Search PubMed⌕ Search

Biomedical subjects

T M Preston

Publications and source records attributed to T M Preston.

At least 19 recordsLinked to original sources
PubMed2001

Locomotion and feeding of Acanthamoeba at the water-air interface of ponds.

Acanthamoeba trophozoites attach to and effect amoeboid locomotion at the water-air interface of ponds. Their locomotory rate (approximately 0.8 microm s(-1)) and manner of independent movement at this interface is similar to that over solid substrata. Adhesion forces developed between amoebae and the water-air interface are greater than gravity and thus amoebae are also transported passively without detachment. Amoebae docked with the water-air interface remain and flourish here as they are shown, by using green fluorescent protein-labelled Aeromonas hydrophila, to feed on bacteria that occur at the interface, digesting them intracellularly.

Acanthamoeba↗
PubMed1993

Purification of an agglutinin from the haemolymph of the snail Bulinus nasutus and demonstration of related proteins in other Bulinus spp.

The snail Bulinus nasutus 1214 possesses a potent haemagglutinin (end-point titre with human erythrocytes, 2(-18)) in its cell-free haemolymph which also binds to the miracidia (but not other larvae) of the incompatible parasite Schistosoma margrebowiei. We have purified a protein possessing this haemagglutinating property from the plasma of this snail. The native Mr of this protein was estimated by SDS polyacrylamide gel electrophoresis to be 210 kDa; under denaturing conditions in a 7.5% PAGE gel it ran as a major band of 135 kDa. Proteins of similar Mr were also found in the haemolymph of 16 other Bulinus spp. (the major intermediate hosts of human and veterinary schistosomiasis in Africa) although the plasma of none of these agglutinated human erythrocytes. Nonetheless, Cleveland mapping of the Mr 135 kDa bands from these different Bulinus spp. revealed 4 identical major peptide fragments (30, 28, 19 and 16 kDa) in each, thus demonstrating a similarity in the primary structure of these plasma proteins. Antisera from Balb/C mice immunized with the 135 kDa polypeptide from Bulinus truncatus 1521 cross-reacted in Western blots with the 135 kDa band of other members of the same truncatus/tropicus species complex but not with species from the africanus or forskalii species groups.

Animals↗
PubMed1992

Evidence for the expression of actomyosin in the infective stage of the sporozoan protist Eimeria.

A high-speed supernatant extract was obtained from infective oocysts of Eimeria tenella homogenised in a sucrose-low ionic strength buffer. Immunoblotting showed this soluble, micropore-filtered preparation (designated E1) to be rich in actin. E1 underwent superprecipitation on addition of ATP but not its non-hydrolysable analogue AMP.PMP--behaviour typical of an actomyosin solution. The superprecipitate fluoresced strongly in the presence of rhodamine-phalloidin (indicative of the presence of F-actin) and electron microscopy of negatively-stained preparations of this flocculent matter confirmed the abundance of filamentous material within it. This is the first demonstration of a functional actomyosin isolated from a member of the economically important phylum Apicomplexa.

Actins↗
PubMed1992

The in vitro transformation of the miracidium to the mother sporocyst of Schistosoma margrebowiei; changes in the parasite surface and implications for interactions with snail plasma factors.

The in vitro transformation of the miracidium to the mother sporocyst of Schistosoma margrebowiei was initiated by placing the miracidium in mammalian physiological saline. The transformation occurs in stages: the cilia cease beating; the ciliated plates become detached from the intercellular ridges and underlying muscle layers; the intercellular ridges spread over the body surface eventually forming a new tegument; the sporocyst changes from an ovoid to a tubular shape in about 48 h at room temperature. The surfaces of the miracidium, sporocyst and cercaria of S. margrebowiei display stage-specific carbohydrates on their surfaces as indicated by lectin staining. Ricin120 stains the cilia alone of the miracidium whereas peanut agglutinin stains the larval surface except for the cilia. The intercellular ridges of the miracidium stain with concanavalin A and wheat germ agglutinin, and these lectins stain the entire surface of the mature mother sporocyst. The cercaria is the only larval stage which stains positively with asparagus pea lectin. Bulinus nasutus is incompatible with Schistosoma margrebowiei; the haemolymph of this snail contains an agglutinin which agglutinates a wide variety of mammalian erythrocytes including those of human ABO blood groups. The haemagglutinin titre of B. nasutus plasma is reduced after incubation with miracidia of S. margrebowiei indicating that the agglutinin is absorbed onto the surface of this larval stage but not that of the mother sporocyst or cercaria. The possible roles of agglutinins in host-parasite interactions together with the significance of the differences in the surface carbohydrates of the larval stages are discussed.

Adsorption↗
PubMed1987

Effect of disruption of plasmatocyte microfilaments on encapsulation in vitro.

