Worming out the biology of Runx

RUNX1 promotes proliferation and migration in non-small cell lung cancer cell lines via the mTOR pathway

RUNX1, a member of the RUNX family of metazoan transcription factors, participates in the regulation of differentiation, proliferation, and other processes involved in growth and development. It also functions in the occurrence and development of tumors. However, the role and mechanism of action of RUNX1 in non-small cell lung cancer (NSCLC) are not yet clear. We used a bioinformatics approach as well as in vitro and in vivo assays to evaluate the role of RUNX1 in NSCLC as the molecular mechanisms underlying its effects. Using the TCGA, GEO, GEPIA (Gene Expression Profiling Interactive Analysis), and Kaplan-Meier databases, we screened the differentially expressed genes (DEGs) and found that RUNX1 was highly expressed in lung cancer and was associated with a poor prognosis. Immunohistochemical staining based on tissue chips from 110 samples showed that the expression of RUNX1 in lung cancer tissues was higher than that in adjacent normal tissues and was positively correlated with lymph node metastasis and TNM staging. In vitro experiments, we found that RUNX1 overexpression promoted cell proliferation and migration functions and affected downstream functional proteins by regulating the activity of the mTOR pathway, as confirmed by an analysis using the mTOR pathway inhibitor rapamycin. In addition, RUNX1 affected PD-L1 expression via the mTOR pathway. These results indicate that RUNX1 is a potential therapeutic target for NSCLC.

CgWnt-1 regulates haemocyte proliferation during immune response of oyster Crassostrea gigas

Recent findings regarding the immunomodulatory role of Wnt signaling suggest that it is significant in regulating the differentiation and proliferation of immune cells. In the present study, a Wnt-1 homolog (designated as CgWnt-1) with a conserved WNT1 domain was identified from oyster Crassostrea gigas. The transcripts of CgWnt-1 were barely expressed in egg to gastrula stage during early embryogenesis, and up-regulated significantly in the trochophore to juvenile stage. The mRNA transcripts of CgWnt-1 were detected in different tissues of adult oyster, with an extremely high expression level in the mantle, which was 77.38-fold (p < 0.05) of that in labial palp. After Vibrio splendidus stimulation, the mRNA expression levels of CgWnt-1 and Cgβ-catenin in haemocytes up-regulated significantly at 3, 12, 24, and 48 h (p < 0.05). After injection of recombinant protein (rCgWnt-1) into oyster in vivo, the expressions of Cgβ-catenin, cell proliferation related genes CgRunx-1 and CgCDK-2 in haemocytes significantly up-regulated, which were 4.86-fold (p < 0.05), 9.33-fold (p < 0.05), 6.09-fold (p < 0.05) of those in rTrx group, respectively. The percentage of EDU⁺ cells in haemocytes also significantly increased (2.88-fold of that in control group, p < 0.05) at 12 h after rCgWnt-1 treatment. When the Wnt signal inhibitor C59 was injected simultaneously with rCgWnt-1, the expressions of Cgβ-catenin, CgRunx-1, and CgCDK-2 were significantly reduced, which were 0.32-fold (p < 0.05), 0.16-fold (p < 0.05), and 0.25-fold (p < 0.05) of that in rCgWnt-1 group, respectively, and the percentage of EDU⁺ cells in haemocytes was also significantly inhibited (0.15-fold compared with that in rCgWnt-1 group, p < 0.05). These results suggested that the conserved CgWnt-1 could modulate haemocytes proliferation via regulating cell cycle related genes and involved in the immune response of oysters.

CgTNF-2 promotes the proliferation of haemocytes by regulating the expressions of CgRunx and cell cycle related genes in the Pacific oyster Crassostrea gigas

A TNF-α family member, CgTNF-2, was previously identified from the oyster Crassostrea gigas to involve in the antibacterial response. In the present study, the role of CgTNF-2 in mediating the proliferation of haemocytes was further explored. The mRNA expression of CgTNF-2 in granulocytes was significantly higher than that in semi-granulocytes and agranulocytes, and the percentages of CgTNF-2 antibody labeled cells in agranulocytes, semi-granulocytes and granulocytes were 19.15%, 40.25% and 94.07%, respectively. After the treatment with rCgTNF-2, the percentage of EdU⁺ cells in haemocytes increased significantly (1.77-fold, p < 0.05) at 6 h compared with that in rGST-treated group, and the mRNA expressions of CgRunx, CgCyclin A, CgCDK2 and CgCDC45 in haemocytes all increased significantly (p < 0.05), which were 1.94-fold, 2.13-fold, 1.97-fold, 1.76-fold of that in rGST-treated group, respectively. Meanwhile, the protein abundance of CgRunx and CgCyclin A in the haemocytes of oysters in the rCgTNF-2-treated group increased, and the percentage of PI⁺ haemocytes in S phase also increased significantly (2.19-fold, p < 0.05) compared with that in rGST-treated group. These results collectively confirmed that CgTNF-2 was highly expressed in granulocytes and involved in the proliferation of haemocytes by regulating the expressions of CgRunx and cell cycle related genes in C. gigas.

