THE UNIQUE ENDOSOMAL/LYSOSOMAL SYSTEM OF GIARDIA LAMBLIA

MARIA CAROLINA TOUZ

Endocytosis

InTech

Lugar: Rijeka; Año: 2012; p. 278 - 298

Endocytosis, which is important for the internalization of nutrients from the plasma membrane as well as extracellular fluids, has been extensively described in mammalian cells and yeast. The protozoan parasite Giardia lamblia (syn. Giardia intestinalis, Giardia duodenalis)is an early branching eukaryote that possesses a reduced membrane network with highly polarized vesicles, denominated peripheral vacuoles (PVs), neighboring the plasma membrane (reviewed by Adam, 2001; Faso and Hehl, 2011; Touz, 2011). This is an important zone of interaction between the parasite and its environment (the host intestine in vivo or the culture medium in vitro), and was shown to be the place involved in fluid-phase and receptor-mediated endocytosis (Gaechter et al., 2008; Rivero et al., 2010). Another characteristic of these PVs is that they contain hydrolytic activity resembling the function performed by lysosomes. These vacuoles have a high lytic capacity and a low luminal pH, both properties of mature lysosomes (Ward et al., 1997; Touz et al., 2002b). More than twenty years after the first morphological description of the PVs, there is a consensus that these vesicles are rather an unusual combination of endosomal and lysosomal compartments. Conserved markers and mechanisms that govern trafficking to the PVs have been found, but there are particularities that show Giardia as a simplified organism compared with higher eukaryotes. This makes Giardia a unique biological cell model for investigating the minimal machinery employed by a eukaryote to regulate endocytosis and degradation. Here, we will discuss emerging data that are beginning to shed light on the endosomal-lysosomal system in Giardia and the molecules involved in this selective trafficking.