Contribution of aboveground litter,belowground litter,and rhizosphere respiration to total soil CO<Subscript>2</Subscript> efflux in an old growth coniferous forest

In an old growth coniferous forest located in the central Cascade Mountains, Oregon, we added or removed aboveground litter and terminated live root activity by trenching to determine sources of soil respiration. Annual soil efflux from control plots ranged from 727 g C m⁻² year⁻¹ in 2002 to 841 g C m⁻² year⁻¹ in 2003. We used aboveground litter inputs (149.6 g C m⁻² year⁻¹) and differences in soil CO₂ effluxes among treatment plots to calculate contributions to total soil efflux by roots and associated rhizosphere organisms and by heterotrophic decomposition of organic matter derived from aboveground and belowground litter. On average, root and rhizospheric respiration (R_r) contributed 23%, aboveground litter decomposition contributed 19%, and belowground litter decomposition contributed 58% to total soil CO₂ efflux, respectively. These values fall within the range of values reported elsewhere, although our estimate of belowground litter contribution is higher than many published estimates, which we argue is a reflection of the high degree of mycorrhizal association and low nutrient status of this ecosystem. Additionally, we found that measured fluxes from plots with doubled needle litter led to an additional 186 g C m⁻² year⁻¹ beyond that expected based on the amount of additional carbon added; this represents a priming effect of 187%, or a 34% increase in the total carbon flux from the plots. This finding has strong implications for soil C storage, showing that it is inaccurate to assume that increases in net primary productivity will translate simply and directly into additional belowground storage.     

Effects of overexpression of pancreatic derived factor (FAM3B) in isolated mouse islets and insulin-secreting betaTC3 cells

PANcreatic DERived factor (PANDER, FAM3B) is a recently discovered islet-specific cytokine. We have previously shown that, in vitro, truncated recombinant PANDER isoforms (20 and 21 kDa) are cytotoxic to beta-cell lines but the effects of full-length PANDER on islet biology remain unclear. In this study, we used adenovirus (Ad-PANDER) to overexpress full-length cDNA of PANDER in islets and betaTC3 cells. BetaTC3 cells were infected with Ad-PANDER or control vector. After 48 h, cell viability was significantly decreased as evaluated by MTT assay. The number of dead cells was significantly increased as indicated by the fluorescent intensity of the propidium iodide-stained cells (160 +/- 13 vs. control 100 +/- 7%, P = 0.001). Flow cytometric Tunel assay showed that overexpressing PANDER induced a significant fourfold increase in beta-cell apoptosis (19.4 +/- 6.3 vs. control 4.1 +/- 0.8%, P < 0.05). There was a significant increase in the number of annexin V-positive (apoptotic) cells and propidium iodide-positive (dead) cells in mouse islets infected with Ad-PANDER compared with control cells infected with Ad-LacZ. Addition of 4 nM recombinant PANDER protein to betaTC3 cells or infection of Ad-PANDER did not affect Akt and STAT1 phosphorylation, Bcl-2, Fas, and NF-kappaB protein levels. However, activation of caspase-3 was observed in betaTC3 and islets infected with Ad-PANDER. Overexpression of PANDER in mouse islets or addition of recombinant PANDER decreased insulin secretion induced by carbachol plus glucose or high potassium but not that by glucose alone. Culture with recombinant PANDER did not affect glucose-induced NAD(P)H elevation in mouse islets. In conclusion, Ad-PANDER infection is as effective as truncated recombinant PANDER to induce betaTC3 cell and mouse islet apoptosis.     

Vessels and nerves: marching to the same tune

The patterning of the nervous system is achieved through coordinated action of a variety of repulsive or attractive neuronal guidance factors that direct the growth of growing axons to specific pathways. Recent studies suggest that the same or similar sets of factors also guide migration of endothelial cells, helping to direct the stereotypical embryonic patterning of the developing vertebrate vascular system.     

Semaphorin-plexin signaling guides patterning of the developing vasculature

Major vessels of the vertebrate circulatory system display evolutionarily conserved and reproducible anatomy, but the cues guiding this stereotypic patterning remain obscure. In the nervous system, axonal pathways are shaped by repulsive cues provided by ligands of the semaphorin family that are sensed by migrating neuronal growth cones through plexin receptors. We show that proper blood vessel pathfinding requires the endothelial receptor PlexinD1 and semaphorin signals, and we identify mutations in plexinD1 in the zebrafish vascular patterning mutant out of bounds. These results reveal the fundamental conservation of repulsive patterning mechanisms between axonal migration in the central nervous system and vascular endothelium during angiogenesis.     

