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Giardia lamblia, a flagellate protozoan that parasitizes the upper small intestine of humans, is one of the most common causes of diarrheal disease worldwide. Giardia has a simple life cycle, alternating between the disease-causing trophozoites and the infective cysts. Giardia is a true eukaryotic organism since it has two nuclei, an endomembranous system including the nuclear envelope/endoplasmic reticulum, transport vesicles and lysosomes-like peripheral vacuoles, as well as a complex cytoskeleton. However, trophozoites possess several prokaryotic features, including bacterial metabolic pathways and the lack of organelles typical of higher eukaryotes, such as mitochondria, peroxisomes, and a recognizable Golgi apparatus. Despite these characteristics, Giardia carries out secretory events implying both constitutive and regulated trafficking pathways. Here we describe the secretory machinery employed by Giardia for intracellular transport of cyst wall materials, their exocytosis, and the extracellular assembly of the protective cyst wall. These processes are essential for both the survival of the parasite outside the host’s intestine and transmission of the disease among susceptible individuals. |
