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At least 1,171 records · Page 65Linked to original sources
PubMed2006

Molecular evolution of plant immune system genes.

Molecular population genetic studies are providing new perspectives on the evolution of genes that confer resistance to pathogens and herbivores. Here, we compare the evolutionary history of different components of the defense response (detection, signaling and response) and of genes with parallel function in plants and Drosophila. A review of the literature indicates that the dominant form of selection acting on defense genes (balancing, positive and purifying) differs among components of defense. Sampling of particular classes of genes and genes from non-model organisms, however, remains limited. Future studies combining molecular evolutionary analyses with ecological genetic and functional analyses should better reveal how natural selection has shaped defense gene evolution.

Animals↗
PubMed2004

Re-assessment of monophyly, evolution of myrmecophytism, and rapid radiation in Neonauclea s.s. (Rubiaceae).

The biologically interesting ant-plant association, myrmecophytism, occurs in ca. 140 of the 11,000 species and 22 of the 630 genera of the coffee family (Rubiaceae). These myrmecophytic Rubiaceae species are predominantly distributed in Southeast Asia, especially the Malesian region, with comparatively few species in mainland Africa and the Neotropics. The mostly Southeast Asian genus Neonauclea s.s is one of the three Rubiaceae genera with extensive radiation of myrmecophytes and also the most speciose genus of the tribe Naucleeae s.l. We perform parsimony phylogenetic analyses of Neonauclea s.s., previously resolved as paraphyletic, and its allied genera using both ETS and ITS sequencing data to test: (1) the paraphyly of Neonauclea s.s.; (2) the phylogenetic relationships within the Ludekia-Myrmeconauclea-Neonauclea complex; and (3) the evolution of myrmecophytism within the complex. The earlier proposed paraphyly of Neonauclea s.s. appears to be the result of the combined effects of parallel substitutions in Metadina trichotoma and the sampled ITS putative pseudogenes of Neonauclea longipedunculata and losses of some synapomorphies of Neonauclea s.s. in the latter. The analyses present strong support for the monophyly of Myrmeconauclea and Neonauclea s.s. and their sister-group relationships. Our findings additionally favor the hypothesis of multiple origins of myrmecophytism in the Bornean Neonauclea, which have independently been exploited by at least three Cladomyrma ant species. Furthermore, we interpret the low levels of variation in both the ETS and ITS sequences as indication of a recent and rapid radiation for Neonauclea s.s. (with 65 species) and a recent and slow radiation for Myrmeconauclea (with three species). We argue that the rapid diversification of Neonauclea s.s. is partly associated with the nature of its fruits and its ability to colonize a wide range of habitats. We postulate that both ecological and geographical events may have been responsible for the radiation of the non-myrmecophytic Neonauclea species. Finally, we argue that the acquisition of the pseudo-multiple fruits and long-tailed seeds has allowed Myrmeconauclea to specialize on rheophytic habitats but its narrow ecological tolerance may have hindered its speciation.

Animals↗
PubMed2006

Evolutionary simulations to detect functional lineage-specific genes.

MOTIVATION: Supporting the functionality of recent duplicate gene copies is usually difficult, owing to high sequence similarity between duplicate counterparts and shallow phylogenies, which hamper both the statistical and experimental inference. RESULTS: We developed an integrated evolutionary approach to identify functional duplicate gene copies and other lineage-specific genes. By repeatedly simulating neutral evolution, our method estimates the probability that an ORF was selectively conserved and is therefore likely to represent a bona fide coding region. In parallel, our method tests whether the accumulation of non-synonymous substitutions reveals signatures of selective constraint. We show that our approach has high power to identify functional lineage-specific genes using simulated and real data. For example, a coding region of average length (approximately 1400 bp), restricted to hominoids, can be predicted to be functional in approximately 94-100% of cases. Notably, the method may support functionality for instances where classical selection tests based on the ratio of non-synonymous to synonymous substitutions fail to reveal signatures of selection. Our method is available as an automated tool, ReEVOLVER, which will also be useful to systematically detect functional lineage-specific genes of closely related species on a large scale. AVAILABILITY: ReEVOLVER is available at http://www.unil.ch/cig/page7858.html.

Animals↗
PubMed2004

Evolution of GCYC, a Gesneriaceae homolog of CYCLOIDEA, within Gesnerioideae (Gesneriaceae).

