Sieve-element plastids ofCyrillaceae,Erythroxylaceae andRhizophoraceae: Description and significance of subtype PV plastids

A new subtype (PV) of protein-containing sieve-element plastids was found to contain a uniquely large number of polygonal protein crystals, sometimes with (PVcf) and sometimes without (PVc) protein filaments. These plastids do not accumulate starch. The PVcf-plastids occur inCyrillaceae only, while the PVc-plastids are limited toErythroxylaceae andRhizophoraceae. The significance of the new P-subtype with respect to the systematic position of the three families is discussed.     

Nutritional status and immune functions in maintenance hemodialysis patients

Epidemiological studies suggest various kinds of immune dysregulation in hemodialysis (HD) patients. The aim of this study was to investigate the relationship between immune functions and nutritional status of HD patients. We studied 54 patients with ESRD on chronic HD, included 34 females and 20 males with mean age 46.6 +/- 16.3 (18-77) years. We measured the height and dry weight of all patients. The BMI was calculated by dividing weight (kg) by height squared (m(2)). In all patients serum urea, creatinine, albumin, iron, cholesterol, triglyceride, CRP, IgG, IgM, IgA, CD4, CD8, CD19, CD16-56 lymphocytes were measured. Kt/V values were calculated according to DOQI guideline. In this study, a positive correlation between albumin, cholesterol, and triglyceride levels as nutritional parameters and immune functions in terms of total and subtype lymphocyte counts was observed. Further prospective studies are needed to determine the clinical importance of this finding and the appropriate means of measurement and effects of nutrition on immune function in hemodialysis patients.     

Protein targeting into plastids: a key to understanding the symbiogenetic acquisitions of plastids

Recent progress in molecular phylogenetics has proven that photosynthetic eukaryotes acquired plastids via primary and secondary endosymbiosis and has given us information about the origin of each plastid. How a photosynthetic endosymbiont became a plastid in each group is, however, poorly understood, especially for the organisms with secondary plastids. Investigating how a nuclear-encoded plastid protein is targeted into a plastid in each photosynthetic group is one of the most important keys to understanding the evolutionary process of symbiogenetic plastid acquisition and its diversity. For organisms which originated through primary endosymbiosis, protein targeting into plastids has been well studied at the molecular level. For organisms which originated through secondary endosymbiosis, molecular-level studies have just started on the plastid-targeted protein-precursor sequences and the targeting pathways of the precursors. However, little information is available about how the proteins get across the inner two or three envelope membranes in organisms with secondary plastids. A good in vitro protein-import system for isolated plastids and a cell transformation system must be established for each group of photosynthetic eukaryotes in order to understand the mechanisms, the evolutionary processes and the diversity of symbiogenetic plastid acquisitions in photosynthetic eukaryotes.     

Parasite Replication and the Evolutionary Epidemiology of Parasite Virulence

Parasite virulence evolution is shaped by both within-host and population-level processes yet the link between these differing scales of infection is often neglected. Population structure and heterogeneity in both parasites and hosts will affect how hosts are exploited by pathogens and the intensity of infection. Here, it is shown how the degree of relatedness among parasites together with epidemiological parameters such as pathogen yield and longevity influence the evolution of virulence. Furthermore, the role of kin competition and the degree of cheating within highly structured parasite populations also influences parasite fitness and infectivity patterns. Understanding how the effects of within-host processes scale up to affect the epidemiology has importance for understanding host-pathogen interactions.     

生物的寄生与共生

寄生和共生是生物彼此交互中的2种关系,也是生物学上2个重要的概念,学生在生物学学习中易对这2个概念产生混淆。主要就寄生和共生的概念以及它们之间的协同进化论述。以期为中学教师和其他生物学工作者提供参考。     

Membrane microdomains: Role of ceramides in the maintenance of their structure and functions

Free-standing giant unilamellar vesicles were used to visualize the complex lateral heterogeneity, induced by ceramide in the membrane bilayer at micron scale using C₁₂-NBD-PC probe partitioning under the fluorescence microscope. Ceramide gel domains exist as leaf-like structures in glycerophospholipid/ceramide mixtures. Cholesterol readily increases ceramide miscibility with glycerophospholipids but cholesterol-ceramide interactions are not involved in the organization of the liquid-ordered phase as exemplified by sphingomyelin/cholesterol mixtures. Sphingomyelin stabilizes the gel phase and thus decreases ceramide miscibility in the presence of cholesterol. Gel/liquid-ordered/liquid-disordered phase coexistence was visualized in quaternary phosphatidylcholine/sphingomyelin/ceramide/cholesterol mixtures as occurrence of dark leaf-like and circular domains within a bright liquid phase. Sphingomyelin initiates specific ceramide-sphingomyelin interactions to form a highly ordered gel phase appearing at temperatures higher than pure ceramide gel phase in phosphatidylcholine/ceramide mixtures. Less sphingomyelin is engaged in formation of liquid-ordered phase leading to a shift in its formation to lower temperatures. Sphingomyelinase activity on substrate vesicles destroys micron L_o domains but induces the formation of a gel-like phase. The activation of phospholipase A₂ by ceramide on heterogeneous membranes was visualized. Changes in the phase state of the membrane bilayer initiates such morphological processes as membrane fragmentation, budding in and budding out was demonstrated.     

ATP-dependent and independent functions of Rad54 in genome maintenance

Rad54, a member of the SWI/SNF protein family of DNA-dependent ATPases, repairs DNA double-strand breaks (DSBs) through homologous recombination. Here we demonstrate that Rad54 is required for the timely accumulation of the homologous recombination proteins Rad51 and Brca2 at DSBs. Because replication protein A and Nbs1 accumulation is not affected by Rad54 depletion, Rad54 is downstream of DSB resection. Rad54-mediated Rad51 accumulation does not require Rad54's ATPase activity. Thus, our experiments demonstrate that SWI/SNF proteins may have functions independent of their ATPase activity. However, quantitative real-time analysis of Rad54 focus formation indicates that Rad54's ATPase activity is required for the disassociation of Rad54 from DNA and Rad54 turnover at DSBs. Although the non-DNA-bound fraction of Rad54 reversibly interacts with a focus, independent of its ATPase status, the DNA-bound fraction is immobilized in the absence of ATP hydrolysis by Rad54. Finally, we show that ATP hydrolysis by Rad54 is required for the redistribution of DSB repair sites within the nucleus.