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PubMed1999

Description and life-cycle of three new species of Dingularis n.g. (Digena: Plagiorchiida), parasites of Australian freshwater turtles.

Dingularus n.g. is proposed to accommodate three new species, D. anfracticirrus, D. pearsoni and D. megapharynx, within the Plagiorchiida. Dingularus is closely related to the Plagiorchiidae, despite the unusual excretory systems of the three species. Adult worms were parasitic in the intestines of freshwater turtles, Chelodina expansa (D. pearsoni and D. megapharynx) and Emydura macquarii (D. anfracticirrus), and appeared to be host-specific. The three species had similar, three-host, aquatic life-cycles and each life-cycle was followed experimentally. The planorbid snail Glyptophysa gibbosa served as the first intermediate host for each species. Tadpoles of Limnodynastes peronii and snails G. gibbosa and Austropeplea lessoni served as second intermediate hosts. Dingularus spp. eggs were fully embryonated and infective when laid. They remained viable for 2-3 months in water but did not hatch until eaten by G. gibbosa. Miracidia were stimulated in the stomach of the snail host but did not hatch until eggs passed into the intestine. Hatching occurred in only the anterior fifth of the intestine. Hatched miracidia were not passed with the snail faeces. The pre-patent period in the snail differed in each species: D. anfracticirrus 42 days, D. pearsoni 23 days and D. megapharynx 32 days.

Animals↗
PubMed2000

Pneumocystis carinii uses a functional cdc13 B-type cyclin complex during its life cycle.

Pneumocystis carinii causes severe pneumonia in immunocompromised patients. Recent studies indicate that P. carinii uses a Cdc2 cyclin-dependent kinase to control its proliferation. To further study the regulation of the life cycle of P. carinii, we characterized the P. carinii B-type cyclin termed Cdc13, whose binding to Cdc2 is necessary for kinase activity. Antibodies to B-type cyclins (Cdc13) specifically immunoprecipitated Cdc2/ Cdc13 complexes with associated kinase activity from P. carinii extracts. To clone P. carinii cdc13, degenerate polymerase chain reaction was undertaken using primers generated from amino-acid motifs conserved in fungal Cdc13 proteins. This amplicon was used to obtain full-length genomic and complementary DNA (cDNA) clones. A specific synthetic peptide antibody generated to P. carinii Cdc13 further demonstrated differential Cdc2/Cdc13 activity over the life cycle of P. carinii, with greater activity in cysts compared with trophic forms of the organism. Finally, P. carinii cdc13 cDNA was used to rescue mutant Schizosaccharomyces pombe strains containing temperature-sensitive deficiencies of endogenous Cdc13 activity, thus verifying function of the P. carinii Cdc13 protein. Therefore, P. carinii contains a Cdc13 cyclin, which is variably active over its life cycle and which promotes fungal proliferation.

Amino Acid Sequence↗
PubMed1999

Life cycle variation and the genetic structure of nematode populations.

Few data are available on population genetic structure in nematode species, and little of the available data allows direct comparison of the genetic structures of species having different life cycles. Here we use mtDNA sequence data to describe the genetic structure of a heterorhabditid nematode, and compare results to published data on other nematode species. Heterorhabditis marelatus is a parasite of soil-dwelling insects. Its life cycle and local ecology should result in small effective population sizes and restricted gene flow. As predicted, H. marelatus shows much lower mtDNA diversity within populations and over the species as a whole, and has a much more strongly subdivided population structure, than parasites of mobile vertebrate hosts. From data such as these we can begin to generalize about the effects of life cycle variation on genetic structure in different nematode species.

Animals↗
PubMed2004

Aging in introductory and life cycle nutrition textbooks.

