Papers by lawrence bannister
Zeitschrift f�r Zellforschung und Mikroskopische Anatomie, 1967
The fine structure of the olfactory epithelium of the domestic duck (Anser cinereus) has been exa... more The fine structure of the olfactory epithelium of the domestic duck (Anser cinereus) has been examined and compared with the olfactory epithelium of other vertebrates, particularly the frog (Rana temporaria). In addition to the usual olfactory cilia, the terminal swellings of the olfactory receptors in the duck bear numerous short microvilli. The supporting cells of the epithelium do not secrete copious amounts of mucus as they do in the frog. The structure of the basal cells and of the glands of Bowman arc briefly described. It is concluded that the receptor microvilli could increase the free surface of a receptor dendrite by about 400 % and that microvilli and cilia together may increase it by about 1000 %. It is also concluded that as yet no phylogenetic pattern can be observed in the olfactory epithelia of various vertebrate groups.
Journal of Cell Science, 1993
Microaggregation of band 3 proteins in hereditary ovalocytic membranes was investigated by rotati... more Microaggregation of band 3 proteins in hereditary ovalocytic membranes was investigated by rotational diffusion measurements and by electron microscopy. It was previously shown that band 3 in ovalocytic membranes has decreased rotational mobility compared with band 3 in normal cells (Tilley, L., Nash, G.B., Jones, G.L. and Sawyer, W.L. (1991) J. Membr. Biol. 121, 59–66). This result could arise from either altered interactions with cytoskeletal proteins or from band 3 microaggregation. In the present study it was found that removal of spectrin and actin from the membrane had no effect on the rotational mobility of ovalocytic band 3. Additional removal of ankyrin and band 4.1, as well as cleavage of the cytoplasmic domain of band 3 with trypsin, did enhance band 3 mobility, as is the case in the membranes from normal cells. However, the rotational mobility of ovalocytic band 3 was always considerably less than that of normal band 3 under the same conditions. Scanning electron microsc...
Annals of Tropical Medicine & Parasitology, 1995
The biochemical, ultrastructural and experimental data concerning the organization and biological... more The biochemical, ultrastructural and experimental data concerning the organization and biological roles of the merozoite cytoskeleton are briefly reviewed. Actin is known to be expressed in the asexual erythrocytic stages, and has also been demonstrated in Plasmodium falciparum merozoites biochemically and visualized by fluorescence microscopy after appropriate labelling. Experimental evidence indicates that actin-myosinbased motility is important in merozoite locomotion during red-cell invasion. Microtubules also occur in P. falciparum merozoites in the form of a small longitudinal band of subpellicular microtubules, and experiments with anti-microtubule drugs indicate that microtubules are involved in some aspect of invasion. In the late-stage schizont, microtubules are also important in merozoite morphogenesis. The numbers and positions of the merozoite apices within the schizont are spatially related to the spindle poles of the final mitotic division, and extranuclear microtubules are probably responsible for the trafficking of vesicles from a single Golgi cisterna to form the apical organelles. In addition to these cytoskeletal structures, numerous short cytoskeletal filaments of unknown composition attach the merozoite plasma membrane to the underlying pellicular cisterna, and this process may drive the budding of merozoites from the parent schizont.
Bulletin of the World Health Organization, 1977
Previous observations on the process of invasion by P. knowlesi are briefly reviewed and new find... more Previous observations on the process of invasion by P. knowlesi are briefly reviewed and new findings concerning the adhesion of parasites to erythrocytes and their intracellular passage are reported. Merozoites adhere to erythrocytes by means of a well-defined coat with the cytochemical characteristics of glycoprotein. This coat has receptors that engage in at least three distinct types of attachment. The ensuing invagination of the erythrocyte surface has two phases, the first consisting of an inward buckling of the membrane to form a vacuole and the second a rapid expansion to create the final parasitophorous vacuole inhabited by the trophic parasite. Some cytochemical evidence concerning the nature of the rhoptry complex is discussed in relation to these changes.
Trends in Parasitology, 2003
The malaria parasite Plasmodium falciparum is a complex eukaryote parasite with a dynamic pattern... more The malaria parasite Plasmodium falciparum is a complex eukaryote parasite with a dynamic pattern of genomic expression, enabling it to exploit a series of different habitats in human and mosquito hosts. In the human bloodstream, the parasite grows and multiplies within red blood cells and modifies them in various ways to gain nutrients and combat the host's defences, before escaping and invading new red blood cells by a multi-step process. These events are reflected in the constantly changing structure of the organism during the red blood cell cycle.
