Abnormal movement of polymorphonuclear neutrophils in the Immotile Cilia Syndrome : Cinemicrographic analysis

Polymorphonuclear leukocytes (PMN) moving on a flat substrate in vitro tend to make fewer turns and persist in a particular direction during periods of rapid movement. It has been suggested that this persistence of unidirectional movement is modulated by the cellular cytoskeleton, particularly the arrangement of microtubules and associated structures. A cinemicrographic analysis of the movement of PMN from five subjects with the Immotile Cilia Syndrome (ICS) showed that there was an abnormality of movement characterized by an increased tendency to turn, resulting in a more tortuous path of movement than seen with controls. Since subjects with ICS are known to have an abnormality of microtubule-associated structures and function of their cilia, it is possible that the abnormalities of ciliated cells and PMN may be the result of the effects of the underlying genetic defect upon microtubule-associated functions in both cell types.     

A fluid-dynamic interpretation of the asymmetric motion of singly flagellated bacteria swimming close to a boundary

The singly flagellated bacterium, Vibrio alginolyticus, moves forward and backward by alternating the rotational direction of its flagellum. The bacterium has been observed retracing a previous path almost exactly and swimming in a zigzag pattern. In the presence of a boundary, however, the motion changes significantly, to something closer to a circular trajectory. Additionally, when the cell swims close to a wall, the forward and backward speeds differ noticeably. This study details a boundary element model for the motion of a bacterium swimming near a rigid boundary and the results of numerical analyses conducted using this model. The results reveal that bacterium motion is apparently influenced by pitch angle, i.e., the angle between the boundary and the swimming direction, and that forward motion is more stable than backward motion with respect to pitching of the bacterium. From these results, a set of diagrammatic representations have been created that explain the observed asymmetry in trajectory and speed between the forward and backward motions. For forward motion, a cell moving parallel to the boundary will maintain this trajectory. However, for backward motion, the resulting trajectory depends upon whether the bacterium is approaching or departing the boundary. Fluid-dynamic interactions between the flagellum and the boundary vary with cell orientation and cause peculiarities in the resulting trajectories.     

Contribution of soil-borne bacteria to the rotation effect in corn

Few efforts have been directed at understanding how the rhizosphere microbiology of continuous corn may effect crop yields. This relationship may explain, in part, the decreases in yield associated with continuous corn as compared to the corn in rotation with a second crop. This study was conducted to determine the importance of soil-borne microorganisms to yield declines in long term continuous corn. Continuous corn (Zea mays L.) or rotated corn-soybean (Glycine max L.) field plots, established in 1975, under either fall plowing or no-till tillage treatments were used. Treatments consisted of methyl bromide applied at 48.8 g m⁻² 3 days prior to planting in all four combinations. Total plant samples from both the fumigated and non-fumigated areas were collected 14 days after planting. Rhizosphere bacteria were recovered and tested for their ability to impact plant growth. Bacterial assessments were made in a test tube bioassay where germinated corn was transported in to agar containing a bacterial isolate. In the first year of the study a highly significant interaction of fumigation and rotation was indicated. With fumigation continuous corn yields were similar to that of rotated corn-bean. Rotated corn yields were less affected by fumigation. In the second year, the effects were similar but less significant. Over 130 bacterial isolates were tested for their effect on plant growth. Approximately 22% were able to inhibit plant growth. Of these, 72% were from the continuous corn system. Clearly, the interaction of rotation and yield is at a microbiological level. The suggestion that microorganisms similar to those isolated are responsible for controlling early plant growth in the continuous corn system is indicated.     

Distribution of bacteria in the velocity gradient centrifuge.

Cells in different parts of the cell cycle can be separated by brief centrifugation in a density stabilized gradient: the Mitchison-Vincent technique. The position of a cell in the tube depends upon its size, shape, and density, upon the gradients of density, viscosity, and centrifugal force through which it sediments, and upon time. A program to compute the velocities and integrate the velocity profile for particles of a particular size class is presented. Because enteric bacteria are a form intermediate between right cylinders and prolate ellipsoids of revolution, the program uses values for the frictional coefficient intermediate between those calculated for ellipsoids and for cylinders. The formula f=6pietab(a/b)1/2 possesses this property and because of its simplicity greatly speeds the calculations. A second program computes the distribution of masses and then of sedimentation constants for a bacterial population, expressed either as a frequency distribution or as total mass per s-class. The effect of the known variation in cell size at division is included in these calculations, which apply to organisms undergoing balanced, asynchronous growth in which mass increase is proportional to cell size. The two programs in conjunction compute the mass or cell-number profile in an arbitrary gradient. The programs have been used to design gradients to maximize the resolution of the technique.     