The aging content in 11 undergraduate nutrition textbooks (8 introductory, 3 life cycle) was evaluated using content analysis. Repeated measures ANOVAs with Bonferroni post hoc procedures and t- tests were used. The 259 relevant pages largely focused on geriatrics (physiological decline, chronic diseases). Gerontological aspects were underemphasized. Mean number of pages on aging was significantly higher in life cycle (M = 37) than in introductory textbooks (M = 18), t (9) = 3.42, p < .008. In introductory textbooks, mean percentage of pages on aging (M = 3.2%) was significantly less than for maternal (M = 4.6%) and childhood topics (M = 6.2%), p < .05. Overall, topic omissions included discussion of ageism, death, dying, and dignity; and end-of-life decisions related to nutrition and hydration. Women and minorities were proportionately represented in generally positive photographs. Aging terminology was 81% neutral (older, aging), 14% negative (impaired, senile), and 5% positive (active, independent). These textbooks may not help students acquire the broad knowledge needed to work with older adults or develop positive attitudes about aging. Recommendations for authors, publishers, and instructors are provided.

Aged↗
PubMed1999

V4 region of small subunit rDNA indicates polyphyly of the Fellodistomidae (Digenea) which is supported by morphology and life-cycle data.

There is no morphological synapomorphy for the disparate digeneans, the Fellodistomidae Nicoll, 1909. Although all known life-cycles of the group include bivalves as first intermediate hosts, there is no convincing morphological synapomorphy that can be used to unite the group. Sequences from the V4 region of small subunit (18S) rRNA genes were used to infer phylogenetic relationships among 13 species of Fellodistomidae from four subfamilies and eight species from seven other digenean families: Bivesiculidae; Brachylaimidae; Bucephalidae; Gorgoderidae; Gymnophallidae; Opecoelidae; and Zoogonidae. Outgroup comparison was made initially with an aspidogastrean. Various species from the other digenean families were used as outgroups in subsequent analyses. Three methods of analysis indicated polyphyly of the Fellodistomidae and at least two independent radiations of the subfamilies, such that they were more closely associated with other digeneans than to each other. The Tandanicolinae was monophyletic (100% bootstrap support) and was weakly associated with the Gymnophallidae (< 50-55% bootstrap support). Monophyly of the Baccigerinae was supported with 78-87% bootstrap support, and monophyly of the Zoogonidae + Baccigerinae received 77-86% support. The remaining fellodistomid species, Fellodistomum fellis, F. agnotum and Coomera brayi (Fellodistominae) plus Proctoeces maculatus and Complexobursa sp. (Proctoecinae), formed a separate clade with 74-92% bootstrap support. On the basis of molecular, morphological and life-cycle evidence, the subfamilies Baccigerinae and Tandanicolinae are removed from the Fellodistomidae and promoted to familial status. The Baccigerinae is promoted under the senior synonym Faustulidae Poche, 1926, and the Echinobrevicecinae Dronen, Blend & McEachran, 1994 is synonymised with the Faustulidae. Consequently, species that were formerly in the Fellodistomidae are now distributed in three families: Felldistomidae; Faustulidae (syn. Baccigerinae Yamaguti, 1954); and Tandanicolidae Johnston, 1927. We infer that the use of bivalves as intermediate hosts by this broad range of families indicates multiple host-switching events within the radiation of the Digenea.

Animals↗
PubMed2005

Interactions with pocket proteins contribute to the role of human papillomavirus type 16 E7 in the papillomavirus life cycle.