Bcl6-Mediated Transcriptional Regulation of Follicular Helper T cells (TFH)

Follicular helper T cells (T_FH) are essential B cell-help providers in the formation of germinal centers (GCs), affinity maturation of GC B cells, differentiation of high-affinity antibody-producing plasma cells, and production of memory B cells. The transcription factor (TF) B cell lymphoma 6 (Bcl6) is at the center of gene regulation in T_FH biology, including differentiation and function, but how Bcl6 does this, and what additional TFs contribute, remain complex questions. This review focuses on advances in our understanding of Bcl6-mediated gene regulation of T_FH functions, and the modulation of T_FH by other TFs. These advances may have important implications in deciphering how repressor TFs can regulate many immunological cell types. An improved understanding of T_FH biology will likely provide insights into biomedically relevant diseases.

ZYG-1 promotes limited centriole amplification in the C. elegans seam lineage

Genome stability relies notably on the integrity of centrosomes and on the mitotic spindle they organize. Structural and numerical centrosome aberrations are frequently observed in human cancer, and there is increasing evidence that centrosome amplification can promote tumorigenesis. Here, we use C. elegans seam cells as a model system to analyze centrosome homeostasis in the context of a stereotyped stem like lineage. We found that overexpression of the Plk4-related kinase ZYG-1 leads to the formation of one supernumerary centriolar focus per parental centriole during the cell cycle that leads to the sole symmetric division in the seam lineage. In the following cell cycle, such supernumerary foci function as microtubule organizing centers, but do not cluster during mitosis, resulting in the formation of a multipolar spindle and then aneuploid daughter cells. Intriguingly, we found also that supernumerary centriolar foci do not assemble in the asymmetric cell divisions that precedes or that follows the symmetric seam cell division, despite the similar presence of GFP::ZYG-1. Furthermore, we established that supernumerary centrioles form earlier during development in animals depleted of the heterochronic gene lin-14, in which the symmetric division is precocious. Conversely, supernumerary centrioles are essentially not observed in animals depleted of lin-28, in which the symmetric division is lacking. These findings lead us to conclude that ZYG-1 promotes limited centriole amplification solely during the symmetric division in the C. elegans seam lineage.

Unique N-terminal sequences in two Runx1 isoforms are dispensable for Runx1 function

Background

The Runt-related transcription factors (Runx) are a family of evolutionarily conserved transcriptional regulators that play multiple roles in the developmental control of various cell types. Among the three mammalian Runx proteins, Runx1 is essential for definitive hematopoiesis and its dysfunction leads to human leukemogenesis. There are two promoters, distal (P1) and proximal (P2), in the Runx1 gene, which produce two Runx1 isoforms with distinct N-terminal amino acid sequences, P1-Runx1 and P2-Runx1. However, it remains unclear whether P2-Runx specific N-terminal sequence have any specific function for Runx1 protein.

Results

To address the function of the P2-Runx1 isoform, we established novel mutant mouse models in which the translational initiation AUG (+1) codon for P2-Runx1 isoform was modulated. We found that a truncated P2-Runx1 isoform is translated from a downstream non-canonical AUG codon. Importantly, the truncated P2-Runx1 isoform is sufficient to support primary hematopoiesis, even in the absence of the P1-Runx1 isoform. Furthermore, the truncated P2-Runx1 isoform was able to restore defect in basophil development caused by loss of the P1-Runx1 isoform. The truncated P2-Runx1 isoform was more stable than the canonical P2-Runx1 isoform.

Conclusions

Our results demonstrate that the N-terminal sequences specific for P2-Runx1 are dispensable for Runx1 function, and likely serve as a de-stabilization module to regulate Runx1 production.

Electronic supplementary material

The online version of this article (10.1186/s12861-017-0156-y) contains supplementary material, which is available to authorized users.

RUNX in Invertebrates

Runx genes have been identified in all metazoans and considerable conservation of function observed across a wide range of phyla. Thus, insight gained from studying simple model organisms is invaluable in understanding RUNX biology in higher animals. Consequently, this chapter will focus on the Runx genes in the diploblasts, which includes sea anemones and sponges, as well as the lower triploblasts, including the sea urchin, nematode, planaria and insect. Due to the high degree of functional redundancy amongst vertebrate Runx genes, simpler model organisms with a solo Runx gene, like C. elegans, are invaluable systems in which to probe the molecular basis of RUNX function within a whole organism. Additionally, comparative analyses of Runx sequence and function allows for the development of novel evolutionary insights. Strikingly, recent data has emerged that reveals the presence of a Runx gene in a protist, demonstrating even more widespread occurrence of Runx genes than was previously thought. This review will summarize recent progress in using invertebrate organisms to investigate RUNX function during development and regeneration, highlighting emerging unifying themes.

