AFLP markers support separation of Solanum nodiflorum from Solanum americanum sensu stricto (Solanaceae)

This study was aimed at examining the relationships between the African material of Solanum americanum (also designated as S. nodiflorum), accessions of this taxon from other geographical areas, and American S. americanum using AFLP markers. 96 individuals representing 39 accessions of S. americanum sensu lato and related diploid species from the widest possible geographical range, and one accession of S. dulcamara (as outgroup) were used. The AFLP results suggested that American S. americanum differs from S. nodiflorum and that the material investigated in this study can be assigned to three different species: S. americanum sensu stricto, S. nodiflorum and a Solanum species from Brazil. These species can be differentiated based on a combination of floral and fruit characteristics.     

Behavioral and neural responses of toads to salt solutions correlate with basolateral membrane potential of epidermal cells of the skin

Dehydrated toads initiated water absorption response (WR) behavior and absorbed water from dilute NaCl solutions. With 200-250 mM NaCl, WR behavior and water absorption were both suppressed. With 200-250 mM Na-gluconate, WR initiation was significantly greater than with NaCl but water loss was greater. Neural recordings from spinal nerve #6 showed a greater integrated response to 250 mM NaCl than to 250 mM Na-gluconate, whereas a larger rinse response was seen with Na-gluconate. Studies with isolated epithelium showed a large increase in conductance (G(t)) when 250 mM NaCl replaced NaCl Ringer's as the apical bathing solution that was accompanied by depolarization of the transepithelial potential (V(t)) and basolateral membrane potential (V(b)). Depolarization of V(b) corresponded with the neural response to 250 mM NaCl. When 250 mM Na-gluconate replaced Ringer's as the apical solution G(t) remained low, V(b) transiently hyperpolarized to values near the equilibrium potential for K(+) and corresponded with the reduced neural response. These results support the hypothesis that chemosensory function of the skin is analogous to that of mammalian taste cells but utilizes paracellular ion transport to a greater degree.     

Distribution and seasonal variability in the benthic eukaryotic community of Río Tinto (SW, Spain), an acidic, high metal extreme environment

The eukaryotic community of the Río Tinto (SW, Spain) was surveyed in fall, winter and spring through the combined use of traditional microscopy and molecular approaches, including Denaturing Gradient Gel Electrophoresis (DGGE) and sequence analysis of 18S rRNA gene fragments. Eukaryotic assemblages of surface sediment biofilms collected in January, May and September 2002 were compared from 13 sampling stations along the river. Physicochemical data revealed extremely acidic conditions (the pH ranged from 0.9 to 2.5) with high concentrations of heavy metals, including up to 20 mg l(-1) Fe, 317 mg l(-1) Zn, 47 mg l(-1) As, 42 mg l(-1) Cd and 4 mg l(-1) Ni. In total, 20 taxa were identified, including members of the Bacillariophyta, Chlorophyta and Euglenophyta phyla as well as ciliates, cercomonads, amoebae, stramenopiles, fungi, heliozoans and rotifers. In general, total cell abundances were highest in fall and spring but decreased drastically in winter, and the sampling stations with the most extreme conditions showed the lowest number of cells, as well as the lowest diversity. Species diversity did not vary much during the year. Only the filamentous algae showed a dramatic seasonal change, since they almost disappeared in winter and reached the highest biomass during the summer. Principal Components Analysis (PCA) showed a high inverse correlation between pH and most of the heavy metals analyzed, as well as Dunaliella sp., while Chlamydomonas sp. was directly related to pH during May and September. Three heavy metals (Zn, Cu and Ni) remained separate from the rest and showed an inverse correlation with most of the species analyzed, except for Dunaliella sp.     

Rapid evolution of female-biased, but not male-biased, genes expressed in the avian brain

The powerful pressures of sexual and natural selection associated with species recognition and reproduction are thought to manifest in a faster rate of evolution in sex-biased genes, an effect that has been documented particularly for male-biased genes expressed in the reproductive tract. However, little is known about the rate of evolution for genes involved in sexually dimorphic behaviors, which often form the neurological basis of intrasexual competition and mate choice. We used microarray data, designed to uncover sex-biased expression patterns in embryonic chicken brain, in conjunction with data on the rate of sequence evolution for >4,000 coding regions aligned between chicken and zebra finch in order to study the role of selection in governing the molecular evolution for sex-biased and unbiased genes. Surprisingly, we found that female-biased genes, defined across a range of cutoff values, show a higher rate of functional evolution than both male-biased and unbiased genes. Autosomal male-biased genes evolve at a similar rate as unbiased genes. Sex-specific genomic properties, such as heterogeneity in genomic distribution and GC content, and codon usage bias for sex-biased classes fail to explain this surprising result, suggesting that selective pressures may be acting differently on the male and female brain.     

Electric field-induced polarization of charged cell surface proteins does not determine the direction of galvanotaxis

Galvanotaxis, that is, migration induced by DC electric fields, is thought to play a significant role in development and wound healing, however, the mechanisms by which extrinsic electric fields orchestrate intrinsic motility responses are unknown. Using mammalian cell lines (3T3, HeLa, and CHO cells), we tested one prevailing hypothesis, namely, that electric fields polarize charged cell surface molecules, and that these polarized molecules drive directional motility. Negatively charged sialic acids, which contribute the bulk of cell surface charge, redistribute preferentially to the surface facing the direction of motility, as measured by labeling with fluorescent wheat germ agglutinin. We treated cells with neuraminidase to remove sialic acids; as expected, this decreased total cell surface charge. We also changed cell surface charge independent of sialic acid moieties, by conjugating cationic avidin to the surface of live cells. Neuraminidase inhibited the electric field-induced directional polarization of membrane ruffling and alpha4 integrin, while avidin treatment actually reversed the directional polarization of sialic acids. Neuraminidase treatment inhibited directionality but did not alter speed of motility. Surprisingly, avidin treatment did not significantly alter either directionality or speed of motility. Thus, our results demonstrate that electric field-induced polarization of charged species indeed occurs. However, polarization of the bulk of charged cell surface proteins is neither necessary nor sufficient to cause motility, thus contradicting the second part of our hypothesis. Because neuraminidase inhibited directional motility, we also conclude that sialic acids are required constituents of some cell surface molecule(s) through which electric fields mount a polarized transmembrane response.     