Protist, 1999
The plastid in Plasmodium fa/ciparum asexual stages is a tubular structure measuring about 0.5 IJ... more The plastid in Plasmodium fa/ciparum asexual stages is a tubular structure measuring about 0.5 IJm x 0.15 IJm in the merozoite, and 1.6 x 0.35 IJm in trophozoites. Each parasite contains a single plastid until this organelle replicates in late schizonts. The plastid always adheres to the (single) mitochondrion, along its whole length in merozoites and early rings, but only at one end in later stages. Regions of the plastid are also closely related to the pigment vacuole, nuclear membrane and endoplasmic reticulum. In merozoites the plastid is anchored to a band of 2-3 subpellicular microtubules. Reconstructions show the plastid wall is characteristically three membranes thick, with regions of additional, complex membranes. These include inner and outer membrane complexes. The inner complex in the interior lumen is probably a rolled invagination of the plastid's inner membrane. The outer complex lies between the outer and middle wall membranes. The interior matrix contains ribosome-like granules and a network of fine branched filaments. Merozoites of P. berghei and P. knowlesi possess plastids similar in structure to those of P. fa/ciparum. A model is proposed for the transfer of membrane lipid from the plastid to other organelles in the parasite.
PLoS Pathogens, 2005
Proteolytic shedding of surface proteins during invasion by apicomplexan parasites is a widesprea... more Proteolytic shedding of surface proteins during invasion by apicomplexan parasites is a widespread phenomenon, thought to represent a mechanism by which the parasites disengage adhesin-receptor complexes in order to gain entry into their host cell. Erythrocyte invasion by merozoites of the malaria parasite Plasmodium falciparum requires the shedding of ectodomain components of two essential surface proteins, called MSP1 and AMA1. Both are released by the same merozoite surface ''sheddase,'' but the molecular identity and mode of action of this protease is unknown. Here we identify it as PfSUB2, an integral membrane subtilisin-like protease (subtilase). We show that PfSUB2 is stored in apical secretory organelles called micronemes. Upon merozoite release it is secreted onto the parasite surface and translocates to its posterior pole in an actin-dependent manner, a trafficking pattern predicted of the sheddase. Subtilase propeptides are usually selective inhibitors of their cognate protease, and the PfSUB2 propeptide is no exception; we show that recombinant PfSUB2 propeptide binds specifically to mature parasite-derived PfSUB2 and is a potent, selective inhibitor of MSP1 and AMA1 shedding, directly establishing PfSUB2 as the sheddase. PfSUB2 is a new potential target for drugs designed to prevent erythrocyte invasion by the malaria parasite.
PLoS ONE, 2008
Plasmodium falciparum Merozoite Surface Protein 1 (MSP1) is synthesized during schizogony as a 19... more Plasmodium falciparum Merozoite Surface Protein 1 (MSP1) is synthesized during schizogony as a 195-kDa precursor that is processed into four fragments on the parasite surface. Following a second proteolytic cleavage during merozoite invasion of the red blood cell, most of the protein is shed from the surface except for the C-terminal 19-kDa fragment (MSP1 19), which is still attached to the merozoite via its GPI-anchor. We have examined the fate of MSP1 19 during the parasite's subsequent intracellular development using immunochemical analysis of metabolically labeled MSP1 19 , fluorescence imaging, and immuno-electronmicroscopy. Our data show that MSP1 19 remains intact and persists to the end of the intracellular cycle. This protein is the first marker for the biogenesis of the food vacuole; it is rapidly endocytosed into small vacuoles in the ring stage, which coalesce to form the single food vacuole containing hemozoin, and persists into the discarded residual body. The food vacuole is marked by the presence of both MSP1 19 and the chloroquine resistance transporter (CRT) as components of the vacuolar membrane. Newly synthesized MSP1 is excluded from the vacuole. This behavior indicates that MSP1 19 does not simply follow a classical lysosome-like clearance pathway, instead, it may play a significant role in the biogenesis and function of the food vacuole throughout the intra-erythrocytic phase.
Parasitology, 1998
Plasmodium falciparum merozoites have an array of 2–3 subpellicular microtubules, designated f-MA... more Plasmodium falciparum merozoites have an array of 2–3 subpellicular microtubules, designated f-MAST. We have previously shown that colchicine inhibits merozoite invasion of erythrocytes, indicating a microtubular involvement in this process. Colchicine inhibition of invasion was reduced by the Taxol®-stabilization of merozoite microtubules prior to colchicine exposure. Immunofluorescence assays showed that the number and length of f-MASTs were reduced in colchicine-treated merozoites, confirming that microtubules were the target of colchicine inhibition. The dinitroaniline drugs, trifluralin and pendimethalin, were shown by immunofluorescence to depolymerize the f-MAST and both drugs were inhibitory in invasion assays. These results demonstrate that the integrity of the f-MAST is important for successful invasion. Fluorescence imaging demonstrated the alignment of mitochondria to f-MAST, suggesting that mitochondrial transport might be perturbed in merozoites with disorganized f-MAS...