An Elk transcription factor is required for Runx-dependent survival signaling in the sea urchin embryo

Elk proteins are Ets family transcription factors that regulate cell proliferation, survival, and differentiation in response to ERK (extracellular-signal regulated kinase)-mediated phosphorylation. Here we report the embryonic expression and function of Sp-Elk, the single Elk gene of the sea urchin Strongylocentrotus purpuratus. Sp-Elk is zygotically expressed throughout the embryo beginning at late cleavage stage, with peak expression occurring at blastula stage. Morpholino antisense-mediated knockdown of Sp-Elk causes blastula-stage developmental arrest and embryo disintegration due to apoptosis, a phenotype that is rescued by wild-type Elk mRNA. Development is also rescued by Elk mRNA encoding a serine to aspartic acid substitution (S402D) that mimics ERK-mediated phosphorylation of a conserved site that enhances DNA binding, but not by Elk mRNA encoding an alanine substitution at the same site (S402A). This demonstrates both that the apoptotic phenotype of the morphants is specifically caused by Elk depletion, and that phosphorylation of serine 402 of Sp-Elk is critical for its anti-apoptotic function. Knockdown of Sp-Elk results in under-expression of several regulatory genes involved in cell fate specification, cell cycle control, and survival signaling, including the transcriptional regulator Sp-Runt-1 and its target Sp-PKC1, both of which were shown previously to be required for cell survival during embryogenesis. Both Sp-Runt-1 and Sp-PKC1 have sequences upstream of their transcription start sites that specifically bind Sp-Elk. These results indicate that Sp-Elk is the signal-dependent activator of a feed-forward gene regulatory circuit, consisting also of Sp-Runt-1 and Sp-PKC1, which actively suppresses apoptosis in the early embryo.

Role of RUNX2 in Breast Carcinogenesis

RUNX2 is a transcription factor playing the major role in osteogenesis, but it can be involved in DNA damage response, which is crucial for cancer transformation. RUNX2 can interact with cell cycle regulators: cyclin-dependent kinases, pRB and p21Cip1 proteins, as well as the master regulator of the cell cycle, the p53 tumor suppressor. RUNX2 is involved in many signaling pathways, including those important for estrogen signaling, which, in turn, are significant for breast carcinogenesis. RUNX2 can promote breast cancer development through Wnt and Tgfβ signaling pathways, especially in estrogen receptor (ER)-negative cases. ERα interacts directly with RUNX2 and regulates its activity. Moreover, the ERα gene has a RUNX2 binding site within its promoter. RUNX2 stimulates the expression of aromatase, an estrogen producing enzyme, increasing the level of estrogens, which in turn stimulate cell proliferation and replication errors, which can be turned into carcinogenic mutations. Exploring the role of RUNX2 in the pathogenesis of breast cancer can lead to revealing new therapeutic targets.

Baicalein increases the expression and reciprocal interplay of RUNX3 and FOXO3a through crosstalk of AMPKα and MEK/ERK1/2 signaling pathways in human non-small cell lung cancer cells

Background

Baicalein, a natural flavonoid obtained from the Scutellaria baicalensis root, has been reported to inhibit growth of human lung cancer. However, the detailed mechanism underlying this has not been well elucidated.

Methods

Cell viability was measured using a 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays. Apoptosis was detected by flow cytometry analysis and caspase 3/7 assays. The expression of RUNX3 and FOXO3a mRNA were measured by real time RT-PCR methods. Western blot analysis was performed to measure the phosphorylation and protein expression of AMP-activated protein kinase alpha (AMPKα) and extracellular signal-regulated kinase 1/2 (ERK1/2), runt-related transcription factor 3 (RUNX3) and forkhead box O3a (FOXO3a). Silencing of FOXO3a and RUNX3 were performed by small interfering RNA (siRNA) methods. Exogenous expression of FOXO3a or RUNX3 was carried out by electroporated transfection assays.

