Bacterial-derived uracil as a modulator of mucosal immunity and gut-microbe homeostasis in Drosophila.

All metazoan guts are subjected to immunologically unique conditions in which an efficient antimicrobial system operates to eliminate pathogens while tolerating symbiotic commensal microbiota. However, the molecular mechanisms controlling this process are only partially understood. Here, we show that bacterial-derived uracil acts as a ligand for dual oxidase (DUOX)-dependent reactive oxygen species generation in Drosophila gut and that the uracil production in bacteria causes inflammation in the gut. The acute and controlled uracil-induced immune response is required for efficient elimination of bacteria, intestinal cell repair, and host survival during infection of nonresident species. Among resident gut microbiota, uracil production is absent in symbionts, allowing harmonious colonization without DUOX activation, whereas uracil release from opportunistic pathobionts provokes chronic inflammation. These results reveal that bacteria with distinct abilities to activate uracil-induced gut inflammation, in terms of intensity and duration, act as critical factors that determine homeostasis or pathogenesis in gut-microbe interactions.

Efficacy of Polydeoxyribonucleotide in Promoting the Healing of Diabetic Wounds in a Murine Model of Streptozotocin-Induced Diabetes: A Pilot Experiment.

We assessed the efficacy of polydeoxyribonucleotide (PDRN) in accelerating the healing of diabetic wounds in a murine model of streptozotocin (STZ)-induced diabetes. After the creation of diabetic wounds, the mice of the PDRN SC, PDRN IP and PBS groups received a subcutaneous, an intra-peritoneal injection of PDRN and a subcutaneous injection of PBS, respectively. After euthanasia, time-dependent changes in the wound diameter and histologic scores were measured and vascular endothelial growth factor (VEGF), transforming growth factor-ß1 (TGF-ß1) and collagen types I and III were assessed for their expression levels. The PDRN SC and the PDRN IP groups showed a significantly smaller diameter of diabetic wounds, significantly higher histologic scores, a significantly greater expression of VEGF, a significantly lower expression of TGF-ß1 and a significantly greater expression of collagen types I and III as compared with the PBS group (p < 0.05 or 0.0001). In conclusion, PDRN might be effective in promoting the healing of diabetic wounds in a murine model of STZ-induced diabetes.

Impact of Obesity on the IL-6 Immune Marker and Th17 Immune Cells in C57BL/6 Mice Models with Imiquimod-Induced Psoriasis.

Obese psoriatic patients experience higher disease severity and exhibit poorer treatment responses and clinical outcomes. It has been proposed that proinflammatory cytokines produced by adipose tissue exacerbate psoriasis; however, the role of obesity in psoriasis remains unclear. This study aimed to elucidate the role of obesity in the pathogenesis of psoriasis, focusing on immunological changes. To induce obesity, mice were fed a high-fat diet for 20 weeks. We then applied imiquimod to the skin on a mouse's back for seven consecutive days to induce psoriasis and scored lesion severity every day for seven days. Cytokine levels in serum and the Th17 cell population in the spleen and draining lymph nodes were studied to identify immunological differences. The clinical severity was more remarkable, and histologically the epidermis was also significantly thicker in the obese group. Increased levels of IL-6 and TNF-α were observed in serum after psoriasis. They were elevated to a greater degree, with greater expansion of the functional Th17 cell population in the obese group. It is concluded that obesity could exacerbate psoriasis through mechanisms that involve elevated proinflammatory cytokine secretion and an expanded Th17 cell population.

Establishment of a useful in vitro decidual induction model using eCG-primed nonpregnant mouse endometrial stromal cells†.

Uterine endometrial differentiation is essential for developmental continuity and female health. A convenient in vitro model mimicking the physiological status is needed to effectively evaluate implantation and uterine response mechanisms. Thus, we developed a promising in vitro model, the FSS (FSH mimic-stimulated synchronized) model, by using primary mouse uterine stromal cells (mUSCs) obtained from equine chorionic gonadotropin (eCG)-primed mice. These mUSCs could be differentiated into decidualized cells with 17 beta-estradiol (E2) and progesterone (P4). The pregnancy day 4 (PD4) model, in which mUSCs are obtained at day 4 of pregnancy, was used as a control. The cell shape index and polyploidy rates were similar between the two models. The staining intensities of lipids and glycogen were significantly higher in the induced groups in both models but stronger in the FSS model than in the PD4 model. The expression levels of AP-TNAP, cathepsin L, Prl8a2, Gja1, Cebpb, and Igfbp1 were increased at 24 h after decidual induction. PR-alpha and PR-beta levels were also increased at 24 h after decidual induction in both models. These results indicate that the FSS model provides a convenient method for obtaining USCs that are usable for various experimental approaches due to their physiological competence and flexibility for triggering induction. This may serve as a model system for the study of pathogeneses originating from the endometrium or communication with other tissues and lead to a better understanding of embryo implantation mechanisms. Furthermore, the results of this study will be integral for further refinements of 3D uterine culture manipulation techniques.

