Abstract
Gamma-tubulin is the major protein involved in the nucleation of microtubules from centrosomes in eukaryotic cells. It is present in both cytoplasm and centrosome. However, before centrosome maturation prior to mitosis, gamma-tubulin concentration increases dramatically in the centrosome, the mechanism of which is not known. Earlier it was reported that cytoplasmic gamma-tubulin complex isolated from goat brain contains non-erythroid spectrin/fodrin. The major role of erythroid spectrin is to help in the membrane organisation and integrity. However, fodrin or non-erythroid spectrin has a distinct pattern of localisation in brain cells and evidently some special functions over its erythroid counterpart. In this study, we show that fodrin and γ-tubulin are present together in both the cytoplasm and centrosomes in all brain cells except differentiated neurons and astrocytes. Immunoprecipitation studies in purified centrosomes from brain tissue and brain cell lines confirm that fodrin and γ-tubulin interact with each other in centrosomes. Fodrin dissociates from centrosome just after the onset of mitosis, when the concentration of γ-tubulin attains a maximum at centrosomes. Further it is observed that the interaction between fodrin and γ-tubulin in the centrosome is dependent on actin as depolymerisation of microfilaments stops fodrin localization. Image analysis revealed that γ-tubulin concentration also decreased drastically in the centrosome under this condition. This indicates towards a role of fodrin as a regulatory transporter of γ-tubulin to the centrosomes for normal progression of mitosis.
Highlights
Centrosomes in mammalian cells direct the nucleation of microtubules which are required for the motility and intracellular transportation of vesicles during interphase
To further characterize and to know the significance of this association, we investigated the localization of fodrin and c-tubulin in brain cells under different conditions
To check if fodrin is co-localized with c-tubulin in all types of brain cells, immunocytochemistry has been performed on glioblastoma cell line U373 and neuroblastoma cell line IMR32
Summary
Centrosomes in mammalian cells direct the nucleation of microtubules which are required for the motility and intracellular transportation of vesicles during interphase. Centrosomes direct the formation of bipolar spindles [1] that are essential for the segregation of chromosomes. Localization of gamma tubulin complex at the centrosome contributes immensely to fulfil this role efficiently. C-tubulin is present in the centrosome throughout the cell cycle. It associates with other proteins to form two types of complexes [4], c-TuSC and c-TuRC. These complexes catalyse the nucleation of microtubules from MTOCs [5] much less prominent, non-centrosomic nucleation of microtubules has been reported [6,7]
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