The deviation from linkage equilibrium with multiple loci varying in a stepping-stone cline

The balance between the creation of associations between alleles at different loci by immigration and the convergence to linkage equilibrium due to the recombination process is studied in a theoretical model. The geographical structure of the model is a stepping-stone chain of populations linking two genetically constant source populations. The model assumes an arbitrary number of autosomal loci and considers genetic variation (two alleles at each locus) that is not subject to natural selection. The gene frequencies at each locus will then show a linear cline through the stepping-stone chain of populations. The deviation from linkage equilibrium through the stepping-stone cline is characterized by an equation for linear measures that provide the linkage disequilibrium measures for a given set of loci in terms of the gene frequencies and the linkage disequilibria in the source populations and in terms of the linkage disequilibrium measures through the cline for lower numbers of loci. Numerical examples of this iterative solution are given, and it is shown that the build-up of the higher order Bennett-disequilibria through the cline is considerably more pronounced than the build-up of two-locus disequilibria.     

Soil legacy effects of plants and drought on aboveground insects in native and range-expanding plant communities

Soils contain biotic and abiotic legacies of previous conditions that may influence plant community biomass and associated aboveground biodiversity. However, little is known about the relative strengths and interactions of the various belowground legacies on aboveground plant–insect interactions. We used an outdoor mesocosm experiment to investigate the belowground legacy effects of range-expanding versus native plants, extreme drought and their interactions on plants, aphids and pollinators. We show that plant biomass was influenced more strongly by the previous plant community than by the previous summer drought. Plant communities consisted of four congeneric pairs of natives and range expanders, and their responses were not unanimous. Legacy effects affected the abundance of aphids more strongly than pollinators. We conclude that legacies can be contained as soil ‘memories’ that influence aboveground plant community interactions in the next growing season. These soil-borne ‘memories’ can be altered by climate warming-induced plant range shifts and extreme drought.     

Catalytic and regulatory roles of species involved in metal–nucleotide equilibriums in human pyridoxal kinase

Pyridoxal 5′-phosphate is the active form of vitamin B₆ and its deficiency is directly related with several human disorders, which make human pyridoxal kinase (hPLK) an important pharmacologic target. In spite of this, a carefully kinetic characterization of hPLK including the main species that regulates the enzymatic activity is at date missing. Here we analyse the catalytic and regulatory mechanisms of hPLK as a function of a precise determination of the species involved in metal–nucleotide equilibriums and describe new regulatory mechanisms for this enzyme. hPLK activity is supported by several metals, being Zn²⁺ the most effective, although the magnitude of the effect observed is highly dependent on the relative concentrations of metal and nucleotide used. The true substrate for the reaction catalyzed by hPLK is the metal nucleotide complex, while ATP^4? and HATP^3? did not affect the activity. The enzyme presents substrate inhibition by both pyridoxal (PL) and ZnATP^2?, although the latter behaves as a weakly inhibitor. Our study also established, for the first time, a dual role for free Zn²⁺; as an activator at low concentrations (19 μM optimal concentration) and as a potent inhibitor with a IC₅₀ of 37 μM. These results highlighted the importance of an accurate estimation of the actual concentration of the species involved in metal–nucleotide equilibriums in order to obtain reliable values for the kinetic parameters, and for determine the true regulators of the PLK activity. They also help to explain the dissimilar kinetic parameters reported in the literature for this enzyme.     

Species Traits as Practical Tools for Ecological Restoration of Marly Eroded Lands

Plant functional traits are increasingly used in restoration ecology because they have the potential to guide restoration practices at a broad scale. This article presents a trait‐based multi‐criteria framework to evaluate and predict the performance of 17 plant seedlings to improve ecological restoration of marly eroded areas in the French Southern Alps. The suitability of these species to limit soil erosion was assessed by studying both their response to erosive forces and their effect on erosion dynamics. We assumed that species efficiency could be explained and predicted from plant traits and we looked for trait‐performance relationships. Our results showed that root slenderness ratio, the percentage of fine roots and root system topology, were the three root morphology traits best describing anchorage strength. Root system characterized by a long and thin tap root and many fine lateral ramifications would be the best to resist concentrated runoff. Species response to burial mainly depended on growth form and morphological flexibility. The abilities of species in reinforcing the soil and reducing erosion rates were negatively correlated to root diameter and positively to the percentage of fine roots. Moreover, root system density and root tensile strength also influenced root reinforcement. Finally, the ability to trap sediment was positively correlated to leaf area and canopy density. Species were then scored and classified in four clusters according to their global performance. This method allows identifying species that possess both response and effect traits related to the goal of preventing erosion during ecological restoration.     