Human papillomaviruses (HPVs), most commonly the HPV16 genotype, are the principle etiological determinant for cervical cancer, a common cancer worldwide resulting in over 200,000 deaths annually. The oncogenic properties of HPVs are attributable in part to the virally encoded protein E7, best known for its ability to bind to and induce the degradation of the retinoblastoma tumor suppressor, pRb, and related "pocket proteins" p107 and p130. Previously, we defined a role for E7 in the productive stage of the HPV16 life cycle, which takes place in stratified squamous epithelia. HPV perturbs the normal processes of cell growth and differentiation of stratified squamous epithelia. HPVs reprogram cells to support continued DNA synthesis and inhibit their differentiation in the suprabasal compartment of the epithelia, where cells normally have withdrawn from the cell cycle and initiated a well-defined pattern of terminal differentiation. These virus-induced perturbations, which contribute to the production of progeny HPVs, are dependent on E7. In this study, we define the mechanism of action by which E7 contributes to the productive stage of the HPV16 life cycle. We found that the ability of HPV16 to reprogram suprabasal cells to support DNA synthesis correlates with E7's ability to bind pocket proteins but not its ability to induce their degradation. In contrast, the ability of HPV16 to perturb differentiation correlated with both E7's binding to and degradation of pocket proteins. These data indicate that different hallmarks of the productive stage of the HPV16 life cycle rely upon different sets of requirements for E7.

Animals↗
PubMed2006

[Carbon balance analysis of corn fuel ethanol life cycle].

The quantity of greenhouse gas emissions (net carbon emissions) of corn-based fuel ethanol, which is known as an alternative for fossil fuel is an important criteria for evaluating its sustainability. The methodology of carbon balance analysis for fuel ethanol from corn was developed based on principles of life cycle analysis. For the production state of fuel ethanol from summer corn in China, carbon budgets in overall life cycle of the ethanol were evaluated and its main influence factors were identified. It presents that corn-based fuel ethanol has no obvious reduction of carbon emissions than gasoline, and potential improvement in carbon emission of the life cycle of corn ethanol could be achieved by reducing the nitrogen fertilizer and irrigation electricity used in the corn farming and energy consumption in the ethanol conversion process.

Carbon↗
PubMed1999

Ecology and the Evolution of Biphasic Life Cycles.

Sexual eukaryotes undergo an alternation between haploid and diploid nuclear phases. In some organisms, both the haploid and diploid phases undergo somatic development and exist as independent entities. Despite recent attention, the mechanisms by which such biphasic life cycles evolve and persist remain obscure. One explanation that has received little theoretical attention is that haploid-diploid organisms may exploit their environments more efficiently through niche differentiation of the two ploidy phases. Even in isomorphic species, in which adults are morphologically similar, slight differences in the adult phase or among juveniles may play an important ecological role and help maintain haploid-diploidy. We develop a genetic model for the evolution of life cycles that incorporates density-dependent growth. We find that ecological differences between haploid and diploid phases can lead to the evolution and maintenance of biphasic life cycles under a broad range of conditions. Parameter estimates derived from demographic data on a population of Gracilaria gracilis, a haploid-diploid red alga with an isomorphic alternation of generations, are used to demonstrate that an ecological explanation for haploid-diploidy is plausible even when there are only slight morphological differences among adults.

Gracilaria↗
PubMed2006

Insight into the role of cetaceans in the life cycle of the tetraphyllideans (Platyhelminthes: Cestoda).

Four types of tetraphyllidean larvae infect cetaceans worldwide: two plerocercoids differing in size, 'small' (SP) and 'large' (LP), and two merocercoids referred to as Phyllobothrium delphini and Monorygma grimaldii. The latter merocercoid larvae parasitize marine mammals exclusively and exhibit a specialised cystic structure. Adult stages are unknown for any of the larvae and thus the role of cetaceans in the life cycle of these species has been a long-standing problem. The SP and LP forms are thought to be earlier stages of P. delphini and M. grimaldii that are presumed to infect large pelagic sharks that feed on cetaceans. A molecular analysis of the D2 variable region of the large subunit ribosomal DNA gene based on several individuals of each larval type collected from three Mediterranean species of cetaceans showed consistent and unique molecular signatures for each type regardless of host species or site of infection. The degree of divergence suggested that LP, P. delphini and M. grimaldii larvae may represent separate species, whereas SP may be conspecific with M. grimaldii. In all host species, individuals of SP accumulated in the gut areas in which the lymphoid tissue was especially developed. We suggest therefore that these larvae use the lymphatic system to migrate to the abdominal peritoneum and mesenteries where they develop into forms recognizable as M. grimaldii. The plerocercoid stage of P. delphini remains unknown. In a partial phylogenetic tree of the Tetraphyllidea, all larvae formed a clade that included a representative of the genus Clistobothrium, some species of which parasitize sharks such as the great white which is known to feed on cetaceans. A bibliographic examination of tetraphyllidean infections in marine mammals indicated that these larvae are acquired mostly offshore. In summary, the evidence suggests that cetaceans play a significant role in the life cycle of these larvae. In addition, it seems clear that cetaceans act as natural intermediate hosts for P. delphini and M. grimaldii, as within these hosts they undergo development from the plerocercoid stage to the merocercoid stage. Because tetraphyllidean species use fish, cephalopods and other marine invertebrates as intermediate hosts, the inclusion of cetaceans in the life cycle would have facilitated their transmission to apex predators such as the large, lamnid sharks. The biological significance of infections of LP in cetaceans is unclear, but infections do not seem to be accidental as such larvae show high prevalence and abundance as well as a high degree of site specificity, particularly in the anal crypts and bile ducts.