Metabolic Rewiring by Human Placenta-Derived Mesenchymal Stem Cell Therapy Promotes Rejuvenation in Aged Female Rats.

Aging is a degenerative process involving cell function deterioration, leading to altered metabolic pathways, increased metabolite diversity, and dysregulated metabolism. Previously, we reported that human placenta-derived mesenchymal stem cells (hPD-MSCs) have therapeutic effects on ovarian aging. This study aimed to identify hPD-MSC therapy-induced responses at the metabolite and protein levels and serum biomarker(s) of aging and/or rejuvenation. We observed weight loss after hPD-MSC therapy. Importantly, insulin-like growth factor-I (IGF-I), known prolongs healthy life spans, were markedly elevated in serum. Capillary electrophoresis-time-of-flight mass spectrometry (CE-TOF/MS) analysis identified 176 metabolites, among which the levels of 3-hydroxybutyric acid, glycocholic acid, and taurine, which are associated with health and longevity, were enhanced after hPD-MSC stimulation. Furthermore, after hPD-MSC therapy, the levels of vitamin B6 and its metabolite pyridoxal 5'-phosphate were markedly increased in the serum and liver, respectively. Interestingly, hPD-MSC therapy promoted serotonin production due to increased vitamin B6 metabolism rates. Increased liver serotonin levels after multiple-injection therapy altered the expression of mRNAs and proteins associated with hepatocyte proliferation and mitochondrial biogenesis. Changes in metabolites in circulation after hPD-MSC therapy can be used to identify biomarker(s) of aging and/or rejuvenation. In addition, serotonin is a valuable therapeutic target for reversing aging-associated liver degeneration.

Coordination of multiple dual oxidase-regulatory pathways in responses to commensal and infectious microbes in drosophila gut.

All metazoan guts are in permanent contact with the microbial realm. However, understanding of the exact mechanisms by which the strength of gut immune responses is regulated to achieve gut-microbe mutualism is far from complete. Here we identify a signaling network composed of complex positive and negative mechanisms that controlled the expression and activity of dual oxidase (DUOX), which 'fine tuned' the production of microbicidal reactive oxygen species depending on whether the gut encountered infectious or commensal microbes. Genetic analyses demonstrated that negative and positive regulation of DUOX was required for normal host survival in response to colonization with commensal and infectious microbes, respectively. Thus, the coordinated regulation of DUOX enables the host to achieve gut-microbe homeostasis by efficiently combating infection while tolerating commensal microbes.

Identification and characterization of GAL4 drivers that mark distinct cell types and regions in the Drosophila adult gut.

The gastrointestinal tract in the adult Drosophila serves as a model system for exploring the mechanisms underlying digestion, absorption and excretion, stem cell plasticity, and inter-organ communication, particularly through the gut-brain axis. It is also useful for studying the cellular and adaptive responses to dietary changes, alterations in microbiota and immunity, and systematic and endocrine signals. Despite the various cell types and distinct regions in the gastrointestinal tract, few tools are available to target and manipulate the activity of each cell type and region, and their gene expression. Here, we report 353 GAL4 lines and several split-GAL4 lines that are expressed in enteric neurons (ENs), progenitors (ISCs and EBs), enterocytes (ECs), enteroendocrine cells (EEs), or/and other cell types that are yet to be identified in distinct regions of the gut. We had initially collected approximately 600 GAL4 lines that may be expressed in the gut based on RNA sequencing data, and then crossed them to UAS-GFP to perform immunohistochemistry to identify those that are expressed selectively in the gut. The cell types and regional expression patterns that are associated with the entire set of GAL4 drivers and split-GAL4 combinations are annotated online at http://kdrc.kr/index.php (K-Gut Project). This GAL4 resource can be used to target specific populations of distinct cell types in the fly gut, and therefore, should permit a more precise investigation of gut cells that regulate important biological processes.

