Transient Potential Research Articles

Molecular pathways during marine fish egg hydration: the role of aquaporins

The pre-ovulatory hydration of the oocyte of marine teleosts, a unique process among vertebrates that occurs concomitantly with meiosis resumption (oocyte maturation), is a critical process for the correct development and survival of the embryo. Increasing information is available on the molecular mechanisms that control oocyte maturation in fish, but the identification of the cellular processes involved in oocyte hydration has remained long ignored. During the past few years, a number of studies have identified the major inorganic and organic osmolytes that create a transient intra-oocytic osmotic potential for hydrating the oocytes, whereas water influx was believed to occur passively. Recent work, however, has uncovered the role of a novel molecular water channel (aquaporin), designated aquaporin-1b (Aqp1b), which facilitates water permeation and resultant swelling of the oocyte. The Aqp1b belongs to a teleost-specific subfamily of water-selective aquaporins, similar to mammalian aquaporin-1 (AQP1) that has possibly evolved by duplication of a common ancestor and further neofunctionalization in oocytes of marine teleosts for water uptake. Strikingly, Aqp1b shows specific regulatory domains at the cytoplasmic tail, which are key to the vesicular trafficking and temporal insertion of Aqp1b in the oocyte plasma membrane during the phase of maximal hydration. These findings are revealing that the mechanism of oocyte hydration in marine teleosts is a highly regulated process based on the interplay between the generation of inorganic and organic osmolytes and the controlled insertion of Aqp1b in the oocyte surface. The discovery of Aqp1b in teleosts provides an important insight into the molecular basis of the production of viable eggs in marine fish.

Cell proliferation in hepatocellular carcinoma by TRPC6

Objective Transient recepter potential (TRP) is a kind of novel Ca2+ -permeant channel and one of the hot topics in the current basic researches. The researches on TRP were mostly focused on nervous system in the past, and now they come to extend to other areas. We hypothesized that TRP channels should be likely related to cell proliferation of bepatocellular carcinoma(HCC). This study was designed to confirm this hypothesis. Methods After inhibiting the function of TRPC channels by pharmacological means (SKF-96365) and RNAi, we observed the effect of this inhibition on cell proliferation in vitro. Results After inhibition of TRP channels by SKF-96365 and RNAi, the proliferation of two HCC cell lines of HepG2 and SMMC-7721 was significantly repressed. Conclusion The TRPC6 channels are implicated in HCC cell proliferation. This study not only provides new insights into proliferation of HCC cells and subsequent cancer intervention strategies but also opens a new area for TRP channel study. Key words: Carcinoma,hepatocellular; TRP channel; Proliferation; Ca2+

Electrochemical perm-selectivity of active layers and diffusion permeability of supports of an asymmetric and a composite NF membrane studied by concentration-step method

Fixed electric charge is believed to play an important role in the transfer of charged solutes in nanofiltration. Electrochemical measurements are useful tools for the determination of electrochemical perm-selectivity, which can be related to the fixed charge density by using a model. In the case of monolayer membranes, the electrochemical perm-selectivity is determined, in particular, through the measurements of stationary membrane potential. With composite/asymmetric NF membranes, the interpretation of this measurement is complicated by the membrane multi-layer structure. In the concentration-step technique, a membrane is equilibrated with an electrolyte solution and left in contact with this solution from the support side alone. The active membrane surface is suddenly touched by a pendant drop of solution of a different concentration, and the electrical response to this is tracked with a pair of reversible electrodes. In the very first moments after the touch, the whole concentration difference is located within the membrane active layer, and the initial electrical response is controlled by its electrochemical perm-selectivity. The characteristictime of relaxation of transient membrane potential is governed by the diffusion permeability of active layer and the porosity of and diffusivity in the membrane support. The concentration-step technique was used to study the electrochemical properties of active layers of a commercial polymer NF membrane (PES10) and a laboratory-made nano-porous ceramic membrane (provided by University of Twente) in KCl solutions of various concentrations. At pH 6, the fixed charge of polymer membrane was found to be negative whereas that of ceramic membrane was positive. The concentration of fixed charges ranged from 0.03 kmol/m 3 to 0.17 kmol/m 3 depending on the salt concentration.

