Exploring phylogeography and species limits in the Altai vole (Rodentia: Cricetidae)

Natural hybridization between species is not a rare event. In arvicoline rodents, hybridization is known to occur in the wild and/or in captivity. In the Microtus arvalis group, cytogenetic studies revealed that there were two distinct chromosomal forms (2n = 46 but a different fundamental number of autosomes). These forms have been attributed to two cryptic species: the common (arvalis) and Altai (obscurus) voles. Recently, individuals with intermediate karyotypes (F₁ and backcrosses) were discovered in central European Russia, and, for this reason, other studies have regarded obscurus and arvalis as conspecific. In the present study, to address the question of the species limits in the Altai vole and to infer its evolutionary history, a phylogeographical analysis combined with multivariate morphometric methods and original chromosome data was performed. Two obscurus lineages were identified: the Sino‐Russian and South Caucasian lineages. Both lineages are characterized by low genetic diversity, resulting, in the former, from a past bottleneck event caused by encroaching periglacial areas and, in the latter, from recent rapid population divergence. Introgressive hybridization between the Altai and common voles appears to be the result of a secondary contact following the Last Glacial Maximum in central European Russia. Despite the fact that speciation is an ongoing process in most arvicoline species, the common and Altai voles are genetically divergent, morphologically and karyologically distinct, and exhibit contrasting evolutionary histories. For all these reasons, they should be ranked as species: M. arvalis and M. obscurus. © 2013 The Linnean Society of London     

MDA-MB-231 breast cancer cell viability,motility and matrix adhesion are regulated by a complex interplay of heparan sulfate,chondroitin−/dermatan sulfate and hyaluronan biosynthesis

Proteoglycans and glycosaminoglycans modulate numerous cellular processes relevant to tumour progression, including cell proliferation, cell-matrix interactions, cell motility and invasive growth. Among the glycosaminoglycans with a well-documented role in tumour progression are heparan sulphate, chondroitin/dermatan sulphate and hyaluronic acid/hyaluronan. While the mode of biosynthesis differs for sulphated glycosaminoglycans, which are synthesised in the ER and Golgi compartments, and hyaluronan, which is synthesized at the plasma membrane, these polysaccharides partially compete for common substrates. In this study, we employed a siRNA knockdown approach for heparan sulphate (EXT1) and heparan/chondroitin/dermatan sulphate-biosynthetic enzymes (β4GalT7) in the aggressive human breast cancer cell line MDA-MB-231 to study the impact on cell behaviour and hyaluronan biosynthesis. Knockdown of β4GalT7 expression resulted in a decrease in cell viability, motility and adhesion to fibronectin, while these parameters were unchanged in EXT1-silenced cells. Importantly, these changes were associated with a decreased expression of syndecan-1, decreased signalling response to HGF and an increase in the synthesis of hyaluronan, due to an upregulation of the hyaluronan synthases HAS2 and HAS3. Interestingly, EXT1-depleted cells showed a downregulation of the UDP-sugar transporter SLC35D1, whereas SLC35D2 was downregulated in β4GalT7-depleted cells, indicating an intricate regulatory network that connects all glycosaminoglycans synthesis. The results of our in vitro study suggest that a modulation of breast cancer cell behaviour via interference with heparan sulphate biosynthesis may result in a compensatory upregulation of hyaluronan biosynthesis. These findings have important implications for the development of glycosaminoglycan-targeted therapeutic approaches for malignant diseases.     

Single VS ribozyme molecules reveal dynamic and hierarchical folding toward catalysis

Non-coding RNAs of complex tertiary structure are involved in numerous aspects of the replication and processing of genetic information in many organisms; however, an understanding of the complex relationship between their structural dynamics and function is only slowly emerging. The Neurospora Varkud Satellite (VS) ribozyme provides a model system to address this relationship. First, it adopts a tertiary structure assembled from common elements, a kissing loop and two three-way junctions. Second, catalytic activity of the ribozyme is essential for replication of VS RNA in vivo and can be readily assayed in vitro. Here we exploit single molecule FRET to show that the VS ribozyme exhibits previously unobserved dynamic and heterogeneous hierarchical folding into an active structure. Readily reversible kissing loop formation combined with slow cleavage of the upstream substrate helix suggests a model whereby the structural dynamics of the VS ribozyme favor cleavage of the substrate downstream of the ribozyme core instead. This preference is expected to facilitate processing of the multimeric RNA replication intermediate into circular VS RNA, which is the predominant form observed in vivo.     

