PubMed Health⌕ Search

Biomedical subjects

R M Warn

Publications and source records attributed to R M Warn.

40 records · Page 3Linked to original sources
PubMed1984

Distribution of F-actin during cleavage of the Drosophila syncytial blastoderm.

The process of cleavage during the syncytial blastoderm stage of the Drosophila embryo was studied in fixed whole-mounts using a triple-staining technique. Plasmalemma was stained with Concanavalin A conjugated to tetramethylrhodamine isothiocyanate, the underlying cortical F-actin with a fluorescein derivative of phalloidin, and nuclei with 4',-6 diamidine-2-phenylindole dihydrochloride. The surface caps, which overlie the superficial nuclei at this stage, were found to be rich in F-actin as compared with the rest of the cortex. After the caps formed, they extended over the surface and flattened. Whilst this was occurring the F-actin network within the caps became more diffuse. By the end of the expansion process F-actin had become concentrated at both poles of the caps. The caps then split in two. The cleavage was not accompanied by the formation of any apparent contractile ring of microfilaments across the cap, rather the break region was depleted in F-actin. The cortical actin associated with each half of the old cap then became reorganized around a nucleus to form a new daughter cap, and the cycle began again.

Actins↗
PubMed1983

F-actin distribution during the cellularization of the Drosophila embryo visualized with FL-phalloidin.

The changing distribution of polymerized actin during the cellularization of the Drosophila blastoderm was investigated in fixed whole embryos using FL-phalloidin as a specific stain. Prior incubation of FL-phalloidin with F-actin from both rabbit and locust muscle blocked the staining action, whereas G-actin at the same concentration had no effect. At the initiation of cellularization bands of F-actin filaments, shaped into rough hexagons, were found around each forming cell close to the surface bulges. These bands interlinked across the whole embryo. Above the level of the hexagons was a fine meshwork of F-actin associated with many folds of the plasmalemma. Below the hexagons was a layer of small irregular actin aggregates. During the process of cellularization the hexagonal actin network was associated with the tips of the extending plasmalemmas until the cells reached their full length. It is suggested that this actin network acts as a contractile ring system which cleaves the embryo into cells. The network was then found to rapidly break down. Microfilament bundles formed rings associated with the bases of the cells. These are presumed to cleave off the fully formed cells from the underlying yolk sac. During the first phase of cell membrane growth the fine F-actin meshwork remained associated with the apical plasmalemmas. However, the mesh rapidly disappeared during the second period of extension. After this, actin aggregates were visible close to the apical surfaces of the cells. F-actin was also observed to be associated with the newly formed plasmalemmas along their length during the whole of the process of cleavage.

Actins↗
PubMed1980

Changes in the distribution of cortical myosin during the cellularization of the Drosophila embryo.

Changes in the distribution of myosin during the formation of the cellular blastoderm of Drosophila melanogaster were followed by staining sections of embryos with antibodies to myosin. These were visualized with indirect immunofluorescence. Prior to the start of cell membrane extension myosin is distributed between the nuclear caps as a thin sub-plasmalemma layer. There is also myosin present beneath the surface of the caps. When plasmalemma growth occurs, myosin is associated with the furrow canals, the tips of the advancing membranes. The fluorescence is distributed in an approximately hexagonal pattern around the growth points of each cell. The hexagons are joined up forming a network. It is suggested that this myosin is associated with bundles of microfilaments, orientated parallel to the surface, to form many interlocking contractile rings. The simultaneous contraction of these rings causes the cleavage of the blastoderm. During the first phase of membrane growth, myosin is also associated with the apical surfaces of the forming cells. At this stage these surfaces are rich in microvilli. However, by the time the furrow canals have reached the bases of the cells much of this myosin has disappeared. At about this time the apical surface becomes taut with a loss of the microvilli.

Animals↗