIR (p<0.01), suggesting successful persistent induction of cardiopoeisis. At 10 and 20 days of differentiation, RNA expression of MYH6 was 10-15 times induced in human pluripotent cells transduced with T (p < 0.0001, and p < 0.001 vs control, respectively), compared to 2 times (p<0.05, p<0.01 vs control, respectively) in CHIR treated cohorts. Accordingly, at 42 days post-induction of differentiation, a greater number of cells expressed MLC2V and cTnT (p<1e-05, <1e-07, respectively vs control), driving a robust beating pattern. Conclusion: This study implements a single gene T M3RNA-based approach to readily induce cardiac differentiation from pluripotent sources, exceeding available commercial platforms.

Residual pluripotency is required for inductive germ cell segregation

Fine-tuned dissolution of pluripotency is critical for proper cell differentiation. Here we show that the mesodermal transcription factor, T, globally affects the properties of pluripotency through binding to Oct4 and to the loci of other pluripotency regulators. Strikingly, lower T levels coordinately affect naïve pluripotency, thereby directly activating the germ cell differentiation program, in contrast to the induction of germ cell fate of primed models. Contrary to the effect of lower T levels, higher T levels more severely affect the pluripotency state, concomitantly enhancing the somatic differentiation program and repressing the germ cell differentiation program. Consistent with such in vitro findings, nascent germ cells in vivo are detected in the region of lower T levels at the posterior primitive streak. Furthermore, T and core pluripotency regulators co-localize at the loci of multiple germ cell determinants responsible for germ cell development. In conclusion, our findings indicate that residual pluripotency establishes the earliest and fundamental regulatory mechanism for inductive germline segregation from somatic lineages.

Brachyury engineers cardiac repair competent stem cells.

To optimize the regenerative proficiency of stem cells, a cardiopoietic protein‐based cocktail consisting of multiple growth factors has been developed and advanced into clinical trials for treatment of ischemic heart failure. Streamlining the inductors of cardiopoiesis would address the resource intensive nature of the current stem cell enhancement protocol. To this end, the microencapsulated‐modified‐mRNA (M3RNA) technique was here applied to introduce early cardiogenic genes into human adipose‐derived mesenchymal stem cells (AMSCs). A single mesodermal transcription factor, Brachyury, was sufficient to trigger high expression of cardiopoietic markers, Nkx2.5 and Mef2c. Engineered cardiopoietic stem cells (eCP) featured a transcriptome profile distinct from pre‐engineered AMSCs. In vitro, eCP demonstrated protective antioxidant capacity with enhanced superoxide dismutase expression and activity; a vasculogenic secretome driving angiogenic tube formation; and macrophage polarizing immunomodulatory properties. In vivo, in a murine model of myocardial infarction, intramyocardial delivery of eCP (600 000 cells per heart) improved cardiac performance and protected against decompensated heart failure. Thus, heart repair competent stem cells, armed with antioxidant, vasculogenic, and immunomodulatory traits, are here engineered through a protein‐independent single gene manipulation, expanding the available regenerative toolkit.

Expanding the mesodermal transcriptional network by genome-wide identification of Zinc finger homeodomain 1 (Zfh1) targets.

The Drosophila transcription factor (TF) Zfh1 has distinct roles compared to the cell lineage-determining TFs in almost all mesoderm-derived tissues. Here, we link Zfh1 to the well-characterized mesodermal transcriptional network. We identify five enhancers integrating upstream regulatory inputs from mesodermal TFs and directing zfh1 expression in mesoderm. Most downstream Zfh1-target genes are co-bound by mesodermal TFs, suggesting that Zfh1 and mesodermal TFs act on the same sets of co-regulated genes during the development of certain mesodermal tissues. Furthermore, we demonstrate that Zfh1 is critical for the expression of a hemocyte marker gene peroxidasin and helps restrict the activity of a hemocyte-specific enhancer of serpent to hemocyte-deriving head mesoderm, suggesting a potential role of Zfh1 in hemocyte development.

