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1.
The hypothalamic–pituitary–gonadal axis (HPG) plays vital roles in reproduction and steroid hormone production in both sexes. The focus of this review is upon gene structures, receptor structures and the signaling pathways of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The hormones' functions in reproduction as well as consequences resulting from mutations are also summarized. Specific characteristics of hormones such as the pulsatile secretions of GnRH are also covered. The different regulators of the HPG axis are introduced including kisspeptin, activin, inhibin, follistatin, androgens and estrogen. This review includes not only their basic information, but also their unique function in the HPG axis. Here we view the HPG axis as a whole, so relations between ligands and receptors are well described crossing different levels of the HPG axis. Hormone interactions and transformations are also considered. The major information of this article is depicted in three figures summarizing the current discoveries on the HPG axis. This article systematically introduces the basic knowledge of the HPG axis and provides information of the current advances relating to reproductive hormones. 相似文献
2.
Molecular dynamics (MD) simulations have been undertaken in order to investigate the collective solvent reorganization following
an instantaneous electronic charge transfer between distinct atomic sites of diatomic probe molecules immersed in methanol–water
mixtures. Our previous studies of solvation dynamics in these mixtures [28,29] are extended here to the analysis of nonequilibrium
time-dependent solute–solvent site–site pair distribution functions for the equimolar mixture using two different solute sizes.
This has allowed us to obtain a more detailed picture of the solvent reorganization in response to the solute's excitation.
Special attention is devoted to the dynamics of rupture and formation of hydrogen bonds between the smaller probe solute and
solvent molecules, and its relationship to the molecular mechanisms of solvation dynamics in these systems on distinct time
scales.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Archie C. A. Clements Elisa Bosqué-Oliva Moussa Sacko Aly Landouré Robert Dembélé Mamadou Traoré Godefroy Coulibaly Albis F. Gabrielli Alan Fenwick Simon Brooker 《PLoS neglected tropical diseases》2009,3(5)
Background
We investigated changes in the spatial distribution of schistosomiasis in Mali following a decade of donor-funded control and a further 12 years without control.Methodology/Principal Findings
National pre-intervention cross-sectional schistosomiasis surveys were conducted in Mali in 1984–1989 (in communities) and again in 2004–2006 (in schools). Bayesian geostatistical models were built separately for each time period and on the datasets combined across time periods. In the former, data from one period were used to predict prevalence of schistosome infections for the other period, and in the latter, the models were used to determine whether spatial autocorrelation and covariate effects were consistent across periods. Schistosoma haematobium prevalence was 25.7% in 1984–1989 and 38.3% in 2004–2006; S. mansoni prevalence was 7.4% in 1984–1989 and 6.7% in 2004–2006 (note the models showed no significant difference in mean prevalence of either infection between time periods). Prevalence of both infections showed a focal spatial pattern and negative associations with distance from perennial waterbodies, which was consistent across time periods. Spatial models developed using 1984–1989 data were able to predict the distributions of both schistosome species in 2004–2006 (area under the receiver operating characteristic curve was typically >0.7) and vice versa.Conclusions/Significance
A decade after the apparently successful conclusion of a donor-funded schistosomiasis control programme from 1982–1992, national prevalence of schistosomiasis had rebounded to pre-intervention levels. Clusters of schistosome infections occurred in generally the same areas accross time periods, although the precise locations varied. To achieve long-term control, it is essential to plan for sustainability of ongoing interventions, including stengthening endemic country health systems. 相似文献4.
