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PubMed2000

Adaptive evolution of larvae and life cycles.

The larval patterns of marine invertebrates pose intriguing questions for both evolutionary and developmental biologists. However, combined investigations have been rare. Quantitative models analyze the selective factors that drive evolutionary change in larval nutrition and timing of metamorphosis. Developmental studies describe the morphogenesis characterizing ancestral and derived larval patterns. Rigorous evolutionary analysis of the transition to derived modes of development is lacking and detailed developmental and ecological data are needed to test and refine theoretical models. A major challenge facing studies of life cycle evolution is the elucidation of the genetic structure and covariance of important developmental and larval traits.

Adaptation, Physiological↗
PubMed2005

Life cycle assessment of active and passive groundwater remediation technologies.

Groundwater remediation technologies, such as pump-and-treat (PTS) and funnel-and-gate systems (FGS), aim at reducing locally appearing contaminations. Therefore, these methodologies are basically evaluated with respect to their capability to yield local improvements of an environmental situation, commonly neglecting that their application is also associated with secondary impacts. Life cycle assessment (LCA) represents a widely accepted method of assessing the environmental aspects and potential impacts related to a product, process or service. This study presents the set-up of a LCA framework in order to compare the secondary impacts caused by two conceptually different technologies at the site of a former manufactured gas plant in the city of Karlsruhe, Germany. As a FGS is already operating at this site, a hypothetical PTS of the same functionality is adopted. During the LCA, the remediation systems are evaluated by focusing on the main technical elements and their significance with respect to resource depletion and potential adverse effects on ecological quality, as well as on human health. Seven impact categories are distinguished to address a broad spectrum of possible environmental loads. A main point of discussion is the reliability of technical assumptions and performance predictions for the future. It is obvious that a high uncertainty exists when estimating impact specific indicator values over operation times of decades. An uncertainty analysis is conducted to include the imprecision of the underlying emission and consumption data and a scenario analysis is utilised to contrast various possible technological variants. Though the results of the study are highly site-specific, a generalised relative evaluation of potential impacts and their main sources is the principle objective rather than a discussion of the calculated absolute impacts. A crucial finding that can be applied to any other site is the central role of steel, which particularly derogates the valuation of FGS due to the associated emissions that are harmful to human health. In view of that, environmental credits can be achieved by selecting a mineral-based wall instead of sheet piles for the funnel construction and by minimising the steel consumption for the gate construction. Granular activated carbon (GAC) is exclusively considered as the treatment material, both in-situ and on-site. Here it is identified as an additional main determinant of the relative assessment of the technologies since it is continuously consumed.

Charcoal↗
PubMed2003

PfSPATR, a Plasmodium falciparum protein containing an altered thrombospondin type I repeat domain is expressed at several stages of the parasite life cycle and is the target of inhibitory antibodies.

The annotated sequence of chromosome 2 of Plasmodium falciparum was examined for genes encoding proteins that may be of interest for vaccine development. We describe here the characterization of a protein with an altered thrombospondin Type I repeat domain (PfSPATR) that is expressed in the sporozoite, asexual, and sexual erythrocytic stages of the parasite life cycle. Immunoelectron microscopy indicated that this protein was expressed on the surface of the sporozoites and around the rhoptries in the asexual erythrocytic stage. An Escherichia coli-produced recombinant form of the protein bound to HepG2 cells in a dose-dependent manner and antibodies raised against this protein blocked the invasion of sporozoites into a transformed hepatoma cell line. Sera from Ghanaian adults and from a volunteer who had been immunized with radiation-attenuated P. falciparum sporozoites specifically recognized the expression of this protein on transfected COS-7 cells. These data support the evaluation of this protein as a vaccine candidate.

Amino Acid Sequence↗
PubMed1993

Protein-primed DNA replication: role of inverted terminal repeats in the Escherichia coli bacteriophage PRD1 life cycle.

Escherichia coli bacteriophage PRD1 and its relatives contain linear double-stranded DNA genomes, the replication of which proceeds via a protein-primed mechanism. Characteristically, these molecules contain 5'-covalently bound terminal proteins and inverted terminal nucleotide sequences (inverted terminal repeats [ITRs]). The ITRs of each PRD1 phage species have evolved in parallel, suggesting communication between the molecule ends during the life cycle of these viruses. This process was studied by constructing chimeric PRD1 phage DNA molecules with dissimilar end sequences. These molecules were created by combining two closely related phage genomes (i) in vivo by homologous recombination and (ii) in vitro by ligation of appropriate DNA restriction fragments. The fate of the ITRs after propagation of single genomes was monitored by DNA sequence analysis. Recombinants created in vivo showed that phages with nonidentical genome termini are viable and relatively stable, and hybrid phages made in vitro verified this observation. However, genomes in which the dissimilar DNA termini had regained identical sequences were also detected. These observations are explained by a DNA replication model involving two not mutually exclusive pathways. The generality of this model in protein-primed DNA replication is discussed.

