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At least 271 records · Page 15Linked to original sources
USGS2006

Costimulatory receptors in a teleost fish: Typical CD28, elusive CTLA4

T cell activation requires both specific recognition of the peptide-MHC complex by the TCR and additional signals delivered by costimulatory receptors. We have identified rainbow trout sequences similar to CD28 (rbtCD28) and CTLA4 (rbtCTLA4). rbtCD28 and rbtCTLA4 are composed of an extracellular Ig-superfamily V domain, a transmembrane region, and a cytoplasmic tail. The presence of a conserved ligand binding site within the V domain of both molecules suggests that these receptors likely recognize the fish homologues of the B7 family. The mRNA expression pattern of rbtCD28 and rbtCTLA4 in naive trout is reminiscent to that reported in humans and mice, because rbtCTLA4 expression within trout leukocytes was quickly up-regulated following PHA stimulation and virus infection. The cytoplasmic tail of rbtCD28 possesses a typical motif that is conserved in mammalian costimulatory receptors for signaling purposes. A chimeric receptor made of the extracellular domain of human CD28 fused to the cytoplasmic tail of rbtCD28 promoted TCR-induced IL-2 production in a human T cell line, indicating that rbtCD28 is indeed a positive costimulator. The cytoplasmic tail of rbtCTLA4 lacked obvious signaling motifs and accordingly failed to signal when fused to the huCD28 extracellular domain. Interestingly, rbtCTLA4 and rbtCD28 are not positioned on the same chromosome and thus do not belong to a unique costimulatory cluster as in mammals. Finally, our results raise questions about the origin and evolution of positive and negative costimulation in vertebrate immune systems. T cell activation is initiated through complex cell-to-cell interactions. TCRs expressed on the surface of T cells first recognize antigenic peptides presented by MHC molecules on the surface of APCs. TCRs and other surface receptors and ligands stabilize the contact between T cells and APCs, which triggers signal transduction pathways resulting in T cell activation. According to the two-signal model ( 1 , 2 ), T cell activation by Ag requires both specific recognition of the peptide by the TCR (signal 1) and additional signals delivered by other costimulatory receptors (signal 2). Among the known costimulatory receptors, CD28 and CTLA4 (also known as CD152), which are expressed on T cells and bind their corresponding ligands B7-1/B7-2 (CD80/CD86) on APCs, represent a well-studied system in mammals ( 3 ). CD28 is a glycosylated homodimeric protein expressed on the surface of double-positive thymocytes, mature CD4 + T cells, CD11b − CD8 + T cells, and γδ CD3 + T cells ( 4 , 5 ). CD28 is expressed at higher levels on activated T cells than on resting cells ( 6 ). In mammals, CD28 binds to B7-1 and B7-2, which are expressed on the surface of APCs, and delivers a critical costimulatory signal to T lymphocytes. In the absence of CD28 ligation, TCR binding either induces apoptosis or anergy in T cells ( 5 ). Engagement of CD28 alone cannot activate T cells, even if synergetic effects are provided via stimulation by T cell mitogens or anti-CD3 treatment ( 7 ). A tyrosine-based motif in cytoplasmic tail of CD28 functions as a binding site for the p85 PI3K subunit when it is phosphorylated ( 8 , 9 ). Other CD28 intracytoplasmic motifs, which associates with IL-2-inducible tyrosine kinase, lymphocyte-specific tyrosine kinase, and the adaptor growth-factor receptor bound protein-2 are responsible for signal transduction ( 10 , 11 , 12 ). The binding of growth-factor receptor bound protein-2 to CD28 also activates the GTPase RAS ( 13 ). CD28 signaling is also thought to contribute