Eukaryotic Cell
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Eukaryotic Cell, August 2004, p. 1004-1014, Vol. 3, No. 4
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.4.1004-1014.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Clathrin-Dependent Targeting of Receptors to the Flagellar Pocket of Procyclic-Form Trypanosoma brucei

Chien-Hui Hung,{dagger} Xugang Qiao,{dagger} Pei-Tseng Lee, and Mary Gwo-Shu Lee*

Department of Pathology, New York University School of Medicine, New York, New York 10016

Received 24 February 2004/ Accepted 16 April 2004

In trypanosomatids, endocytosis and exocytosis occur exclusively at the flagellar pocket, which represents about 0.43% of the pellicle membrane and is a deep invagination of the plasma membrane where the flagellum extends from the cell. Receptor molecules are selectively retained at the flagellar pocket. We studied the function of clathrin heavy chain (TbCLH) in the trafficking of the flagellar pocket receptors in Trypanosoma brucei by using the double-stranded RNA interference approach. It appears that TbCLH is essential for the survival of both the procyclic form and the bloodstream form of T. brucei, even though structures resembling large coated endocytic vesicles are absent in procyclic-form trypanosomes. Down-regulation of TbCLH by RNA interference (RNAi) for 24 h rapidly and drastically reduced the uptake of macromolecules via receptor-mediated endocytosis in procyclic-form trypanosomes. This result suggested the importance of TbCLH in receptor-mediated endocytosis of the procyclic-form trypanosome, in which the formation of large coated endocytic vesicles may not be required. Surprisingly, induction of TbCLH RNAi in the procyclic T. brucei for a period of 48 h prohibited the export of the flagellar pocket-associated transmembrane receptor CRAM from the endoplasmic reticulum to the flagellar pocket, while trafficking of the glycosylphosphatidylinositol-anchored procyclin coat was not significantly affected. After 72 h of induction of TbCLH RNAi, procyclics exhibited morphological changes to an apolar round shape without a distinct structure of the flagellar pocket and flagellum. Although trypanosomes, like other eukaryotes, use similar organelles and machinery for protein sorting and transport, our studies reveal a novel role for clathrin in the secretory pathway of trypanosomes. We speculate that the clathrin-dependent trafficking of proteins to the flagellar pocket may be essential for the biogenesis and maintenance of the flagellar pocket in trypanosomes.

* Corresponding author. Mailing address: Department of Pathology, New York University School of Medicine, 550 First Ave., New York, NY 10016. Phone: (212) 263-8260. Fax: (212) 263-8179. E-mail: leeg02{at}med.nyu.edu.

{dagger} C.-H.H. and X.Q. contributed equally to this paper.

Eukaryotic Cell, August 2004, p. 1004-1014, Vol. 3, No. 4
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.4.1004-1014.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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Copyright © 2004 by the American Society for Microbiology.