GDF3 at the crossroads of TGF-beta signaling

Whole-genome mapping of APOBEC mutagenesis in metastatic urothelial carcinoma identifies driver hotspot mutations and a novel mutational signature

Apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like (APOBEC) enzymes mutate specific DNA sequences and hairpin-loop structures, challenging the distinction between passenger and driver hotspot mutations. Here, we characterized 115 whole genomes of metastatic urothelial carcinoma (mUC) to identify APOBEC mutagenic hotspot drivers. APOBEC-associated mutations were detected in 92% of mUCs and were equally distributed across the genome, while APOBEC hotspot mutations (ApoHMs) were enriched in open chromatin. Hairpin loops were frequent targets of didymi (twins in Greek), two hotspot mutations characterized by the APOBEC SBS2 signature, in conjunction with an uncharacterized mutational context (Ap[C>T]). Next, we developed a statistical framework that identified ApoHMs as drivers in coding and non-coding genomic regions of mUCs. Our results and statistical framework were validated in independent cohorts of 23 non-metastatic UCs and 3,744 samples of 17 metastatic cancers, identifying cancer-type-specific drivers. Our study highlights the role of APOBEC in cancer development and may contribute to developing novel targeted therapy options for APOBEC-driven cancers.

De novo assembly, characterization and comparative transcriptome analysis of gonads reveals sex-biased genes in Coreoperca whiteheadi

The wild Coreoperca whiteheadi is considered as the primordial species in sinipercine fish, which has valuable genetic information. Unfortunately, C. whiteheadi was listed as a near-threatened species because of the environmental pollution, over-exploitation and species invasion. Therefore, more genetic information is needed to have a better understanding of gonadal development in C. whiteheadi. Here, the first gonadal transcriptomes analysis of C. whiteheadi was conducted and 277.14 million clean reads were generated. A total of 96,753 unigenes were successfully annotated. By comparing ovary and testis transcriptomes, a total of 21,741 differentially expressed genes (DEGs) were identified, of which 12,057 were upregulated and 9684 were downregulated in testes. Among them, we also identified about 53 differentially expressed sex-biased genes. Subsequently, the expression of twenty-four DEGs were confirmed by real-time fluorescence quantitative PCR. Furthermore, the histological analysis was conducted on ovaries and testes of one-year-old C. whiteheadi. Our results provided basic support for further studies on the function of sex-biased genes and the molecular mechanism of sex determination and reproduction in C. whiteheadi.

Clinicopathological relevance of stem cell marker growth and differentiation factor 3 in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is the second leading cause of cancer-related deaths in Iran, often diagnosed in advanced stages with a poor prognosis. Growth and differentiation factor 3 (GDF3) is a member of the transforming growth factor-beta (TGF-β) superfamily. It acts as an inhibitor of bone morphogenetic proteins (BMPs) signaling pathway associated with pluripotent embryonic and cancer stem cells (CSCs) characteristics. Since its expression in ESCC has not yet been evaluated, the clinicopathological relevance of GDF3 expression was elucidated in ESCC patients. Expression of GDF3 in tumor tissues from 40 ESCC patients was compared to the related margin normal tissues by relatively comparative real-time polymerase chain reaction (PCR). Glyceraldehydes 3-phosphate dehydrogenase (GAPDH) was used as the endogenous control. Likewise, the function of GDF3 in the differentiation and development of embryonic stem cells (ESCs) was also reviewed. GDF3 was significantly overexpressed in 17.5% of tumors and a significant correlation between GDF3 expression and the depth of tumor invasion was observed (P = 0.032). The results suggest that GDF3 expression is likely to have substantial roles in the progression and invasiveness behavior of ESCC. Having considered the importance of CSC markers identification and their exploitation in targeted cancer therapy, GDF3 may be introduced as a promising therapeutic target to inhibit the invasion of tumor cells in ESCC.

Novel Cardiokine GDF3 Predicts Adverse Fibrotic Remodeling After Myocardial Infarction

BACKGROUND

Myocardial infarction (MI) induces a repair response that ultimately generates a stable fibrotic scar. Although the scar prevents cardiac rupture, an excessive profibrotic response impairs optimal recovery by promoting the development of noncontractile fibrotic areas. The mechanisms that lead to cardiac fibrosis are diverse and incompletely characterized. We explored whether the expansion of cardiac fibroblasts after MI can be regulated through a paracrine action of cardiac stromal cells.

METHODS

We performed a bioinformatic secretome analysis of cardiac stromal PW1⁺ cells isolated from normal and post-MI mouse hearts to identify novel secreted proteins. Functional assays were used to screen secreted proteins that promote fibroblast proliferation. The expressions of candidates were subsequently analyzed in mouse and human hearts and plasmas. The relationship between levels of circulating protein candidates and adverse post-MI cardiac remodeling was examined in a cohort of 80 patients with a first ST-segment-elevation MI and serial cardiac magnetic resonance imaging evaluations.

RESULTS

Cardiac stromal PW1⁺ cells undergo a change in paracrine behavior after MI, and the conditioned media from these cells induced a significant increase in the proliferation of fibroblasts. We identified a total of 12 candidates as secreted proteins overexpressed by cardiac PW1⁺ cells after MI. Among these factors, GDF3 (growth differentiation factor 3), a member of the TGF-β (transforming growth factor-β) family, was markedly upregulated in the ischemic hearts. Conditioned media specifically enriched with GDF3 induced fibroblast proliferation at a high level by stimulation of activin-receptor-like kinases. In line with the secretory nature of this protein, we next found that GDF3 can be detected in mice and human plasma samples, with a significant increase in the days after MI. In humans, higher GDF3 circulating levels (measured in the plasma at day 4 after MI) were significantly associated with an increased risk of adverse remodeling 6 months after MI (adjusted odds ratio, 1.76 [1.03-3.00]; P=0.037), including lower left ventricular ejection fraction and a higher proportion of akinetic segments.

