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Y Li, Q Zhang, Q Wei, Y Zhang, K Ling and J Hu (2012)
SUMOylation of the small GTPase ARL-13 promotes ciliary targeting of sensory receptors.
J Cell Biol. 2012 Nov 12; 199(4): 589-98. PMID: 23128241 DOI: 10.1083/jcb.201203150
This paper is intriguing because it shows that SUMOylation of a very small pool of the small GTPase Arl13 is required for trafficking of some receptors into primary cilia. Arl13 is essential for cilia function, with mutations in Arl13 leading the Joubert syndrome. Arl13 is required for the formation of primary cilia (ciliogenesis) and also for the trafficking of certain receptors into the cilium. Here, the authors show that SUMOylation of Arl13 is not required for ciliogenesis itself, but is required for the trafficking of cargo, including polycystin-2, to the cilium once formed. The mechanistic basis of this role remains to be determined. The fact that only a very small pool of Arl13 is SUMOYlated at any one time will complicate analysis, but also hints at either a highly specialized pathway or, perhaps more likely, a very dynamic SUMOylation/deSUMOylation pathway being in operation.