Influence of lipolysis and fatty acid availability on fuel selection during exercise

The aim of the present study was to investigate the influence of substrate availability on fuel selection during exercise. Eight endurance-trained male cyclists performed 90-min exercise at 70 % of their maximal oxygen uptake in a cross-over design, either in rested condition (CON) or the day after 2-h exercise practised at 70 % of maximal oxygen uptake (EX). Subjects were given a sucrose load (0.75 g kg^?1 body weight) 45 min after the beginning of the 90-min exercise test. Lipolysis was measured in subcutaneous abdominal adipose tissue (SCAT) by microdialysis and substrate oxidation by indirect calorimetry. Lipid oxidation increased during exercise and tended to decrease during sucrose ingestion in both conditions. Lipid oxidation was higher during the whole experimental period in the EX group (p?=?0.004). Interestingly, fuel selection, assessed by the change in respiratory exchange ratio (RER), was increased in the EX session (p?=?0.002). This was paralleled by a higher rate of SCAT lipolysis reflected by dialysate glycerol, plasma glycerol, and fatty acids (FA) levels (p?<?0.001). Of note, we observed a significant relationship between whole-body fat oxidation and dialysate glycerol in both sessions (r ²?=?0.33, p?=?0.02). In conclusion, this study highlights the limiting role of lipolysis and plasma FA availability to whole-body fat oxidation during exercise in endurance-trained subjects. This study shows that adipose tissue lipolysis is a determinant of fuel selection during exercise in healthy subjects.     

A bacterial effector counteracts host autophagy by promoting degradation of an autophagy component

Beyond its role in cellular homeostasis, autophagy plays anti‐ and promicrobial roles in host–microbe interactions, both in animals and plants. One prominent role of antimicrobial autophagy is to degrade intracellular pathogens or microbial molecules, in a process termed xenophagy. Consequently, microbes evolved mechanisms to hijack or modulate autophagy to escape elimination. Although well‐described in animals, the extent to which xenophagy contributes to plant–bacteria interactions remains unknown. Here, we provide evidence that Xanthomonas campestris pv. vesicatoria (Xcv) suppresses host autophagy by utilizing type‐III effector XopL. XopL interacts with and degrades the autophagy component SH3P2 via its E3 ligase activity to promote infection. Intriguingly, XopL is targeted for degradation by defense‐related selective autophagy mediated by NBR1/Joka2, revealing a complex antagonistic interplay between XopL and the host autophagy machinery. Our results implicate plant antimicrobial autophagy in the depletion of a bacterial virulence factor and unravel an unprecedented pathogen strategy to counteract defense‐related autophagy in plant–bacteria interactions.     

The GUS gene fusion system (Escherichia coli beta-D-glucuronidase gene), a useful tool in studies of root colonization by Fusarium oxysporum.

The plant-pathogenic fungus Fusarium oxysporum was successfully transformed with the beta-D-glucuronidase gene from Escherichia coli (gusA) (GUS system) in combination with the gene for nitrate reductase (niaD) as the selectable marker. The frequency of cotransformation, as determined by GUS expression on plates containing medium supplemented with 5-bromo-4-chloro-3-indolyl glucuronide (GUS+), was very high (up to 75%). Southern hybridization analyses of GUS+ transformants revealed that single or multiple copies of the gusA gene were integrated into the genomes. High levels of GUS activity are expressed in some transformants, but activity in F. oxysporum does not appear to be correlated with the copy number of the gusA gene. Since the highest activity was found in a transformant with a single copy, it can be assumed that sequence elements of F. oxysporum integrated upstream of the gene can act as a promoter or enhancer. Expression of the gusA gene was also detected during growth of the fungus in plants, indicating that the GUS system can be used as a sensitive and easy reporter gene assay in F. oxysporum.     

In and out: adipose tissue lipid turnover in obesity and dyslipidemia

Adipose tissue is the main site of storage and mobilization of lipid. In a recent study published in Nature, Arner et?al. (2011) report that high storage and low removal of adipose triglycerides promotes obesity, whereas low storage and low removal favor the development of dyslipidemia in humans.     

