A blessing in disguise: Transposable elements are more than parasites

Transposable elements (TEs) are various DNA fragments inserted throughout genomes, which are able to move or duplicate themselves. Recent advances in genomics have placed them back at the center of genome dynamics. One of the emerging observations, especially in plants, is the importance of interactions between TEs and genes to generate or to participate in relevant functions essential for development, adaptation and/or life cycle. A recent publication illustrates the influence of TEs epigenetic control on the expression of a neighboring gene crucial for reproduction. Different reports lately showed that a fundamental mechanism such as imprinting is likely to be closely linked to the dynamics of TEs epigenetic control. Here we discuss and bring together these and others recent findings, to underline that the cis-vicinity or the trans-relation between TEs and genes could bring unexpected but positive outcomes.     

铜绿假单胞菌PA1550基因对泳动及蹭动的影响

[目的]:研究与铜绿假单胞菌运动能力相关的基因.[方法]:以一株临床分离的铜绿假单胞菌PA68做受体菌,应用人工Mu转座技术建立了库容为2000的突变子文库,从中筛选出泳动能力和蹭动能力丧失或减弱的突变子,通过基因克隆、测序,GenBankBLAST比对测序结果,互补基因表达确定与铜绿假单胞菌运动能力相关的基因.[结果]:突变子Y46在丧失了泳动运动能力的同时,蹭动能力也发生了减弱.在Y46突变子中,Mu转座子插入到功能完全未知的基因PA1550中.对极性效应及PA1550所在操纵子的分析表明,Mu转座子对插入点下游的基因的转录并不造成影响.[结论]:PA1550与铜绿假单胞菌的泳动及蹭动能力有关.     

Nematode parasites of animals are more prone to develop xenobiotic resistance than nematode parasites of plants

In this paper, we concentrate on a comparison of plant and animal-parasitic nematodes, to gain insight into the factors that influence the acquisition of the drug resistance by nematodes. Comparing nematode parasite of domestic animals and cultivated plants, it appears that drug resistance threatens only domestic animal production. Does the paucity of report on nematicide field resistance reflect reality or, is nematicide resistance bypassed by other management practices, specific to cultivated plants (i.e. agricultural control)? First, it seems that selection pressure by treatments in plants is not as efficient as selection pressure in ruminants. Agronomic practices (i.e. sanitation, early planting, usage of nematodes resistant cultivar and crop rotation) are frequently used to control parasitic-plant nematodes. Although the efficiency of such measures is generally moderate to high, integrated approaches are developing successfully in parasitic-plant nematode models. Secondly, the majority of anthelmintic resistance cases recorded in animal-parasitic nematodes concern drug families that are not used in plant-parasitic nematodes control (i.e. benzimidazoles, avermectines and levamisole). Thirdly, particular life traits of parasitic-plant nematodes (low to moderate fecundity and reproductive strategy) are expected to reduce probability of appearance and transmission of drug resistance genes. It has been demonstrated that, for a large number of nematodes such as Meloidogyne spp., the mode of reproduction by mitotic parthenogenesis reduced genetic diversity of populations which may prevent a rapid drug resistance development. In conclusion, anthelmintic resistance develops in nematode parasite of animals as a consequence of an efficient selection pressure. Early detection of anthelmintic resistance is then crucial: it is not possible to avoid it, but only to delay its development in farm animal industry.     

Introduced species: domestic mammals are more significant transmitters of parasites to native mammals than are feral mammals

The study of parasitism related to biological invasion has focused on attributes and impacts of parasites as invaders and the impact of introduced hosts on endemic parasitism. Thus, there is currently no study of the attributes of hosts which influence the invasiveness of parasites. We aimed to determine whether the degree of domestication of introduced mammalian species – feral introduced mammals, livestock or pets, hereafter ‘D’ – is important in the spillover of introduced parasites. The literature on introduced parasites of mammals in Chile was reviewed. We designed an index for estimating the relevance of the introduced host species to parasite spillover and determined whether the D of introduced mammals predicted this index. A total of 223 introduced parasite species were found. Our results indicate that domestic mammals have a higher number of introduced parasites and spillover parasites, and the index indicates that these mammals, particularly pets, are more relevant introducers than introduced feral mammals. Further analyses indicated that the higher impact is due to higher parasite richness, a longer time since introduction and wider dispersal, as well as how these mammals are maintained. The greater relevance of domestic mammals is important given that they are basically the same species distributed worldwide and can become the main transmitters of parasites to native mammals elsewhere. This finding also underlines the feasibility of management in order to reduce the transmission of parasites to native fauna through anti-parasitic treatment of domestic mammals, animal-ownership education and the prevention of importing new parasite species.     