Animals↗
PubMed1995

Cell adhesion to extracellular matrix regulates the life cycle of integrins.

The expression of alpha 5 beta 1 integrin on the surface of fibroblasts requires adhesion to substratum. We have examined the basis for this adhesion-dependent surface expression by comparing the life cycle of integrins in parallel cultures of adherent and nonadherent cells. Results of biosynthetic labeling experiments in NRK fibroblasts showed that the synthesis and biosynthetic processing of the beta 1 integrin subunit proceed in the absence of cell attachment; however, when examining the behavior of preexisting cell surface integrins, we observed that the alpha beta 1 integrins are internalized and degraded when adhesion to substratum is blocked. A kinetic analysis of integrin internalization in cycloheximide-treated NRK cells showed that each of the fibroblast integrins we examined (in both the beta 1 and beta 3 families) are lost from the cell surface after detachment from substratum. Thus, the default integrin life cycle in fibroblasts involves continuous synthesis, processing, transport to the cell surface, and internalization/degradation. Interestingly, studies with NIH-3T3 cells expressing alpha 1 beta 1 integrin showed that the loss of cell-surface alpha 5 beta 1 integrin is blocked by adhesion of cells to dishes coated with type IV collagen (a ligand for alpha 1 beta 1 integrin) as well as fibronectin. Similarly, adhesion of these cells to dishes coated with type IV collagen stabilizes the surface expression of alpha 5 beta 1 as well as alpha 1 beta 1 integrin. We propose that the adhesion of fibroblasts to extracellular matrix protein alters the integrin life cycle and permits retention of these proteins at the cell surface where they can play important roles in transmitting adhesion-dependent signals.

3T3 Cells↗
PubMed2002

Use of life cycle assessment in environmental management.

The aim of this paper is to demonstrate how life cycle assessment (LCA) can be used to develop strategic policies that can lead to a minimization of the environmental burden resulting from the provision of services or the manufacture, use, and disposal of products within the economy. We accomplish this aim by presenting a case study that evaluates the greenhouse gas contributions of each stage in the life cycle of containerboard packaging and the potential impact on emissions of various policy options available to decision-makers. Our analysis showed that, in general, the most useful strategy was to recycle the used packaging. However, our analysis also indicated that when measures are taken to eliminate sources of methane emissions, then recycling is no longer beneficial from a greenhouse perspective. This is because the process energy required in the form of gas and electricity is substantially greater for containerboard manufactured from recycled material than it is for virgin fiber.

Conservation of Natural Resources↗
PubMed2000

Genetic evidence for assortative mating between 13-year cicadas and sympatric "17-year cicadas with 13-year life cycles" provides support for allochronic speciation.

