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At least 919 records · Page 51Linked to original sources
PubMed1988

Non-invasive quantitative estimation of bone density in rats throughout the life cycle and in arthritic osteopenia: preliminary results.

A longitudinal bone survey was conducted in 86 female Wistar rats in order to assess mineral density kinetics from young age (5 weeks: 115 g) till late adulthood (64 weeks: 586 g). In vivo quantitative radiographic scanning was performed on the caudal vertebrae, taking trabecular mass as the parameter. Measurements were expressed as Relative Optical Density (ROD) units by means of a high resolution densitometric device. Results showed a progressive increase in mineral density throughout the life cycle, with a tendency to level in the higher weight range, indicating that progressive mineral aposition occurs in rats in dependency of age. This phenomenon, however, should be always considered within the context of continuous skeletal growth and related changes typical of this species. Twelve different animals were also examined following induction of articular inflammation with Freund's adjuvant in six of them. Bone survey conducted 12 to 18 days after inoculation revealed a significant (P less than 0.01) reduction in trabecular bone mass of scanned vertebrae in comparison with the weight-matched untreated controls. It is concluded that the in vivo quantitative assessment of bone density illustrated in this report represents a sensitive and useful tool for the long-term survey of naturally occurring or experimentally induced bone changes. Scanning of the same part of the skeleton can be repeated, thereby avoiding sacrifice of the animal and time-consuming preparation of post-mortem material.

Animals↗
PubMed2003

High frequency of alternative splicing of human genes participating in the HIV-1 life cycle: a model using TSG101, betaTrCP, PPIA, INI1, NAF1, and PML.

Alternative splicing may generate splice forms with different biologic roles or missing protein domains implicated in the interaction with HIV-1. To address this issue, 6 human genes were investigated-tumor suppressor gene 101 (TSG101), beta-transducin repeats containing protein (betaTrCP), peptidyl-proly cis-trans isomerase, cyclophilin A (PPIA), integrase interactor 1 protein (INI1), Nef-associated factor 1 (NAF1), and promyelacytic leukemia (PML)-involved in the viral life cycle and HIV-1 pathogenesis. All 6 genes presented alternative splicing, and a combined bioinformatic and reverse transcription polymerase chain reaction (RT-PCR) analysis identified 27 new variants for a total of 53 splice forms (an average of 9 variants per gene). The predicted frequency of the various splice forms based on expressed sequence tags (EST) analysis corresponded to the semiquantitative findings on RT-PCR analysis for the cell culture systems and for native CD4 cells investigated. Interindividual variation in the frequencies of various splice forms in CD4 T cells from blood donors was observed for INI1. Cell type-specific variation of splice pattern was observed for NAF1. Eight splice forms lacked or modified motifs implicated in the interaction with HIV-1, underscoring the potential interest of assessing alternative splicing when investigating viral cell biology and pathogenesis.

Alternative Splicing↗
PubMed2005

HIV-1-associated uracil DNA glycosylase activity controls dUTP misincorporation in viral DNA and is essential to the HIV-1 life cycle.

Uracilation of DNA represents a constant threat to the survival of many organisms including viruses. Uracil may appear in DNA either by cytosine deamination or by misincorporation of dUTP. The HIV-1-encoded Vif protein controls cytosine deamination by preventing the incorporation of host-derived APOBEC3G cytidine deaminase into viral particles. Here, we show that the host-derived uracil DNA glycosylase UNG2 enzyme, which is recruited into viral particles by the HIV-1-encoded integrase domain, is essential to the viral life cycle. We demonstrate that virion-associated UNG2 catalytic activity can be replaced by the packaging of heterologous dUTPase into virion, indicating that UNG2 acts to counteract dUTP misincorporation in the viral genome. Therefore, HIV-1 prevents incorporation of dUTP in viral cDNA by UNG2-mediated uracil excision followed by a dNTP-dependent, reverse transcriptase-mediated endonucleolytic cleavage and finally by strand-displacement polymerization. Our findings indicate that pharmacologic strategies aimed toward blocking UNG2 packaging should be explored as potential HIV/AIDS therapeutics.

Base Sequence↗
PubMed1975

Quantitative ultrastructural investigations of the life cycle of Trypanosoma brucei: a morphometric analysis.

The quantitative ultrastructure of the developmental stages of Trypanosoma brucei brucei in its vector Glossina morsitans was studied by morphometric analysis. Values from ectoperitrophic midgut forms, proventricular forms, epimastigote and metacyclic forms in the salivary gland are compared with results from bloodstream forms, published previously. Significant differences in the volume densities of the trypanosome's single mitochondrion, of microbody-like organelles and in the surface densities of inner and outer mitochondrial membranes were found throughout the whole life cycle. A great increase in volume density of the mitochondrion was observed after transfer to the insect host; reduction took place during metacyclic development. Parallel to the biogenesis of the mitochondrion a reduction of microbodies was found in proventricular forms and there was a great increase in metacyclic forms concomitant with the regression of the mitochondrion. Metacyclic forms had a close quantitative morphologic similarity to bloodstream forms. The results are discussed in connection with changes in structure and in oxidative metabolism.

