排序方式: 共有34条查询结果,搜索用时 15 毫秒
1.
The molecular evolution of mammalian Y-linked DNA sequences is of special
interest because of their unique mode of inheritance: most Y- linked
sequences are clonally inherited from father to son. Here we investigate
the use of Y-linked sequences for phylogenetic inference. We describe a
comparative analysis of a 515-bp region from the male sex- determining
locus, Sry, in 22 murine rodents (subfamily Murinae, family Muridae),
including representatives from nine species of Mus, and from two additional
murine genera--Mastomys and Hylomyscus. Percent sequence divergence was
< 0.01% for comparisons between populations within a species and was
0.19%-8.16% for comparisons between species. Our phylogenetic analysis of
12 murine taxa resulted in a single most- parsimonius tree that is highly
concordant with phylogenies based on mitochondrial DNA and allozymes. A
total evidence tree based on the combined data from Sry, mitochondrial DNA,
and allozymes supports (1) the monophyly of the subgenus Mus, (2) its
division into a Palearctic group (M. musculus, M. domesticus, M.
spicilegus, M. Macedonicus, and M. spretus) and an Oriental group (M.
cookii++, M. cervicolor, and M. caroli), and (3) sister-group relationships
between M. spicilegus and M. macedonicus and between M. cookii and M.
cervicolor. We argue that Y- chromosome DNA sequences represent a valuable
new source of characters for phylogenetic inference.
相似文献
2.
The acrosomic status of spermatozoa prepared for IVF has been evaluated by means of immunofluorescence test from Fenichel and Hsi using calcium A 23187 ionophore as inductor of acrosome reaction (AR). The spontaneous AR remains slight, even after 6 hour-incubation in Menezo B2 (6,8+2,7%). The response to ionophore, moderate before (11,2+9%), frankly increases after a 6h-capacitation (28,9+8,3%) in a group of 25 IVF couples (tubal indication, normal semen, positive fertilization). Nevertheless, it remains slight or null in 4 cases of unexplained repeated failure of fertilization. The response to ionophore A 23187 allows to explore the kinetics of capacitation of spermatozoa and their ability to perform AR. Its significance in terms of fecondance remains to be precised. 相似文献
3.
1. Interspecific competition among ants is common, and so is competitive exclusion among dominant ant species. In contrast, specific associations between non‐parasitic ant species are rare, especially in the temperate zones. As an exception, the subordinate ant Camponotus lateralis frequently co‐occurs with the dominant Crematogaster scutellaris but rarely with other dominant ants. 2. This association is one of various associations between Camponotus and Crematogaster species across the world. However, the mechanisms behind these co‐occurences are largely unknown. 3. In the present study, we therefore investigated the association of Ca. lateralis and Cr. scutellaris. We studied the spatial association of the nests, interspecific aggression, both species' cuticular hydrocarbon profiles, and their propensity to follow the other species' pheromone trails. 4. Crematogaster scutellaris usually attacked and displaced the generally submissive Ca. lateralis, but was significantly less aggressive at jointly used trails. Camponotus nests were always in close proximity to Crematogaster nests. 5. The cuticular hydrocarbons of both species consisted of alkanes with chain lengths between C21 and C35. The two species had 25 hydrocarbons in common, including mono‐, di‐, and tetramethyl alkanes. Despite this qualitative similarity, however, the quantitative hydrocarbon composition differed between the two species. 6. Camponotus lateralis followed artificial trails containing trail pheromones of Cr. scutellaris, but the latter did not follow Ca. lateralis trail pheromones. Interspecific trail‐following by Camponotus, but not vice versa, has been observed in another Camponotus–Crematogaster association and may be a more general mechanism that facilitates associations between the two ant genera. 相似文献
4.
