Identification of proteins associated with microtubule-organizing centres and filaments in the oral apparatus of the ciliate Paramecium tetraurelia

Abstract

ABSTRACT In an effort to study the assembly of microtubules in ciliates we have isolated the oral apparatus of Paramecium tetraurelia, a major microtubule-organizing centre (MTOC) and identified several proteins localized in the fibrillar system associated with basal bodies. Using a monoclonal antibody raised against human centrosomes (CTR210) and a polyclonal antibody (OF1) directed against a 87×10-3Mr protein of the oral apparatus of Tetrahymena, we observed the same decoration of the oral apparatus of Paramecium, both in situ and after isolation. Ultrastructural localization further showed the presence of the antigens in the fibrillar network that forms a layer under almost all the buccal cavity in close apposition to the basal bodies. CTR210 recognized two sets of polypeptides of Mr72 and 80×103, whereas OF1 recognized a single polypeptide of 80×103. Only the 80×103Mr polypeptide was also decorated with the monoclonal antibody MPM-2, previously shown to decorate the oral apparatus of Paramecium and known to react with phosphorylated epitopes in a large variety of MTOCs. All the proteins identified with the three antibodies are insoluble at high ionic strength, display several isoforms and apparently belong to the same fibrillar material. The function of this material in the spatial organization, the structure, and activity of the MTOCs is discussed.