Fig 1.
Mitochondria of animals and fungi undergo constant cycles of opposing fission and fusion events. For division, the molecules of DRP are recruited to the mitochondrial surface by DRP receptors. The sites of membrane fission often coincide with the ER-mitochondria connections. Membrane-anchored DRPs specific for the outer (Mfn1,2/Fzo1) and the inner (Opa1/Mgm1) mitochondrial membrane mediate the fusion. Defective mitochondria are removed from the cycle by mitophagy. DRP, dynamin-related proteins; ER, endoplasmic reticulum.
Fig 2.
Key aspects of mitochondrial dynamics in parasitic protists.
Single mitochondrion of P. falciparum in synchrony with the specific cell division known as schizogony. The elongated mitochondrion branches and segregates into emerging daughter cells at the very end of the cell division. Throughout most of the cell cycle, the mitochondrion maintains the association with the apicoplast. Similarly, two daughter cells of T. gondii develop within the mother cell by a process known as endodyogeny. Here, the mitochondrion is also in contact with the IMC—a membranous compartment underneath the cytoplasmic membrane specific to Alveolata. In T. brucei, the mitochondrial genome is arranged into a kinetoplast disc, which is physically connected to the basal body of the flagellum by a TAC. The division of the single parasite mitochondrion is thus fully coordinated with the maturation of a new flagellum and the segregation of two daughter kinetoplasts. MROs of anaerobic parasitic protists are always present in higher numbers. In T. vaginalis, hydrogenosomes associate with the main cytoskeletal structures, the axostyle and costa. In G. intestinalis, central and peripheral mitosomes can be distinguished. The first are proposed to be in contact with the axonemes of flagella. Both populations divide during mitosis, which is also part of the encystation process. The mature cyst thus contains a doubled set of nuclei and mitosomes. In E. histolytica, hundreds of mitosomes are distributed all over the cell. IM, inner mitochondrial membrane; IMC, inner membrane complex; OM, outer mitochondrial membrane; MRO, mitochondrion-related organelle; RBC, red blood cell; TAC, tripartite attachment complex.
Table 1.
Distribution of components involved in mitochondrial division and fusion in parasitic protists.
Fig 3.
Parasitic protists in the eukaryotic tree of life.
The schematic tree shows the position of the discussed protist parasites across the eukaryotic diversity. Currently, two large domains of eukaryotes called Amorphea and Diaphoretickes are distinguished with several additional clades of uncertain position [103]. Plasmodium, Toxoplasma, and Cryptosporidium belong to Apicomplexa, which together with Dinoflagellata and Ciliata constitute a group of Alveolata. Alveolata further combine with Stramenopiles and Rhizaria to form SAR group [103]. Discoba and Metamonada groups, which contain Trypanosoma with Leishmania and Giardia with Trichomonas, respectively, were previously part of the Excavata supergroup of eukaryotes. According to current classification, these groups belong neither to Amorphea or Diaphoretickes and remain without clear position in the tree (dotted lines). Entamoeba is part of the Amoebozoa supergroup. The comparative analyses proposed that the LECA already contained dynamin homologue, most likely capable of dual function in both mitochondrial division and vesicle scission [92]. There was also a mitochondrial targeted FtsZ, a prokaryotic homologue of tubulin, involved in the mitochondrial division [91]. Widespread distribution of Fis1 suggests that the protein was also used by LECA, although its specific involvement in mitochondrial division is unclear. Similarly, the components of the ERMES complex described as the molecular tether of the ER and mitochondria were common to Amorphea and the former Excavata group (Discoba, Metamonada, Malawimonada), while being absent in the common ancestor of Diaphoretickes [83]. However, the presence of individual ERMES components does not automatically imply the existence of functional ERMES complex. Mitochondrial fusion mediated by a DRP was confirmed only for the members of Amorphea and CRuMs; question mark depicts the uncertain position of the root of the tree. CRuMs, Collodictyonid + Rigifilida + Mantamonas clade; DRP, dynamin-related protein; ER, endoplasmic reticulum; ERMES, ER-mitochondria encounter structure; LECA, last eukaryotic common ancestor; SAR, Stramepiles-Alveolata-Rhizaria.