Results

We showed that baicalein significantly inhibited growth and induced apoptosis of non-small cell lung cancer (NSCLC) cells in a time- and dose-dependent manner. Baicalein induced RUNX3 and FOXO3a protein expression, and increased phosphorylation of AMPKα and ERK1/2. Moreover, the inhibitors of AMPK and MEK/ERK1/2 reversed the effect of baicalein on RUNX3 and FOXO3a protein expression. Interestingly, while compound C had little effect on blockade of baicalein-induced phosphorylation of ERK1/2, PD98059 significantly abrogated baicalein-induced phosphorylation of AMPKα. Intriguingly, while silencing of RUNX3 abolished the effect of baicalein on expression of FOXO3a and apoptosis, silencing of FOXO3a significantly attenuated baicalein-reduced cell proliferation. On the contrary, overexpression of FOXO3a restored the effect of baicalein on cell growth inhibition in cells silencing of endogenous FOXO3a gene and enhanced the effect of baicalein on RUNX3 protein expression. Finally, exogenous expression of RUNX3 increased FOXO3a protein and strengthened baicalein-induced phosphorylation of ERK1/2.

Conclusion

Collectively, our results show that baicalein inhibits growth and induces apoptosis of NSCLC cells through AMPKα- and MEK/ERK1/2-mediated increase and interaction of FOXO3a and RUNX3 protein. The crosstalk between AMPKα and MEK/ERK1/2 signaling pathways, and the reciprocal interplay of FOXO3a and RUNX3 converge on the overall response of baicalein. This study reveals a novel mechanism for regulating FOXO3a and RUNX3 signaling axis in response to baicalein and suggests a new strategy for NSCLC associated targeted therapy.

The C. elegans TPR Containing Protein, TRD-1, Regulates Cell Fate Choice in the Developing Germ Line and Epidermis

Correct cell fate choice is crucial in development. In post-embryonic development of the hermaphroditic Caenorhabitis elegans, distinct cell fates must be adopted in two diverse tissues. In the germline, stem cells adopt one of three possible fates: mitotic cell cycle, or gamete formation via meiosis, producing either sperm or oocytes. In the epidermis, the stem cell-like seam cells divide asymmetrically, with the daughters taking on either a proliferative (seam) or differentiated (hypodermal or neuronal) fate. We have isolated a novel conserved C. elegans tetratricopeptide repeat containing protein, TRD-1, which is essential for cell fate determination in both the germline and the developing epidermis and has homologs in other species, including humans (TTC27). We show that trd-1(RNAi) and mutant animals have fewer seam cells as a result of inappropriate differentiation towards the hypodermal fate. In the germline, trd-1 RNAi results in a strong masculinization phenotype, as well as defects in the mitosis to meiosis switch. Our data suggests that trd-1 acts downstream of tra-2 but upstream of fem-3 in the germline sex determination pathway, and exhibits a constellation of phenotypes in common with other Mog (masculinization of germline) mutants. Thus, trd-1 is a new player in both the somatic and germline cell fate determination machinery, suggestive of a novel molecular connection between the development of these two diverse tissues.

RUNX1 is essential for mesenchymal stem cell proliferation and myofibroblast differentiation

Myofibroblasts are a key cell type in wound repair, cardiovascular disease, and fibrosis and in the tumor-promoting microenvironment. The high accumulation of myofibroblasts in reactive stroma is predictive of the rate of cancer progression in many different tumors, yet the cell types of origin and the mechanisms that regulate proliferation and differentiation are unknown. We report here, for the first time to our knowledge, the characterization of normal human prostate-derived mesenchymal stem cells (MSCs) and the TGF-β1-regulated pathways that modulate MSC proliferation and myofibroblast differentiation. Human prostate MSCs combined with prostate cancer cells expressing TGF-β1 resulted in commitment to myofibroblasts. TGF-β1-regulated runt-related transcription factor 1 (RUNX1) was required for cell cycle progression and proliferation of progenitors. RUNX1 also inhibited, yet did not block, differentiation. Knockdown of RUNX1 in prostate or bone marrow-derived MSCs resulted in cell cycle arrest, attenuated proliferation, and constitutive differentiation to myofibroblasts. These data show that RUNX1 is a key transcription factor for MSC proliferation and cell fate commitment in myofibroblast differentiation. This work also shows that the normal human prostate gland contains tissue-derived MSCs that exhibit multilineage differentiation similar to bone marrow-derived MSCs. Targeting RUNX1 pathways may represent a therapeutic approach to affect myofibroblast proliferation and biology in multiple disease states.

Thrombospondin-1 is a putative target gene of Runx2 and Runx3

Thrombospondin-1 (TSP-1), a matricellular protein widely acclaimed to be involved in the inhibition of angiogenesis and tumorigenesis, is synthesized and secreted by many cell types, including osteoblast and cancer cells. TSP-1 is highly upregulated during early stage of osteogenesis, whereas it inhibits terminal osteoblast differentiation. Expression of TSP-1 is downregulated in cancer cells, and its ectopic expression has been shown to restrain tumor growth. Transcriptional regulation of TSP-1 in osteogenesis and cancer is poorly understood; this prompted us to study its regulation by the two key regulators of the aforementioned processes: Runx2 and Runx3. Through a PCR-based cDNA subtraction technique, we identified and cloned a cDNA fragment for mouse TSP-1, whose expression was dramatically upregulated in response to Runx2 expression in mesenchymal stem cells. Moreover, TSP-1 expression was considerably reduced in the lung of Runx2 knockout mouse. On the other hand, TSP-1 gene expression drastically increased at both the transcriptional and translational levels in response to Runx3 expression in B16-F10 melanoma cells. In line with this, Runx2 and Runx3 bound to the TSP-1 promoter and stimulated its activity. Hence, these results provide first line of evidence that TSP-1 is a transcriptional target gene of Runx2 and Runx3.