CONCLUSIONS

Our findings define a mechanism for the profibrotic action of cardiac stromal cells through secreted cardiokines, such as GDF3, a candidate marker of adverse fibrotic remodeling after MI.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT01113268.

Secreted key regulators (Fgf1, Bmp4, Gdf3) are expressed by PAC1-immunopositive retinal ganglion cells in the postnatal rat retina

Identified as a member of the secretin/glucagon/VIP superfamily, pituitary adenylate cyclase-activating polypeptide (PACAP1-38) has been recognized as a hormone, neurohormone, transmitter, trophic factor, and known to be involved in diverse and multiple developmental processes. PACAP1-38 was reported to regulate the production of important morphogens (Fgf1, Bmp4, Gdf3) through PAC1-receptor in the newborn rat retina. To follow up, we aimed to reveal the identity of retinal cells responsible for the production and secretion of Fgf1, Bmp4, and Gdf3 in response to PACAP1-38 treatment. Newborn (P1) rats were treated with 100 pmol PACAP1-38 intravitreally. After 24 h, retinas were dissected and processed for immunohistochemistry performed either on flat-mounted retinas or cryosections. Brn3a and PAC1-R double labeling revealed that 90% of retinal ganglion cells (RGCs) expressed PAC1-receptor. We showed that RGCs were Fgf1, Bmp4, and Gdf3- immunopositive and PAC1-R was co-expressed with each protein. To elucidate if RGCs release these secreted regulators, the key components for vesicle release were examined. No labeling was detected for synaptophysin, Exo70, or NESP55 in RGCs but an intense Rab3a-immunoreactivity was detected in their cell bodies. We found that the vast majority of RGCs are responsive to PACAP, which in turn could have a significant impact on their development or/and physiology. Although Fgf1, Bmp4, and Gdf3 were abundantly expressed in PAC1-positive RGCs, the cells lack synaptophysin and Exo70 in the newborn retina thus unable to release these proteins. These proteins could regulate postnatal RGC development acting through intracrine pathways.

Global Histone H3 Lysine 4 Trimethylation (H3K4me3) Landscape Changes in Response to TGFβ

TGFβ expression acts as a biomarker of poor prognosis in prostate cancer. It plays a dual functional role in prostate cancer. In the early stages of the tumor, it acts as a tumor suppressor while at the later stages of tumor development, it promotes metastasis. The molecular mechanisms of action of TGFβ are largely understood through the canonical and non-canonical signal transduction pathways. Our understanding of the mechanisms that establish transient TGFβ stimulation into stable gene expression patterns remains incomplete. Epigenetic marks like histone H3 modifications are directly linked with gene expression and they play an important role in tumorigenesis. In this report, we performed chromatin immunoprecipitation-sequencing (ChIP-Seq) to identify the genome-wide regions that undergo changes in histone H3 Lysine 4 trimethylation (H3K4me3) occupancy in response to TGFβ stimulation. We also show that TGFβ stimulation can induce acute epigenetic changes through the modulation of H3K4me3 signals at genes belonging to special functional categories in prostate cancer. TGFβ induces the H3K4me3 on its own ligands like TGFβ, GDF1, INHBB, GDF3, GDF6, BMP5 suggesting a positive feedback loop. The majority of genes were found to be involved in the positive regulation of transcription from the RNA polymerase II promoter in response to TGFβ. Other functional categories were intracellular protein transport, brain development, EMT, angiogenesis, antigen processing, antigen presentation via MHC class II, lipid transport, embryo development, histone H4 acetylation, positive regulation of cell cycle arrest, and genes involved in mitotic G2 DNA damage checkpoints. Our results link TGFβ stimulation to acute changes in gene expression through an epigenetic mechanism. These findings have broader implications on epigenetic bases of acute gene expression changes caused by growth factor stimulation.

Aging of the immune system and impaired muscle regeneration: A failure of immunomodulation of adult myogenesis

Skeletal muscle regeneration that follows acute injury is strongly influenced by interactions with immune cells that invade and proliferate in the damaged tissue. Discoveries over the past 20 years have identified many of the key mechanisms through which myeloid cells, especially macrophages, regulate muscle regeneration. In addition, lymphoid cells that include CD8+ T-cells and regulatory T-cells also significantly affect the course of muscle regeneration. During aging, the regenerative capacity of skeletal muscle declines, which can contribute to progressive loss of muscle mass and function. Those age-related reductions in muscle regeneration are accompanied by systemic, age-related changes in the immune system, that affect many of the myeloid and lymphoid cell populations that can influence muscle regeneration. In this review, we present recent discoveries that indicate that aging of the immune system contributes to the diminished regenerative capacity of aging muscle. Intrinsic, age-related changes in immune cells modify their expression of factors that affect the function of a population of muscle stem cells, called satellite cells, that are necessary for normal muscle regeneration. For example, age-related reductions in the expression of growth differentiation factor-3 (GDF3) or CXCL10 by macrophages negatively affect adult myogenesis, by disrupting regulatory interactions between macrophages and satellite cells. Those changes contribute to a reduction in the numbers and myogenic capacity of satellite cells in old muscle, which reduces their ability to restore damaged muscle. In addition, aging produces changes in the expression of molecules that regulate the inflammatory response to injured muscle, which also contributes to age-related defects in muscle regeneration. For example, age-related increases in the production of osteopontin by macrophages disrupts the normal inflammatory response to muscle injury, resulting in regenerative defects. These nascent findings represent the beginning of a newly-developing field of investigation into mechanisms through which aging of the immune system affects muscle regeneration.

