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The influence of antibodies to gangliosides of sea urchin Strongylocetltrotus intermedius eggs on early embryos of this species was studied. γ-Globulins were isolated from rabbit anti-ganglioside serum by micropreparative electrophoresis. These γ-globulins produced anomalies in the development of embryos permeabilized in Triton X-100. The anomalies were not observed when anti-ganglioside γ-globulins were added to the incubation medium together with gangliosides or when the permeabilized embryos were incubated with γ-globulins of normal rabbit serum. Pretreatment of S. intermedius embryos with serotonin, tryptamine or some other indole derivatives led to the disappearance of ganglioside determinants from the cell surface and sharply increased immunofluorescence within the cell. Such pretreatment of embryos increased the amount of cell-associated gangliosides more than threefold as compared to untreated embryos. Serotonin was shown to bind specifically to sea urchin gangliosides immobilized on octyl-Sepharose. These observations suggest that cell-surface gangliosides, after binding drugs, are internalized and that serotonin and its antagonists inhibit the transport of newly synthesized gangliosides to the cell-surface membrane. [ABSTRACT FROM AUTHOR]

From eggs and embryos of the sea urchin Strongylocentrotus intermedius two gangliosides, provisionally named G-1 and G-2, were isolated in the pure state. Both gangliosides contained glucose, N-glycoloylneuraminic acid and sphingosines in a 2:2:1 ratio; G-2 contained also a sulfate group, and yielded 0-1 on desulfation. By periodate oxidation/borohydride reduction, permethylation analysis, neuraminidase degradation, analysis of the aldohexitol acetates and mass-spectrometry G-1 and G-2 were shown to have hitherto unknown structures: 0-1 was identified as N-glycoloylneuraminosyl-(x2→6)-glucosyl-(1→8)-N-glycoloylneuramiuosyl-(2→6)-glucosyl- (1→1)-ceramide. and (3-2 as sulfated G-1, carrying a sulfate ester group at C-8 of the terminal sialic acid. Antisera against the two gangliosides were prepared in rabbits by immunization with ganglioside 0-1 or 0-2. The specificity of the antisera was revealed by immunoelectrophoresis and immunodiffusion. The antisera did not react with bovine-brain and rat-liver gangliosides, with glucosylceramide and with various hydrolytic fragments of CH-1 and G-2. The surface localization of the gangliosides in embryos incubated at different cell densities was studied by immunofluorescence microscopy. The intensity of the immunofluorescence was found to increase with decreasing cell density, indicating a different surface organization in sparse and dense embryos. In the sparse embryos immunofluorescence was seen mainly in the contact regions between the blastomers. [ABSTRACT FROM AUTHOR]

Recent data has extended a large array of melatonin functions by the discovery of melatonin's involvement in the organization and regulation of the rhythm of intracellular protein synthesis. An ultradian rhythm in total protein synthesis has been detected in primary hepatocyte cultures 5 min after addition of 1-5 nM melatonin to the medium. The melatonin effect was mediated via its receptors (as shown in experiments with luzindole), leading to the cell synchronization as well as the mean rate of protein synthesis rate being increased. The chain of processes synchronizing the oscillation of the rate protein synthesis throughout the hepatocyte population includes Ca²+ fluxes {experiments with BAPTA-AM [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetomethyl ester)]}. Inhibition of protein kinase activity (experiments with H7) inhibited the synchronizing function of melatonin. Activation of protein kinase activity results in a shift of the protein synthesis oscillation; the effect was the same as melatonin added to the culture medium. In another series of experiments, after melatonin was intraperitoneally injected to rat (0.015-0.020 μg/kg), hepatocytes were isolated and cultures established. A synchronizing effect of melatonin in vivo was detected as early as in the estimates from the direct action of melatonin on cell cultures. In the cultures obtained from old rats provided with melatonin, the amplitude of protein synthesis rhythm was enhanced, i.e. cell-cell interactions were increased, as well as rate of the protein synthesis being enhanced.