The Ontogeny of Definitive Hematopoiesis in the Zebrafish.

Abstract Shifting sites of blood cell production during development is common across widely divergent phyla. In zebrafish, like other vertebrates, hematopoietic development has been roughly divided into two waves, termed “primitive” and “definitive.” Primitive hematopoiesis rapidly generates erythrocytes and macrophages through monopotent precursors for immediate use in the developing embryo. Definitive hematopoiesis arises later and generates multipotent precursors, including hematopoietic stem cells (HSCs). We have recently performed the first prospective isolation and functional characterization of hematopoietic stem and progenitor cells in the zebrafish and shown that definitive hematopoiesis generates two distinct precursor types during embryogenesis. First to arise are erythromyeloid progenitors (EMPs) in the posterior blood island (PBI), cells that possess robust but transient proliferation potential but lack self-renewal and lymphoid differentiation capacities. Next to develop are HSCs in the aorta/gonad/mesonephros (AGM) region. Unlike EMPs, HSCs colonize the developing thymus to initiate T-lymphopoiesis and seed the pronephros, the site of adult hematopoiesis. In vivo fate mapping studies similarly demonstrate that EMPs possess only transient proliferative potential, with differentiated progeny remaining largely within caudal hematopoietic tissue. By contrast, fate mapping of CD41:eGFP+ cells residing in the AGM region demonstrate robust colonization of the pronephros and thymus. Using time-lapse microscopy, we have observed directly the behaviors of the first HSCs to arise in the embryo. AGM HSCs, marked by a CD41:eGFP or c-myb:eGFP transgene, enter circulation to seed the thymic anlage and migrate along the pronephric tubules to seed the pronephros. We are currently performing retrospective time-lapse analyses to determine where in the early embryo HSC and EMP precursors are born. These data will be informative in analyzing where instructive ligands are expressed, including the Delta genes that provide paracrine signals to cells expressing the Notch receptor. We have demonstrated that Notch signaling is necessary for the generation of HSCs but dispensable for EMP formation. We have utilized new and existing Notch reporter lines to determine more precisely where and when HSC precursors receive Notch signals. Together, these studies highlight the power of the zebrafish system in combining genetic approaches with the direct imaging of hematopoietic stem and progenitor cells in living embryos.

Decreased astroglial cell adhesion and proliferation on zinc oxide nanoparticle polyurethane composites.

Nanomaterials offer a number of properties that are of interest to the field of neural tissue engineering. Specifically, materials that exhibit nanoscale surface dimensions have been shown to promote neuron function while simultaneously minimizing the activity of cells such as astrocytes that inhibit central nervous system regeneration. Studies demonstrating enhanced neural tissue regeneration in electrical fields through the use of conductive materials have led to interest in piezoelectric materials (or those materials which generate a transient electrical potential when mechanically deformed) such as zinc oxide (ZnO). It has been speculated that ZnO nanoparticles possess increased piezoelectric properties over ZnO micron particles. Due to this promise in neural applications, the objective of the present in vitro study was, for the first time, to assess the activity of astroglial cells on ZnO nanoparticle polymer composites. ZnO nanoparticles embedded in polyurethane were analyzed via scanning electron microscopy to evaluate nanoscale surface features of the composites. The surface chemistry was characterized via X-ray photoelectron spectroscopy. Astroglial cell response was evaluated based on cell adhesion and proliferation. Astrocyte adhesion was significantly reduced on ZnO nanoparticle/polyurethane (PU) composites with a weight ratio of 50:50 (PU:ZnO) wt.%, 75:25 (PU:ZnO) wt.%, and 90:10 (PU:ZnO) wt.% in comparison to pure PU. The successful production of ZnO nanoparticle composite scaffolds suitable for decreasing astroglial cell density demonstrates their potential as a nerve guidance channel material with greater efficiency than what may be available today.