Long-term arsenic exposure impairs differentiation in mouse embryonal stem cells

Arsenic is a contaminant found in many foods and drinking water. Exposure to arsenic during development can cause improper neuronal progenitor cell development, differentiation, and function, while in vitro studies have determined that acute arsenic exposure to stem and progenitor cells reduced their ability to differentiate. In the current study, P19 mouse embryonal stem cells were exposed continuously to 0.1-μM (7.5 ppb) arsenic for 32 weeks. A cell lineage array examining messenger RNA (mRNA) changes after 8 and 32 weeks of exposure showed that genes involved in pluripotency were increased, whereas those involved in differentiation were reduced. Therefore, temporal changes of select pluripotency and neuronal differentiation markers throughout the 32-week chronic arsenic exposure were investigated. Sox2 and Oct4 mRNA expression were increased by 1.9- to 2.5-fold in the arsenic-exposed cells, beginning at Week 12. Sox2 protein expression was similarly increased starting at Week 16 and remained elevated by 1.5-fold to sixfold. One target of Sox2 is N-cadherin, whose expression is a hallmark of epithelial-mesenchymal transitions (EMTs). Exposure to arsenic significantly increased N-cadherin protein levels beginning at Week 20, concurrent with increased grouping of N-cadherin positive cells at the perimeter of the embryoid body. Expression of Zeb1, which helps increase the expression of Sox2, was also increased started at Week 16. In contrast, Gdf3 mRNA expression was reduced by 3.4- to 7.2-fold beginning at Week 16, and expression of its target protein, phospho-Smad2/3, was also reduced. These results suggest that chronic, low-level arsenic exposure may delay neuronal differentiation and maintain pluripotency.

Bta-miR-24-3p Controls the Myogenic Differentiation and Proliferation of Fetal, Bovine, Skeletal Muscle-Derived Progenitor Cells by Targeting ACVR1B

Simple Summary

MicroRNAs play pivotal roles in skeletal muscle development, but the molecular basis of their functions in fetal bovine skeletal muscle development is largely unknown. Here, we report a mechanistic study of bta-miR-24-3p, a key miRNA regulator of the myogenic differentiation of fetal bovine platelet-derived growth factor receptor alpha negative (PDGFRα^-) progenitor cells. We isolated progenitor cells from the bovine fetal longissimus dorsi muscle and purified them with PDGFRα antibodies to remove fibro-adipogenic progenitors. We observed elevated bta-miR-24-3p expression during differentiation, and bta-miR-24-3p overexpression led to promoted myogenic differentiation but suppressed proliferation. Moreover, activin receptor type 1B (ACVR1B) was identified as a direct target of bta-miR-24-3p, and ACVR1B-silencing cells exhibited similar phenotypes to bta-miR-24-3p-overexpressing bovine PDGFRα^- progenitor cells. These results extended our understanding on the roles of miRNA in fetal muscle development. The method of removing fibro-adipogenic progenitors in our study will also provide useful information for other investigators.

Abstract

MicroRNAs modulate a variety of cellular events, including skeletal muscle development, but the molecular basis of their functions in fetal bovine skeletal muscle development is poorly understood. In this study, we report that bta-miR-24-3p promotes the myogenic differentiation of fetal bovine PDGFRα^- progenitor cells. The expression of bta-miR-24-3p increased during myogenic differentiation. Overexpression of bta-miR-24-3p significantly promoted myogenic differentiation, but inhibited proliferation. A dual-luciferase assay identified ACVR1B as a direct target of bta-miR-24-3p. Similarly, knocking down ACVR1B by RNA interference also significantly inhibited proliferation and promoted the differentiation of bovine PDGFRα^- progenitor cells. Thus, our study provides a mechanism in which bta-miR-24-3p regulates myogenesis by inhibiting ACVR1B expression.

TGF-β Family Signaling in Mesenchymal Differentiation

Mesenchymal stem cells (MSCs) can differentiate into several lineages during development and also contribute to tissue homeostasis and regeneration, although the requirements for both may be distinct. MSC lineage commitment and progression in differentiation are regulated by members of the transforming growth factor-β (TGF-β) family. This review focuses on the roles of TGF-β family signaling in mesenchymal lineage commitment and differentiation into osteoblasts, chondrocytes, myoblasts, adipocytes, and tenocytes. We summarize the reported findings of cell culture studies, animal models, and interactions with other signaling pathways and highlight how aberrations in TGF-β family signaling can drive human disease by affecting mesenchymal differentiation.

A recurrent, non-penetrant sequence variant, p.Arg266Cys in Growth/Differentiation Factor 3 (GDF3) in a female with unilateral anophthalmia and skeletal anomalies

Purpose

The genetic causes of anophthalmia, microphthalmia and coloboma remain poorly understood. Missense mutations in Growth/Differentiation Factor 3 (GDF3) gene have previously been reported in patients with microphthalmia, iridial and retinal colobomas, Klippel-Feil anomaly with vertebral fusion, scoliosis, rudimentary 12th ribs and an anomalous right temporal bone. We used whole exome sequencing with a trio approach to study a female with unilateral anophthalmia, kyphoscoliosis and additional skeletal anomalies.

Observations

Exome sequencing revealed that the proposita was heterozygous for c.796C > T, predicting p.Arg266Cys, in GDF3. Sanger sequencing confirmed the mutation and showed that the unaffected mother was heterozygous for the same missense substitution.

