Grazing Rates in Euplotes mutabilis: Relationship between Particle Size and Concentration

Abstract Grazing behavior of both individual cells and populations of the marine hypotrich Euplotes mutabilis, a largely benthic ciliate that feeds on suspended particles, was studied using fluorescent latex microspheres. Microspheres of sizes 0.57-, 1.90-, 3.06-, 5.66-, and 10.0-μm diam were offered at concentrations from 10² to 10⁶ ml⁻¹. Their uptake in a ten-min period was determined. Food particles within such ranges of size and concentration are found under natural conditions. The ciliates ingested particles of all sizes offered. Uptake rates at all concentrations were dependent upon particle size, with 1.90- and 3.06-μm diam microspheres having the highest uptake rate in all cases. For all sizes, there was an increase in the percentage of feeding cells and in the uptake rate (the number of particles ingested cell⁻¹ h⁻¹), with increasing particle concentration. When uptake was expressed as the volume ingested, maximum values were obtained for 5.85-μm diam microspheres at a concentration of 10⁶ ml⁻¹. By taking a small number of large particles, present at a low concentration in the medium, a ciliate can ingest a greater biovolume than by taking a high number of small particles which are abundant in the medium. These results demonstrate that some ciliates can graze particles of a wide range of sizes. Also, its nutrition can be affected by changing ambient concentrations of different prey, both through effects on the proportion of feeding cells and through the relative food content of the particles. The data can also add to the understanding of food niche partitioning between species. At low particle concentrations, particularly, it is important to consider the behavior of individual ciliates as well as of the whole population. Received: 11 February 1997; Accepted: 21 October 1997     

The Interplay between Myc and CTP Synthase in Drosophila

CTP synthase (CTPsyn) is essential for the biosynthesis of pyrimidine nucleotides. It has been shown that CTPsyn is incorporated into a novel cytoplasmic structure which has been termed the cytoophidium. Here, we report that Myc regulates cytoophidium formation during Drosophila oogenesis. We have found that Myc protein levels correlate with cytoophidium abundance in follicle epithelia. Reducing Myc levels results in cytoophidium loss and small nuclear size in follicle cells, while overexpression of Myc increases the length of cytoophidia and the nuclear size of follicle cells. Ectopic expression of Myc induces cytoophidium formation in late stage follicle cells. Furthermore, knock-down of CTPsyn is sufficient to suppress the overgrowth phenotype induced by Myc overexpression, suggesting CTPsyn acts downstream of Myc and is required for Myc-mediated cell size control. Taken together, our data suggest a functional link between Myc, a renowned oncogene, and the essential nucleotide biosynthetic enzyme CTPsyn.     

Egg-Mass Size and Cell Size: Effects of Temperature on Oxygen Distribution

Two processes strongly influence the distribution of oxygenwithin egg masses and cells: the supply of oxygen by diffusionand the consumption of oxygen by embryos and mitochondria. Theseprocesses are differentially sensitive to temperature. The diffusioncoefficient of oxygen depends only weakly on temperature, havinga Q₁₀ of approximately 1.4. In contrast, the consumption ofoxygen depends strongly on temperature, having a Q₁₀ between1.5 and 4.0. Thus, at higher temperatures, the ratio of oxygensupply to demand decreases. I show, by extending a model ofoxygen distribution within metabolizing spheres, that maximalegg-mass sizes and cell sizes are predicted to be smaller athigher temperatures. For egg masses, definitive data are notyet available. For ectothermic cells, this prediction appearsto be supported; cells from a variety of ectothermic organisms,unicellular and multicellular, are smaller when the cells areproduced at warmer temperatures. Establishing a specific connectionbetween this pattern and oxygen distributions requires demonstrationof (1) oxygen concentration gradients within metabolizing spheresand (2) central oxygen concentrations low enough to affect function.Egg masses from a variety of taxa show steep oxygen concentrationgradients and often are severely hypoxic or anoxic in centrallocations. Severe hypoxia appears capable of retarding developmentor killing embryos. Similar kinds of data for ectothermic cellshave not yet been collected, but the literature on oxygen gradientswithin mammalian cells suggests that intracellular gradientsmay be important.     

Interplay between low-temperature pathways and light reduction

Low temperature is one of the major factors that adversely affect crop yields by causing restraints on plant growth and productivity. However, most temperate plants have the ability to acclimate to cooler temperatures. Cold acclimation is a process which increases the freezing tolerance of an organism after exposure to low, non-freezing temperatures. The main trigger is a decrease in temperature levels, but light reduction has also been shown to have an important impact on acquired tolerance. Since the lowest temperatures are commonly reached during the night hours in winter time and is an annually recurring event, a favorable trait for plants is the possibility of sensing an imminent cold period. Consequently, extensive crosstalk between light- and temperature signaling pathways has been demonstrated and in this review interesting interaction points that have been previously reported in the literature are highlighted.Key words: cold acclimation, light-reduction, signaling pathways, photoperiodism, circadian clock, light quality     

Interplay between mitochondria and cellular calcium signalling

Mitochondria are increasingly ascribed central roles in vital cell signalling cascades. These organelles are now recognised as initiators and transducers of a range of cell signals, including those central to activation and amplification of apoptotic cell death. Moreover, as the main source of cellular ATP, mitochondria must be responsive to fluctuating energy demands of the cell. As local and global fluctuations in calcium concentration are ubiquitous in eukaryotic cells and are the common factor in a dizzying array of intra- and inter-cellular signalling cascades, the relationships between mitochondrial function and calcium transients is currently a subject of intense scrutiny. It is clear that mitochondria not only act as local calcium buffers, thus shaping spatiotemporal aspects of cytosolic calcium signals, but that they also respond to calcium uptake by upregulating the tricarboxylic acid cycle, thus reacting metabolically to local signalling. In this chapter we review current knowledge of mechanisms of mitochondrial calcium uptake and release and discuss the consequences of mitochondrial calcium handling for cell function, particularly in conjunction with mitochondrial oxidative stress.     