Thirteen-year cicadas of brood XIX from northern Arkansas, Missouri, and southern Illinois (lineage A) are known to be genetically different at two marker loci (mitochondrial DNA and abdominal color) from 13-year cicadas to the south (lineage B) that emerge in the same year. Because 17-year cicadas from all broods (year classes) are indistinguishable from lineage A at these two marker loci, previous workers suggested that the lineage A cicadas of 13-year brood XIX were derived from 17-year cicadas by life-cycle switching (allochrony). Data presented here show that, over the same northern geographic range, lineage A is also present in 13-year cicadas belonging to brood XXIII (which always emerges four years later than brood XIX). Detailed sampling along the putative life-cycle-switching boundary in 13-year brood XXIII revealed a previously unsuspected broad zone of overlap where populations contained individuals of both lineages A and B. Despite this sympatry, and previous reports of a lack of behavioral barriers to interbreeding, a strong correlation between mitochondrial haplotype and abdominal color suggests that assortative mating has taken place. Lineage A 13-year cicadas from both broods XIX and XXIII are only found within a gap in the spatial distribution of 17-year cicadas. This, in combination with the lack of differentiation between lineage A 13- and 17-year cicadas at the marker loci and new behavioral data for 13-year brood XIX, suggests a recent derivation of all northern 13-year cicadas from the 17-year cicadas via life-cycle switching. We discuss the implications of these allochronic shifts for speciation.

Animals↗
PubMed2001

Claire ponds as an experimental model for Marteilia refringens life-cycle studies: new perspectives.

Since its first description, the paramyxean parasite Marteilia refringens (Grizel et al.) has been recognised as a significant pathogen of the European flat oyster Ostrea edulis L. The existence of a complex life-cycle involving several hosts was postulated early on by many authors, although it remains unsolved. Recent developments in the DNA-based diagnosis of M. refringens provides new prospects for the detection of the parasite in potential hosts. However, this screening remains impeded by the number of species living in the vicinity of oyster beds. We report here on the use of semi-closed oyster ponds (so called 'claire' in Marennes-Oléron Bay) as a study model for the life-cycle of M. refringens. Claires are located in an endemic area for M. refringens and transmission of the disease to healthy oysters has been shown to be effective during the course of this study. The environmental characteristics of the claires strongly limit the number of species compared with intertidal areas and oyster beds. Consequently, extensive sampling of a limited number of species cohabiting with oysters was possible. These were preserved for future screening of M. refringens. The experimental model should bring new insights to the life-cycle of M. refringens, as it enables us to propose new conceptual schemes of M. refringens transmission. The role of species as potential hosts is discussed regarding their biology and geographical distribution.

Journal Article↗
PubMed1985

Differential expression of mitochondrial genes between life cycle stages of Trypanosoma brucei.

The mitochondrial respiratory system is differentially produced during the life cycle of the parasitic protozoan, Trypanosoma brucei. We have found 14 transcripts that are derived from a maxicircle (mitochondrial DNA) region that contains sequences homologous to cytochrome c oxidase subunits I and II, unassigned reading frame 1 from mitochondrial DNA of other organisms, and two other open reading frames. Ten of these transcripts occur as pairs that differ in size by approximately equal to 200 nucleotides. While most of these transcripts occur in both life cycle forms, four transcripts are differentially expressed. Of these, two are more abundant in bloodstream forms, one is more abundant in procyclic forms, and one is present in procyclic but not bloodstream forms. These results indicate that the differential production of the mitochondrial respiratory system in T. brucei entails regulation of mitochondrial transcriptional and/or posttranscriptional processes.

Animals↗
PubMed2005

Life cycle approaches to sustainable consumption: a critical review.