Conclusions and importance

Although transfection studies with the p.Arg266Cys mutation have shown that this amino acid substitution is likely to impair function, non-penetrance for the ocular defects was apparent in this family and has been observed in other families with sequence variants in GDF3. We conclude p.Arg266Cys and other GDF3 mutations can be non-penetrant, making pathogenicity more difficult to establish when sequence variants in this gene are present in patients with structural eye defects.

Network-driven plasma proteomics expose molecular changes in the Alzheimer's brain

Background

Biological pathways that significantly contribute to sporadic Alzheimer’s disease are largely unknown and cannot be observed directly. Cognitive symptoms appear only decades after the molecular disease onset, further complicating analyses. As a consequence, molecular research is often restricted to late-stage post-mortem studies of brain tissue. However, the disease process is expected to trigger numerous cellular signaling pathways and modulate the local and systemic environment, and resulting changes in secreted signaling molecules carry information about otherwise inaccessible pathological processes.

Results

To access this information we probed relative levels of close to 600 secreted signaling proteins from patients’ blood samples using antibody microarrays and mapped disease-specific molecular networks. Using these networks as seeds we then employed independent genome and transcriptome data sets to corroborate potential pathogenic pathways.

Conclusions

We identified Growth-Differentiation Factor (GDF) signaling as a novel Alzheimer’s disease-relevant pathway supported by in vivo and in vitro follow-up experiments, demonstrating the existence of a highly informative link between cellular pathology and changes in circulatory signaling proteins.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0095-2) contains supplementary material, which is available to authorized users.

TGF-β superfamily signaling in testis formation and early male germline development

The TGF-β ligand superfamily contains at least 40 members, many of which are produced and act within the mammalian testis to facilitate formation of sperm. Their progressive expression at key stages and in specific cell types determines the fertility of adult males, influencing testis development and controlling germline differentiation. BMPs are essential for the interactive instructions between multiple cell types in the early embryo that drive initial specification of gamete precursors. In the nascent foetal testis, several ligands including Nodal, TGF-βs, Activins and BMPs, serve as key masculinizing switches by regulating male germline pluripotency, somatic and germline proliferation, and testicular vascularization and architecture. In postnatal life, local production of these factors determine adult testis size by regulating Sertoli cell multiplication and differentiation, in addition to specifying germline differentiation and multiplication. Because TGF-β superfamily signaling is integral to testis formation, it affects processes that underlie testicular pathologies, including testicular cancer, and its potential to contribute to subfertility is beginning to be understood.

Live fluorescent RNA-based detection of pluripotency gene expression in embryonic and induced pluripotent stem cells of different species

The generation of induced pluripotent stem (iPS) cells has successfully been achieved in many species. However, the identification of truly reprogrammed iPS cells still remains laborious and the detection of pluripotency markers requires fixation of cells in most cases. Here, we report an approach with nanoparticles carrying Cy3-labeled sense oligonucleotide reporter strands coupled to gold-particles. These molecules are directly added to cultured cells without any manipulation and gene expression is evaluated microscopically after overnight incubation. To simultaneously detect gene expression in different species, probe sequences were chosen according to interspecies homology. With a common target-specific probe we could successfully demonstrate expression of the GAPDH house-keeping gene in somatic cells and expression of the pluripotency markers NANOG and GDF3 in embryonic stem cells and iPS cells of murine, human, and porcine origin. The population of target gene positive cells could be purified by fluorescence-activated cell sorting. After lentiviral transduction of murine tail-tip fibroblasts Nanog-specific probes identified truly reprogrammed murine iPS cells in situ during development based on their Cy3-fluorescence. The intensity of Nanog-specific fluorescence correlated positively with an increased capacity of individual clones to differentiate into cells of all three germ layers. Our approach offers a universal tool to detect intracellular gene expression directly in live cells of any desired origin without the need for manipulation, thus allowing conservation of the genetic background of the target cell. Furthermore, it represents an easy, scalable method for efficient screening of pluripotency which is highly desirable during high-throughput cell reprogramming and after genomic editing of pluripotent stem cells.

Feeder-free generation and long-term culture of human induced pluripotent stem cells using pericellular matrix of decidua derived mesenchymal cells

Human ES cells (hESCs) and human induced pluripotent stem cells (hiPSCs) are usually generated and maintained on living feeder cells like mouse embryonic fibroblasts or on a cell-free substrate like Matrigel. For clinical applications, a quality-controlled, xenobiotic-free culture system is required to minimize risks from contaminating animal-derived pathogens and immunogens. We previously reported that the pericellular matrix of decidua-derived mesenchymal cells (PCM-DM) is an ideal human-derived substrate on which to maintain hiPSCs/hESCs. In this study, we examined whether PCM-DM could be used for the generation and long-term stable maintenance of hiPSCs. Decidua-derived mesenchymal cells (DMCs) were reprogrammed by the retroviral transduction of four factors (OCT4, SOX2, KLF4, c-MYC) and cultured on PCM-DM. The established hiPSC clones expressed alkaline phosphatase, hESC-specific genes and cell-surface markers, and differentiated into three germ layers in vitro and in vivo. At over 20 passages, the hiPSCs cultured on PCM-DM held the same cellular properties with genome integrity as those at early passages. Global gene expression analysis showed that the GDF3, FGF4, UTF1, and XIST expression levels varied during culture, and GATA6 was highly expressed under our culture conditions; however, these gene expressions did not affect the cells’ pluripotency. PCM-DM can be conveniently prepared from DMCs, which have a high proliferative potential. Our findings indicate that PCM-DM is a versatile and practical human-derived substrate that can be used for the feeder-cell-free generation and long-term stable maintenance of hiPSCs.

