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At least 1,207 records · Page 67Linked to original sources
PubMed2003

Determination of in vivo oxygen uptake and carbon dioxide evolution rates from off-gas measurements under highly dynamic conditions.

In vivo kinetics of Saccharomyces cerevisiae are studied, in a time window of 150 s, by analyzing the response of O(2) and CO(2) in the fermentor off-gas after perturbation of chemostat cultures by metabolite pulses. Here, a new mathematical method is presented for the estimation of the in vivo oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER) directly from the off-gas data in such perturbation experiments. The mathematical construction allows effective elimination of delay and distortion in the off-gas measurement signal under highly dynamic conditions. A black box model for the fermentor off-gas system is first obtained by system identification, followed by the construction of an optimal linear filter, based on the identified off-gas model. The method is applied to glucose and ethanol pulses performed on chemostat cultures of S. cerevisiae. The estimated OUR is shown to be consistent with the independent dissolved oxygen measurement. The estimated in vivo OUR and CER provide valuable insights into the complex dynamic behavior of yeast and are essential for the establishment and validation of in vivo kinetic models of primary metabolism.

Bioreactors↗
PubMed1990

Concentration of bone elements in osteoporosis.

In aging and in osteoporosis, decreased bone density is associated with decreased bone mass. However, changes in the bone mineral phase remain a matter for investigation. In particular, it is unknown whether bone mineral loss is directly related to reduction in bone mass or associated with changes in the concentration of mineral elements in mineralized bone tissue. In this study, the cortical bone concentration of elements was determined in biopsies of the ilium from 33 subjects (12 controls and 21 individuals with untreated severe osteoporosis). Calcium and phosphorus concentrations were evaluated in cortical and trabecular bone using energy-dispersive x-ray (EDX) microanalysis and inductively coupled plasma optical emission spectrometry (ICPOES). Bone concentrations of Na, K, Mg, Cu, Zn, Fe, Sr, Al, B, and Si were also determined in cortical bone using ICPOES. Additionally, the concentration of F in cortical bone was measured with a specific ion electrode and the concentration of Pb was determined by atomic absorption spectrometry. In mineralized bone tissue there was no significant age-dependent variation in the concentration of Ca, P, or other elements either in controls or in osteoporotic subjects. Moreover, the concentration of elements in bone tissue did not differ in the two groups. These results suggest that the decrease in bone density in osteoporosis is directly related to evolution of the bone mass, without detectable changes in the concentration of elements in bone.

Adult↗
PubMed2000

Flow-Induced Anisotropy in Mixtures of Associative Polymers and Latex Particles.

The effect of associative polymers on the structure and rheological behavior of colloidal suspensions is discussed. Adding associative polymer is known to increase the viscosity of the suspensions. At high shear rates the increase is close to what could be expected on the basis of the hydrodynamic effects of the added polymer. At low shear rates the viscosity increases much more. Small-angle light scattering (SALS) during flow is used here to investigate the underlying structural mechanisms. The SALS patterns indicate that the associative polymer changes the particulate structure: characteristic butterfly patterns appear even at relatively low particle volume fractions. They are not present in the suspensions without associative polymer. The patterns indicate that fluctuations in particle concentration are more pronounced in the flow direction than in the vorticity direction and that anisotropic particulate structures with an orientation along the vorticity direction develop. The evolution of their characteristic length scale during flow has been followed over time. Changing the hydrophilic part of the polymer from polyacrylamide to polyacrylic acid induces stronger associative interactions. In the suspensions this results in a reduction of the relative viscosity rather than an increase. The difference in degree of associativity between the polymers also has an effect on the SALS patterns in the suspensions both at rest and during flow. The rheology as well as the SALS suggest the presence of a strong polymer network in the second system. The competition between adsorption of the associative polymer on the particles with the intermolecular associations between the polymer chains seems to be responsible for the observed differences. Copyright 2000 Academic Press.

Journal Article↗
PubMed1981

Estimating genetic correlations from inbred strains.

Genetic correlations measure the extent of pleiotropic effects of polygenes on pairs of characters or the closeness of linkage between sets of loci influencing the traits and held in allelic (gametic) disequilibrium. Their importance for research lies primarily in predicting correlated responses of one trait to selection based on values for another, and secondarily in analyzing the complex organization of biological systems. Genetic correlations appear to limit the rate and set the direction of multivariate evolution. In view of this, efficient methods for estimating genetic correlations may be essential for understanding the role of behavior in adaptation and for predicting behavioral change in evolution. In this paper we present methods for the estimation of genetic correlations from inbred strain comparisons. Estimates from inbred strains are relatively easy to obtain and appear to be valid when compared to those derived from more demanding parent-offspring comparisons and to correlated responses to selection.