Ordered Mesoporous Carbons with Graphitic Tubular Frameworks by Dual Templating for Efficient Electrocatalysis and Energy Storage.

Ordered mesoporous carbons (OMCs) have attracted considerable interest owing to their broad utility. OMCs reported to date comprise amorphous rod-like or tubular or graphitic rod-like frameworks, which exhibit tradeoffs between conductivity and surface area. Here we report ordered mesoporous carbons constructed with graphitic tubular frameworks (OMGCs) with tunable pore sizes and mesostructures via dual templating, using mesoporous silica and molybdenum carbide as exo- and endo-templates, respectively. OMGCs simultaneously realize high electrical conductivity and large surface area and pore volume. Benefitting from these features, Ru nanoparticles (NPs) supported on OMGC exhibit superior catalytic activity for alkaline hydrogen evolution reaction and single-cell performance for anion exchange membrane water electrolysis compared to Ru NPs on other OMCs and commercial catalysts. Further, the OMGC-based full-carbon symmetric cell demonstrates excellent performances for Li-ion capacitors.

Comparison of the efficacy and safety of povidone-iodine foam dressing (Betafoam), hydrocellular foam dressing (Allevyn), and petrolatum gauze for split-thickness skin graft donor site dressing.

We evaluated the efficacy and safety of a povidone-iodine (PVP-I) foam dressing (Betafoam) for donor site dressing versus a hydrocellular foam dressing (Allevyn) and petrolatum gauze. This prospective Phase 4 study was conducted between March 2016 and April 2017 at eight sites in Korea. A total of 106 consenting patients (aged ≥ 19 years, scheduled for split-thickness skin graft) were randomised 1:1:1 to PVP-I foam, hydrocellular, or petrolatum gauze dressings for up to 28 days after donor site collection. We assessed time to complete epithelialisation, proportion with complete epithelialisation at Day 14, and wound infection. Epithelialisation time was the shortest with PVP-I foam dressing (12.74 ± 3.51 days) versus hydrocellular foam dressing (16.61 ± 4.45 days; P = 0.0003) and petrolatum gauze (15.06 ± 4.26 days, P = 0.0205). At Day 14, 83.87% of PVP-I foam dressing donor sites had complete epithelialisation, versus 36.36% of hydrocellular foam dressing donor sites (P = 0.0001) and 55.88% of petrolatum gauze donor sites (P = 0.0146). There were no wound infections. Incidence rates of adverse events were comparable across groups (P = 0.1940). PVP-I foam dressing required less time to complete epithelialisation and had a good safety profile.

Oocyte Cytoplasmic Gas6 and Heparan Sulfate (HS) are Required to Establish the Open Chromatin State in Nuclei During Remodeling and Reprogramming.

BACKGROUND/AIMS: Previously, we found that silencing of growth arrest-specific gene 6 (Gas6) in oocytes impaired cytoplasmic maturation, resulting in failure of sperm chromatin decondensation (SCD) and pronuclear (PN) formation after fertilization. Thus, we conducted this study to determine the effect of Gas6 RNAi on downstream genes and to elucidate the working mechanism of Gas6 on oocyte cytoplasmic maturation and SCD. METHODS: Using RT-PCR, Western blot and immunofluorescence, the expression levels of various target genes and the localization of heparan sulfate (HS) were analyzed after Gas6 RNAi. The roles of Gas6 in HS biosynthesis, production of ATP and GSH, ROS generation and ΔΨm were also investigated. SCD and micrococcal nuclease (MNase) analyses were used to examine the effects of HS on the open chromatin state in sperm and somatic cell nuclei, respectively. RESULTS: Disruption of Gas6 expression led to the inhibition of HS biosynthesis through the reduction of several HS biosynthetic enzymes. The rescue experiment, HS treatment in vitro, significantly recovered SCD and PN formation, confirming that HS had the ability to induce sperm head remodeling during fertilization. Interestingly, excessive mitochondrial activation in Gas6-depleted MII oocytes caused ROS generation and glutathione (GSH) degradation via mitochondrial activation, such as elevated ΔΨm and ATP production. Indeed, HS-treated NIH3T3 cell nuclei showed an open chromatin state, as determined by diffuse DAPI staining and increased sensitivity to MNase. CONCLUSION: We propose that the addition of HS to sperm and/or oocyte maturation would improve the efficiency of in vitro fertilization and somatic cell nuclear transfer (SCNT) reprogramming.

