Light and ultrastructural description of Meglitschia mylei n. sp. (myxozoa) from Myleus rubripinnis (Teleostei: Serrasalmidae) in the Amazon River system

Meglitschia mylei n. sp. found in the gall bladder of the teleostean fish Myleus rubripinnis (Serrasalmidae) from the middle Amazonian region of Brazil is described using light and transmission electron microscopy. The spores observed in the bile averaged 24.6±0.8 μm long, 8.7±0.4 μm wide and 5.1±0.3 μm thick and were strongly furcate and arcuate ∩-shaped composed of two symmetric equal-sized valves, up to ～70 nm thick. Each valve possessed one opposed tapering appendage, 20.1±0.7 μm long, oriented parallel towards the basal tip of the appendages and joined along a right suture line forming a thick strand. The strand goes around the central part of the spore, which in turn surrounds two equal and symmetric spherical polar capsules (PC), 2.1±0.3 μm in diameter, located at the same level. Each capsule contains a polar filament with five (rarely six) coils. The binucleate sporoplasm was irregular in shape, contained several sporoplasmosomes, ～175 nm in diameter and filled all the space of the two caudal appendages. Based on the arc shape of the spore with two tapering caudal appendages oriented to the basis of spores, on the number and position of the PC and of the polar filament coils and arrangements, and on the host specificity, we propose the name M. mylei n. sp. for this new myxozoan. Accordingly, this is the second described species of this genus.     

Agent-based modeling of the context dependency in T cell recognition

Antigen recognition by T cells is a key event in the adaptive immune response. T cells scan the surface of antigen-presenting cells (APCs) or target cells for specific peptides bound to MHC molecules. In the physiological setting, a typical APC presents tens of thousands of diverse endogenous self-derived peptides complexed to MHC (pMHC complexes). When 'foreign' peptides are presented, they constitute a small fraction of the total surface peptide repertoire. As T cells seem to be capable of discerning minute amounts of 'foreign' peptides among a complex background of self-peptides, endogenous peptides are generally assumed to play no role in recognition. However, recent results suggest that these background peptides may alter the sensitivity of T cells to foreign peptides. Current experimental limitations preclude analysis of peptide mixtures approaching physiological complexity, making it difficult to further address the role of complex background peptides. In this paper, we present a computational model to test how complex, varied peptide populations on an APC could potentially modulate a T cell's ability to detect the presence of small numbers of agonist peptides among a diverse population. We use the model to investigate the notion that under physiological conditions, T cell recognition of foreign peptides is context dependent, that is, T cells process signals gathered from all pMHC interactions, not just from a few agonist peptides while ignoring all others.     

Developmental compartments and planar polarity in Drosophila

BACKGROUND: Planar polarity refers to the asymmetry of a cell within the plane of the epithelium; for example, cells may form hairs that point in a posterior direction, or cilia may beat in one way. This property implies that cells have information about their orientation; we wish to understand the nature of this information. Relevant also is the body plan of insects, which, in the ectoderm and somatic mesoderm, consists of a chain of alternating anterior and posterior compartments - basic units of development with independent cell lineage and subject to independent genetic control.RESULTS: Using the abdomen of adult Drosophila, we have taken genes required for normal polarity and either removed the gene or constitutively expressed it in small clones of cells and observed the effects on polarity. Hitherto, all such studies of polarity genes have not found any difference of behavior between the different compartments. We report here that the three genes, four-jointed, dachsous, and fat, cause opposite effects in anterior and posterior compartments. For example, in anterior compartments, clones ectopically expressing four-jointed reverse the polarity of cells in front of the clone, while, in posterior compartments, they reverse behind the clone. These three genes have been reported by others to be functionally linked.CONCLUSIONS: This discovery impacts on models of how cells read polarity. At the heart of one class of models is the hypothesis that cell polarity is determined by the vector of a morphogen gradient. Here, we present evidence that cell polarity in the abdomen depends on at least two protein gradients (Fj and Ds), each of which is reflected at compartment borders. Consequently, these gradients have opposing slopes in the two compartments. Because all polarized structures made by abdominal cells point posteriorly, we surmise that cells in each compartment are programmed to interpret these protein gradients with opposite signs, pointing up the gradient in one compartment and down the gradient in the other.     

Role of monocarboxylate transporters in human cancers: state of the art

Monocarboxylate transporters (MCTs) belong to the SLC16 gene family, presently composed by 14 members. MCT1-MCT4 are proton symporters, which mediate the transmembrane transport of pyruvate, lactate and ketone bodies. The role of MCTs in cell homeostasis has been characterized in detail in normal tissues, however, their role in cancer is still far from understood. Most solid tumors are known to rely on glycolysis for energy production and this activity leads to production of important amounts of lactate, which are exported into the extracellular milieu, contributing to the acidic microenvironment. In this context, MCTs will play a dual role in the maintenance of the hyper-glycolytic acid-resistant phenotype of cancer, allowing the maintenance of the high glycolytic rates by performing lactate efflux, and pH regulation by the co-transport of protons. Thus, they constitute attractive targets for cancer therapy, which have been little explored. Here we review the literature on the role of MCTs in solid tumors in different locations, such as colon, central nervous system, breast, lung, gynecologic tract, prostate, stomach, however, there are many conflicting results and in most cases there are no functional studies showing the dependence of the tumors on MCT expression and activity. Additional studies on MCT expression in other tumor types, confirmation of the results already published as well as additional functional studies are needed to deeply understand the role of MCTs in cancer maintenance and aggressiveness.     