Shrawan Kumar 《Journal of electromyography and kinesiology》2010,20(6):1146-1154
The objective of this study was to determine the magnitude and phasic relationship of the torso muscles in rotation–flexion of varying degree of asymmetries of the trunk. Nineteen normal young subjects (7 males and 12 females) were stabilized on a posture stabilizing platform and instructed to assume a flexed and right rotated posture. A combination 20°, 40° and 60° of rotation and 20°, 40° and 60° of flexion resulted in nine postures. These postures were assumed in a random order. The subjects were asked to exert their maximal voluntary isometric contraction (MVC) in the plane of rotation of the posture assumed for a period of 5 s. The surface EMG from the external and internal obliques, rectus abdominis, latissimus dorsi and erector spinae at the 10th thoracic and 3rd lumbar vertebral levels was recorded. The abdominal muscles had the least response at 40° of flexion, the dorsal muscles had the highest magnitude.With increasing right rotation, the left external oblique continued to decrease its activity. The ANOVA revealed that rotation and muscles had a significant main effect on normalized peak EMG (p < 0.02) in both genders. There was a significant interaction between rotation and flexion in both genders (p < 0.02) and rotation and muscle in females. The erector spinae activity was highest at 40° flexion, due to greater mechanical disadvantage and having not reached the state of flexion–relaxation. The abdominal muscle activity declined with increasing asymmetry, due to the decreasing initial muscle length. The EMG activity was significantly affected by rotation than flexion (p < 0.02). 相似文献
5.
In experiments on non-anesthetized Wistar white rats there was studied reaction of kidney to an intramuscular injection of arginine vasotocin or arginine vasopressin at doses from 0.001 to 0.05 µg/100 g body mass on the background of a water load. Water (5 ml/100 g body mass) was administered through a catheter into stomach to suppress secretion of endogenous antidiuretic hormone (ADH). In experiments with water administration, diuresis increased due to a decrease of osmotic permeability of renal tubules and to excretion of osmotically free water, with the constant clearance of sodium ions. Injection of 0.05 µg arginine vasopressin led to a marked decrease of diuresis due to a rise of reabsorption of osmotically free water without elevation of excretion of osmotically active substances. Injection of the same dose of arginine vasotocin resulted in no increase of diuresis; however, reabsorption of osmotically free water and excretion of osmotically active substances including sodium ions were more pronounced. Hence, both vasotocin and vasopressin increased osmotic permeability of the tubular epithelium, but vasotocin, unlike vasopressin, promoted reduction of reabsorption of sodium ions and their loss with urine. A suggestion is made that one of the reasons for replacement in mammals of the molecular ADH forms (vasotocin by vasopressin) was the absence of the pronounced natriuretic effect in arginine vasopressin. This was of crucial significance to preserve sodium ions in the organism, to maintain water–salt balance in animals adapted to the terrestrial life, and to provide not only osmo-, but also volumoregulation. 相似文献
6.
This investigation considers the peristaltic flow of a Phan–Thien–Tanner fluid in the presence of slip condition and induced magnetic field. By use of the long wavelength and low Reynolds number approximations, closed form series solutions for stream function, pressure gradient, magnetic force function, axial induced magnetic field, and current density were obtained. The pressure gradient and frictional forces per wavelength were computed by numerical integration. The velocity slip condition in terms of shear stress is taken into account. Graphical results show the comparison between no-slip and viscous fluid cases. Pumping and trapping phenomena are discussed. 相似文献
7.
Hong Zhu Sara Guariglia Raymond Y. L. Yu Wenjing Li Deborah Brancho Hector Peinado David Lyden James Salzer Craig Bennett Chi-Wing Chow 《Molecular biology of the cell》2013,24(11):1619-1637
Charcot–Marie–Tooth (CMT) disease is an inherited neurological disorder. Mutations in the small integral membrane protein of the lysosome/late endosome (SIMPLE) account for the rare autosomal-dominant demyelination in CMT1C patients. Understanding the molecular basis of CMT1C pathogenesis is impeded, in part, by perplexity about the role of SIMPLE, which is expressed in multiple cell types. Here we show that SIMPLE resides within the intraluminal vesicles of multivesicular bodies (MVBs) and inside exosomes, which are nanovesicles secreted extracellularly. Targeting of SIMPLE to exosomes is modulated by positive and negative regulatory motifs. We also find that expression of SIMPLE increases the number of exosomes and secretion of exosome proteins. We engineer a point mutation on the SIMPLE allele and generate a physiological mouse model that expresses CMT1C-mutated SIMPLE at the endogenous level. We find that CMT1C mouse primary embryonic fibroblasts show decreased number of exosomes and reduced secretion of exosome proteins, in part due to improper formation of MVBs. CMT1C patient B cells and CMT1C mouse primary Schwann cells show similar defects. Together the data indicate that SIMPLE regulates the production of exosomes by modulating the formation of MVBs. Dysregulated endosomal trafficking and changes in the landscape of exosome-mediated intercellular communications may place an overwhelming burden on the nervous system and account for CMT1C molecular pathogenesis. 相似文献
8.