Relationships between transposable elements based upon the integrase-transposase domains: Is there a common ancestor?

The integrase domain of RNA-mediated elements (class I) and the transposase domain of DNA-mediated transposable elements (class II) were compared. A number of elements contain the DDE signature, which plays an important role in their integration. The possible relationships between mariner-Tc1 and IS elements, retrotransposons, and retroviruses were analyzed from an alignment of this region. The mariner-Tc1 superfamily, and LTR retrotransposons and retroviruses were found to be monophyletic groups. However, the IS elements of bacteria were found in several groups. These results were used to propose an evolutionary history that suggests a common ancestor for some integrases and transposases. Received: 3 July 1995 / Accepted: 9 October 1995     

Adrenergic Receptors and Fat Cells: Differential Recruitment by Physiological Amines and Homologous Regulation

The control of fat cell lipolysis by the catecholamines involves at least four different adrenoceptor subtypes; three β (β1-, β2-, and β3-ARs) and one α2-adrenoceptor(α2-AR). The physiological importance of the β- and α2A-ARs varies according to the species, the sex, the age, the anatomical location of fat deposits and the degree of obesity in humans and animals. The physiological amines operate through differential recruitment of these sites on the basis of their relative affinities. This point has been assessed by in vitro studies and has partly been confirmed in in vivo experiments using selected a/β-AR antagonists and in situ microdialysis. The affinity of the β3-AR for catecholamines is less than that of the classical β1- and β2-ARs in the various species investigated. Conversely, it is the α2-AR which exhibit the highest affinity for the physiological amines in all fat cells. The relative order of affinity of the various fat cell ARs for the physiological amines defined in binding studies and in vitro ass ays is α2 > β1 > β2 > β3 for norepinephrine and α2 >β2 > β1> β3 for epinephrine. When considering differential β-AR recruitment by catecholamines, it is the β1-AR which is always activated at the lowest norepinephrine levels, whatever the species, while the activation of the β3-AR requires higher norepinephrine levels. In addition to the differential recruitment, differential regulation by hormones could also occur for each fat cell AR subtype. The α2-and β3-ARs are less prone to desensitization and down-regulation by comparison with the β1- and β2-AR.     

Isolation of the transposable element hupfer from the entomopathogenic fungus Beauveria bassiana by insertion mutagenesis of the nitrate reductase structural gene

A transposable element has been isolated from the entomopathogenic fungus Beauveria bassiana by trapping it in the nitrate reductase structural gene, which has been cloned from this species. The element had inserted in the first exon of the nia gene and appeared to have duplicated the sequence TA at the site of insertion. It was 3336?bp long with 30-bp imperfect, inverted, terminal repeats. The element, called hupfer, contained an open reading frame encoding a 321-amino acid protein similar to the IS630- or mariner-Tc1-like transposases, and a residual sequence of about 2?kb which was not significantly similar to any published sequence. There are fewer than five copies of this transposable element present per genome in the fungus.     

Islands within an island: Repeated adaptive divergence in a single population

Physical barriers to gene flow were once viewed as prerequisites for adaptive evolutionary divergence. However, a growing body of theoretical and empirical work suggests that divergence can proceed within a single population. Here we document genetic structure and spatially replicated patterns of phenotypic divergence within a bird species endemic to 250 km² Santa Cruz Island, California, USA. Island scrub‐jays (Aphelocoma insularis) in three separate stands of pine habitat had longer, shallower bills than jays in oak habitat, a pattern that mirrors adaptive differences between allopatric populations of the species’ mainland congener. Variation in both bill measurements was heritable, and island scrub‐jays mated nonrandomly with respect to bill morphology. The population was not panmictic; instead, we found a continuous pattern of isolation by distance across the east–west axis of the island, as well as a subtle genetic discontinuity across the boundary between the largest pine stand and adjacent oak habitat. The ecological factors that appear to have facilitated adaptive differentiation at such a fine scale—environmental heterogeneity and localized dispersal—are ubiquitous in nature. These findings support recent arguments that microgeographic patterns of adaptive divergence may be more common than currently appreciated, even in mobile taxonomic groups like birds.     

