Cylindrospermopsis raciborskii Virus and host: genomic characterization and ecological relevance

Cylindrospermopsis (Raphidiopsis) raciborskii is an invasive, filamentous, nitrogen-fixing cyanobacterium that forms frequent blooms in freshwater habitats. While viruses play key roles in regulating the abundance, production and diversity of their hosts in aquatic ecosystems, the role(s) of viruses in the ecology of C. raciborskii is almost unexplored. Progress in this field has been hindered by the absence of a characterized virus–host system in C. raciborskii. To bridge this gap, we sequenced the genome of CrV-01T, a previously isolated cyanosiphovirus, and its host, C. raciborskii strain Cr2010. Analyses suggest that CrV-01T represents a distinct clade of siphoviruses infecting, and perhaps lysogenizing, filamentous cyanobacteria. Its genome contains unique features that include an intact CRISPR array and a 12 kb inverted duplication. Evidence suggests CrV-01T recently gained the ability to infect Cr2010 and recently lost the ability to form lysogens. The cyanobacterial host contains a CRISPR-Cas system with CRISPR spacers matching protospacers within the inverted duplication of the CrV-01T genome. Examination of metagenomes demonstrates that viruses with high genetic identity to CrV-01T, but lacking the inverted duplication, are present in C. raciborskii blooms in Australia. The unique genomic features of the CrV/Cr2010 system offers opportunities to investigate in more detail virus–host interactions in an ecologically important bloom-forming cyanobacterium.     

Uncharged thioflavin-T derivatives bind to amyloid-beta protein with high affinity and readily enter the brain

In vivo assessment of the beta-sheet proteins deposited in amyloid plaques (A beta peptide) or neurofibrillary tangles (tau protein) presents a target for the development of biological markers for Alzheimer's disease (AD). In an effort to develop in vivo beta-sheet imaging probes, derivatives of thioflavin-T (ThT) were synthesized and evaluated. These compounds lack the positively charged quaternary heterocyclic nitrogen of ThT and are therefore uncharged at physiological pH. They are 600-fold more lipophilic than ThT. These ThT derivatives bind to A beta(1-40) fibrils with higher affinity (Ki = 20.2 nM) than ThT (Ki = 890 nM). The uncharged ThT derivatives stained both plaques and neurofibrillary tangles in post-mortem AD brain, showing some preference for plaque staining. A carbon-11 labeled compound, [N-methyl-11C]6-Me-BTA-1, was prepared, and its brain entry and clearance were studied in Swiss-Webster mice. This compound entered the brain at levels comparable to commonly used neuroreceptor imaging agents (0.223 %ID-kg/g or 7.61 %ID/g at 2 min post-injection) and showed good clearance of free and non-specifically bound radioactivity in normal rodent brain tissue (brain clearance t(1,2) = 20 min). The combination of relatively high affinity for amyloid, specificity for staining plaques and neurofibrillary tangles in post-mortem AD brain, and good brain entry and clearance makes [N-methyl-11C]6-Me-BTA-1 a promising candidate as an in vivo positron emission tomography (PET) beta-sheet imaging agent.     

Direct effects of lithium chloride on the activities of delta 5-3 beta and 17 beta-hydroxysteroid dehydrogenase in the testis and Bidder's organ of the adult toad (Bufo melanostictus)--in vitro study

Steroidogenic key enzymes, i.e. delta 5-3 beta and 17 beta-hydroxysteroid dehydrogenase (delta 5-3 beta and 17 beta-HSD) activities, in the testis and Bidder's organ of the toad were inhibited and ascorbic acid synthesis in these organs was decreased by a wide range of lithium concentration in in vitro study. A significant inhibition was noted at a concentration of 2.0 mM, which is easily achieved in the blood during the treatment of manic patients by lithium chloride. This experiment reflected that lithium exerts a direct inhibitory effect on hydroxysteroid dehydrogenase activities in the testis and Bidder's organ--a rudimentary ovary in Bufo.     

Synthesis and anti-HIV-1 activity of 4-[4-(4,6-bisphenylamino-triazin-2-ylamino)-5-methoxy-2-methylphenylazo]-5-hydroxynaphthalene-2,7-disulfonic acid and its derivatives

A structure-based design approach has been used to optimize a lead HIV-1 entry inhibitor targeted to the envelope glycoprotein gp41. The docking study on this lead compound revealed important structural requirements that need to be preserved as well as structural non-requirements that could be eliminated to substantially reduce the molecular size of the lead compound. Based on the results from docking study, a limited number of analogues were designed and synthesized. This approach yielded a new analogue (compound 4) that retained the anti-HIV-1 activity with reduced molecular size approaching towards more drug-like character.     

QSAR study on some pyridoacridine ascididemin analogues as anti-tumor agents

Pyridoacridine ascididemin analogues have been reported as anticancer agents for their interesting antitumor activity against human cancer cells. A quantitative structure–activity relationship (QSAR) analysis of ascididemin analogues was attempted using the physicochemical parameters and the electrotopological state atom (ETSA) indices. This study indicates that the electron withdrawing substituents with higher MR (molar refractivity) value at R₁ position favor the anti-tumor activity and the presence of NHR (R is hydrogen or alkyl group) at the R₃ position has contribution to the anti-tumor activity. ETSA indices have been incorporated as independent variable in the QSAR model with physicochemical parameters. It clearly suggests the importance of atoms 2, 3, 4, 5, 6 and 7 to the anti-tumor activity.     

