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81.
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
82.
P. P. Athanassiadou P. H. Athanassiades P. Davaris E. I. Petrakakou CH. I. Zerva & K. A. Kyrkou 《Cytopathology》1998,9(4):240-247
athanassiadou p.p., athanassiades p. h., daffaris p., petrakakou e. i., fflerffa ch. i. and kffirkou k. a. (1998) Cytopathology 9, 240–247
Expression of Cathepsin D and pS2 in imprint smears of breast carcinoma
The aim of this study was to add to existing information on the effects of certain tumour markers expressed by breast cancers on tumour malignancy as evidenced by size of primary and occurrence of lymph node invasion. One hundred freshly resected breast cancers were examined by immunocytochemical staining of imprint smears for Cathepsin D and pS2. Oestrogen receptor (ER) and progesterone receptor (PR) were tested for by dextrose-coated charcoal (DCC) assay and the results correlated with tumour size, histology and presence or absence of lymph node metastases at the time of surgery using χ2 analysis. A significant positive correlation was demonstrated between Cathepsin D positivity and ER, PR and pS2 positivity. In tumours < 2 cm in diameter at surgery a positive correlation was observed between Cathepsin D positivity and the presence of lymph node metastases. The findings support the hypothesis that Cathepsin D may promote early metastasis, possibly by its proteolytic activity. 相似文献
Expression of Cathepsin D and pS2 in imprint smears of breast carcinoma
The aim of this study was to add to existing information on the effects of certain tumour markers expressed by breast cancers on tumour malignancy as evidenced by size of primary and occurrence of lymph node invasion. One hundred freshly resected breast cancers were examined by immunocytochemical staining of imprint smears for Cathepsin D and pS2. Oestrogen receptor (ER) and progesterone receptor (PR) were tested for by dextrose-coated charcoal (DCC) assay and the results correlated with tumour size, histology and presence or absence of lymph node metastases at the time of surgery using χ
83.
Fucose is a major constituent of the protein- and lipid-linked glycans of
the various life-cycle stages of schistosomes. These fucosylated glycans
are highly antigenic and seem to play a role in the pathology of
schistosomiasis. In this article we describe the identification and
characterization of two fucosyltransferases (FucTs) in cercariae of the
avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1--
>4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-R
alpha1-- >2-FucT. Triton X-100 extracts of cercariae were assayed for
FucT activity using a variety of acceptor substrates. Type 1 chain
(Galbeta1- ->3GlcNAc) based compounds were poor acceptors, whereas those
based on a type 2 chain (Galbeta1-->4GlcNAc), whether
alpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whether
present as oligosaccharide or contained in a glycopeptide or glycoprotein,
all served as acceptor substrates. In this respect the schistosomal alpha3-
FucT resembles human FucT V and VI rather than other known FucTs. N-
ethylmaleimide, an inhibitor of several human FucTs, had no effect on the
activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly
inhibitory. Large scale incubations were carried out with
Galbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 and
Fucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and the
products of the incubations were isolated using a sequence of
chromatographic techniques. By methylation analysis and 2D-TOCSY and
ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1--
>4[Fucalpha1-->2Fucalpha1-->3]GlcNAc,
GalNAcbeta1-->4[Fucalpha1-- >2Fucalpha1-->3]GlcNAcbe
ta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1--
>3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-
FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric)
Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structural
element that have been described on schistosomal glycoconjugates.
相似文献
84.
Summary Rosettes of six particles have been visualized by freeze-fracture in the protoplasmic fracture (PF) faces of: a) the plasma membrane, b) Golgi cisternae, and c) Golgi-derived vesicles in mesophyll cells ofZinnia elegans that had been induced to differentiate synchronously into tracheary elements in suspension culture. These rosettes have been observed previously in the PF face of the plasma membranes of a variety of cellulose-synthesizing cells and are thought to be important in cellulose synthesis. InZinnia tracheary elements, the rosettes are localized in the membrane over regions of secondary wall thickening and are absent between thickenings. The observation of rosettes in the Golgi cisternae and vesicles suggests that the Golgi apparatus is responsible for the selective transport and exocytosis of rosettes in higher plants, as has been previously indicated in the algaMicrasterias (Giddings
et al. 1980). The data presented indicate that the Golgi apparatus has a critical role in the control of cell wall deposition because it is involved not only in the synthesis and export of matrix components but also in the export of an important component of the cellulose synthesizing apparatus. The rosettes are present in the plasma membrane and Golgi vesicles throughout the enlargement of the secondary thickening, suggesting that new rosettes must be continually inserted into the membrane to achieve complete cell wall thickening.Abbreviations
EF
Golgi vesicles, exoplasmic fracture; the plasma membrane, extracellular fracture
-
PF
protoplasmic fracture 相似文献
85.
Ida C Helmark Ulla R Mikkelsen Jens Børglum Anders Rothe Marie CH Petersen Ove Andersen Henning Langberg Michael Kjaer 《Arthritis research & therapy》2010,12(4):R126-11
Introduction
The microdialysis method was applied to the human knee joint with osteoarthritis (OA) in order to reveal changes in biochemical markers of cartilage and inflammation, intraarticularly and in the synovium, in response to a single bout of mechanical joint loading. 相似文献86.
87.
Summary A novel nickel resistant, hyperaccumulatingN.crassa nir-2 mutant, isolated by us, sequestered 90% of Ni2+ from medium with 120 mg/l Ni2+. The parent wild strain showed comparable efficiency only at much lower concentrations (<10mg/l). The initial rapid rate and efficiency of Ni2+ removal could be maintained beyond 2 h by fresh addition of mycelial biomass. The results have been discussed from the stand point of the utility of metal resistant fungi in the control of environmental pollution. 相似文献
88.
89.
90.