Studies of microbial toxins in Xenopus laevis oocytes |
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Authors: | François Godeau Patrice Boquet Sabine Schorderet-Slatkine Michel Schorderet Etienne-Emile Baulieu |
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Institution: | 1. Unité de Recherches sur le Métabolisme Moléculaire et la Physio-Pathologie des Stéroides de l''Institut National de la Santé et de la Recherche Médicale, U33, Inserm, Faculté de Médecine, Université Paris Sud, 94270 Bicêtre, France;2. Institut Pasteur, 75015 Paris, France;3. Hôpital Cantonal, Gynécologie et Obstétrique, Suisse;4. Ecole de Médecine Pharmacologie, CH-1211, Genéve 4, Suisse |
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Abstract: | Xenopus laevis oocytes have been incubated or microinjected with cholera and diphtheria holotoxins or their respective isolated fragments A and B. Effects on progesterone-induced maturation, protein synthesis and cAMP levels were observed. Xenopus laevis oocytes were highly susceptible to cholera toxin upon incubation as evidenced by the increase of cAMP (two-fold increase in cAMP with 0.1 nM cholera toxin) and the blockade of progesterone-induced maturation. When isolated cholera toxin fragments A or B were incubated with oocytes, no activity could be detected. However, microinjection of cholera toxin fragment A into oocyte was able to mimic the effects of incubated holotoxin. Microinjection of cholera toxin B fragment was only effective at very high concentrations, probably due to trace contaminations by the A fragment. On the other hand, Xenopus laevis oocytes were very resistant to diphtheria toxin action upon incubation, a result attributable to lack of specific membrane receptors since, after microinjection of diphtheria toxin A fragment into oocytes, inhibition of protein synthesis was demonstrated. By simultaneous microinjection of highly radioactive adenine-labelled NAD and diphtheria toxin fragment A into oocytes, radioactive ADP ribosylation of the elongation factor 2 (EF2) was observed. It is proposed that Xenopus laevis oocytes provide a new experimental approach for studying the mechanisms of action of microbial toxins. |
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