Effects of contrasting demographic histories on selection at major histocompatibility complex loci in two sympatric species of tuco‐tucos (Rodentia: Ctenomyidae)

To explore the impact of history on selection and genetic structure at functional loci, we compared patterns of major histocompatibility complex (MHC) variability in two sympatric species of ctenomyid rodents with different demographic backgrounds. Although Ctenomys talarum has experienced a stable demographic history, Ctenomys australis has undergone a recent demographic expansion. Accordingly, we predicted that MHC allele frequency distributions should be more skewed, differences between coding and noncoding regions should be less pronounced, and evidence of current selection on MHC loci should be reduced in C. australis relative to C. talarum. To test these predictions, we compared variation at the MHC class II DRB and DQA genes with that at multiple neutral markers, including DQA intron 2, the mitochondrial control region, and 8–12 microsatellite loci. These analyses supported the first two of our predictions but indicated that estimates of selection (based on ω‐values) were greater for C. australis. Further exploration of these data, however, revealed differences in the time frames over which selection appears to have acted on each species, with evidence of contemporary selection on MHC loci being limited to C. talarum. Collectively, these findings indicate that demographic history can substantially influence genetic structure at functional loci and that the effects of history on selection may be temporally complex and dynamic. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 260–277.     

Genetic footprints of late Quaternary climate change in the diversity of Patagonian‐Fueguian rodents

Species are impacted by climate change at both ecological and evolutionary time scales. Studies in northern continents have provided abundant evidence of dramatic shifts in distributions of species subsequent to the last glacial maximum (LGM), particularly at high latitudes. However, little is known about the history of southern continents, especially at high latitudes. South America is the only continent, other than Antarctica, that extends beyond 40 °S. Genetic studies of a few Patagonian species have provided seemingly conflicting results, indicating either postglacial colonization from restricted glacial refugia or persistence through glacial cycles and in situ differentiation. Using mitochondrial DNA sequences of 14 species of sigmodontine rodents, a major faunal ensemble of Patagonia and Tierra del Fuego, we show that at least nine of these species bear genetic footprints of demographic expansion from single restricted sources. However, timing of demographic expansion precedes the LGM in most of these species. Four species are fragmented phylogeographically within the region. Our results indicate that (i) demographic instability in response to historical climate change has been widespread in the Patagonian‐Fueguian region, and is generally more pronounced at high latitudes in both southern and northern continents; (ii) colonization from lower latitudes is an important component of current Patagonian‐Fueguian diversity; but (iii) in situ differentiation has also contributed to species diversity.     

Cell organisation,sulphur metabolism and ion transport-related genes are differentially expressed in Paracoccidioides brasiliensis mycelium and yeast cells

Background

Bread wheat (Triticum aestivum) is an important staple food. However, wheat gluten proteins cause celiac disease (CD) in 0.5 to 1% of the general population. Among these proteins, the α-gliadins contain several peptides that are associated to the disease.

Results

We obtained 230 distinct α-gliadin gene sequences from severaldiploid wheat species representing the ancestral A, B, and D genomes of the hexaploid bread wheat. The large majority of these sequences (87%) contained an internal stop codon. All α-gliadin sequences could be distinguished according to the genome of origin on the basis of sequence similarity, of the average length of the polyglutamine repeats, and of the differences in the presence of four peptides that have been identified as T cell stimulatory epitopes in CD patients through binding to HLA-DQ2/8. By sequence similarity, α-gliadins from the public database of hexaploid T. aestivum could be assigned directly to chromosome 6A, 6B, or 6D. T. monococcum (A genome) sequences, as well as those from chromosome 6A of bread wheat, almost invariably contained epitope glia-α9 and glia-α20, but never the intact epitopes glia-α and glia-α2. A number of sequences from T. speltoides, as well as a number of sequences fromchromosome 6B of bread wheat, did not contain any of the four T cell epitopes screened for. The sequences from T. tauschii (D genome), as well as those from chromosome 6D of bread wheat, were found to contain all of these T cell epitopes in variable combinations per gene. The differences in epitope composition resulted mainly from point mutations. These substitutions appeared to be genome specific.

Conclusion

Our analysis shows that α-gliadin sequences from the three genomes of bread wheat form distinct groups. The four known T cell stimulatory epitopes are distributed non-randomly across the sequences, indicating that the three genomes contribute differently to epitope content. A systematic analysis of all known epitopes in gliadins and glutenins will lead to better understanding of the differences in toxiCity among wheat varieties. On the basis of such insight, breeding strategies can be designed to generate less toxic varieties of wheat which may be tolerated by at least part of the CD patient population.     