Alleles↗
PubMed2005

Sequence, transcription activity, and evolutionary origin of the R-body coding plasmid pKAP298 from the intracellular parasitic bacterium Caedibacter taeniospiralis.

We isolated the intracellular parasitic bacterium Caedibacter taeniospiralis from cultures of the freshwater ciliate Paramecium tetraurelia strain 298. Plasmid pKAP298 as well as the total RNA were isolated from the bacteria. pKAP298 was totally sequenced (49.1 kb; NCBI accession number AY422720). From southern blots of pKAP-fragments and Digoxigenin-labeled cDNA of the Caedibacter-RNA, we generated transcription maps of pKAP298. The observed transcription activity indicated functions of the plasmid besides the synthesis of the R-body, a complex protein inclusion associated with toxic effects of Caedibacter cells on host paramecia. We identified 63 potential protein coding regions on pKAP298, and a novel transposon as well as known transposons were characterized. A group II intron was identified. Homologies with putative phage genes were detected on pKAP298 that direct to the evolution of pKAP298 from a bacteriophage. This original phage most probably belonged to the Caudovirales. Hints on a toxin coding region of pKAP298 are given: a protein with homology to the Soj-/ParA-family also has homologies to a membrane associated ATPase, which is involved in eukaryotic ATPase dependent ion carriers and may be associated with toxic effects on paramecia ingesting this protein.

Alphaproteobacteria↗
PubMed1995

Evolution of parasite life history traits: myths and reality.

Parasitism has evolved independently several times in many different animal lineages. Observations made on distantly related parasites have revealed a variety of adaptations to parasitism, including changes in physiology, morphology, and life history traits. These observations have led parasitologists to formulate general rules about the evolution of parasites, rules that define a common evolutionary path presumably followed by all parasitic organisms. Robert Poulin uses recent evidence to question the generality of these rules and to show that parasite evolution may take different roads. The selective pressures acting on parasites are diverse and may guide their evolution in any direction, just as they have shaped a wide variety of free-living organisms.

Journal Article↗
PubMed1990

Molecular cytotaxonomy of primates by chromosomal in situ suppression hybridization.

A new strategy for analyzing chromosomal evolution in primates is presented using chromosomal in situ suppression (CISS) hybridization. Biotin-labeled DNA libraries from flow-sorted human chromosomes are hybridized to chromosome preparations of catarrhines, platyrrhines, and prosimians. By this approach rearrangements of chromosomes that occurred during hominoid evolution are visualized directly at the level of DNA sequences, even in primate species with pronounced chromosomal shuffles.

Animals↗
PubMed2004

Atypical PKC phosphorylates PAR-1 kinases to regulate localization and activity.

The establishment and maintenance of cellular polarity are essential biological processes that must be maintained throughout the lifetime of eukaryotic organisms. The Par-1 protein kinases are key polarity determinants that have been conserved throughout evolution. Par-1 directs anterior-posterior asymmetry in the one-cell C. elegans embryo and the Drosophila oocyte. In mammalian cells, Par-1 may regulate epithelial cell polarity. Relevant substrates of Par-1 in these pathways are just being identified, but it is not yet known how Par-1 itself is regulated. Here, we demonstrate that human Par-1b (hPar-1b) interacts with and is negatively regulated by atypical PKC. hPar-1b is phosphorylated by aPKC on threonine 595, a residue conserved in Par-1 orthologs in mammals, worms, and flies. The equivalent site in hPar-1a, T564, is phosphorylated in vivo and by aPKC in vitro. Importantly, phosphorylation of hPar-1b on T595 negatively regulates the kinase activity and plasma membrane localization of hPar-1b in vivo. This study establishes a novel functional link between two central determinants of cellular polarity, aPKC and Par-1, and suggests a model by which aPKC may regulate Par-1 in polarized cells.

Blotting, Western↗
PubMed2004

BAF: roles in chromatin, nuclear structure and retrovirus integration.

Barrier-to-autointegration factor (BAF) is an essential protein that is highly conserved in metazoan evolution. BAF binds directly to double-stranded DNA, nuclear LEM-domain proteins, lamin A and transcription activators. BAF is also a host cell component of retroviral pre-integration complexes. BAF binds matrix, a retroviral protein, and facilitates efficient retroviral DNA integration in vitro through unknown mechanisms. New findings suggest that BAF has structural roles in nuclear assembly and chromatin organization, represses gene expression and might interlink chromatin structure, nuclear architecture and gene regulation in metazoans.

Amino Acid Sequence↗
PubMed2004

A phylogenetic approach to cultural evolution.