Amino Acid Sequence↗
PubMed1990

Proteases in the schistosome life cycle: a paradigm for tumour metastasis.

Cancers and parasites have a number of properties in common, particularly those that relate to their respective capacities to evade host defence mechanisms. This review highlights the similarities between metastatic tumours and schistosomes in particular, and describes the role that proteases may have in the migration, growth, survival and transmission of the different stages of the schistosome life-cycle in the vertebrate host. An elastase-like serine protease of schistosome larvae has been particularly well characterized, and its substrate profile and other properties are indicative of a role in facilitating migration of the parasite through skin tissue early after infection. The primary structures of a cathepsin B-like enzyme, and a putative 'haemoglobinase' found in adult worms have also recently been derived, these enzymes being responsible for degradation of haemoglobin in erythrocytes upon which the adults feed. Adult schistosome worms reside and produce eggs intravascularly, and the processes that mediate the extravasation and subsequent migration of the egg through host tissue are dependent on both blood platelets and the immune response. Fibrino(geno)lytic enzymatic activity that is present in the egg could modulate the thrombogenic potential that eggs might have as a result of their capacity to cause platelet aggregation in vitro and in vivo. The roles of other proteases and peptidases that have been found in schistosome larvae, worms and eggs are less clear. Some of these enzymes may modulate immunological and haemostatic defence mechanisms and thus prolong survival of the parasite, and the consequences of the interactions between schistosomes and host protease inhibitors could also be immune modulatory.

Animals↗
PubMed1991

The life cycle of Amblyomma parvum Aragao, 1908 (Acari: Ixodidae) under laboratory conditions.

A colony of Amblyomma parvum was started with engorged females collected from cattle in the Province of Salta (25 degrees 01' S, 63 degrees 56' W), Argentina. The progeny of those ticks were fed on rabbits and the non-parasitic stages maintained at 27 +/- 1 degrees C, 83-86% RH in darkness. The life cycle (prefeeding period not evaluated) had a mean duration of 99.6 days. The mean time (days) for the different phases of the cycle were as follows: feeding period of females, 8.0; pre-oviposition period, 5.7; oviposition period, 17.5; minimum incubation period of the eggs, 31.8; feeding period of larvae, 3.2; premoult period to nymphs, 10.9; feeding period of nymphs, 4.7; premoult period to adults, 17.8. The oviposition pattern was typical of an ixodid tick, including a linear relationship between weights of engorged females and the number of eggs laid (r = 0.8659). The males increased 18% in weight after feeding on hosts (P less than 0.01). The mean recovery rates of larvae, nymphs and females were 28.2%, 95.3% and 90.7%, respectively. The nymphs moulting to females were heavier (6.8 +/- 0.69 mg) than those moulting to males (3.2 +/- 0.29 mg) (P less than 0.01). A comparison of biological values of A. parvum with American and non-American Amblyomma species is presented.

Animals↗
PubMed2000

Meso-scale life-cycle impact assessment of novel technology policies: the case of renewable energy.

Assessing the environmental risk of novel technological systems and of the European Union (EU) policies supporting them and regulating their implementation requires good understanding of (i) the pressure on the environment posed by the large-scale use of new technology, and (ii) the vulnerability of the receptor of this pressure. Generic life-cycle assessments (LCAs) provide exhaustive accounting of environmental pressure, yet they do not take into account the vulnerability of the receiving ecosystem. Generic studies of technology externalities fail to produce conclusions on the impacts in a certain area of the systems envisaged due to lack of site-specific information. The combined use of generic (LCA) and spatially referenced data offers new opportunities for comprehensively analysing the environmental impact of novel technologies. A novel information fusion methodology is suggested. Example applications are presented herein focusing on the evaluation of renewable energy technologies as an example of the implementation of meso-scale LCA for integrated environmental risk assessment of EU technology policies.

Algorithms↗
PubMed1998

The 5' and 3' TAR elements of human immunodeficiency virus exert effects at several points in the virus life cycle.

The human immunodeficiency virus type 1 RNA genome contains a terminal repeat (R) sequence that encodes the TAR hairpin motif, which has been implicated in Tat-mediated activation of transcription. More recently, a variety of other functions have been proposed for this structured RNA element. To determine the replicative roles of the 5' and 3' TAR hairpins, we analyzed multiple steps in the life cycle of wild-type and mutant viruses. A structure-destabilizing mutation was introduced in either the 5', the 3', or both TAR motifs of the proviral genome. As expected, opening of the 5' TAR hairpin caused a transcription defect. Because the level of protein expression was not similarly reduced, the translation of this mRNA was improved. No effect of the 3' hairpin on transcription and translation was measured. Mutations of the 5' and 3' hairpin structures reduced the efficiency of RNA packaging to similar extents, and RNA packaging was further reduced in the 5' and 3' TAR double mutant. Upon infection of cells with these virions, a reduced amount of reverse transcription products was synthesized by the TAR mutant. However, no net reverse transcription defect was observed after correction for the reduced level of virion RNA. This result was confirmed in in vitro reverse transcription assays. These data indicate that the 5' and 3' TAR motifs play important roles in several steps of the replication cycle, but these structures have no significant effect on the mechanism of reverse transcription.