Parasitology, 2004
During asexual developmentPlasmodiumschizonts undergo a series of complex biochemical and structu... more During asexual developmentPlasmodiumschizonts undergo a series of complex biochemical and structural changes. Using tightly synchronized cultures of 2P. falciparumlines (clone C10 and strain ITO4) for light microscopy and fluorescence imaging we monitored the timing and sequence of expression of proteins associated with invasion-related organelles. Antibodies to rhoptry, micronemal and dense granule proteins (Rhoptry Associated Protein 1, Apical Membrane Antigen 1, Erythrocyte Binding Antigen 175, Ring-infected Erythrocyte Surface Antigen) and to pellicle-associated proteins (Merozoite Surface Protein 1, PfMyosin-A) were used. Clone C10 developed faster than ITO4; this difference was also found in the timing of protein expression seen by immunofluorescence. Light microscopic data were combined with transmission electron microscopic analysis using serial sectioning of ITO4 schizonts to determine nuclear number and organellar development. Thus a timetable of schizont structural matura...
Parasitology, 2009
SUMMARYThe invasive blood stage of malaria parasites, merozoites, are complex entities specialize... more SUMMARYThe invasive blood stage of malaria parasites, merozoites, are complex entities specialized for the capture and entry of red blood cells. Their potential for vaccination and other anti-malaria strategies have attracted much research attention over the last 40 years, and there is now a considerable body of data relating to their biology. In this article some of the major advances over this period and remaining challenges are reviewed.
Molecular and Cellular Neuroscience, 2008
Slit proteins regulate distinct aspects of retinal ganglion cell axon guidance within dorsal and ... more Slit proteins regulate distinct aspects of retinal ganglion cell axon guidance within dorsal and ventral retina. J. Neurosci. 26, 8082-8091]. However, the roles of Slit receptors in mammals, (termed Robos), have not been investigated in visual system development. Here we examined Robo1 and 2 mutant mice and found that Robos regulate the correct targeting of retinal ganglion cell (RGC) axons along the entire visual projection. We noted aberrant projections of RGC axons into the cerebral cortex, an area not normally targeted by RGC axons. The optic chiasm was expanded along the rostro-caudal axis (similar to Slit mutant mice, Plump, A.
Journal of Comparative Neurology, 2003
The Robo family of molecules is important for axon guidance across the midline during central ner... more The Robo family of molecules is important for axon guidance across the midline during central nervous system (CNS) development in invertebrates and vertebrates. Here we describe the patterns of Robo protein expression in the developing mouse CNS from embryonic day (E) 9.5 to postnatal day (P) 4, as determined by immunohistochemical labeling with an antibody (S3) raised against a common epitope present in the Robo ectodomain of Robos 1 and 2. In the spinal cord, midline-crossing axons are initially (at E11) S3-positive. At later times, midline Robo expression disappears, but is strongly upregulated in longitudinally running postcrossing axons. It is also strongly expressed in noncrossing longitudinal axons. Differential expression of Robo along axons was also found in axons cultured from E14 spinal cord. These findings resemble those from the Drosophila ventral nerve cord and indicate that in vertebrates a low level of Robo expression occurs in the initial crossing of the midline, while a high level of expression in the postcrossing fibers prevents recrossing. Likewise, Robopositive ipsilateral axons are prevented from crossing at all. However, in the brain different rules appear to apply. Most commissural axons including those of the corpus callosum are strongly S3-positive along their whole length from their time of formation to postnatal life, but some have more complex age-dependent expression patterns. S3 labeling of the optic pathway is also complex, being initially strong in the retinal ganglion cells, optic tract, and chiasma but thereafter being lost except in a proportion of postchiasmal axons. The corticospinal tract is strongly positive throughout its course at all stages examined, including its decussation, formed at about P2 in the central part of the medulla oblongata.
Journal of Cell Science, 2003
During the assembly of Plasmodium falciparum merozoites within the schizont stage, the parasite s... more During the assembly of Plasmodium falciparum merozoites within the schizont stage, the parasite synthesizes and positions three sets of secretory vesicles (rhoptries, micronemes and dense granules) that are active during red cell invasion. There are up to 40 micronemes per merozoite, shaped like long-necked bottles, about 160 nm long and 65 nm at their widest diameter. On their external surfaces, they bear bristle-like filaments, each 3-4 nm thick and 25 nm long. Micronemes are translocated from a single Golgi-like cisterna near the nucleus along a band of two or three subpellicular microtubules to the merozoite apex, where they dock with the rhoptry tips. Dense granules are also formed around the periphery of the Golgi cisternae but their distribution is unrelated to microtubules. Three polyclonal antibodies raised against the recombinant PfAMA-1 ectodomain sequence recognizing both the 83 kDa and processed 66 kDa molecules label the peripheries of translocating and mature micronem...
