Multi-membrane-bound structures of Apicomplexa: II. the ovoid mitochondrial cytoplasmic (OMC) complex of Toxoplasma gondii tachyzoites |
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Authors: | Sabine Köhler |
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Institution: | 1. Institute for Zoomorphology, Cell Biology and Parasitology, Heinrich Heine Universit?t Düsseldorf, Universit?tsstrasse 1, 40225, Düsseldorf, Germany
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Abstract: | Apicomplexa including the causative agents of toxoplasmosis and malaria reportedly possess one or few tubular-shaped mitochondria
that permeate, more or less branched, throughout these unicellular parasites. Electron micrographs generated herein from serial-sectioned
Toxoplasma gondii tachyzoites demonstrated, however, a greater diversity regarding both the shape of the cultured parasite’s single mitochondrion
and its sub-structural organization. Moreover, a unique subcellular construction was detected that basically comprised a pouch-shaped
subdivision of the tachyzoite mitochondrion plus a fraction of parasitic cytoplasm enclosed therein. This composite assembling,
termed ovoid mitochondrial cytoplasmic (OMC) complex, characteristically displayed a highly reduced matrix lumen of its mitochondrial
border construction, which furthermore often failed to possess any cristae or contained tightly pleated cristae, thus creating
a pouch-shaped multi-laminar wall of four or more membranous layers, respectively. Given this architecture, cross-sectioned
OMC complexes of T. gondii tachyzoites frequently mimicked in size and shape the parasites’ plastid-like organelle (apicoplast). Moreover, like the
apicoplast, the OMC complex was often found adjacent to the tachyzoite’s single Golgi complex and constantly located in close
proximity to the outer membrane of the parasite’s nuclear envelope. The T. gondii OMC complex differed, however, from the apicoplast in its exact fine structural organization and a stage-restricted presence
that was apparently linked to mitochondrial growth and/or division. Any special function(s) possibly performed by the T. gondii OMC complex remains, nevertheless, to be elucidated. |
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