Nitrogen transformations revealed by isotope dilution in an organically fertilized hybrid poplar plantation

Measuring nitrogen (N) transformations from organic fertilizers can help in selecting applications rates that provide sufficient soluble N to promote tree growth in short-rotation plantations. The objective of this study was to determine how organic fertilizers (papermill biosolids, liquid pig slurry) affected microbially-mediated N transformations in soils. Soil samples were collected from a hybrid poplar plantation before fertilization, 1 month after fertilizer application and at the end of the growing season. Net N mineralization and nitrification were evaluated during a 28 d laboratory incubation, while gross N transformations were assessed using a ¹⁵N isotope dilution technique. Pig slurry application increased soil ammonium (NH₄-N) and nitrate (NO₃-N) concentrations within 1 month, while papermill biosolids increased soil NH₄-N and NO₃-N concentrations at the end of the growing season. Gross N consumption rates were greater than gross N production rates. The NH₄-N and NO₃-N consumption rates were positively correlated with labile carbon and microbial biomass. The gross nitrification rate was 18 to 67% of the gross mineralization rate but 30% or less of the gross NH₄-N consumption rate, indicating that NH₄ consumption was overestimated by the isotope dilution technique. We conclude that N cycling in this hybrid poplar plantation was characterized by rapid consumption of plant-available N following N mineralization and nitrification.     

RasGAP Shields Akt from Deactivating Phosphatases in Fibroblast Growth Factor Signaling but Loses This Ability Once Cleaved by Caspase-3

Fibroblast growth factor receptors (FGFRs) are involved in proliferative and differentiation physiological responses. Deregulation of FGFR-mediated signaling involving the Ras/PI3K/Akt and the Ras/Raf/ERK MAPK pathways is causally involved in the development of several cancers. The caspase-3/p120 RasGAP module is a stress sensor switch. Under mild stress conditions, RasGAP is cleaved by caspase-3 at position 455. The resulting N-terminal fragment, called fragment N, stimulates anti-death signaling. When caspase-3 activity further increases, fragment N is cleaved at position 157. This generates a fragment, called N2, that no longer protects cells. Here, we investigated in Xenopus oocytes the impact of RasGAP and its fragments on FGF1-mediated signaling during G₂/M cell cycle transition. RasGAP used its N-terminal Src homology 2 domain to bind FGFR once stimulated by FGF1, and this was necessary for the recruitment of Akt to the FGFR complex. Fragment N, which did not associate with the FGFR complex, favored FGF1-induced ERK stimulation, leading to accelerated G₂/M transition. In contrast, fragment N2 bound the FGFR, and this inhibited mTORC2-dependent Akt Ser-473 phosphorylation and ERK2 phosphorylation but not phosphorylation of Akt on Thr-308. This also blocked cell cycle progression. Inhibition of Akt Ser-473 phosphorylation and entry into G₂/M was relieved by PHLPP phosphatase inhibition. Hence, full-length RasGAP favors Akt activity by shielding it from deactivating phosphatases. This shielding was abrogated by fragment N2. These results highlight the role played by RasGAP in FGFR signaling and how graded stress intensities, by generating different RasGAP fragments, can positively or negatively impact this signaling.     

Dose-dependent immunomodulation of human dendritic cells by the probiotic Lactobacillus rhamnosus Lcr35