Abstract B41: Modeling bone development and cancer predisposition in Diamond Blackfan anemia (DBA)

Abstract DBA is an inherited bone marrow failure syndrome characterized by pure red cell aplasia, congenital physical anomalies, and cancer predisposition, in particular an increased incidence of osteogenic sarcoma (O:E 42.44). In order to investigate the mechanism of defective bone development and ultimately oncogenesis, we used an in vitro model consisting of mouse embryonic stem cells gene trapped for the Ribosomal Protein 19 gene (Rps19) and developed an in vivo transgenic conditional mouse model with floxed Rps19 alleles and a bone-specific expressing Col1a1-CreER. Using a 23-day stepwise osteoblast differentiation model, haploinsufficient Rps19+/- mouse ES cells did not show differences in the ability to develop into mesodermal progenitors based on qPCR analysis of mesodermal transcription factors, but displayed a decreased ability to produce mature osteoblasts based upon decreased alizarin red staining. In addition, higher levels of the Trp53 protein were found in Rps19+/- mouse ES cells at both the pluripotent and mesodermal stages of differentiation. Further, Rps19+/- mouse ES cells presented with aberrant WNT signaling, as represented by decreased levels of β-catenin early in osteoblast differentiation and rising to higher levels towards late osteoblast differentiation. We assessed the hypothesis of WNT signaling involvement in lineage specification and found that Rps19+/- mouse ES cell-derived osteoblasts show decreased levels of Runx2 and increased levels of Sox9. In the transgenic mouse model, tamoxifen-induced recombination of Rps19 at E15-17 did not show gross morphologic skeletal defects at E20.5 for Rps19fl/+ embryos, although Rps19fl/fl embryos displayed severe skeletal defects through alizarin red and alcian blue staining. In conclusion, haploinsufficient levels of Rps19 found in mice contribute to improper skeletal development and probably reflect the clinical scenario. We plan to utilize these in vitro and in vivo models to provide clues into the mechanism of ribosomal protein haploinsufficiency in tumor development, which may suggest surveillance and treatment strategies. Citation Format: Jimmy Hom, Brian Dulmovits, Luanne Peters, Adrianna Vlachos, Jeffrey M. Lipton, Lionel Blanc. Modeling bone development and cancer predisposition in Diamond Blackfan anemia (DBA) [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B41.

Mesodermal differentiation of human pluripotent stem cells increases Mitofusin‐2 mediated Mitophagy

Pluripotent stem cells rely on glycolysis for their energy needs and shift their metabolism towards mitochondrial oxidative phosphorylation during differentiation in order to adapt to the metabolic needs of mature differentiated cells. Oxidative phosphorylation generates reactive oxygen species and can thus lead to collateral protein oxidation and damage. Excessive mitochondrial damage leads to mitochondrial autophagy or mitophagy during which mitochondria are marked for degradation. A key regulator of mitophagy is the outer mitochondrial membrane protein Mitofusin‐2 (Mfn2) which either directs mitochondria towards fusion with other mitochondria to optimize mitochondrial function or towards mitophagy. We hypothesized that differentiation of pluripotent stem cells would necessitate increased mitophagy to contain the oxidative damage due to enhanced oxidative phosphorylation.Human induced pluripotent stem cells (iPSCs) of human embryonic stem cells (hESCs) were treated with Bone Morphogenetic Protein 4 (BMP4) to induce differentiation to the mesodermal lineage. These cells exhibited an expected increase in the mesodermal transcription factor Brachyury. Cells were stained with MitoTracker to visualize mitochondria and assess mitochondrial network formation. We observed an increase in mitochondrial fusion during mesodermal differentiation. There was also a two‐fold increase in Mitofusin 2 protein levels with BMP4 treatment. The ratiometric fluorescent sensor mitoKeima which detects the pH of mitochondria and assesses mitophagy indicated significantly higher basal mitophagy after three days of BMP4 induced differentiation with an increase in the relative mitophagy index from 2.7 to 9.7 (p<0.01) within three days.These findings suggest that mitophagy and mitochondrial networking are critical Mitofusin‐2 mediated adaptive processes required for the metabolic reprogramming of differentiating stem cells.Support or Funding InformationNIH T32 Training Grant

Tbx15 controls skeletal muscle fibre-type determination and muscle metabolism.