Low,but not high,doses of melatonin entrained a free-running blind person with a long circadian period

In a previous report, we were unable to entrain one out of seven totally blind people with free-running endogenous melatonin rhythms to 10 mg of exogenous melatonin. This person had the longest circadian period (24.9 h) of the group. We now find that this person can be entrained to 0.5 mg of melatonin, but not to 20 mg. These results are consistent with the idea that too much melatonin may spill over onto the wrong zone of the melatonin phase-response curve.     

Phosphatidylinositol 3-Kinase γ Is Required for the Development of Experimental Cerebral Malaria

Experimental cerebral malaria (ECM) is characterized by a strong immune response, with leukocyte recruitment, blood-brain barrier breakdown and hemorrhage in the central nervous system. Phosphatidylinositol 3-kinase γ (PI3Kγ) is central in signaling diverse cellular functions. Using PI3Kγ-deficient mice (PI3Kγ^-/-) and a specific PI3Kγ inhibitor, we investigated the relevance of PI3Kγ for the outcome and the neuroinflammatory process triggered by Plasmodium berghei ANKA (PbA) infection. Infected PI3Kγ^-/- mice had greater survival despite similar parasitemia levels in comparison with infected wild type mice. Histopathological analysis demonstrated reduced hemorrhage, leukocyte accumulation and vascular obstruction in the brain of infected PI3Kγ^-/- mice. PI3Kγ deficiency also presented lower microglial activation (Iba-1+ reactive microglia) and T cell cytotoxicity (Granzyme B expression) in the brain. Additionally, on day 6 post-infection, CD3⁺CD8⁺ T cells were significantly reduced in the brain of infected PI3Kγ^-/- mice when compared to infected wild type mice. Furthermore, expression of CD44 in CD8+ T cell population in the brain tissue and levels of phospho-IkB-α in the whole brain were also markedly lower in infected PI3Kγ^-/- mice when compared with infected wild type mice. Finally, AS605240, a specific PI3Kγ inhibitor, significantly delayed lethality in infected wild type mice. In brief, our results indicate a pivotal role for PI3Kγ in the pathogenesis of ECM.     

Patterns and Mechanisms of Nutrient Resorption in Plants

Nutrient resorption (NR) plays a key role in the nutrient conservation of plants. However, a fundamental understanding of the mechanisms that control NR remains limited. In this review, we examine how intrinsic controls (e.g., genetic variability and plant development) and extrinsic environmental controls (e.g., climate and soil fertility) influence NR. We also examined conceptual NR advances, mass loss correction, measurement in non-leaf plant tissues for whole-plant nutrient budget accounting, and the use of stoichiometric ratios in place of individual elements. Nutrient resorption from senescing leaves is greater than that from stems/culms or roots. Nutrients resorbed from stems and roots in woody plants are lower than in non-woody plants. Deciduous plants are more efficient in resorbing leaf nutrients prior to senescence than are evergreen plants. Furthermore, reproductive efforts tend to increase NR. Along a latitudinal gradient of terrestrial biomes, nitrogen resorption efficiency decreases and phosphorus resorption efficiency increases with increasing temperature and precipitation; however, latitudinal patterns reflect the influences of several coupling factors such as genetic variation, climate, soil, and disturbance history. Nutrient fertilization experiments have demonstrated that increased soil fertility reduces NR. The inquiries into the impacts of ongoing climate change on NR are still at a nascent stage. Future NR studies are needed to better understand the independent effects of a wide range of genetic variation, plant development, and environment, and possibly the different responses of plants to environmental change; particularly elevated atmospheric CO₂ concentrations and global warming.     

Rapid generation of long tandem DNA repeat arrays by homologous recombination in yeast to study their function in mammalian genomes

We describe here a method to rapidly convert any desirable DNA fragment, as small as 100 bp, into long tandem DNA arrays up to 140 kb in size that are inserted into a microbe vector. This method includes rolling-circle phi29 amplification (RCA) of the sequence in vitro and assembly of the RCA products in vivo by homologous recombination in the yeast Saccharomyces cerevisiae. The method was successfully used for a functional analysis of centromeric and pericentromeric repeats and construction of new vehicles for gene delivery to mammalian cells. The method may have general application in elucidating the role of tandem repeats in chromosome organization and dynamics. Each cycle of the protocol takes ~ two weeks to complete.