CEH-20/Pbx and UNC-62/Meis function upstream of rnt-1/Runx to regulate asymmetric divisions of the C. elegans stem-like seam cells

Caenorhabditis elegans seam cells divide in the stem-like mode throughout larval development, with the ability to both self-renew and produce daughters that differentiate. Seam cells typically divide asymmetrically, giving rise to an anterior daughter that fuses with the hypodermis and a posterior daughter that proliferates further. Previously we have identified rnt-1 (a homologue of the mammalian cancer-associated stem cell regulator Runx) as being an important regulator of seam development, acting to promote proliferation; rnt-1 mutants have fewer seam cells whereas overexpressing rnt-1 causes seam cell hyperplasia. We isolated the interacting CEH-20/Pbx and UNC-62/Meis TALE-class transcription factors during a genome-wide RNAi screen for novel regulators of seam cell number. Animals lacking wild type CEH-20 or UNC-62 display seam cell hyperplasia, largely restricted to the anterior of the worm, whereas double mutants have many additional seam cells along the length of the animal. The cellular basis of the hyperplasia involves the symmetrisation of normally asymmetric seam cell divisions towards the proliferative stem-like fate. The hyperplasia is completely suppressed in rnt-1 mutants, and rnt-1 is upregulated in ceh-20 and unc-62 mutants, suggesting that CEH-20 and UNC-62 function upstream of rnt-1 to limit proliferative potential to the appropriate daughter cell. In further support of this we find that CEH-20 is asymmetrically localised in seam daughters following an asymmetric division, being predominantly restricted to anterior nuclei whose fate is to differentiate. Thus, ceh-20 and unc-62 encode crucial regulators of seam cell division asymmetry, acting via rnt-1 to regulate the balance between proliferation and differentiation.

Expression and regulation of Runx3 in mouse uterus during the peri-implantation period

The aim of this study was to investigate the differential expression and regulation of Runt-related transcription factor 3 (Runx3) in mouse uterus during early pregnancy and its regulation by steroid hormones using in situ hybridization. There was a low level of the Runx3 mRNA expression in the mouse uterus on days 1-4 of pregnancy. On day 5 when embryo implanted, Runx3 mRNA signal was obviously observed in the stromal cells surrounding the implanting blastocyst. From day 6 to 8 of pregnancy, Runx3 mRNA was highly expressed in the decidual cells and mesometrial decidual beds. Similarly, Runx3 mRNA was strongly expressed in decidualized cells under artificial decidualization. Compared with the delayed uterus, a high level of Runx3 mRNA signal was detected in the uterus with activated implantation. In the ovariectomized mouse uterus, estrogen could induce the expression of Runx3, while progesterone had no effects. These results suggest that Runx3 may play an important role during mouse implantation and decidualization. Estrogen can induce the expression of Runx3 in the ovariectomized mouse uterus.

Sea urchin akt activity is Runx-dependent and required for post-cleavage stage cell division

In animal development following the initial cleavage stage of embryogenesis, the cell cycle becomes dependent on intercellular signaling and controlled by the genomically encoded ontogenetic program. Runx transcription factors are critical regulators of metazoan developmental signaling, and we have shown that the sea urchin Runx gene runt-1, which is globally expressed during early embryogenesis, functions in support of blastula stage cell proliferation and expression of the mitogenic genes pkc1, cyclinD, and several wnts. To obtain a more comprehensive list of early runt-1 regulatory targets, we screened a Strongylocentrotus purpuratus microarray to identify genes mis-expressed in mid-blastula stage runt-1 morphants. This analysis showed that loss of Runx function perturbs the expression of multiple genes involved in cell division, including the pro-growth and survival kinase Akt (PKB), which is significantly underexpressed in runt-1 morphants. Further genomic analysis revealed that Akt is encoded by two genes in the S. purpuratus genome, akt-1 and akt-2, both of which contain numerous canonical Runx target sequences. The transcripts of both genes accumulate several fold during blastula stage, contingent on runt-1 expression. Inhibiting Akt expression or activity causes blastula stage cell cycle arrest, whereas overexpression of akt-1 mRNA rescues cell proliferation in runt-1 morphants. These results indicate that post-cleavage stage cell division requires Runx-dependent expression of akt.