to the mobilization of lipid rafts to the immunological synapse ( 14 ), the region of contact between T cell and APC, which lowers the overall threshold of TCR engagement required for effective cytokine production and proliferation ( 15 ). In contrast, CTLA4 is a powerful negative regulator of T cell activation and was first cloned via differential screening of a cytotoxic T cell cDNA library ( 16 ). CD28 and CTLA4 belong to the same family and share high sequence similarity to each other ( 16 , 17 ). Both receptors interact with B7-1 and/or B7-2 but induce different signals: CD28 amplifies signaling triggered by the TCR-CD3 complex, whereas CTLA4 generates negative signals that inhibit T cell activation ( 18 ). CTLA4 has higher affinity for B7-1 and B7-2 compared with CD28, and its expression is also induced by TCR engagement ( 19 ). The mechanisms of CTLA4-mediated suppression likely involve both competition with CD28 for B7-1/B7-2 binding and potent inhibitory signals delivered by CTLA4 ( 20 ). The inhibitory signaling mechanisms triggered by CTLA4 are not clear. The CTLA4 cytoplasmic tail lacks typical ITIM motifs and shares with CD28 a p85 binding site ( 21 ). Thus, the extent of an immune response is likely controlled through the finely tuned expression of costimulatory receptors from the CD28/CTLA4 family on the surface of activated T cells ( 22 , 23 ). Very little is known about T cell responses and activation in bony fish. TCR-αβ cDNAs ( 24 , 25 , 26 , 27 ) and polymorphic class IA and class IIA/B MHC molecules ( 28 , 29 , 30 ) have been reported in several species, suggesting that the fish TCR recognizes antigenic peptides presented by MHC molecules similar to that of mammals. T cell-mediated responses in fish are supported by several lines of evidence. Allograft rejection provided the first experimental indications suggesting that bony fish possess a functional T cell-mediated immune response ( 31 , 32 ). In vitro assays for allospecific cytotoxicity have also been established using clonal and nonclonal catfish cell lines ( 33 , 34 ) or clonal rainbow trout ( 35 ). Autologous cell-mediated specific lysis of virus-infected syngenic target cells has also been reported in cloned goldfish ( 36 , 37 ). Finally, both public and private T cell-specific expansions have been observed in rainbow trout during secondary immune responses to viral hemorrhagic septicemia virus (VHSV), 3 a fish rhabdovirus, using TCR-β CDR3-length spectratyping ( 38 ). TCR-MHC-peptide interactions induce signaling events through CD3 in mammals and most likely in lower vertebrates because a complete set of CD3 genes, including TCR ζ, CD3 ε, and CD3 γδ, has been found in Pufferfish and Xenopus ( 39 , 40 ). CD8α has been identified in rainbow trout ( 41 ); however, the cytoplasmic tail lacks the consensus p56 lck motif, suggesting that TCR/CD3/CD8-mediated signaling events may be different in teleosts. In this study, we have identified and initially characterized two members of the CD28 family in rainbow trout, rbtCD28 and rbtCTLA4. Their sequence features and expression patterns suggest that they are the likely homologues of mammalian CD28 and CTLA4. The potential costimulatory capacities of these fish receptors were investigated using a human T cell line expressing chimeric receptors composed of the extracellular domain of human CD28 (hCD28) fused to the cytoplasmic tail of rbtCD28 or rbtCTLA4. The chimeric hCD28-rbtCD28 receptor mediated enhanced TCR-induced IL-2 production, suggesting a costimulatory function for rbtCD28. In contrast, the divergent cytoplasmic tail from rbtCTLA4 did not mediate similar signaling activities. This study therefore provides the first characterization of costimulatory receptors in lower vertebrates.