The 2002 World Summit for Sustainable Development in Johannesburg called for a comprehensive set of programs focusing on sustainable consumption and production. According to world leaders, these programs should rely on life cycle assessment (LCA) to promote sustainable patterns of production and consumption. Cleaner production is a well-established activity, and it uses LCA. UNEP, the European Union, and a number of national organizations have now begun to work on sustainable consumption. In developing sustainable consumption policies and activities, the use of LCA presents interesting opportunities that are not yet well understood by policy makers. This paper reviews how life cycle approaches, primarily based on input-output analysis, have been used in the area of sustainable consumption: to inform policy making, select areas of action, identify which lifestyles are more sustainable, advise consumers, and evaluate the effectiveness of sustainable consumption measures. Information on consumption patterns usually comes from consumer expenditure surveys. Different study designs and a better integration with consumer research can provide further interesting insights. Life-cycle approaches still need to be developed and tested. Current research is mostly descriptive; policy makers, however, require more strategic analysis addressing their decision options, including scenario analysis and backcasting.

Community Participation↗
PubMed1998

[Genotypic variability in populations of the mound-builder mouse Mus spicilegus Pet., 1882, at various life cycle stages].

Genotypic variability in two Moldovian populations of moundbuilder mice Mus spicilegus Pet. was examined at different stages of their life cycle--at the beginning of overwintering in mounds and in the middle of summer in agrocenoses. Thirty allozymes were assayed. Significant differences in allele frequencies and heterozygosity between overwintered and mice born in the year of the experiment were recorded only for Idh-1. This fact was related to the presence of differential mortality among overwintered mice in the populations by the middle of summer. The increase in heterozygosity for Idh-1 in the populations occurred because of "old" mice that lived until the middle of summer, at which point they still have not contributed to the gene pool of the population. The genetic effect of the annual separation of generations of mound-builder mice due to their overwintering in mounds is analyzed. Overwintering has a bottleneck effect on the population. The relatively low genetic variability in mound-builder-mice populations is considered with regard to their biological and ecological features. Based on obtained data, a conclusion on the high genetic stability of moundbuilder-mice populations during their entire life cycle is made.

Animals↗
PubMed1959

Changes in the pattern of nitrogen excretion during the life cycle of the newt.

In the course of its life cycle the eastern newt, Triturus (Diemyctylus) viridescens, undergoes two metamorphoses, the first from the aquatic larva to the terrestrial red eft; the second, 2 to 3 years later, from the eft to the permanently aquatic and sexually mature adult newt. The pattern of nitrogen exretion changes during both transformations. Older larvae excrete about 75 percent of the nitrogen as ammonia, 25 percent as urea; during the first metamorphosis the ratio of ammonia to urea is about 57:43; completely transformed efts excrete 87 percent of the nitrogen as urea. Adult aquatic newts show a partial return to the larval pattern, with an increase in the proportion of ammonia from the 13 percent typical for the eft to 26 percent, a highly significant difference.

Adult↗
PubMed2001

Aspects of the life cycle and pathogenesis of Elaphostrongylus alces in moose (Alces alces).

Aspects of the migratory life cycle and pathogenesis of Elaphostrongylus alces were studied in 7 randomly selected moose calves and 7 yearlings killed during August to November. One calf and 1 yearling were uninfected. The 6 infected calves had recent infections, whereas the 6 yearlings showed older infections from the summer of the previous year. The 2 calves killed in September had a total of 26 adult E. alces in the epidural space of the caudal vertebral canal and none in the skeletal muscles, whereas the remaining calves killed 1 to 2 mo later had 25 nematodes in the caudal and cranial vertebral canal and 7 in the skeletal muscles. The yearlings had a total of 101 adult E. alces in the skeletal muscles and 2 in the vertebral canal. There were no findings indicating involvement of the central nervous system in the life cycle of E. alces. Our findings suggest that E. alces migrates directly from the gut to the epidural space of the caudal vertebral canal where development to the adult stage takes place. During development, the nematode produces inflammation of the epidural tissue and spinal nerves. Development in the caudal vertebral canal is followed by some anterior dispersion of nematodes along the canal, and migration into skeletal muscles. Here the nematodes seem to live in reproductive pairs and groups. The predilection site for E. alces in moose is the muscles of the thigh.

Animals↗