Stable isotopes challenge the perception of ocean sunfish Mola mola as obligate jellyfish predators

Evidence is provided from stable isotope analysis that aggregations of small ocean sunfish Mola mola (total length <1 m) feed broadly within coastal food webs and their classification as obligate predators of gelatinous zooplankton requires revision.     

Quantification of the age-pigment lipofuscin in known-age octopus (Octopus pallidus): A potential tool for age determination

Stylet increment analysis (SIA) is the key method to age octopus, however, currently it is not reliable for all species. The suitability of the age-pigment lipofuscin as an alternative ageing method for octopus was examined. To determine the relationship between age and lipofuscin known-age octopus (Octopus pallidus) were reared in the laboratory from hatching to eight months old. Twenty-eight individuals at three different ages (3, 6 and 8 months old) were collected for lipofuscin analysis. The first two age groups (n = 5 each) were reared under ambient temperatures, while the oldest group (n = 18) was reared under three different controlled temperature regimes (n = 6 per treatment). For comparison, five wild O. pallidus were also collected for lipofuscin analysis and aged using SIA. Lipofuscin was analysed in the brain tissue and quantified at a commercial ageing centre using standard histological methods. Lipofuscin granules were clearly discernable in the brain tissue, and there was a strong exponential relationship between age and lipofuscin (R² = 0.86). Lipofuscin concentration was not related to sex, temperature or body weight in same-age individuals. Except for one individual, the predicted age of the wild animals, based on the relationship between lipofuscin and age, was close to the age determined using SIA. This study is the first to report lipofuscin in an octopus species and shows that lipofuscin has excellent potential as an alternative ageing method for octopus. This research will have important applications for species which cannot be reliably aged using current ageing methods.     

Crystallographic and in silico analysis of the sialoside-binding characteristics of the Siglec sialoadhesin

The Siglec family of receptors mediates cell-surface interactions through recognition of sialylated glycoconjugates. Previously reported structures of the N-terminal domain of the Siglec sialoadhesin (SnD1) in complex with various sialic acid analogs revealed the structural template for sialic acid binding. To characterize further the carbohydrate-binding properties, we have determined the crystal structures of SnD1 in the absence of ligand, and in complex with 2-benzyl-Neu5NPro and 2-benzyl-Neu5NAc. These structures reveal that SnD1 undergoes very few structural changes on ligand binding and detail how two novel classes of sialic acid analogs bind, one of which unexpectedly can induce Siglec dimerization. In conjunction with in silico analysis, this set of structures informs us about the design of putative ligands with enhanced binding affinities and specificities to different Siglecs, and provides data with which to test the effectiveness of different computational drug design protocols.     

Spatial,ontogenetic and interspecific variability in stable isotope ratios of nitrogen and carbon of Merluccius capensis and Merluccius paradoxus off South Africa

General linear models (GLMs) were used to determine the relative importance of interspecific, ontogenetic and spatial effects in explaining variability in stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) of the co‐occurring Cape hakes Merluccius capensis and Merluccius paradoxus off South Africa. Significant GLMs were derived for both isotopes, explaining 74 and 56% of observed variance in Merluccius spp. δ¹⁵N and δ¹³C, respectively. Spatial effects (west or south coast) contributed most towards explaining variability in the δ¹⁵N model, with Merluccius spp. off the west coast having higher (by c. 1·4‰) δ¹⁵N levels than Merluccius spp. off the south coast. Fish size and species were also significant in explaining variability in δ¹⁵N, with both species showing significant linear increases in δ¹⁵N with size and M. capensis having higher (by c. 0·7‰) δ¹⁵N values than M. paradoxus. Species and coast explained most and similar amounts of variability in the δ¹³C model, with M. capensis having higher (by c. 0·8‰) δ¹³C values than M. paradoxus, and values being lower (by c. 0·7‰) for fishes off the west coast compared with the south coast. These results not only corroborate the knowledge of Merluccius spp. feeding ecology gained from dietary studies, in particular the ontogenetic change in trophic level corresponding to a changing diet, but also that M. capensis feeds at a slightly higher trophic level than M. paradoxus. The spatial difference in Merluccius spp. δ¹⁵N appears due to a difference in isotopic baseline, and not as a result of Merluccius spp. feeding higher in the food web off the west than the south coast, and provides new evidence that corroborates previous observations of biogeographic differences in isotopic baselines around the South African coast. This study also provides quantitative data on the relative trophic level and trophic width of Cape hakes over a large size range that can be used in ecosystem models of the southern Benguela.     

