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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
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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
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6.
Cardounel A Regelson W Kalimi M 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1999,222(2):145-149
Dehydroepiandrosterone (DHEA), an adrenal cortex hormone secreted in large quantities in humans, protects cells of the clonal mouse hippocampal cell line HT-22 against the excitatory amino acid glutamate (5 mM), and amyloid beta-protein (2 microM) toxicity in a dose-dependent manner with optimum protection obtained at 5 microM concentration of DHEA. The protective effects of DHEA appear to be specific in that other related steroids and metabolites of DHEA, such as 5-androstene-3beta,17beta-diol, etiocholan-3alpha-ol-17-one, etiocholan-3beta-ol-17-one, testosterone, and 5alpha-androstane-3, 17-dione, offered no protection even at 50 microM concentrations. In addition, using immunocytochemical techniques, we observed that 20 hr of treatment with 5 mM glutamate remarkably increased glucocorticoid receptor (GR) nuclear localization in neuronal cells. Interestingly, 5 microM DHEA treatment for 24 hr, followed by 5 mM glutamate treatment for 20 hr almost completely reversed the copious nuclear localization of GR observed by glutamate treatment alone. Results obtained suggest that DHEA protects hippocampal neurons, at least in part, by its antiglucocorticoid action via decreasing hippocampal cells nuclear GR levels. 相似文献
7.
Nitric oxide (NO) has a critical role in neuronal function; however, high levels lead to cellular injury. While guanidino-methylated arginines (MA) including asymmetric dimethylarginine (ADMA) and N(G)-methyl-l-arginine (NMA) are potent competitive inhibitors of nitric oxide synthase (NOS) and are released upon protein degradation, it is unknown whether their intracellular concentrations are sufficient to critically regulate neuronal NO production and secondary cellular function or injury. Therefore, we determine the intrinsic neuronal MA concentrations and their effects on neuronal NOS function and excitotoxic injury. Kinetic studies demonstrated that the K(m) for l-arginine is 2.38 microm with a V(max) of 0.229 micromol mg(-1) min(-1), while K(i) values of 0.67 microm and 0.50 microm were determined for ADMA and NMA, respectively. Normal neuronal concentrations of all NOS-inhibiting MA were determined to be approximately 15 microm, while l-arginine concentration is approximately 90 microm. These MA levels result in >50% inhibition of NO generation from neuronal NOS. Down-modulation or up-modulation of these neuronal MA levels, respectively, dramatically enhanced or suppressed NO-mediated excitotoxic injury. Thus, neuronal MA profoundly modulate NOS function and suppress NO mediated injury. Pharmacological modulation of the levels of these intrinsic NOS inhibitors offers a novel approach to modulate neuronal function and injury. 相似文献
8.
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
9.
In the present work we have examined whether the neurosteroid pregnenolone has any neuroprotective effects against glutamate and amyloid beta protein neurotoxicity using immortalized clonal mouse hippocampal cell line (HT-22). The neurosteroid pregnenolone protects HT-22 cells against both 5 mM glutamate and 2 M amyloid beta protein induced cell death in a concentration dependent manner. Optimum protection was attained at 500 nM pregnenolone, against both 5 mM glutamate as well as 2 M amyloid beta protein induced HT-22 cell death. Furthermore, using confocal immunoflourescence microscopy we observed that 20 hours of treatment with 5 mM glutamate resulted in intense nuclear localization of the glucocorticoid receptor (GR) in HT-22 cells as compared to control untreated cells. Interestingly, 500 nM pregnenolone treatment for 24 hours, followed by 20 hours treatment with 5 mM glutamate resulted in dramatic reduction in GR nuclear localization. These results show that (i) pregnenolone has neuroprotective effects against both glutamate and amyloid beta protein neuropathology and (ii) prevention of glucocorticoid receptor (GR) localization to the nucleus may be involved in the observed neuroprotective effects of pregnenolone against glutamate neurotoxicity. 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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