Localization of γ-tubulin in the mitotic and meiotic nuclei of Euplotes octocarinatus

Summary Several polyclonal antibodies raised against distinct γ-tubulin sequences previously showed the presence of γ-tubulin in the cortical MTOCs (basal bodies of dorsal cilia, cirri and membranelles) and also in the micronucleus [21]. In using one of these antibodies during the successive stages of conjugation, we analysed by immunofluorescence the precise dynamics of the localization of γ-tubulin in the intranuclear mitotic and meiotic nuclei, whose spindle, like in other ciliates, is assembled without visible polar structures. The interphase micronucleus exhibits a spotted distribution of γ-tubulin. In prophase, the labeling is weaker than in interphase, but remains punctate. When the chromatin condense during metaphase, the γ-tubulin exhibits a longitudinal distribution similar to the chromatin repartition. At the end of metaphase and beginning of anaphase, this labeling condenses into an equatorial region, between the two migrating clusters of chromosomes. This equatorial labeling becomes thinner until it disappears in late anaphase A. At this time, both extremities of the spindle are strongly labeled. Finally, in telophase the two daughter nuclei already show the spotted interphase labeling, while a relocalization of γ-tubulin results in a strong decoration at the level of the intermediate portion of the long spindle that separates the two nuclei. We also report the detection of γ-tubulin in the macronuclear anlage only during certain stages of its development, and raise the question of its significance. Our observations on Euplotes, although not entirely identical to those made on several evolutionarily distant organisms (for review see [13]), demonstrate that the relocalization of γ-tubulin during the successive mitotic stages are of general occurrence.