Knockdown of PRKAR2B Results in the Failure of Oocyte Maturation.

BACKGROUND/AIMS: Cyclic adenosine monophosphate (cAMP)-dependent type 2 regulatory subunit beta (Prkar2b) is a regulatory isoform of cAMP-dependent protein kinase (PKA), which is the primary target for cAMP actions. In oocytes, PKA and the pentose phosphate pathway (PPP) have important roles during the germinal vesicle (GV) stage arrest of development. Although the roles of the PKA signal pathway have been studied in the development of oocyte, there has been no report on the function of PRKAR2B, a key regulator of PKA. METHODS: Using reverse transcription polymerase chain reaction (RT-PCR), quantitative real-time PCR (qRT-PCR), immunohistochemistry, and immunofluorescence, we determined the relative expression of Prkar2b in various tissues, including ovarian follicles, during oocyte maturation. Prkar2b-interfering RNA (RNAi) microinjection was conducted to confirm the effect of Prkar2b knockdown, and immunofluorescence, qRT-PCR, and time-lapse video microscopy were used to analyze Prkar2b-deficient oocytes. RESULTS: Prkar2b is strongly expressed in the ovarian tissues, particularly in the growing follicle. During oocyte maturation, the highest expression of Prkar2b was during metaphase I (MI), with a significant decrease at metaphase II (MII). RNAi-mediated Prkar2b suppression resulted in MI-stage arrest during oocyte development, and these oocytes exhibited abnormal spindle formation and chromosome aggregation. Expression of other members of the PKA family (except for Prkaca) were decreased, and the majority of the PPP factors were also reduced in Prkar2b-deficient oocytes. CONCLUSION: These results suggest that Prkar2b is closely involved in the maturation of oocytes by controlling spindle formation and PPP-mediated metabolism.

Anisocoria After Repair of Blowout Fracture.

Anisocoria may indicate a life-threatening neurosurgical emergency, unlike bilateral mydriasis. In patients with periorbital fracture, anisocoria can be caused by direct or indirect injury to the oculomotor nerve, excessive retraction of the orbital contents, or constriction of the muscles responsible for eyeball movement. Herein, the author reports a patient, 15-year-old boy, who developed anisocoria after an operation for a blowout fracture. The anisocoria was improved, self-limiting, and transient. The author has also reviewed the literature regarding anisocoria.

B Cell Lymphoma Underlying Paraffinoma of Glabella.

Soft tissue reactions to paraffin include inflammation, fibrosis, disfigurement, and granulomatous inflammation with foreign body giant cell reaction. The authors report the case of a 77-year-old woman with cutaneous marginal zone B cell lymphoma located on glabella, arising in association with underlying paraffinoma. While it is unclear whether the implant directly contributed to the development of lymphoma, this association has not been previously documented, prompting this report.

Genetic evidence of a redox-dependent systemic wound response via Hayan protease-phenoloxidase system in Drosophila.

Systemic wound response (SWR) through intertissue communication in response to local wounds is an essential biological phenomenon that occurs in all multicellular organisms from plants to animals. However, our understanding of SWR has been greatly hampered by the complexity of wound signalling communication operating within the context of an entire organism. Here, we show genetic evidence of a redox-dependent SWR from the wound site to remote tissues by identifying critical genetic determinants of SWR. Local wounds in the integument rapidly induce activation of a novel circulating haemolymph serine protease, Hayan, which in turn converts pro-phenoloxidase (PPO) to phenoloxidase (PO), an active form of melanin-forming enzyme. The Haemolymph Hayan-PO cascade is required for redox-dependent activation of the c-Jun N-terminal kinase (JNK)-dependent cytoprotective program in neuronal tissues, thereby achieving organism level of homeostasis to resist local physical trauma. These results imply that the PO-activating enzyme cascade, which is a prominent defense system in humoral innate immunity, also mediates redox-dependent SWR, providing a novel link between wound response and the nervous system.

RASD1 Knockdown Results in Failure of Oocyte Maturation.