Skeletal muscle is composed of both slow-twitch oxidative myofibers and fast-twitch glycolytic myofibers that differentially impact muscle metabolism, function and eventually whole-body physiology. Here we show that the mesodermal transcription factor T-box 15 (Tbx15) is highly and specifically expressed in glycolytic myofibers. Ablation of Tbx15 in vivo leads to a decrease in muscle size due to a decrease in the number of glycolytic fibres, associated with a small increase in the number of oxidative fibres. This shift in fibre composition results in muscles with slower myofiber contraction and relaxation, and also decreases whole-body oxygen consumption, reduces spontaneous activity, increases adiposity and glucose intolerance. Mechanistically, ablation of Tbx15 leads to activation of AMPK signalling and a decrease in Igf2 expression. Thus, Tbx15 is one of a limited number of transcription factors to be identified with a critical role in regulating glycolytic fibre identity and muscle metabolism.

Ginsenosides May Enhance the Functionality of Human Embryonic Stem Cell–Derived Cardiomyocytes In Vitro

Various chemicals have been reported to induce the differentiation of human embryonic stem cells (hESCs) into cardiomyocytes (CMs), however, their contributions to the functionality of hESC-derived CMs are still limited. In this study, we evaluated the effects of red ginseng extract (RGE), ginsenoside-Rb1 (gRb1, panaxadiol), and ginsenoside-Re (gRe, panaxatriol) on the differentiation of hESCs and the functionality of derived CMs. Undifferentiated hESCs were treated with 0.25 mg/mL RGE, 10 μmol/L gRb1, or 10 μmol/L gRe for 48 hours at the differentiation induction (early stage) or maturation (late stage) period. The expression of mesodermal and cardiac transcription factor genes was upregulated in the ginsenoside-treated groups from early stage. The expression of cardiac sarcomeric genes was significantly upregulated at the late stage. The gRb1- and gRe-treated groups upregulated the expression of potassium voltage-gated channel subfamily E member 1 (KCNE1) and the gRe-treated group showed a longer beating duration compared to the control. Taken together, ginsenosides may enhance the functionality of hESC-derived CMs in vitro.

Highly parallel assays of tissue-specific enhancers in whole Drosophila embryos

Transcriptional enhancers are a primary mechanism by which tissue-specific gene expression is achieved. Despite the importance of these regulatory elements in development, responses to environmental stresses, and disease, testing enhancer activity in animals remains tedious, with a minority of enhancers having been characterized. Here, we have developed ‘enhancer-FACS-Seq’ (eFS) technology for highly parallel identification of active, tissue-specific enhancers in Drosophila embryos. Analysis of enhancers identified by eFS to be active in mesodermal tissues revealed enriched DNA binding site motifs of known and putative, novel mesodermal transcription factors (TFs). Naïve Bayes classifiers using TF binding site motifs accurately predicted mesodermal enhancer activity. Application of eFS to other cell types and organisms should accelerate the cataloging of enhancers and understanding how transcriptional regulation is encoded within them.

An Intact Brachyury Function Is Necessary to Prevent Spurious Axial Development in Xenopus laevis

We have previously shown that the member of the HES family hairy2 induces the ectopic expression of dorsal markers when it is overexpressed in the ventral side of Xenopus embryos. Intriguingly, hairy2 represses the mesoderm transcription factor brachyury (bra) throughout its domain in the marginal zone. Here we show that in early gastrula, bra and hairy2 are expressed in complementary domains. Overexpression of bra repressed hairy2. Interference of bra function with a dominant-negative construct expanded the hairy2 domain and, like hairy2 overexpression, promoted ectopic expression of dorsal axial markers in the ventral side and induced secondary axes without head and notochord. Hairy2 depletion rescued the ectopic dorsal development induced by interference of bra function. We concluded that an intact bra function is necessary to exclude hairy2 expression from the non-organiser field, to impede the ectopic specification of dorsal axial fates and the appearance of incomplete secondary axes. This evidence supports a previously unrecognised role for bra in maintaining the dorsal fates inhibited in the ventral marginal zone, preventing the appearance of trunk duplications.