Paracrine regulation of neural stem cells in the subependymal zone

Stem cells maintain their self-renewal and multipotency capacities through a self-organizing network of transcription factors and intracellular pathways activated by extracellular signaling from the microenvironment or "niche" in which they reside in vivo. In the adult mammalian brain new neurons continue to be generated throughout life of the organisms and this lifelong process of neurogenesis is supported by a reservoir of neural stem cells in the germinal regions. The discovery of adult neurogenesis in the mammalian brain has sparked great interest in defining the conditions that guide neural stem cell (NSC) maintenance and differentiation into the great variety of neuronal and glial subtypes. Here we review current knowledge regarding the paracrine regulation provided by the components of the niche and its function, focusing on the main germinal region of the adult central nervous system (CNS), the subependymal zone (SEZ).

Defining an EPOR- regulated transcriptome for primary progenitors, including Tnfr-sf13c as a novel mediator of EPO- dependent erythroblast formation

Certain concepts concerning EPO/EPOR action modes have been challenged by in vivo studies: Bcl-x levels are elevated in maturing erythroblasts, but not in their progenitors; truncated EPOR alleles that lack a major p85/PI3K recruitment site nonetheless promote polycythemia; and Erk1 disruption unexpectedly bolsters erythropoiesis. To discover novel EPO/EPOR action routes, global transcriptome analyses presently are applied to interrogate EPO/EPOR effects on primary bone marrow-derived CFUe-like progenitors. Overall, 160 EPO/EPOR target transcripts were significantly modulated 2-to 21.8-fold. A unique set of EPO-regulated survival factors included Lyl1, Gas5, Pim3, Pim1, Bim, Trib3 and Serpina 3g. EPO/EPOR-modulated cell cycle mediators included Cdc25a, Btg3, Cyclin-d2, p27-kip1, Cyclin-g2 and CyclinB1-IP-1. EPO regulation of signal transduction factors was also interestingly complex. For example, not only Socs3 plus Socs2 but also Spred2, Spred1 and Eaf1 were EPO-induced as negative-feedback components. Socs2, plus five additional targets, further proved to comprise new EPOR/Jak2/Stat5 response genes (which are important for erythropoiesis during anemia). Among receptors, an atypical TNF-receptor Tnfr-sf13c was up-modulated >5-fold by EPO. Functionally, Tnfr-sf13c ligation proved to both promote proerythroblast survival, and substantially enhance erythroblast formation. The EPOR therefore engages a sophisticated set of transcriptome response circuits, with Tnfr-sf13c deployed as one novel positive regulator of proerythroblast formation.

Pluripotency and nuclear reprogramming

Pluripotency is a "blank" cellular state characteristic of specific cells within the early embryo (e.g., epiblast cells) and of certain cells propagated in vitro (e.g., embryonic stem cells, ESCs). The terms pluripotent cell and stem cell are often used interchangeably to describe cells capable of differentiating into multiple cell types. In this review, we discuss the prevailing molecular and functional definitions of pluripotency and the working parameters employed to describe this state, both in the context of cells residing within the early embryo and cells propagated in vitro.

Neurogenesis at the brain-cerebrospinal fluid interface

Cerebral cortical progenitor cells can be classified into several different types, and each progenitor type integrates cell-intrinsic and cell-extrinsic cues to regulate neurogenesis. On one hand, cell-intrinsic mechanisms that depend upon appropriate apical-basal polarity are established by adherens junctions and apical complex proteins and are particularly important in progenitors with apical processes contacting the lateral ventricle. The apical protein complexes themselves are concentrated at the ventricular surface, and apical complex proteins regulate mitotic spindle orientation and cell fate. On the other hand, remarkably little is known about how cell-extrinsic cues signal to progenitors and couple with cell-intrinsic mechanisms to instruct neurogenesis. Recent research shows that the cerebrospinal fluid, which contacts apical progenitors at the ventricular surface and bathes the apical complex of these cells, provides growth- and survival-promoting cues for neural progenitor cells in developing and adult brain. This review addresses how the apical-basal polarity of progenitor cells regulates cell fate and allows progenitors to sample diffusible signals distributed by the cerebrospinal fluid. We also review several classes of signaling factors that the cerebrospinal fluid distributes to the developing brain to instruct neurogenesis.

Bone morphogenic protein: an elixir for bone grafting--a review

Bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor beta superfamily. This literature review focuses on the molecular biology of BMPs, their mechanism of action, and subsequent applications. It also discusses uses of BMPs in the fields of dentistry and orthopedics, research on methods of delivering BMPs, and their role in tissue regeneration. BMP has positive effects on bone grafts, and their calculated and timely use with other growth factors can provide extraordinary results in fractured or nonhealing bones. Use of BMP introduces new applications in the field of implantology and bone grafting. This review touches on a few unknown facts about BMP and this ever-changing field of research to improve human life.

The cerebrospinal fluid provides a proliferative niche for neural progenitor cells

Cortical development depends on the active integration of cell-autonomous and extrinsic cues, but the coordination of these processes is poorly understood. Here, we show that the apical complex protein Pals1 and Pten have opposing roles in localizing the Igf1R to the apical, ventricular domain of cerebral cortical progenitor cells. We found that the cerebrospinal fluid (CSF), which contacts this apical domain, has an age-dependent effect on proliferation, much of which is attributable to Igf2, but that CSF contains other signaling activities as well. CSF samples from patients with glioblastoma multiforme show elevated Igf2 and stimulate stem cell proliferation in an Igf2-dependent manner. Together, our findings demonstrate that the apical complex couples intrinsic and extrinsic signaling, enabling progenitors to sense and respond appropriately to diffusible CSF-borne signals distributed widely throughout the brain. The temporal control of CSF composition may have critical relevance to normal development and neuropathological conditions.