The genetics of Otosclerosis. I. Distorted sex ratio.

The offspring of 214 otosclerotic x normal couples were investigated, and within these sibships, the segregation of otosclerosis is compatible with autosomal dominant inheritance. However, the overall sex ratio is approximately 0.73, with otosclerosis being approximately 1.8 times more frequent in female offspring. These observations are interpreted as the consequence of selection against males carrying the otosclerosis gene. Elimination of such males occurs only in certain sibships. The remaining families demonstrate a sex ratio approximating unity with similar rates of otosclerosis in both sexes. This selection operates mainly, and possibly only, prenatally.     

The sensitivity of chlamydomonas photoreceptor is optimized for the frequency of cell body rotation.

For phototactic migration, Chlamydomonas scans the surrounding light environment by rotating the cell body with an eyespot located on the equator. The intensity of the light signal received by the eyespot should therefore change cyclically at the frequency of the cell body rotation. In this study, the response of the photoreceptor to cyclically changing light stimuli was analyzed using immotile mutant cells. To simulate the light intensity change perceived by a rotating cell, light stimuli were applied that consisted of a light phase with the intensity changing similar to a half cycle of a sine wave and a dark phase of the same length. The fluence rate at the peak of the sine wave was of the order of 10(19) photons m(-2) s(-1), i.e. high intensity at which phototaxis is saturated. A photoreceptor current (PRC) was produced at the onset of each light phase. Interestingly, its amplitude varied depending on the frequency and was largest at 1-5 Hz, a frequency range similar to the frequency of cell body rotation. Experiments on the kinetics of the PRC indicate that the response was small at low frequency because of the inactivation of the PRC before full activation. In contrast, at high frequency the PRC was suppressed by adaptation to the repetitive stimuli. These characteristic kinetics of the PRC should be important for Chlamydomonas cells to extract information from the signals generated by the cell body rotation.     

Changing the direction of flagellar rotation in bacteria by modulating the ratio between the rotational states of the switch protein FliM

One of the major questions in bacterial chemotaxis is how the switch, which controls the direction of flagellar rotation, functions. It is well established that binding of the signaling molecule CheY to the switch protein FliM shifts the rotation from the default direction, counterclockwise, to clockwise. How this shift is done is still a mystery. Our aim in this study was to determine the correlation between the fraction of FliM molecules in the clockwise state (i.e. occupied by CheY) and the probability of clockwise rotation. For this purpose we gradually expressed, from a plasmid, a clockwise FliM mutant protein in cells that express, from the chromosome, wild-type FliM but no chemotaxis proteins. We verified that plasmid-borne FliM exchanges chromosomal FliM in the switch. Surprisingly, a substantial clockwise probability was not obtained before the large majority of the FliM molecules in the switch were clockwise molecules. Thereafter, the rise in clockwise probability was very steep. These results suggest that an increase in the clockwise probability requires a high level of FliM occupancy by CheY approximately P. They further suggest that the steep increase in clockwise rotation upon increasing CheY levels, reported in several studies, is due, at least in part, to cooperativity of post-binding interactions within the switch. We also carried out the inverse experiment, in which wild-type FliM was gradually expressed in a background of a clockwise fliM mutant. In this case, the level of the clockwise mutant protein, required for establishing a certain clockwise probability, was lower than in the original experiment. If our system (in which the ratio between the rotational states of FliM in the switch is established by slow exchange) and the native system (in which the ratio is established by fast changes in FliM occupancy) are comparable, the results suggest that hysteresis is involved in the switch function. Such a situation might reflect a damping mechanism, which prevents a situation in which fluctuations in the phosphorylation level of CheY throw the switch from one direction of rotation to the other.     

