Ultrastructure of rhoptry development in Plasmodium falciparum erythrocytic schizonts

Abstract

Prior to the separation of merozoites from the Plasmodium falciparum schizont, various stage-specific organelles are synthesized and assembled within each merozoite bud. The apical ends of the merozoites are initiated close to the ends of endomitotic spindles. At each of these sites, the nuclear membrane forms coated vesicles, and a single discoidal or cup-like Golgi cisterna appears. Reconstruction from serial sections indicates that this structure receives vesicles from the nuclear envelope and in turn gives off coated vesicles to generate the apical secretory organelles. Rhoptries first form as spheroidal structures and grow by progressive fusion of small vesicles around their margins. As each rhoptry develops, 2 distinctive regions separate within it, an apical reticular zone with electron-lucent areas separated by cords of granular material, and a more homogenously granular basal region. The apical part elongates into the duct, with evidence for further vesicular fusion at the duct apex. The rounded rhoptry base becomes progressively more densely packed to form a spheroidal mass, and compaction also occurs in the duct. Typically, one rhoptry matures before the other. Cryofractured rhoptry membranes show asymmetry in the sizes and numbers of intramembranous particles at the internally- and externally-directed fracture faces.

AP-1 in Toxoplasma gondii Mediates Biogenesis of the Rhoptry Secretory Organelle from a Post-Golgi Compartment

“…Importantly, both the ROP2⌬ mutant and the L529A/L530A mutant substantially colocalized with a multivesicular endosomal compartment marked by the endosomal marker VPS4 (vacuolar protein sorting-4). 4 Altogether, these data provide further evidence that rhoptry targeting occurs along the endocytic pathway and is mediated by adaptins. They also implicate adaptin machinery in mediating targeting from a post-Golgi compartment to a mature secretory organelle.…”

“…These are flask-shaped secretory organelles that are assembled and positioned at the apical pole of the invasive forms of Apicomplexa (reviewed in Refs. [2][3][4]. At the onset of host cell invasion, prepackaged proteins and membranous materials from rhoptries are secreted through an apical opening.…”

Organellar dynamics during the cell cycle of Toxoplasma gondii

“…Parasitespecific secretory organelles include dense granules (constitutive secretory vesicles), micronemes (regulated secretory organelles involved in host cell attachment and invasion) and rhoptries (regulated secretory organelles involved in establishment and maintenance of the intracellular parasitophorous vacuole) (Carruthers and Sibley, 1997;Joiner and Roos, 2002). Previous reports have suggested that these organelles may be synthesized de novo, within each daughter cell, during endodyogeny (Ogino and Yoneda, 1966;Sheffield and Melton, 1968;Bannister et al, 2000b). This process could be visualized by time-lapse microscopy of fluorescently labelled parasites, as illustrated in Fig.…”

Plasmodium falciparumapical membrane antigen 1 (PfAMA-1) is translocated within micronemes along subpellicular microtubules during merozoite development

“…To address this situation, we have begun a detailed structural analysis of P. falciparum merozoite development, paying special attention to the role of the cytoskeleton. Peripheral microtubules are present in all invasive stages of Plasmodium [as in related apicomplexan genera (Morrissette and Sibley, 2002)] although, in P. falciparum merozoites, they are represented minimally by a band of just two or three (Bannister and Mitchell, 1995;Hopkins et al, 1999;Bannister et al, 2000;Bannister et al, 2001). Merozoite microtubules are destabilized by treating schizonts with colchicine and dinitroanilines, and this might be the root cause of the inhibitory effects of these compounds on merozoite During the assembly of Plasmodium falciparum merozoites within the schizont stage, the parasite synthesizes and positions three sets of secretory vesicles (rhoptries, micronemes and dense granules) that are active during red cell invasion.…”