Myxobolus myleus n. sp. infecting the bile of the Amazonian freshwater fish Myleus rubripinnis (Teleostei: Serrasalmidae): morphology and pathology

Myxobolus myleus n. sp. is described from the gall-bladder of the freshwater fish Myleus rubripinnis collected near the city of Oriximiná in the Amazon System, Brazil. The spores obtained from the bile contained two equal symmetrical and smooth valves, each forming the spore wall. The spores were large, with a cone-like form, a semi spherical basal contour and measured (in μm) 19.3 ± 0.5 (n = 25) × 8.3 ± 0.5 (n = 25) × 4.0 ± 0.3 (n = 15). The apical end of the spores contained two elongate, equal and pointed conical polar capsules measuring 13.2 ± 0.4 μm (n = 25) in length and 3.0 ± 0.3 μm (n = 15) in width, each having a slightly tapering polar filament with 19 to 21 turns. The polar capsules were extended below at about 4/5 of the total length of the spores. The sporoplasm was binucleate and contained some sporoplasmosomes. All infected fish presented hypertrophy of the gall-bladder due to presence of the brownish parasite floating in the bile. In this paper we describe this new species of myxosporean based on light and ultrastructural observations, together with its associated pathology.     

Dissecting the molecular bridges that mediate the function of Frizzled in planar cell polarity

Many epithelia have a common planar cell polarity (PCP), as exemplified by the consistent orientation of hairs on mammalian skin and insect cuticle. One conserved system of PCP depends on Starry night (Stan, also called Flamingo), an atypical cadherin that forms homodimeric bridges between adjacent cells. Stan acts together with other transmembrane proteins, most notably Frizzled (Fz) and Van Gogh (Vang, also called Strabismus). Here, using an in vivo assay for function, we show that the quintessential core of the Stan system is an asymmetric intercellular bridge between Stan in one cell and Stan acting together with Fz in its neighbour: such bridges are necessary and sufficient to polarise hairs in both cells, even in the absence of Vang. By contrast, Vang cannot polarise cells in the absence of Fz; instead, it appears to help Stan in each cell form effective bridges with Stan plus Fz in its neighbours. Finally, we show that cells containing Stan but lacking both Fz and Vang can be polarised to make hairs that point away from abutting cells that express Fz. We deduce that each cell has a mechanism to estimate and compare the numbers of asymmetric bridges, made between Stan and Stan plus Fz, that link it with its neighbouring cells. We propose that cells normally use this mechanism to read the local slope of tissue-wide gradients of Fz activity, so that all cells come to point in the same direction.     

Transport of carboxylic acids in yeasts

Carboxylic acid transporters form a heterogeneous group of proteins, presenting diverse mechanisms of action and regulation, and belonging to several different families. Multiple physiological and genetic studies in several organisms, from yeast to mammals, have allowed the identification of various genes coding for carboxylate transporters. Detailed understanding of the metabolism and transport of these nutrients has become more important than ever, both from a fundamental and from an applied point of view. Under a biotechnological perspective, the increasing economic value of these compounds has boosted this field of research considerably. Here we review the current knowledge on yeast carboxylate transporters, at the biochemical and molecular level, focusing also on recent biotechnological developments.     

Effects of forest fire ash on germination and early growth of four pinus species

Fire modifies the germination of seeds of numerous species. One of the fire factors that cause these modifications is the ash. This study analysed the germination of seeds of Pinus sylvestris L., Pinus nigra Arn. Pinus radiata D. Don and Pinus pinaster Aiton, subjected to different ash treatments, and the development of seedlings that grew in these conditions for 14 weeks. We obtained the ash by completely burning leaves and small twigs from the most abundant woody species in populations of pines. The ash treatments applied were as follows: Control (without ash), Low (half of the amount registered in a fire), Medium (equal to the amount registered in a fire) and High (double the amount registered in a fire). Germination took place on paper inside Petri dishes and in soil, and growth was only analysed for the plants that grew in the soil. For all species, and especially P. nigra, germination rate decreased as the amount of ash applied increased. The negative effects of the ash were more apparent following treatments in Petri dishes than in the soil. In the dishes, the average germination time varies little between the four species of pine. In soil, the average germination time is more prolonged, and only some differences were observed between treatments in P. sylvestris and P. nigra. In these species the high treatment significantly increased the average germination time. We found a greater sensitivity of P. sylvestris and P. nigra to the addition of ash, showing a higher seedling mortality rate. However, it appears that seedling development (length and weight) was not affected in any of the species through the addition of ash. These tests allow us to deduce that, in P. sylvestris, P. nigra, P. radiata and P. pinaster, the ash produced by forest fires has an inhibiting effect on germination and little effect on the development of seedlings in the first months of life. This revised version was published online in June 2006 with corrections to the Cover Date.     

Simultaneous determination of retinol, β-carotene and α-tocopherol in adipose tissue by high-performance liquid chromatography

A method is described for evaluation of fat-soluble vitamin in human adipose tissue with the aim to obtain, accurately and within the shortest analysis time, a time-integrated measure of exposure to vitamins from the diet. Fat tissue was deproteinized with ethanol and extracted with n-hexane. Normal-phase HPLC was performed in a Lichrosorb Si60 column with a gradient of n-hexane–2-propanol at 1 ml/min. Detection was accomplished using a diode-array system (for retinol and β-carotene) in series with a fluorescence detector (α-tocopherol). The method was validated and applied to human adipose tissue in a total of 140 subjects. The mean contents found were 0.43, 0.84, 240.3 μg/g for retinol, β-carotene and α-tocopherol, respectively. The method is sensitive enough for detecting the compounds in 1.6 mg of adipose tissue considering the lowest concentration found.