Interplay between intra- and extracellular calcium ions

Two, well characterized cationic channels, the ryanodine receptor (RyR) and the canonical transient receptor potential cation channel (TRPC) are briefly reviewed with a particular attention on recent developments related to the interplay between the two channel families.     

Interplay between viruses and host mRNA degradation

Messenger RNA degradation is a fundamental cellular process that plays a critical role in regulating gene expression by controlling both the quality and the abundance of mRNAs in cells. Naturally, viruses must successfully interface with the robust cellular RNA degradation machinery to achieve an optimal balance between viral and cellular gene expression and establish a productive infection in the host. In the past several years, studies have discovered many elegant strategies that viruses have evolved to circumvent the cellular RNA degradation machinery, ranging from disarming the RNA decay pathways and co-opting the factors governing cellular mRNA stability to promoting host mRNA degradation that facilitates selective viral gene expression and alters the dynamics of host–pathogen interaction. This review summarizes the current knowledge of the multifaceted interaction between viruses and cellular mRNA degradation machinery to provide an insight into the regulatory mechanisms that influence gene expression in viral infections. This article is part of a Special Issue entitled: RNA Decay mechanisms.     

Interplay between Toxin Transport and Flotillin Localization

The flotillin proteins are localized in lipid domains at the plasma membrane as well as in intracellular compartments. In the present study, we examined the importance of flotillin-1 and flotillin-2 for the uptake and transport of the bacterial Shiga toxin (Stx) and the plant toxin ricin and we investigated whether toxin binding and uptake were associated with flotillin relocalization. We observed a toxin-induced redistribution of the flotillins, which seemed to be regulated in a p38-dependent manner. Our experiments provide no evidence for a changed endocytic uptake of Stx or ricin in cells silenced for flotillin-1 or -2. However, the Golgi-dependent sulfation of both toxins was significantly reduced in flotillin knockdown cells. Interestingly, when the transport of ricin to the ER was investigated, we obtained an increased mannosylation of ricin in flotillin-1 and flotillin-2 knockdown cells. The toxicity of both toxins was twofold increased in flotillin-depleted cells. Since BFA (Brefeldin A) inhibits the toxicity even in flotillin knockdown cells, the retrograde toxin transport is apparently still Golgi-dependent. Thus, flotillin proteins regulate and facilitate the retrograde transport of Stx and ricin.     

一次性氧气湿化瓶与重复使用湿化瓶应用的对比观察

目的：检测一次性氧气湿化瓶与重复使用湿化瓶用后细菌污染的程度和患者对噪音感受的舒适程度,对比两者的成本效益。方法：随机选出心内科病房内持续吸氧时间超过10天的患者100名,以随机分组的方法分出A组50名、B组50名。A组使用一次性氧气湿化瓶,B组使用重复使用的氧气湿化瓶。按照《医疗卫生机构消毒技术规范》进行采样后送微生物检验室进行病原学检验;同时对两组患者进行噪音感受舒适度的调查;根据使用的氧气湿化瓶成本费用、氧气湿化用灭菌注射用水的价格、含氯消毒剂健之素的费用计算成本。结果：50只一次性氧气湿化瓶使用时间120小时（5天）,微生物学检测未发现致病菌,成本费用9-3元／日,患者噪音感受舒适度满意度调查结果为100％;重复使用氧气湿化瓶使用24小时染茵率28％,成本费用9．6元／日,患者噪音感受舒适度满意度调查结果为60％。结论：使用合格的一次性氧气湿化瓶,在患者费用不会增加的前提下,减少了医院感染机会,增加了患者的舒适度,值得推广使用。     

体积排阻液相色谱法质粒的含量测定

首次以体积排阻液相色谱法进行质粒提取液浓度的测定研究,通过纯质粒溶液在260 nm处的紫外吸峰面积与质粒浓度之间数据的线性最小二乘拟合,得到了反映质粒浓度和紫外吸收峰峰面积之间关系的标准曲线:Y=2×10~(-5) X,通过验证实验,确定了质粒提取液中不同组分,如核糖核酸,蛋白质等在色谱图中的出峰位置.结合标准曲线测定了自制的质粒提取液的质粒浓度为0.32 mg/mL.该方法方便,快捷,准确.     

Interplay between HIV-1 infection and host microRNAs

Using microRNA array analyses of in vitro HIV-1-infected CD4(+) cells, we find that several host microRNAs are significantly up- or downregulated around the time HIV-1 infection peaks in vitro. While microRNA-223 levels were significantly enriched in HIV-1-infected CD4(+)CD8(-) PBMCs, microRNA-29a/b, microRNA-155 and microRNA-21 levels were significantly reduced. Based on the potential for microRNA binding sites in a conserved sequence of the Nef-3'-LTR, several host microRNAs potentially could affect HIV-1 gene expression. Among those microRNAs, the microRNA-29 family has seed complementarity in the HIV-1 3'-UTR, but the potential suppressive effect of microRNA-29 on HIV-1 is severely blocked by the secondary structure of the target region. Our data support a possible regulatory circuit at the peak of HIV-1 replication which involves downregulation of microRNA-29, expression of Nef, the apoptosis of host CD4 cells and upregulation of microRNA-223.