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S Doxsey

Publications and source records attributed to S Doxsey.

12 recordsLinked to original sources
PubMed2001

Re-evaluating centrosome function.

Over the past 100 years, the centrosome has risen in status from an enigmatic organelle, located at the focus of microtubules, to a key player in cell-cycle progression and cellular control. A growing body of evidence indicates that centrosomes might not be essential for spindle assembly, whereas recent data indicate that they might be important for initiating S phase and completing cytokinesis. Molecules that regulate centrosome duplication have been identified, and the expanding list of intriguing centrosome-anchored activities, the functions of which have yet to be determined, promises continued discovery.

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PubMed1999

Centrosome proteins: a major class of autoantigens in scleroderma.

Autoantibodies to intracellular antigens are a hallmark of autoimmune diseases, although their role in disease pathogenesis is unclear. Centrosomes are organelles involved in the organization of the mitotic spindle and they are targets of autoantibodies in systemic sclerosis (SSc). We used recombinant centrosome autoantigens, centrosome-specific antibodies, and immunoassays to demonstrate that a significant proportion of SSc patients exhibited centrosome reactivity. Two centrosome proteins cloned in our laboratory were used to screen 129 SSc sera by Western blotting. The same sera were screened by immunofluorescence using centrosome-specific antibodies to distinguish centrosomes from nuclear speckles commonly stained by SSc sera. Using these criteria, 42.6% of SSc patients were autoreactive to centrosomes, a larger percentage than reacted with all other known SSc autoantigens. Most centrosome-positive sera reacted with both centrosome proteins and half were negative for other routinely assayed SSc autoantibodies. By these criteria, we have identified a novel class of SSc autoreactivity. Only a small percentage of normal individuals and patients with other connective tissue diseases had centrosome reactivity. These results demonstrate that centrosome autoantibodies are a major component of autoreactivity in SSc and thus have potential in disease diagnosis. Centrosome autoantigens may be useful in studying the development of autoantibodies and chronic inflammation in SSc and perhaps other autoimmune diseases.

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PubMed1998

Functional analysis of Tpr: identification of nuclear pore complex association and nuclear localization domains and a role in mRNA export.

Tpr is a 270-kD coiled-coil protein localized to intranuclear filaments of the nuclear pore complex (NPC). The mechanism by which Tpr contributes to the structure and function of the nuclear pore is currently unknown. To gain insight into Tpr function, we expressed the full-length protein and several subdomains in mammalian cell lines and examined their effects on nuclear pore function. Through this analysis, we identified an NH2-terminal domain that was sufficient for association with the nucleoplasmic aspect of the NPC. In addition, we unexpectedly found that the acidic COOH terminus was efficiently transported into the nuclear interior, an event that was apparently mediated by a putative nuclear localization sequence. Ectopic expression of the full-length Tpr caused a dramatic accumulation of poly(A)+ RNA within the nucleus. Similar results were observed with domains that localized to the NPC and the nuclear interior. In contrast, expression of these proteins did not appear to affect nuclear import. These data are consistent with a model in which Tpr is tethered to intranuclear filaments of the NPC by its coiled coil domain leaving the acidic COOH terminus free to interact with soluble transport factors and mediate export of macromolecules from the nucleus.

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PubMed1984

Blast transformation of adherent macrophages infected in vitro with sporozoites of Theileria parva.

Rhipicephalus appendiculatus ticks were fed on cows with parasitemia from Theileria parva infection (East Coast fever). Homogenates of salivary glands with infective sporozoites were added to cultures of (i) monocyte-derived adherent macrophages from normal bovine peripheral blood and (ii) macrophages from spleen and bone marrow. It was shown by light, phase-contrast, and electron microscopies and by tests for lysosomal enzymes, phagocytosis of carbon particles, and cell markers (fibronectin and Fc receptors) that macrophages transformed in vitro to blast cells containing macroschizonts in 2 to 3 weeks. These blasts detached from the monolayer and grew indefinitely in suspension culture.

Animals↗
PubMed1982

Salivary gland of the tick vector of East Coast fever. III. The ultrastructure of sporogony in Theileria parva.

