Initiation of multicellular differentiation in Dictyostelium discoideum is regulated by coronin A

Many biological systems respond to environmental changes by activating intracellular signaling cascades, resulting in an appropriate response. One such system is represented by the social amoeba Dictyostelium discoideum. When food sources become scarce, these unicellular cells can initiate a cAMP-driven multicellular aggregation program to ensure long-term survival. On starvation, the cells secrete conditioned medium factors that initiate cAMP signal transduction by inducing expression of genes such as cAMP receptors and adenylate cyclase. The mechanisms involved in the activation of the first pulses of cAMP release have been unclear. We here show a crucial role for the evolutionarily conserved protein coronin A in the initiation of the cAMP response. On starvation, coronin A–deficient cells failed to up-regulate the expression of cAMP-regulated genes, thereby failing to initiate development, despite a normal prestarvation response. Of importance, external addition of cAMP to coronin A–deficient cells resulted in normal chemotaxis and aggregate formation, thereby restoring the developmental program and suggesting a functional cAMP relay in the absence of coronin A. These results suggest that coronin A is dispensable for cAMP sensing, chemotaxis, and development per se but is part of a signal transduction cascade essential for system initiation leading to multicellular development in Dictyostelium.     

Antiamoebic and spasmolytic activities of extracts from some antidiarrhoeal traditional preparations used in Kinshasa, Congo.

Three major extracts from some traditional preparations, based on medicinal plants, used as antidiarrhoeal agents were investigated for their putative antiamoebic and spasmolytic activities in vitro. Results indicated that both biological activities are concentrated in the polyphenolic fraction, and not in the saponin or alkaloid containing fractions. The most active polyphenolic extracts were those from Euphorbia hirta whole plant, leaves of Alchornea cordifolia, Crossopteryx febrifuga, Nauclea latifolia, Psidium guajava, Tithonia diversifolia, stem bark of Harungana madagascariensis, Mangifera indica, Maprounea africana and Psidium guajava, inhibiting Entamoeba histolytica growth with MAC < 10 micrograms/ml. The same extracts, at a concentration of 80 micrograms/ml in an organ bath, also exhibited more than 70% inhibition of acetylcholine and/or KCl solution-induced contractions on isolated guinea-pig ileum.     

Antiviral activity of Rwandan medicinal plants against human immunodeficiency virus type-1 (HIV-1)

Selected plants used in Rwandan traditional medicine for the treatment of infections and/or rheumatoid diseases were investigated for antiviral activity in vitro against human immunodeficiency virus type-1 (HIV-1). Of the 38 tested 80% ethanolic extracts, belonging to plants of 21 different families only the extracts from the leaves of Aspilia pluriseta (Asteraceae) and Rumex bequaertii (Polygonaceae) had interesting selectivity indices (SI = ratio of the 50% cytotoxic concentration to the 50% effective antiviral concentration) higher than 1. Further fractionation of the initially antivirally inactive ethanolic extract of Tithonia diversifolia, however, led to an aqueous fraction with a high anti-HIV-1 activity (SI > 461), indicating that the cytotoxicity of some plant components may mask the antiviral properties of the active plant substances in total plant extracts.     

Effect of irradiance and plant age on the dimensions of the growing shoot of poplar

Populus euramericana (Dode) Guinier cv. Robusta plants were cultivated at irradiances of 7.5, 15 and 30 W m⁻² (32.5, 65 and 130 μmol m² s⁻¹), 400–700 nm at 22°C and a relative humidity between 40 and 60% on a gravel culture subirrigated with Hoagland's nutrient solution. The basal diameter of the growing shoot, a measure of the number of apical cells participating in growth, increased proportionally to irradiance and was correlated with mature leaf length. The development of the length of the growing shoot (L_gs) depended also on the nutritional status of the (young) shoot. L_gs was strongly correlated with the rate of height growth.     

Thermodynamics of the various forms of the dodecamer d(ATTACCGGTAAT) and of its constituent hexamers from proton nmr chemical shifts and UV melting curves: three-state and four-state thermodynamic models

Chemical shifts of base and H1' protons of the single-stranded hexamers d(ATTACC) and d(GGTAAT), of the 1:1 mixtures of these complementary hexamers, and of the self-complementary dodecamer d(ATTACCGGTAAT) were measured at various temperatures in aqueous solution. Four different sample concentrations were used in the case of the dodecamer and of the mixture of the complementary hexamers; the individual hexamers were measured at two different DNA concentrations. Absorbance temperature profiles at five different NaCl concentrations were measured for the dodecamer in order to quantify the effect of the ionic strength on the duplex formation. Under suitable conditions of nucleotide concentration, temperature, and ionic strength, the dodecamer adopts either a B-DNA duplex or a hairpin-loop structure. Chemical shift vs temperature profiles, constructed for all samples, were used to obtain thermodynamic parameters either for the various stacking interactions in the single strands or for the duplex or the hairpin-loop formation. In the analysis of the duplex formation of the hexamers, a two-state approach appeared too simple, because systematic deviations were revealed. Therefore, a new three-state model (DUPSTAK) was developed. In order to investigate the magnitude of error arising from the use of the two-state approach in cases where the DUPSTAK model appears more appropriate, a series of test calculations was made. The magnitude of error in the enthalpy and in the entropy of duplex melting is found to depend linearly upon the actual melting temperature and not upon the individual delta Hd degrees and delta Sd degrees values. Thermodynamic analysis of the chemical shift vs temperature profiles in D2O solution (no added salt) yields an average Tmd value of 341 K (1M DNA) and delta Hd degrees of - 121 kJ.mol-1 for the dimer/random-coil transition of the hexamer duplex d(ATTACC).d(GGTAAT). For the duplex in equilibrium random-coil transition of the 12-mer d(ATTACCGGTAAT) an average Tmd value of 336 K (1M DNA) and delta Hd degrees of -372 kJ.mol-1 are found. The hairpin/random-coil transition of d(ATTACCGGTAAT) is characterized by a rather large delta Hh degrees value, -130 kJ.mol-1, and an average Tmh value of 304 K.     

Holothuria triterpene glycosides: a comprehensive guide for their structure elucidation and critical appraisal of reported compounds

Phytochemistry Reviews - Sea cucumbers or holothurians are marine invertebrates, belonging to the phylum Echinodermata (kingdom Animalia). In Asia, they are commonly used as food, while they are...     

Polyphenols isolated from antiradical extracts of Mallotus metcalfianus

Six flavonoids including two new flavones, luteolin 7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside), chrysoeriol-7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside) and a mixture of two pairs of diastereoisomeric flavonolignans, (±)-hydnocarpin 7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside)/(±)-hydnocarpin-D 7-O-(4″-O-(E)-coumaroyl)-β-glucopyranoside) with a 2:1 ratio were isolated from the whole plant of Mallotus metcalfianus Croizat, in addition to 10 known compounds. Their structures were evaluated on the basis of different spectroscopic methods, including extensive 1D and 2D NMR spectroscopy. Some extracts have moderate antimicrobial properties and interesting antiradical (DPPH) activity, as well as some compounds isolated from this species. Tannins were also identified in some active extracts.