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排序方式: 共有389条查询结果,搜索用时 46 毫秒
111.
Margaret M. Hanes Susan Shell Tahsina Shimu Clarissa Crist Salima MachkourMRabet 《Ecology and evolution》2022,12(2)
The spiny thicket of southwestern Madagascar represents an extreme and ancient landscape with extraordinary levels of biodiversity and endemism. Few hypotheses exist for explaining speciation in the region and few plant studies have explored hypotheses for species diversification. Here, we investigate three species in the endemic genus Megistostegium (Malvaceae) to evaluate phylogeographic structure and explore the roles of climate, soil, and paleoclimate oscillations on population divergence and speciation throughout the region. We combine phylogenetic and phylogeographic inference of RADseq data with ecological niche modeling across space and time. Population structure is concurrent with major rivers in the region and we identify a new, potentially important biogeographic break coincident with several landscape features. Our data further suggests that niches occupied by species and populations differ substantially across their distribution. Paleodistribution modeling provide evidence that past climatic change could be responsible for the current distribution, population structure, and maintenance of species in Megistostegium. 相似文献
112.
Carmen Segura Manuela Alonso Cristóbal Fraga Tomás García-Caballero Carlos Diéguez Román Pérez-Fernández 《Histochemistry and cell biology》1999,112(2):163-167
Vitamin D through its receptor (VDR) plays a major role in bone mineral metabolism. However, VDR is also present in a variety
of cell lines as well as in numerous tissues, suggesting other functions of the hormone beyond bone metabolism and mineral
homeostasis. At the liver level, it has been shown that vitamin D induces numerous changes (i.e. enzyme activity level, stimulation
of some metabolic pathways and stimulation of the normal liver recovery after partial hepatectomy). However, some works did
not find VDR in the liver, and also used liver tissue as a negative control of VDR gene expression. In this paper, we examined
fetal, neonatal and adult rat tissues for the presence of VDR using a sensitive RT-PCR technique and immunohistochemistry.
We found VDR mRNA and VDR protein in rat liver at all different periods of rat life. Thus, we suggest that some of the actions
of vitamin D on liver could be mediated at the genomic level through the VDR, and that the use of this tissue as a negative
control of VDR gene expression is clearly inappropriate.
Accepted: 7 June 1999 相似文献
113.
114.
Tanya Marchant Ritgak Dimka Tilley-Gyado Tsegahun Tessema Kultar Singh Meenakshi Gautham Nasir Umar Della Berhanu Simon Cousens Joanna RM Armstrong Schellenberg 《PloS one》2015,10(5)
BackgroundFamilies in high mortality settings need regular contact with high quality services, but existing population-based measurements of contacts do not reflect quality. To address this, in 2012, we designed linked household and frontline worker surveys for Gombe State, Nigeria, Ethiopia, and Uttar Pradesh, India. Using reported frequency and content of contacts, we present a method for estimating the population level coverage of high quality contacts.ConclusionsMeasuring content of care to reflect the quality of contacts can reveal missed opportunities to deliver best possible health care. 相似文献
115.
Obar JJ Crist SG Gondek DC Usherwood EJ 《Journal of immunology (Baltimore, Md. : 1950)》2004,172(2):1213-1219
Gammaherpesviruses can persist in the host in the face of an aggressive immune response. T cells recognize Ags expressed in both the productive and latent phases of the virus life cycle, however little is known about their relative roles in the long-term control of the infection. In this study we used the murine gammaherpesvirus 68 model system to investigate the relative properties of CD8 T cells recognizing lytic and latent viral Ags. We report that the CD8 T cell response to lytic phase epitopes is maximal in the lungs of infected mice at approximately 10 days postinfection, and is of progressively lesser magnitude in the mediastinal lymph nodes and spleen. In contrast, the CD8 T cell response to the latent M2 protein is maximal at approximately 19 days postinfection and is most prominent in the spleen, then progressively less in the mediastinal lymph node and the lung. Latent and lytic Ag-specific CD8 T cells had markedly different cell surface phenotypes during chronic infection, with latent Ag-specific cells being predominantly CD62L(high) or CD43 (1B11)(high). Lytic Ag-specific T cells had significantly lower expression of these markers. Importantly, latent but not lytic Ag-specific T cells could kill target cells rapidly in vivo during the chronic infection. These two different sets of CD8 T cells also responded differentially to IL-7, a cytokine involved in T cell homeostasis and the maintenance of T cell memory. These data have important implications for our understanding of immunological control during chronic gammaherpesvirus infections. 相似文献
116.