Animals↗
PubMed2005

Describing the life cycle of U.S. Marine Hospital #17, Port Townsend, Washington, 1855-1933.

This study was undertaken to determine why U.S. Marine Hospital #17, Port Townsend, Washington, closed at the peak of its utilization. A social history approach was taken, examining the hospital's developmental changes in the context of its role in the larger society. Both firsthand and interpretive sources were reviewed, and numerous photographs and drawings confirmed the hospital was an active participant in the economy. Regarding the hospital's transitions over time as a life cycle was a useful organizing framework. Inpatient census patterns as a measure of the hospital's growth and development informed and enlightened this study. It became clear the Marine Hospital responded to and influenced events in the Port Townsend seaport whose importance diminished when other port cities at the base of the Puget Sound began and sustained rapid growth.

History, 19th Century↗
PubMedDate not supplied

[Experimental studies on Gregarina ovata Dufour, 1828: macro and microsporocysts, parasitic specificity, lasting of the life cycle (author's transl)].

The present study based mostly on experimental infestations deals with three questions related to Gregarina ovata, an Eugregarine parasite of Dermaptera: a) Gregarina ovata does not provide two patterns of sporocysts (macro and micro) as it has been thought until now. Through the experimentation, two species can be determined only by their mature gametocysts and sporocysts; b) The host specificity is not strict. Two species or even two genus of Dermaptera can be parasitized by the same Gregarine; c) The life-cycle, from ingested sporocysts to new sporocysts, is from 13 to 16 days for Gragarina ovata (species with large sporocysts) and from 11 to 13 days for Gregarian fallax (species with small sporocysts.

Animals↗
PubMed1987

Changes in penicillin-binding proteins during the life cycle of Micromonospora.

The penicillin-binding proteins (PBPs) of Micromonospora were studied. Only one PBP (48,000 mol weight) was found in membranes isolated from primary mycelia, whereas three PBPs were observed in secondary mycelia and designated PBP 1 (89,000 mol weight), PBP2 (69,000) and PBP3 (48,000). Both the unique PBP produced by primary mycelia and PBP3 of secondary mycelia had the same affinity for penicillin which was higher than that of PBP2 and 3. The role of these proteins in the cell life cycle of Micromonospora is discussed.

Bacterial Proteins↗
PubMed1983

Life cycle efficiency of beef production: I. Cow efficiency ratios for progeny weaned.

Weights and individual feed consumption collected on 160 beef, dairy and beef X dairy dams and their progeny were used to estimate several measures of lifetime cow efficiency. Dams were fed either a high or a low energy diet. Efficiency was expressed as the ratio of outputs to inputs. Outputs included progeny weaning weights plus cow salvage weight, and inputs were progeny creep feed consumption plus the dam's lifetime feed consumption. In the first approach, life cycle cow efficiency was estimated by expressing weight output as a ratio to feed inputs when weights and feed consumptions were weighted by their probabilities; probabilities were a function of age distribution and percentage calf crop in a theoretical herd consisting of 100 cows and 20 yearling replacement heifers. In the second approach, actual lifetime cow efficiency was estimated by expressing weight outputs as a ratio to feed inputs when all components were weighted equally. Both approaches included efficiency estimates calculated with and without cow salvage value. Dams receiving low energy diets generally had lifetime efficiencies equal or superior to those fed high energy diets in spite of older ages at calving. Dams on the high energy diet had greater salvage value, but did not wean calves of sufficient additional size to offset their own increased metabolizable energy (ME) intake. Dam breeds and breed crosses of smaller size tended to be more efficient than those of large size, demonstrating the effectiveness of mating small dams to large sire breeds for improving cow efficiency. Breeds calving at later ages were less efficient. Efficiency ratios improved as number of progeny weaned increased.

Age Factors↗
PubMed1993

Synaptic vesicle life cycle and synaptic turnover.