Recursive estimation of transient inhomogeneous zeta potential in microchannel turns using velocity measurements

In the various biomedical microfluidic devices the target biomolecules are delivered by activating electroosmotic flows. The zeta potential of a microchannel wall, which determines the strength of the electroosmotic flow, is apt to change due to the adhesion of biomolecules such as DNA or protein especially around the microchannel turns. The resulting transient inhomogeneous profile of zeta potential alters flow pattern, volumetric flow rate and the band broading of solutes. In the present work, we have developed a method for the recursive estimation of transient inhomogeneous zeta potential in microchannel turns using velocity measurements. For the real time implementation of the present method, a compact and accurate reduced-order model is derived using the Karhunen-Loève Galerkin method and the Helmholtz-Smoluchowski slip velocity. The present scheme of recursive estimation is an important prerequisite to the real time control of microfluidic devices.

Ultrafast Electron Transfer Dynamics at NH3/Cu(111) Interfaces: Determination of the Transient Tunneling Barrier

Electron transfer (ET) dynamics at molecule-metal interfaces plays a key role in various fields as surface photochemistry or the development of molecular electronic devices. The bare transfer process is often described in terms of tunneling through an interfacial barrier that depends on the distance of the excited electron to the metal substrate. However, a quantitative characterization of such potential barriers is still lacking. In the present time-resolved two-photon photoemission (2PPE) study of amorphous NH 3 layers on Cu(111) we show that photoinjection of electrons is followed by charge solvation leading to the formation of a transient potential barrier at the interface that determines the ET to the substrate. We demonstrate that the electrons are localized at the ammonia-vacuum interface and that the ET rate depends exponentially on the NH 3 layer thickness with inverse range parameters beta between 1.8 and 2.7 nm (-1). Systematic analysis of this time-resolved and layer thickness-dependent data finally enables the determination of the temporal evolution of the interfacial potential barrier using a simple model description. We find that the tunneling barrier forms after tau E = 180 fs and subsequently rises more than three times faster than the binding energy gain of the solvated electrons.

Tumor necrosis factor α enhances the sensitivity of rat trigeminal neurons to capsaicin

Tumor necrosis factor α (TNFα), a pro-inflammatory cytokine, enhances the development of pain and hyperalgesia, although the molecular mechanisms are not well understood. This study evaluated the hypothesis that TNFα increases the sensitivity of rat trigeminal neurons to capsaicin via two different mechanisms triggered by either brief or sustained exposure to the cytokine. A brief (5 min) application of TNFα significantly sensitized capsaicin-evoked accumulation of intracellular calcium ([Ca2+]i) (226.4±37.7 nM vs. 167.5±31.3 nM) and increased capsaicin-evoked nocifensive behavior (78.3±9.7 vs. 30.9±3.6 s) as compared with vehicle pretreatment (P<0.01 for both). Sustained (30 min to 4 h) exposure of cultured neurons to TNFα evoked a twofold increase in mRNA transcript (P<0.05) and protein levels (P<0.01) of transient potential receptor vanilloid type 1 (TRPV1). This long-term up-regulation of TRPV1 expression by TNFα correlated with enhancement in capsaicin-induced calcitonin gene-related peptide release (P<0.05). Demonstration of colocalization of TNFα receptor subtypes I and II with TRPV1 in almost all (>90%) TRPV1 expressing neurons provides evidence consistent with a direct interaction on the same subpopulation of sensory neurons. In summary, our data demonstrate that TNFα directly enhances the sensitivity of rat trigeminal neurons to capsaicin via both rapid, non-genomic mechanisms as well as sustained genomic regulation in TRPV1 expression. Thus, increased sensitization and up-regulation of TRPV1 constitutes a potential mechanism by which TNFα mediates inflammatory hyperalgesia and pain.

