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排序方式: 共有112条查询结果,搜索用时 15 毫秒
91.
92.
SAMILA SIAVOSHIAN HERV M BLOTTIRE ERIC LE FOLL BERTRAND KAEFFER CHRISTINE CHERBUT JEAN-PAUL GALMICHE 《Cell biology international》1997,21(5):281-287
The aim of this study was to compare the effects of acetate, propionate, butyrate, iso-butyrate, valerate, iso-valerate and caproate on cell growth and on the activities of alkaline phosphatase (AP) and dipeptidyl aminopeptidase IV (DPP IV) by three human colonic adenocarcinoma cell lines. In addition to butyrate, propionate and valerate inhibited cell proliferation of the three cell lines. The other SCFAs did not influence cell proliferation. AP and DPP IV activities were strongly stimulated by butyrate on two of the three cell lines. On HT-29, AP was strongly stimulated, however DPPIV expression remained undetectable. Propionate and valerate exhibited a weaker stimulation, the other SCFAs being ineffective. The effect of SCFAs on cell proliferation and differentiation clearly depends on the number of carbons and on the configuration of the basic structure of the molecule. 相似文献
93.
MATTHEW D. HALL LUC F. BUSSIÈRE MARCO DEMONT PAUL I. WARD ROBERT C. BROOKS 《Molecular ecology》2010,19(3):610-619
The outcome of mate choice depends on complex interactions between males and females both before and after copulation. Although the competition between males for access to mates and premating choice by females are relatively well understood, the nature of interactions between cryptic female choice and male sperm competition within the female reproductive tract is less clear. Understanding the complexity of postcopulatory sexual selection requires an understanding of how anatomy, physiology and behaviour mediate sperm transfer and storage within multiply mated females. Here we use a newly developed molecular technique to directly quantify mixed sperm stores in multiple mating females of the black field cricket, Teleogryllus commodus. In this species, female postcopulatory choice is easily observed and manipulated as females delay the removal of the spermatophore in favour of preferred males. Using twice‐mated females, we find that the proportion of sperm in the spermatheca attributed to the second male to mate with a female (S2) increases linearly with the time of spermatophore attachment. Moreover, we show that the insemination success of a male increases with its attractiveness and decreases with the size of the female. The effect of male attractiveness in this context suggests a previously unknown episode of mate choice in this species that reinforces the sexual selection imposed by premating choice and conflicts with the outcome of postmating male harassment. Our results provide some of the clearest evidence yet for how sperm transfer and displacement in multiply mated females can lead directly to cryptic female choice, and that three distinct periods of sexual selection operate in black field crickets. 相似文献
94.
95.
Conserved sequence motifs, alignment, and secondary structure for the third domain of animal 12S rRNA 总被引:17,自引:3,他引:14
Hickson RE; Simon C; Cooper A; Spicer GS; Sullivan J; Penny D 《Molecular biology and evolution》1996,13(1):150-169
Secondary structure models are an important step for aligning sequences,
understanding probabilities of nucleotide substitutions, and evaluating the
reliability of phylogenetic reconstructions. A set of conserved sequence
motifs is derived from comparative sequence analysis of 184 invertebrate
and vertebrate taxa (including many taxa from the same genera, families,
and orders) with reference to a secondary structure model for domain III of
animal mitochondrial small subunit (12S) ribosomal RNA. A template is
presented to assist with secondary structure drawing. Our model is similar
to previous models but is more specific to mitochondrial DNA, fitting both
invertebrate and vertebrate groups, including taxa with markedly different
nucleotide compositions. The second half of the domain III sequence can be
difficult to align precisely, even when secondary structure information is
considered. This is especially true for comparisons of anciently diverged
taxa, but well-conserved motifs assist in determining biologically
meaningful alignments. Patterns of conservation and variability in both
paired and unpaired regions make differential phylogenetic weighting in
terms of "stems" and "loops" unsatisfactory. We emphasize looking carefully
at the sequence data before and during analyses, and advocate the use of
conserved motifs and other secondary structure information for assessing
sequencing fidelity.
相似文献
96.
Evolutionary dynamics of tandem repeats in the mitochondrial DNA control region of the minnow Cyprinella spiloptera 总被引:3,自引:0,他引:3
Length variation due to tandem repeats is now recognized as a common
feature of animal mitochondrial DNA; however, the evolutionary dynamics of
repeated sequences are not well understood. Using phylogenetic analysis,
predictions of three models of repeat evolution were tested for arrays of
260-bp repeats in the cyprinid fish Cyprinella spiloptera. Variation at
different nucleotide positions in individual repeats supported different
models of repeat evolution. One set of characters included several
nucleotide variants found in all copies from a limited number of
individuals, while the other set included an 8- bp deletion found in a
limited number of copies in all individuals. The deletion and an associated
nucleotide change appear to be the result of a deterministic, rather than
stochastic, mutation process. Parallel origins of repeat arrays in
different mitochondrial lineages, possibly coupled with a homogenization
mechanism, best explain the distribution of nucleotide variation.