164 taxa were identified in the net zooplankton of the pelagial of L. Peipsi-Pihkva in 1909–1987, including 3 species of protozoans, 74 species of rotifers, 58 species of cladocerans, 28 species of copepods and 1 mollusc. One rotifer species, Ploesoma peipsiense Mäemets et Kutikova, has been described as new for science here. The zooplankton of L. Peipsi-Pihkva is remarkably rich in species including rarities in Estonia: Limnosida frontosa, Drepanothrix dentata, Bythotrephes longimanus, B. cederstroemi etc. Due to its large surface area, L. Peipsi-Pihkva provides a large scale of biotopes of a diverse trophic state and humic content, which support species with different ecological requirements. Most of the aquatory of the lake has lately been mesotrophic, favouring the coexistence of indicators of oligo- and mesotrophic state and species preferring a higher trophic state. The occurrece of 10 species of the genus Bosmina including B. berolinensis, B. gibbera, B. lilljeborgi, B. thersites and B. crassicornis, sparse in Estonian lakes, is the most noteworthy feature of the zooplankton of L. Peipsi-Pihkva. The coexistence of B. coregoni and B. berolinensis, B. gibbera, B. lilljeborgi etc. which were earlier regarded as subspecies of B. c. coregoni proves that they are different species producing usually no hybrids. The species composition was subjected to certain changes during the years under consideration. Larvae of Dreissena were first found in zooplankton in 1962. The oligo-mesotrophic indicator Holopedium gibberum occurred in the lake in 1909–1964, but was lacking in later samples. 相似文献
9.
The article deals with the historical development of material use in the Bohemia and Moravia-Silesia/Czechoslovakia in 1855–2007. We calculate domestic material consumption (DMC), an indicator based on the concept of socio-economic metabolism and economy-wide material flow analysis, and relate it to various socio-economic factors such as changes in political regimes, industrialization and consequent growth in GDP and population. DMC is good at reflecting the gradual industrialization which took place up to the First World War, then the strong focus on the development of heavy industry under communist rule, and finally the swing to a more consumer industry and service-oriented economy after the fall of the communist regime and the subsequent transition from a centrally planned to a market economy. The comparable DMC figures per capita for Czechoslovakia and the United Kingdom prove that we arrived at feasible values of material consumption. 相似文献
10.
Buchelnikov AS Hernandez Santiago AA Gonzalez Flores M Vazquez Ramirez R Davies DB Evstigneev MP 《European biophysics journal : EBJ》2012,41(3):273-283
A general model of competitive binding in drug–interceptor–DNA systems has been developed in order to quantify both the interceptor
and protector mechanisms. The model involves full parameterization of the basic equations governing the mutual competition
between drugs binding to DNA and incorporates as partial cases various similar models existing in the literature. The generality
of the model results from strict accounting of the statistical effects of the binding of the drug and interceptor with DNA
according to the McGhee-von Hippel formalism, and to the strict treatment of hetero-association between the drug and interceptor,
which includes formation of all possible types of self- and hetero-complexes in solution. Indirect experimental evidence is
provided for the importance of the protector mechanism in drug–caffeine–DNA systems, which is sometimes ignored in the literature
because of the small magnitude of the CAF-DNA binding constant. 相似文献
11.
