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排序方式: 共有184条查询结果,搜索用时 171 毫秒
1.
2.
Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews
(genus Sorex) for the region between the tRNA(Pro) and the conserved
sequence block-F revealed variable numbers of 79-bp tandem repeats. These
repeats were found in all 19 individuals sequenced, representing three
subspecies and one closely related species of the masked shrew group (Sorex
cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an
outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an
adjacent 76-bp imperfect copy of the tandem repeats. One individual was
heteroplasmic for length variants consisting of five and seven copies of
the 79-bp tandem repeat. The sequence of the repeats is conducive to the
formation of secondary structure. A termination-associated sequence is
present in each of the repeats and in a unique sequence region 5' to the
tandem array as well. Mean genetic distance between the masked shrew taxa
and the pygmy shrew was calculated separately for the unique sequence
region, one of the tandem repeats, the imperfect repeat, and these three
regions combined. The unique sequence region evolved more rapidly than the
tandem repeats or the imperfect repeat. The small genetic distance between
pairs of tandem repeats within an individual is consistent with a model of
concerted evolution. Repeats are apparently duplicated and lost at a high
rate, which tends to homogenize the tandem array. The rate of D- loop
sequence divergence between the masked and pygmy shrews is estimated to be
15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid
sequence evolution in shrews may be due either to their high metabolic rate
and short generation time or to the presence of variable numbers of tandem
repeats.
相似文献
3.
4.
大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育 总被引:1,自引:0,他引:1
本实验用免疫组织化学ABC法研究了大鼠胼胝体内神经肽Y免疫反应阳性(NPY-IR)纤维的生后发育。结果发现,许多NPY-IR纤维在大鼠出生时便存在于胼胝体内。NPY-IR胼胝体纤维的密度在生后1周内继续逐渐增高,在第2周内达到最高峰。之后,NPY-IR胼胝体纤维的密度逐渐下降,至第3周末时接近成年时的水平,即仅有少量NPY-IR纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多NPY-IR胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。 相似文献
5.
Two experiments were conducted to study the time of occurrence of the preovulatory LH surge in pigs. Sampling every ten minutes in six cycling gilts before and after onset of standing estrus revealed the preovulatory surge began from 8 hr before to 12 hr after the lordosis reflex was elicited. Three of six gilts initiated the preovulatory LH release coincident with the onset of estrus. Data from 28 postpartum sows, with samples drawn every six hours commencing with the onset of estrus, indicated maximum LH levels were present at the first observance of estrus. Six of the 28 sows had an LH peak 18-24 hr after the onset of estrus. 相似文献
6.
Kowalczyk AE Kaczmarek MM Schams D Ziecik AJ 《Molecular reproduction and development》2008,75(10):1558-1566
The purpose of the present study was to investigate the effects of prostaglandin (PG) E(2) and tumor necrosis factor (TNF) alpha on expression of vascular endothelial growth factor (VEGF) and its receptors, fms-like tyrosine kinase (Flt-1) and fetal liver kinase-1/kinase insert domain-containing receptor (Flk-1/KDR), in cultured porcine luteal cells. Real-time PCR was used for quantification of VEGF and its receptors mRNA, whereas VEGF release by luteal cells was determined by radioimmunoassay (RIA). Only the highest dose of PGE(2) (1 microM) after 6 hr of incubation stimulated VEGF release by luteal cells collected in the mid-luteal phase (P < 0.05). Moreover, PGE(2) (100 nM, 1 microM) significantly stimulated VEGF secretion by luteal cells in the late phase and during pregnancy on Days 10-12 (P < 0.05). Elevated mRNA expression of both VEGF 120 and VEGF 164 isoforms was found in luteal cells cultured with PGE(2). The lack of an effect of PGE(2) on VEGF receptors mRNA expression was observed. TNFalpha was able to significantly stimulate VEGF release from cells obtained in the mid- and late luteal phase or during early pregnancy. All tested doses enhanced mRNA levels of VEGF 120 isoform, but not VEGF 164. Additionally, TNFalpha was able to decrease Flk-1/KDR mRNA expression, whereas Flt-1 mRNA levels were not affected. These results indicated that PGE(2) and TNFalpha influenced VEGF ligand-receptor system expression in porcine luteal cells and may therefore play an important role in regulation of luteal functions during the estrous cycle and pregnancy in pigs. 相似文献
7.
