Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Life Cycle”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed1998

Temporal usage of multiple promoters during the life cycle of human papillomavirus type 31b.

The life cycles of human papillomaviruses (HPVs) are dependent upon the differentiation of the epithelial cells they infect. HPV type 31b (HPV31b) virions can be purified following the growth of a latently HPV-infected cell line (CIN-612 9E) in the organotypic or raft system. Treatment of the CIN-612 9E raft tissues with protein kinase C (PKC) activators is required for upregulation of late gene expression and efficient production of virions. We employed the raft culture system to study the temporal usage of HPV31b promoters during the viral life cycle. We compared monolayer cultures of CIN-612 9E cells, untreated CIN-612 9E raft tissues, and PKC-induced CIN-612 9E raft tissues harvested at various time points during epithelial differentiation. We found that the HPV31b major early promoter precisely maps to nucleotide (nt) 99 (P99). A transcriptional start site for both early and late gene transcripts mapped upstream of P99 at nt 77 (P77). The P77 and P99 promoters were used constitutively throughout the HPV31b life cycle; however, initiation from P99 was much stronger than from P77. Mapping of the differentiation-induced P742 promoter revealed multiple start sites. These start sites were difficult to detect in monolayer cultures, were induced in untreated rafts, and were greatest in PKC-induced raft tissues at 8 to 12 days. A constitutively active promoter, P3320, was also defined and is responsible for the transcription of unspliced and spliced RNAs containing E5a, E5b, L2, and L1 open reading frames.

Base Sequence↗
PubMed1991

Endopeptidase variations among different life-cycle stages of African trypanosomes.

Lysates of different life-cycle stages of Trypanosoma congolense, Trypanosoma vivax and Trypanosoma brucei were analysed for endopeptidase activity, using reaction conditions which permitted a distinction to be made between lysosomal and non-lysosomal activity [Lonsdale-Eccles, J. D. & Grab, D. J. (1987) Eur. J. Biochem. 169, 467-475]. Hydrolysis of Z-Arg-Arg-NHMec (Z = benzyloxycarbonyl, NHMec = 7-amino-4-methylcoumaryl) and Z-Gly-Gly-Arg-NHMec occurred predominantly at alkaline pH and was observed in lysates of both insect and mammalian infective forms of T. brucei and T. congolense. Compared to their other life-cycle stages, procyclic forms of T. brucei and epimastigote forms of T. congolense exhibited enhanced hydrolysis of these substrates. Low levels of hydrolysis of Z-Arg-Arg-NHMec were observed in the bloodstream and epimastigote forms of T. vivax. The hydrolysis of Z-Gly-Gly-Arg-NHMec in each of the life-cycle stages of T. vivax was generally below detectable levels. In lysates of T. congolense, proteolytic and Z-Phe-Arg-NHMec-hydrolytic activity in bloodstream forms greater than metacyclic greater than epimastigote greater than procyclic forms. In T. vivax Z-Phe-Arg-NHMec-hydrolytic activity differed slightly according to the origin of the parasite but, in general, followed the same pattern (i.e. bloodstream forms greater than epimastigote forms, with metacyclic forms usually intermediate between these two). In T. brucei, Z-Phe-Arg-NHMec-hydrolytic activity in bloodstream forms greater than procyclic forms. Upon differentiation of the long, slender bloodstream forms into short, stumpy forms the Z-Phe-Arg-NHMec-hydrolytic activity was elevated even further. Thus, during their life cycle, each of these African trypanosomes exhibits complex changes of endopeptidase activity, suggestive of an induction of lysosomal activity between the insect and mammalian forms.

Amino Acid Sequence↗
PubMed2006

Development of the method and U.S. normalization database for Life Cycle Impact Assessment and sustainability metrics.