Transcriptional mechanisms of developmental cell cycle arrest: problems and models

Metazoans begin their life as a single cell. Then, this cell enters a more or less protracted period of active cell proliferation, which can be considered as the default cellular state. A crucial event, the developmental cell cycle exit, occurs thereafter. This phenomenon allows for differentiation to happen and regulates the final size of organs and organisms. Its control is still poorly understood. Herein, we review some transcriptional mechanisms of cell cycle exit in animals, and propose to use cellular conveyor belts as model systems for its study. We finally point to evidence that suggests that the mechanisms of developmental cell cycle arrest may have to be maintained in adult tissues.

The canonical BMP signaling pathway is involved in human monocyte-derived dendritic cell maturation

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-β superfamily, are multifunctional polypeptides regulating a broad spectrum of functions in embryonic and adult tissues. Recent reports have demonstrated that BMPs regulate the survival, proliferation and differentiation of several cell types in the immune system. In this study, we investigate the effects of BMP signaling activation on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human DCs express type I and type II BMP receptors (BMPRIA, BMPRIB, type IA activin receptor, BMPRII) and BMP signal transduction molecules (Smad1, 5, and 8, as well as Smad4). On BMP stimulation, Id1-3 (inhibitor of differentiation 1-3/DNA binding) mRNA expression is upregulated and this effect can be blocked with the inhibitor dorsomorphin, showing that the canonical BMP signal transduction pathway is functionally active in DCs. BMP signaling activation promotes the phenotypic maturation of human DCs by increasing the expression of co-stimulatory molecules and also CD83, programmed cell death ligand 1 (PD-L1) and PD-L2, and stimulates cytokine secretion, mainly interleukin-8 and tumor necrosis factor-α. Accordingly, BMP-treated DCs exhibit an enhanced T-cell stimulatory capacity. BMP signaling also enhances the survival of human DCs increasing the Bcl-2/Bax ratio. Finally, the expression of Runx transcription factors is increased in mature DCs, and the mRNA levels of Runx1-3 are upregulated in response to BMP stimulation, indicating that Runx transcription factor family may mediate the effects of BMP signaling in human DC maturation.

Transcriptional regulation of Foxp3 in regulatory T cells

Regulatory T (Treg) cells constitute a unique T-cell lineage that plays a pivotal role in the maintenance of the peripheral tolerance. The transcription factor Foxp3 (Forkhead box P3) was identified as a master regulator for the development and function of Treg cells. It is well defined that Foxp3 expression is critical to program CD4+CD25+ Treg cell development and function; however, the molecular mechanisms that are involved in the regulation of the Foxp3 expression remain unclear. Recent studies have showed an indication that this process is influenced by a number of transcription factors. In this review, we summarize the current knowledge of how Foxp3 expression is controlled at molecular level by focusing on these factors.

Caenorhabditis elegans as a model for stem cell biology

We review the application of Caenorhabditis elegans as a model system to understand key aspects of stem cell biology. The only bona fide stem cells in C. elegans are those of the germline, which serves as a valuable paradigm for understanding how stem-cell niches influence maintenance and differentiation of stem cells and how somatic differentiation is repressed during germline development. Somatic cells that share stem cell-like characteristics also provide insights into principles in stem-cell biology. The epidermal seam cell lineages lend clues to conserved mechanisms of self-renewal and expansion divisions. Principles of developmental plasticity and reprogramming relevant to stem-cell biology arise from studies of natural transdifferentiation and from analysis of early embryonic progenitors, which undergo a dramatic transition from a pluripotent, reprogrammable condition to a state of committed differentiation. The relevance of these developmental processes to our understanding of stem-cell biology in other organisms is discussed.

Runx transcription factors: lineage-specific regulators of neuronal precursor cell proliferation and post-mitotic neuron subtype development

Runt-related (RUNX) genes encode evolutionarily conserved transcription factors that play essential roles during development and adult tissue homeostasis. RUNX proteins regulate the transition from proliferation to differentiation in a variety of cell lineages. Moreover, they control the diversification of distinct cellular phenotypes in numerous tissues. Alterations of RUNX functions are associated with several cancers and other human pathologies, underscoring the vital roles of these transcription factors in adult organs. Insights into the functions and regulations of mammalian RUNX proteins have been provided mostly by studies of RUNX involvement in mechanisms of hematopoietic and skeletal development and disease. A growing number of recent investigations are revealing new functions for RUNX family members during the development of the mammalian nervous system. This review will discuss recent progress in the study of RUNX protein involvement in mammalian neural development, with emphasis on the differentiation of olfactory, sensory, and motor neuron lineages.

