Toxoplasma gondii: further studies on the subpellicular network

Abstract

The association of the pellicle with cytoskeletal elements in Toxoplasma gondii allows this parasite to maintain its mechanical integrity and makes possible its gliding motility and cell invasion. The inner membrane complex (IMC) Toxoplasma gondii is an important opportunistic pathogen that can lead to serious complications in congenitally infected newborns and in HIV-positive individuals and other immunocompromised patients (Israelski & Remington 1993, Luft et al. 1993, Wong & Remington 1994.In order to survive in different challenging environments, such as the digestive tract and the circulatory system of hosts (i.e., both intra and extra-cellular milieus), T. gondii must maintain its structural integrity, a property greatly dependent upon the organism's pellicle and cytoskeletal components. The association of the plasma membrane with a system of flattened vesicles composes the pellicle. Connected with this structure, there are 22 subpellicular microtubules running down two-thirds of the parasite from its apical pole . A network of interwoven filaments called the subpellicular network extends along the parasite's entire cell body (Mann & Beckers 2001). This network is resistant to detergent extraction and is also connected to the pellicle, suggesting that it functions as a part of the membrane skeleton in T. gondii.Membrane skeletons are commonly found in freeliving protozoa, maintaining the cell shape and providing mechanical stability. Examples of such cytoskeletal proteins are the tetrins, described in Tetrahymena (Honts & Williams 1990, Brimmer & Weber 2000, the epiplasmins, identified in Paramecium (Nahon et al. 1993, Coffe et al. 1996, Pomel et al. 2006) and other protists (Huttenlauch et al. 1998, Bouchard et al. 2001, and (Huttenlauch et al. 1998). Kloetzel et al. (2003) first described a sub-family of articulins, the plateins, which are the major structural components of a monolayer of flattened scales (the "alveolar plates") located within membranous sacs (cortical alveoli) in the free-living protozoon Euplotes aediculatus. As the alveolar plates of these free-living protozoa constitute a skeletal system related to that described in Apicomplexa, we decided to use specific antibodies recognising these structures to determine if articulins are found in T. gondii. Our present results suggest that components of the subpellicular network have a common nature with cytoskeletal elements of free-living protozoa. MATERIALS AND METHODSIndirect immunofluorescence -T. gondii RH strain tachyzoites were harvested in MTSB (4 M glycerol, 100 mM PIPES, 1 mM EGTA, 5 mM MgCl 2 ), pH 6.8 and fixed in 2% paraformaldehyde in the same buffer. After fixation, the cells were rinsed in MTSB, allowed to adhere to previously poly-l-lysine-coated coverslips and permeabilised with 0.2% (v/v) Triton X-100 for 10 min. After washing, unspecific sites were quenched with 3% (w/v) bovine serum albumin solution for 1 h and the cells were incubated with undiluted primary antibody -mouse monoclonal mAB PL-5 (which recognises all plate...

Positioning of large organelles by a membrane- associated cytoskeleton inPlasmodiumsporozoites

“…This density underlies the IMC all around the cell and appeared continuous with the density originating from the polar rings at both the apical and the proximal ends of the sporozoite. We therefore presume that this density reflects the subpellicular network found in detergent‐extracted T. gondii tachyzoites (Mann and Beckers, 2001; Lemgruber et al. , 2009), which might serve to confer the crescent shape onto the sporozoite and endow it with the observed elasticity.…”

“…, 1997). A subpellicular network of filaments has been localized between microtubules and the IMC in T. gondii (Mann and Beckers, 2001; Lemgruber et al. , 2009).…”

Epiplasts: Membrane Skeletons and Epiplastin Proteins in Euglenids, Glaucophytes, Cryptophytes, Ciliates, Dinoflagellates, and Apicomplexans

“…D’Haese et al ( 6 ) first showed that after several parasitic apicomplexans were subjected to nonionic detergent extraction, the resultant cell ghosts retained their full-length cellular shape even though in some cases the cortical microtubules extended for only half the length of the cells, suggesting the presence of an additional skeletal component (see also references 34 and 90 ). Mann and Beckers ( 8 ) made similar ghost preparations using Toxoplasma and detected a filamentous meshwork between the microtubules that they termed the subpellicular network and that we designate here the epiplast.…”

“…Several investigators have previously pointed out similarities between what we are calling epiplasts/epiplastins present in the euglenids and in the three alveolate radiations ( 21 – 23 , 45 , 46 , 49 , 67 , 90 , 106 , 133 , 139 , 148 ), and Santore ( 124 ) notes similarities between the epiplasts of euglenids and cryptophytes. In this study, we subjected these similarities to comprehensive scrutiny and also analyzed two additional lineages—the glaucophytes and cryptophytes—that had not been previously recognized as epiplastin producers.…”

Plasmodium sporozoite motility: an update

“…The current status of knowledge places the motor machinery, which includes the myosin heavy and light chains and their anchoring proteins, tethered to IMC (98). The IMC is composed of flattened cisternae derived from the endomembrane system that extends beneath the entire surface of the parasite, except at its very apex, and is supported on their cytoplasmic side by microtubules and a network of ill-defined filaments (99)(100)(101)(102). The myosin driving parasite motility is myosin A (MyoA) (103)(104)(105), which belongs to an unconventional class of "neckless" myosins (class XIV) that is unique to Apicomplexa (103,106).…”