Purification of African trypanosomes can cause biochemical changes in the parasites

Bloodstream forms of African trypanosomes are routinely purified from blood components by a combination of centrifugation and chromatography on DEAE cellulose at pH 8.0. Here we report that the nonphysiological conditions used for DEAE chromatography of the parasites result in changes in the ATP levels of the trypanosomes and an enhanced release from the parasites of proteins such as variable surface glycoprotein, peptidase, and phospholipase. Some of these changes can be reduced by the addition of nucleosides to the elution buffer and, after the elution of the parasites, by immediate readjustment of the external pH to the normal physiological level of blood (pH 7.4).     

High-speed video observation of swimming behavior and flagellar motility ofProrocentrum minimum (Dinophyceae)

Summary To understand the functions of the longitudinal and transverse flagella of dinoflagellates, the flagellar waveform and frequency of each flagellum were observed by high-speed video-recording. The longitudinal flagellum emerged from the anterior end of the cell and beat with a planar undulating wave whose plane was perpendicular to the valval sutural plane. The transverse flagellum curved around the anterior end of the cell and beat with a helical wave, with different alternating half pitches. The half pitch corresponding to the parts farther from the cellular antero-posterior axis was shorter than that of the parts closer to the axis. This pattern is described by the ratio of the outer-parts half pitch to the pitch of the whole period of the helix and seems to be characteristic of the dinoflagellates' transverse flagellum.Abbreviations p _in half pitch corresponding to the inner parts of the transverse flagellum - p _out half pitch corresponding to the outer parts of the transverse flagellum - P _p pitch of helical swimming trajectory - R _p radius of helical swimming trajectory - _c rotational frequency of the cell     

Impact of acanthocephalan parasites on aggregation behavior of amphipods (Gammarus pseudolimnaeus)

Acanthocephalan parasites can manipulate the behavior of their amphipod intermediate hosts in ways that increase the amphipod's risk of being eaten by a predator that serves as the final host for the parasite. Some asocial amphipod species have been shown to increase the likelihood of aggregation in response to chemical cues associated with predators. If such aggregation has anti-predation benefits, it might be subject to manipulation by parasites. We tested this hypothesis by comparing the preference of parasitized and unparasitized amphipods (Gammarus pseudolimnaeus) for associating with a group of unparasitized conspecifics, both in the presence and absence of chemical cues from predatory brook sticklebacks (Culaea inconstans). Amphipods with encysted parasites (Corynosoma sp.) avoided aggregating, whereas unparasitized amphipods preferred to aggregate. We also found that the risk of predation by sticklebacks faced by an individual amphipod was significantly lower when the amphipod was in a group compared to when it was alone. This suggests that the aggregation response of unparasitized amphipods is an adaptive response to escape predation. This study provides evidence for a novel parasitic manipulation of intermediate host behavior that is likely to increase transmission to the definitive host.     

Microtubule cross-linking triggers the directional motility of kinesin-5

Although assembly of the mitotic spindle is known to be a precisely controlled process, regulation of the key motor proteins involved remains poorly understood. In eukaryotes, homotetrameric kinesin-5 motors are required for bipolar spindle formation. Eg5, the vertebrate kinesin-5, has two modes of motion: an adenosine triphosphate (ATP)-dependent directional mode and a diffusive mode that does not require ATP hydrolysis. We use single-molecule experiments to examine how the switching between these modes is controlled. We find that Eg5 diffuses along individual microtubules without detectable directional bias at close to physiological ionic strength. Eg5's motility becomes directional when bound between two microtubules. Such activation through binding cargo, which, for Eg5, is a second microtubule, is analogous to known mechanisms for other kinesins. In the spindle, this might allow Eg5 to diffuse on single microtubules without hydrolyzing ATP until the motor is activated by binding to another microtubule. This mechanism would increase energy and filament cross-linking efficiency.     

