DISSOCIATION OF CENTROSOME REPLICATION EVENTS FROM CYCLES OF DNA-SYNTHESIS AND MITOTIC DIVISION IN HYDROXYUREA-ARRESTED CHINESE-HAMSTER OVARY CELLS

Relatively little is known about the mechanisms used by somatic cells to regulate the replication of the centrosome complex. Centrosome doubling was studied in CHO cells by electron microscopy and immunofluorescence microscopy using human autoimmune anticentrosome antiserum, and by Northern blotting using the cDNA encoding portion of the centrosome autoantigen pericentriolar material (PCM)-1. Centrosome doubling could be dissociated from cycles of DNA synthesis and mitotic division by arresting cells at the G(1)/S boundary of the cell cycle using either hydroxyurea or aphidicolin. Immunofluorescence microscopy using SPJ human autoimmune anticentrosome antiserum demonstrated that arrested cells were able to undergo numerous rounds of centrosome replication in the absence of cycles of DNA synthesis and mitosis. Northern blot analysis demonstrated that the synthesis and degradation of the mRNA encoding PCM-1 occurred in a cell cycle-dependent fashion in CHO cells with peak levels of PCM-1 mRNA being present in G(1) and S phase cells before mRNA amounts dropped to undetectable levels in G(2) and M phases. Conversely, cells arrested at the G(1)/S boundary of the cell cycle maintained PCM-1 mRNA at artificially elevated levels, providing a possible molecular mechanism for explaining the multiple rounds of centrosome replication that occurred in CHO cells during prolonged hydroxyurea-induced arrest. The capacity to replicate centrosomes could be abolished in hydroxyurea-arrested CHO cells by culturing the cells in dialyzed serum. However, the ability to replicate centrosomes and to synthesize PCM-1 mRNA could be re-initiated by adding EGF to the dialyzed serum. This experimental system should be useful for investigating the positive and negative molecular mechanisms used by somatic cells to regulate the replication of centrosomes and for studying and the methods used by somatic cells for coordinating centrosome duplication with other cell cycle progression events.