Thermal-to-electric energy conversion of a nanoporous carbon

As two nanoporous carbon electrodes are soaked by an electrolyte solution and placed at different temperatures, a significant transient potential was measured, providing a novel mechanism for thermal-to-electric energy conversion.

Causal impulse response for circular sources in viscous media.

The causal impulse response of the velocity potential for the Stokes wave equation is derived for calculations of transient velocity potential fields generated by circular pistons in viscous media. The causal Green's function is numerically verified using the material impulse response function approach. The causal, lossy impulse response for a baffled circular piston is then calculated within the near field and the far field regions using expressions previously derived for the fast near field method. Transient velocity potential fields in viscous media are computed with the causal, lossy impulse response and compared to results obtained with the lossless impulse response. The numerical error in the computed velocity potential field is quantitatively analyzed for a range of viscous relaxation times and piston radii. Results show that the largest errors are generated in locations near the piston face and for large relaxation times, and errors are relatively small otherwise. Unlike previous frequency-domain methods that require numerical inverse Fourier transforms for the evaluation of the lossy impulse response, the present approach calculates the lossy impulse response directly in the time domain. The results indicate that this causal impulse response is ideal for time-domain calculations that simultaneously account for diffraction and quadratic frequency-dependent attenuation in viscous media.

The Effect of Transient Potential Exposure on the Electrochemical Oxidation of Carbon Black in Low-Temperature Fuel Cells

The electrochemical oxidation of carbon black catalyst supports is recognized as a durability challenge to the commercialization of low-temperature fuel cells in the transportation sector. An investigation of the effect of the transient potentials experienced in this environment is presented. The exposure of carbon black to square wave potential cycling results in an oxidation process different than the constant potential hold historically used to characterize this corrosion process. The differences are characterized using the liquid half-cell and single fuel cell testing, coupled with electrochemical techniques and online gas analysis. Although cyclic voltammetry and X-ray photoelectron spectroscopy are unable to quantify significant differences in the surface oxide chemistry, online gas analysis measurements demonstrate different corrosion activities.

Conditions required for the appearance of double responses in hippocampal field CA1 to application of single stimuli to Shäffer collaterals in freely moving rats

Stimulation of Shäffer collaterals with single current impulses could evoke double responses in hippocampal field CA1 in freely moving rats. The late response - the population excitatory postsynaptic potential with a preceding transient potential, often biphasic - occurred only after an early population spike and was time-locked to it. The shape characteristics of the late response, its polarity, and its latent period relative to the early population spike suggest that stimulation of Shäffer collaterals gives rise, in CA1, to a wave of excitation which passes through the entorhinal cortex and returns to CA1 directly via fibers of the perforant path. In conscious rats, medium-strength stimulation of Shäffer collaterals, sufficient to evoke a quite early population spike in CA1, did not usually lead to the appearance of a late response; the same stimulation became effective after tetanization of Shäffer collaterals in conditions of long-term potentiation of the early population spike. Furthermore, the appearance of the late response was facilitated in rats falling asleep on the background of high-amplitude, low-frequency EEG oscillations in CA1 characteristic of slow-wave sleep, as well as in sleeping rats, regardless of the EEG pattern.

Mice lacking the transient receptor vanilloid potential 1 channel display normal thirst responses and central Fos activation to hypernatremia