Normalization is an optional step within Life Cycle Impact Assessment (LCIA) that may be used to assist in the interpretation of life cycle inventory data as well as life cycle impact assessment results. Normalization transforms the magnitude of LCI and LCIA results into relative contribution by substance and life cycle impact category. Normalization thus can significantly influence LCA-based decisions when tradeoffs exist. The U. S. Environmental Protection Agency (EPA) has developed a normalization database based on the spatial scale of the 48 continental U.S. states, Hawaii, Alaska, the District of Columbia, and Puerto Rico with a one-year reference time frame. Data within the normalization database were compiled based on the impact methodologies and lists of stressors used in TRACI-the EPA's Tool for the Reduction and Assessment of Chemical and other environmental Impacts. The new normalization database published within this article may be used for LCIA case studies within the United States, and can be used to assist in the further development of a global normalization database. The underlying data analyzed for the development of this database are included to allow the development of normalization data consistent with other impact assessment methodologies as well.

Air Pollutants↗
PubMedDate not supplied

[Certain principles of the secondary simplication of the life cycles of helminths].

On the basis of the analysis of regularities accompanying the secondary simplification of the life cycles of helminths on account of the reduction in the number of the animals-hosts 8 rules have been formulated. They are based on the following important regularities. 1. At the secondary simplification of the life cycles of helminths never fall out the first intermediate host in Trematoda and the definitive host in Nematoda. This phenomenon is suggested to be called "the host stability in the life cycle". 2. Mostly often from the life cycles fall secondarily out those hosts which join in the life cycle at its first complication later. 3. The phase of the helminth having transformed into a parasitic form at the first complication of its life cycle remains the same at the secondary simplification of this cycle.

Adaptation, Physiological↗
PubMed2000

Cladistic analysis of myxozoan species with known alternating life-cycles.

The phylogenetic relationships of 15 myxozoan taxa with known alternating life-cycles were investigated in order to provide insight into the puzzling matches between myxosporeans and actinosporeans of the myxozoan life-cycle data. Phylogenetic analyses were performed using two partitioned data-sets of life-cycle stages, myxosporean stage from fish hosts versus actinosporean stage from annelid hosts, and a combined data-set of myxosporean and actinosporean stages. A cnidarian parasite of fish, Polypodium hydriforme Ussov, 1885, was used as the outgroup. The supraspecific level grouping in the conventional classification of actinosporeans was not supported in the analysis of the partitioned data from the actinosporean phase, which yielded two equally parsimonious trees. Analysis of the partitioned data from the myxosporean phase provided 24 equally parsimonious trees and did not support the current classification of myxosporeans. The analyses of the partitioned data of myxozoans by life-cycle stage revealed a lack of taxonomic congruence between the two life-stage partitions. Two equally parsimonious trees were obtained from analysis of the combined data. The suborder Variisporina of the Myxozoa was not supported by the total evidence trees, while the monophyly of the species of Myxobolus Butschli, 1882 and of the Myxidiidae were supported. The cladograms from the combined data revealed that these myxozoan species formed four major monophyletic groups. Among them, two were supported by the partitioned data of the actinosporean phase. The phylogenetic signals and the better resolution reflected by the trees of combined data suggest that the phylogenetic total evidence approach should be employed in future studies of the systematics of myxozoans.

Animals↗
PubMed2002

Successful in vitro cultivation of Cryptosporidium andersoni: evidence for the existence of novel extracellular stages in the life cycle and implications for the classification of Cryptosporidium.

The present study describes the complete development of all life cycle stages of Cryptosporidium andersoni in the HCT-8 cell line. The in vitro cultivation protocols were the same as those used for the successful growth of all life cycle stages of Cryptosporidium parvum (Int. J. Parasitol. 31 (2001) 1048). Under these culture conditions, C. andersoni grew and proliferated rapidly with the completion of the entire life cycle within 72h post-infection. The developmental stages of C. andersoni are larger than those of C. parvum enabling easier identification of life cycle stages including a previously unrecognised extracellular stage. The presence of this extracellular stage was further confirmed following its isolation from the faeces of infected cattle using a laser microdissection technique. This stage was present in large numbers and some of them were seen undergoing syzgy. Extraction of DNA from the extracellular stage, followed by polymerase chain reaction-restriction fragment length polymorphism and sequencing of the 18S rDNA confirmed that this is a stage in the life cycle of C. andersoni. In vitro, extracellular stages were always observed moving over the HCT-8 cells infected with C. andersoni. Comparative observations with C. parvum also confirmed the presence of extracellular stages. Extracellular stages were recovered from in vitro culture after 5 days post-infection with the cattle genotype of C. parvum and from infected mice. At least two morphologically different stages (stages one and two) were purified from mice after 72h of infection. The presence and morphological characterisation of extracellular developmental stages in the life cycle of Cryptosporidium confirms its relationship to gregarines and provides important implications for our understanding of the taxonomic and phylogenetic affinities of the genus Cryptosporidium. The growth of C. andersoni in cell culture now provides a means of studying its development, metabolism, and behaviour as well as testing its response to different therapeutic agents.

