Ischemic Preconditioning in the Liver Is Independent of Regulatory T Cell Activity

Ischemic preconditioning (IPC) protects organs from ischemia reperfusion injury (IRI) through unknown mechanisms. Effector T cell populations have been implicated in the pathogenesis of IRI, and T regulatory cells (Treg) have become a putative therapeutic target, with suggested involvement in IPC. We explored the role of Treg in hepatic IRI and IPC in detail. IPC significantly reduced injury following ischemia reperfusion insults. Treg were mobilized rapidly to the circulation and liver after IRI, but IPC did not further increase Treg numbers, nor was it associated with modulation of circulating pro-inflammatory chemokine or cytokine profiles. We used two techniques to deplete Treg from mice prior to IRI. Neither Treg depleted FoxP3.LuciDTR mice, nor wildtyoe mice depleted of Tregs with PC61, were more susceptible to IRI compared with controls. Despite successful enrichment of Treg in the liver, by adoptive transfer of both iTreg and nTreg or by in vivo expansion of Treg with IL-2/anti-IL-2 complexes, no protection against IRI was observed.We have explored the role of Treg in IRI and IPC using a variety of techniques to deplete and enrich them within both the liver and systemically. This work represents an important negative finding that Treg are not implicated in IPC and are unlikely to have translational potential in hepatic IRI.     

Symbiosis research, technology, and education: Proceedings of the 6th International Symbiosis Society Congress held in Madison Wisconsin, USA, August 2009

Symbiosis, the intimate association between two or more organisms, is a fundamental component of biological systems. Our ability to understand the processes involved in the establishment and function of Symbiosis has critical consequences for the health of humans and the world we live in. For example, a deeper understanding of how legumes and insects have harnessed the nitrogen-fixing capacity of microbes can pave the way toward novel strategies to decrease fertilizer use. Also, using insect models to elucidate links between diet, gut microbiota, and toxin sensitivity not only has implications for biological control strategies, but also will lend insights into similar links in the human gut ecosystem. These types of ideas were presented and discussed at the 6th International Symbiosis Society Congress held in Madison, Wisconsin August, 2009. Over 300 participants from 20 countries attended the 7-day event, which featured cutting-edge symbiosis research from many different perspectives and disciplines. The conference was organized thematically, with oral sessions focused on Evolution, Ecology, Metabolism, the Host-Microbe Interface, Threats to Earth Systems, Symbiosis Models and the Human Microbiome, Viruses and Organelles, and Symbiosis Education. World-renowned scientists, post-doctoral fellows, and students were given the opportunity to describe their most recent discoveries. Session chairs provided overviews of their programs which highlight how the comparative analysis of different systems reveal common trends underlying symbiotic associations, what tools and theory are being developed that may be applied more broadly in symbiosis research, how symbiosis research contributing solutions to global issues such as emerging antibiotic resistance, a need for alternative energy sources, the pursuit of sustainable agriculture and natural resources, and how symbiotic systems are ideal for educating people about the fascinating natural world around us. The following paragraphs provide an overview of the research and discussions that took place during the congress.     

Homoploid hybrid speciation in a rare endemic Castilleja from Idaho (Castilleja christii,Orobanchaceae)

• Premise of the study: Hybridization is an important evolutionary force in the history of angiosperms; however, there are few examples of stabilized species derived through homoploid hybrid speciation. Homoploid hybrid species are generally detected via the presence of genetic additivity of parental markers, novel ecological and spatial distinctions, and novel morphological traits, all of which may aid in the successful establishment of hybrid species from parental types. Speciation and diversification within the genus Castilleja (Orobanchaceae) has been attributed to high levels of hybridization and polyploidy, though currently there are no examples of homoploid hybrid speciation within the genus. We employed multiple lines of evidence to examine a putative hybrid origin in C. christii, a rare endemic, known only from 80 hectares at the summit of Mt. Harrison (Cassia Co., Idaho). • Methods: We used granule-bound starch synthase II (waxy) sequences and 26 morphological characters to address hybridization between C. christii and widespread congeners C. miniata and/or C. linariifolia in an area of sympatry. Chromosomes of C. christii were also counted for the first time. • Key results: All 230 direct-sequenced C. christii individuals had the additive genomes of both C. miniata and C. linariifolia. Castilleja christii shares traits with both parents but also has floral characters that are unique and transgressive. Cytological counts indicated that all three taxa are diploid. • Conclusions: We conclude that C. christii is a stabilized homoploid hybrid derivative of C. linariifolia and C. miniata and is likely following an independent evolutionary trajectory from its progenitors.     

Tree mycorrhizal type predicts within‐site variability in the storage and distribution of soil organic matter

Forest soils store large amounts of carbon (C) and nitrogen (N), yet how predicted shifts in forest composition will impact long‐term C and N persistence remains poorly understood. A recent hypothesis predicts that soils under trees associated with arbuscular mycorrhizas (AM) store less C than soils dominated by trees associated with ectomycorrhizas (ECM), due to slower decomposition in ECM‐dominated forests. However, an incipient hypothesis predicts that systems with rapid decomposition—e.g. most AM‐dominated forests—enhance soil organic matter (SOM) stabilization by accelerating the production of microbial residues. To address these contrasting predictions, we quantified soil C and N to 1 m depth across gradients of ECM‐dominance in three temperate forests. By focusing on sites where AM‐ and ECM‐plants co‐occur, our analysis controls for climatic factors that covary with mycorrhizal dominance across broad scales. We found that while ECM stands contain more SOM in topsoil, AM stands contain more SOM when subsoil to 1 m depth is included. Biomarkers and soil fractionations reveal that these patterns are driven by an accumulation of microbial residues in AM‐dominated soils. Collectively, our results support emerging theory on SOM formation, demonstrate the importance of subsurface soils in mediating plant effects on soil C and N, and indicate that shifts in the mycorrhizal composition of temperate forests may alter the stabilization of SOM.     