Sialosignaling: Sialyltransferases as engines of self-fueling loops in cancer progression

Background

Glycosylation is increasingly recognized as one of the most relevant postranslational modifications. Sialic acids are negatively charged sugars which frequently terminate the carbohydrate chains of glycoproteins and glycolipids. The addition of sialic acids is mediated by sialyltransferases, a family of glycosyltransferases with a crucial role in cancer progression.

Scope of the review

To describe the phenotypic and clinical implications of altered expression of sialyltransferases and of their cognate sialylated structures in cancer. To propose a unifying model of the role of sialyltransferases and sialylated structures on cancer progression.

Major conclusions

We first discuss the biosynthesis and the role played by the major cancer-associated sialylated structures, including Thomsen–Friedenreich-associated antigens, sialyl Lewis antigens, α2,6-sialylated lactosamine, polysialic acid and gangliosides. Then, we show that altered sialyltransferase expression in cancer, consequence of genetic and epigenetic alterations, generates a flow of information toward the membrane through the biosynthesis of aberrantly sialylated molecules (inside-out signaling). In turn, the presence of aberrantly sialylated structures on cell membrane receptors generates a flow of information toward the nucleus, which can exacerbate the neoplastic phenotype (outside-in signaling). We provide examples of self-fueling loops generated by these flows of information.

General significance

Sialyltransferases have a wide impact on the biology of cancer and can be the target of innovative therapies. Our unified view provides a conceptual framework to understand the impact of altered glycosylation in cancer.     

Sustained intracellular acidosis activates the myocardial Na/H exchanger independent of amino acid Ser and p90

The mammalian Na⁺/H⁺ exchanger isoform 1 (NHE1) is a ubiquitously expressed pH-regulatory membrane protein that functions in the myocardium and other tissues. It is an important mediator of the myocardial damage that occurs after ischemia-reperfusion injury and is implicated in heart hypertrophy. Regulation of NHE1 has been proposed as a therapeutic target for cardioprotection. We therefore examined mechanisms of control of NHE1 in the myocardium. Several different amino acids have been implicated as a being critical to NHE1 regulation in a number of tissues including Ser⁷⁰³, Ser⁷⁷⁰, and Ser⁷⁷¹. In the myocardium, NHE1 is activated in response to a variety of stimuli including activation by an ERK-dependent sustained intracellular acidosis. In this study, we determined whether Ser⁷⁰³ and p90^rsk activity are critical in activation of NHE1 by sustained intracellular acidosis. In vitro phosphorylation of NHE1 C-terminal fusion proteins determined that ERK-dependent phosphorylation of the cytoplasmic region was not dependent on Ser⁷⁰³; however, phosphorylation by p90^rsk required Ser⁷⁰³. A Ser703Ala mutation decreased basal NHE1 activity in CHO cells but not in cardiomyocytes. NHE1 with a Ser703Ala mutation was activated in response to sustained intracellular acidosis in CHO cells. In addition, sustained intracellular acidosis also activated the Ser703Ala mutant protein in isolated cardiomyocytes and phosphorylation levels were also increased by acidosis. The presence of a dominant-negative p90^rsk kinase also did not prevent activation and phosphorylation of NHE1 by sustained intracellular acidosis in isolated cardiomyocytes. We conclude that Ser⁷⁰³ and p90^rsk are not required for activation by sustained intracellular acidosis and that p90^rsk phosphorylation of Ser⁷⁰³ is independent of this type of activation.     