8.
Ovarian steroids modulate uterine receptivity in domestic species. Luteinizing hormone (LH) stimulates prostaglandin (PG)F(2alpha) release from the porcine endometrium. However, the combined action of LH and steroids on PGs secretion has not yet been studied in pigs. The aim of the present study was to examine the effect of estradiol (E(2)) and progesterone (P(4)) on basal and LH-stimulated PGF(2alpha) and PGE(2) secretion and cyclooxygenase-2 (COX-2) protein expression in porcine endometrial stromal cells obtained on days 12-13 of the estrous cycle. Cells were cultured for 48 h in a medium containing charcoal-stripped newborn calf serum alone or supplemented with 10 nM E(2) and/or 50 nM P(4). Then, the cells were incubated for 6 h in the presence or absence of LH (20 ng/ml). Long exposure of stromal cells to steroids had no effect on PGF(2alpha) secretion, but PGE(2) release increased in the presence of E(2) plus P(4) (p<0.05). Pre-incubation of cells with E(2) plus P(4) resulted in enhanced PGF(2alpha) (p<0.05) and PGE(2) (p<0.001) secretion. Moreover, LH increased PG(2alpha) secretion in control (p<0.05) and E(2)-treated stromal cells (p<0.01). LH tended (p=0.07) to elevate PGE(2) release only in cells pre-exposed to E(2) plus P(4). The expression of COX-2 protein was increased by LH (p<0.05), but not by steroids. These results confirm the stimulatory effect of LH on PGF(2alpha) secretion and COX-2 expression in porcine stromal cells before luteolysis. PG release from porcine endometrium seems to be controlled by ovarian steroids, however only E(2)-treated-treated cells responded to LH. 相似文献
9.
Black AP Bhayani H Ryder CA Pugh MT Gardner-Medwin JM Southwood TR 《Arthritis research & therapy》2003,5(5):R277-R284
The aim of this research was to determine whether all memory T cells have the same propensity to migrate to the joint in patients
with juvenile idiopathic arthritis. Paired synovial fluid and peripheral blood mononuclear cell proliferative responses to
a panel of antigens were measured and the results correlated with a detailed set of laboratory and clinical data from 39 patients
with juvenile idiopathic arthritis. Two distinct patterns of proliferative response were found in the majority of patients:
a diverse pattern, in which synovial fluid responses were greater than peripheral blood responses for all antigens tested;
and a restricted pattern, in which peripheral blood responses to some antigens were more vigorous than those in the synovial
fluid compartment. The diverse pattern was generally found in patients with a high acute phase response, whereas patients
without elevated acute phase proteins were more likely to demonstrate a restricted pattern. We propose that an association
between the synovial fluid T cell repertoire and the acute phase response suggests that proinflammatory cytokines may influence
recruitment of memory T cells to an inflammatory site, independent of their antigen specificity. Additionally, increased responses
to enteric bacteria and the presence of αEβ7 T cells in synovial fluid may reflect accumulation of gut associated T cells
in the synovial compartment, even in the absence of an elevated acute phase response. This is the first report of an association
between the acute phase response and the T cell population recruited to an inflammatory site. 相似文献
10.
Rates and patterns of evolution in partial sequences of five mitochondrial
genes (cytochrome b, ATPase 6, NADH dehydrogenase subunit 5, tRNA(Glu), and
the control region) were compared among taxa in the passerine bird genera
Fringilla and Carduelis. Rates of divergence do not vary significantly
among genes, even in comparisons with the control region. Rate variation
among lineages is significant only for the control region and NADH
dehydrogenase subunit 5, and patterns of variation are consistent with the
expectations of neutral theory. Base composition is biased in all genes but
is stationary among lineages, and there is evidence for directional
mutation pressure only in the control region. Despite these similarities,
patterns of substitution differ among genes, consistent with alternative
regimes of selective constraint. Rates of nonsynonymous substitution are
higher in NADH dehydrogenase subunit 5 than in other protein-coding genes,
and transitions exist in elevated proportions relative to transversions.
Transitions appear to accumulate linearly with time in tRNA(Glu), and
despite exhibiting the highest overall rate of divergence among species,
there are no transversional changes in this gene. Finally, for resolving
phylogenetic relationships among Fringilla taxa, the combined
protein-coding data are broadly similar to those of the control region in
terms of phylogenetic informativeness and statistical support.
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