相似文献
97.
Ixodes (Pholeoixodes) hexagonus, an efficient vector of Borrelia burgdorferi in the laboratory 总被引:2,自引:0,他引:2
LISE GERN LINA N. TOUTOUNGI CHANG MIN HU RE AESCHLIMANN 《Medical and veterinary entomology》1991,5(4):431-435
Borrelia burgdorferi Johnson et al. was first isolated from the midgut of Ixodes dammini Spielman et al. in the U.S.A. and from the midgut of I.ricinus (L.) in Europe. I.ricinus was considered to be the only tick vector of this borrelia, in Europe, until I.hexagonus Leach, the hedgehog tick, was found to harbour spirochaetes. This paper reports an evaluation of the vector competence of I.hexagonus for the spirochaete B.burgdorferi. Transovarial and trans-stadial survival were demonstrated and the spirochaete was transmitted to laboratory mice via the bites of trans-stadially infected I.hexagonus females. 相似文献
98.
LESLIE G. UNDERHILL PETER A. BARTLETT LUKAS BAUMANN ROBERT J.M. CRAWFORD BRUCE M. DYER RE GILDENHUYS DEON C. NEL TERENCE B. OATLEY MEREDITH THORNTON LEISHA UPFOLD ANTHONY J. WILLIAMS PHILIP A. WHITTINGTON ANTON C. WOLFAARDT 《Ibis》1999,141(1):29-37
The bulk ore carrier Apollo Sea sank near Dassen Island, South Africa, on 20 June 1994 during a period of winter storms. Approximately 10 000 African (Jackass) Penguins Spheniscus demersus were oiled, collected and transported to the SANCCOB rescue centre; 5213 were released after cleaning, 4076 with flipper bands. We believe that most of the penguins oiled during this incident reached an island or the mainland alive, and that there was no mass mortality in the wild at the time of the oil spill. Birds from all parts of the breeding range were oiled, but most were from Robben and Dassen Islands. The overwhelming majority of released birds made the transition from the rescue centre to the wild successfully; 2652 had been resighted at breeding colonies within two years of their release; the cumulative number of birds was increasing steadily and an asymptote had not been reached by August 1996. There was a wide dispersal of released penguins, with recoveries and resightings over 1800 km of coastline between Algoa Bay and Walvis Bay. 相似文献
99.
CengizTURE ElifSALKURT 《植物学报(英文版)》2005,47(6):660-667
Airborne pollen grains in the atmosphere of Bozuyuk were investigated over a 2 yr period from 2000 to 2001 using a Durham sampler. A total number of pollen grains of 5 170 pollen grains belonging to 32 taxa were identified and recorded along with some unidentified pollen grains. Of all the pollen grains, 78.66% were arboreal, 19.20% were non-arboreal, and 2.12% were unidentified. The majority of pollen grains investigated were Pinus, Platanus, Quercus, Cupressaceae, Poaceae, Fagus, Salix, Rosaceae, Urticaceae, Asteraceae, and Chenopodiaceae. The maximum number of pollen grains was recorded in May. 相似文献
100.
Reactive oxygen species promote tyrosine phosphorylation and capacitation in equine spermatozoa 总被引:6,自引:0,他引:6
The objective of this study was to examine the influence of reactive oxygen species (ROS) on equine sperm capacitation. Motile equine spermatozoa were separated on a discontinuous Percoll gradient, resuspended at 10 x 10(6)ml in Tyrode's medium supplemented with BSA (0.5%) and polyvinyl alcohol (0.5%) and incubated at 39 degrees C for 2h with or without the xanthine (X; 0.1mM)-xanthine oxidase (XO; 0.01 U/ml) system or NADPH (0.25 mM). The importance of hydrogen peroxide or superoxide for capacitation was determined by the addition of catalase (CAT; 150 U/ml) or superoxide dismutase (SOD; 150 U/ml), respectively. Following incubation, acrosomal exocytosis was induced by a 5 min incubation at 39 degrees C with progesterone (3.18 microM), and sperm viability and acrosomal integrity were then determined by staining with Hoechst 33258 and fluoroisothiocyanate-conjugated Pisum sativum agglutin. To examine tyrosine phosphorylation, treatments were subjected to sodium dodecyl sulfate-polyacrylaminde gel electrophoresis (SDS-PAGE) followed by Western blot analysis with the anti-phosphotyrosine antibody (alpha-PY; clone 4G10). Capacitation with the X-XO system or NADPH led to a significant (P<0.0001) increase in live acrosome-reacted spermatozoa compared to controls. The addition of CAT or SOD prevented the increase in live acrosome-reacted spermatozoa associated with X-XO treatment. Incubation with the X-XO system was also associated with a significant (P<0.005) increase in tyrosine phosphorylation when compared to controls, which could be prevented by the addition of CAT but not SOD. This study indicates that ROS can promote equine sperm capacitation and tyrosine phosphorylation, suggesting a physiological role for ROS generation by equine spermatozoa. 相似文献