Cysteamine restores glutathione redox status in cultured cystinotic proximal tubular epithelial cells

Recent evidence implies that impaired metabolism of glutathione has a role in the pathogenesis of nephropathic cystinosis. This recessive inherited disorder is characterized by lysosomal cystine accumulation and results in renal Fanconi syndrome progressing to end stage renal disease in the majority of patients. The most common treatment involves intracellular cystine depletion by cysteamine, delaying the development of end stage renal disease by a yet elusive mechanism. However, cystine depletion does not arrest the disease nor cures Fanconi syndrome in patients, indicating involvement of other yet unknown pathologic pathways. Using a newly developed proximal tubular epithelial cell model from cystinotic patients, we investigate the effect of cystine accumulation and cysteamine on both glutathione and ATP metabolism. In addition to the expected increase in cystine and defective sodium-dependent phosphate reabsorption, we observed less negative glutathione redox status and decreased intracellular ATP levels. No differences between control and cystinosis cell lines were observed with respect to protein turnover, albumin uptake, cytosolic and mitochondrial ATP production, total glutathione levels, protein oxidation and lipid peroxidation. Cysteamine treatment increased total glutathione in both control and cystinotic cells and normalized cystine levels and glutathione redox status in cystinotic cells. However, cysteamine did not improve decreased sodium-dependent phosphate uptake. Our data implicate that cysteamine increases total glutathione and restores glutathione redox status in cystinosis, which is a positive side-effect of this agent next to cystine depletion. This beneficial effect points to a potential role of cysteamine as anti-oxidant for other renal disorders associated with enhanced oxidative stress.     

Stable isotope niche differentiation in sticklebacks with symmetric and asymmetric pectoral fins

Fluctuating asymmetry (FA) is often, but controversially, viewed as an indicator of fitness and a target of selection. In the brook stickleback, Culaea inconstans (Kirtland), FA of the pectoral fins, which are the main source of propulsion, is inversely correlated with fecundity. We examined the hypothesis that asymmetry of the pectoral fins could affect locomotion in such a way as to influence foraging and niche use in prereproductive brook stickleback. Nitrogen and carbon stable isotope analysis showed the diet of symmetric and asymmetric males diverged with increasing body size. Larger symmetric males fed at higher trophic levels and had a diet based on carbon emanating from a more pelagic source than their asymmetric counterparts. Such effects were not observed in females or smaller males. The number of chironomid larvae found in the gut was greater on average in asymmetric than symmetric fish. The results from this study strongly suggest FA of pectoral fins affects the foraging behaviour of C. inconstans and that stable isotope analyses of individual phenotypes provides a useful tool for assessing the ecological consequences of FA.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 617–623.     

Automated approach for the evaluation of glutathione-S-transferase P1-1 inhibition by organometallic anticancer compounds

A novel automated method based on sequential injection analysis (SIA), a non-segmented flow injection technique, was developed to evaluate glutathione S-transferase P1-1 (GST P1-1) activity in the presence of organometallic complexes with putative anticancer activity. The assay is based on the reaction of L-glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB) in the presence of GST P1-1 to afford the GS-DNB conjugate and the reaction may be monitored by an increase in absorbance at 340 nm. A series of ruthenium, iron, osmium and iridium complexes were evaluated as GST P1-1 inhibitors by evaluating their half-maximal inhibitory concentration (IC₅₀). An iridium compound displays the lowest IC₅₀ value of 6.7 ± 0.7 µM and an iron compound displays the highest IC₅₀ value of 275 ± 9 µM. The SIA method is simple to use, robust, reliable, and efficient and uses fewer reagents than batch methods and each analysis takes only 5 minutes.