Dose-dependent effects of Runx2 on bone development

Runx2 controls the commitment of mesenchymal cells to the osteoblastic lineage. Distinct promoters, designated P1 and P2, give rise to functionally similar Runx2-II and Runx2-I isoforms. We postulate that this dual promoter gene structure permits temporal and spatial adjustments in the amount of Runx2 isoforms necessary for optimal bone development. To evaluate the gene dose-dependent effect of Runx2 isoforms on bone development, we intercrossed selective Runx2-II(+/-) with nonselective Runx2-II(+/-)/Runx2-I(+/-) mice to create compound mutant mice: Runx2-II(+/-), Runx2-II(+/-)/Runx2-I(+/-), Runx2-II(-/-), Runx2-II(-/-)/Runx2-I(+/-), Runx2-II(-/-)/Runx2-I(-/-). Analysis of the different Runx2-deficient genotypes showed gene dose-dependent differences in the level of expression of the Runx2 isoforms. In addition, we found that Runx2-I is predominately expressed in the perichondrium and proliferating chondrocytes, whereas Runx2-II is expressed in hypertrophic chondrocytes and metaphyseal osteoblasts. Newborn mice showed impaired development of a mineralized skeleton, bone length, and widening of the hypertrophic zone that were proportionate to the reduction in total Runx2 protein expression. Osteoblast differentiation ex vivo was also proportionate to total amount of Runx2 expression that correlated with reduced Runx2 binding to the osteocalcin promoter by quantitative chromatin immunoprecipitation analysis. Functional analysis of P1 and P2 promoters showed differential regulation of the two promoters in osteoblastic cell lines. These findings support the possibility that the total amount of Runx2 derived from two isoforms and the P1 and P2 promoters, by regulating the time, place, and amount of Runx2 in response to changing environmental cues, impacts on bone development.

Is Runx a linchpin for developmental signaling in metazoans?

The Runt domain (Runx) is a 128 amino acid sequence motif that defines a metazoan family of sequence-specific DNA binding proteins, which appears to have originated in concert with the intercellular signaling systems that coordinate multicellular development in animals. In the model organisms where they have been studied (fruit fly, mouse, sea urchin, and nematode) Runx genes are essential for normal development, and in humans they are causally associated with a variety of cancers, manifesting both oncogenic and tumor suppressive attributes. During development Runx proteins support both cell proliferation and differentiation, and function in both transcriptional activation and repression. Runx function is thus context-dependent, with the context provided genetically by cis-regulatory sequence architecture and epigenetically by development. This context dependency makes it difficult to formulate reductionistic generalizations concerning Runx function in normal and carcinogenic development. However, a growing body of literature links Runx function to each of the major intercellular signaling systems in animals, suggesting that the general function of Runx transcription factors may be to potentiate and govern genomic responsiveness to developmental signaling.

The evolution of Runx genes II. The C-terminal Groucho recruitment motif is present in both eumetazoans and homoscleromorphs but absent in a haplosclerid demosponge

Background

The Runt DNA binding domain (Runx) defines a metazoan family of sequence-specific transcription factors with essential roles in animal ontogeny and stem cell based development. Depending on cis-regulatory context, Runx proteins mediate either transcriptional activation or repression. In many contexts Runx-mediated repression is carried out by Groucho/TLE, recruited to the transcriptional complex via a C-terminal WRPY sequence motif that is found encoded in all heretofore known Runx genes.

Findings

Full-length Runx genes were identified in the recently sequenced genomes of phylogenetically diverse metazoans, including placozoans and sponges, the most basally branching members of that clade. No sequences with significant similarity to the Runt domain were found in the genome of the choanoflagellate Monosiga brevicollis, confirming that Runx is a metazoan apomorphy. A contig assembled from genomic sequences of the haplosclerid demosponge Amphimedon queenslandica was used to construct a model of the single Runx gene from that species, AmqRunx, the veracity of which was confirmed by expressed sequences. The encoded sequence of the Runx protein OscRunx from the homoscleromorph sponge Oscarella carmella was also obtained from assembled ESTs. Remarkably, a syntenic linkage between Runx and Supt3h, previously reported in vertebrates, is conserved in A. queenslandica. Whereas OscRunx encodes a C-terminal Groucho-recruitment motif, AmqRunx does not, although a Groucho homologue is found in the A. queenslandica genome.

Conclusion

Our results are consistent with the hypothesis that sponges are paraphyletic, and suggest that Runx-WRPY mediated recruitment of Groucho to cis-regulatory sequences originated in the ancestors of eumetazoans following their divergence from demosponges.