Influence of the uterine environment on rat sperm motility and swimming speed

The present study compared several rat sperm parameters in semen samples recovered from a natural uterine environment (i.e., intact estrous female) to those recovered from an artificially induced uterine environment (i.e., ovariectomized hormonally primed female). The sperm parameters measured were percent motile, percent exhibiting forward progressive motility, actual swimming speed, and linear swimming speed. The comparisons were conducted at four postcopulatory time points (0.25, 1.5, 3, and 6 hours) in order to detect differences as a function of residence time within the uterus. No significant differences (P less than 0.05) in the parameters were seen between the two types of uterine environments. Residence time within the reproductive tract had no significant effect on the parameters with the exception of percent motile, which was significantly increased (P less than 0.01) at the 1.5-hour postcopulatory time point.     

The blood parasites of anurans from Costa Rica with reflections on the taxonomy of their trypanosomes

During May 1997, specimens of 7 species of anurans, that included 5 Phrynohyas venulosa Laurenti, 5 Rana forreri Boulenger, 7 Rana vaillanti Brucchi, 6 Eleutherodactylus fitzingeri Schimdt, 4 Smilisca baudinii Duméril and Bibron, 1 Leptodactylus melanonotus, and 3 Bufo marinus Linneaus, from the Guanacaste Conservation Area, Costa Rica were examined for blood parasites. Their hematozoan fauna included intraerythrocytic and intraleukocytic icosahedral viruses, a rickettsia (Aegyptianella sp.), 2 species of Hepatozoon, Lankesterella minima, 2 unknown species of apicomplexans, 9 morphologically distinct types of trypanosomes, and 2 species of microfilariae. Rana vaillanti, the most aquatic species of frog, harbored the most species of parasites. Recent evidence indicates that morphological changes in the highly pleomorphic trypanosomes of anurans from different geographical regions have not kept pace with biochemical (isozyme) and molecular (DNA sequence) changes. Describing new species based solely on bloodstream trypomastigotes is discouraged. Additional criteria described herein should be applied when naming new species of anuran trypanosomes.     

Intracellular motility apparatus of halobacteria: Electron microscopic study

The intracellular disc-like lamellar structure (DLS) earlier detected in the motility apparatus of Halobacterum salinarum and details of insertion of proximal ends of flagella into DLS were studied using electron microscopy. Analysis of ultrathin sections obtained after fixation with potassium permanganate established that DLS, absent in bacteria, contains a membrane-like structure. Electron microscopic studies of cell ghosts obtained by mild cytolysis in low-NaCl solutions shed additional light as on details of DLS structure and so on localization of flagellar proximal ends. Structural organization of the motility apparatus of bacteria and archaebacteria as representatives of two distinct taxonomic domains is discussed.     

Actin motility: staying on track takes a little more effort

The pigment cells of amphibians and fish have provided excellent models for understanding how actin and microtubule motors move organelles along the complex trailway of filaments in the cytoplasm. Recent work provides more evidence that these motors are engaged in a continuous tug-of-war.     

Ectoparasites are more vulnerable to host extinction than co-occurring endoparasites: evidence from metazoan parasites of freshwater and marine fishes

Hydrobiologia - The extinction of fish species can direct and indirectly affect many groups of associated species, among which parasite communities can be the most susceptible. However, the...     

Modulation of swimming behavior in the medicinal leech

Expression of swimming in the medicinal leech (Hirudo medicinalis) is modulated by serotonin, a naturally occurring neurohormone. Exogenous application of serotonin engenders spontaneous swimming activity in nerve-cord preparations. We examined whether this activity is due to enhanced participation of swim motor neurons (MNs) in generating the swimming rhythm. We found that depolarizing current injections into MNs during fictive swimming are more effective in shifting cycle phase in nerve cords following serotonin exposure. In such preparations, the dynamics of membrane potential excursions following current injection into neuronal somata are substantially altered. We observed: 1) a delayed outward rectification (relaxation) during depolarizing current injection, most marked in inhibitory MNs; and 2) in excitor MNs, an enhancement of postinhibitory rebound (PIR) and afterhyperpolarizing potentials (AHPs) following hyperpolarizing and depolarizing current pulses, respectively. In contrast, we found little alteration in MN properties in leech nerve cords depleted of amines. We propose that enhanced expression of swimming activity in leeches exposed to elevated serotonin is due, partly, to enhancement of relaxation, PIR and AHP in MNs. We believe that as a consequence of alterations in cellular properties and synaptic interactions (subsequent paper) by serotonin, MNs are reconfigured to more effectively participate in generating and expressing the leech swimming rhythm.Abbreviations AHP Afterhyperpolarizing potential - DCC Discontinuous current clamp - DE Dorsal excitor motor neuron - DI Dorsal inhibitor motor neuron - IPSP Inhibitory postsynaptic potential - MN Motor neuron - PIR Postinhibitory rebound - VE Ventral excitor motor neuron - VI Ventral inhibitor motor neuron     

