The taxonomic utility of micromorphology in Lepidaploa (Vernonieae: Asteraceae)

Lepidaploa belongs to tribe Vernonieae, one of the most complex tribes of Asteraceae, and the relationships within Lepidaploa and among related genera are poorly understood. Microcharacters may be of taxonomic value and may be used in the identification of taxa at different ranks. To evaluate the reliability of microcharacters as taxonomic markers in this group, we analysed the micromorphology of phyllaries, florets and cypselae in detail in 23 species of Lepidaploa .The species were studied using stereo, light, and scanning electron microscopy. Eight trichome types (eglandular and glandular) were observed on phyllaries, florets and cypselae, in addition to crystals, idioblasts and other microstructures. The results demonstrates that the ocurrence of different combinations of trichome types and crystals, presence of a stylar basal node, idioblasts and glandular apical anther appendages are highly useful to differentiate between related species of Lepidaploa and a diagnostic key using these characters is presented. However, these characters are not of much use to distinguish between closely related genera of Vernonieae since most characters appear homeoplasic and are found in representatives of different genera.     

Meiotic behavior and pollen morphology variation in Centaurium pulchellum (Gentianaceae)

Centaurium pulchellum is an annual herb native to Europe, but introduced in South America, where it is widely used in the preparation of digestive infusions and bitter drinks. In this species, a wide variation in the aperture pattern of pollen grains was reported and has been attributed to environmental factors or irregularities at meiosis. For this reason, cytological and palynological studies have been undertaken on two different populations. The pollen grain analysis showed that some types are more frequent within each population, but the most common forms were the typical 3-colporate and 4-colporate. The cytological analysis revealed that the analyzed populations of C. pulchellum have chromosome number 2n = 36. The presence of tetravalents at meiosis strongly suggests that these populations are autotetraploid based on x = 9. The meiotic behavior showed a significant percentage of irregularities in different phases: off-plate bivalents, precocious segregation, laggard chromosomes, bridges, and cytomixis. However these irregularities are not related to the variation in the aperture pattern of pollen grains. The heteromorphism in the pollen grains observed in C. pulchellum could be a normal condition to which the species is well adapted.     

TNFalpha up‐regulates SLUG via the NF‐kappaB/HIF1alpha axis,which imparts breast cancer cells with a stem cell‐like phenotype

Extracellular and intracellular mediators of inflammation, such as tumor necrosis factor alpha (TNFα) and NF‐kappaB (NF‐κB), play major roles in breast cancer pathogenesis, progression and relapse. SLUG, a mediator of the epithelial–mesenchymal transition process, is over‐expressed in CD44⁺/CD24^? tumor initiating breast cancer cells and in basal‐like carcinoma, a subtype of aggressive breast cancer endowed with a stem cell‐like gene expression profile. Cancer stem cells also over‐express members of the pro‐inflammatory NF‐κB network, but their functional relationship with SLUG expression in breast cancer cells remains unclear. Here, we show that TNFα treatment of human breast cancer cells up‐regulates SLUG with a dependency on canonical NF‐κB/HIF1α signaling, which is strongly enhanced by p53 inactivation. Moreover, SLUG up‐regulation engenders breast cancer cells with stem cell‐like properties including enhanced expression of CD44 and Jagged‐1 in conjunction with estrogen receptor alpha down‐regulation, growth as mammospheres, and extracellular matrix invasiveness. Our results reveal a molecular mechanism whereby TNFα, a major pro‐inflammatory cytokine, imparts breast cancer cells with stem cell‐like features, which are connected to increased tumor aggressiveness. J. Cell. Physiol. 225: 682–691, 2010. © 2010 Wiley‐Liss, Inc.     

The molecular basis of filamin binding to integrins and competition with talin

The ability of adhesion receptors to transmit biochemical signals and mechanical force across cell membranes depends on interactions with the actin cytoskeleton. Filamins are large, actin-crosslinking proteins that connect multiple transmembrane and signaling proteins to the cytoskeleton. Here, we describe the high-resolution structure of an interface between filamin A and an integrin adhesion receptor. When bound, the integrin beta cytoplasmic tail forms an extended beta strand that interacts with beta strands C and D of the filamin immunoglobulin-like domain (IgFLN) 21. This interface is common to many integrins, and we suggest it is a prototype for other IgFLN domain interactions. Notably, the structurally defined filamin binding site overlaps with that of the integrin-regulator talin, and these proteins compete for binding to integrin tails, allowing integrin-filamin interactions to impact talin-dependent integrin activation. Phosphothreonine-mimicking mutations inhibit filamin, but not talin, binding, indicating that kinases may modulate this competition and provide additional means to control integrin functions.     