Inhibition of fibroblast growth by Notch1 signaling is mediated by induction of Wnt11-dependent WISP-1

Fibroblasts are an integral component of stroma and important source of growth factors and extracellular matrix (ECM). They play a prominent role in maintaining tissue homeostasis and in wound healing and tumor growth. Notch signaling regulates biological function in a variety of cells. To elucidate the physiological function of Notch signaling in fibroblasts, we ablated Notch1 in mouse (Notch1(Flox/Flox)) embryonic fibroblasts (MEFs). Notch1-deficient (Notch1(-/-)) MEFs displayed faster growth and motility rate compared to Notch1(Flox/Flox) MEFs. Such phenotypic changes, however, were reversible by reconstitution of Notch1 activation via overexpression of the intracellular domain of Notch1 (NICD1) in Notch1-deficient MEFs. In contrast, constitutive activation of Notch1 signaling by introducing NICD1 into primary human dermal fibroblasts (FF2441), which caused pan-Notch activation, inhibited cell growth and motility, whereas cellular inhibition was relievable when the Notch activation was countered with dominant-negative mutant of Master-mind like 1 (DN-MAML-1). Functionally, "Notch-activated" stromal fibroblasts could inhibit tumor cell growth/invasion. Moreover, Notch activation induced expression of Wnt-induced secreted proteins-1 (WISP-1/CCN4) in FF2441 cells while deletion of Notch1 in MEFs resulted in an opposite effect. Notably, WISP-1 suppressed fibroblast proliferation, and was responsible for mediating Notch1's inhibitory effect since siRNA-mediated blockade of WISP-1 expression could relieve cell growth inhibition. Notch1-induced WISP-1 expression appeared to be Wnt11-dependent, but Wnt1-independent. Blockade of Wnt11 expression resulted in decreased WISP-1 expression and liberated Notch-induced cell growth inhibition. These findings indicated that inhibition of fibroblast proliferation by Notch pathway activation is mediated, at least in part, through regulating Wnt1-independent, but Wnt11-dependent WISP-1 expression.     

Phenolic derivatives from Ruprechtia polystachya and their inhibitory activities on the glucose-6-phosphatase system

Two new compounds, 5-methyl-2-(2-methylbutanoyl)phloroglucinol 1-O-(6-O-β-D-apiofuranosyl)-β-D-glucopyranoside (1) and trans-2,3-dihydrokaempferol 3-O-(4-O-sulfo)-α-L-arabinopyranoside (2), together with 14 known flavonoids, trans-dihydrokaempferol 3-O-α-L-arabinopyranoside (3), trans-taxifolin 3-O-α-L-arabinofuranoside (4), quercetin 3-O-α-L-rhamnopyranoside (5), quercetin 3'-O-α-L-arabinofuranoside (6), catechin 3-O-α-L-rhamnopyranoside (7), trans-taxifolin 3-O-α-L-arabinopyranoside (8), cis-dihydrokaempferol 3-O-α-L-arabinopyranoside (9), catechin (10), myricetin 3-O-α-L-rhamnopyranoside (11), quercetin 3-O-α-L-arabinopyranoside (12), quercetin 3-O-α-L-arabinofuranoside (13), quercetin 3-O-(3″-galloyl)-α-L-rhamnopyranoside (14), quercetin 3-O-(2″-galloyl)-α-L-rhamnopyranoside (15), and epicatechin 3-O-gallate (16), were isolated from the leaves of Ruprechtia polystachya Griseb. (Polygonaceae). Their structures were established on the basis of extensive 1D- and 2D-NMR experiments as well as MS analyses. All compounds, except 1, showed inhibition of the enzyme glucose-6-phosphatase in intact microsomes.     

