Figure 1.

Centriole biogenesis. This schematic representation of the centriole duplication cycle shows centrioles (green) and PCM (grey), with emphasis on two distinct linker structures. The G1–G2 tether (GGT; blue) connects the proximal ends of the two parental centrioles from G1 to late G2; it is important to ensure microtubule nucleation from a single microtubule organizing centre. The S–M Linker (SML; red) forms during S phase and connects the proximal end of the nascent procentriole to the lateral surface of the mother centriole. The removal of this tight connection in late M phase (disengagement) is an important element of cell cycle control of centriole duplication. Both the molecular components of the GGT and SML as well as the regulation of the formation and dissolution of these structures are expected to be distinct, although some PCM components are likely to be important for both GGT and SML. Also depicted are subdistal and distal appendages (triangles); although readily visible in electron micrographs during interphase, these appendages are difficult to visualize during M phase. In quiescent cells, the appendage-bearing centriole associates with the plasma membrane (PM) and acts as a basal body to form a primary cilium. Finally, in multi-ciliated epithelial cells, multiple centrioles form simultaneously from an amorphous structure termed the deuterosome (D).