Lysozyme and antilysozyme activities present in a wide range of microorganisms determine the so-called lysozyme–antilysozyme system of hydrobionts, which greatly contribute to the formation of aquatic biocenoses. However, the mechanism of the functioning of this system in natural freshwater communities remains obscure. The experimental investigation of lysozyme–antilysozyme interactions in a model Tetrahymena–Escherichiacommunity showed that the antilysozyme activity of Escherichia colileads to incomplete phagocytosis, thus enhancing bacterial survival in a mixed culture with infusoria. The selection and reproduction of bacterial cells resistant to grazing by infusoria determine the character of host–parasite interactions and allow bacteria to survive. It was demonstrated that the antilysozyme activity of microorganisms, which is responsible for bacterial persistency in natural biocenoses, is involved in the maintenance of protozoa–bacteria communities in bodies of water. 相似文献
12.
Plants and soil are the base for sustainably surviving human beings on the globe as the role of materials, energy, resources and environment (Shao & Chu 2008; Shao et al. 2008, 2009, 2010, 2012a,b; Liu & Shao, 2010; Ruan et al. 2010; Xu et al. 2010, 2012; Shao 2012; Huang et al. 2013). This topic has been extensively investigated for 100 years with more achievements in many sectors and practical significance in conducting high-efficient agriculture and eco-environmental construction. The plant–soil interaction is the core issue of this topic, which has been given much attention for the past 30 years (Wu et al. 2007, 2010; Zhang et al. 2011, 2013; Xu et al. 2012, 2013). 相似文献
13.
Three species of tortoise (Testudinidae) occur in Greece (Testudo hermanni, T. graeca and the endemic T. marginata), all of which have been listed as rare or vulnerable. This paper describes the current situation of 75 populations that were last observed in the 1970s and 1980s and described in 1989. Twenty-nine populations had declined in density and/or status (significantly more than had improved), 10 of which were functionally extinct. A particularly notable loss was a dense population of T. marginata at Gytheion in the Peloponnese due to a widespread fire. Declining populations were significantly associated with identified high threat in 1989 and with close proximity to human settlement. There were no significant effects of tortoise species, area of site, characteristics of surrounding areas or original density on these changes. Declines were less associated with agriculture than predicted in 1989, reflecting changing economic conditions in Greece in the 1990s. Continuing threats to tortoise habitats make their long-term future appear bleak outside of protected areas. The risk of extinction from stochastic variation in small populations was also assessed, using the VORTEX program. This risk was much lower than that from habitat loss; 60–96% of populations of 100 tortoises would survive for 1000 years, depending on adult body size, compared to only 0–0.02% of habitats. The high survival potential of small populations would facilitate conservation of the high intraspecific diversity of tortoises in Greece. 相似文献
14.
《Cell cycle (Georgetown, Tex.)》2013,12(13):1366-1370
DNA–protein cross-links are generated by both endogenous and exogenous DNA damaging agents, as intermediates during normal DNA metabolism, and during abortive base excision repair. Cross-links are relatively common lesions that are lethal when they block progression of DNA polymerases. DNA–protein cross-links may be broadly categorized into four groups by the DNA and protein chemistries near the cross-link and by the source of the cross-link: DNA–protein cross-links may be found (1) in nicked DNA at the 3' end of one strand (topo I), (2) in nicked DNA at the 5' end of one strand (pol beta), (3) at the 5' ends of both strands adjacent to nicks in close proximity (topo II; Spo 11), and (4) in one strand of duplex DNA (UV irradiation; bifunctional carcinogens and chemotherapeutic agents). Repair mechanisms are reasonably well-defined for groups 1 and 3, and suggested for groups 2 and 4. Our work is focused on the recognition and removal of DNA–protein cross-links in duplex DNA (group 4). 相似文献
15.