Infection and Immunity, 2003
Apical membrane antigen 1 (AMA-1) of Plasmodium merozoites is established as a candidate molecule... more Apical membrane antigen 1 (AMA-1) of Plasmodium merozoites is established as a candidate molecule for inclusion in a human malaria vaccine and is strongly conserved in the genus. We have investigated its function in merozoite invasion by incubating Plasmodium knowlesi merozoites with red cells in the presence of a previously described rat monoclonal antibody (MAb R31C2) raised against an invasion-inhibitory epitope of P. knowlesi AMA-1 and then fixing the material for ultrastructural analysis. We have found that the random, initial, long-range (12 nm) contact between merozoites and red cells occurs normally in the presence of the antibody, showing that AMA-1 plays no part in this stage of attachment. Instead, inhibited merozoites fail to reorientate, so they do not bring their apices to bear on the red cell surface and do not make close junctional apical contact. We conclude that AMA-1 may be directly responsible for reorientation or that the molecule may initiate the junctional con...
European Journal of Protistology, 2003
Myosins are motor proteins which, through interaction with filamentous actin, create movement. Mu... more Myosins are motor proteins which, through interaction with filamentous actin, create movement. Multiple myosins have been identified in many of the apicomplexans, however, little is known regarding provenance over the life cycle or biological function. Six Plasmodium ...
Cell, 2007
The most virulent form of malaria is caused by waves of replication of blood stages of the protoz... more The most virulent form of malaria is caused by waves of replication of blood stages of the protozoan pathogen Plasmodium falciparum. The parasite divides within an intraerythrocytic parasitophorous vacuole until rupture of the vacuole and host-cell membranes releases merozoites that invade fresh erythrocytes to repeat the cycle. Despite the importance of merozoite egress for disease progression, none of the molecular factors involved are known. We report that, just prior to egress, an essential serine protease called PfSUB1 is discharged from previously unrecognized parasite organelles (termed exonemes) into the parasitophorous vacuole space. There, PfSUB1 mediates the proteolytic maturation of at least two essential members of another enzyme family called SERA. Pharmacological blockade of PfSUB1 inhibits egress and ablates the invasive capacity of released merozoites. Our findings reveal the presence in the malarial parasitophorous vacuole of a regulated, PfSUB1-mediated proteolytic processing event required for release of viable parasites from the host erythrocyte.
Journal of anatomy, 1992
Stimulation with alternating current at the round window causes an accelerated uptake of extracel... more Stimulation with alternating current at the round window causes an accelerated uptake of extracellular HRP by endocytotic vesicles in inner hair cells at the base of the stimulated cochlea, near the site of the electrode, but does not noticeably affect uptake into outer hair cells. After unilateral electrical stimulation, efferent endings on outer hair cells at the cochlear base show increased vesicular and endosomal labelling in both the ipsilateral and contralateral ears. It is concluded that round-window electrical stimulation increases afferent synaptic activity in inner hair cells near the electrode site, and also increases synaptic activity in OHC efferent endings, not only of the ipsilateral cochlea but also of the corresponding region of the contralateral cochlea. Rapid diffuse cytoplasmic labelling of inner and outer hair cells also occurs sporadically in both stimulated and unstimulated cochleae. However, in efferent terminals, diffuse labelling is restricted to stimulated...
Microscopy and Microanalysis, 2004
The three-dimensional structure of thePlasmodium falciparumring stage has been explored by recons... more The three-dimensional structure of thePlasmodium falciparumring stage has been explored by reconstruction from serial sections and stereoscopic examination of tilted sections. The ring-like light microscopic appearance is related to the shape and contents of the biconcave discoidal parasite at this stage, its thick perimeter containing most of the ribosomes and its thin center containing smooth membrane organelles. The shapes of rings vary between flat and curved cuplike forms. The rough endoplasmic reticulum is a branched network continuous with the nuclear envelope. Evidence for a simple Golgi complex is seen in the presence on the outer nuclear envelope of a locus of coated vesicle budding associated with a single membranous cisterna or cluster of smooth vesicles. In middle and late stage rings this complex migrates along an extension of the nuclear envelope continuous with the rough endoplasmic reticulum. Evidence is also presented for a mechanism of exporting membrane from the ...
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Papers by lawrence bannister