Cholinergic synaptic vesicles contain a mixture of soluble low molecular mass constituents. Besides acetylcholine these include Ca2+, ATP, GTP, small amounts of ADP and AMP, and also the diadenosine polyphosphates Ap4A and Ap5A. In synaptic vesicles isolated from the electric ray these diadenosine polyphosphates occur in mmol concentrations and might represent a novel cotransmitter. The membrane proteins of cholinergic synaptic vesicles presumably are identical to those in other types of electron-lucent synaptic vesicles. A presumptive exception are the transmitter-specific carriers. The life cycle of the synaptic vesicle in intact neurons and in situ was investigated by analysis of all cytoplasmic membrane compartments that share membrane integral proteins with synaptic vesicles. The results suggest that the synaptic vesicle membrane compartment might originate from the trans-Golgi network and, after cycles of exo- and endocytosis in the nerve terminal, might fuse into an endosomal membrane compartment early on retrograde transport. Tracer experiments using membrane proteins and soluble contents suggest that the synaptic vesicle membrane compartment does not intermix with the presynaptic plasma membrane on repeated cycles of exo- and endocytosis if low frequency stimulation is applied. A cDNA has been isolated from the electric ray electric lobe that codes for o-rab3, a small GTP-binding protein highly homologous to mammalian rab3. While abundant in the nerve terminals of the electric organ and at the neuromuscular junction this protein occurs only in limited subpopulations of nerve terminals in electric ray brain. Immunocytochemical analysis using the colloidal gold technique and a monospecific antibody against o-rab3 suggests that the GTP-binding protein remains attached to recycling synaptic vesicles. No evidence was found for a major contribution of an intraterminal endosomal sorting compartment involved in synaptic vesicle recycling.

Acetylcholine↗
PubMed2006

Biochemical differentiation of APOBEC3F and APOBEC3G proteins associated with HIV-1 life cycle.

APOBEC3G and APOBEC3F are cytidine deaminase with duplicative cytidine deaminase motifs that restrict HIV-1 replication by catalyzing C-to-U transitions on nascent viral cDNA. Despite 60% protein sequence similarity, APOBEC3F and APOBEC3G have a different target consensus sequence for editing, and importantly, APOBEC3G has 10-fold higher anti-HIV activity than APOBEC3F. Thus, APOBEC3F and APOBEC3G may have distinctive characteristics that account for their functional differences. Here, we have biochemically characterized human APOBEC3F and APOBEC3G protein complexes as a function of the HIV-1 life cycle. APOBEC3G was previously shown to form RNase-sensitive, enzymatically inactive, high molecular mass complexes in immortalized cells, which are converted into enzymatically active, low molecular mass complexes by RNase digestion. We found that APOBEC3F also formed high molecular mass complexes in these cells, but these complexes were resistant to RNase treatment. Further, the N-terminal half determined RNase sensitivity and was necessary for the high molecular mass complex assembly of APOBEC3G but not APOBEC3F. Unlike APOBEC3F, APOBEC3G strongly interacted with cellular proteins via disulfide bonds. Inside virions, both APOBEC3F and APOBEC3G were found in viral cores, but APOBEC3G was associated with low molecular mass, whereas APOBEC3F was still retained in high molecular mass complexes. After cell entry, both APOBEC3F and APOBEC3G were localized in low molecular mass complexes associated with viral reverse transcriptional machinery. These results demonstrate that APOBEC3F and APOBEC3G complexes undergo dynamic conversion during HIV-1 infection and also reveal biochemical differences that likely determine their different anti-HIV-1 activity.

APOBEC-3G Deaminase↗
PubMed1976

RNA virus in Allomyces arbuscula: ultrastructural localization during the life-cycle.

Strain Bali I of Allomyces arbuscula is infected with a RNA virus; strain North Carolina is not. The virus appears to be avirulent, for strain Bali I showed no signs of pathogenicity. Virus aggregates occurred mostly in the cytoplasm during different stages of the gametophytic and sporophytic generations. Small intra-nuclear aggregates were found only in differentiating gametophytic hyphae and immature gametangia. In motile cells (gametes and zoospores) the aggregates are exclusively contained within the nuclear cap. This represents a reliable mechanism of transmission throughout the life-cycle.

Cell Nucleus↗
PubMedDate not supplied

The roles of biomedical maintenance branch, automation management & informatics departments throughout a clinical information systems's life cycle.

The introduction of new technology, such as a Clinical Information System (CIS), requires hospitals to re-evaluate the roles of the Biomedical Maintenance Branch, Automation Management, and Informatics departments. This paper describes the process a 400-bed hospital underwent to resolve role ambiguity among the three activities. The institution's goal was to reach an optimal solution to using the resources offered by each activity through redrawing lines of responsibilities. This experience demonstrated that relationships among departments are dynamic and vary depending on the stage of the CIS life cycle.

Biomedical Engineering↗
PubMed2001

In vitro spore formation and completion of the asexual life cycle of Neozygites parvispora, an obligate biotrophic pathogen of thrips.