Neurons of the organum vasculosum of the lamina terminalis (OVLT) are necessary for thirst and vasopressin secretion during hypersmolality in rodents. Recent evidence suggests the osmosensitivity of these neurons is mediated by a gene product encoding the transient receptor potential vanilloid-1 (TRPV1) channel. The purpose of the present study was to determine whether mice lacking the TRPV1 channel had blunted thirst responses and central Fos activation to acute and chronic hyperosmotic stimuli. Surprisingly, TRPV1-/- vs. wild-type mice ingested similar amounts of water after injection (0.5 ml sc) of 0.5 M NaCl and 1.0 M NaCl. Chronic increases in plasma osmolality produced by overnight water deprivation or sole access to a 2% NaCl solution for 48 h produced similar increases in water intake between wild-type and TRPV1-/- mice. There were no differences in cumulative water intakes in response to hypovolemia or isoproterenol. In addition, the number of Fos-positive cells along the lamina terminalis, including the OVLT, as well as the supraoptic nucleus and hypothalamic paraventricular nucleus, was similar between wild-type and TRPV1-/- mice after both acute and chronic osmotic stimulation. These findings indicate that TRPV1 channels are not necessary for osmotically driven thirst or central Fos activation, and thereby suggest that TRPV1 channels are not the primary ion channels that permit the brain to detect changes in plasma sodium concentration or osmolality.

A New Algorithm for the Seismo-Electrokinetic effect generated by different seismic waves and it’s application to shallow depths.

A new approach to modeling the seismoelectric (seismo-electrokinetic) effect is presented. It is based on the concept that at a specific time each location on the wave front that proceeds through the medium imparts equal pressure on the solid matrix and pore space. Consequently two fundamental equations contribute to the basis for the calculation of the electrokinetic effect (EKE): the first describes the relative displacement of particles in the sediment at the arrivals of the seismic wave and second, the transient streaming potential, induced in a pore, when the pressure pulse is applied to a cylindrical pore. To calculate the EKE on the surface the following are required: calculate the pressure gradient in a single pore caused by a seismic wave, the transfer from EKE arising in a single pore to the porous media, integrate the EKE signals all over the sediment space or layer and access the electrokinetic coefficients. A new algorithm has been developed. Being able to model field data mathematically shows the viability of this approach and allows the estimation of permeability of layers. To obtain a realistic geological and groundwater model test site, several geophysical methods were applied to a small area (shallow refraction seismic, DC resistivity, SP, FDEM, magnetic gradiometry). Comparing the EKE result modelled with the new algorithm with the above methods shows that the seismo-electrokinetic method can be successfully used for the exploration for ground water at shallow depths.

Transient potential receptor channel 4 controls thrombospondin‐1 secretion and angiogenesis in renal cell carcinoma

Angiogenic switch in renal cell carcinoma (RCC) is attributed to the inactivation of the von Hippel-Lindau tumor suppressor, stabilization of hypoxia inducible factor-1 transcription factor and increased vascular endothelial growth factor. To evaluate the role of an angiogenesis inhibitor, thrombopsondin-1 (TSP1), we compared TSP1 production in human RCC and normal tissue and secretion by the normal renal epithelium (human normal kidney, HNK) and RCC cells. Normal and RCC tissues stained positive for TSP1, and the levels of TSP1 mRNA and total protein were similar in RCC and HNK cells. However, HNK cells secreted high TSP1, which rendered them nonangiogenic, whereas RCC cells secreted little TSP1 and were angiogenic. Western blot and immunostaining revealed TSP1 in the cytoplasm of RCC cells on serum withdrawal, whereas, in HNK cells, it was rapidly exported. Seeking mechanisms of defective TSP1 secretion, we discovered impaired calcium uptake by RCC in response to vascular endothelial growth factor. In HNK cells, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, a calcium chelator, simulated TSP1 retention, mimicking the RCC phenotype. Further analysis revealed a profound decrease in transient receptor potential canonical ion channel 4 (TRPC4) Ca(2+) channel expression in RCC cells. TRPC4 silencing in HNK cells caused TSP1 retention and impaired secretion. Double labeling of the secretory system components revealed TSP1 colocalization with coatomer protein II (COPII) anterograde vesicles in HNK cells. In contrast, in RCC cells, TSP1 colocalized with COPI vesicles, pointing to the retrograde transport to the endoplasmic reticulum caused by misfolding. Our study indicates that TRPC4 loss in RCC leads to impaired Ca(2+) intake, misfolding, retrograde transport and diminished secretion of antiangiogenic TSP1, thus enabling angiogenic switch during RCC progression.