Animals↗
PubMedDate not supplied

[Toxoplasmids, their life cycle and systematic position].

Recent evidence on the life cycles of the toxoplasmids (Toxoplasma, Besnoitia, Sarcocystis, Hammondia, Frenkelia) has been analysed. The availability of the complex life cycles, including the alternation of sexual and asexual reproduction, in addition to gametogenesis involving the independent development of gametes that produce unequal numbers of gametes, makes it possible to include the toxoplasmids into the family Eimeriidae within the order Coccidiida. A detailed evidence recently provided for Isospora has suggested a kinship of this typical coccidian genus with toxoplasmids. At the same time much similarity is obvious between Isospora and Eimeria in the general pattern of their life cycles. Hence, the family Eimeriidae is suggested to be divided into two subfamilies: Eimeriinae Wenyon, 1926 with Eimeria as the type genus and Isosporinae Wenyon, 1926 with Isospora, Toxoplasma, Besnoitia, Sarcocystis, Frenkelia and Hammondia. The main features of the former subfamily are: various oocyst structures, the lack of the extra-intestinal development, obligatory monoxeny. The main characters of the latter subfamily: oocysts of the same pattern, the involvement of extra-intestinal development, shifts from facultative to obligatory heteroxeny.

Animals↗
PubMed1998

Temporal and spatial expression of the E5a protein during the differentiation-dependent life cycle of human papillomavirus type 31b.

Human papillomaviruses (HPVs) are epitheliotropic viruses, and their life cycle is intimately linked to the stratification and differentiation state of the host epithelial tissues. Defining a role for the E5 gene product in the differentiation-dependent viral life cycle has been difficult due to the lack of a suitable culture system. We used the organotypic (raft) culture system to investigate the spatial and temporal expression pattern of the E5 protein during the differentiation-dependent life cycle of HPV-31b. We report the generation of antisera specific to the HPV-31b E5a protein. The HPV-31b E5a protein was detected throughout the viral life cycle in raft cultures as determined by immunostaining analyses, and the protein was localized predominantly to the basal and granular layers. Expression of epidermal growth factor receptor or platelet-derived growth factor receptors, two proteins with which E5 has been shown to interact in cell culture, did not specifically colocalize with E5a expression. However, HPV-31b E5a expression did colocalize with the epithelial differentiation-specific marker filaggrin. The kinetics of E5a protein expression during the complete viral life cycle was analyzed by immunoblotting, and the highest level was found to be coincidental with the onset of virion morphogenesis.

Animals↗
PubMed1985

Variations in interstate migration of men across the early stages of the life cycle.

The results reported here show that the stage of an individual's life cycle not only has direct effects on the likelihood of migration, but also establishes a context within which the motives to migrate are evaluated and acted upon. One contextual impact of the life cycle concerns the effects of length of residence on migration. The results show that the probability of migrating declines more rapidly over time for married males with children than for singles males--i.e., the difference between the likelihood of migration for single males and married males with children widens with increasing length of residence. Much of this difference may be due to the greater number and strength of community ties for individuals who are married with children. These ties are not well developed at the beginning of a residence but continue to strengthen over the course of a residence. In addition, there are variations in the levels of job rewards and location-specific resources across the life cycle and there are two variations across the early life cycle in the effects of independent variables on the initial rate of migration. One resource (self-employment) and one job reward (prestige) have different effects for single individuals than for either group of married males. If the span of the life cycle considered in this analysis were broadened to include older men, additional differences in the effects of independent variables might be uncovered. In research with cross-sectional data containing a wider range of ages than the data used here, Heaton et al. (1981) found that economic variables were more important in determining the migration of younger individuals than that of older individuals, whereas noneconomic factors were more important determinants of the migration of older than of younger individuals. The results of this paper and Heaton's results suggest that at different stages of life people use a somewhat different "subjective cost-benefit calculus" in making migration decisions. The importance of certain migration determinants may vary significantly depending on whether an individual is married, whether he or she has children, and/or whether he or she is in the labor force or retired. Additional research on these issues could greatly contribute to our understanding of migration.