Journal of Immunology↗
USGS2018

Mercury on a landscape scale—Balancing regional export with wildlife health

The Cosumnes River watershed requires a 57–64 percent reduction in loads to meet the new Delta methylmercury (MeHg) total maximum daily load allocation, established by the Central Valley Regional Water Quality Control Board. Because there are no large point sources of MeHg in the watershed, the focus of MeHg load reductions will fall upon non-point sources, particularly the expansive wetlands considered to be a primary source of MeHg in the region. Few management practices have been implemented and tested in order to meet load reductions in managed wetlands, but recent efforts have shown promise. This project examines a treatment approach to reduce MeHg loads to the Sacramento-San Joaquin River Delta by creating open-water deep cells with a small footprint at the downstream end of wetlands to promote net demethylation of MeHg and to minimize MeHg and Hg loads exiting wetlands at the Cosumnes River Preserve. Specifically, the deep cells were were located immediately up gradient of the wetland’s outflow weir and were deep enough (75–91 centimeter depth) to be vegetation-free. The topographic and hydrologic structure of each treatment wetland was modified to include open-water deep cells so that the removal of aqueous MeHg might be enhanced through (1) particle settling, (2) photo-degradation, and (3) benthic microbial demethylation. These deep cells were, therefore, expected to clean MeHg from surface water prior to its discharge to the Cosumnes River and the downstream Delta. Our goal was to test whether the implementation of the deep cells within wetlands would minimize MeHg and total Hg export. Further, we sought to test whether continuous flow-through hydrology, would lower MeHg concentrations in resident biota, compared to traditional wetland management operations. The dominant practice in seasonal wetlands management is the “fill-and-maintain” approach, in which wetlands are filled with water and the water levels maintained without substantial draining until drawdown. Our approach was to create and characterize replicate treatment wetland complexes, in conjunction with monitoring of hydrologic, biologic, and chemical indicators of MeHg exposure for two full annual cycles within winter-spring flooded seasonal wetlands. In addition to the creation of deep cells within treatment wetlands, hydrology was manipulated so that there was a constant flow-through of water, while the control wetlands utilized the fill-and-maintain approach. Specifically, the treatment wetlands were maintained in a flow-through manner, while the control wetlands were maintained in a fill-and-maintain manner from September through May, to test the hypothesis that the flow of water through the seasonal wetland can lower fish bioaccumulation through dilution of MeHg-concentrated water within the wetland by constant inflows of water into the wetland. The major tasks of this study included: (1) field design and implementation, (2) water and wetland management, (3) hydrologic monitoring and water quality sampling, (4) MeHg export and load estimates, (5) caged fish experiments for examining MeHg bioaccumulation, (6) site and process characterization to improve understanding and transferability of results, (7) adaptive management, transferability, and outreach, and (8) reporting of results and conclusions. This report summarizes the key findings of this study, which focuses on MeHg load estimates from control and treatment wetlands, quantification of three MeHg removal mechanisms (particulate settling, benthic demethylation, and photo-demethylation) in the deep cells within the treatment wetlands, and MeHg bioaccumulation in wetland fishes. Key findings include: Over two years of study, mean whole-water MeHg load decreased 37 percent in deep cells, when comparing inlet of check weir flows to outlet. Of the 37 percent MeHg load removed within the deep cell, photodegradation accounted for 7 percent and particle flux to the benthos accounted for 24 percent of the mass removed, with the remaining 6 percent apparent MeHg loss unexplained. Benthic MeHg degradation did not appear to be a major MeHg removal process in the deep cells, as changes in the ambient MeHg pool over 7-day bottle incubations showed that the surface sediment exhibited net MeHg production in the majority (87 percent) of incubation experiments. In only 13 percent of the incubations (3 out of 24) was net MeHg degradation observed. Estimates of benthic diffusive flux of MeHg across the sediment/water interface were small relative to particulate flux and variable (positive or negative), suggesting this is likely a minor term in the overall MeHg budget within the deep cells. Although the deep cells served as net MeHg sink overall, MeHg export from the flow-through treatment wetlands (shallow and deep combined) exceeded export from the fill-and-maintain managed control wetlands, because of the differences in hydrologic management between the two wetland types. Shallow wetlands under flow-through conditions generated a net export of MeHg. Most of the annual MeHg export from the treatment wetlands occurred within the first 3 months of flood up (September to November), shortly after hydrologic management began. Despite the effectiveness of the deep cell in lowering MeHg export concentrations, total mercury (THg) concentration did not decrease in biosentinel fish ( Gambusia affinis , Mosquitofish) between the deep cell inlet and outlet. Mosquitofish THg concentrations were higher in treatment wetlands than in control wetlands during the first year of study, likely because of an associated increase in MeHg availability immediately following wetland construction activities. Mosquitofish THg concentrations declined in the treatment wetlands during the second year of study, and fish THg concentrations in treatment wetlands were no different from those in the control. Similarly, the increased hydrologic flow rates in the treatment wetlands did not lower fish THg concentrations nor aqueous MeHg concentrations in the shallow cells, suggesting that MeHg flux from the sediment to water column exceeded the flow-through flushing rate in the shallow portion of the treatment wetlands. Reductions in MeHg concentrations of surface water and fish may require higher flow rates than used in the study to achieve the region’s regulatory goals. However, the flow rates necessary may not be feasible for these managed wetlands because of limited water supply and the associated costs for water and pumping. The use of deep cells in seasonal wetlands were effective in lowering MeHg exports under continuous water flow-through hydrology. However, fill-and-maintain hydrology had lower exports overall, because of a single major drainage event at the end of the flood season. Future studies focused on limiting MeHg export should consider combining deep cells with the fill-and-maintain or fill-and-trickle hydrologic management approach.

California↗
USGS1985

Automated derivation of hydrologic basin characteristics from digital elevation model data

Digital elevation model (DEM) data in a raster format can be used to automatically derive the drainage characteristics of an area. A procedure has been designed that is capable of operating on matrices of elevation data having no algorithmically imposed size limit, while performing within the resolution and accuracy tolerances of the DEM data. Each cell is processed as the center of a 3- by 3-cell spatial window in the raster elevation data. If a cell is a local minimum in comparison with two of its non-adjacent neighbors, it is labeled as a drainage cell. The linkages of the drainage cells within user-specified distance and elevation thresholds are established in a separate process. The products of these processing steps are digital masks of the drainage cells and the watershed basins, both in raster format. A drainage cell mask derived using this procedure is useful in computing slope values for a raster data base. Slope has traditionally been calculated for each cell by fitting a plane through the eight nearest cells. However, if the terrain represented by these cells is V-shaped, such as a gully, a plane does not fit well; in fact, the desired slope value is the slope along the bottom of the gully, regardless of the steepness of the gully sides. The automated drainage process will label such a cell as a drainage cell, and its slope can then be computed from the elevation values of neighboring drainage cells.

