Centriole assembly in CHO cells expressing Plk4/SAS6/SAS4 is similar to centriogenesis in ciliated epithelial cells

Centriole assembly is initiated by Plk4, a Polo-like kinase 4, which causes the recruitment of downstream regulators, such as SAS6 and SAS4, to a nascent centriole. Simultaneous expression of Plk4, SAS6 and SAS4 in CHO cells resulted in the formation of massive fibrogranular aggregates of various sizes and shapes. These aggregates were surrounded by dense particles of about 70 nm in diameter, similar to the centriolar satellite that has been observed around the centrosome in normal cycling cells. Within the fibrillar material, ring-like structures appeared and eventually differentiated into centrioles by association with short microtubule bundles. Centrioles were also assembled around a parent centriole in a cluster, a configuration that has been described as a "flower structure" formation [Kleylein-Sohn et al., 2007]. This pattern of centriole duplication is reminiscent of the arrangement of new centrioles induced in normal ciliated trachea/oviduct cells by the centriole-dependent pathway, which was reported several decades ago [Sorokin, 1968; Anderson and Brenner, 1971; Dirksen, 1971]. Prior to the production of hundreds of centrioles, these differentiating epithelial cells were also shown to induce a dense filamentous material similar to that detected in transfected CHO cells. These results suggest a common mechanism of centriole assembly regulated by Plk4 in both transfected cycling cells and normal ciliated epithelial cells undergoing differentiation.