BACKGROUND: Ras dexamethasone-induced protein (RASD1) is a member of Ras superfamily of small GTPases. RASD1 regulates various signaling pathways involved in iron homeostasis, growth hormone secretion, and circadian rhythm. However, RASD1 function in oocyte remains unknown. METHODS: Using immunohistochemistry, immunofluorescence, and quantitative real-time RT-PCR, RASD1 expression in mouse ovary and RASD1 role in oocyte maturation-related gene expression, spindle formation, and chromosome alignment were analyzed. RNAi microinjection and time-lapse video microscopy were used to examine the effect of Rasd1 knockdown on oocyte maturation. RESULTS: RASD1 was highly detected in oocytes transitioning from primordial to secondary follicles. Rasd1 was highly expressed in germinal vesicle (GV), during GV breakdown, and in metaphase I (MI) stage as oocytes mature, and its expression was significantly downregulated in MII stage. With knockdown of Rasd1, maturation in GV oocytes was arrested at MI stage, showing disrupted meiotic spindling and chromosomal misalignment. In addition, Obox4 and Arp2/3, engaged in MI-MII transition and cytokinesis, respectively, were misregulated in GV oocytes by Rasd1 knockdown. CONCLUSION: These findings suggest that RASD1 is a novel factor in MI-MII oocyte transition and may be involved in regulating the progression of cytokinesis and spindle formation, controlling related signaling pathways during oocyte maturation.

Obox4-silencing-activated STAT3 and MPF/MAPK signaling accelerate nuclear membrane breakdown in mouse oocytes.

Mouse oocytes begin to mature in vitro once liberated from ovarian follicles. Previously, we showed that oocyte-specific homeobox 4 (Obox4) is critical for maintaining the intact nuclear membrane of the germinal vesicle (GV) in oocytes and for completing meiosis at the metaphase I-II (MI-MII) transition. This study further examines the molecular mechanisms of OBOX4 in regulating GV nuclear membrane breakdown. Maturation-promoting factor (MPF) and MAPK are normally inactive in GV stage oocytes but were activated prematurely in arrested GV stage oocytes by 3-isobutyl-1-metyl-xanthine (IBMX) in vitro after Obox4 RNA interference (RNAi). Furthermore, signal transducer and activator of transcription 3 (STAT3) was significantly activated by Obox4 RNAi. We confirmed that this Obox4 RNAi-induced premature STAT3 and MPF/MAPK activation at the GV stage provoked subsequent GV breakdown (GVBD) despite the opposing force of high cAMP in the IBMX-supplemented medium to maintain intact GV. When cumulus-oocyte complexes were exposed to interferon α (IFNA), a STAT3 activator, oocytes matured and cumulus cells expanded to resume nuclear maturation in IBMX-supplemented medium, suggesting that STAT3 activation is sufficient for stimulating the continuation of meiosis. Using Stattic, a specific STAT3 inhibitor, we confirmed that GVBD involves STAT3 activation in Obox4-silenced oocytes. Based on these findings, we concluded that i) Obox4 is an important upstream regulator of MPF/MAPK and STAT3 signaling, and ii) Obox4 is a key regulator of the GV arrest mechanism in oocytes.

Youth access to cigarettes in six sub-Saharan African countries.

OBJECTIVE: Tobacco smoking is initiated and established mostly during adolescence. The World Health Organization (WHO) Framework Convention on Tobacco Control (FCTC) Article 16 outlines the obligation of parties to prohibit the sale of tobacco products to minors. This study examined where and how student smokers obtain cigarettes. METHODS: We examined Global Youth Tobacco Survey (GYTS) data from 2009 to 2011 on cigarette access among students aged 13-15 in six sub-Saharan African countries. RESULTS: In all countries analyzed, over 20% of student smokers obtained their cigarettes in a store or shop (52.6% in South Africa, 37.7% in Republic of Congo, 28.2% in Swaziland, 27.4% in Cote d'Ivoire, 26.9% in Ghana, and 22.6% in Uganda). In Cote d'Ivoire and South Africa, 68.9% and 68.7% of student cigarette smokers, respectively, were not refused the sale of cigarettes because of age. The percentage of students who were offered free cigarettes by a tobacco company representative ranged from 4.7% in Cote d'Ivoire to 12.1% in South Africa. CONCLUSIONS: The method of obtaining cigarettes and access to cigarettes among students varies among sub-Saharan African countries. Adopting and enforcing interventions that prevent youth from accessing tobacco products could be an effective strategy for reducing smoking initiation among youth in sub-Saharan African countries.

