Centriole disassembly in vivo and its effect on centrosome structure and function in vertebrate cells

Glutamylation is the major posttranslational modification of neuronal and a xonemal tubulin and is restricted predominantly to centrioles in nonneurona l cells (Bobinnec, Y., M. Moudjou, J.P. Fouquet, E. Desbruyeres, B. Edde, a nd M. Bornens. 1998. Cell Motil. Cytoskel. 39:223-232). To investigate a po ssible relationship between the exceptional stability of centriole microtub ules and the compartmentalization of glutamylated isoforms, we loaded HeLa cells with the monoclonal antibody GT335, which specifically reacts with po lyglutamylated tubulin. The total disappearance of the centriole pair was o bserved after 12 h, as judged both by immunofluorescence labeling with spec ific antibodies and electron microscopic observation of cells after complet e thick serial sectioning. Strikingly, we also observed a scattering of the pericentriolar material (PCM) within the cytoplasm and a parallel disappea rance of the centrosome as a defined organelle. However, centriole disappea rance was transient, as centrioles and discrete centrosomes ultimately reap peared in the cell population. During the acentriolar period, a large proportion of monopolar half-spindle s or of bipolar spindles with abnormal distribution of PCM and NuMA were ob served. However, as judged by a quasinormal increase in cell number, these cells likely were not blocked in mitosis. Our results suggest that a posttranslational modification of tubulin is cri tical for long-term stability of centriolar microtubules. They further demo nstrate that in animal cells, centrioles are instrumental in organizing cen trosomal components into a structurally stable organelle.