T Cell Costimulation through CD28 Depends on Induction of the Bcl-xγ Isoform: Analysis of Bcl-xγ–deficient Mice

The molecular basis of CD28-dependent costimulation of T cells is poorly understood. Bcl-xγ is a member of the Bcl-x family whose expression is restricted to activated T cells and requires CD28-dependent ligation for full expression. We report that Bcl-xγ–deficient (Bcl-xγ−/−) T cells display defective proliferative and cytokine responses to CD28-dependent costimulatory signals, impaired memory responses to proteolipid protein peptide (PLP), and do not develop PLP-induced experimental autoimmune encephalomyelitis (EAE). In contrast, enforced expression of Bcl-xγ largely replaces the requirement for B7-dependent ligation of CD28. These findings identify the Bcl-xγ cytosolic protein as an essential downstream link in the CD28-dependent signaling pathway that underlies T cell costimulation

Thermal Hydraulic and Neutronics Coupling Analysis for Plate Type Fuel in Nuclear Reactor Core

The thermal hydraulic and neutronics coupling analysis is an important part of the high-fidelity simulation for nuclear reactor core. In this paper, a thermal hydraulic and neutronics coupling method was proposed for the plate type fuel reactor core based on the Fluent and Monte Carlo code. The coupling interface module was developed using the User Defined Function (UDF) in Fluent. The three-dimensional thermal hydraulic model and reactor core physics model were established using Fluent and Monte Carlo code for a typical plate type fuel assembly, respectively. Then, the thermal hydraulic and neutronics coupling analysis was performed using the developed coupling code. The simulation results with coupling and noncoupling analysis methods were compared to demonstrate the feasibility of coupling code, and it shows that the accuracy of the proposed coupling method is higher than that of the traditional method. Finally, the fuel assembly blockage accident was studied based on the coupling code. Under the inlet 30% blocked conditions, the maximum coolant temperature would increase around 20°C, while the maximum fuel temperature rises about 30°C. The developed coupling method provides an effective way for the plate type fuel reactor core high-fidelity analysis

Glyoxylate rather than ascorbate is an efficient precursor for oxalate biosynthesis in rice

Oxalate is widely distributed in the plant kingdom. While excess oxalate in food crops is detrimental to animal and human health, it may play various functional roles in plants, particularly for coping with environmental stresses. Understanding its biosynthetic mechanism in plants, therefore, becomes increasingly important both theoretically and practically. However, it is still a matter of debate as to what precursor and pathway are ultimately used for oxalate biosynthesis in plants. In this study, both physiological and molecular approaches were applied to address these questions. First, it was observed that when glycolate or glyoxylate was fed into detached leaves, both organic acids were equally effective in stimulating oxalate accumulation. In addition, the stimulation could be completely inhibited by cysteine, a glyoxylate scavenger that forms cysteine–glyoxylate adducts. To verify the role of glyoxylate further, various transgenic plants were generated, in which several genes involved in glyoxylate metabolism [i.e. SGAT (serine-glyoxylate aminotransferase), GGAT (glutamate-glyoxylate aminotransferase), HPR (hydroxypyruvate reductase), ICL (isocitrate lyase)], were transcriptionally regulated through RNAi or over-expression. Analyses on these transgenic plants consistently revealed that glyoxylate acted as an efficient precursor for oxalate biosynthesis in rice. Unexpectedly, it was found that oxalate accumulation was not correlated with photorespiration, even though this pathway is known to be a major source of glyoxylate. Further, when GLDH (L-galactono-1,4-lactone dehydrogenase), a key enzyme gene for ascorbate biosynthesis, was down-regulated, the oxalate abundance remained constant, despite ascorbate having been largely reduced as expected in these transgenic plants. Taken together, our results strongly suggest that glyoxylate rather than ascorbate is an efficient precursor for oxalate biosynthesis, and that oxalate accumulation and regulation do not necessarily depend on photorespiration, possibly due to the occurrence of the anaplerotic reaction that may compensate for glyoxylate formation in rice