Identifying the minimal copper- and zinc-binding site sequence in amyloid-beta peptides

With a combination of complementary experimental techniques, namely sedimentation assay, Fourier transform infrared spectroscopy, and x-ray absorption spectroscopy, we are able to determine the atomic structure around the metal-binding site in samples where amyloid-beta (Abeta) peptides are complexed with either Cu(II) or Zn(II). Exploiting information obtained on a selected set of fragments of the Abeta peptide, we identify along the sequence the histidine residues coordinated to the metal in the various peptides we have studied (Abeta(1-40), Abeta(1-16), Abeta(1-28), Abeta(5-23), and Abeta(17-40)). Our data can be consistently interpreted assuming that all of the peptides encompassing the minimal 1-16 amino acidic sequence display a copper coordination mode that involves three histidines (His(6), His(13), and His(14)). In zinc-Abeta complexes, despite the fact that the metal coordination appears to be more sensitive to solution condition and shows a less rigid geometry around the binding site, a four-histidine coordination mode is seen to be preferred. Lacking a fourth histidine along the Abeta peptide sequence, this geometrical arrangement hints at a Zn(II)-promoted interpeptide aggregation mode.     

Involvement of etfA gene during CaCO3 precipitation in Bacillus subtilis biofilm

The eftA gene in Bacillus subtilis has been suggested to be involved in the oxidation/reduction reactions during fatty acid metabolism. Interestingly etfA deletion in B. subtilis results in impairment in CaCO₃ precipitation on the biofilm. Comparisons between the wild type B. subtilis 168 and its etfA mutant during in vitro CaCO₃ crystal precipitation (calcite) revealed changes in phospholipids membrane composition with accumulation of up to 10% of anteiso-C_17:0 and 11% iso-C_17:0 long fatty acids. Ca²⁺ nucleation sites such as dipicolinic acid and teichoic acids seem to contribute to the CaCO₃ precipitation. etfA mutant strain showed up to 40% less dipicolinic acid accumulation compared with B. subtilis 168, while a B. subtilis mutant impaired in teichoic acids synthesis was unable to precipitate CaCO₃. In addition, B. subtilis etfA mutant exhibited acidity production leading to atypical flagella formation and inducing extensive lateral growth on the biofilm when grown on 1.4% agar. From the ecological point of view, this study shows a number of physiological aspects that are involved in CaCO₃ organomineralization on biofilms.     

Escherichia coli DnaE Polymerase Couples Pyrophosphatase Activity to DNA Replication

DNA Polymerases generate pyrophosphate every time they catalyze a step of DNA elongation. This elongation reaction is generally believed as thermodynamically favoured by the hydrolysis of pyrophosphate, catalyzed by inorganic pyrophosphatases. However, the specific action of inorganic pyrophosphatases coupled to DNA replication in vivo was never demonstrated. Here we show that the Polymerase-Histidinol-Phosphatase (PHP) domain of Escherichia coli DNA Polymerase III α subunit features pyrophosphatase activity. We also show that this activity is inhibited by fluoride, as commonly observed for inorganic pyrophosphatases, and we identified 3 amino acids of the PHP active site. Remarkably, E. coli cells expressing variants of these catalytic residues of α subunit feature aberrant phenotypes, poor viability, and are subject to high mutation frequencies. Our findings indicate that DNA Polymerases can couple DNA elongation and pyrophosphate hydrolysis, providing a mechanism for the control of DNA extension rate, and suggest a promising target for novel antibiotics.     

Structural and dynamical properties of KTS‐disintegrins: A comparison between Obtustatin and Lebestatin

Obtustatin and Lebestatin are lysine‐threonine‐serine (KTS)‐disintegrins, which are a family of low molecular weight polypeptides present in many viperidae venoms and are potent and specific inhibitors of collagen‐binding integrins. The integrin binding loop, harboring the ²¹KTS²³ motif, and the C‐terminal tail are known to be responsible for the selective binding to the α1β1 integrin. Despite a very high sequence homology (only two mutations are present in Lebestatin relative to Obtustatin, namely R24L and S38L), Lebestatin exhibits a higher inhibitory effect than Obtustatin on cell adhesion and cell migration to collagens I and IV. Here we show, by means of molecular dynamics simulations of the two polypeptides in aqueous solution, that Lebestatin possesses a higher flexibility of the C‐terminal tail and a greater solvent accessibility of the integrin binding loop than Obtustatin. It may be hypothesized that these properties may contribute to the higher binding‐affinity of Lebestatin to its biological partner. © 2012 Wiley Periodicals, Inc.