Base Sequence↗
PubMed1995

Mitochondrial genome repositioning during the differentiation of the African trypanosome between life cycle forms is microtubule mediated.

The cell cycle of the African trypanosome requires a precise orchestration of nuclear and mitochondrial genome (kinetoplast) positioning to ensure faithful segregation during division. The controls underlying these events must be subject to modulation, however, as the respective positioning of these organelles changes during the parasite's complex life cycle. We have studied mitochondrial DNA repositioning during differentiation between the trypanosome's bloodstream and procyclic form. We have found that repositioning occurs simultaneously with the DNA replication phase of the cell cycle of the differentiating parasite. Furthermore, we demonstrate, at the cell and individual microtubule level, that this organelle repositioning is achieved via microtubule-dependent processes. Our results have implications for the control of cell differentiation and division in African trypanosomes.

Animals↗
PubMed2005

A structural perspective of the flavivirus life cycle.

Dengue, Japanese encephalitis, West Nile and yellow fever belong to the Flavivirus genus, which is a member of the Flaviviridae family. They are human pathogens that cause large epidemics and tens of thousands of deaths annually in many parts of the world. The structural organization of these viruses and their associated structural proteins has provided insight into the molecular transitions that occur during the viral life cycle, such as assembly, budding, maturation and fusion. This review focuses mainly on structural studies of dengue virus.

Capsid Proteins↗
PubMed2006

Greenhouse gas emissions from forestry operations: a life cycle assessment.

Most forest carbon assessments focus only on biomass carbon and assume that greenhouse gas (GHG) emissions from forestry activities are minimal. This study took an in-depth look at the direct and indirect emissions from Pacific Northwest (PNW) Douglas-fir [Pseudotsuga menziesii (Mirbel) Franco] forestry activities to support or deny this claim. Greenhouse gas budgets for 408 "management regimes" were calculated using Life Cycle Assessment (LCA) methodology. These management regimes were comprised of different combinations of three types of seedlings (P + 1, 1 + 1, and large plug), two types of site preparation (pile and burn, and chemical), 17 combinations of management intensity including fertilization, herbicide treatment, pre-commercial thinning (PCT), commercial thinning (CT), and nothing, and four different rotation ages (30, 40, 50, and 60 yr). Normalized to 50 yr, average direct GHG emissions were 8.6 megagrams (Mg) carbon dioxide equivalents (CO2e) ha(-1), which accounted for 84% of total GHG emissions from the average of 408 management regimes. Harvesting (PCT, CT, and clear cutting) contributed the most to total GHG emissions (5.9 Mg CO2e per 700 m3 harvested timber), followed by pile and burn site preparation (4.0 Mg CO2e ha(-1) or 32% of total GHG emissions) and then fertilization (1.9 Mg CO2e ha(-1) or 15% of total GHG emissions). Seedling production, seedling transportation, chemical site preparation, and herbicide treatment each contributed less than 1% of total GHG emissions when assessed per hectare of planted timberland. Total emissions per 100 m3 averaged 1.6 Mg CO2e ha(-1) over all 408 management regimes. An uncertainty analysis using Monte Carlo simulations revealed that there are significant differences between most alternative management regimes.

Agriculture↗
PubMed1995

Life-cycle influences on staff nurse career expectations.

While exploring the diversity of women's work experiences, this study determined which factors were associated with retaining staff nurses. Findings reaffirm the importance of understanding women's relationships to their work through a personal and a professional context. Results suggest that the emphasis placed on working conditions and professional and fringe benefits vary according to three distinct life-cycle changes.

Adult↗
PubMed1998

Reproductive seasonality and maturation throughout the complete life-cycle in the mouflon ram (Ovis musimon).