Adult↗
PubMed1999

A review of performance and pathogenicity of male and female Schistosoma mansoni during the life-cycle.

The sexual life-history traits of Schistosoma mansoni have been reviewed to compare male and female performance and pathogenicity against Biomphalaria glabrata during the life-cycle. A meta-analysis was used on pooled results from different experiments. In most cases, there was no difference between males and females but male cercariae were significantly more infectious than female cercariae. Conversely, cercarial production and cercarial life-span were significantly greater for females than for males; furthermore, females have a tendency to occur in molluscs of larger size. Each difference is discussed and interpreted when possible in terms of male and female differences in transmission strategies. The female strategy may consist of producing many long-living larvae. The male strategy may consist of producing few short-living larvae and would invest in the quality of these larvae instead of their quantity or their life-span.

Animals↗
PubMed2001

The life cycle of Trypanosoma cruzi revisited.

The basic features of the life cycle of Trypanosoma cruzi have been known for nearly a century. Various aspects of the life cycle, however, have been elucidated only recently, whilst others remain either controversial or unstudied. Here, we present a revised life cycle influenced by recent findings and specific questions that remain unresolved.

Animals↗
PubMed2006

Lipid rafts play an important role in the early stage of severe acute respiratory syndrome-coronavirus life cycle.

Lipid rafts are involved in the life cycle of many viruses. In this study, we showed that lipid rafts also play an important role in the life cycle of severe acute respiratory syndrome (SARS)-coronavirus (CoV). Cholesterol depletion by pretreatment of Vero E6 cells with methyl-beta-cyclodextrin (MbetaCD) inhibited the production of SARS-CoV particles released from the infected cells. This inhibition was prevented by addition of cholesterol to the culture medium, indicating that the reduction of virus particle release was caused by the loss of cholesterol in the cell membrane. In contrast, cholesterol depletion at the post-entry stage (3h post-infection) caused only a limited effect on virus particle release. Northern blot analysis revealed that the levels of viral mRNAs were significantly affected by pretreatment with MbetaCD, but not by treatment at 3h post-infection. Interestingly, no apparent evidence for colocalization of angiotensin converting enzyme 2 with lipid rafts in the membrane of Vero E6 cells was obtained. These results suggest that lipid rafts could contribute to SARS-CoV infection in the early replication process in Vero E6 cells.

Angiotensin-Converting Enzyme 2↗
PubMed1998

Coevolutionary interactions between host life histories and parasite life cycles.

Several recent studies have discussed the interaction of host life-history traits and parasite life cycles. It has been observed that the life-history of a host often changes after infection by a parasite. In some cases, changes of host life-history traits reduce the costs of parasitism and can be interpreted as a form of resistance against the parasite. In other cases, changes of host life-history traits increase the parasite's transmission and can be interpreted as manipulation by the parasite. Alternatively, changes of host's life-history traits can also induce responses in the parasite's life cycle traits. After a brief review of recent studies, we treat in more detail the interaction between the microsporidian parasite Edhazardia aedis and its host, the mosquito Aedes aegypti. We consider the interactions between the host's life-history and parasite's life cycle that help shape the evolutionary ecology of their relationship. In particular, these interactions determine whether the parasite is benign and transmits vertically or is virulent and transmits horizontally.

Aedes↗
PubMed1990

The use of computer-aided learning for teaching parasite life cycles.