Through recent advances in molecular developmental biology it has become clear that similar morphological traits may sometimes arise from different genetic bases. The molecular developmental biology of floral symmetry has been examined recently in detail and several genes important in controlling floral symmetry in diverse Asteridae have been identified. One of the most important among these is the floral symmetry gene CYCLOIDEA (CYC). We compared GCYC (the Gesneriaceae homolog of CYC) sequences in Gesneriaceae genera with the typical bilaterally symmetric flowers and genera with radial or near radial symmetry. Parsimony, Bayesian and maximum likelihood analyses of GCYC sequences among members of Gesnerioideae are mostly congruent with previous phylogenetic hypotheses, but suggest two unexpected generic positions: Diastema as sister to Gesneria, and Bellonia within Gloxinieae. In order to evaluate whether these results might be artifactual we obtained new gene sequences from chloroplast and nuclear ribosomal regions. These data disagree with GCYC regarding the placement of Diastema, but agree with GCYC regarding Bellonia. We did not find any mutations in GCYC that could explain the shift in symmetry and there were no consistent differences in molecular evolution between taxa with bilaterally or radially symmetric flowers. Likewise taxa with radial floral symmetry are not sister to each other showing that the loss of bilateral symmetry has occurred multiple times in parallel. Further investigations of GCYC expression will be necessary to determine if any of these independent events involved changes in the regulation of GCYC.

Asteraceae↗
PubMed2003

Dynamics in the evolution of sexual traits: losses and gains, radiation and convergence in yellow wagtails (Motacilla flava).

We analyse patterns of genetic diversity and song complexity in the Palaearctic yellow wagtail (Motacilla flava), a highly polytypic species complex. Mitochondrial and nuclear DNA show that the complex is polyphyletic, despite parallel plumage variation in western and eastern clades. In the western clade there is genetic structure among southern subspecies, haplotype diversity decreases with latitude, and northern subspecies show evidence of bottlenecking and rapid expansions, as expected from isolation in glacial refugia followed by postglacial colonization. However, northern subspecies, which have more divergent male plumages, lack genetic structure and sing simpler songs. Loss of song complexity and evolution of plumage in founder populations are consistent with the Kaneshiro model, which posits that variation among species is a consequence of founder-induced shifts in female preference leading to loss of ancestral male sexual traits. Our results suggest possible postglacial founder-effect mechanisms for the morhological diversification of the yellow wagtail complex.

Animals↗
PubMed1998

Structure, stability, and thermodynamics of lamellar DNA-lipid complexes.

We develop a statistical thermodynamic model for the phase evolution of DNA-cationic lipid complexes in aqueous solution, as a function of the ratios of charged to neutral lipid and charged lipid to DNA. The complexes consist of parallel strands of DNA intercalated in the water layers of lamellar stacks of mixed lipid bilayers, as determined by recent synchrotron x-ray measurements. Elastic deformations of the DNA and the lipid bilayers are neglected, but DNA-induced spatial inhomogeneities in the bilayer charge densities are included. The relevant nonlinear Poisson-Boltzmann equation is solved numerically, including self-consistent treatment of the boundary conditions at the polarized membrane surfaces. For a wide range of lipid compositions, the phase evolution is characterized by three regions of lipid to DNA charge ratio, rho: 1) for low rho, the complexes coexist with excess DNA, and the DNA-DNA spacing in the complex, d, is constant; 2) for intermediate rho, including the isoelectric point rho = 1, all of the lipid and DNA in solution is incorporated into the complex, whose inter-DNA distance d increases linearly with rho; and 3) for high rho, the complexes coexist with excess liposomes (whose lipid composition is different from that in the complex), and their spacing d is nearly, but not completely, independent of rho. These results can be understood in terms of a simple charging model that reflects the competition between counterion entropy and inter-DNA (rho < 1) and interbilayer (rho > 1) repulsions. Finally, our approach and conclusions are compared with theoretical work by others, and with relevant experiments.

Biophysical Phenomena↗
PubMed1992

Three-dimensional echocardiography: techniques and applications.

Current echocardiographic devices provide only 2-dimensional views of the heart. To appreciate 3-dimensional structural relations, therefore, requires mental reconstruction of 2-dimensional views by an experienced observer. Our ability to answer new questions about the heart could be increased if 2-dimensional images could be combined to display 3-dimensional relations. Such 3-dimensional reconstruction would permit analysis of structures of unknown or complex shape and the noninvasive quantification of cardiac chamber size and function without making geometric assumptions. To overcome previous limitations, mechanisms have been developed for automated integration of images and positional data during routine echocardiographic scanning, thereby greatly enhancing the efficiency and application of image reconstruction. Refining the diagnosis of mitral valve prolapse has presented a uniquely 3-dimensional problem requiring information previously unavailable from the 2-dimensional technique. To date, 3-dimensional studies have demonstrated that the mitral valve is saddle-shaped in systole, so that apparent superior leaflet displacement in the mediolateral 4-chamber view, often seen in otherwise normal individuals, lies entirely within the bounds defined by the mitral annulus and occurs without leaflet distortion or actual displacement above the entire mitral valve. Other applications of 3-dimensional image reconstruction include calculation of ventricular volume and ejection fraction by transthoracic or transesophageal scanning without geometric assumptions; improving the standardization and accuracy of 2-dimensional measurements by improving spatial appreciation; and 3-dimensional reconstruction of vascular walls to guide interventions. In the future, systems for acquiring multiple views more rapidly by parallel processing and improving endocardial border extraction should allow more routine application of 3-dimensional methods as the next stage in the evolution of cardiac ultrasound, thereby expanding the range of questions that can be answered. Achieving these goals will depend, in large measure, on persistence in developing the necessary technology.