Intrapulmonary TNF gene therapy reverses sepsis-induced suppression of lung antibacterial host defense 总被引:11,自引:0,他引:11
Chen GH Reddy RC Newstead MW Tateda K Kyasapura BL Standiford TJ 《Journal of immunology (Baltimore, Md. : 1950)》2000,165(11):6496-6503
Sepsis syndrome is frequently complicated by the development of nosocomial infections, particularly Gram-negative pneumonia. Although TNF-alpha (TNF) has been shown to mediate many of the pathophysiologic events in sepsis, this cytokine is a critical component of innate immune response within the lung. Therefore, we hypothesized that the transient transgenic expression of TNF within the lung during the postseptic period could augment host immunity against nosocomial pathogens. To test this, mice underwent 26-gauge cecal ligation and puncture (CLP) as a model of abdominal sepsis, followed 24 h later by intratracheal (i.t.) administration of PSEUDOMONAS: aeruginosa. In animals undergoing sham surgery followed by bacterial challenge, PSEUDOMONAS: were nearly completely cleared from the lungs by 24 h. In contrast, mice undergoing CLP were unable to clear P. aeruginosa and rapidly developed bacteremia. Alveolar macrophages (AM) recovered from mice 24 h after CLP produced significantly less TNF ex vivo, as compared with AM from sham animals. Furthermore, the adenoviral mediated transgenic expression of TNF within the lung increased survival in CLP animals challenged with PSEUDOMONAS: from 25% in animals receiving control vector to 91% in animals administered recombinant murine TNF adenoviral vector. Improved survival in recombinant murine TNF adenoviral vector-treated mice was associated with enhanced lung bacterial clearance and proinflammatory cytokine expression, as well as enhanced AM phagocytic activity and cytokine expression when cultured ex vivo. These observations suggest that intrapulmonary immunostimulation with TNF can reverse sepsis-induced impairment in antibacterial host defense. 相似文献
5.
ROBERT R. JUNKER RICHARD BLEIL CURTIS C. DAEHLER NICO BLÜTHGEN 《Ecological Entomology》2010,35(6):760-767
1. Sympatric flower visitor species often partition nectar and pollen and thus affect each other's foraging pattern. Consequently, their pollination service may also be influenced by the presence of other flower visiting species. Ants are solely interested in nectar and frequent flower visitors of some plant species but usually provide no pollination service. Obligate flower visitors such as bees depend on both nectar and pollen and are often more effective pollinators. 2. In Hawaii, we studied the complex interactions between flowers of the endemic tree Metrosideros polymorpha (Myrtaceae) and both, endemic and introduced flower‐visiting insects. The former main‐pollinators of M. polymorpha were birds, which, however, became rare. We evaluated the pollinator effectiveness of endemic and invasive bees and whether it is affected by the type of resource collected and the presence of ants on flowers. 3. Ants were dominant nectar‐consumers that mostly depleted the nectar of visited inflorescences. Accordingly, the visitation frequency, duration, and consequently the pollinator effectiveness of nectar‐foraging honeybees (Apis mellifera) strongly decreased on ant‐visited flowers, whereas pollen‐collecting bees remained largely unaffected by ants. Overall, endemic bees (Hylaeus spp.) were ineffective pollinators. 4. The average net effect of ants on pollination of M. polymorpha was neutral, corresponding to a similar fruit set of ant‐visited and ant‐free inflorescences. 5. Our results suggest that invasive social hymenopterans that often have negative impacts on the Hawaiian flora and fauna may occasionally provide neutral (ants) or even beneficial net effects (honeybees), especially in the absence of native birds. 相似文献
6.
Suresh Mishra Geetika Bassi BL Grgoire Nyomba 《Experimental biology and medicine (Maywood, N.J.)》2021,246(7):749
Posttranslational modification of proteins, which include both the enzymatic alterations of protein side chains and main-chain peptide bond connectivity, is a fundamental regulatory process that is crucial for almost every aspects of cell biology, including the virus-host cell interaction and the SARS-CoV-2 infection. The posttranslational modification of proteins has primarily been studied in cells and tissues in an intra-proteomic context (where both substrates and enzymes are part of the same species). However, the inter-proteomic posttranslational modifications of most of the SARS-CoV-2 proteins by the host enzymes and vice versa are largely unexplored in virus pathogenesis and in the host immune response. It is now known that the structural spike (S) protein of the SARS-CoV-2 undergoes proteolytic priming by the host serine proteases for entry into the host cells, and N- and O-glycosylation by the host cell enzymes during virion packaging, which enable the virus to spread. New evidence suggests that both SARS-CoV-2 and the host proteins undergo inter-proteomic posttranslational modifications, which play roles in virus pathogenesis and infection-induced immune response by hijacking the host cell signaling. The purpose of this minireview is to bring attention of the scientific community to recent cutting-edge discoveries in this understudied area. It is likely that a better insight into the molecular mechanisms involved may open new research directions, and thereby contribute to novel therapeutic modality development against the SARS-CoV-2. Here we briefly discuss the rationale and touch upon some unanswered questions in this context, especially those that require attention from the scientific community. 相似文献
7.