Transforming growth factor-beta superfamily in mouse embryonic stem cell self-renewal

Embryonic stem (ES) cells are pluripotent cells that maintain the capability of undifferentiated self-renewal in culture. As mouse ES cells have the capacity to give rise to all the tissues of the body, they are an excellent developmental biology model system and a model for regenerative therapies. The extracellular cues and the intracellular signaling cascades that regulate ES cell self-renewal and cell-fate choices are complex and actively studied. Many developmental signaling pathways regulate the ES cell phenotype, and their intracellular programs interact to modulate the gene networks controlling ES cell pluripotency. This review focuses on the current understanding and outstanding questions of the roles of the transforming growth factor-beta-related signaling pathways in regulating pluripotency and differentiation of mouse ES cells. The complex dichotomic roles of bone morphogenetic protein signaling in maintaining the undifferentiated state and also inducing specific cell fates will be reviewed. The emerging roles of Nodal signaling in ES cell self-renewal will also be discussed.

Hypoxic culture maintains self-renewal and enhances embryoid body formation of human embryonic stem cells

Hypoxic environment is theoretically more physiological for the growth of human embryonic stem (hES) cells. It has been reported that hypoxic culture maintained better undifferentiation of hES cells, but the effects on differentiation are less well established. The hES cells were thus cultured and compared in hypoxia (2% oxygen [O2]) and normoxia (21% O2). The data showed that the undifferentiated state of hES cells was maintained more favorably in hypoxia during prolonged culture. Most tested genes belonging to FGF, TGF-beta/GMP, and Wnt signaling pathways were enriched in undifferentiated hES cells and downregulated upon differentiation, accompanied with differential expression of FGFR1, FGFR2, and FRAT2 between hypoxia and normoxia. Higher P-Smad2/3 level was identified in hypoxia, favoring the maintenance of hES cells in undifferentiation. Bisulfite sequencing showed similar imprinting status between different O2 tensions at H19 differentially methylated region (DMR) and KvDMR loci. Embryoid body formation was enhanced in hypoxia accompanied with suppressed Sox17, Desmin, Gata4, Brachyury, and Cdx2 expression. We concluded that hypoxia improved self-renewal of hES cells through modulation of major signaling pathways and was also more efficient for differentiation to embryoid bodies, though they might present with suppressed expression of some lineage-specific genes across all the three embryonic germ layers and trophectoderm.

An embryo-specific expressing TGF-β family protein, growth-differentiation factor 3 (GDF3), augments progression of B16 melanoma

Malignant tumor cells often express embryonic antigens which share the expression with embryonic stem (ES) cells. The embryonic antigens are usually encoded by ES cell-specific genes, a number of which are associated with tumorigenesis and/or tumor progression. We examined the expression of ES cell-specific genes in the mouse B16 melanoma cell line to identify the factors promoting tumorigenesis. We found that endogenous growth-differentiation factor 3 (GDF3) expression was induced in implant B16 tumor during tumor progression in syngenic C57BL/6 mice. B16 F10, a subline with a high metastatic potential, continuously expressed GDF3 while low metastatic B16 F1 expressed comparatively decreased levels of GDF3. Overexpression of GDF3 promoted growth of implanted melanoma B16 F1 and F10 in syngenic mice. Ectopic expression of GDF3 was accompanied by an increased level of production of CD24/CD44. Such a profile was reported to be characteristic of melanoma stem cell-like cells. GDF3 expression was observed in embryonal carcinomas, primary testicular germ cell tumors, seminomas and breast carcinomas. However, the role of GDF3 in these cancers remains undetermined. Overexpression of GDF3 did not affect the growth of mouse hepatoma high or low metastatic sublines G5 or G1, both of which do not express GDF3. Since GDF3-driven CD24 acts as a receptor for endogenous innate immune ligands that modulate cell proliferation, CD24 is an effective determinant of tumorigenesis in malignant cell transformation. Finally, our results support the view that GDF3 has the ability to induce progression of CD24-inducible melanoma in mice.

Extrinsic regulation of pluripotent stem cells

During early mammalian development, as the pluripotent cells that give rise to all of the tissues of the body proliferate and expand in number, they pass through transition states marked by a stepwise restriction in developmental potential and by changes in the expression of key regulatory genes. Recent findings show that cultured stem-cell lines derived from different stages of mouse development can mimic these transition states. They further reveal that there is a high degree of heterogeneity and plasticity in pluripotent populations in vitro and that these properties are modulated by extrinsic signalling. Understanding the extrinsic control of plasticity will guide efforts to use human pluripotent stem cells in research and therapy.

Role of Cripto-1 in stem cell maintenance and malignant progression

Cripto-1 is critical for early embryonic development and, together with its ligand Nodal, has been found to be associated with the undifferentiated status of mouse and human embryonic stem cells. Like other embryonic genes, Cripto-1 performs important roles in the formation and progression of several types of human tumors, stimulating cell proliferation, migration, epithelial to mesenchymal transition, and tumor angiogenesis. Several studies have demonstrated that cell fate regulation during embryonic development and cell transformation during oncogenesis share common signaling pathways, suggesting that uncontrolled activation of embryonic signaling pathways might drive cell transformation and tumor progression in adult tissues. Here we review our current understanding of how Cripto-1 controls stem cell biology and how it integrates with other major embryonic signaling pathways. Because many cancers are thought to derive from a subpopulation of cancer stem-like cells, which may re-express embryonic genes, Cripto-1 signaling may drive tumor growth through the generation or expansion of tumor initiating cells bearing stem-like characteristics. Therefore, the Cripto-1/Nodal signaling may represent an attractive target for treatment in cancer, leading to the elimination of undifferentiated stem-like tumor initiating cells.

