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71.
The vascular system is unique in that extensive branching morphogenesis may take place in the adult. Developmental neovascularization is guided by precise spatial cues but vessel formation in the adult is not genetically programmed. Here, we review different adult modes for branch patterning, acquiring artery or vein identity and allocating vascular progenitor cells. The endothelium shows a remarkable degree of self-organization into a treelike network and hemodynamic forces are important in rectifying abnormal branching. This discussion is in the context of a contemplated therapy for improving organ perfusion by creating new vascular loops properly integrated within the existing network. 相似文献
72.
Regulatory T cells control autoimmunity in vivo by inducing apoptotic depletion of activated pathogenic lymphocytes 总被引:7,自引:0,他引:7
Madakamutil LT Maricic I Sercarz E Kumar V 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(6):2985-2992
Clinical autoimmunity requires both activation of self-reactive T cells as well as a failure of peripheral tolerance mechanisms. We previously identified one such mechanism that involves regulatory T cells recognizing TCR V beta 8.2 chain-derived peptides in the context of MHC. How this regulation affects the fate of target V beta 8.2(+) T lymphocytes in vivo that mediate experimental autoimmune encephalomyelitis has remained unknown. The present study using immunoscope and CFSE-labeling analysis demonstrates that the expansion of regulatory CD4 and CD8 T cells in vivo results in apoptotic depletion of the dominant, myelin basic protein-reactive V beta 8.2(+) T cells, but not subdominant V beta 13(+) T cells. The elimination of only activated T cells by this negative feedback mechanism preserves the remainder of the naive V beta 8.2(+) T cell repertoire and at the same time results in protection from disease. These studies are the first in clearly elucidating the fate of myelin basic protein-specific encephalitogenic T cells in vivo following regulation. 相似文献
73.
Utzinger J Müller I Vounatsou P Singer BH N'Goran EK Tanner M 《The Journal of parasitology》2003,89(4):686-692
Schistosomes and soil-transmitted helminths currently infect a third of the world's human population. An important feature of these parasitic infections is their focal distribution, which has significant implications for control. Only a few studies have been carried out at the microepidemiological scale, comparing infection levels among individuals or households within a single village. In this study, data are presented from a cross-sectional survey, examining all children attending a primary school in rural C?te d'Ivoire over several consecutive days for Schistosoma mansoni, soil-transmitted helminths, and intestinal protozoa. All houses in the main village were mapped, and school children were linked to these households for small-area spatial analyses. Comparison between the 260 school children who live within the main village and the 89 children who reside in nearby settlements revealed significant differences in the overall prevalence and intensity of infections with S. mansoni and hookworm, confirming the focal nature of these 2 parasites. On the other hand, S. mansoni and hookworm infections exhibited random spatial patterns within the main village. The validity of these results is discussed in the context of this epidemiological setting, drawing attention to the issue of scale. Our findings have direct implications for intervention because they call for a uniform, community-wide approach to control schistosomiasis and soil-transmitted helminthiasis. Implementation can be relatively straightforward, and the proposed control approach might be cost-effective and prove sustainable. 相似文献
74.
Chamoun D Choi D Tavares AB Udoff LC Levitas E Resnick CE Rosenfeld RG Adashi EY 《Biology of reproduction》2002,67(3):1003-1012
75.
The amino acid l-alpha-alanine has attracted considerable interest for use in radiation dosimetry and has been formally accepted as a secondary standard for high-dose and transfer dosimetry. Recent results have shown that the alanine EPR spectrum consists of contributions from three different radicals. A set of benchmark spectra describing the essential spectral features of these three radical components was used for reconstructions of the experimental spectra. In the present work, these basis spectra have been used to investigate the differential effects of variations in radiation doses and microwave power, as well as the dependence upon temperature annealing and UV illumination. The results presented here, based solely on relatively low-energy (60-80 keV) X rays, indicate that the three components behave very similarly with respect to radiation dose at room temperature. However, with respect to the thermal annealing/fading behavior and microwave power saturation properties, the three species behave significantly differently. It is concluded that even if it is now realized that three different radicals contribute to the composite EPR alanine spectrum, this has a minor impact on the established protocols for present-day applications (high-dose) of EPR/alanine dosimetry. However, some care should be exercised when e.g. constructing calibration curves, since fading and power saturation behavior may vary over the dose range in question. New results from UV-illumination experiments suggest a possible procedure for experimental spectral separation of the EPR signals due to the three radicals. 相似文献
76.