A Nomadic Subtelomeric Disease Resistance Gene Cluster in Common Bean

The B4 resistance (R) gene cluster is one of the largest clusters known in common bean (Phaseolus vulgaris [Pv]). It is located in a peculiar genomic environment in the subtelomeric region of the short arm of chromosome 4, adjacent to two heterochromatic blocks (knobs). We sequenced 650 kb spanning this locus and annotated 97 genes, 26 of which correspond to Coiled-Coil-Nucleotide-Binding-Site-Leucine-Rich-Repeat (CNL). Conserved microsynteny was observed between the Pv B4 locus and corresponding regions of Medicago truncatula and Lotus japonicus in chromosomes Mt6 and Lj2, respectively. The notable exception was the CNL sequences, which were completely absent in these regions. The origin of the Pv B4-CNL sequences was investigated through phylogenetic analysis, which reveals that, in the Pv genome, paralogous CNL genes are shared among nonhomologous chromosomes (4 and 11). Together, our results suggest that Pv B4-CNL was derived from CNL sequences from another cluster, the Co-2 cluster, through an ectopic recombination event. Integration of the soybean (Glycine max) genome data enables us to date more precisely this event and also to infer that a single CNL moved from the Co-2 to the B4 cluster. Moreover, we identified a new 528-bp satellite repeat, referred to as khipu, specific to the Phaseolus genus, present both between B4-CNL sequences and in the two knobs identified at the B4 R gene cluster. The khipu repeat is present on most chromosomal termini, indicating the existence of frequent ectopic recombination events in Pv subtelomeric regions. Our results highlight the importance of ectopic recombination in R gene evolution.In the human genome, extensive cytogenetic and sequence analyses have revealed that subtelomeres are hot spots of interchromosomal recombination and segmental duplications (Linardopoulou et al., 2005). This peculiar dynamic activity of subtelomeres has been reported in such diverse organisms as yeast and the malaria parasite Plasmodium (Louis, 1995; Freitas-Junior et al., 2000, 2005). As expected for a plastic region of the genome subject to reshuffling through recombination events, subtelomeres exhibit unusually high levels of within-species structural and nucleotide polymorphism (Mefford and Trask, 2002). In plants, this plasticity of subtelomeres has not been identified in Arabidopsis (Arabidopsis thaliana; Heacock et al., 2004; Kuo et al., 2006) and, to our knowledge, has not yet been investigated at a large scale for other plant species with full genome sequences available. Regarding Arabidopsis, the apparent lack of high subtelomeric recombination may reflect its small and simple subtelomeres, mirroring its small genome size and relative paucity of repetitive sequences (Heacock et al., 2004; Kuo et al., 2006).Repetitive sequences, such as satellite DNA and retroelements, constitute an important fraction of every eukaryotic genome and therefore constitute the environment in which genes are expressed. Satellite DNA can be defined as highly reiterated noncoding DNA sequences, organized as long arrays of head-to-tail linked repeats of 150- to 180-bp or 300- to 360-bp monomers located in the constitutive heterochromatin (Plohl et al., 2008). Despite their ubiquity in eukaryotic genomes, little is known about the mechanisms that allow these elements to accumulate. Early hypotheses considered them to be nonfunctional “selfish” or “junk” DNA segments that increase or decrease their frequency without any advantage or disadvantage for an organism (Ohno, 1972; Orgel and Crick, 1980). However, identification of satellite DNA at structurally important parts of chromosomes, such as centromeres, has suggested functional roles of satellite DNA (Ma and Jackson, 2006; Kawabe and Charlesworth, 2007). Satellite DNA can also be localized in knobs, which are cytologically visible regions of highly condensed chromatin (heterochromatin) that are distinct from pericentromeric regions in pachytene chromosomes (Fransz et al., 2000; Gaut et al., 2007; Lamb et al., 2007).The survival of most organisms depends on the presence of specific genetic systems that maintain diversity in order to respond to changing environments. Plants, like animals, are continually challenged by a large array of pathogens. To perceive and counter pathogen attack, plants have evolved disease resistance (R) genes. The largest class of R genes encodes proteins containing a central Nucleotide-Binding Site (NBS) domain, a C-terminal Leucine-Rich Repeat (LRR) domain, and a variable N-terminal domain. These R proteins detect the presence of disease-causing bacteria, oomycetes, fungi, nematodes, insects, and viruses by sensing either specific pathogen effector molecules produced during the infection process or key molecules in the plant cell that may be attacked by pathogen effectors (Dangl and McDowell, 2006). The evolution of new R genes serves to counteract the evolution of novel virulence factors from the pathogens (McDowell and Simon, 2008). Among this prevalent class of R gene, two subclasses, corresponding to two ancient lineages (Bai et al., 2002; Meyers et al., 2003; Ameline-Torregrosa et al., 2008), have been identified based on the N-terminal domain of the R protein: the Coiled-Coil (CC)-NBS-LRR (CNL) and the Toll-Interleukin receptor (TIR)-NBS-LRR (TNL). Genome studies have demonstrated that NBS-LRR (NL) sequences are abundant in any plant genome. For example, annotation of the Arabidopsis, rice (Oryza sativa), poplar (Populus trichocarpa), Medicago truncatula (Mt), grape (Vitis vinifera), Lotus japonicus (Lj), and papaya (Carica papaya) genomes identified at least 149, 480, 317, 333, 233, 229, and 55 genes encoding NL proteins, respectively (Bai et al., 2002; Meyers et al., 2003; Zhou et al., 2004; Tuskan et al., 2006; Velasco et al., 2007; Ameline-Torregrosa et al., 2008; Kohler et al., 2008; Ming et al., 2008; Sato et al., 2008). NL sequences are often located at complex loci (Smith et al., 2004), as exemplified by Arabidopsis, where two-thirds of them are organized in tightly linked clusters (Meyers et al., 2003; Leister, 2004; McDowell and Simon, 2006). Evolution of NL sequences in the Arabidopsis genome has been investigated according to their phylogenetic positions and physical locations. Although tandem duplications explain the origin of a large fraction of NLs, it seems that ectopic recombination has also played a role in Arabidopsis NL evolution, since mixed clusters comprising evolutionarily distant NL exist. Ectopic recombination is also evident when phylogenetically close R genes are physically dispersed on different chromosomes (Leister, 2004; McDowell and Simon, 2006). These results confirm pioneer macrosynteny studies between related monocot species suggesting the existence of NL movement in plant genomes. Indeed, extensive loss of collinearity between NL sequences between rice and barley (Hordeum vulgare), which diverged 50 million years ago (Mya), has suggested rapid reorganization of NL sequences (Leister et al., 1998; Leister, 2004). However, our knowledge of the molecular evolution of R genes remains limited due to the still small number of complete plant genome sequences available to date. Detailed comparative study across taxa at different evolutionary distances is needed to see how R gene clusters evolve at various time scales.Legumes (Fabaceae) constitute the third largest family of flowering plants and represent the second most important family of agronomically important plants after Poaceae (Graham and Vance, 2003). As a result of recent sequencing efforts, legumes are one of the few plant families with extensive genome sequences in different species, since the soybean (Glycine max [Gm]) genome sequence is complete (http://www.phytozome.net/soybean.php) and both Mt and Lj genome sequences are nearly complete (Young et al., 2005; Sato et al., 2008). Consequently, the legume family is extremely well adapted for comparative phylogenomic approaches, in which phylogenetic inference is combined with structural genomic analyses (Ammiraju et al., 2008). Common bean (Phaseolus vulgaris [Pv]) is the most important grain legume for direct human consumption (Broughton et al., 2003). Pv is a selfing species and has a small diploid genome (2n = 22) of 588 Mb (Bennett and Leitch, 1995). Conservation of genome macrostructure (macrosynteny) has been reported between several legumes, including common bean and the two model legume species Mt and Lj genomes (Zhu et al., 2005; Hougaard et al., 2008). However, the extent of gene order conservation at the DNA sequence level has not yet been evaluated within orthologous chromosome segments between Pv and the two model legume species.In the genome of common bean, many disease R genes are clustered at complex loci located at the ends (rather than the centers) of linkage groups (LGs; Vallejos et al., 2006; Geffroy et al., 2008). For example, Colletotrichum lindemuthianum Co-2 R specificity maps at one end of LG B11 (Adam-Blondon et al., 1994). Molecular analysis has revealed that this locus consists of a tandem array of CNL sequences (Geffroy et al., 1998; Creusot et al., 1999). Another CNL-rich region has been identified at the end of LG B4 in the vicinity of R specificities and R quantitative trait loci against a large selection of pathogens, including C. lindemuthianum, Uromyces appendiculatus, and the bacterium Pseudomonas syringae (Geffroy et al., 1998, 1999; Miklas et al., 2006). Recently, fluorescence in situ hybridization (FISH) analysis revealed that this complex R cluster is located in the subtelomeric region of the short arm of chromosome 4 and includes two knobs (Geffroy et al., 2009). In a sequencing effort focused on CNL sequences, we have previously identified 17 CNL sequences of the B4 locus (referred to as B4-CNL) from Pv genotype BAT93 (Ferrier Cana et al., 2003, 2005; Geffroy et al., 2009). In the BAT93 genotype, these B4-CNL sequences are located on both sides of the subterminal knob (Geffroy et al., 2009).To investigate the organization and the evolutionary origin of the subtelomeric B4 R gene cluster, we have sequenced approximately 650 kb of the Pv B4 R gene cluster, revealing that, in genotype BAT93, CNL are spread out in four subclusters, separated by non-CNL-encoding genes. This Pv sequence was then compared gene by gene with the sequenced portions of the three sequenced legume genomes, Mt, Lj, and Gm. Conserved microsynteny (conservation of local gene repertoire, order, and orientation) was observed, except for the CNL sequences, which appear to be completely absent in the corresponding regions of Mt and Lj. In this study, by combining genomics, phylogenetic, and cytogenetic approaches, we provide evidence that ectopic recombination in subtelomeric regions between nonhomologous chromosomes (4 and 11), involving a single CNL, gave rise to the Pv B4 R gene cluster. Chromosomal distribution of a new satellite DNA tandem repeat, referred to as khipu, suggests that ectopic recombination events in subtelomeric regions of bean nonhomologous chromosomes are frequent. Our results highlight the importance of ectopic recombination as an important evolutionary mechanism for the evolution of disease resistance genes.     