The Ontogeny of Definitive Hematopoiesis in the Zebrafish.

Shifting sites of blood cell production during development is common across widely divergent phyla. In zebrafish, like other vertebrates, hematopoietic development has been roughly divided into two waves, termed primitive and definitive. Primitive hematopoiesis is characterized by the generation of embryonic erythrocytes in the intermediate cell mass and a distinct population of macrophages that arises from cephalic mesoderm. The generation of definitive, or multilineage, hematopoietic precursors during embryogenesis remains less well understood. Here we show, using a combination of gene expression analyses, prospective isolation approaches, hematopoietic progenitor cultures, transplantation, and in vivo lineage tracing experiments, that definitive hematopoiesis initiates through committed erythromyeloid progenitors (EMPs) in the posterior blood island (PBI) that arise independently of hematopoietic stem cells (HSCs). EMPs isolated by coexpression of fluorescent transgenes driven by the lmo2 and gata1 promoters exhibit an immature, blastic morphology and express only erythroid and myeloid genes. Transplanted EMPs home to the PBI, show limited proliferative potential, and do not seed subsequent hematopoietic sites such as the thymus or pronephros. In vivo fate mapping studies similarly demonstrate that EMPs possess only transient proliferative potential, with differentiated progeny remaining largely within caudal hematopoietic tissue. By contrast, fate mapping studies of CD41:eGFP+ cells residing in the aorta/gonads/mesonephros (AGM) region demonstrate robust colonization of the pronephros and thymus. Using timelapse microscopy, we show that these sites of adult hematopoiesis are seeded by CD41+ cells that migrate along the pronephric ducts from the AGM. These studies provide phenotypic and functional analyses of the first hematopoietic stem and progenitor cells in the zebrafish embryo and demonstrate that definitive hematopoiesis proceeds through two distinct waves during embryonic development.

Mechanisms of Electrically Mediated Cytosolic Ca 2+ Transients in Aequorin-Transformed Tobacco Cells

Cytosolic Ca 2+ changes induced by electric field pulses of 50- μs duration and 200–800 V/cm strength were monitored by measuring chemiluminescence in aequorin-transformed BY-2 tobacco cells. In Ca 2+-substituted media, electropulsing led to a very fast initial increase of the cytosolic Ca 2+ concentration reaching a peak value within <100–200 ms. Peaking of [Ca 2+] cyt was followed by a biphasic decay due to removal of Ca 2+ (e.g., by binding and/or sequestration in the cytosol). The decay had fast and slow components, characterized by time constants of ∼0.5 and 3–5 s, respectively. Experiments with various external Ca 2+ concentrations and conductivities showed that the fast decay arises from Ca 2+ fluxes through the plasmalemma, whereas the slow decay must be assigned to Ca 2+ fluxes through the tonoplast. The amplitude of the [Ca 2+] cyt transients increased with increasing field strength, whereas the time constants of the decay kinetics remained invariant. Breakdown of the plasmalemma was achieved at a critical field strength of ∼450 V/cm, whereas breakdown of the tonoplast required ∼580 V/cm. The above findings could be explained by the transient potential profiles generated across the two membranes in response to an exponentially decaying field pulse. The dielectric data required for calculation of the tonoplast and plasmalemma potentials were derived from electrorotation experiments on isolated vacuolated and evacuolated BY-2 protoplasts. The electrorotation response of vacuolated protoplasts could be described in terms of a three-shell model (i.e., by assuming that the capacitances of tonoplast and plasmalemma are arranged in series). Among other things, the theoretical analysis together with the experimental data show that genetic manipulations of plant cells by electrotransfection or electrofusion must be performed in low-conductivity media to minimize release of vacuolar Ca 2+ and presumably other vacuolar ingredients.