Biomechanical analysis of movement strategies in human forward trunk bending. I. Modeling

 Two behavioral goals are achieved simultaneously during forward trunk bending in humans: the bending movement per se and equilibrium maintenance. The objective of the present study was to understand how the two goals are achieved by using a biomechanical model of this task. Since keeping the center of pressure inside the support area is a crucial condition for equilibrium maintenance during the movement, we decided to model an extreme case, called “optimal bending”, in which the movement is performed without any center of pressure displacement at all, as if standing on an extremely narrow support. The “optimal bending” is used as a reference in the analysis of experimental data in a companion paper. The study is based on a three-joint (ankle, knee, and hip) model of the human body and is performed in terms of “eigenmovements”, i.e., the movements along eigenvectors of the motion equation. They are termed “ankle”, “hip”, and “knee” eigenmovements according to the dominant joint that provides the largest contribution to the corresponding eigenmovement. The advantage of the eigenmovement approach is the presentation of the coupled system of dynamic equations in the form of three independent motion equations. Each of these equations is equivalent to the motion equation for an inverted pendulum. Optimal bending is constructed as a superposition of two (hip and ankle) eigenmovements. The hip eigenmovement contributes the most to the movement kinematics, whereas the contributions of both eigenmovements into the movement dynamics are comparable. The ankle eigenmovement moves the center of gravity forward and compensates for the backward center of gravity shift that is provoked by trunk bending as a result of dynamic interactions between body segments. An important characteristic of the optimal bending is the timing of the onset of each eigenmovement: the ankle eigenmovement onset precedes that of the hip eigenmovement. Without an earlier onset of the ankle eigenmovement, forward bending on the extremely narrow support results in falling backward. This modeling approach suggests that during trunk bending, two motion units – the hip and ankle eigenmovements – are responsible for the movement and for equilibrium maintenance, respectively. Received: 1 July 1999 / Accepted in revised form: 23 October 2000     

Quantitative EMG analysis to investigate synergistic coactivation of ankle and knee muscles during isokinetic ankle movement. Part 2: time frequency analysis.

Fundamental to intralimb coordination in the lower extremity, ankle-knee synergy induced by motor irradiation has long been employed to secure facilitation of paralyzed muscles. This study, a companion research subsequent to the time amplitude analysis of surface electromyography in part 1, was to investigate the recruitment strategy of irradiated muscles and prime movers during ankle isokinetic contraction at different contraction speeds (30, 60, 120 and 240 degrees/s) with time frequency analysis. The results indicated the recruitment strategies of the major irradiated muscles (ipsilateral rectus femoris/ipsilateral biceps femoris) and prime movers (anterior tibialis/gastrocnemius) were time-dependent and significantly different in terms of the instantaneous median frequency. In general, the prime movers for ankle isokinetic concentric contraction demonstrated a similar recruitment strategy, irrespective of different contraction speeds. This finding is consistent with the idea of generalized motor programs that speed is one of the constraint parameters supplied to motor programs. Nevertheless, the recruitment strategies of the irradiated muscles were highly inconsistent, varying across trials at different contraction speeds, and were not relevant to those of the prime movers. In addition, the recruitment in the irradiated muscles seemly limited to motor units of low threshold, in spite of maximal voluntary contraction of the prime movers.     

基于双核酸频率分布特征的细菌亲缘关系定量分析

目的采用生物信息学方法定量分析细菌的亲缘关系。方法抽取全基因组核酸序列的双核苷酸频率特征向量,表征数字特征。采用Pearson相关系数分析特征向量之间的距离。结果以119个细菌的全基因组核酸序列为研究对象,两两比对的结果为:越是相近的物种,Pearson相关系数越大,PCC距离越小。结论该方法对细菌亲缘关系的定量描述做了有益的探索。     

Clinico-genetical analysis of colonic cancer. I. Occurrence, frequency in families and segregation analysis

The data on clinico-genealogic studies of colon cancer are presented. 694 families were examined with 432 probands having rectal and 262 colonic carcinoma among them. Clear family accumulation of colon cancer (2.4 +/- 0.35%) as well as other malignant tumors (6.8 +/- 0.6%) (p less than 0.01) was shown among the relatives of the first degree of relation. The values of segregation rates obtained for clinical forms of colon cancer were lower than theoretically expected for simple monogenic types of inheritance. The analysis of incomplete penetration of genotypes showed that, though formally the inheritance of colon cancer and its clinico-anatomical forms may be described by quasi-dominant types of inheritance, the penetration values are very low: from 4.3 to 13.3% for homozygotes and from 2.1 to 6.6% for heterozygotes. It shows that the supposition about the monogenic types of the colon cancer inheritance is doubtful and suggests that the colon cancer is to be regarded on the basis of the multifactorial model.     

