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21.
JB Parentes-Vieira PV Lopes-Costa CG Pires AR dos Santos JD Pereira-Filho BB da Silva 《International Seminars in Surgical Oncology : ISSO》2007,4(1):22
Background
The objective of this study was to evaluate angiogenesis according to CD34 antigen expression in estrogen receptor (ER)-positive and negative breast carcinomas.Methods
This study comprised 64 cases of infiltrating ductal carcinoma in postmenopausal women divided into two groups: Group A: ER-positive, n = 35; and Group B: ER-negative, n = 29. The anti-CD34 monoclonal antibody was used as a marker for endothelial cells. Microvessel count was carried out in 10 fields per slide using a 40× objective lens (magnification 400×). Statistical analysis of the data was performed using Student's t-test (p < 0.05).Results
The mean number of vessels stained with the anti-CD34 antibody in the estrogen receptor-positive and negative tumors was 23.51 ± 1.15 and 40.24 ± 0.42, respectively. The number of microvessels was significantly greater in the estrogen receptor-negative tumors (p < 0.001).Conclusion
ER-negative tumors have significantly greater CD34 antigen expression compared to ER-positive tumors.22.
Substitution bias, rapid saturation, and the use of mtDNA for nematode systematics 总被引:13,自引:0,他引:13
Only relatively recently have researchers turned to molecular methods for
nematode phylogeny reconstruction. Thus, we lack the extensive literature
on evolutionary patterns and phylogenetic usefulness of different DNA
regions for nematodes that exists for other taxa. Here, we examine the
usefulness of mtDNA for nematode phylogeny reconstruction and provide data
that can be used for a priori character weighting or for parameter
specification in models of sequence evolution. We estimated the
substitution pattern for the mitochondrial ND4 gene from intraspecific
comparisons in four species of parasitic nematodes from the family
Trichostrongylidae (38-50 sequences per species). The resulting pattern
suggests a strong mutational bias toward A and T, and a lower
transition/transversion ratio than is typically observed in other taxa. We
also present information on the relative rates of substitution at first,
second, and third codon positions and on relative rates of saturation of
different types of substitutions in comparisons ranging from intraspecific
to interordinal. Silent sites saturate extremely quickly, presumably owing
to the substitution bias and, perhaps, to an accelerated mutation rate.
Results emphasize the importance of using only the most closely related
sequences in order to infer patterns of substitution accurately for
nematodes or for other taxa having strongly composition-biased DNA. ND4
also shows high amino acid polymorphism at both the intra- and
interspecific levels, and in higher level comparisons, there is evidence of
saturation at variable amino acid sites. In general, we recommend using
mtDNA coding genes only for phylogenetics of relatively closely related
nematode species and, even then, using only nonsynonymous substitutions and
the more conserved mitochondrial genes (e.g., cytochrome oxidases). On the
other hand, the high substitution rate in genes such as ND4 should make
them excellent for population genetics studies, identifying cryptic
species, and resolving relationships among closely related congeners when
other markers show insufficient variation.
相似文献
23.
J. B. T. M. Roerdink 《Journal of mathematical biology》1988,26(2):199-215
A discrete-time population model with two age classes is studied which describes the growth of biennial plants in a randomly varying environment. A fraction of the oldest age class delays its flowering each year. The solution of the model involves products of random matrices. We calculate the exact mean and variance of the long-run geometric growth rate assuming a gamma distribution for the random number of offspring per flowering plant after one year. It is shown, both by analytical calculation and numerical examples, that it is profitable for the population to delay its flowering, in the sense that the average growth rate increases and the extinction probability decreases. The optimal values of the flowering fraction depend upon the environmental and model parameters. 相似文献
24.
25.