Characterization of the vasorelaxant mechanisms of the endocannabinoid anandamide in rat aorta

Studies in isolated preparations of vascular tissue (mainly resistance vessels) provide evidence that anandamide exerts vasorelaxation. The aim of the present work was to further characterize the mechanisms involved in the vascular response induced by anandamide in a conduit vessel, rat aorta. Isometric tension changes in response to a cumulative concentration-response curve of anandamide (1 nM-100 micro M) were recorded in aortic rings from male Wistar rats. The involvement of a number of factors in this relaxation was investigated including endothelium-derived vasorelaxant products, cannabinoid and vanilloid receptors (transient potential vanilloid receptor-1 (TRPV1)), release of calcitonin gene-related peptide (CGRP), anandamide metabolism and the membrane transporter for anandamide. Anandamide caused a significant concentration-dependent vasorelaxation in rat aorta. This vasorelaxation was significantly inhibited by Pertussis toxin, by a non-CB1/non-CB2 cannabinoid receptor antagonist, by endothelial denudation, by inhibition of nitric oxide synthesis or inhibition of prostanoid synthesis via cyclooxygenase-2 (COX-2), by blockade of prostaglandin receptors EP4 and by a fatty acid amino hydrolase inhibitor. Antagonists for CB1, CB2, TRPV1 or CGRP receptors, an inhibitor of the release of endothelium-derived hyperpolarizing factor, and an inhibitor of anandamide transport did not modify the vascular response to anandamide. Our results demonstrate, for the first time, the involvement of the non-CB1/non-CB2 cannabinoid receptor and an anandamide-arachidonic acid-COX-2 derived metabolite (which acts on EP4 receptors) in the endothelial vasorelaxation caused by anandamide in rat aorta.

Definitive hematopoiesis initiates through a committed erythromyeloid progenitor in the zebrafish embryo

Shifting sites of blood cell production during development is common across widely divergent phyla. In zebrafish, like other vertebrates, hematopoietic development has been roughly divided into two waves, termed primitive and definitive. Primitive hematopoiesis is characterized by the generation of embryonic erythrocytes in the intermediate cell mass and a distinct population of macrophages that arises from cephalic mesoderm. Based on previous gene expression studies, definitive hematopoiesis has been suggested to begin with the generation of presumptive hematopoietic stem cells (HSCs) along the dorsal aorta that express c-myb and runx1. Here we show, using a combination of gene expression analyses, prospective isolation approaches, transplantation, and in vivo lineage-tracing experiments, that definitive hematopoiesis initiates through committed erythromyeloid progenitors (EMPs) in the posterior blood island (PBI) that arise independently of HSCs. EMPs isolated by coexpression of fluorescent transgenes driven by the lmo2 and gata1 promoters exhibit an immature, blastic morphology and express only erythroid and myeloid genes. Transplanted EMPs home to the PBI, show limited proliferative potential, and do not seed subsequent hematopoietic sites such as the thymus or pronephros. In vivo fate-mapping studies similarly demonstrate that EMPs possess only transient proliferative potential, with differentiated progeny remaining largely within caudal hematopoietic tissue. Additional fate mapping of mesodermal derivatives in mid-somitogenesis embryos suggests that EMPs are born directly in the PBI. These studies provide phenotypic and functional analyses of the first hematopoietic progenitors in the zebrafish embryo and demonstrate that definitive hematopoiesis proceeds through two distinct waves during embryonic development.

The Effect of Transient Potential Exposure on the Electrochemical Oxidation of Carbon Black in Low-Temperature Fuel Cells

The electrochemical oxidation of carbon black catalyst supports is recognized as a durability challenge to the commercialization of low-temperature fuel cells in the transportation sector. An investigation in the effect of the transient potentials experienced in this environment is presented. The exposure of carbon black to square wave potential cycling results in an oxidation process different than the constant potential hold historically used to characterize this corrosion process. The differences are characterized using the liquid half cell and single fuel cell testing coupled with electrochemical techniques and inline gas analysis. Although cyclic voltammetry and XPS are unable to quantify significant differences in the surface oxide chemistry, inline gas analysis measurements demonstrate different corrosion activities.