Cell surface tetraspanin Tspan8 contributes to molecular pathways of exosome-induced endothelial cell activation

Tumor-derived exosomes containing the tetraspanin Tspan8 can efficiently induce angiogenesis in tumors and tumor-free tissues. However, little information exists on exosome-endothelial cell (EC) interactions or the proangiogenic role of tetraspanins, which are a constitutive component of exosomes. In this study, we used a rat adenocarcinoma model (AS-Tspan8) to explore the effects of exosomal Tspan8 on angiogenesis. Tspan8 contributed to a selective recruitment of proteins and mRNA into exosomes, including CD106 and CD49d, which were implicated in exosome-EC binding and EC internalization. We found that EC internalized Tspan8-CD49d complex-containing exosomes. Exosome uptake induced vascular endothelial growth factor (VEGF)-independent regulation of several angiogenesis-related genes, including von Willebrand factor, Tspan8, chemokines CXCL5 and MIF, chemokine receptor CCR1, and, together with VEGF, VEGF receptor 2. EC uptake of Tspan8-CD49d complex-containing exosomes was accompanied by enhanced EC proliferation, migration, sprouting, and maturation of EC progenitors. Unraveling these new pathways of exosome-initiated EC regulation could provide new options for therapeutic interference with tumor-induced angiogenesis.

Cell-specific interaction of retinoic acid receptors with target genes in mouse embryonic fibroblasts and embryonic stem cells

All-trans retinoic acid (RA) induces transforming growth factor beta (TGF-beta)-dependent autocrine growth of mouse embryonic fibroblasts (MEFs). We have used chromatin immunoprecipitation to map 354 RA receptor (RAR) binding loci in MEFs, most of which were similarly occupied by the RAR alpha and RAR gamma receptors. Only a subset of the genes associated with these loci are regulated by RA, among which are several critical components of the TGF-beta pathway. We also show RAR binding to a novel series of target genes involved in cell cycle regulation, transformation, and metastasis, suggesting new pathways by which RA may regulate proliferation and cancer. Few of the RAR binding loci contained consensus direct-repeat (DR)-type elements. The majority comprised either degenerate DRs or no identifiable DRs but anomalously spaced half sites. Furthermore, we identify 462 RAR target loci in embryonic stem (ES) cells and show that their occupancy is cell type specific. Our results also show that differences in the chromatin landscape regulate the accessibility of a subset of more than 700 identified loci to RARs, thus modulating the repertoire of target genes that can be regulated and the biological effects of RA.

Bone morphogenetic proteins in orthopaedic surgery

Bone healing is a predictable process that has a high rate of success. For some patients, and in certain clinical settings, this process can be delayed or completely inhibited. This leads to significant morbidity and may also result in time lost from work, costs related to prolonged medical treatment, and continued pain at the site of nonunion or failed spinal fusion. Several growth factors, specifically BMP-2 and BMP-7, have been approved in several countries for specific indications. The use of these products and potential complications of their use are reviewed.

Bone morphogenetic protein 15 (BMP15) acts as a BMP and Wnt inhibitor during early embryogenesis

Bone morphogenetic protein 15 (BMP15) belongs to an unusual subgroup of the transforming growth factor beta (TGFbeta) superfamily of signaling ligands as it lacks a key cysteine residue in the mature region required for proper intermolecular dimerization. Naturally occurring BMP15 mutation leads to early ovarian failure in humans, and BMP15 has been shown to activate the Smad1/5/8 pathway in that context. Despite its important role in germ cell specification, the embryological function of BMP15 remains unknown. Surprisingly, we find that during early Xenopus embryogenesis BMP15 acts solely as an inhibitor of the Smad1/5/8 pathway and the Wnt pathway. BMP15 gain-of-function leads to embryos with secondary ectopic heads and to direct neural induction in intact explants. BMP15 inhibits BMP4-mediated epidermal induction in dissociated explants. BMP15 strongly inhibits BRE response induced by BMP4 and blocks phosphorylation and activation of Smad1/5/8 MH2-domain. Mechanistically, BMP15 protein specifically interacts with BMP4 protein, suggesting inhibition upstream of receptor binding. Loss-of-function experiments using morpholinos or a naturally occurring human BMP15 dominant-negative mutant (BMP15-Y235C) leads to embryos lacking head. BMP15-Y235C also eliminates the inhibitory activity of BMP15 on BRE (BMP-responsive element). Finally, we show that BMP15 inhibits the canonical branch of the Wnt pathway, upstream of beta-catenin. We, thus, demonstrate that BMP15 is necessary and sufficient for the specification of dorso-anterior structures and highlight novel mechanisms of BMP15 function that strongly suggest a reinterpretation of its function in ovaries specially for ovarian failure.

Identifying novel genes involved in both deer physiological and human pathological osteoporosis

Osteoporosis attacks 10% of the population worldwide. Humans or even the model animals of the disease cannot recover from porous bone. Regeneration in skeletal elements is the unique feature of our newly investigated osteoporosis model, the red deer (Cervus elaphus) stag. Cyclic physiological osteoporosis is a consequence of the annual antler cycle. This phenomenon raises the possibility to identify genes involved in the regulation of bone mineral density on the basis of comparative genomics between deer and human. We compare gene expression activity of osteoporotic and regenerating rib bone samples versus autumn dwell control in red deer by microarray hybridization. Identified genes were tested on human femoral bone tissue from non-osteoporotic controls and patients affected with age-related osteoporosis. Expression data were evaluated by Principal Components Analysis and Canonical Variates Analysis. Separation of patients into a normal and an affected group based on ten formerly known osteoporosis reference genes was significantly improved by expanding the data with newly identified genes. These genes include IGSF4, FABP3, FABP4, FKBP2, TIMP2, TMSB4X, TRIB, and members of the Wnt signaling. This study supports that extensive comparative genomic analyses, here deer and human, provide a novel approach to identify new targets for human diagnostics and therapy.

