title: Neogenesis and maturation of transient Golgi-like cisternae in a simple eukaryote.
abstract: The highly reduced protozoan parasite Giardia lamblia has minimal machinery for cellular processes such as protein trafficking. Giardia trophozoites maintain diverse and regulated secretory pathways but lack an identifiable Golgi complex. During differentiation to cysts, however, they produce specialized compartments termed encystation-specific vesicles (ESVs). ESVs are hypothesized to be unique developmentally regulated Golgi-like organelles dedicated to maturation and export of pre-sorted cyst wall proteins. Here we present a functional analysis of this unusual compartment by direct interference with the functions of the small GTPases Sar1, Rab1 and Arf1. Conditional expression of dominant-negative variants revealed an essential role of Sar1 in early events of organelle neogenesis, whilst inhibition of Arf1 uncoupled morphological changes and cell cycle progression from extracellular matrix export. The latter led to development of ;naked cysts', which lacked water resistance and thus infectivity. Time-lapse microscopy and photobleaching experiments showed that putative Golgi-like cisternae in Giardia develop into a network capable of exchanging soluble cargo at a high rate via dynamic, tubular connections, presumably to synchronize maturation. The minimized and naturally pulsed trafficking machinery for export of the cyst wall biopolymer in Giardia is a simple model for investigating basic principles of neogenesis and maturation of Golgi compartments.
authors.affiliation: Institute of Parasitology, University of Zürich, Zürich, Switzerland.
authors.forename: Sasa
authors.initials: S
authors.lastname: Stefanic
authors.forename: Laura
authors.initials: L
authors.lastname: Morf
authors.forename: Caroline
authors.initials: C
authors.lastname: Kulangara
authors.forename: Attila
authors.initials: A
authors.lastname: Regös
authors.forename: Sabrina
authors.initials: S
authors.lastname: Sonda
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Schraner
authors.forename: Cornelia
authors.initials: C
authors.lastname: Spycher
authors.forename: Peter
authors.initials: P
authors.lastname: Wild
authors.forename: Adrian B
authors.initials: AB
authors.lastname: Hehl
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D005057:Eukaryotic Cells / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D036681:Fluorescence Recovery After Photobleaching; D016829:Giardia lamblia / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D015800:Protozoan Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D020761:rab1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D015800:Protozoan Proteins; D020823:ADP-Ribosylation Factor 1; D020761:rab1 GTP-Binding Proteins