Efficient Commitment to Functional CD34+ Progenitor Cells from Human Bone Marrow Mesenchymal Stem-Cell-Derived Induced Pluripotent Stem Cells

The efficient commitment of a specialized cell type from induced pluripotent stem cells (iPSCs) without contamination from unknown substances is crucial to their use in clinical applications. Here, we propose that CD34+ progenitor cells, which retain hematopoietic and endothelial cell potential, could be efficiently obtained from iPSCs derived from human bone marrow mesenchymal stem cells (hBMMSC-iPSCs) with defined factors. By treatment with a cocktail containing mesodermal, hematopoietic, and endothelial inducers (BMP4, SCF, and VEGF, respectively) for 5 days, hBMMSC-iPSCs expressed the mesodermal transcription factors Brachyury and GATA-2 at higher levels than untreated groups (P<0.05). After culturing with another hematopoietic and endothelial inducer cocktail, including SCF, Flt3L, VEGF and IL-3, for an additional 7–9 days, CD34+ progenitor cells, which were undetectable in the initial iPSC cultures, reached nearly 20% of the total culture. This was greater than the relative number of progenitor cells produced from human-skin-fibroblast-derived iPSCs (hFib-iPSCs) or from the spontaneous differentiation groups (P<0.05), as assessed by flow cytometry analysis. These induced cells expressed hematopoietic transcription factors TAL-1 and SCL. They developed into various hematopoietic colonies when exposed to semisolid media with hematopoietic cytokines such as EPO and G-CSF. Hematopoietic cell lineages were identified by phenotype analysis with Wright-Giemsa staining. The endothelial potential of the cells was also verified by the confirmation of the formation of vascular tube-like structures and the expression of endothelial-specific markers CD31 and VE-CADHERIN. Efficient induction of CD34+ progenitor cells, which retain hematopoietic and endothelial cell potential with defined factors, provides an opportunity to obtain patient-specific cells for iPSC therapy and a useful model for the study of the mechanisms of hematopoiesis and drug screening.

Abstract P015: Hypoxia Regulates Embryonic Cardiac Myocyte Proliferation and Differentiation

Mammalian cardiac myocytes (CM) proliferate readily during development but exit the cell cycle perinatally. The molecular mechanism for this is poorly understood could lead to new approaches for cardiac regeneration. We employed a novel bioinformatics approach to identify transcription factors that may control perinatal cell-cycle arrest and identified hypoxia inducible factor 1α (Hif1α) as a potential regulator of CM proliferation and differentiation. To test our hypothesis, e12.5d embryonic heart cells were cultured in atmospheric (17%) or hypoxic (3%) [O2] and then assessed for proliferation over 4 days. Total cell numbers were significantly increased (∼2 fold, P&lt;0.005) in cells cultured in 3% vs. 17% [O2] after 4 days. Hypoxia increased numbers of cTn+ cells labeled with p-Histone-H3 indicating an increase in CM proliferation. Carboxyfluorescein succinimidyl ester staining indicated that the majority (70%) of cells cultured in 3% [O2] divided 2–3 times while the majority (73%) of cells in 17% [O2] divided 0–1 times after 3 days of culture. As expected, hypoxia stabilized the Hif1α protein and induced the expression of Vegf. Messenger RNA for the G1-S phase cyclin dependent kinase Ccnd2 was increased (&gt;2 fold) in hypoxic vs. atmospheric cultured cells indicating that hypoxia my increase proliferation by regulating the expression of cell cycle machinery. Furthermore, early mesodermal transcription factors Brachyury and Mesp1 and the CM progenitor marker Nkx2.5 were induced (&gt;5 fold) in hypoxic vs. atmospheric [O2] cultured cells suggesting that hypoxia positively regulates early mesodermal and CM progenitor cell differentiation. To validate this hypothesis, we differentiated mouse embryonic stem cells in atmospheric and hypoxic [O2] and observed similar increases in the expression of Brachyury, Mesp1 and Nkx2.5 in hypoxic differentiated cells. Transient culture (2 d) of embryoid bodies (EBs) in hypoxia increased the frequency of beating EBs and the % of cTn+ cells compared to cells differentiated in atmospheric O2. Taken together these data suggest that the hypoxic environment in which CMs develop may serve as a key signal that regulates mesodermal progenitor marker expression and CM progenitor cell differentiation and proliferation.

