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91.
Burgess BL Parkinson PF Racke MM Hirsch-Reinshagen V Fan J Wong C Stukas S Theroux L Chan JY Donkin J Wilkinson A Balik D Christie B Poirier J Lütjohann D Demattos RB Wellington CL 《Journal of lipid research》2008,49(6):1254-1267
Cholesterol homeostasis is of emerging therapeutic importance for Alzheimer's disease (AD). Agonists of liver-X-receptors (LXRs) stimulate several genes that regulate cholesterol homeostasis, and synthetic LXR agonists decrease neuropathological and cognitive phenotypes in AD mouse models. The cholesterol transporter ABCG1 is LXR-responsive and highly expressed in brain. In vitro, conflicting reports exist as to whether ABCG1 promotes or impedes Abeta production. To clarify the in vivo roles of ABCG1 in Abeta metabolism and brain cholesterol homeostasis, we assessed neuropathological and cognitive outcome measures in PDAPP mice expressing excess transgenic ABCG1. A 6-fold increase in ABCG1 levels did not alter Abeta, amyloid, apolipoprotein E levels, cholesterol efflux, or cognitive performance in PDAPP mice. Furthermore, endogenous murine Abeta levels were unchanged in both ABCG1-overexpressing or ABCG1-deficient mice. These data argue against a direct role for ABCG1 in AD. However, excess ABCG1 is associated with decreased levels of sterol precursors and increased levels of SREBP-2 and HMG-CoA-reductase mRNA, whereas deficiency of ABCG1 leads to the opposite effects. Although functions for ABCG1 in cholesterol efflux and Abeta metabolism have been proposed based on results with cellular model systems, the in vivo role of this enigmatic transporter may be largely one of regulating the sterol biosynthetic pathway. 相似文献
92.
93.
Paola Bressan 《Acta ethologica》2002,4(2):113-118
It has been suggested that in a socially monogamous system where fathers invest in their mate's offspring but paternity is
far from certain, it will be adaptive on the part of infants to conceal their father's identity; but the opposite claim has
also been made that this is against the genetic interests of the fathers, and a high frequency of adulterine births will select
instead for paternal resemblance. In this article, I present a simple theoretical model that suggests that neonatal anonymity
benefits fathers, mothers, and children. Once anonymity becomes established, however, all babies start paying the cost of
paternity uncertainty, that is, the reduction in paternal care due to fathers not knowing whether they have truly sired their
mate's offspring. By diminishing the fitness of babies, such a cost bounces back as lowered fitness for parents as well. We
should then expect the evolution of maternal strategies directed to decrease paternity uncertainty, in the form of instinctive
and unsolicited comments on babies' resemblance to their putative fathers. In contradiction to the widespread belief that
it would be in fathers' interest to be skeptical of these allegations, the model suggests that, under conditions of infant
anonymity, fathers will actually promote their own fitness by believing their spouses.
Received in revised form: 5 September 2001
Electronic Publication 相似文献
94.
Reversal of digestive interactions between Pacific reef corals: Mediation by sweeper tentacles 总被引:2,自引:0,他引:2
Gerard M. Wellington 《Oecologia》1980,47(3):340-343
Summary Aggressive interactions among reef corals involving direct interference through extracoelenteric digestion has previously been considered as a potential mechanism for the maintenance of high species diversity. In this report I show that induced development of sweeper tentacles can reverse initial digestive interactions. In the eastern Pacific these reversals contribute to resource monopolization by fast growing pocilloporid corals. This suggests that other mechanisms must account for the maintenance of local species diversity. 相似文献
95.
