Location of actin, myosin, and microtubular structures during directed locomotion of Dictyostelium amebae.

During their life cycle, amebae of the cellular slime mould Dictyostelium discoideum aggregate to form multicellular structures in which differentiation takes place. Aggregation depends upon the release of chemotactic signals of 3',5'-cAMP from aggregation centers. In response to the signals, aggregating amebae elongate, actively more toward the attractive source, and may be easily identified from the other cells because of their polarized appearance. To examine the role of cytoskeletal components during ameboid locomotion, immunofluorescence microscopy with antibodies to actin, myosin, and to a microtubule-associated component was used. In addition, rhodamine-labeled phallotoxin was employed. Actin and myosin display a rather uniform distribution in rounded unstretched cells. In polarized locomoting cells, actin fluorescence (due to both labeled phallotoxin and specific antibody) is prevalently concentrated in the anterior pseudopod while myosin fluorescence appears to be excluded from the pseudopod. Similarly, microtubules in locomoting cells are excluded from the leading pseudopod. The cell nucleus is attached to the microtubule network by way of a nucleus-associated organelle serving as a microtubule-organizing center and seems to be maintained in a rather fixed position by the microtubules. These findings, together with available morphological and biochemical evidences, are consistent with a mechanism in which polymerized actin is moved into the pseudopod through its interaction with myosin at the base of the pseudopod. Microtubules, apparently, do not actively participate in movement but seem to behave as anchorage structures for the nucleus and possibly other cytoplasmic organelles.

Usefulness and potential pitfalls of sialic acid determination in sera of patients with ovarian tumors.

Increasing evidence in the literature indicates that serum sialic acid is increased in cancer patients suggesting a possible usefulness of its determination as a tumor marker. However there are many discrepancies in the data reported, probably due to methodological errors, mainly in lipid bound sialic measurement. In this paper we illustrate the results obtained when we applied a method worked out in our laboratory for the determination of total and fractionated sialic acid (lipid and protein bound) to the analysis of sera from patients with ovarian tumors and the preliminary data on the follow up of selected cases. The potential pitfalls in using this relatively new tumor marker will be critically evaluated.

Differentiation without mitosis in Dictyostelium discoideum.

Dictyoselium discoideum Ax-2 amoebae incubated in the presence of the microtubule inhibitor nocodazole, irreversibly lost their ability to multiply. Nocodazole-treated cells remained viable and RNA and protein synthesis continued for at least 48 h. When nocodazole-treated amoebae were allowed to develop on Millipore filters or on agar slides they differentiated with some delay when compared with controls. These results show that mitosis, naturally present during the developmental cycle of Dictyostelium discoideum Ax-2, is not indispensible for differentiation.

Cybrids and heterokaryons PEG-induced between D. discoideum amoebae and mouse fibroblasts.

Optimal conditions for fusion of Dictyostelium discoideum amoebae with mouse fibroblasts using polyethylene glycol (PEG) are described. Three different kinds of experiments were done to look for the ways to obtain new cell lines heterokaryons or cybrids. In all cases, the final products of the fusion were cells showing new features, still viable for at least one week. To detect the cell membrane fusion, samples were observed by scanning electron microscope (SEM).

Evidence of abnormal differentiation of Paracentrotus lividus fertilized eggs contamined by zincethylenebisdithiocarbamate.

Embryos of the Sea Urchin Paracentrotus lividus were incubated for different periods of time in various concentrations of Zinc-ethylenebisdithiocarbamate (ZINEB) in artificial (or natural) sea water. Dramatic developmental modifications have been observed after 48 hour treatment with 0.4 ug/ml ZINEB solution. The abnormalities concern the formation of spiculae.

Possible involvement of nuclei in cadmium-induced modifications of cultured cells.

Reduced metaphase number and shortening of metaphase chromosomes were detected in McCoy cells exposed to 100 microM CdSO4 (maximal exposure time: 7 h). One hour exposure to 109Cd was enough to label the cell nucleus. This possibly suggests an early nuclear involvement in Cd-induced cell damage.