Abstract SY24-02: Development of recombinant vaccines for the prevention and therapy of human carcinomas

Abstract SY24-02: Development of recombinant vaccines for the prevention and therapy of human carcinomas

Coordinated epigenetic repression of the miR‐200 family and miR‐205 in invasive bladder cancer

MicroRNAs (miRNA) are small noncoding RNAs commonly deregulated in cancer. The miR-200 family (miR-200a, -200b, -200c, -141 and -429) and miR-205 are frequently silenced in advanced cancer and have been implicated in epithelial to mesenchymal transition (EMT) and tumor invasion by targeting the transcriptional repressors of E-cadherin, ZEB1 and ZEB2. ZEB1 is also known to repress miR-200c-141 transcription in a negative feedback loop, but otherwise little is known about the transcriptional regulation of the miR-200 family and miR-205. Recently, miR-200 silencing was also reported in cancer stem cells, implying that miR-200 deregulation is a key event in multiple levels of tumor biology. However, what prevents miR-200 expression remains largely unanswered. Here we report concerted transcriptional regulation of the miR-200 and miR-205 loci in bladder tumors and bladder cell lines. Using a combination of miRNA expression arrays, qPCR assays and mass spectrometry DNA methylation analyses, we show that the miR-200 and miR-205 loci are specifically silenced and gain promoter hypermethylation and repressive chromatin marks in muscle invasive bladder tumors and undifferentiated bladder cell lines. Moreover, we report that miR-200c expression is significantly correlated with early stage T1 bladder tumor progression, and propose miR-200 and miR-205 silencing and DNA hypermethylation as possible prognostic markers in bladder cancer. In addition, we observe that the mesoderm transcription factor TWIST1 and miR-200 expression are inversely correlated in bladder tumor samples and cell lines. TWIST1 associates directly with the miR-200 and miR-205 promoters, and may act as a repressor of miR-200 and miR-205 expression.

C. elegans twist gene expression in differentiated cell types is controlled by autoregulation through intron elements

The temporospatial regulation of genes encoding transcription factors is important during development. The hlh-8 gene encodes the C. elegans mesodermal transcription factor CeTwist. Elements in the hlh-8 promoter restrict gene expression to predominantly undifferentiated cells of the M lineage. We have discovered that hlh-8 expression in differentiated mesodermal cells is controlled by two well-conserved E box elements in the large first intron. Additionally, we found that these elements are bound in vitro by CeTwist and its transcription factor partner, CeE/DA. The E box driven expression is eliminated or diminished in an hlh-8 null allele or in hlh-2 (CeE/DA) RNAi, respectively. Expression of hlh-8 is also diminished in animals harboring an hlh-8 intron deletion allele. Altogether, our results support a model in which hlh-8 is initially expressed in the undifferentiated M lineage cells via promoter elements and then the CeTwist activates its own expression further (autoregulation) in differentiated cells derived from the M lineage via the intron elements. This model provides a mechanism for how a transcription factor may regulate distinct target genes in cells both before and after initiating the differentiation program. The findings could also be relevant to understanding human Twist gene regulation, which is currently not well understood.

Dimeric integrin α5β1 ligands confer morphological and differentiation responses to murine embryonic stem cells

We present the first report utilizing, and showing the functional relevance of, self-assembling polyvalent ligands specific for integrin α5β1 in murine embryonic stem (mES) cell adhesion. Di, tri and tetrameric 9th–10th type III fibronectin domains (FIII9′10) were used to generate clustered integrin α5β1 ligand surfaces for mES cell culture. Compared to gelatin, FIII9′10 (monomer), FIII9′10-trimer and -tetramer, the FIII9′10-dimer supported the highest number of mES cell colonies. No evidence of domain unfolding upon surface adsorption was found. Colonies appeared disperse with a spread cell morphology unless subdued back to a tight morphology with increasing concentrations of leukemia inhibitory factor (LIF). In the presence of LIF, mES cells adherent to the FIII9′10-dimer showed transient upregulation of Oct-4, the mesodermal transcription factor, Brachyury, and the ectodermal marker, Nestin. However, dual upregulation of Nanog maintained the mES cells in a pluripotent state, confirmed by alkaline phosphatase staining. Therefore, the behavior of mES cells adherent to dimeric integrin α5β1 ligands is a largely morphological phenomenon conferring pro-differentiation signals towards mesodermal and ectodermal lineages. This work will be of interest to cell and tissue engineering groups aiming to control ES cell behavior through integrin ligand presentation and synthetic substrates.