The pathways of calcium movement to the xylem.

Calcium is an essential plant nutrient. It is acquired from the soil solution by the root system and translocated to the shoot via the xylem. The root must balance the delivery of calcium to the xylem with the need for individual root cells to use [Ca2+]cyt for intracellular signalling. Here the evidence for the current hypothesis, that Ca2+ travels apoplastically across the root to the Casparian band which it then circumvents via the cytoplasm of the endodermal cell, is critically reviewed. It is noted that, although Ca2+ channels and Ca2+-ATPases are present and could catalyse Ca2+ influx and efflux across the plasma membrane of endodermal cells, their transport capacity is unlikely to be sufficient for xylem loading. Furthermore, there seems to be no competition, or interactions, between Ca2+, Ba2+ and Sr2+ for transport to the shoot. This seems incompatible with a symplastic pathway involving at least two protein-catalysed transport steps. Thus, a quantity of purely apoplastic Ca2+ transport to the xylem is indicated. The relative contributions of these two pathways to the delivery of Ca2+ to the xylem are unknown. However, the functional separation of symplastic Ca2+ fluxes (for root nutrition and cell signalling) and apoplastic Ca2+ fluxes (for transfer to the shoot) would enable the root to fulfil the demand of the shoot for calcium without compromising intracellular [Ca2+]cyt signals. This is also compatible with the observed correlation between transpiration rate and calcium delivery to the shoot.     

The expected changes in the frequency of alleles affecting the sex ratio

An equation is derived giving the changes per generation in the frequency of alleles affecting the sex ratio. The alleles considered are assumed to be those of an autosomal locus and to act only in one sex. The results indicate that alleles determining the production of more males should always be more common in males than in females.     

The effect of air velocity on the wingstroke frequency of the blowflyCalliphora erythrocephala

Summary The effect of air velocity and pressure on the wingstroke frequency ofCalliphora erythrocephala, flying in a windtunnel, was studied. The results can be understood by considering the flight mechanism as a mechanical oscillator with an inertia, that depends on air velocity and pressure, without any need for nervous control.The effect of changes in air velocity on the wingstroke frequency was calculated, taking the inertia of a steady two-dimensional boundary layer around the wings as the variable part of the inertia of the flight mechanism. The calculated effect was ten times smaller than that observed experimentally. The reason for this discrepancy is discussed.     

The reliability of eye movement quantitative evaluation. I. Saccadic eye movements.

We adopted the estimate of the intraclass coefficient of reliability, R, to evaluate the reliability of saccadic eye movements quantitative analysis. At a one-week interval we recorded refixative saccadic eye movements twice from fifteen healthy subjects by means of the binocular electrooculographic technique. R was computed for the constants and the slopes of the amplitude/duration and the amplitude/peak velocity relationships, for the mean precision values and for the mean latency values adjusted for subject's age. Our data demonstrated that the reliability of saccade parameters is fairly good for the amplitude/peak velocity relationship, good for the precision and very good for the amplitude/duration relationship. Finally, we believe that the normal variability values we obtained can be usefully employed in neurophysiological longitudinal studies not only in normal subjects, but also in pathological condition provided the more reliable parameters and the more adequate strategies to compute normal variability values are chosen.     

The new approaches to whole genome analysis of bacteria

A range of recombinant DNA techniques now enables whole genome analysis of any bacterium to be carried out without recourse to the classical means of bacterial genetic exchange. Using enzymes which cut infrequently, such as SpeI, combined with pulsed field gel electrophoresis, a physical map of ordered fragments can be constructed. By means of cloned fragments of known genes or oligonucleotides synthesized using data from DNA or protein sequence banks, the location of individual genes on this map can be determined. We have used these techniques to study whole genome structure in three species of Pseudomonas: P. aeruginosa, P. putida and P. solanacearum.