FLORIAN MENZEL MICHAEL STAAB ARTHUR Y. C. CHUNG GERHARD GEBAUER NICO BLÜTHGEN 《Austral ecology》2012,37(5):537-546
Organisms associated with another species may experience both costs and benefits from their partner. One of these costs is competition, which is the more likely if the two species are ecologically similar. Parabioses are associations between two ant species that share a nest and often attend the same food sources. Albeit parabioses are probably mutualistic, parabiotic partners may compete for food. We therefore investigated feeding niches and dietary overlap of two parabiotically associated ants in Borneo using cafeteria experiments and stable isotope analyses. The two species strongly differed in their food choices. While Crematogaster modiglianii mostly foraged at carbohydrate‐rich baits, Camponotus rufifemur preferred urea‐rich sources. Both species also consumed animal protein. The 15N concentration in Ca. rufifemur workers was consistently lower than in Cr. modiglianii. Camponotus rufifemur but not Cr. modiglianii possesses microbial endosymbionts, which can metabolize urea and synthesize essential amino acids. Its lower 15N signature may result from a relatively higher intake of plant‐based or otherwise 15N‐depleted nitrogen. Isotopic signatures of the two partners in the same parabiosis showed strongly parallel variation across nests. As we did not find evidence for spatial autocorrelation, this correlation suggests an overlap of food sources between the two ant species. Based on model simulations, we estimated a diet overlap of 22–66% for nitrogen sources and 45–74% for carbon sources. The overlap may arise from either joint exploitation of the same food sources or trophallactic exchange of food. This suggests an intense trophic interaction and potential for competition between the parabiotic partners. 相似文献
8.
RALF METZNER MICHAEL R. THORPE UWE BREUER PETER BLÜMLER ULRICH SCHURR HEIKE U. SCHNEIDER WALTER H. SCHROEDER 《Plant, cell & environment》2010,33(8):1393-1407
Lateral exchange of water and nutrients between xylem and surrounding tissues helps to de‐couple uptake from utilization in all parts of a plant. We studied the dynamics of these exchanges, using stable isotope tracers for water (H218O), magnesium (26Mg), potassium (41K) and calcium (44Ca) delivered via a cut stem for various periods to the transpiration stream of bean shoots (Phaseolus vulgaris cv. Fardenlosa Shiny). Tracers were subsequently mapped in stem cross‐sections with cryo‐secondary ion mass spectrometry. The water tracer equilibrated within minutes across the entire cross‐section. In contrast, the nutrient tracers showed a very heterogeneous exchange between xylem vessels and the different stem tissues, even after 4 h. Dynamics of nutrients in the tissues revealed a fast and extensive exchange of nutrients in the xylem parenchyma, with, for example, calcium being completely replaced by tracer in less than 5 min. Dilution of potassium tracer during its 30 s transit in xylem sap through the stem showed that potassium concentration was up‐regulated over many hours, to the extent that some of it was probably supplied by phloem recirculation from the shoot. 相似文献
9.
The Pterogeniidae, a family of beetles from Indoaustralia, are revised. They comprise five genera and 24 species. Three genera and 17 species are described as new and one species is synonymized. It is shown that the male and particularly the female genitalia provide useful means for species definition. The phylogenetic relationships are discussed based on a cladistic analysis of 23 morphological characters using PAUP. The analysis resulted in a single cladogram with following grouping: ( Kryptogenius + ( Tychogenius + ( Katagenius + ( Plerogenins + Histanocerus )))). For rooting the cladogram and polarizing the characters, Sivacrypticus indicus (Archeocrypticidae) was used as an outgroup. The majority of the species is restricted to insular tropical Asia and Oceania but four of them extend their range onto the Malayan Peninsula. Another four species are known only from continental Asia, i.e. two species from South India and one each from Malayan Peninsula and Vietnam respectively. Species of Kryptogenius, Pterogenius, Katagenius and Tychogenius are highly endemic and could therefore potentially be useful for analysing areas of endemism. For this, however, the cladistic relationships should be resolved at species level. Species of Histanocerus are more widely distributed but none is found on both sides of Wallace's line. 相似文献
10.