Echocardiography↗
PubMed1999

DNA cleavage and proteolysis of microtubule-associated protein 2 after cerebral ischemia of different severity.

We report temporal profiles of cytoplasmic proteolysis and genomic DNA cleavage after cerebral ischemia of different severity in gerbils. Global forebrain ischemia by bilateral common carotid artery occlusion for 5 min with reperfusion, severe unilateral hemispheric ischemia by unilateral common carotid artery occlusion for 30 min with reperfusion, and complete ischemia by decapitation were used. The hippocampus was examined for proteolysis by using immunohistochemistry for microtubule-associated protein 2, DNA cleavage by using in situ nick-end labelling, and nuclear morphology by Hematoxylin staining. During evolution of delayed neuronal death after transient forebrain ischemia, loss of the immunoreaction for microtubule-associated protein 2 occurred almost in parallel with DNA cleavage in the CA1 region. In contrast, disappearance of the immunoreaction for microtubule-associated protein 2 was much faster than genomic DNA cleavage after unilateral hemispheric ischemia and reperfusion. The microtubule-associated protein 2 immunoreactivity was completely lost before development of changes in nuclear morphology or DNA cleavage after complete ischemia. The present study demonstrated the differences between necrosis and delayed neuronal death, but the nuclear morphology in the latter was not exactly the same as seen in apoptosis. Some elements of both necrotic and apoptotic machineries may work following transient ischemia, and the degree of ischemic insult may determine the character of cell death process.

Animals↗
PubMed2004

Germline imprinting: battle of the sexes or battle of the X's?

The X chromosome is largely inactivated in spermatogenesis of heterogametic males, and in multiple phyla it encodes few genes specifically expressed in the male germline. Writing in Nature Genetics, Bean et al. report a parallel between male germline X inactivation in nematodes and a fungal gene-silencing mechanism that alters the way we view the evolution of both phenomena.

Animals↗
PubMed2005

Fabrication of malachite with a hierarchical sphere-like architecture.

Malachite (Cu2(OH)2CO3) with a hierarchical sphere-like architecture has been successfully synthesized via a simple and mild hydrothermal route in the absence of any external inorganic additives or organic structure-directing templates. Powder X-ray diffraction, scanning electron microscopy, and Fourier transmission infrared spectrometry are used to characterize various properties of the obtained malachite samples. The hierarchical malachite particles are uniform spheres with a diameter of 10-20 microm, which are comprised of numerous two-dimensional microplatelets paralleling the sphere surface. The initial concentration of reagents, the hydrothermal reaction time, and temperature are important factors which dominantly affect the evolution of crystal morphologies. The growth of the hierarchical architecture is believed to be a layer-by-layer growth process. Further, copper oxide with the similar morphology can be easily obtained from the as-prepared malachite.

Copper↗
PubMed1966

Sulfolipid metabolism in chlorella.

When S-deficient cells of Chlorella cllipsoidea were incubated in radio-sulfate in light or in aerobic darkness for 1 hour, equal amounts of radioactivity were found in sulfolipid and glutathione but none was detected in sulfoquinovosyl glycerol which is one of the major S-compounds in this alga. No assimilation of radiosulfate was observed under anaerobic darkness.To elucidate the function of sulfolipid in algal cells uniformly (35)S-labeled Chlorella cells were transferred to S-deficient culture medium or unlabeled normal culture medium and the changes of radioactivity in sulfolipid and the related compounds were followed. A) On incubating (35)S-labeled algal cells in S-deficient medium under photosynthetic conditions, the amounts of radioactivity in sulfate, sulfoquinovosyl glycerol and sulfolipid decreased rapidly. B) When (35)S-labeled cells were cultured photoautotrophically in unlabeled medium, no decrease of radioactivity was observed in sulfoquinovosyl glycerol and sulfolipid. C) A decrease of (35)S-sulfolipid and an increase of (35)S-sulfoquinovosyl glycerol were observed when the uniformly (35)S-labeled algal cells were illuminated in CO(2)-free air.When S-deficient Chlorella cells were incubated in (35)S-sulfolipid under photosynthetic conditions, significant radioactivity was found in the insoluble fraction of the cells. A similar result was observed when normal Chlorella cells were incubated in (14)C-sulfolipid and CO(2)-free air.It is inferred from these observations that sulfolipid is a reservoir of sulfur and carbon compounds.In order to ascertain if the sulfolipid is involved in the mechanism of photosynthetic oxygen evolution, the rate of photosynthesis was measured during the incubation of (35)S-labeled cells in a S-deficient medium. Parallelism was not observed between the rate of photosynthetic activity and the decrease of sulfolipid.