Optical density, viscosity, and light scattering measurements for calf thymus DNA in water–N,N dimethyl formamide (DMF) solutions are presented. DMF content varied between 0 and 60% (v/v) and DNA molecular weight varied between 15 × 106 and 0.5 × 106. Complementary measurements of the solubility of adenine, thymine, guanine, and cytosine in H2O–DMF mixtures are presented. The denaturation temperature of DNA, manifested by about a 35% increase of optical density, is gradually depressed by increasing DMF content. However, a significant increase of OD occurs even before (and even after) the denaturation point, when DMF content is increased isothermally. The intrinsic viscosity also exhibits a large decrease when DMF content is increased both before and after the denaturation point. Light scattering data for high-molecular-weight DNA in the predenaturation range indicate a decrease of the mean-square radius and a constant molecular weight on increasing DMF content. The results, interpreted in terms of the wormlike chain of Kratky and Porod, indicate a large decrease of the persistence length of DNA. For low-molecular-weight DNA, radius and molecular weight increase with DMF content, indicating intermolecular aggregation. The formation of compact structures of native DNA is discussed in terms of an increased solubility of uncharged bases, and a decreased solubility of phosphate and deoxyribose groups, when a less polar environment is provided by the addition of DMF. 相似文献
96.
97.
Fausto Almeida Aline Sardinha-Silva Thiago Aparecido da Silva André Moreira Pessoni Camila Figueiredo Pinzan Ana Claudia Paiva Alegre-Maller Nerry Tatiana Cecílio Nilmar Silvio Moretti André Ricardo Lima Damásio Wellington Ramos Pedersoli José Roberto Mineo Roberto Nascimento Silva Maria Cristina Roque-Barreira 《PloS one》2015,10(12)
Toxoplasma gondii is an obligate intracellular protozoan parasite found worldwide that is able to chronically infect almost all vertebrate species, especially birds and mammalians. Chitinases are essential to various biological processes, and some pathogens rely on chitinases for successful parasitization. Here, we purified and characterized a chitinase from T. gondii. The enzyme, provisionally named Tg_chitinase, has a molecular mass of 13.7 kDa and exhibits a Km of 0.34 mM and a Vmax of 2.64. The optimal environmental conditions for enzymatic function were at pH 4.0 and 50°C. Tg_chitinase was immunolocalized in the cytoplasm of highly virulent T. gondii RH strain tachyzoites, mainly at the apical extremity. Tg_chitinase induced macrophage activation as manifested by the production of high levels of pro-inflammatory cytokines, a pathogenic hallmark of T. gondii infection. In conclusion, to our knowledge, we describe for the first time a chitinase of T. gondii tachyzoites and provide evidence that this enzyme might influence the pathogenesis of T. gondii infection. 相似文献
98.
P.E. Turpin K.A. Maycroft C.L. Rowlands E.M.H. Wellington 《Journal of applied microbiology》1993,74(2):181-190
A method that uses a cation-exchange resin (Chelex 100) and differential centrifugation for the extraction and detection of salmonellas in soil was developed. The extraction efficiencies of a range of materials were examined and Chelex plus polyethylene glycol was identified as the best combination. Shake speeds, shake times and differential centrifugation speeds were selected to give an optimum salmonella recovery. The Chelex method accurately enumerated 1 cell per 10 g of nonsterile soil within 24 h. Addition of glycerol to soil samples enabled storage at — 70°C for 85 d without significant decreases in salmonella numbers. The Oxoid Salmonella Rapid Test (SRT) could be used to pre-screen large numbers of soil samples for the presence of salmonellas, prior to analysis by the Chelex method. The SRT method detected Salmonella typhimurium at levels as low as 2·5 cells per 10 g of nonsterile soil. 相似文献
99.
Kevin W. Wellington Steven A. Benner 《Nucleosides, nucleotides & nucleic acids》2013,32(12):1309-1333
In this article, we focus on the synthesis of aryl C-glycosides via Heck coupling. It is organized based on the type of structures used in the assembly of the C-glycosides (also called C-nucleosides) with the following subsections: pyrimidine C-nucleosides, purine C-nucleosides, and monocyclic, bicyclic, and tetracyclic C-nucleosides. The reagents and conditions used for conducting the Heck coupling reactions are discussed. The subsequent conversion of the Heck products to the corresponding target molecules and the application of the target molecules are also described. 相似文献
100.