Pericentrin pivotal in primary cilia

Pericentrin pivotal in primary cilia he centrosome protein pericentrin acts as an anchor for primary cilia formation in human cells, according to a report by Jurczyk et al. (page 637). The finding further unites the centrosome and primary cilia, both of which are based around centri-oles, and both of which use pericentrin as an anchor for other proteins. The authors show that pericentrin is located not only at centrosomes but also around the centrioles at the base of primary and motile cilia. After depletion of most pericentrin using RNAi, primary cilia failed to assemble, but centrosomes could still nucleate microtubules. The divergent outcomes may result from selective depletion of pericentrin's large isoform by RNAi, with remaining smaller isoforms perhaps acting in centrosomes. Depletion of pericentrin also disrupted the localization of both the intraflagellar transport (IFT) proteins that help build cilia and PC2, a cation channel important in ciliary signaling. Furthermore, depletion of IFT proteins with RNAi caused pericentrin mislocalization and disrupted primary cilia formation. Endogenous pericentrin copurifies and coimmunoprecipitates with IFT proteins. Additional studies are needed to understand exactly how this complex acts to direct primary cilia formation. The association is certainly reminiscent of pericentrin's function in centrosomes, where it is needed to anchor the ␥-tubulin ring complexes that nucleate microtubules. ᭿ T Pericentrin (green) is needed to build primary cilia (red). Flagellar microtubules do the twist n many organisms, the central pairs (CPs) of 9 ϩ 2 cilia and flagella spin. Mitchell and Nakatsugawa (page 709) now claim that this spinning is an effect, not a cause, of flagellar bend propagation. Motile 9 ϩ 2 cilia and flagella owe their whip-like movement to motors in the outside barrel of fused doublet microtubules, with motors anchored to one doublet pushing on a neighboring doublet. But the more enigmatic part of this structure is the CP. This doublet of microtubules is connected to the outside barrel via radial spokes that are thought to modulate motor action. That modulation requires a constant relationship between a particular face of the CP and those microtubule motors that are active at any one time—which is where spinning and twisting come in. Looking at electron micrographs of wild-type Chlamydomonas , Mitchell and Nakatsugawa see that the CP is twisted in straight, quiescent flagella. In mutants that lack the radial spoke heads, and therefore lack a physical connection between the outer and inner microtubules, the CP remains …