Conditions controlling tumor cytotoxicity of rat liver macrophages mediated by liposomal muramyl dipeptide 总被引:1,自引:0,他引:1
Activation of rat liver macrophages with free and liposome-encapsulated muramyl dipeptide (MDP) to a tumorcytotoxic state was characterized by employing various experimental conditions. Macrophage-mediated tumor cytotoxicity was determined using two standard assay systems: a [methyl-3H]thymidine release assay to measure the extent of tumor cell lysis and a [methyl-3H]thymidine incorporation assay to measure the combined effects of tumor cell lysis and stasis. The extent of cell lysis was not affected by the ratio of macrophages to tumor cells within the ratio range of 30:1 to 5:1, provided that the macrophages form a confluent monolayer. Tumor cell lysis, however, was significantly influenced by macrophage density; a low macrophage density for example resulted in a low percentage of tumor cell lysis. Tumor target cells used in this study, i.e., C26 adenocarcinoma, B16 melanoma and P815 mastocytoma, differed in their susceptibility towards macrophage-mediated cell lysis, whereas no differences were observed with respect to tumor cell stasis. Non-tumorigenic cell lines such as human fibroblastic cells and LLC monkey kidney cells were not lysed by activated macrophages, although proliferation of these cells was markedly inhibited. Additionally, the effects of liposomal lipid composition on macrophage activation were studied. With a basic composition of phospholipid/cholesterol/dicetylphosphate, we used either egg-yolk, dipalmitoyl-, distearoyl- or dihexadecylphosphatidylcholine as the bulk phospholipid constituent. Although these liposomes display a widely different susceptibility to lysosomal phospholipase activities, we could not detect any significant difference in either the extent or the duration of the tumoricidal activity induced by MDP encapsulated in these different types of liposomes. 相似文献
26.
Phylogeny of the Drosophila saltans species group based on combined analysis of nuclear and mitochondrial DNA sequences 总被引:2,自引:0,他引:2
Nucleotide sequences from two nuclear loci, alcohol dehydrogenase and
internal transcribed spacer-1 of the nuclear ribosomal DNA repeats, and two
mitochondrial genes, cytochrome oxidase I and cytochrome oxidase II, were
determined from nine species in the Drosophila saltans species group. The
partition homogeneity test and partitioned Bremer support were used to
measure incongruence between phylogenetic hypotheses generated from
individual partitions. Individual loci were generally congruent with each
other and consistent with the previously proposed morphological hypothesis,
although they differed in level of resolution. Since extreme conflict
between partitions did not exist, the data were combined and analyzed
simultaneously. The total evidence method gave a more resolved and highly
supported phylogeny, as indicated by bootstrap proportions and decay
indices, than did any of the individual analyses. The cordata and elliptica
subgroups, considered to have diverged early in the history of the D.
saltans group, were sister taxa to the remainder of the saltans group. The
sturtevanti subgroup, represented by D. milleri and D. sturtevanti,
occupies an intermediate position in this phylogeny. The saltans and
parasaltans subgroups are sister clades and occupy the most recently
derived portion of the phylogeny. As with previous morphological studies,
phylogenetic relationships within the saltans subgroup were not
satisfactorily resolved by the molecular data.
相似文献
27.
Ronald van den Berg Jos B. T. M. Roerdink Frans W. Cornelissen 《PLoS computational biology》2010,6(1)
An object in the peripheral visual field is more difficult to recognize when surrounded by other objects. This phenomenon is called “crowding”. Crowding places a fundamental constraint on human vision that limits performance on numerous tasks. It has been suggested that crowding results from spatial feature integration necessary for object recognition. However, in the absence of convincing models, this theory has remained controversial. Here, we present a quantitative and physiologically plausible model for spatial integration of orientation signals, based on the principles of population coding. Using simulations, we demonstrate that this model coherently accounts for fundamental properties of crowding, including critical spacing, “compulsory averaging”, and a foveal-peripheral anisotropy. Moreover, we show that the model predicts increased responses to correlated visual stimuli. Altogether, these results suggest that crowding has little immediate bearing on object recognition but is a by-product of a general, elementary integration mechanism in early vision aimed at improving signal quality. 相似文献
28.
Y Deng J Zhao D Sakurai KM Kaufman JC Edberg RP Kimberly DL Kamen GS Gilkeson CO Jacob RH Scofield CD Langefeld JA Kelly ME Alarcón-Riquelme BIOLUPUS GENLES Networks JB Harley TJ Vyse BI Freedman PM Gaffney KM Sivils JA James TB Niewold RM Cantor W Chen BH Hahn EE Brown PROFILE BP Tsao 《Arthritis research & therapy》2012,14(Z3):A5
29.
Nucleotide sequence comparisons were used to investigate the evolution of P
transposable elements and the possibility that horizontal transfer has
played a role in their occurrence in natural populations of Drosophila and
other Diptera. The phylogeny of P elements was examined using published
sequences from eight dipteran taxa and a new, partial sequence from
Scaptomyza elmoi. The results from a number of different analyses are
highly consistent and reveal a P-element phylogeny that contradicts the
phylogeny of the species. At least three instances of horizontal transfer
are necessary to explain this incongruence, but other explanations cannot
be ruled out at this time.
相似文献
30.