Conference Paper↗
USGS2005

Simulated changes in water levels caused by potential changes in pumping from shallow aquifers of Virginia Beach, Virginia

A steady-state ground-water flow model of the southern watersheds of Virginia Beach, Virginia, was refined and used to simulate changes in aquifer water levels caused by potential changes in pumping in the Transition Area of Virginia Beach, Va., a 20-square mile planning zone that runs through the middle of the city. Cessation of dewatering at borrow pits, pumping to irrigate a golf course, pumping to irrigate lawns of a hypothetical neighborhood, and pumping to irrigate both the golf course and lawns of the hypothetical neighborhood were simulated. Simulated recoveries from cessation of dewatering of borrow pits were generally restricted to the immediate area of the pits. The simulated recoveries averaged about 20 feet (ft) near the center of the cells representing the active areas of the pits and 2 ft at the cells representing the extent of the pits. At a golf course, 4 hypothetical wells pumping 300,000 gallons per day (gal/d) from the Yorktown sand aquifer resulted in drawdowns averaging 10 ft in the pumping cells and 1 ft at a distance of 1.2 miles (mi) from the center of the pumping cells. The extent of the 1-ft drawdown was virtually the same as that simulated previously and reported in a permit application for the golf course. Simulated pumping of 150,000 gal/d from 4 cells in the confined sand aquifer representing a 40-acre neighborhood resulted in drawdowns averaging 7 ft in the pumping cells and 1 ft at a distance of 0.8 mi from the center of the cells. Simulated pumping of 300,000 gal/d from the same 4 cells resulted in drawdowns averaging 15 ft in the pumping cells and 1 ft at a distance of 1.4 mi from the center of the cells. Simulated pumping of 150,000 gal/d at the golf course and another 150,000 gal/d in the hypothetical neighborhood resulted in drawdowns that averaged 5 ft around the cells representing the golf course wells spaced 1,300 ft apart and 7 ft around the contiguous cells representing the 40-acre neighborhood. A drawdown of 1 ft encompassed most of the eastern half of the Transition Area.

Virginia↗
USGS2010

Accounting for intracell flow in models with emphasis on water table recharge and stream-aquifer interaction: 1. Problems and concepts

Intracell flow is important in modeling cells that contain both sources and sinks. Special attention is needed if recharge through the water table is a source. One method of modeling multiple sources and sinks is to determine the net recharge per cell. For example, for a model cell containing both a sink and recharge through the water table, the amount of recharge should be reduced by the ratio of the area of influence of the sink within the cell to the area of the cell. The reduction is the intercepted portion of the recharge. In a multilayer model this amount is further reduced by a proportion factor, which is a function of the depth of the flow lines from the water table boundary to the internal sink. A gaining section of a stream is a typical sink. The aquifer contribution to a gaining stream can be conceptualized as having two parts; the first part is the intercepted lateral flow from the water table and the second is the flow across the streambed due to differences in head between the water level in the stream and the aquifer below. The amount intercepted is a function of the geometry of the cell, but the amount due to difference in head across the stream bed is largely independent of cell geometry. A discharging well can intercept recharge through the water table within a model cell. The net recharge to the cell would be reduced in proportion to the area of influence of the well within the cell. The area of influence generally changes with time. Thus the amount of intercepted recharge and net recharge may not be constant with time. During periods when the well is not discharging there will be no intercepted recharge even though the area of influence from previous pumping may still exist. The reduction of net recharge per cell due to internal interception of flow will result in a model-calculated mass balance less than the prototype. Additionally the “effective transmissivity” along the intercell flow paths may be altered when flow paths are occupied by intercepted recharge.