There has been a rapid increase in the use of phylogenetic methods to study the evolution of languages and culture. Languages fit a tree model of evolution well, at least in their basic vocabulary, challenging the view that blending, or admixture among neighbouring groups, was predominant in cultural history. Here, we argue that we can use language trees to test hypotheses about not only cultural history and diversification, but also bio-cultural adaptation. Phylogenetic comparative methods take account of the non-independence of cultures (Galton's problem), which can cause spurious statistical associations in comparative analyses. Advances in phylogenetic methods offer new possibilities for the analysis of cultural evolution, including estimating the rate of evolution and the direction of coevolutionary change of traits on the tree. They also enable phylogenetic uncertainty to be incorporated into the analyses, so that one does not have to treat phylogenetic trees as if they were known without error.

Journal Article↗
PubMed1989

Intermediates in membrane fusion and bilayer/nonbilayer phase transitions imaged by time-resolved cryo-transmission electron microscopy.

Bilayer-to-nonbilayer phase transitions in phospholipids occur by means of poorly characterized intermediates. Many have proposed that membrane fusion can also occur by formation of these intermediates. Structures for such intermediates were proposed in a recent theory of these transition mechanisms. Using time-resolved cryo-transmission electron Microscopy (TRC-TEM), we have directly visualized the evolution of inverted phase micro-structure in liposomal aggregates. We have identified one of the proposed intermediates, termed an interlamellar attachment (ILA), which has the structure and dimensions predicted by the theory. We show that ILAs are likely to be the structure corresponding to "lipidic particles" observed by freeze-fracture electron microscopy. ILAs appear to assemble the inverted cubic (III) phase by formation of an ILA lattice, as previously proposed. ILAs are also observed to mediate membrane fusion in the same systems, on the same time scale, and under nearly the same conditions in which membrane fusion was observed by fluorescence methods in earlier studies. These earlier studies indicated a linkage between a membrane fusion mechanism and III phase formation. Our micrographs suggest that the same intermediate structure mediates both of those processes.

Lipid Bilayers↗
PubMed2000

Allopatric combination of Fasciola hepatica and Lymnaea truncatula is more efficient than sympatric ones.

Parasites are capable of rapid evolutionary changes relative to their hosts, due to short life cycle, short generation time, and high fecundity. The direction of the evolution of parasite virulence can be studied in cross-transfer experiments, combining hosts and parasites from different localities, and comparing the outcome of established (sympatric and potentially locally adapted) and novel (allopatric) combinations of hosts and parasites. We aimed to compare the compatibility with snails hosts, the infectivity of metacercariae in rabbits and rats, and the fitness among different combinations (French-FF and Spanish-SS sympatries and allopatry-FS). The first isolate of Fasciola hepatica and its corresponding intermediate host, Lymnaea truncatula originated from Lugo's northwestern Spain. The second isolate of parasite and snail was collected in the Limoges area in central France. The Spanish snails were more susceptible to their sympatric trematode than the French snails. The Spanish flukes were more infective to intermediate hosts (snails) than the French flukes, but subsequent definitive hosts (rats or rabbits) infections remained similar. The estimated fitness was low in sympatric infections and highly similar (from 4.7 to 5.3). The fitness similarity corresponds, however, to different variations in life-history traits that could represent different strategies among the host-parasite local combinations. The infection rate in snails, metacercarial productivity, metacercarial infectivity, and the estimated fitness were better for allopatric combination (FS). The susceptibility data showed a higher efficiency of flukes in the allopatric snail population than in their local snail population. However, our results were obtained after one generation and from a single isolate and it remains to be determined if all allopatric fluke-snail isolates may present a better fitness. Nevertheless our results indicate that introduction of liver fluke-infected cattle should be monitored carefully, as it could result in the introduction of more efficient parasites.

Animals↗
PubMed2003

Shape change of prism solids in different liquid systems during local corrosion.

As reported in many previous publications, the cross section shape of prism solids will maintain the original square or become round after a certain duration of dipping and corrosion in certain melts. This paper gives theoretical explanations for these phenomena. Based on the deduction of the Laplace equation, it is found that for the solid-liquid system with contact angle (theta) smaller than 90 degrees, the maximum height of liquid surface on the lateral faces (H(f)) is greater than that at the prism edges (H(e)) before corrosion. If the corrosion and dissolution of the solid sample reduce the liquid surface tension, the case of H(f)>H(e) will be maintained or intensified due to the larger extent of dissolution at the edges, and the down-and-up motion of the liquid surface on the prism will mainly occur on the lateral faces, resulting in the maintenance of the original square shape of the sample's cross section. However, if the dissolution of the solid sample increases the liquid surface tension, the case H(f) 90 degrees, the liquid surface height exhibits the opposite direction, and the evolution trends of the cross section shape are similar.

Journal Article↗
PubMed2001

Mitochondria make a come back.