Journal Article↗
PubMed1974

Ethylene-induced Tropism of Trifolium fragiferum L. Stolons.

The hypothesis that ethylene regulates prostrate stem growth was investigated using stolons of strawberry clover (Trifolium fragiferum L. var. Salina). Stolons became erect when treated with ethylene or 2-chloroethylphosphonic acid. Curvature was visibly detectable 2 hours after ethylene treatment, and subsequent stem elongation was rapid. Indoleacetic acid application to prostrate stolons caused only a small transitory curvature persisting less than 48 hours. Indoleacetic acid-stimulated curvature was accompanied by an increase in ethylene evolution. When stolon curvature was induced by placing strawberry clover plants in darkness or by applying gibberellic acid, ethylene production did not parallel stolon curvature.

Journal Article↗
PubMed2004

Interneurone bursts are spontaneously associated with muscle contractions only during early phases of mouse spinal network development: a study in organotypic cultures.

For a short time during development immature circuits in the spinal cord and other parts of the central nervous system spontaneously generate synchronous patterns of rhythmic activity. In the case of the spinal cord, it is still unclear how strongly synchronized bursts generated by interneurones are associated with motoneurone firing and whether the progressive decline in spontaneous bursting during circuit maturation proceeds in parallel for motoneurone and interneurone networks. We used organotypic cocultures of spinal cord and skeletal muscle in order to investigate the ontogenic evolution of endogenous spinal network activity associated with the generation of coordinate muscle fibre contractions. A combination of multiunit electrophysiological recordings, videomicroscopy and optical flow computation allowed us to measure the correlation between interneurone firing and motoneurone outputs after 1, 2 and 3 weeks of in vitro development. We found that, in spinal organotypic slices, there is a developmental switch of spontaneous activity from stable bursting to random patterns after the first week in culture. Conversely, bursting recorded in the presence of strychnine and bicuculline became increasingly regular with time in vitro. The time course of spontaneous activity maturation in organotypic slices is similar to that previously reported for the spinal cord developing in utero. We also demonstrated that spontaneous bursts of interneurone action potentials strongly correlate with muscular contractions only during the first week in vitro and that this is due to the activation of motoneurones via AMPA-type glutamate receptors. These results indicate the occurrence in vitro of motor network development regulating bursting inputs from interneurones to motoneurones.

Action Potentials↗
PubMed1997

Changes in TGF-beta 1 levels in gingiva, crevicular fluid and serum associated with periodontal inflammation in humans and dogs.

Transforming growth factor-beta (TGF-beta) represents a family of polypeptide growth factors, involved in embryogenesis, inflammation, regulation of immune responses and wound healing. To determine whether TGF-beta contributes to the evolution of periodontal disease, we assayed TGF-beta levels in gingiva and crevicular fluid of patients with gingivitis and periodontitis. In parallel, TGF-beta was quantified in gingival fluid and serum of beagles with experimentally-induced periodontitis. Disease was monitored by several clinical parameters including Plaque Index, Gingival Index, probing depth, and epithelial attachment loss. Gingival tissues were obtained from 9 patients at the time of periodontal surgery, and gingival fluid samples were collected from an additional population of 10 periodontal patients. In 14 beagles, experimental periodontitis was induced and gingival fluids collected 6 months later. Fluid was collected by paper strips and volume measured by Periotron. Additionally, sera was collected before and 9 months after the ligature-induced periodontitis in 7 beagles. The levels of TGF-beta 1 were measured by ELISA. In the patients, a significantly higher concentration of TGF-beta 1 was observed both in the gingival tissues and fluid samples obtained from the sites with deeper periodontal pockets than in the less involved sites. In beagles, TGF-beta 1 levels measured in gingival fluid were elevated in moderate disease, declining in fluid samples obtained from the pockets during more advanced experimental periodontitis. Furthermore, with the progression of experimental periodontitis, a decrease in TGF-beta 1 occurred in the sera of the beagle dogs. These data suggest that TGF-beta 1 may play a rôle in the pathogenesis and diagnosis of periodontal disease, and that its actions can be further explored in an animal model.