Water Resources Research↗
USGS2008

Morphology and histology of the alimentary canal of Lygus hesperus (Heteroptera: Cimicomoropha: Miridae)

Microdissection and transverse semithin sections were used to perform a light microscopy survey of the gross morphology and cellular anatomy of the alimentary canal, respectively, of Lygus hesperus Knight, a key pest of cotton (Gossypium hirsutum L.), alfalfa (Medicago sativa L.), and other crops. The gross morphology of the alimentary canal showed a relatively unadorned tube compared with other hemipterans, with variably shaped compartments and one small diverticulum. However, the epithelial cell anatomy of the gut was relatively complex, with the midgut having the most diverse structure and cell types. The midgut was typical of the "Lygus-type gut" seen in the older literature, i.e., it consisted of three major regions, the first (descending), second (ascending), and third (descending) ventriculi, with different variants of three major epithelial cell types in each region. Our light microscopy (LM) study suggests that the three cell types are nondifferentiated regenerative cells (which sparsely occurred throughout the midgut but were abundant in the anterior region of the first ventriculus), endocrine cells, and columnar cells. Although the Lygus gut cells strongly resemble those cell types seen in other insects, their identification should be confirmed via transmission electron microscopy to be considered definitive. These cell types differed in the size and opacity of vesicles, geometry of cell surface in the gut lumen, and size, shape, and concentration of brush-border microvilli and location within the gut. Comparison of gut structure in L. hesperus with that of other hemipterans, especially in relation to hemipteran phylogeny and feeding strategies, is discussed.

Annals of the Entomological Society of America↗
USGS1997

Clonal foraging in perennial wheatgrasses: A strategy for exploiting patchy soil nutrients

1. Foraging by means of plasticity in placement of tillers in response to low- and high-nutrient patches was examined in the rhizomatous wheatgrass Elymus lanceolatus ssp. lanceolatus . Its ability to exploit soil nutrient patches was compared to that of the closely related but caespitose E. lanceolatu s ssp. wawawaiensis . 2. Clones of 14 genets of each taxon were planted in boxes consisting of two 30 × 30 cm cells: the `origin cell' where clones were planted, and the adjacent `destination cell', with each cell containing soil with either low or high levels of nutrients. 3. The rhizomatous taxon, which can produce intravaginal, short-rhizome and long-rhizome tillers, preferentially produced short-rhizome and intravaginal tillers in high-nutrient destination cells. Effects of nutrient status of the origin cell as well as of the destination cell on total tiller numbers indicated clonal integration, yet tiller placement responded to local conditions. 4. Roots of both taxa accessed nutrients in destination cells (the caespitose subspecies by root growth only), and above-ground biomass of both taxa increased to a similar extent with high-nutrient destination cells. With the patch sizes used in this experiment, root growth was as important as ramet placement in exploiting nutrients in destination cells. 5 There was no relationship between degree of plasticity in ramet placement and biomass of the clone when high-nutrient destination cells were present.

Journal of Ecology↗
USGS1976

An evaluation of methods for measuring algal growth

Algal growth was expressed as milligrams dry weight per litre with use of the electronic particle counter for determining cell number and cell volume. A gravimetric constant in milligrams dry weight per cubic micrometre was determined. This constant was applicable throughout the growth curve since there was a linear relationship between total cell weight and total cell volume. Cell volume must be considered in measuring growth because there is a change in average cell volume in addition to an increase in cell numbers throughout the growth curve. Chlorella vulgaris and Selenastrum capricornutum exhibited similar growth curves when growth was expressed as cells per litre or as milligrams dry weight per litre. Chlamydomonas reinhardtii appeared to have a lower algal growth potential when measured in cells per litre but had the same growth potential as C. vulgaris and S. capricornutum when expressed as milligrams dry weight per litre. The growth rate for Scenedesmus quadricauda was less than the other three, regardless of how the results were expressed. The image analysis system was used to count different types of algae in a mixed culture. C. reinhardtii , C. vulgaris , and Anacystis nidulans were not grossly distorted by the sample preparation method and could be distinguished from one another by variations in morphology. The counts could be separated by computing the ratio of area to length for each particle and by allowing the computer to sort and count each of the three types. Typical ratios ranged from 5 to 7 for G. reinhardtii , 2 to 4 C. vulgaris , and 0.2 to 1.3 for A. nidulans . The number of types to be counted in a mixture was limited only by the ability to apply shape factors without having an overlap between each type. Both the image analysis and electronic particle counter produced equal count and size measurements. Fluorescence was a sensitive measure of growth on a laboratory prepared medium since there was a logarithmic relationship between fluorescence and cells per millilitre for both C. vulgaris and S. capricornutum . Fluorescence measurements were not satisfactory for determining growth in samples of varying chemical composition (which occurs in natural samples) because the chlorophyll-to-cell ratio varied with media composition. This was especially pronounced with C. vulgaris .

Journal of Research of the U.S. Geological Survey↗