Sporogony of the sporozoan Theileria parva in the salivary gland of the tick vector of East Coast fever was studied in electron micrographs. The findings differ in several respects from previous interpretations based upon light microscopy. Cytokinesis of the primary sporoblast to form secondary and tertiary sporoblasts is not substantiated. Instead it is suggested that the parasite develops as a ramifying, multinucleate syncytium rapidly increasing in size and complexity until it gives rise to myriad sporozoites in a terminal episode of cytoplasmic fission. The proliferating nuclei initially occupy peripheral lobules that are continuous with a central labyrinth of branching and anastomosing processes which present a very large surface area for interchange of metabolites with the host cell cytoplasm. The membrane of the labyrinth is rich in cytostomes, but no evidence if found to bulk uptake of host cytoplasmic matrix or organelles into food vacuoles. Rhoptries are the first of the polar organelles of the parasite to develop and are associated with dense plaques irregularly distributed on the inner aspect of the parasite membrane. Micronemes form independently of the rhoptries at a later stage. After 3-4 days of tick feeding, sporogeny is complete and the infected salivary gland cell contains up to 50, 000 spherical or ovoid sporozoites about 1 micrometer in diameter. These are limited by a simple plasma membrane. The inner layer of the 'pellicle', the polar ring, and the conoid described for zoites of other Apicomplexa are lacking. Maturational changes are noted in sporozoites after sporogony is completed. Micronemes appear to increase in size, and possibly in number, from days 3-5 and the majority take up positions immediately subjacent to the plasmalemma.

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PubMed1982

Salivary gland of the tick vector of East Coast fever. IV. Cell type selectivity and host cell responses to Theileria parva.

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000-50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.

Animals↗
PubMed1982

The entry of sporozoites of Theileria parva into bovine lymphocytes in vitro. Electron microscopic observations.

The entry of sporozoites of Theileria parva into bovine lymphoid cells in vitro was studied with the electron microscope. Endocytosis is completed in less than 10 min. No local mobilization of actin or other cytoskeletal elements is detected in the cytoplasm of the cell being invaded and no engulfing pseudopods are formed. At the site of initial contact, the membranes of parasite and host cell come into very close apposition. As the zippering up of the membranes spreads laterally, the sporozoite sinks into a progressively deepening recess in the surface of the host cell until the rim of the invagination closes and fuses over the parasite. The observation that sporozoites are interiorized at 1-2 degrees C as well as at 37 degrees C suggests that endocytosis depends mainly upon a ligand-receptor interaction of the parasite and host cell membranes and requires little energy. Sporozoites may enter in any orientation, unlike other sporozoan parasites in which the membrane overlying an apical complex is invariably the site of attachment. 24 h after entry, the sporozoite is located in the Golgi region and the investing host cell membrane acquired during endocytosis has disappeared. The Golgi complex has been activated to form small lysosomes which gather around the parasite but are ineffective for lack of a membrane which they can fuse. It is suggested that removal of the investing host-cell membrane permits the parasite to evade destruction by the phagolysosomal system of the host cell. Persistence of micronemes after entry of the sporozoite and their subsequent disappearances invites the speculation that these parasite organelles may play a role in dispersal of the invaginated host cell membrane.

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PubMed1981

Salivary gland of the tick vector (R. appendiculatus) of East Coast fever. I. Ultrastructure of the type III acinus.

The brown ear tick Rhipicephalus appendiculatus is the vector for East Coast fever, a disease that seriously limits livestock production in East Africa. The sporozoites of the infectious agent Theileria parva develop in the tick salivary gland. This paper describes the organization of the type III acinus of the gland and establishes unambiguous ultrastructural criteria for identification of the three secretory cell types: the d-cell, e-cell and f-cell. These observations are basic to exploration of possible cell-type specificity of the invading theileria and other aspects of host-parasite relations.

Animals↗
PubMed1981

Salivary gland of the tick vector (R. appendiculatus) of East Coast fever. II. Cellular basis for fluid secretion in the type III acinus.

Fluid balance is a major physiological problem for hematophagous ticks. To maintain osmotic balance they must conserve water for prolonged periods while seeking a mammalian host, and they must eliminate a very large volume of excess fluid taken in during a relatively short period of feeding. This is accomplished in part by modification of the salivary gland during 7-10 days of feeding to secrete a copious saliva which is pumped into the bovine host. This function has previously been attributed to certain interstitial epithelial cells of the type III acinus which differentiate in the course of feeding into cells reminiscent of those of the avian salt gland. The ultrastructural changes in the type III acinus during the blood-meal were studied. In addition to the differentiation of the interstitial cells, this paper describes a remarkable sequence of changes in external form and internal organization of the e-cells. This results in their transformation from typical protein-secreting glandular cells to transport cells having myriad basolateral processes interdigitating with those of the ablumenal interstitial cells to form a basal labyrinth comparable to that of other fluid-transporting epithelia. The findings are discussed in relation to various postulated mechanisms for fluid and electrolyte transport.

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