Gómez AM Company MD Agocs A Uriel C Valverde S López JC 《Carbohydrate research》2005,340(11):1872-1875
2,3:4,6-Di-O-isopropylidene-d-allopyranose can be conveniently prepared from d-glucose via a synthetic sequence, which includes Mitsunobu inversion at O-3, di-O-isopropylidenation of phenyl-1-thio-d-alloside and anomeric deprotection on treatment with NBS/CaCO3. 相似文献
117.
The environmental contaminants methylmercury (MeHg) and mercuric chloride (HgCl2) stimulated the spontaneous release of [3H]noradrenaline ([3H]NA) from hippocampal slices in a time- and concentration-dependent manner. Both MeHg and HgCl2 were similarly potent, with an EC50 of 88.4 microM and 75.9 microM, respectively. The releasing effects of MeHg and HgCl2 increased in the presence of desipramine, showing that the mechanism does not involve reversal of the transmitter transporter, and were completely blocked by reserpine preincubation, indicating a vesicular origin of [3H]NA release. The voltage-gated Na+ channel blocker tetrodotoxin (TTX) did not affect the response to mercury compounds. [3H]NA release elicited by MeHg was partially dependent on extracellular Ca2+, since it decreased significantly in a Ca2+-free EGTA-containing medium whereas HgCl2 induced a release of [3H]NA independent of extracellular Ca2+. Neither Ca2+-channels blockers, cobalt chloride (CoCl2) and (omega-conotoxin-GVIA, nor the Na+/Ca2+-exchanger inhibitor benzamil reduced MeHg-evoked [3H]NA release. Moreover, thapsigargin or caffeine, endoplasmic reticulum Ca2+-depletors, did not modify metal-evoked [3H]NA release, whereas ruthenium red, which inhibits the mitochondrial Ca2+ transport, decreased the effect of both MeHg and HgCl2. All these data indicate that, in hippocampal slices, mercury compounds release [3H]NA from the vesicular pool by a mechanism involving Ca2+ mobilization from mitochondrial stores. 相似文献
118.
Cristóbal-Azkarate J Veà JJ Asensio N Rodríguez-Luna E 《American journal of primatology》2005,67(2):209-222
This research focuses on identifying the principal habitat characteristics that influence the presence and abundance of mantled howlers in forest fragments. We provide information on the demography of several fragmented Alouatta palliata mexicana subpopulations at Los Tuxtlas, Mexico, and relate this to the biogeographical and floristic characteristics of the forest fragments inhabited. The most important habitat characteristics related to the presence and abundance of howlers in the fragments were fragment size and floristic diversity. On the other hand, some evidence suggests that given the conditions under which howlers in our study area live (i.e., small and degraded fragments with high densities), secondary vegetation may be beneficial for the survival of the howlers. Finally, we discuss the possibility that the very low immature-to-female ratio (IFR) in the groups, and the lack of juveniles found in many of the study groups may be due to high mortality rates in immatures. A reduction in food availability because of the high population densities of these groups may be responsible for this process. 相似文献
119.
Coco WM Levinson WE Crist MJ Hektor HJ Darzins A Pienkos PT Squires CH Monticello DJ 《Nature biotechnology》2001,19(4):354-359
We introduce a method of in vitro recombination or "DNA shuffling" to generate libraries of evolved enzymes. The approach relies on the ordering, trimming, and joining of randomly cleaved parental DNA fragments annealed to a transient polynucleotide scaffold. We generated chimeric libraries averaging 14.0 crossovers per gene, a several-fold higher level of recombination than observed for other methods. We also observed an unprecedented four crossovers per gene in regions of 10 or fewer bases of sequence identity. These properties allow generation of chimeras unavailable by other methods. We detected no unshuffled parental clones or duplicated "sibling" chimeras, and relatively few inactive clones. We demonstrated the method by molecular breeding of a monooxygenase for increased rate and extent of biodesulfurization on complex substrates, as well as for 20-fold faster conversion of a nonnatural substrate. This method represents a conceptually distinct and improved alternative to sexual PCR for gene family shuffling. 相似文献
120.
John Bellettiere Jordan A. Carlson Dori Rosenberg Anant Singhania Loki Natarajan Vincent Berardi Andrea Z. LaCroix Dorothy D. Sears Kevin Moran Katie Crist Jacqueline Kerr 《PloS one》2015,10(8)