An investigation of the centriole cycle using 3T3 and CHO cells.

An investigation of the centriole cycle was based on serial-section electron microscopy of the centrioles of 790 3T3 cells and 40 CHO cells (incomplete sets of sections were excluded from the analysis). Time-course studies indicated that procentrioles first appear 4 h after the start of S-phase; evidence was obtained to suggest that they elongate progressively during the subsequent stages of the cell cycle, and that they start to separate from their parents during mitosis. An association of the structural features of the centriole cycle with the Two-transition Model of the Cell Cycle was ruled out by the finding of two centrioles in most quiescent cells, and the appearance of procentrioles in S-phase in transiently stimulated cells.