Capilliconidia, the asexual secondary spores of Neozygites parvispora (Zygomycetes, Entomophthorales) were produced in vitro either by entrapment of vegetative cells (hyphal bodies) in alginate pellets or after plating them onto water agar. Cultivation of the fungus for 3 days in a medium lacking hemolymph increased spore production 30 to 40-fold, and about 10% of the cells produced capilliconidia. The in vitro produced capilliconidia were infectious to Thrips tabaci and the fungus was reisolated from infected insects, thus completing its asexual life cycle under laboratory conditions. A decrease in capilliconidia production and a modification of the number of nuclei per spore were observed for isolates cultivated in vitro for more than 2 months, but subsequent host passages restored and increased sporulation efficiency without influencing the number of nuclei. Fungal cultures were stored at - 80 degrees C for up to 7 months, and the capability to sporulate and infect T. tabaci was preserved. A bioassay procedure for infecting T. tabaci with N. parvispora is described, the first mycosed insects dying usually after 8 d of incubation.

Alginates↗
PubMed1976

Contribution to the understanding of the life-cycle of Sarcocystis of the short-tailed vole Microtus agrestis.

Attempts were made to transmit to clean voles a species of Sarcocystis found in the muscle of the European short-tailed vole Microtus agrestis, by inoculation of bradyzoites, feeding of infected muscle and feeding of faeces collected from voles and cats fed on infected vole flesh. Transmission was not achieved. The results are discussed in the light of the positive findings reported in the older literature with other rodent Sarcocystis spp. and the recent elucidation of the coccidian life-cycle of several species of Sarcocystis. In view of the reported successful faecal transmission of Sarcocystis of Mus musculus, mouse-to-mouse by "coccidia-like bodies" and cat-to-mouse by sporocysts and by oocysts, it is suggested that more than one species of Sarcocystis involving the same or different final hosts may infect a single rodent species. It is furthermore speculated that the Sarcocystis species of Microtus, with which this paper is mainly concerned, will be found to undergo a coccidian sexual developmental cycle in the intestinal tissue of wild vole predators, e.g. mustelids or owls.

Animals↗
PubMed1980

Eimeria meleagrimitis Tyzzer in turkeys: the life cycle and effects of inoculum size and time on severity of infection and intestinal distribution.

Developmental stages of Eimeria meleagrimitis Tyzzer were found throughout the intestine and ceca of turkeys given inocula ranging from 10(4) to 7.5 x 10(5) sporulated oocysts/bird. Infection initially occurred in the duodenum and upper jejunum but later moved down the intestine and into the ceca. The speed with which the infection moved into these areas was rougly proportional to the inoculum size. Heaviest infections were in the ileum, neck of the cecum, and large intestine. The life cycle consisted of 5 asexual generations before gametogony, a 6th asexual generation developing simultaneously with gametogony. First- and 2nd-generations were located along the sides of villi in the upper intestine rather than in the crypts of Lieberkühn, as previously described in England for this species. Transitory first-generation stages that were abnormally large and usually degenerate were found in the neck of the cecum.

Animals↗
PubMed1996

Targeting human immunodeficiency virus type 1 reverse transcriptase by intracellular expression of single-chain variable fragments to inhibit early stages of the viral life cycle.

Novel molecular approaches to inhibit human immunodeficiency virus type 1 (HIV-1) infection have received increasing attention because of the lack of effective antiviral drug therapies in vivo. We now demonstrate that cells can be intracellularly immunized by cytoplasmic expression of single-chain variable antibody fragments (SFv) which bind to the HIV-1 reverse transcriptase (RT) enzyme. The expression of anti-RT SFv in T-lymphocytic cells specifically neutralizes the RT activity in the preintegration stage and affects the reverse transcription process, an early event of the HIV-1 life cycle. Blocking the virus at these early stages dramatically decreased HIV-1 propagation, as well as the HIV-1-induced cytopathic effects in susceptible human T lymphocytes, by impeding the formation of the proviral DNA. These data also demonstrate that intracellular, complete SFvs may gain access to viral proteins of the HIV-1 preintegration complex. These SFvs will provide a tool with which to better understand the molecular mechanisms involved in restricting viral replication in HIV-1-infected cells.

Animals↗
PubMed1985

Completion of Schistosoma mansoni life cycle in thyroidectomized rats and effects of thyroid hormone replacement therapy.

The survival and maturation of Schistosoma mansoni worms was analyzed in normal, thyroidectomized (Thyrox), and hormone-restored Thyrox rats. Restoration therapy was conducted with both T3 and T4; weight gain of treated rats was monitored to assess hormone-replacement efficacy. Worm yields, lengths, and sex-ratios were compared. Egg yields and the capacity of miracidia to hatch from eggs were also analyzed. The results of these studies support the conclusion that the sequence of steps leading to completion of the S. mansoni life cycle are operational in Thyrox rats. Hormone-treated Thyrox rats are restored to the nonpermissive status, although the worms isolated from these rats still differ in certain respects when compared to worms isolated from normal rats.

Animals↗