Breeding latitude and timing of spring migration in songbirds crossing the Gulf of Mexico

Each spring, millions of songbirds migrate across the Gulf of Mexico on their way to breeding sites in North America. Data from radar and migration monitoring stations have revealed broad patterns in the spatial and temporal course of trans-Gulf migration. Unfortunately, we have limited information on where these birds have previously spent the winter and where they are migrating to breed. Here we measure stable-hydrogen isotopes in feathers (δD_f) to infer the breeding latitude of five species of songbirds – hooded warblers Wilsonia citrina , American redstarts Setophaga ruticilla , black-and-white warblers Mniotilta varia , ovenbirds Seiurus aurocapilla , and northern waterthrushes S. noveboracensis – that were captured at a stopover site along the coast of southwestern Louisiana in spring 2004. Values of δD_f across all species ranged from −163 to −35‰ (n=212), and within most species the range was consistent with the latitudinal extent of known breeding sites in central and eastern North America. Individuals that arrived first along the northern Gulf coast had δD_f values indicative of southerly breeding sites in hooded warblers, American redstarts, black-and-white warblers, and ovenbirds, but no relationship was found between passage timing and δD_f for northern waterthrushes. Our findings suggest that spring passage is often timed to coincide with the emergence of suitable conditions on breeding areas, with southern breeding birds migrating first.