Adult↗
PubMed1997

Temporal filtering properties of ampullary electrosensory neurons in the torus semicircularis of Eigenmannia: evolutionary and computational implications.

Weakly electric fish have parallel electrosensory systems, the phylogenetically older ampullary system and the novel tuberous system. The tuberous system is an adaptation related to the evolution of active electrolocation. To examine the evolutionary relationship of the ampullary and tuberous systems, the temporal filtering properties of ampullary neurons in the dorsal torus semicircularis of Eigenmannia were studied. 'Whole-cell' recordings were made in vivo using patch-type pipettes. The responses of 19 neurons to sinusoidal electric signals (< 40 Hz) were recorded and the anatomy of these neurons demonstrated by injection of biocytin. All eight low-pass ampullary neurons had broad, relatively smooth post-synaptic potentials (psps) that at low frequencies nicely reflected the sinusoidal stimuli. These neurons had somata of 10-14 microns diameter and thick, spiny dendrites. Eight high-pass neurons were recorded, representing three physiological classes. The first class (3 neurons) had psps that roughly followed the sinusoidal time course of the stimulus; the psp morphology was similar to low-pass neurons. The second class had many small, fast, individual psps; their rate of occurrence varied with the stimulus. Finally, four neurons showed psps that were of constant width across stimulus frequencies. All three classes of high-pass neurons had small somata (8-10 microns diameter) with thin dendrites and either few or no spines. Some of these neurons had large varicosities on the dendrites. Three neurons had band-pass filtering properties: neurons that showed strong band-pass properties were morphologically similar to low-pass neurons. Comparisons of the temporal filtering, shapes of post-synaptic potentials, and anatomy of ampullary and tuberous neurons in the torus suggest that the circuitry for tuberous processing in the torus may have evolved as an elaboration or duplication of the ampullary system. The mechanisms underlying the low-pass filtering characteristics of tuberous neurons therefore appear to have predated the evolution of the tuberous system and to have served as a pre-adaptation for the evolution of the jamming avoidance response. In addition, these data support the hypothesis that spine density influences the temporal filtering properties of neurons.

Animals↗
PubMed2000

Relationships within Cupressaceae sensu lato: a combined morphological and molecular approach.

Parsimony analysis of matK and rbcL sequence data, together with a nonmolecular database, yielded a well-resolved phylogeny of Cupressaceae sensu lato. Monophyly of Cupressaceae sensu stricto is well supported, and separate northern and southern hemisphere subclades are resolved, with Tetraclinis within the northern subclade; there is no support for any of the tribes sensu Li. Taxodiaceae comprise five separate lineages. Chamaecyparis nootkatensis falls within Cupressus, clustering with a robust clade of New World species. Libocedrus Florin is paraphyletic and should incorporate Pilgerodendron. Evolution of several characters of wood and leaf anatomy and chemistry is discussed in light of this estimate of the phylogeny; numerous parallelisms are apparent. A new infrafamilial classification is proposed in which seven subfamilies are recognized: Callitroideae Saxton, Athrotaxidoideae Quinn, Cunninghamioideae (Sieb. & Zucc.) Quinn, Cupressoideae Rich. ex Sweet, Sequoioideae (Luerss.) Quinn, Taiwanioideae (Hayata) Quinn, Taxodioideae Endl. ex K. Koch. The rbcL sequence for Taxodium distichum is corrected, and the implications for a previously published estimate of the minimum rate of divergence of the gene since the Miocene are highlighted.

Journal Article↗
PubMed1990

[Candida albicans uveopapillitis. Diagnostic and therapeutic discussion apropos of a case].

Due to the difficulties encountered in the etiologie diagnosis of papillo uveitis along with the increasing occurrence of fungal infections (in paralleled with the number of AIDS affected patients), we found of interest to report a case of exsudative macular chorioretinitis with poor evolution under steroid therapy. In this patient infection by Candida Albicans was suspected and confirmed only after isolation and culture of the fungal from a vitrectomy specimen. A therapeutic apponch using Fluconazole (Triflucan allowed a dramatic improvement of visual acuity within a few months. Thus, vitrectomy appears as a decisive step in the diagnosis of endogenous ocular candidiasis. This diagnosis is even more difficult to suspect in patient without immun deficiency more any extraocular focal infestation.

Adult↗