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Eukaryotic Cell, November 2009, p. 1665-1676, Vol. 8, No. 11
1535-9778/09/$08.00+0     doi:10.1128/EC.00123-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

A Contiguous Compartment Functions as Endoplasmic Reticulum and Endosome/Lysosome in Giardia lamblia{triangledown} ,{dagger}

Marla Abodeely,1,2,{ddagger} Kelly N. DuBois,1,2,{ddagger} Adrian Hehl,3 Sasa Stefanic,1,3 Mohammed Sajid,1 Wanderley deSouza,4 Marcia Attias,4 Juan C. Engel,1 Ivy Hsieh,1 Richard D. Fetter,1 and James H. McKerrow1*

Department of Pathology, The Sandler Center for Basic Research in Parasitic Diseases,1 Biomedical Sciences Graduate Program, University of California, San Francisco, California 94158,2 Institute of Parasitology, University of Zürich, Zürich, CH-8057, Switzerland,3 Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 1941-900, Brazil4

Received 29 April 2009/ Accepted 4 September 2009

The dynamic evolution of organelle compartmentalization in eukaryotes and how strictly compartmentalization is maintained are matters of ongoing debate. While the endoplasmic reticulum (ER) is classically envisioned as the site of protein cotranslational translocation, it has recently been proposed to have pluripotent functions. Using transfected reporter constructs, organelle-specific markers, and functional enzyme assays, we now show that in an early-diverging protozoan, Giardia lamblia, endocytosis and subsequent degradation of exogenous proteins occur in the ER or in an adjacent and communicating compartment. The Giardia endomembrane system is simple compared to those of typical eukaryotes. It lacks peroxisomes, a classical Golgi apparatus, and canonical lysosomes. Giardia orthologues of mammalian lysosomal proteases function within an ER-like tubulovesicular compartment, which itself can dynamically communicate with clathrin-containing vacuoles at the periphery of the cell to receive endocytosed proteins. These primitive characteristics support Giardia's proposed early branching and could serve as a model to study the compartmentalization of endocytic and lysosomal functions into organelles distinct from the ER. This system also may have functional similarity to the retrograde transport of toxins and major histocompatibility complex class I function in the ER of mammals.

* Corresponding author. Mailing address: University of California, San Francisco, QB3, Room 508B, Box 2550, 1700 4th St., San Francisco, CA 94158-2330. Phone: (415) 476-2940. Fax: (415) 502-8193. E-mail: jmck{at}cgl.ucsf.edu

{triangledown} Published ahead of print on 11 September 2009.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

{ddagger} M.A. and K.N.D. contributed equally to the work.

Eukaryotic Cell, November 2009, p. 1665-1676, Vol. 8, No. 11
1535-9778/09/$08.00+0     doi:10.1128/EC.00123-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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