Early pulmonary cytokine and chemokine responses in mice immunized with three different vaccines against Mycobacterium tuberculosis determined by PCR array

In this study, the early pulmonary cytokine and chemokine responses in mice immunized with either BCG vaccine, a DeltasecA2 mutant of Mycobacterium tuberculosis, or a DNA vaccine expressing an ESAT6-antigen 85B fusion protein and then aerogenically challenged with a low dose of M. tuberculosis were evaluated by PCR array. The cellular immune responses at day 10 postchallenge were essentially equivalent in the lungs of mice immunized with either the highly immunogenic BCG vaccine or the DeltasecA2 M. tuberculosis mutant strain. Specifically, 12 immune biomolecules (including gamma interferon [IFN-gamma], interleukin-21 [IL-21], IL-27, IL-17f, CXCL9, CXCL10, and CXCL11) were differentially regulated, relative to the levels for naïve controls, in the lungs of vaccinated mice at this time point. Although the vaccine-related immune responses evoked in mice immunized with the DNA vaccine were relatively limited at 10 days postinfection, upregulation of IFN-gamma RNA synthesis as well as increased expression levels of CXCL9, CXCL10, and CXCL11 chemokines were detected.

TSG-6 regulates bone remodeling through inhibition of osteoblastogenesis and osteoclast activation

TSG-6 is an inflammation-induced protein that is produced at pathological sites, including arthritic joints. In animal models of arthritis, TSG-6 protects against joint damage; this has been attributed to its inhibitory effects on neutrophil migration and plasmin activity. Here we investigated whether TSG-6 can directly influence bone erosion. Our data reveal that TSG-6 inhibits RANKL-induced osteoclast differentiation/activation from human and murine precursor cells, where elevated dentine erosion by osteoclasts derived from TSG-6^-/- mice is consistent with the very severe arthritis seen in these animals. However, the long bones from unchallenged TSG-6^-/- mice were found to have higher trabecular mass than controls, suggesting that in the absence of inflammation TSG-6 has a role in bone homeostasis; we have detected expression of the TSG-6 protein in the bone marrow of unchallenged wild type mice. Furthermore, we have observed that TSG-6 can inhibit bone morphogenetic protein-2 (BMP-2)-mediated osteoblast differentiation. Interaction analysis revealed that TSG-6 binds directly to RANKL and to BMP-2 (as well as other osteogenic BMPs but not BMP-3) via composite surfaces involving its Link and CUB modules. Consistent with this, the full-length protein is required for maximal inhibition of osteoblast differentiation and osteoclast activation, although the isolated Link module retains significant activity in the latter case. We hypothesize that TSG-6 has dual roles in bone remodeling; one protective, where it inhibits RANKL-induced bone erosion in inflammatory diseases such as arthritis, and the other homeostatic, where its interactions with BMP-2 and RANKL help to balance mineralization by osteoblasts and bone resorption by osteoclasts.

The Stem Cell Identity of Testicular Cancer

Testicular germ cell tumors account for 1% of all cancers, and are the most common malignancies to affect males between the ages of 15 and 34. Understanding the pathogenesis of testis cancer has been challenging because the molecular and cellular events that result in the formation of germ cell tumors are hypothesized to occur during human fetal development. In this review, the molecular pathways involved in human testis cancer will be presented based on our research in human embryonic stem cells (hESCs), and also research using animal models. Testis germ cell tumors are unique in that the normal germ cell from which the tumor is derived has distinct stem cell characteristics that are shared with pluripotent hESCs. In particular, normal fetal germ cells express the core pluripotent transcription factors NANOG, SOX2 and OCT4. In contrast to hESCs, the germ line is not pluripotent. As a result, germ cell tumorigenesis may arise from loss of germ line-specific inhibitors which in normal germ cells prevent overt pluripotency and self-renewal and when absent in abnormal germ cells, result in the conversion to germ line cancer stem cells. At the conclusion of this review, a model for the molecular events involved in germ cell tumor formation and the relationship between germ cell tumorigenesis and stem cell biology will be presented.

Erythropoietin modulation of podocalyxin and a proposed erythroblast niche

Epo's erythropoietic capacity is ascribed largely to its antiapoptotic actions. In part via gene profiling of bone marrow erythroblasts, Epo is now shown to selectively down-modulate the adhesion/migration factors chemokine receptor-4 (Cxcr4) and integrin alpha-4 (Itga4) and to up-modulate growth differentiation factor-3 (Gdf3), oncostatin-M (OncoM), and podocalyxin like-1 (PODXL). For PODXL, Epo dose-dependent expression of this CD34-related sialomucin was discovered in Kit(+)CD71(high) proerythroblasts and was sustained at subsequent Kit(-)CD71(high) and Ter119(+) stages. In vivo, Epo markedly induced PODXL expression in these progenitors and in marrow-resident reticulocytes. This was further associated with a rapid release of PODXL(+) reticulocytes to blood. As studied in erythroblasts expressing minimal Epo receptor (EpoR) alleles, efficient PODXL induction proved dependence on an EpoR-PY343 Stat5 binding site. Moreover, in mice expressing an EpoR-HM F343 allele, compromised Epo-induced PODXL expression correlated with abnormal anucleated red cell representation in marrow. By modulating this select set of cell-surface adhesion molecules and chemokines, Epo is proposed to mobilize erythroblasts from a hypothesized stromal niche and possibly promote reticulocyte egress to blood.