Radical formation and hole transfer were investigated in crystals of cytosine.HCl (C.HCl) doped with 0-1.1 mol-% 5-methylcytosine x HCl (5MC x HCl). The doping level was determined by NMR spectroscopy. Crystals and polycrystalline samples were X-irradiated at 295 K, 77 K and 12 K and studied with EPR, ENDOR and FSE spectroscopy at these temperatures. At 295 K the dominant radicals were the so-called 3alphaH radical, formed in 5MC by a net H-abstraction from the methyl group, and the cytosine C6 H-addition (5-yl) radical. At 12 K five radicals were identified. These were the 3alphaH radical, cytosine reduction and oxidation products, and the cytosine C6 and C5 H-addition (5-yl and 6-yl, respectively) radicals. The spectroscopic parameters for the 3alphaH radical are very similar to those of a radical observed previously in the crystalline cytosine derivatives cytidine (CR), 2'deoxycytidine hydrochloride (CdR x HCl), 5'dCMP and 3'CMP as well as in the uracil derivative 2-thiouracil (2-TU). It was shown that amounts of the order of tenths of a percent 5MC x HCl doped into crystals of C.HCl give rise to a considerable yield of 3alphaH radicals after exposure to ionizing radiation both at room temperature and at lower temperatures. This supports a previous suggestion that naturally occurring 5-methylated cytosine impurities may be responsible for the formation of 3alphaH radicals in the crystalline cytosine derivatives CR, CdR.HCl, 5'dCMP and 3'CMP and suggests that the 3alphaH radical in these systems is a 5-methylated base-centered radical. The total radical yield in doped C x HCl crystals increased considerably with the doping level, both at low temperatures and at room temperature, implying that the 3alphaH radical is more stable than the primary cytosine radicals. The relative amounts of the 3alphaH radical were obtained by using simulated benchmark spectra to reconstruct experimental EPR spectra of doped polycrystalline samples. Evidence is presented suggesting that the enhanced yield of the 3alphaH radical in doped samples is due to holes originally formed at cytosine bases and transferred to 5-methylcytosine bases in addition to the 3alphaH radical being less exposed to recombination than other cytosine radicals. 相似文献
77.
When we reach out for an object with our hand, we transform visual information about the object's position into muscle contractions that will bring our digits to that position. If we reach out with a tool the transformation is different, because the muscle contractions must bring the critical part of the tool to the object, rather than the digits. The difference between the motion of the hand and that of the tool can be quite large, as when moving a computer mouse across a table to bring a cursor to a position on a screen. We examined the responses to unpredictable visual perturbations during such movements. People responded about as quickly to changes in the position of the target when pointing with the mouse as when doing so with their hand. They also responded about as quickly when the cursor was displaced as when the target was displaced. We show that this is not because the visually perceived separation between target and cursor is transformed into a desired displacement of the hand. Our conclusion is that our actions are controlled by the judged positions of the end-effector and the target, even when the former is quite detached from the muscles and joints that are involved in the action. 相似文献
78.
