Electron microscopic autoradiographic and electron microscopic immunohistochemical studies on the anti-HPO antibody-producing cells

The secondary immune responses in mouse popliteal lymph nodes to horseradish peroxidase (HPO) were studied by a combination of electron microscopic autoradiography and electron microscopic immunohistochemistry in order to clarify the relationship between antibody-producing and DNA-synthesizing capacities of the plasmacytic series. The anti-HPO antibody-containing cells, which increased in number 72 h after the secondary antigenic stimulation, were mainly immunoblasts and immature plasma cells. Immunoblasts containing anti-HPO antibody incorporated [³H]thymidine more actively than did immature plasma cells containing anti-HPO antibody. In 144 h after the secondary antigenic stimulation, antibody containing cells consisted mainly of mature plasma cells and immature plasma cells. Immature plasma cells containing the anti-HPO antibody incorporated a little [³H]thymidine, but mature plasma cells containing anti-HPO antibody did not incorporate any [³H]thymidine.     

Effects of antimicrotubular agents on the fine structure of the Golgi complex in embryonic chick osteoblasts

Embryonic chick frontal bones were cultured in the presence of colchicine or vinblastine and subsequently examined by tranmission electron microscopy. In control cultures the osteoblasts showed a large Golgi complex consisting of dictyosomes arranged in a well-defined juxtanuclear area. Microtubules were particularly numerous within this Golgi area although they could be observed throughout the cytoplasm. Colchicine and vinblastine caused the disappearance of cytoplasmic microtubules, while bundles of 10 nm diameter filaments appeared more frequently. In addition, cell polarity was lost and the Golgi complex became disorganized, with the dictyosomes randomly dispersed in the cytoplasm and showing a decreased number of cisternae and an increased number of vacuoles, the latter generally lacking stainable material. Increased number of autophagosomes were also noted. These findings indicate that microtubules function in the organization of the Golgi complex in osteoblasts. In view of the well documented role of this organelle system in collagen secretion it is suggested that previously observed secretory disturbances produced by antimicrotubular drugs may be due to a defective transfer of material to the dictyosomes and/or a defect in the packaging and transport of such material away from them.     

Electron microscopic studies on mouse Leydig cells in vitro

The ultrastructure of cultured Leydig cells isolated from mice testes was studied in the early and late phases of culture. Cells were cultured in Leighton tubes on glass evaporated with carbon and covered with Formvar films. Additionally a histochemical test was carried out in order to evaluate the delta 5, 3 beta-hydroxysteroid dehydrogenase activity of Leydig cells in vitro. Levels of androgen released into the culture medium were measured by radioimmunoassay. Both the histochemical and radioimmunological analyses showed high activity of the enzyme studied and a higher androgen level in the first 4 days of culture. During culture a progressive decrease of the steroidogenic function of Leydig cells in vitro as well as some degenerational changes of the cells were observed. The ultrastructural studies showed the difference between Leydig cells in vitro and in vivo and proved the occurrence of the degenerational modifications of cells in the late phase of culture.     

Electron microscopical studies of the synapse in the developing chick spinal cord

Summary A search for synaptic strutures in the developing spinal cord of the chick has been made with the help of the electron microscope. We used as criteria of identification the presence of a) a thickening of neuronal membrane in contact with one another b) mitochondria and c) a type of vesicle usually associated with synapses. Structures fulfilling some of these requirements apear at the five day incubation stage and are clearly present at the ten day stage. Fully matured axosomatic and axo-dendritic synapses of both types appear at 16–18 days.Departmental technician for electronmicroscopy.We should like to acknowledge our gratitude to the Deutsche Forschungsgemeinschaft for their support, to Miss U. Wihlfahrt for technical assistance, Mrs. Bothe for the drawing of the diagramm, to the Welcome Trustees, London, for the loan of the Akashi microscope, and to the Volkswagenstiftung for the grant of the Siemens Elmiskop I.     

Electron microscopic studies onNosema mesnili Paillot (Microsporidia: Nosematidae) infecting the Malpighian tubules ofPieris canidia larva

Summary An entire coding region of theCDC24/CLS4 gene and its truncated derivatives were overexpressed in yeast cells under the control of theGAL1 promoter. Western blotting analysis of the yeast cell lysates showed that the CDC24/CLS4 protein (Cdc24p) was induced to reach its maximum level after 9 h incubation of the cells in galactose medium. Overexpression of Cdc24p within the cells caused the morphological change, accumulating large spherical unbudded cells which exhibited actin cytoskeleton disturbed, chitin delocalized on the cell surface, and cell viability decreased. Multiple nuclei were observed in these cells, indicating that only budding cycle but not nuclear division cycle is blocked by the overproduction of Cdc24p. In order to identify the region of Cdc24p responsible for the growth inhibition, several truncatedCDC24 genes were expressed. Surprisingly, overexpression of fragments either containing the C-terminal 76 amino acid residues or deleting the same region inhibited cellular growth. This suggests that Cdc24p contains multiple functional domains for its tasks, likely cooperating signals of bud positioning and bud timing.     

Association of the Golgi complex with the plasma membrane of amphibian embryonic cells

Summary The Golgi complexes of early embryonic cells fromXenopus laevis have been examined. The predominant location for this organelle in this cell is subjacent to the plasma membrane. This observation is discussed in relation to the probable role of the Golgi complex in surface formation.     

Epicardial formation in embryonic chick heart: computer-aided reconstruction, scanning, and transmission electron microscopic studies

Epicardial formation in the embryonic chick heart from initial to final stages was revealed by means of computer-aided reconstructions based on serial resin sections for light microscopy, with further detailed observations using scanning and transmission electron microscopy. The origin of the epicardium was recognized as protrusions of mesothelial cell clusters on the right side of the external surface of the sinus venosus at 23 somites (stage 14+). These protrusions elongated to give rise to several villous processes, the tips of which eventually touched the dorsal wall of the embryonic heart at 30 somites (stage 17). Originating from these adhesion sites, mesothelial cells spread gradually onto myocardial cells in all directions to form a monolayered sheetlike cover. Thus, by stage 23, the ventricle was completely overlaid with epicardium, and blood-island-like structures appeared within the subepicardial layer. The atrium was not enveloped by epicardium until stage 25, and the extreme distal end of the bulbus cordis was reached by the advancing epicardium at stage 27. A chronological table of epicardial formation in the chick heart is presented.     

Electron microscopic studies on chromatin loop of rat ascites hepatoma cells

Isolated nuclei from rat ascites hepatoma cells were treated with 0.09% detergent Joy and chromatin, protruded from the nucleus, was observed with an electron microscope. It was demonstrated that most, but not all of the protruded chromatin fibers had a loop structure. The protrusion of chromatin from the nucleus was 3 microns in average length. A high magnification view showed that the protruded chromatin consisted mainly of beaded nucleosomal fiber. Therefore, the chromatin loop size at the level of nucleosomal fiber was estimated to be at least 6 microns in length.