This review attempts to summarize our present state of knowledge of mitochondria in relation to a number of areas of biology, and to indicate where future research might be directed. In the evolution of eukaryotic cells mitochondria have for a long time played a prominent role. Nowadays their integration into many activities of a cell, and their dynamic behavior as subcellular organelles within a cell and during cell division are a major focus of attention. The crystal structures of the major complexes of the electron transport chain (except complex I) have been established, permitting increasingly detailed analyses of the important mechanism of proton pumping coupled to electron transport. The mitochondrial genome and its replication and expression are beginning to be understood in considerable detail, but more questions remain with regard to mutations and their repair, and the segregation of the mtDNA in oogenesis and development. Much emphasis and a large effort have recently been devoted to understand the role of mitochondria in programmed cell death (apoptosis). The understanding of their central role in mitochondrial diseases is a major achievement of the past decade. Finally, various drugs have traditionally played a part in understanding biochemical mechanisms within mitochondria; the repertoire of drugs with novel and interesting targets is expanding.

Animals↗
PubMed1999

Cuckoos, cowbirds and the persistence of brood parasitism.

Brood parasites provide a particularly good opportunity for the study of host-parasite evolution because they directly affect the reproductive success of their hosts. Two parasitic species, the common cuckoo (Cuculus canorus) and the brown-headed cowbird (Molothrus ater), differ widely in their relationships with their hosts, yet share the attribute of having been particularly well studied by biologists. Recent work on the cuckoo and the cowbird has resulted in new answers to the question begged by all brood parasites: why do host species raise parasitic young?

Journal Article↗
PubMed2004

Comparative ontogeny in humans and chimpanzees: similarities, differences and paradoxes in postnatal growth and development of the skull.

The hypothesis of retarded development is a classic and controversial issue in human evolution. It depends directly on the understanding of ontogenetic trajectories and their basic constituents: timing, rate and associated patterns of maturation. In the present study, we applied geometric morphometrics to investigate postnatal ontogeny in human and chimpanzee skulls (N = 302). We evaluated postnatal ontogenetic rates, based on comparisons of properties of size and shape in adults. At different dental ages the percentage of the adult mean size (growth) and adult mean shape (development) was used to quantify patterns of maturation. We found significantly higher levels of ontogenetic maturity in humans than chimpanzees during pre-M1 and M1 eruption. However, during this ontogenetic period the human increments were lower than those of chimpanzees suggesting lower rates. During and after M2-eruption species did not differ in their ontogenetic trajectories. The results indicate that higher prenatal and lower peri- and postnatal maturation rates characterize human ontogeny when compared with chimpanzees. If mandibular ontogeny is considered alone, a paradox was found. Whereas growth maturation proceeded in an expected trajectory continuously approximating 100% adult mean size, developmental maturity was different. After M1-eruption in both species the morphological distance, which had increased before, became reduced again, and reached adult mean shape in a second developmental peak. Such a tendency was found in humans and chimpanzees. This indicates that both size and shape maturation must be considered to understand the complexity of postnatal mandibular ontogeny.

Adolescent↗
PubMed2003

Fast multi-dimensional Hadamard spectroscopy.

Multi-dimensional NMR spectroscopy can be speeded up by large factors by replacing the time-domain evolution dimensions by direct irradiation at signal-bearing sites with a frequency-domain multiplex scheme. There is no loss in sensitivity per unit time. The excitation and transfer operations are encoded according to Hadamard matrices and the detected NMR signals are decoded by reference to the same matrices. Most traditional multi-dimensional NMR pulse sequences can be readily converted into this new Hadamard mode. Three-dimensional TOCSY-HSQC experiments on strychnine at 700 MHz bear out these ideas, indicating that the measurement time can be reduced by as much as three orders of magnitude in favorable cases.

Algorithms↗
PubMed2001

[Can donor insemination be optimised?].

OBJECTIVE: To compare the different donor insemination technics. MATERIAL AND METHOD: Analysis of the published studies about donor insemination which value the effectiveness of Intra Cervical Insemination (ICID) and Intra Uterine Insemination (IUID), the interest of ovulation induction, the possible complications, and the cost-effectiveness ratio. RESULTS: The meta-analysis of the Cochrane data base (10 comparative studies IUID versus ICID, 2568 donor insemination cycles) lead to a pregnancy rate per cycle (PRC) 17.77% with IUID versus 7.68% with ICID. The odds ratio is 2.63 (CI from 1.85 to 3.73). With these PRC, the direct cost per evolutive pregnancy is 54,780 F with ICID and 25,675 F with IUID. CONCLUSION: If it is possible to propose ICID to patient with an excellent regularity of ovulation. IUID with ovulation induction by gonadotropins is today the gold standard, and more especially as the law restrict the number of donor inseminations. Indeed, the IUID is two or three times more effective than ICID, consume the half of sperm straws, use a semen of moderate quality, there is no complication provided that the cycle is cancelled if there is more than two mature follicles and the cost-effectiveness ratio is greatly in favour with IUID.

Cervix Uteri↗