Trans-activity of Plasma Membrane-associated Ganglioside Sialyltransferase in Mammalian Cells

Gangliosides are acidic glycosphingolipids that contain sialic acid residues and are expressed in nearly all vertebrate cells. They are synthesized at the Golgi complex by a combination of glycosyltransferase activities followed by vesicular delivery to the plasma membrane, where they participate in a variety of physiological as well as pathological processes. Recently, a number of enzymes of ganglioside anabolism and catabolism have been shown to be associated with the plasma membrane. In particular, it was observed that CMP-NeuAc:GM3 sialyltransferase (Sial-T2) is able to sialylate GM3 at the plasma membrane (cis-catalytic activity). In this work, we demonstrated that plasma membrane-integrated ecto-Sial-T2 also displays a trans-catalytic activity at the cell surface of epithelial and melanoma cells. By using a highly sensitive enzyme-linked immunosorbent assay combined with confocal fluorescence microscopy, we observed that ecto-Sial-T2 was able to sialylate hydrophobically or covalently immobilized GM3 onto a solid surface. More interestingly, we observed that ecto-Sial-T2 was able to sialylate GM3 exposed on the membrane of neighboring cells by using both the exogenous and endogenous donor substrate (CMP-N-acetylneuraminic acid) available at the extracellular milieu. In addition, the trans-activity of ecto-Sial-T2 was considerably reduced when the expression of the acceptor substrate was inhibited by using a specific inhibitor of biosynthesis of glycolipids, indicating the lipidic nature of the acceptor. Our findings provide the first direct evidence that an ecto-sialyltransferase is able to trans-sialylate substrates exposed in the plasma membrane from mammalian cells, which represents a novel insight into the molecular events that regulate the local glycosphingolipid composition.     

Species assignment and population genetic studies of Gran Paraná pejerrey (<Emphasis Type="Italic">Odontesthes</Emphasis> sp., Atheriniformes,Atherinopsidae) from La Plata Basin in South America

Since 2013, the pelagic zone of Upper Lake Constance (ULC) has been subject to a massive invasion of the non-native three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758). Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) were used to compare weight-at-age and abundance of pelagic whitefish for years before (1997–2012) and after the invasion (2013–2015). Growth and abundance of pelagic whitefish is shown to be heavily influenced by stickleback presence. Mean autumn weight-at-age of whitefish decreased by 33.3% after the invasion took place and a significant decline in autumn CPUE in otherwise unfished cohorts of the population was also recorded. The results imply direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth and survival, and predation of eggs and larvae, hampering recruitment. These observations coincide with a sharp decline in whitefish yield. In conclusion, this study shows that the invasion of stickleback has substantially altered the pelagic fish community of ULC, with severe consequences for commercial fisheries.     

Rodent control at different spatial scales on poultry farms in the province of Buenos Aires,Argentina

In poultry farms of central Argentina rodents cause economic losses by the consumption and contamination of chicken food, and also pose a serious sanitary risk as transmitters of several diseases to human and domestic animals, such as leptospirosis, salmonellosis, trichinosis, hantavirus pulmonary syndrome, hantavirus renal syndrome, and Argentine hemorrhagic fever. Because one of the problems in controlling rodents is recolonization from the surroundings, we wanted to assess the effect of control measures applied at different spatial scales on rodent abundance in farm sheds. The treatments applied were the following: anticoagulant application in farms and their surroundings (F + S), anticoagulant application only within farms (F), and standard management (C). Rodent abundance was assessed previous to treatments (t₀), at the moment of bait removal (t₁), and after 15 (t₂), 30 (t₃), and 60 days (t₄). Differences in rodent abundance between t₀ and t₁, t₂, t_3, and t₄ were compared among treatments by means of a Kruskal Wallis test. We only found significant differences among treatments between t₀ and t₂, where F and F + S treatments showed differences with respect to the C treatment. This result suggests that the effect of control measures was due to the control of the perimeter, and not of farther areas. Also, reproduction of remaining individuals may have contributed to the population recovery in sheds of experimental farms. We conclude that more effective control must include the perimeter of the farm, but the effect of control of more distant areas may depend on the characteristics of the particular farm, its surroundings, and the ecology of the species involved.     

Alteration of Plasma Membrane Organization by an Anticancer Lysophosphatidylcholine Analogue Induces Intracellular Acidification and Internalization of Plasma Membrane Transporters in Yeast

The lysophosphatidylcholine analogue edelfosine is a potent antitumor lipid that targets cellular membranes. The underlying mechanisms leading to cell death remain controversial, although two cellular membranes have emerged as primary targets of edelfosine, the plasma membrane (PM) and the endoplasmic reticulum. In an effort to identify conditions that enhance or prevent the cytotoxic effect of edelfosine, we have conducted genome-wide surveys of edelfosine sensitivity and resistance in Saccharomyces cerevisiae presented in this work and the accompanying paper (Cuesta-Marbán, Á., Botet, J., Czyz, O., Cacharro, L. M., Gajate, C., Hornillos, V., Delgado, J., Zhang, H., Amat-Guerri, F., Acuña, A. U., McMaster, C. R., Revuelta, J. L., Zaremberg, V., and Mollinedo, F. (January 23, 2013) J. Biol. Chem. 288,), respectively. Our results point to maintenance of pH homeostasis as a major player in modulating susceptibility to edelfosine with the PM proton pump Pma1p playing a main role. We demonstrate that edelfosine alters PM organization and induces intracellular acidification. Significantly, we show that edelfosine selectively reduces lateral segregation of PM proteins like Pma1p and nutrient H⁺-symporters inducing their ubiquitination and internalization. The biology associated to the mode of action of edelfosine we have unveiled includes selective modification of lipid raft integrity altering pH homeostasis, which in turn regulates cell growth.     

A recent invasive population of the European starling sturnus vulgaris has lower genetic diversity and higher fluctuating asymmetry than primary invasive and native populations

Biological Invasions - Fluctuating asymmetries (FA) are small stress-induced random deviations from perfect symmetry that arise during the development of bilaterally symmetrical traits. One of the...     

Genomic data reveal deep genetic structure but no support for current taxonomic designation in a grasshopper species complex

Taxonomy has traditionally relied on morphological and ecological traits to interpret and classify biological diversity. Over the last decade, technological advances and conceptual developments in the field of molecular ecology and systematics have eased the generation of genomic data and changed the paradigm of biodiversity analysis. Here we illustrate how traditional taxonomy has led to species designations that are supported neither by high throughput sequencing data nor by the quantitative integration of genomic information with other sources of evidence. Specifically, we focus on Omocestus antigai and Omocestus navasi, two montane grasshoppers from the Pyrenean region that were originally described based on quantitative phenotypic differences and distinct habitat associations (alpine vs. Mediterranean‐montane habitats). To validate current taxonomic designations, test species boundaries, and understand the factors that have contributed to genetic divergence, we obtained phenotypic (geometric morphometrics) and genome‐wide SNP data (ddRADSeq) from populations covering the entire known distribution of the two taxa. Coalescent‐based phylogenetic reconstructions, integrative Bayesian model‐based species delimitation, and landscape genetic analyses revealed that populations assigned to the two taxa show a spatial distribution of genetic variation that do not match with current taxonomic designations and is incompatible with ecological/environmental speciation. Our results support little phenotypic variation among populations and a marked genetic structure that is mostly explained by geographic distances and limited population connectivity across the abrupt landscapes characterizing the study region. Overall, this study highlights the importance of integrative approaches to identify taxonomic units and elucidate the evolutionary history of species.