Effect of an extract of nereis virens on mammalian spermatozoa

Epididymal sperm of the mouse, rat, and guinea pig and ejaculated sperm of rabbits are cleaved at the head-tail junction by an extract of Nereis virens. Annelids are extracted with water and the extract is purified by ion exchange chromatography. Electron microscopy shows that the extract acts on the filaments connecting the capitulum of the tail with the basal plate lining the nuclear envelope. Following detachment, the basal plate remains with the head. The extract contains proteases as indicated by hydrolysis of tosyl arginine methyl ester (TAME), benzoyl arginine ethyl ester (BAEE), and Azocoll, a general protease substrate. The hydrolysis of TAME is inhibited by tosyl lysine chloromethyl ketone (TLCK), a trypsin inhibitor, but TLCK does not prevent head-tail separation by the Nereis extract. Similarly tosyl phenylalanine chloromethyl ketone (TPCK), a chymotrypsin inhibitor, and phosphoramidon and leucyltryptophan, both thermolysin and acrolysin inhibitors — singly or in combination — do not prevent hydrolysis of Azocoll. Head-tail separation activity of the extract was inhibited by dithiothreitol, which reduces disulfide bonds, and phenylmethyl sulfonyl fluoride, an inhibitor of serine proteases. These results indicate that the extract is a mixture of proteases, one being a serine protease similar to trypsin. Digestion of the connecting filaments with the pure proteases, trypsin and Staphylococcus aureus V8 protease, has yielded the following information on the proteins of the filaments. The accessibility of arginine and/or lysine peptide bonds to enzyme action is highest in rat sperm filaments, whereas those in the filaments of mouse, rabbit, and guinea pig sperm are less accessible than in the rat. Another possibility is that the total content of arginine and/or lysine varies between the species. The most dramatic difference is the enzymatic action on glutamyl peptide bonds of the filaments, the order being: mouse 〉 rat 〉 rabbit, with guinea pig sperm filaments completely resistant over the time course of the experiment.     

A GIPC1-Palmitate Switch Modulates Dopamine Drd3 Receptor Trafficking and Signaling

Palmitoylation is involved in several neuropsychiatric and movement disorders for which a dysfunctional signaling of the dopamine D3 receptor (Drd3) is hypothesized. Computational modeling of Drd3''s homologue, Drd2, has shed some light on the putative role of palmitoylation as a reversible switch for dopaminergic receptor signaling. Drd3 is presumed to be palmitoylated, based on sequence homology with Drd2, but the functional attributes afforded by Drd3 palmitoylation have not been studied. Since these receptors are major targets of antipsychotic and anti-Parkinsonian drugs, a better characterization of Drd3 signaling and posttranslational modifications, like palmitoylation, may improve the prospects for drug development. Using molecular dynamics simulations, we evaluated in silico how Drd3 palmitoylation could elicit significant remodeling of the C-terminal cytoplasmic domain to expose docking sites for signaling proteins. We tested this model in cellulo by using the interaction of Drd3 with the G-alpha interacting protein (GAIP) C terminus 1 (GIPC1) as a template. From a series of biochemical studies, live imaging, and analyses of mutant proteins, we propose that Drd3 palmitoylation acts as a molecular switch for Drd3-biased signaling via a GIPC1-dependent route, which is likely to affect the mode of action of antipsychotic drugs.     

Notch1 control of oligodendrocyte differentiation in the spinal cord

We have selectively inhibited Notch1 signaling in oligodendrocyte precursors (OPCs) using the Cre/loxP system in transgenic mice to investigate the role of Notch1 in oligodendrocyte (OL) development and differentiation. Early development of OPCs appeared normal in the spinal cord. However, at embryonic day 17.5, premature OL differentiation was observed and ectopic immature OLs were present in the gray matter. At birth, OL apoptosis was strongly increased in Notch1 mutant animals. Premature OL differentiation was also observed in the cerebrum, indicating that Notch1 is required for the correct spatial and temporal regulation of OL differentiation in various regions of the central nervous system. These findings establish a widespread function of Notch1 in the late steps of mammalian OPC development in vivo.