Heparin affin regulatory peptide/pleiotrophin negatively affects diverse biological activities in C6 glioma cells

Heparin affin regulatory peptide (HARP) or pleiotrophin seems to be involved in the progression of several tumors of diverse origin. In this study, we tried to determine the role of HARP in rat C6 glioma cells by using an antisense strategy for inhibition of HARP expression. Decrease of the expression of endogenous HARP in C6 cells (AS-C6 cells) significantly increased proliferation, migration, and anchorage-independent growth of cells. Implantation of AS-C6 cells onto chicken embryo chorioallantoic membranes resulted in a significant increase of tumor-induced angiogenesis compared with that induced by non-transfected or C6 cells transfected with the plasmid alone (PC-C6 cells). In the same line, conditioned medium from AS-C6 cells significantly increased endothelial cell proliferation, migration, and tube formation in vitro compared with the effect of conditioned medium from C6 or PC-C6 cells. Interestingly, vascular endothelial growth factor (VEGF) induced C6 cell proliferation and migration, and SU1496, a selective inhibitor of VEGF receptor 2 (VEGFR2), blocked increased glioma cell growth, migration, and angiogenicity observed in AS-C6 cell cultures. The above results seem to be due to a direct interaction between HARP and VEGF in the culture medium of C6 and PC-C6 cells, while AS-C6 cells secreted comparable amounts of VEGF that do not interact with HARP. Collectively, these data suggest that HARP negatively affects diverse biological activities in C6 glioma cells, mainly due to binding of HARP to VEGF, which may sequester secreted VEGF from signalling through VEGFR2.     

The synthetic strigolactone GR24 influences the growth pattern of phytopathogenic fungi

Strigolactones that are released by plant roots to the rhizosphere are involved in both plant symbiosis with arbuscular mycorrhizal fungi and in plant infection by root parasitic plants. In this paper, we describe the response of various phytopathogenic fungi to the synthetic strigolactone GR24. When GR24 was embedded in the growth medium, it inhibited the growth of the root pathogens Fusarium oxysporum f. sp. melonis, Fusarium solani f. sp. mango, Sclerotinia sclerotiorum and Macrophomina phaseolina, and of the foliar pathogens Alternaria alternata, Colletotrichum acutatum and Botrytis cinerea. In the presence of this synthetic strigolactone, intense branching activity was exhibited by S. sclerotiorum, C. acutatum and F. oxysporum f. sp. melonis. Slightly increased hyphal branching was observed for A. alternata, F. solani f. sp. mango and B. cinerea, whereas suppression of hyphal branching by GR24 was observed in M. phaseolina. These results suggest that strigolactones not only affect mycorrhizal fungi and parasitic plants, but they also have a more general effect on phytopathogenic fungi.     

Carbon sequestration and turnover in soil under the energy crop Miscanthus: repeated 13C natural abundance approach and literature synthesis

The stability and turnover of soil organic matter (SOM) are a very important but poorly understood part of carbon (C) cycling. Conversion of C₃ grassland to the C₄ energy crop Miscanthus provides an ideal opportunity to quantify medium‐term SOM dynamics without disturbance (e.g., plowing), due to the natural shift in the δ¹³C signature of soil C. For the first time, we used a repeated ¹³C natural abundance approach to measure C turnover in a loamy Gleyic Cambisol after 9 and 21 years of Miscanthus cultivation. This is the longest C₃–C₄ vegetation change study on C turnover in soil under energy crops. SOM stocks under Miscanthus and reference grassland were similar down to 1 m depth. However, both increased between 9 and 21 years from 105 to 140 mg C ha^?1 (P < 0.05), indicating nonsteady state of SOM. This calls for caution when estimating SOM turnover based on a single sampling. The mean residence time (MRT) of old C (>9 years) increased with depth from 19 years (0–10 cm) to 30–152 years (10–50 cm), and remained stable below 50 cm. From 41 literature observations, the average SOM increase after conversion from cropland or grassland to Miscanthus was 6.4 and 0.4 mg C ha^?1, respectively. The MRT of total C in topsoil under Miscanthus remained stable at ~60 years, independent of plantation age, corroborating the idea that C dynamics are dominated by recycling processes rather than by C stabilization. In conclusion, growing Miscanthus on C‐poor arable soils caused immediate C sequestration because of higher C input and decreased SOM decomposition. However, after replacing grasslands with Miscanthus, SOM stocks remained stable and the MRT of old C₃‐C increased strongly with depth.