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1.
2.
The distribution of amiloride-sensitive sodium channels (ASSCs) in taste
buds isolated from the oral cavity of hamsters was assessed by patch clamp
recording. In contrast to the case for rats, taste cells from the
fungiform, foliate and vallate papillae and from the soft palate all
contain functional ASSCs. The differential distribution of ASSCs between
the hamster and the rat may be important for understanding the physiology
underlying the differing behavioral responses of these species to sodium
salts.
相似文献
3.
Fossil plants from the lower part of Xianshuihe Formation in the Lanzhou Basin, Gansu
Province were studied. The flora contains 29 species, representing 20 genera and 12 families, which
include Lauraceae ( Daphnogene ), Lardizabalaceae ( Akebia ), Berberidaceae ( Berberis ), Ulmaceae
( Planera, Ulmus, Zelkova ), Betulaceae ( Alnus, Carpinus ), Myricaceae( Myrica ), Salicaceae
( Populus, Salix), Myrsinaceae(Ardisia), Rosaceae ( Prunus, Sorbus, Sorbaria, Spiraea ), Leguminosae ( Gleditsia, Sophora), Anacardiaceae (Rhus), Caprifoliaceae(Viburnum). An analysis
of the floristic elements and their foliar physiognomy shows that most members of the flora are deciduous broad-leaved trees or shrubs with a few evergreen shrubs. The most noteworthy species is Rhus
turcomanica which was present in the Middle Eocene to Late Eocene of Central Asia (Kazakhstan,
Turkmenistan). Generally, Rhus turcomanica occurred at the same beds as Palibinia, an extinct
fossil plant whose presence indicates a subtropical dry climate. Another species, Sorbaria callicomifolia Kornilova was present from the Early Oligocene to Early Miocene of Central Asia (Kazakhstan
and Turkmenistan). According to an analysis of spores and pollen, this flora contains over 20 species. It is predominated by the angiosperm pollen. There appeared Ephedripites and Nitrariadites
which were important elements in the dry area. Ephedripites was found from the Upper Cretaceous to
Early Tertiary. Nitrariadites occurred in the Late Miocene, whereas Rhus turcomanica and Sorbaria
callicomifolia were both reported in the subtropical dry area from the Middle Eocene to Early Oligocene. The latest record of Rhus turcomanica is from the Middle Eocene to Early Oligocene of Central
Asia. The presence of this element in the lower part of Xianshuihe Formation may indicate that itsage is the latest stage of the Early Oligocene. 相似文献
4.
对κ-卡拉胶进行酸降解得到三种卡拉胶低聚糖,并进一步琥珀酰基化得到分子量分别为2720、4000和5960的κ-卡拉胶琥珀酰衍生物(A、B和C)。对产物进行FT-IR表征,并测得其琥珀酰基取代度(DS)分别为0.61、0.29和0.83。检测了三种κ-卡拉胶琥珀酰衍生物对超氧阴离子自由基O2.-、DPPH自由基、羟基自由基.OH以及过氧化氢的清除活性。结果表明:随着取代度的增加,其清除超氧阴离子自由基O2.-和DPPH自由基的能力增强;随着分子量的增加,其清除羟基自由基.OH和过氧化氢的能力增强。这可能与衍生物的羟基含量、取代基团的性质以及取代度等因素有关。 相似文献
5.
Replication fidelity is not constant among strains within a species or at all genetic loci within a genome. Altered fidelity of replication may affect patterns of pathogenesis and the evolution of these strains. We have been studying replication fidelity in Escherichia coli, both in laboratory attenuated strains and in food-borne pathogens. To understand the altered patterns of mutagenesis at the molecular level, we used a shuttle vector plasmid with a tRNA mutational marker gene which had been altered to include homopolymeric runs of five, seven and nine [G:C] pairs, as well as non-repetitive DNA. Replication of the plasmid in mutS strains resulted in a 20-fold increase in mutant progeny plasmids. The mutations were almost all (>90%) frameshift mutations, while base substitution mutations were rare. Most mutations were insertions or deletions of one or two [G:C] pairs in the longest homopolymeric runs. Larger deletions (5 to >70bp), also targeted to the repetitive sequence, were likewise common. Mutations increased exponentially with the length of the homopolymeric run. These patterns of mutation, including unexpectedly high levels in repair proficient strains, led to an examination of the E. coli K-12 genome for homopolymeric DNA. This sequence motif was found to be rare, particularly in genes and open reading frames. Amino acid homotrimers were found to avoid usage of homopolymeric codons, even when they are preferred among synonymous codons in E. coli. There appears to be active selection against tandem direct nucleotide repeats in the E. coli genome, correlated with the inability of the organism to accurately replicate such sequence. 相似文献
6.