ULTRASTRUCTURE AND SYSTEMATICS OF TWO NEW FRESHWATER RED CRYPTOMONADS, STOREATULA RHINOSA, SP. NOV. AND PYRENOMONAS OVALIS, SP. NOV.

The ultrastructure and systematics of two red colored freshwater cryptomonads, Storeatula rhinosa , sp. nov. and Pyrenomonas ovalis , sp. nov., are described for the first time. Storeatula, which had been described from marine waters only, has a single inner periplast sheet and a fibrous surface periplast component. Cells lack a furrow but possess a gullet, a bilobed chloroplast connected by a pyrenoid and a nucleomorph located in an indentation of the pyrenoid. This freshwater Storeatula possesses the same general features as the marine species, but it has a contractile vacuole and lacks the lobed chloroplast of S. major. P. ovalis has the generic characteristics described for marine species of Rhodomonas. These characteristics include a short furrow, a deep gullet, square inner periplast plates with beveled corners, a slightly fibrillar surface periplast component, a single chloroplast with two lobes connected by a pyrenoidal bridge and a nucleomorph located in an indentation of the pyrenoid.     

The solution structure and activation of visual arrestin studied by small-angle X-ray scattering.

Visual arrestin is converted from a 'basal' state to an 'activated' state by interaction with the phosphorylated C-terminus of photoactivated rhodopsin (R*), but the conformational changes in arrestin that lead to activation are unknown. Small-angle X-ray scattering (SAXS) was used to investigate the solution structure of arrestin and characterize changes attendant upon activation. Wild-type arrestin forms dimers with a dissociation constant of 60 micro m. Small conformational changes, consistent with local movements of loops or the mobile N- or C-termini of arrestin, were observed in the presence of a phosphopeptide corresponding to the C-terminus of rhodopsin, and with an R175Q mutant. Because both the phosphopeptide and the R175Q mutation promote binding to unphosphorylated R*, we conclude that arrestin is activated by subtle conformational changes. Most of the arrestin will be in a dimeric state in vivo. Using the arrestin structure as a guide [Hirsch, J.A., Schubert, C., Gurevich, V.V. & Sigler, P.B. (1999) Cell 97, 257-269], we have identified a model for the arrestin dimer that is consistent with our SAXS data. In this model, dimerization is mediated by the C-terminal domain of arrestin, leaving the N-terminal domains free for interaction with phosphorylated R*.     

QUANTITATIVE VARIATION OF PROGENY FROM CHASMOGAMOUS AND CLEISTOGAMOUS FLOWERS IN THE GRASS DANTHONIA SPICATA

Progeny from chasmogamous (CH) and cleistogamous (CL) flowers of the grass Danthonia spicata were raised in their native habitat and in the greenhouse in order to determine how genetic variation was distributed among families and between CH and CL progeny within families. Twelve quantitative characters were measured on clones from individuals known to have arisen from either CH or CL flowers on a particular plant. Significant genetic variation existed for all characters measured. Most genetic variation was between families and two morphologically similar groups of families were identified. Relatively little genetic variation was found within families (approximately 5% of the total phenotypic variance). In field-raised plants, variance component analysis suggested that CL progeny were genetically more similar to each other than were CH progeny from the same plant. Levene's test of the average deviation of CH and CL progenies from their group means was nonsignificant but suggested there was a trend (0.05 < P < 0.10) for CH progeny to be more variable than CL progeny in the field but less variable in the greenhouse. The amount and distribution of genetic variation in the study population indicates that selective differentials would be larger among families than within families.     

THE FEEDING MECHANISM OF AVIAN MALARIAL PARASITES

Electron microscope studies of the erythrocytic forms, including gametocytes and asexual schizonts, of the protozoa Plasmodium fallax, P. lophurae, and P. cathemerium, have revealed a "cytostome," a specialized organelle of the pellicular membrane which is active in the ingestion of host cell cytoplasm. In material fixed in glutaraldehyde and postfixed in OsO₄, the cytostome appears in face view as a pore limited by two dense circular membranes and having an inside diameter of approximately 190 mµ. In cross-section, the cytostome is a cavity bounded on each side by two dense segments corresponding to the two dense circles observed in face view; its base consists of a single unit membrane. In the process of feeding, the cytostome cavity enlarges by expansion of its membrane, permitting a large quantity of red cell cytoplasm to come into contact with the cytostome wall. Subsequent digestion of erythrocyte cytoplasm occurs exclusively in food vacuoles which emanate from the cytostome invagination. As digestion progresses, the food vacuoles initially stain more densely and there is a marked build-up of hemozoin granules. In the final stage of digestion, a single membrane surrounds a cluster of residual pigment particles and very little of the original host cell cytoplasm remains. The cytostome in exoerythrocytic stages of P. fallax has been observed only in merozoites and does not seem to play the same role in the feeding mechanism.