The response of the immune system to probiotics remains controversial. Some strains modulate the cytokine production of dendritic cells (DCs) in vitro and induce a regulatory response, while others induce conversely a pro-inflammatory response. These strain-dependent effects are thought to be linked to specific interactions between bacteria and pattern recognition receptors. We investigated the effects of a well characterized probiotic strain, Lactobacillus rhamnosus Lcr35, on human monocyte-derived immature DCs, using a wide range of bacterial concentrations (multiplicity of infection, MOI, from 0.01 to 100). DNA microarray and qRT-PCR analysis showed that the probiotic induced a large-scale change in gene expression (nearly 1,700 modulated genes, with 3-fold changes), but only with high doses (MOI, 100). The upregulated genes were mainly involved in immune response and identified a molecular signature of inflammation according to the model of Torri. Flow cytometry analysis also revealed a dose-dependent maturation of the DC membrane phenotype, until DCs reached a semi-mature state, with an upregulation of the membrane expression of CD86, CD83, HLA-DR and TLR4, associated with a down-regulation of DC-SIGN, MR and CD14. Measurement of the DC-secreted cytokines showed that Lcr35 induced a strong dose-dependent increase of the pro-Th1/Th17 cytokine levels (TNFα, IL-1β, IL-12p70, IL-12p40 and IL-23), but only a low increase in IL-10 concentration. The probiotic L. rhamnosus Lcr35 therefore induce a dose-dependent immunomodulation of human DCs leading, at high doses, to the semi-maturation of the cells and to a strong pro-inflammatory effect. These results contribute to a fuller understanding of the mechanism of action of this probiotic, and thus of its potential clinical indications in the treatment of either infectious or IgE-dependent allergic diseases.     

Oogenesis in the viviparous matrotrophic lizard Mabuya brachypoda

Oogenesis in the lizard Mabuya brachypoda is seasonal, with oogenesis initiated during May-June and ovulation occurring during July-August. This species ovulates an egg that is microlecithal, having very small yolk stores. The preovulatory oocyte attains a maximum diameter of 0.9-1.3 mm. Two elongated germinal beds, formed by germinal epithelia containing oogonia, early oocytes, and somatic cells, are found on the dorsal surface of each ovary. Although microlecithal eggs are ovulated in this species, oogenesis is characterized by both previtellogenic and vitellogenic stages. During early previtellogenesis, the nucleus of the oocyte contains lampbrush chromosomes, whereas the ooplasm stains lightly with a perinuclear yolk nucleus. During late previtellogenesis the ooplasm displays basophilic staining with fine granular material composed of irregularly distributed bundles of thin fibers. A well-defined zona pellucida is also observed. The granulosa, initially composed of a single layer of squamous cells during early previtellogenesis, becomes multilayered and polymorphic. As with other squamate reptiles, the granulosa at this stage is formed by three cell types: small, intermediate, and large or pyriform cells. As vitellogenesis progresses the oocyte displays abundant vacuoles and small, but scarce, yolk platelets at the periphery of the oocyte. The zona pellucida attains its maximum thickness during late oogenesis, a period when the granulosa is again reduced to a single layer of squamous cells. The vitellogenic process observed in M. brachypoda corresponds with the earliest vitellogenic stages seen in other viviparous lizard species with larger oocytes. The various species of the genus Mabuya provided us with important models to understand a major transition in the evolution of viviparity, the development of a microlecithal egg.     

Correlation analyses and regression modeling between isokinetic testing and on-court performance in competitive adolescent tennis players

Tennis requires skill, physical attributes, and strategy. Ball velocity and placement are two of the most important components in winning the faster-paced modern game. Although isokinetic testing has been used to evaluate physical characteristics and injury potential in tennis players, few studies have compared isokinetics and on-court performance. Such a comparison would help establish links between speed-specific properties of functioning muscles and stroke production and could affect overall training strategy. This study compared isokinetic peak torque (PT), average power (AP), and total work (TW) during specific testing patterns correlated with ball velocity or stroke accuracy during the service, forehand, and backhand and developed predictive equations for each stroke using these variables. Thirty-five players, aged 13-18 years with at least 4 years playing experience, were evaluated using internal and external shoulder rotation, leg extension, and diagonal throwing motions. Ball velocity was measured using a radar gun. Accuracy was evaluated on the basis of shot position and depth. Significant correlations were found between ball velocity and a number of isokinetic variables, while no significant correlations were observed with shot accuracy. Significant isokinetic variables for each stroke were entered into regression models. One isokinetic speed sufficiently predicted ball velocity for each stroke, since no increase in predictive capacity was observed with the addition of other isokinetic parameters. We conclude that isokinetics at testing speeds between 1.57 and 4.71 rad.s(-1) can effectively predict ball velocity, but not accuracy, and that our results may be helpful in planning strategies for training and rehabilitation.