The difficulty of presenting parasite life cycles in a textual or diagrammatic form is discussed and the use of computer-aided learning to solve this is described. The design and use of a Hypercard stack for teaching parasite life cycles on an Apple Macintosh microcomputer are outlined.

Animals↗
PubMed1983

Temporal and status dimensions of life cycles.

An alternative approach to the life cycle is developed which avoids the creation of monolithic age categories and exclusive reliance upon the unidimensional index of chronological age. An age status graph is constructed by intersecting age with a status dimension. Using a card sort technique, age norms of status transition for family and work are ascertained. These data exemplify the potential utility of age status graphing in understanding the life cycle. The methodological strengths of operationalizing variables, explicitness of criteria, and conceptual flexibility are discussed.

Adolescent↗
PubMed2000

A life-cycle comparison of alternative automobile fuels.

We examine the life cycles of gasoline, diesel, compressed natural gas (CNG), and ethanol (C2H5OH)-fueled internal combustion engine (ICE) automobiles. Port and direct injection and spark and compression ignition engines are examined. We investigate diesel fuel from both petroleum and biosources as well as C2H5OH from corn, herbaceous bio-mass, and woody biomass. The baseline vehicle is a gasoline-fueled 1998 Ford Taurus. We optimize the other fuel/powertrain combinations for each specific fuel as a part of making the vehicles comparable to the baseline in terms of range, emissions level, and vehicle lifetime. Life-cycle calculations are done using the economic input-output life-cycle analysis (EIO-LCA) software; fuel cycles and vehicle end-of-life stages are based on published model results. We find that recent advances in gasoline vehicles, the low petroleum price, and the extensive gasoline infrastructure make it difficult for any alternative fuel to become commercially viable. The most attractive alternative fuel is compressed natural gas because it is less expensive than gasoline, has lower regulated pollutant and toxics emissions, produces less greenhouse gas (GHG) emissions, and is available in North America in large quantities. However, the bulk and weight of gas storage cylinders required for the vehicle to attain a range comparable to that of gasoline vehicles necessitates a redesign of the engine and chassis. Additional natural gas transportation and distribution infrastructure is required for large-scale use of natural gas for transportation. Diesel engines are extremely attractive in terms of energy efficiency, but expert judgment is divided on whether these engines will be able to meet strict emissions standards, even with reformulated fuel. The attractiveness of direct injection engines depends on their being able to meet strict emissions standards without losing their greater efficiency. Biofuels offer lower GHG emissions, are sustainable, and reduce the demand for imported fuels. Fuels from food sources, such as biodiesel from soybeans and C2H5OH from corn, can be attractive only if the co-products are in high demand and if the fuel production does not diminish the food supply. C2H5OH from herbaceous or woody biomass could replace the gasoline burned in the light-duty fleet while supplying electricity as a co-product. While it costs more than gasoline, bioethanol would be attractive if the price of gasoline doubled, if significant reductions in GHG emissions were required, or if fuel economy regulations for gasoline vehicles were tightened.

Air Pollution↗
PubMed2005

Greenhouse gas emissions from Canadian peat extraction, 1990-2000: a life-cycle analysis.

This study uses life-cycle analysis to examine the net greenhouse gas (GHG) emissions from the Canadian peat industry for the period 1990-2000. GHG exchange is estimated for land-use change, peat extraction and processing, transport to market, and the in situ decomposition of extracted peat. The estimates, based on an additive GHG accounting model, show that the peat extraction life cycle emitted 0.54 x 10(6) t of GHG in 1990, increasing to 0.89 x 10(6) t in 2000 (expressed as CO2 equivalents using a 100-y time horizon). Peat decomposition associated with end use was the largest source of GHGs, comprising 71% of total emissions during this 11-y period. Land use change resulted in a switch of the peatlands from a GHG sink to a source and contributed an additional 15%. Peat transportation was responsible for 10% of total GHG emissions, and extraction and processing contributed 4%. It would take approximately 2000 y to restore the carbon pool to its original size if peatland restoration is successful and the cutover peatland once again becomes a net carbon sink.

Air Pollutants↗