Particular serovars of Salmonella enterica have emerged as significant foodborne pathogens in humans. At the chromosomal level, discrete regions in the Salmonella genome have been identified that are known to play important roles in the maintenance, survival, and virulence of S. enterica within the host. Interestingly, several of these loci appear to have been acquired by horizontal transfer of DNA among and between bacterial species. The profound importance of recombination in pathogen emergence is just now being realized, perhaps explaining the sudden interest in developing novel and facile ways for detecting putative horizontal transfer events in bacteria. The incongruence length difference (ILD) test offers one such means. ILD uses phylogeny to trace sequences that may have been acquired promiscuously by exchange of DNA during chromosome evolution. We show here that the ILD test readily detects recombinations that have taken place in several housekeeping genes in Salmonella as well as genes composing the type 1 pilin complex (14 min) and the inv-spa invasion gene complex (63 min). Moreover, the ILD test indicated that the mutS gene (64 min), whose product helps protect the bacterial genome from invasion by foreign DNA, appears to have undergone intragenic recombination within S. enterica subspecies I. ILD findings were supported using additional tests known to be independent of the ILD approach (e.g., split decomposition analysis and compatibility of sites). Taken together, these data affirm the application of the ILD test as one approach for identifying recombined sequences in the Salmonella chromosome. Furthermore, horizontally acquired sequences within mutS support a model whereby evolutionarily important recombinants of S. enterica are rescued from strains carrying defective mutS alleles via horizontal transfer. 相似文献
7.
8.
Salivary gland duct ligation is an alternative to gland excision for treating sialorrhea or reducing salivary gland size prior to tumor excision. Duct ligation also is used as an approach to study salivary gland aging, regeneration, radiotherapy, sialolithiasis and sialadenitis. Reports conflict about the contribution of each salivary cell population to gland size reduction after ductal ligation. Certain cell populations, especially acini, reportedly undergo atrophy, apoptosis and proliferation during reduction of gland size. Acini also have been reported to de-differentiate into ducts. These contradictory results have been attributed to different animal or salivary gland models, or to methods of ligation. We report here a bilateral double ligature technique for rabbit parotid glands with histologic observations at 1, 7, 14, 30, 60 days after ligation. A large battery of special stains and immunohistochemical procedures was employed to define the cell populations. Four stages with overlapping features were observed that led to progressive shutdown of gland activities: 1) marked atrophy of the acinar cells occurred by 14 days, 2) response to and removal of the secretory material trapped in the acinar and ductal lumens mainly between 30 and 60 days, 3) reduction in the number of parenchymal (mostly acinar) cells by apoptosis that occurred mainly between 14–30 days, and 4) maintenance of steady-state at 60 days with a low rate of fluid, protein, and glycoprotein secretion, which greatly decreased the number of leukocytes engaged in the removal of the luminal contents. The main post- ligation characteristics were dilation of ductal and acinar lumens, massive transient infiltration of mostly heterophils (rabbit polymorphonuclear leukocytes), acinar atrophy, and apoptosis of both acinar and ductal cells. Proliferation was uncommon except in the larger ducts. By 30 days, the distribution of myoepithelial cells had spread from exclusively investing the intercalated ducts pre-ligation to surrounding a majority of the residual duct-like structures, many of which clearly were atrophic acini. Thus, both atrophy and apoptosis made major contributions to the post-ligation reduction in gland size. Structures also occurred with both ductal and acinar markers that suggested acini differentiating into ducts. Overall, the reaction to duct ligation proceeded at a considerably slower pace in the rabbit parotid glands than has been reported for the salivary glands of the rat. 相似文献
9.
Phylogenetic evidence for horizontal transfer of mutS alleles among naturally occurring Escherichia coli strains 下载免费PDF全文
mutS mutators accelerate the bacterial mutation rate 100- to 1,000-fold and relax the barriers that normally restrict homeologous recombination. These mutators thus afford the opportunity for horizontal exchange of DNA between disparate strains. While much is known regarding the mutS phenotype, the evolutionary structure of the mutS(+) gene in Escherichia coli remains unclear. The physical proximity of mutS to an adjacent polymorphic region of the chromosome suggests that this gene itself may be subject to horizontal transfer and recombination events. To test this notion, a phylogenetic approach was employed that compared gene phylogeny to strain phylogeny, making it possible to identify E. coli strains in which mutS alleles have recombined. Comparison of mutS phylogeny against predicted E. coli "whole-chromosome" phylogenies (derived from multilocus enzyme electrophoresis and mdh sequences) revealed striking levels of phylogenetic discordance among mutS alleles and their respective strains. We interpret these incongruences as signatures of horizontal exchange among mutS alleles. Examination of additional sites surrounding mutS also revealed incongruous distributions compared to E. coli strain phylogeny. This suggests that other regional sequences are equally subject to horizontal transfer, supporting the hypothesis that the 61.5-min mutS-rpoS region is a recombinational hot spot within the E. coli chromosome. Furthermore, these data are consistent with a mechanism for stabilizing adaptive changes promoted by mutS mutators through rescue of defective mutS alleles with wild-type sequences. 相似文献
10.
Shin-Ru Shih Tzu-Yun Chu Gadarla Randheer Reddy Sung-Nain Tseng Hsiun-Ling Chen Wen-Fang Tang Ming-sian Wu Jiann-Yih Yeh Yu-Sheng Chao John TA Hsu Hsing-Pang Hsieh Jim-Tong Horng 《Journal of biomedical science》2010,17(1):13