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PubMed1983

Characterization of the spreading process in human T lymphocytes.

Substratum-bound concanavalin A (conA) caused attachment and spreading of human T lymphocytes identified by monoclonal anti-T cell antibodies and sheep erythrocyte rosette formation. The simultaneous presence of conA in the medium increased the spreading, whereas preincubation of the cells with conA inhibited spreading. The tendency of conA to induce spreading was dependent on the concentration used, the higher the conA concentration the more pronounced was the spreading. For example, conA at 10 micrograms ml-1 triggered the formation of prominent substratum-attached filopodia with a length of 1-10 micron in 60-80% of T-enriched lymphocytes obtained from separate individuals. At the same conA dose the filopodia were, in 10-20% of the lymphocytes, accompanied by development of lamellipodia. With conA at 100 micrograms ml-1 the number of cells that underwent pronounced spreading was 55-90% in separate individuals. Observation of T-enriched cells fixed at different times after initiation of spreading induced by conA at 100 micrograms ml-1 indicated that filopodia formation represented the initial morphological alteration during the spreading process. This process thereafter proceeded with development of lamellipodia, extensive cytoplasmic spreading and flattening of the central cell mass. Quiescent and mitogen-activated cells exhibited the same sequence of changes during spreading. Spreading led to disappearance of the microvilli with a length of 0.1-0.7 micron present on lymphocytes in suspension, although some microvilli persisted over the cell center.

Cell Movement↗
PubMed1985

F-actin rings are associated with the ring canals of the Drosophila egg chamber.

Staining of Drosophila egg chambers with rhodaminyl-lysine-phallotoxin (RLP), a specific stain for F-actin, has demonstrated the presence of dense F-actin rings associated with the inner surfaces of the ring canals. They were first observed in the distal part of the germarium where rings of four different size classes were found, differing in diameter by up to twofold. The ring sizes are considered to correspond to the ring canals formed at each of four successive incomplete cleavages. During the growth of the egg chamber the actin rings were found to increase in diameter from less than 1 micron to approx. 10 micron. Concomitantly a secondary outer ring of more diffuse material is built up in association with the cell membranes. A well developed array of microfilament bundles was also associated with the nurse cell plasmalemma. In stages where the transfer of the bulk of the nurse cell cytoplasm into the oocyte was occurring the rings came closer together in a central area. In late stage chambers the F-actin rings and the microfilament bundles appeared to be incorporated into large irregular masses of actin, which subsequently disappeared as the mature oocyte formed. The F-actin rings are suggested to act as mechanical strengthening elements for the canal plasmalemma, whilst cytoplasmic transport occurs through the ring canals.

Actins↗