This paper considers plant–pollinator systems in which plants are divided into two categories: The plants that secret a substantial volume of nectar in their flowers are called secretors, while those without secreting nectar are called nonsecretors (cheaters). The interaction between pollinators and secretors is mutualistic, while the interaction between pollinators and nonsecretors is parasitic. Both interactions can be described by Beddington–DeAngelis functional responses. Using dynamical systems theory, we show global dynamics of a pollinator–secretor–cheater model and demonstrate mechanisms by which nectarless flowers/nonsecretors can invade the pollinator–secretor system and by which the three species could coexist. We define a threshold in the nonsecretors’ efficiency in translating pollinator–cheater interaction into fitness, which is determined by parameters (factors) in the systems. When their efficiency is above the threshold, non-secretors can invade the pollinator–secretor system. While the nonsecretors’ invasion often leads to their persistence in pollinator–secretor systems, the model demonstrates situations in which the non-secretors’ invasion can drive secretors into extinction, which consequently leads to extinction of the nonsecretors themselves. 相似文献
16.
Matthew J. Ferrari Ali Djibo Rebecca F. Grais Nita Bharti Bryan T. Grenfell Ottar N. Bjornstad 《Proceedings. Biological sciences / The Royal Society》2010,277(1695):2775-2782
Seasonally driven cycles of incidence have been consistently observed for a range of directly transmitted pathogens. Though frequently observed, the mechanism of seasonality for directly transmitted human pathogens is rarely well understood. Despite significant annual variation in magnitude, measles outbreaks in Niger consistently begin in the dry season and decline at the onset of the seasonal rains. We estimate the seasonal fluctuation in measles transmission rates for the 38 districts and urban centres of Niger, from 11 years of weekly incidence reports. We show that transmission rates are consistently in anti-phase to the rainfall patterns across the country. The strength of the seasonal forcing of transmission is not correlated with the latitudinal rainfall gradient, as would be expected if transmission rates were determined purely by environmental conditions. Rather, seasonal forcing is correlated with the population size, with larger seasonal fluctuation in more populous, urban areas. This pattern is consistent with seasonal variation in human density and contact rates due to agricultural cycles. The stronger seasonality in large cities drives deep inter-epidemic troughs and results in frequent local extinction of measles, which contrasts starkly to the conventional observation that large cities, by virtue of their size, act as reservoirs of measles. 相似文献
17.
18.
Darren Michael Green 《Population Ecology》2009,51(2):253-260
Interspecific interactions and the evolution of dispersal are both of interest when considering the potential impact of habitat
fragmentation on community ecology, but the interaction between these processes is not well studied. We address this by considering
the coevolution of dispersal strategies in a host–parasitoid system. An individual-based host–parasitoid metapopulation model
was constructed for a patchy environment, allowing for evolution in dispersal rates of both species. Highly rarefied environments
with few suitable patches selected against dispersal in both species, as did relatively static environments. Provided that
parasitoids persist, all the variables studied led to stable equilibria in dispersal rates for both species. There was a tendency
toward higher dispersal rates in parasitoids because of the asymmetric relationships of the two species to the patches: vacant
patches are most valuable for hosts, but unsuitable for parasitoids, which require an established host population to reproduce.
High host dispersal rate was favoured by high host population growth rate, and in the parasitoid by high growth rates in both
species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
20.
The roles of ABA in plant–pathogen interactions 总被引:1,自引:0,他引:1
Defence against abiotic and biotic stresses is crucial for the fitness and survival of plants under adverse or suboptimal
growth conditions. The phytohormone abscisic acid (ABA) is not only important for mediating abiotic stress responses, but
also plays a multifaceted and pivotal role in plant immunity. This review presents examples demonstrating the importance of
crosstalk between ABA and the key biotic stress phytohormone salicylic acid in determining the outcome of plant–pathogen interactions.
We then provide an overview of how ABA influences plant defence responses against various phytopathogens with particular emphasis
on the Arabidopsis–Pseudomonas syringae model pathosystem. Lastly, we discuss future directions for studies of ABA in plant immunity with emphasis on, its role in
the crosstalk between biotic and abiotic stress responses, the importance of distinguishing direct and indirect effects of
ABA, as well as the prospect of utilizing the recently elucidated core ABA signaling network to gain further insights into
the roles of ABA in plant immunity. 相似文献