Jaroslav Červinka Martin Šálek Eliška Padyšáková Petr Šmilauer 《Journal for Nature Conservation》2013,21(2):105-113
Corridors are thought to reduce the negative biological effects of habitat loss and fragmentation by providing connectivity and suitable habitat for many species, including carnivores. Although corridor structure maintenance is considered to be an essential tool for carnivore conservation in a human-dominated landscape, surprisingly little is known about the effects of different factors at various spatial scales. The main aim of this study was to determine how local and landscape-scale habitat characteristics and prey availability influence the corridor use by carnivores in a Central European agricultural landscape. Moreover we investigated carnivore corridor occurrence in two contrasting landscapes that differ in level of habitat loss and fragmentation to evaluate relative effect of species-specific response to regional context. Results show that the availability of principal prey (small mammals) was the most crucial factor affecting carnivore corridor use. Other important factors influencing corridor use were corridor width (positive), proportion of shrubs (positive) and presence of local, low-traffic, roads (positive). Single species models revealed interspecific and area-specific differences in carnivore preference at both spatial scales. Our findings confirm the general importance of multi-level approach to evaluating species-specific habitat requirements as a crucial tool for determining suitable methods for carnivore efficient conservation in human-dominated agricultural landscape. 相似文献
79.
Ben J. Evans Timothy F. Carter Eli Greenbaum Václav Gvo?dík Darcy B. Kelley Patrick J. McLaughlin Olivier S. G. Pauwels Daniel M. Portik Edward L. Stanley Richard C. Tinsley Martha L. Tobias David C. Blackburn 《PloS one》2015,10(12)
African clawed frogs, genus Xenopus, are extraordinary among vertebrates in the diversity of their polyploid species and the high number of independent polyploidization events that occurred during their diversification. Here we update current understanding of the evolutionary history of this group and describe six new species from west and central sub-Saharan Africa, including four tetraploids and two dodecaploids. We provide information on molecular variation, morphology, karyotypes, vocalizations, and estimated geographic ranges, which support the distinctiveness of these new species. We resurrect Xenopus calcaratus from synonymy of Xenopus tropicalis and refer populations from Bioko Island and coastal Cameroon (near Mt. Cameroon) to this species. To facilitate comparisons to the new species, we also provide comments on the type specimens, morphology, and distributions of X. epitropicalis, X. tropicalis, and X. fraseri. This includes significantly restricted application of the names X. fraseri and X. epitropicalis, the first of which we argue is known definitively only from type specimens and possibly one other specimen. Inferring the evolutionary histories of these new species allows refinement of species groups within Xenopus and leads to our recognition of two subgenera (Xenopus and Silurana) and three species groups within the subgenus Xenopus (amieti, laevis, and muelleri species groups). 相似文献
80.
Eric Dumonteil Henry Pronovost Eli F. Bierman Anna Sanford Alicia Majeau Ryan Moore Claudia Herrera 《Molecular ecology》2020,29(19):3747-3761
Integrating how biodiversity and infectious disease dynamics are linked at multiple levels and scales is highly challenging. Chagas disease is a vector‐borne disease, with specificities of the triatomine vectors and Trypanosoma cruzi parasite life histories resulting in a complex multihost and multistrain life cycle. Here, we tested the hypothesis that T. cruzi transmission cycles are shaped by triatomine host communities and gut microbiota composition by comparing the integrated interactions of Triatoma sanguisuga in southern Louisiana with feeding hosts, T. cruzi parasite and bacterial microbiota in two habitats. Bugs were collected from resident's houses and animal shelters and analysed for genetic structure, blood feeding sources, T. cruzi parasites, and bacterial diversity by PCR amplification of specific DNA markers followed by next‐generation sequencing, in an integrative metabarcoding approach. T. sanguisuga feeding host communities appeared opportunistic and defined by host abundance in each habitat, yielding distinct parasite transmission networks among hosts. The circulation of a large diversity of T. cruzi DTUs was also detected, with TcII and TcV detected for the first time in triatomines in the US. The bacterial microbiota was highly diverse and varied significantly according to the DTU infecting the bugs, indicating specific interactions among them in the gut. Expanding such studies to multiple habitats and additional triatomine species would be key to further refine our understanding of the complex life cycles of multihost, multistrain parasites such as T. cruzi, and may lead to improved disease control strategies. 相似文献