Cell Biology

A Needle in a Haystack

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Science  10 Aug 2007:
Vol. 317, Issue 5839, pp. 725
DOI: 10.1126/science.317.5839.725c

Primary cilia are composed of a stereotypical arrangement of microtubules that are anchored to a basal body and extend within a membrane sheath from many animal cells. Primary cilia act as microscopic sensory organs in sampling the extracellular environment and play a role during development in morphogen sensing, as well as contributing to sight and smell and other functions in multiple organs. Defects in primary cilium formation are associated with several diseases, such as retinal degeneration and neural tube defects. Primary cilium induction and function require the coordination of both membrane trafficking and microtubule assembly pathways.

Yoshimura et al. wanted to define the mechanisms involved in primary cilium formation and undertook a systematic approach to identify which members of the multitudinous Rab GTPase family of membrane traffic regulators were important. Only one of them, Rab8a, localized to the primary cilum; it interacted specifically with cenexin, a microtubule- and basal body-binding protein known to be involved in primary cilium production. Two other family members, Rab17 and Rab23, and their partnered GTPase activators also participated in primary cilium generation, whereas other Rabs and their activators were not required. This study paves the way for an understanding of the requirements for the specific recruitment of membrane trafficking and microtubule assembly machineries during primary cilium biogenesis, and how deficiencies lead inexorably to disease. — SMH

J. Cell Biol. 178, 363 (2007).

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