Bone microstructure and developmental plasticity in birds and other dinosaurs

Patterns of bone microstructure have frequently been used to deduce dynamics and processes of growth in extant and fossil tetrapods. Often, the various types of primary bone tissue have been associated with different bone deposition rates and more recently such deductions have extended to patterns observed in dinosaur bone microstructure. These previous studies are challenged by the findings of the current research, which integrates an experimental neontological approach and a paleontological comparison. We use tetracycline labeling and morphometry to study the variability of bone deposition rates in Japanese quail (Coturnix japonica) growing under different experimental conditions. We compare resulting patterns in bone microstructure with those found in fossil birds and other dinosaurs. We found that a single type of primary bone varies significantly in rates of growth in response to environmental conditions. Ranging between 10-50 microm per day, rates of growth overlap with the full range of bone deposition rates that were previously associated with different patterns of bone histology. Bone formation rate was significantly affected by environmental/experimental conditions, skeletal element, and age. In the quail, the experimental conditions did not result in formation of lines of arrested growth (LAGs). Because of the observed variation of bone deposition rates in response to variation in environmental conditions, we conclude that bone deposition rates measured in extant birds cannot simply be extrapolated to their fossil relatives. Additionally, we observe the variable incidence of LAGs and annuli among several dinosaur species, including fossil birds, extant sauropsids, as well as nonmammalian synapsids, and some extant mammals. This suggests that the ancestral condition of the response of bone to environmental conditions was variable. We propose that such developmental plasticity in modern birds may be reduced in association with the shortened developmental time during the later evolution of the ornithurine birds.     

A theropod tooth from the Late Triassic of southern Africa

An isolated, large recurved and finely serrated tooth found associated with the prosauropodEuskelosaurus from the Late Triassic part of the Elliot Formation is described here. It is compared to the Triassic thecodonts and carnivorous dinosaurs and its possible affinity is discussed. The tooth possibly belongs to a basal theropod and shows some features similar to the allosauroids. This tooth is of significance, as dinosaur remains except for some footprints and trackways, are poorly known in the Late Triassic horizons of southern Africa.     

Insights from stable light isotopes on enamel defects and weaning in Pliocene herbivores

A high prevalence of enamel hypoplasia in several herbivores from the early Pliocene Langebaanweg locality, South Africa, indicates general systemic stress during the growing years of life. The presence of several linear enamel hypoplasias per tooth crown in many teeth further suggest that these stress events may be episodic. The δ¹⁸O values along tooth crowns of mandibular second molars ofSivatherium hendeyi (Artiodactyla, Giraffidae) were used to investigate the cause of the stress events in this tooth type. Results show that weaning in this fossil giraffid occurred at a similar ontogenetic age to that in extant giraffes, and that the observed enamel hypoplasia towards the base of this tooth type manifested post-weaning. Further, high-resolution oxygen isotope analyses acrossS. hendeyi third molars suggest that the entire development of defective tooth crowns occurred under conditions of increased aridity in which the cool, rainy part of the seasonal cycle was missing. The high prevalence of this defect in many herbivores suggests that climatic conditions were not favourable. This study reiterates the value of stable isotope analyses in determining both the behaviour of fossil animals and the environmental conditions that prevailed during tooth development.     

Conserved residue Lys574 in the cavity of HIV-1 Gp41 coiled-coil domain is critical for six-helix bundle stability and virus entry

The fusion-active HIV-1 gp41 core structure is a stable six-helix bundle (6-HB) formed by its N- and C-terminal heptad-repeat sequences (NHR and CHR). A highly conserved, deep hydrophobic cavity on the surface of the N-helical trimer is important for stability of the 6-HB and serves as an ideal target for developing anti-human immunodeficiency virus (HIV) fusion inhibitors. We have recently identified several small molecule HIV-1 fusion inhibitors that bind to the gp41 cavity through hydrophobic and ionic interactions and block the gp41 6-HB formation. Molecular docking analysis reveals that these small molecules fit inside the hydrophobic cavity and interact with positively charged residue Lys574 to form a conserved salt bridge. In this study, the functionality of Lys574 has been finely characterized by mutational analysis and biophysical approaches. We found that substitutions of Lys574 with non-conserved residues (K574D, K574E, and K574V) could completely abolish virus infectivity. With a set of wild-type and mutant N36 peptides derived from the NHR sequence as a model, we demonstrated that non-conservative Lys574 substitutions severely impaired the stability and conformation of 6-HBs as detected by circular dichroism spectroscopy, native polyacrylamide gel electrophoresis, and enzyme-linked immunosorbent assay. The binding affinity of N36 mutants bearing non-conservative Lys574 substitutions to the peptide C34 derived from the CHR sequence dramatically decreased as measured by isothermal titration calorimetry. These substitutions also significantly reduced the potency of N-peptides to inhibit HIV-1 infection. Collectively, these data suggest that conserved Lys574 plays a critical role in 6-HB formation and HIV-1 infectivity, and may serve as an important target for designing anti-HIV drugs.