Dissection of the insulin-sensitizing effect of liver X receptor ligands

The liver X receptors (LXRalpha and beta) are nuclear receptors that coordinate carbohydrate and lipid metabolism. Treatment of insulin-resistant mice with synthetic LXR ligands enhances glucose tolerance, inducing changes in gene expression expected to decrease hepatic gluconeogenesis (via indirect suppression of gluconeogenic enzymes) and increase peripheral glucose disposal (via direct up-regulation of glut4 in fat). To evaluate the relative contribution of each of these effects on whole-body insulin sensitivity, we performed hyperinsulinemic-euglycemic clamps in high-fat-fed insulin-resistant rats treated with an LXR agonist or a peroxisome proliferator-activated receptor gamma ligand. Both groups showed significant improvement in insulin action. Interestingly, rats treated with LXR ligand had lower body weight and smaller fat cells than controls. Insulin-stimulated suppression of the rate of glucose appearance (Ra) was pronounced in LXR-treated rats, but treatment failed to enhance peripheral glucose uptake (R'g), despite increased expression of glut4 in epididymal fat. To ascertain whether LXR ligands suppress hepatic gluconeogenesis directly, mice lacking LXRalpha (the primary isotype in liver) were treated with LXR ligand, and gluconeogenic gene expression was assessed. LXR activation decreased expression of gluconeogenic genes in wild-type and LXRbeta null mice, but failed to do so in animals lacking LXRalpha. Our observations indicate that despite inducing suggestive gene expression changes in adipose tissue in this model of diet-induced insulin resistance, the antidiabetic effect of LXR ligands is primarily due to effects in the liver that appear to require LXRalpha. These findings have important implications for clinical development of LXR agonists as insulin sensitizers.     

Membrane inlet for mass spectrometric measurement of nitric oxide

We point out the advantages of membrane inlet mass spectrometry for the measurement of nitric oxide in aqueous solution. The membrane inlet probe was a 1.0-cm segment of Silastic tubing attached to the vacuum inlet leading to the ion source. Silastic is a semipermeable silicon rubber that allows flux of uncharged substances including nitric oxide (NO). The use of such an inlet to measure NO has several advantages that we demonstrate in this report. It provides a direct, continuous, and quantitative determination of dissolved nitric oxide concentrations over long periods of real time. The use of such an inlet in our system had a response time of 5 to 7 s and a detection lower limit with the current model of 1.0 nM. This apparatus was used to measure the generation of NO from solutions of nitrite, NONOates, and nitroprusside. The usefulness of such an inlet in measuring NO in physiological systems is discussed.     

Cerebellar LTD and pattern recognition by Purkinje cells

Many theories of cerebellar function assume that long-term depression (LTD) of parallel fiber (PF) synapses enables Purkinje cells to learn to recognize PF activity patterns. We have studied the LTD-based recognition of PF patterns in a biophysically realistic Purkinje-cell model. With simple-spike firing as observed in vivo, the presentation of a pattern resulted in a burst of spikes followed by a pause. Surprisingly, the best criterion to distinguish learned patterns was the duration of this pause. Moreover, our simulations predicted that learned patterns elicited shorter pauses, thus increasing Purkinje-cell output. We tested this prediction in Purkinje-cell recordings both in vitro and in vivo. In vitro, we found a shortening of pauses when decreasing the number of active PFs or after inducing LTD. In vivo, we observed longer pauses in LTD-deficient mice. Our results suggest a novel form of neural coding in the cerebellar cortex.     

Asymmetric dispersal and survival indicate population sources for grassland butterflies in agricultural landscapes

We tested the hypothesis that populations in small habitat fragments remaining in agricultural landscapes are maintained by repeated immigration, using three grassland butterflies ( Aphantopus hyperantus , Coenonympha pamphilus and Maniola jurtina ). Transect counts in 12 matched sets of semi-natural pastures, and linear habitat elements proximate and isolated from the pastures showed that population densities of M.  jurtina and C.  pamphilus were significantly higher in pastures and in linear habitats adjacent to these than in isolated linear elements. A mark-recapture study in a 2×2 km landscape indicated that individuals of all three species are able to reach even the isolated linear elements situated at least 1 km from the grasslands. For two of the species, A.  hyperantus and C.  pamphilus , analysis of the mark-recapture data revealed higher daily local survival rates in the semi-natural pastures and more individuals dispersing from pastures to linear habitat elements. The proportion of old compared to young individuals of C.  pamphilus and M.  jurtina were significantly higher in linear elements than in semi-natural pastures, which suggests that butterflies emerging in pastures subsequently dispersed to the linear elements. In combination, these results suggest that semi-natural pastures act as population sources, from which adult butterflies disperse to surrounding linear elements. Hence, preservation of the remaining fragments of semi-natural grassland is necessary to keep the present butterfly abundance in the surrounding agricultural landscape.