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Vol. 19, Issue 7, 2682-2695, July 2008

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UNC-108/Rab2 Regulates Postendocytic Trafficking in Caenorhabditis elegans

Denise K. Chun^*, Jason M. McEwen^*,, Michelle Burbea, and Joshua M. Kaplan

Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston MA 02114

Submitted November 8, 2007; Revised April 8, 2008; Accepted April 11, 2008
Monitoring Editor: Sandra Lemmon

After endocytosis, membrane proteins are often sorted between two alternative pathways: a recycling pathway and a degradation pathway. Relatively little is known about how trafficking through these alternative pathways is differentially regulated. Here, we identify UNC-108/Rab2 as a regulator of postendocytic trafficking in both neurons and coelomocytes. Mutations in the Caenorhabditis elegans Rab2 gene unc-108, caused the green fluorescent protein (GFP)-tagged glutamate receptor GLR-1 (GLR-1::GFP) to accumulate in the ventral cord and in neuronal cell bodies. In neuronal cell bodies of unc-108/Rab2 mutants, GLR-1::GFP was found in tubulovesicular structures that colocalized with markers for early and recycling endosomes, including Syntaxin-13 and Rab8. GFP-tagged Syntaxin-13 also accumulated in the ventral cord of unc-108/Rab2 mutants. UNC-108/Rab2 was not required for ubiquitin-mediated sorting of GLR-1::GFP into the multivesicular body (MVB) degradation pathway. Mutations disrupting the MVB pathway and unc-108/Rab2 mutations had additive effects on GLR-1::GFP levels in the ventral cord. In coelomocytes, postendocytic trafficking of the marker Texas Red-bovine serum albumin was delayed. These results demonstrate that UNC-108/Rab2 regulates postendocytic trafficking, most likely at the level of early or recycling endosomes, and that UNC-108/Rab2 and the MVB pathway define alternative postendocytic trafficking mechanisms that operate in parallel. These results define a new function for Rab2 in protein trafficking.

* These authors contributed equally to this work.

Present address: Department of Biological Chemistry, University of California Los Angeles, Los Angeles, CA 90095.

Address correspondence to: Joshua M. Kaplan (kaplan{at}molbio.mgh.harvard.edu)

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