Very little is known about the functional basis of plasmatocyte motile behaviour. In this study we documented the effects of cytochalasin B (CB) on the cytoskeletal organisation and behaviour of plasmatocytes during spreading on a planar surface in vitro, and during in vitro encapsulation. CB produced a reversible and dose-dependent effect on the rate of plasmatocyte spreading. Moreover, incubation of fully spread plasmatocytes in CB caused their microfilaments to coalesce and the cells to arborise and eventually revert to the less adhesive spindle-shaped morphology characteristic of free plasmatocytes in circulation. The use of cytochalasins B and D on haemocytes encapsulating cotton fibre loops in vitro resulted in the development of abnormally flocculent capsules. The data demonstrate the importance of microfilament-dependent PL motility, both during the secondary "compaction phase" of encapsulation and in the laboratory manifestation of this process, spreading on a planar substratum.

Actin Cytoskeleton↗
PubMed1985

A prominent microtubule cytoskeleton in Acanthamoeba.

A method for preparing by detergent extraction the cytoskeletons of substrate-attached, motile Acanthamoeba castellanii is described. A monoclonal antibody to yeast alpha tubulin has been used to demonstrate the presence of abundant microtubules in the cytoskeleton of this amoeba by fluorescence and whole-mount electron microscopy. Individual microtubules, often more than 10 micron long, interweave to form a well-developed 3-D network pervading the cytoplasm and embracing the nucleus. In some cases immunofluorescent staining reveals distinct nodes in the perinuclear region of this microtubular network.

Amoeba↗
PubMed1984

Amoeboid locomotion of Acanthamoeba castellanii with special reference to cell-substratum interactions.

The amoeboid locomotion of Acanthamoeba castellanii has been studied by observation of individual cells moving on a planar glass substratum. Cell-substratum interactions involved in traction have been observed by reflexion interference microscopy. A variable part of the ventral surface of A. castellanii formed a protean platform, the 'associated contact', from which filopodia were subtended; these established stable, focal adhesions (approximately 0.4 micron diameter) on the substratum beneath. Surprisingly, acanthopodia, a prominent feature of this protozoon, did not play an obvious role in traction. The dimensions of the cell-substratum gap in the associated contact could be modulated by the concentration of ambient electrolyte. Dilution of electrolyte from 50 mM-KC1 to 2mM resulted in (i) an increase in the cell-substratum gap, (ii) a marked decrease in cell motility, (iii) reduced cell adhesion to glass.

Adhesiveness↗
PubMed1983

Cell-substrate interactions in amoeboid locomotion - a matched reflexion interference and transmission electron microscopy study.

Cell-substrate separation distance were measured on Naegleria gruberi amoebae moving in deionized H2O on an untreated glass substratum (weakly adhesive) and on a polylysine treated glass surface (strongly adhesive). The values obtained by transmission electron microscopy on fixed cells and reflexion interference microscopy on live cells were in broad agreement.

Amoeba↗
PubMed1978

An experimental study of the interaction between the soil amoeba Naegleria gruberi and a glass substrate during amoeboid locomotion.

The amoeboid locomotion of the soil protozoon Naegleria gruberi has been studied using reflexion-interference microscopy. Two types of contact are made with a planar glass substrate. One, formed at a considerable distance from the substrate in deionized water (congruent to 100 nm) has been termed 'associated contact' and usually involves a considerable surface area (of the order of 100 micrometer2), i.e. about a third of the cell profile. From this broad platform filopodia are produced which form close contacts ('focal contacts'). In locomotion the area of associated contact is very mobile, in contrast to the focal contacts which, once established, are stable. Focal contact sites are left behind on the glass surface ('footprints') when the amoeba moves away. The cell-substrate gap in the associated contact is greatly affected by the ionic strength of the medium and particularly the valency of the cation component. This suggests that long-range forces of attraction play an important role in keeping the amoeba close to a substrate and thus allow the production of filopodia from the ventral surface to form focal contacts.

Amoeba↗
PubMed1977

Studies of anionic sites on the cell surface of the amoeba Naegleria gruberi using cationized ferritin.

Interaction of cationized ferritin with the anionic groups on the cell surface of Naegleria was studied using transmission electron microscopy in conjunction with fluorescence microscopy. Most of the experiments involved the use of fluorescein-labelled cationized ferritin (FITC-CF) incubated with living amoebae. Initially the FITC-CF was located over the posterior two-thirds of the amoebae but the label was rapidly redistributed to form a cap at the posterior end in the region of the uroid; frequently this cap was shed. Pinosomes containing FITC-CF were clearly visible within the amoebae. Amoebae prefixed in glutaraldehyde were uniformly stained and did not show redistribution of the label. Exposure of live amoebae, previously incubated with cationized ferritin and allowed to cap, to fresh FITC-CF failed to produce fluorescent staining of the general cell surface, i.e. depletion of binding sites had occurred. The binding of the FITC-CF was not affected by pretreatment of the amoebae with neuraminidase or pronase. The possible nature of the anionic sites on the membrane is discussed.

Amoeba↗