To document the process of physical and reproductive maturation in a long-lived mammal, the long-term changes in endocrine (follicle stimulating hormone-FSH, prolactin and testosterone) and morphological parameters (body weight, testis diameter, neck girth, sex skin colour, horn growth, wool growth, moult and pelage characteristics) were measured throughout the full life-span in a group of captive mouflon rams, Ovis musimon (n=4, 12-year study). Live body weight increased to a maximum at 7 years of age and declined in old age, while horn size (length and volume) increased throughout the full life-span. Every year there was a marked and consistent cycle in the blood plasma concentrations of FSH and testosterone, and growth of the testes, with peak reproductive function in September and October associated with the rut. The annual maximum in plasma FSH and testosterone concentrations, and the size of the testes increased progressively from 1-6 years of age (or later into the life-cycle for testosterone). There was also a marked annual cycle in plasma prolactin concentrations (peak in May and June), and growth of the horns and pelage. The annual maximum in prolactin concentrations increased throughout the life-cycle, while the rate of horn growth (annual increments) decreased. The overall conclusion is that neuroendocrine mechanisms regulate both the annual and the age-related changes in the reproductive axis, and reproductive maturation proceeds gradually through the life-cycle. Because the acquisition of adult characteristics (large body size, large horns, conspicuous male secondary sexual characteristics) greatly affects male competitiveness, sexual maturity is closely linked to physical maturity, and this occurs long after the initial onset of fertility at puberty.

Aging↗
PubMed1985

Coping and depression. The relative contribution of internal and external resources during a life cycle transition.

This study addresses two questions relevant to psychiatric epidemiological models of the stress-distress relationship: Are personality and social support resources independent phenomena or highly correlated? and What are the relative contributions of these two types of resources in protecting against the development of depressive symptomatology? A cohort of beginning medical students was administered self-report questionnaires measuring social supports, locus of control, interpersonal dependency, and depressive symptomatology. On the basis of correlation and regression analysis, the data show that the personality characteristics more strongly predict depressive symptomatology than do social supports, and that social supports are unrelated to locus of control but directly correlated with interpersonal dependency. The authors discuss these findings in the context of a life cycle transition.

Adaptation, Psychological↗
PubMed2003

Investigations into the life cycle of the bacterial predator Bdellovibrio bacteriovorus 109J at an interface by atomic force microscopy.

Atomic force microscopy was used to image Bdellovibrio bacteriovorus 109J, a gram-negative bacterial predator that consumes a variety of other gram-negative bacteria. In predator-prey communities grown on filters at hydrated air-solid interfaces, repeated cycles of hunting, invasion, growth, and lysis occurred readily even though the cells were limited to near two-dimensional movement. This system allowed us to image the bacteria directly without extensive preparation or modification, and many of the cells remained alive during imaging. Presented are images of the life cycle in two species of prey organisms, both Escherichia coli (a small prey bacterium that grows two-dimensionally on a surface) and Aquaspirillum serpens (a large prey bacterium that grows three-dimensionally on a surface), including high-resolution images of invaded prey cells called bdelloplasts. We obtained evidence for multiple invasions per prey cell, as well as significant heterogeneity in morphology of bdellovibrios. Mutant host-independent bdellovibrios were observed to have flagella and to excrete a coating that causes the predators to clump together on a surface. Most interestingly, changes in the texture of the cell surface membranes were measured during the course of the invasion cycle. Thus, coupled with our preparation method, atomic force microscopy allowed new observations to be made about Bdellovibrio at an interface. These studies raise important questions about the ways in which bacterial predation at interfaces (air-solid or liquid-solid) may be similar to or different from predation in solution.

Bacterial Adhesion↗
PubMed1999

The life cycle of Amblyomma neumanni Ribaga, 1902 (Acari: Ixodidae) in the laboratory.

A colony of Amblyomma neumanni was started with engorged females collected from cattle in the province of Salta (24 degrees 51'S, 65 degrees 33'W), Argentina. The larvae and nymphs were fed on rabbits and the adults on calves. The non-parasitic stages were maintained in darkness at 27 +/- 1 degrees C and 83-86% RH. The life cycle (pre-feeding period not tested) had a mean duration of 205.7 days. The mean time (days) for the different phases of the cycle were as follows: feeding of females 8.8, pre-oviposition 23.8, oviposition 41.4, minimum egg incubation 76.1, feeding of larvae 8.5, pre-moult to nymphs 16.4, feeding of nymphs 7.9 and pre-moult to adults 22.8. The mean recovery rates of larvae, nymphs and females were 83.8, 85.6 and 89.3%, respectively. The nymphs moulting to females were heavier (8.1 +/- 2.34 mg) than those moulting to males (6.0 +/- 2.34 mg; p < 0.01), but their range of engorgement weight showed overlap (2.3-16.2 versus 2.2-12.8 mg, respectively). Two gynandromorphs were detected between the nymphs. A comparison of biological parameters of A. neumanni with other American Amblyomma species from mammals is presented.

Animals↗
PubMed1990

Association of country, sex, social class, and life cycle to locus of control in western European countries.

Relatively few studies have focused on causal factors in the development of locus of control. Here nine western European countries are studied to assess the hypothesis that the society in which one lives is important in the scores on locus of control. The data indicate greater variation resulting from country of residence on locus of control than that from the variables of life cycle, sex, and social class. Findings regarding these latter variables are congruent with previous research. In addition, being single was related to having an external locus of control.

Adolescent↗