'Runxs and regulations' of sensory and motor neuron subtype differentiation: implications for hematopoietic development

Runt-related (RUNX) transcription factors are evolutionarily conserved regulators of a number of developmental mechanisms. RUNX proteins often control the balance between proliferation and differentiation and alterations of their functions are associated with different types of cancer and other human pathologies. Moreover, RUNX factors control important steps during the developmental acquisition of mature phenotypes. A number of investigations are beginning to shed light on the involvement of RUNX family members in the development of the nervous system. This review summarizes recent progress in the study of the roles of mammalian RUNX proteins during the differentiation of sensory and motor neurons in the peripheral and central nervous system, respectively. The implications of those findings for RUNX-mediated regulation of hematopoietic development will also be discussed.

Evolutionary origin and genomic organisation of runt-domain containing genes in arthropods

BACKGROUND

Gene clusters, such as the Hox gene cluster, are known to have critical roles in development. In eukaryotes gene clusters arise primarily by tandem gene duplication and divergence. Genes within a cluster are often co-regulated, providing selective pressure to maintain the genome organisation, and this co-regulation can result in temporal or spatial co-linearity of gene expression. It has been previously noted that in Drosophila melanogaster, three of the four runt-domain (RD) containing genes are found in a relatively tight cluster on chromosome 1, raising the possibility of a putative functional RD gene cluster in D. melanogaster.

RESULTS

To investigate the possibility of such a gene cluster, orthologues of the Drosophila melanogaster RD genes were identified in several endopterygotan insects, two exopterygotan insects and two non-insect arthropods. In all insect species four RD genes were identified and orthology was assigned to the Drosophila sequences by phylogenetic analyses. Although four RD genes were found in the crustacean D. pulex, orthology could not be assigned to the insect sequences, indicating independent gene duplications from a single ancestor following the split of the hexapod lineage from the crustacean lineage.In insects, two chromosomal arrangements of these genes was observed; the first a semi-dispersed cluster, such as in Drosophila, where lozenge is separated from the core cluster of three RD genes often by megabases of DNA. The second arrangement was a tight cluster of the four RD genes, such as in Apis mellifera.This genomic organisation, particularly of the three core RD genes, raises the possibility of shared regulatory elements. In situ hybridisation of embryonic expression of the four RD genes in Drosophila melanogaster and the honeybee A. mellifera shows no evidence for either spatial or temporal co-linearity of expression during embryogenesis.

CONCLUSION

All fully sequenced insect genomes contain four RD genes and orthology can be assigned to these genes based on similarity to the D. melanogaster protein sequences. Examination of the genomic organisation of these genes provides evidence for a functional RD gene cluster. RD genes from non-insect arthropods are also clustered, however the lack of orthology between these and insect RD genes suggests this cluster is likely to have resulted from a duplication event independent from that which created the insect RD gene cluster. Analysis of embryonic RD gene expression in two endopterygotan insects, A. mellifera and D. melanogaster, did not show evidence for coordinated gene expression, therefore while the functional significance of this gene cluster remains unknown its maintenance during insect evolution implies some functional significance to the cluster.

Runx expression is mitogenic and mutually linked to Wnt activity in blastula-stage sea urchin embryos

Background

The Runt homology domain (Runx) defines a metazoan family of sequence-specific transcriptional regulatory proteins that are critical for animal development and causally associated with a variety of mammalian cancers. The sea urchin Runx gene SpRunt-1 is expressed throughout the blastula stage embryo, and is required globally during embryogenesis for cell survival and differentiation.

Methodology/Principal Findings

Depletion of SpRunt-1 by morpholino antisense-mediated knockdown causes a blastula stage deficit in cell proliferation, as shown by bromodeoxyuridine (BrdU) incorporation and direct cell counts. Reverse transcription coupled polymerase chain reaction (RT-PCR) studies show that the cell proliferation deficit is presaged by a deficit in the expression of several zygotic wnt genes, including wnt8, a key regulator of endomesoderm development. In addition, SpRunt-1-depleted blastulae underexpress cyclinD, an effector of mitogenic Wnt signaling. Blastula stage cell proliferation is also impeded by knockdown of either wnt8 or cyclinD. Chromatin immunoprecipitation (ChIP) indicates that Runx target sites within 5′ sequences flanking cyclinD, wnt6 and wnt8 are directly bound by SpRunt-1 protein at late blastula stage. Furthermore, experiments using a green fluorescent protein (GFP) reporter transgene show that the blastula-stage operation of a cis-regulatory module previously shown to be required for wnt8 expression (Minokawa et al., Dev. Biol. 288: 545–558, 2005) is dependent on its direct sequence-specific interaction with SpRunt-1. Finally, inhibitor studies and immunoblot analysis show that SpRunt-1 protein levels are negatively regulated by glycogen synthase kinase (GSK)-3.

Conclusions/Significance

These results suggest that Runx expression and Wnt signaling are mutually linked in a feedback circuit that controls cell proliferation during development.