Light-to-dark transitions trigger a transient increase in intracellular Ca2+ modulated by the redox state of the photosynthetic electron transport chain in the cyanobacterium Anabaena sp. PCC7120

Light‐to‐dark transitions represent one of the most crucial environmental stresses that photosynthetic organisms must cope with, since substantial metabolism adaptations are required in order to utilize alternative energy and carbon sources. Although signal transduction systems for changing light regimes are not sufficiently understood, calcium has been implicated in plants as a second messenger in light‐on and light‐off events. Much less is known about light signalling in cyanobacteria, but it has been shown that calcium probably performs similar signalling roles in these organisms and other prokaryotes. Herein it is reported that light‐to‐dark transitions trigger a calcium transient in aequorin expressing Anabaena sp. PCC7120. The magnitude of this transient depends on the fluence rate previously irradiated and can reach a peak height over 2 µm free calcium when the fluence rate of light is around 400 µmol photons s^?1 m^?2. The use of increasing calcium concentration, ethylene glycol‐bis (β‐aminoethylether) N,N,N′,N′‐tetraacetic acid (EGTA), verapamil and trifluoperazine indicated that these transients are originated by a calcium influx probably through verapamil‐sensitive Ca²⁺ channels and are probably modulated by calcium‐binding proteins. Experiments with different light spectral qualities and the photosynthetic inhibitors 3‐(3,4 dichlorophenyl)1,1,dimelthylurea (DCMU) and 3,5‐dibromo‐3‐methyl‐b‐isopropyl‐p‐benzoquinone (DBMIB) indicate that the calcium transient triggered by the light‐to‐dark transition is not coupled to a specific photoreceptor but rather to changes in the redox state of photosynthetic electron transport chain components other than the plastoquinone pool.     

Application of a sensitive near‐field microwave microprobe to the nondestructive characterization of microbial rhodopsin

We study the opto‐electrical properties of Natronomonas pharaonis sensory rhodopsin II (NpSRII) by using a near‐field microwave microprobe (NFMM) under external light illumination. To investigate the possibility of application of NFMM to biological macromolecules, we used time dependent properties of NPSRII before/after light activation which has three distinct states – ground‐state, M‐state, and O‐state. The diagnostic ability of NFMM is demonstrated by measuring the microwave reflection coefficient (S₁₁) spectrum of NpSRII under steady‐state illumination in the wavelength range of 350–650 nm. Moreover, we present microwave reflection coefficient S₁₁ spectra in the same wavelength range for two fast‐photocycling rhodopsins: green light‐absorbing proteorhodopsin (GPR) and Gloeobacter rhodopsin (GR). In addition the frequency sweep shift can be detected completely even for tiny amounts of sample (～10^–3 OD of rhodopsin). Based on these results NFMM shows both very high sensitivity for detecting conformational changes and produces a good time‐resolved spectrum. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Protection of HepG2 cells against acrolein toxicity by 2-cyano-3,12-dioxooleana-1,9-dien-28-imidazolide via glutathione-mediated mechanism

Acrolein is an environmental toxicant, mainly found in smoke released from incomplete combustion of organic matter. Several studies showed that exposure to acrolein can lead to liver damage. The mechanisms involved in acrolein-induced hepatocellular toxicity, however, are not completely understood. This study examined the cytotoxic mechanisms of acrolein on HepG2 cells. Acrolein at pathophysiological concentrations was shown to cause apoptotic cell death and an increase in levels of protein carbonyl and thiobarbituric acid reactive acid substances. Acrolein also rapidly depleted intracellular glutathione (GSH), GSH-linked glutathione-S-transferases, and aldose reductase, three critical cellular defenses that detoxify reactive aldehydes. Results further showed that depletion of cellular GSH by acrolein preceded the loss of cell viability. To further determine the role of cellular GSH in acrolein-mediated cytotoxicity, buthionine sulfoximine (BSO) was used to inhibit cellular GSH biosynthesis. It was observed that depletion of cellular GSH by BSO led to a marked potentiation of acrolein-mediated cytotoxicity in HepG2 cells. To further assess the contribution of these events to acrolein-induced cytotoxicity, triterpenoid compound 2-cyano-3,12-dioxooleana-1,9-dien-28-imidazolide (CDDO-Im) was used for induction of GSH. Induction of GSH by CDDO-Im afforded cytoprotection against acrolein toxicity in HepG2 cells. Furthermore, BSO significantly inhibited CDDO-Im-mediated induction in cellular GSH levels and also reversed cytoprotective effects of CDDO-Im in HepG2 cells. These results suggest that GSH is a predominant mechanism underlying acrolein-induced cytotoxicity as well as CDDO-Im-mediated cytoprotection. This study may provide understanding on the molecular action of acrolein which may be important to develop novel strategies for the prevention of acrolein-mediated toxicity.