Comparative analysis of improved soy-mozzarella cheeses made of ultrafiltrated and partly skimmed soy blends with other mozzarella types.

The objective of this study was to improve the physicochemical properties and functional qualities of soy based mozzarella cheeses by ultrafiltration (UF) of soy milk blends, adding skim milk instead of cow's milk or increasing the soy milk proportions in cheese milk. Eight types of mozzarella cheeses made using soy milk and analyzed for nutritional, structural, and functional characteristics for 4 weeks at 4 °C. Cheeses made with cow milk, 10, 20, and 30 % soy milk in cow milk, skim milk, 10 % soy milk in skim milk, and ultrafiltrated 10 % soy milk in cow milk for first and second volume concentrations. Refrigerated storage of the soy-mozzarella led to a decrease in total solid, mineral, protein, fat, and lactose contents and rheological characteristics after 2 weeks. The nutritive quality of the mozzarella tended to increase proportionally to soy milk content, but the physical and functional qualities decreased. The UF-fortified soy-mozzarella showed more improved qualities among the other soy cheeses like long shelf life, improved nutritional, structural and functional qualities. Blends of 10-20 % soy milk and UF soy milk blends can be used to achieve good quality, nutritive mozzarella cheese, even with skim milk instead of cow milk in a milk shortage.

Transcription elongation factor Tcea3 regulates the pluripotent differentiation potential of mouse embryonic stem cells via the Lefty1-Nodal-Smad2 pathway.

Self-renewal and pluripotency are hallmark properties of pluripotent stem cells, including embryonic stem cells (ESCs) and iPS cells. Previous studies revealed the ESC-specific core transcription circuitry and showed that these core factors (e.g., Oct3/4, Sox2, and Nanog) regulate not only self-renewal but also pluripotent differentiation. However, it remains elusive how these two cell states are regulated and balanced during in vitro replication and differentiation. Here, we report that the transcription elongation factor Tcea3 is highly enriched in mouse ESCs (mESCs) and plays important roles in regulating the differentiation. Strikingly, altering Tcea3 expression in mESCs did not affect self-renewal under nondifferentiating condition; however, upon exposure to differentiating cues, its overexpression impaired in vitro differentiation capacity, and its knockdown biased differentiation toward mesodermal and endodermal fates. Furthermore, we identified Lefty1 as a downstream target of Tcea3 and showed that the Tcea3-Lefty1-Nodal-Smad2 pathway is an innate program critically regulating cell fate choices between self-replication and differentiation commitment. Together, we propose that Tcea3 critically regulates pluripotent differentiation of mESCs as a molecular rheostat of Nodal-Smad2/3 signaling.

Distinct transcriptional profiles of angioblasts derived from human embryonic stem cells.

Identification of differentially expressed genes in angioblasts derived from human embryonic stem cells (hESCs) is of great interest for elucidating the molecular mechanisms underlying human vasculogenesis. The aim of this study was to define hESC-derived angioblasts at the clonal level and to perform comparative transcriptional analysis to characterize their distinct gene expression profiles. In a clonal analysis performed in cell-specific differentiation media, hESC-derived CD34(+)CD31(+) cells were identified as angioblasts in that they exhibited a significantly higher ability to form endothelial cell (EC) and smooth muscle cell (SMC) colonies than CD34(+)CD31(-) and CD34(-) cell populations did. Microarray analysis showed that many genes involved in vascular development and signaling transduction were overexpressed in hESC-derived CD34(+)CD31(+) cells, whereas those related to mitosis, the DNA damage response, and translation were substantially downregulated. In addition, comparative gene expression profiling of hESC-derived CD34(+)CD31(+) cells and human somatic primary vascular cells demonstrated that hESC-derived CD34(+)CD31(+) cells expressed key genes involved in the EC and SMC differentiation processes, which supports the result that hESC-derived CD34(+)CD31(+) cells are bipotent angioblasts. Our results may provide insights into the identity and function of hESC-derived angioblasts and may also facilitate further investigation of the molecular mechanisms regulating human embryonic vasculogenesis.