Transposon mutagenesis in a marine synechococcus strain: isolation of swimming motility mutants

Certain marine unicellular cyanobacteria of the genus Synechococcus exhibit a unique type of swimming motility characterized by the absence of flagella or any other obvious organelles of motility. While the abundant cell surface-associated 130-kDa glycoprotein SwmA is known to be required for the generation of thrust, identification of other components of the motility apparatus has, until recently, been unsuccessful. Here we report on the development of a transposon mutagenesis system for use with marine Synechococcus sp. strain WH8102, a model organism for which the genome has been sequenced. Utilizing this mutagenesis technique, we have isolated 17 independent mutants impaired in swimming motility. These 17 transposon insertions are located in nine open reading frames, which cluster in three separate regions of the genome. Included within these clusters are several multicomponent transport systems as well as a number of glycosyltransferases.     

Modulation of swimming behavior in the medicinal leech

The effects of serotonin on the electrical properties of swim-gating neurons (cell 204) were examined in leech (Hirudo medicinalis) nerve cords. Exposure to serotonin decreased the threshold current required to elicit swim episodes by prolonged depolarization of an individual cell 204 in isolated nerve cords. This effect was correlated with a more rapid depolarization and an increased impulse frequency of cell 204 in the first second of stimulation. In normal leech saline, brief depolarizing current pulses (1 s) injected into cell 204 failed to elicit swim episodes. Following exposure to serotonin, however, identical pulses consistently evoked swim episodes. Thus, serotonin appears to transform cell 204 from a gating to a trigger cell.Serotonin had little effect on the steady-state currentvoltage relation of cell 204. However, serotonin altered the membrane potential trajectories in response to injected current pulses and increased the amplitude of rebound responses occurring at the offset of current pulses. These changes suggest that serotonin modulates one or more voltage dependent conductances in cell 204, resulting in a more rapid depolarization and greater firing rate in response to injected currents. Thus, modulation of intrinsic ionic conductances in cell 204 may account in part for the increased probability of swimming behavior induced by serotonin in intact leeches.Abbreviations AHP afterhyperpolarizing potential - DCC discontinuous current clamp - DP dorsal posterior nerve - G2 segmental ganglion 2 - PIR postinhibitory rebound - RMP resting membrane potential     

The swimming behavior of the copepod Metridia pacfica

The swimming behavior of the copepod Metridia pacifica was studied.Animals exposed to algae showed lower average swimming speedand fewer high-speed bursts. Animals exposed to Artemia naupliialone exhibited no change in swimming behavior.     

不同流速对鱇(鱼良)白鱼游泳行为的影响

在25℃水温下,采用特制的鱼类游泳行为测定装置对实验鱼在静水和0.1、0.2和0.25 m·s-1流速下的游泳状态、游泳速度、趋流率和摆尾频率等参数进行测定,研究水流速度对鱇(鱼良)白鱼(Anabarilius grahami)游泳行为的影响.结果表明:有流速组的趋流率显著高于静水组,但不同流速组间的趋流率无显著差别;在0 ～0.2 m·s-1流速范围内,摆尾频率随流速加快而显著增大,但在0.25 m·s-1流速下40 min后摆尾频率显著低于0.2m·s-1流速组;随着流速的增大,主要游泳状态由逆流前进变为逆流静止;在有流速组,顺流而下状态所占时间比例相对其他游泳状态都较少;在逆流游泳的3种状态中,游泳速度均随流速的增加而增大,在顺流而下状态中,游泳速度和水速间无显著相关;游泳速度、摆尾频率和水流速度两两之间均存在显著的线性相关.