Intracellular vesicle movement, cAMP and myosin II in Dictyostelium

Dictyostelium amoebae were analyzed before and after rapid addition of 10(-6) M cAMP for cellular motility, dynamic shape changes, and intracellular particle movement. Before cAMP addition, amoebae moved in a persistent anterior fashion and were elongate with F-actin localized predominantly in the anterior pseudopod. Intracellular particles moved rapidly and anteriorly. Within seconds after 10(-6) M cAMP addition, cells stopped translocating, pseudopod formation ceased, intracellular particle movement was depressed, and F-actin was lost from the pseudopod and concomitantly relocalized in the cell cortex. After 10 seconds, expansion zones reappeared but were small and no longer anteriorly localized. Vesicle movement partially rebounded but was no longer anteriorly directed. The myosin II null mutant HS2215 exhibited both depressed cellular translocation and vesicle movement. The addition of cAMP to HS2215 cells did not result in any detectable change in the random, depressed movement of particles. The results with HS2215 suggest that myosin II is essential for (1) rapid cellular translocation, (2) cellular polarity, (3) rapid particle movement, (4) anteriorly directed particle movement, and (5) the cAMP response. Electron micrographs suggest that at least half of the particles examined in this study contain in turn smaller membrane bound vesicles or multilamellar membrane bodies. The possible role of these vesicles is discussed.     

Determinants of Dominance in the Tree Lizard Urosaurus ornatus: the Relative Importance of Mass,Previous Experience and Coloration

A determination of some of the factors that predict the outcome of contests between male tree lizards, Urosaurus ornatus, was made using logistic regression modelling on matched-pair data. Two-day-long encounters were staged between pairs of males differing in size (snout-vent length and mass), previous contest status (previous winners and previous losers), and coloration (dorsal coloration during their previous contest and throat coloration, a fixed trait). Mass proved to be the best single predictor of contest outcome, resulting in an 80% correct classification rate for predicting winners and losers, far better than the less than 57% correct classification rate for snout-vent length. Previous social status (winner or loser) also was a powerful single predictor of contest outcome with a 793% correct classification rate, as was previous dorsal coloration (76.7%). When combined, mass and previous status produced the strongest combination of predictors with a better than 86% correct classification rate. Contrary to several previous studies, which implicated throat coloration as an important status signal of dominance, our results failed to show that throat coloration is a strong predictor of contest outcome. Possible reasons for this discrepancy with earlier findings are discussed. The logistic regression models also allow prediction of the magnitude of difference in mass between two contestants for there to be an equal chance of winning, given a second asymmetry in contest predictors.     

Modelling the spatial patterning of teeth primordia in the alligator

We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator, Alligator mississippiensis. Detailed embryological studies by Westergaard and Ferguson (1986, 1987, 1990) have shown that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a dynamic patterning mechanism, which crucially includes domain growth. The mechanism can reproduce the spatial pattern development of the first seven teeth primordia in each half jaw of A. mississippiensis. The results for the precise spatio-temporal sequence compare well with experiment. Simulation of the model also predicts that certain transplantations can alter the spatial sequence of teeth primordia initiation.     

Seasonal variation in the effects of hard substratum biofilming on settlement of marine invertebrate larvae

The effect of season on "biofilming";, as a cue for the settlement of marine invertebrate larvae, was investigated in a long-term field study during the years 1992-1994. The series of settlement experiments was conducted in a tidal rapid on the west coast of Scotland, and involved manipulations of artificial panels. Biofilming of substrata, whilst excluding larval settlement, was achieved by the enclosure of panels within tight-fitting (but removable) mesh screens so that the number of settlers on filmed and unfilmed substrata were counted in the initial absence of other incumbent post-larvae. Depending on larval species, the effects of biofilming were found to be either facilitatory or inhibitory. Significant within- and between-species seasonal differences in the settlement responses were detected, and a reversal of the effect of biofilming on larval settlement response, from inhibitory to facilitatory and vice versa, was noted with season in the case of some taxonomic groups and species (e.g. Tubulipora sp., Plagioecia sp., Electra pilosa (L.)). The present study emphasizes the need for extended field studies of larval responses to environmental cues, when the focus of interest is in drawing general inferences about naturally occurring behavioural patterns at settlement.     

A mathematical model of glioma growth: the effect of chemotherapy on spatio-temporal growth

During the past two decades computerized tomography (CT) and magnetic resonance imaging (MRI) have permitted the detection of tumours at much earlier stages in their development than was previously possible. In spite of this earlier diagnosis the effects of earlier and more extensive treatments have been difficult to document. This failure has led to an increasing awareness of the importance of infiltration of glioma cells into surrounding grossly normal brain tissue such that recurrence still occurs. In this paper a simple mathematical model for the proliferation and infiltration of such tumours is introduced, based in part on quantitative image analysis of histological sections of a human brain glioma and especially on cross-sectional area/volume measurements of serial CT images while the patient was undergoing chemotherapy. The model parameters were estimated using optimization techniques to give the best fit of the simulated tumour area to the CT scan data. Numerical solution of the model on a two-dimensional domain, which took into account the geometry of the brain and its natural barriers to diffusion, was used to determine the effect of chemotherapy on the spatiotemporal growth of the tumour.     

Skeletal changes associated with vascular malformations

Five hundred and eighty birthmarks were reviewed; 356 were hemangiomas and 224 were malformations. Bony alterations occurred in association with only 1 percent of hemangiomas, in contrast with 34 percent of patients with vascular malformations. These alterations in bone development were classified according to size, shape, and density changes. Hypertrophy and distortion were typical of lymphatic malformations. Hypoplasia and demineralization were characteristic findings in the extremity venous malformations. Destructive and intraosseous changes were more commonly noted in the arterial or high-flow lesions. Possible mechanisms of altered skeletal growth include mechanical, physiological, and developmental processes.     

Characteristics of patients found not to have multiple sclerosis.

Of 400 consecutive patients referred to Dalhousie University''s multiple sclerosis research unit 52 (13%) were found not to have multiple sclerosis. Forty-one (79%) of the patients were female and 11 (21%) were male. About half of the patients had raised the suspicion of multiple sclerosis, and about half had either a medical background or a close association with a patient with the disease. Although in many cases a diagnosis was made at the initial visit, in difficult cases the most effective diagnostic technique was repeated assessment of the patient over a long period. It is important to keep an open mind when assessing patients suspected of having multiple sclerosis and to apply the recognized criteria for diagnosis of the disease.     

The adverse effect of iron repletion on the course of certain infections.

The incidence of infections was studied in 137 iron-deficient Somali nomads, 67 of whom were treated with placebo and 71 with iron. Seven episodes of infection occurred in the placebo group and 36 in the group treated with iron; these 36 episodes included activation of pre-existing malaria, brucellosis, and tuberculosis. This difference suggested that host defence against these infections was better during iron deficiency than during iron repletion. Iron deficiency among Somali nomads may be part of an ecological compromise, permitting optimum co-survival of host and infecting agent.