Understanding the molecular and biochemical basis of cellular growth and division involves the investigation of regulatory events that most often occur in a cell-cycle phase-dependent fashion. Studies examining cell-cycle regulatory mechanisms and progression invariably require cell-cycle synchronization of cell populations. Thus, many methods have been established to synchronize cells at specific phases of the cell cycle. Several of the common methods involve pharmacological agents, which act at various points throughout the cell cycle. Because of adverse cellular perturbations resulting from many of the synchronizing drugs used, other synchrony methods that involve less perturbation of biological systems, such as serum deprivation, contact inhibition, and centrifugal elutriation have a significant advantage. The advantages and disadvantages of these cell synchronization methods are discussed in this review.

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Karyotypic alterations, including whole chromosome loss or gain, ploidy changes, and a variety of chromosome aberrations are common in cancer cells. If proliferating cells fail to coordinate centrosome duplication with DNA replication, this will inevitably lead to a change in ploidy, and the formation of monopolar or multipolar spindles will generally provoke abnormal segregation of chromosomes. Indeed, it has long been recognized that errors in the centrosome duplication cycle may be an important cause of aneuploidy and thus contribute to cancer formation. This view has recently received fresh impetus with the description of supernumerary centrosomes in almost all solid human tumors. As the primary microtubule organizing center of most eukaryotic cells, the centrosome assures symmetry and bipolarity of the cell division process, a function that is essential for accurate chromosome segregation. Centrosomes undergo duplication precisely once before cell division. Recent reports have revealed that this process is linked to the cell division cycle via cyclin-dependent kinase (cdk) 2 activity that couples centriole duplication to the onset of DNA replication at the G₁/S phase transition. Alterations of regulatory G₁/S phase proteins like the retinoblastoma protein, cyclins D and E, cdk4 and 6, cdk inhibitors p16 ^INK4A and p15 ^INK4B , and p53 are among the most frequent aberrations observed in human malignancies. These alterations might not only lead to unrestrained proliferation but also cause karyotypic instability by uncontrolled centrosome replication. Since several excellent reports on cell cycle regulation and cancer have been published, this review will focus on causes and consequences of aberrant centrosome replication in human neoplasias.

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