title: Giardia intestinalis mitosomes undergo synchronized fission but not fusion and are constitutively associated with the endoplasmic reticulum.
abstract: Mitochondria of opisthokonts undergo permanent fission and fusion throughout the cell cycle. Here, we investigated the dynamics of the mitosomes, the simplest forms of mitochondria, in the anaerobic protist parasite Giardia intestinalis, a member of the Excavata supergroup of eukaryotes. The mitosomes have abandoned typical mitochondrial traits such as the mitochondrial genome and aerobic respiration and their single role known to date is the formation of iron-sulfur clusters.
  
  
  
  In live experiments, no fusion events were observed between the mitosomes in G. intestinalis. Moreover, the organelles were highly prone to becoming heterogeneous. This suggests that fusion is either much less frequent or even absent in mitosome dynamics. Unlike in mitochondria, division of the mitosomes was absolutely synchronized and limited to mitosis. The association of the nuclear and the mitosomal division persisted during the encystation of the parasite. During the segregation of the divided mitosomes, the subset of the organelles between two G. intestinalis nuclei had a prominent role. Surprisingly, the sole dynamin-related protein of the parasite seemed not to be involved in mitosomal division. However, throughout the cell cycle, mitosomes associated with the endoplasmic reticulum (ER), although none of the known ER-tethering complexes was present. Instead, the ER-mitosome interface was occupied by the lipid metabolism enzyme long-chain acyl-CoA synthetase 4.
  
  
  
  This study provides the first report on the dynamics of mitosomes. We show that together with the loss of metabolic complexity of mitochondria, mitosomes of G. intestinalis have uniquely streamlined their dynamics by harmonizing their division with mitosis. We propose that this might be a strategy of G. intestinalis to maintain a stable number of organelles during cell propagation. The lack of mitosomal fusion may also be related to the secondary reduction of the organelles. However, as there are currently no reports on mitochondrial fusion in the whole Excavata supergroup, it is possible that the absence of mitochondrial fusion is an ancestral trait common to all excavates.
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University, Průmyslová 595, Vestec, 252 42, Czech Republic.
authors.forename: Luboš
authors.initials: L
authors.lastname: Voleman
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University, Průmyslová 595, Vestec, 252 42, Czech Republic.
authors.forename: Vladimíra
authors.initials: V
authors.lastname: Najdrová
authors.affiliation: Department of Cell and Molecular Biology, BMC, Uppsala University, Uppsala, Sweden.
authors.forename: Ásgeir
authors.initials: Á
authors.lastname: Ástvaldsson
authors.affiliation: Institute of Immunology and Microbiology, First Faculty of Medicine, Charles University and General University Hospital, Prague, Czech Republic.
authors.forename: Pavla
authors.initials: P
authors.lastname: Tůmová
authors.affiliation: Department of Cell and Molecular Biology, BMC, Uppsala University, Uppsala, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Einarsson
authors.affiliation: Institute of Cellular Biology and Pathology, First Faculty of Medicine, Charles University, Prague, Czech Republic.
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Švindrych
authors.affiliation: Institute of Cellular Biology and Pathology, First Faculty of Medicine, Charles University, Prague, Czech Republic.
authors.forename: Guy M
authors.initials: GM
authors.lastname: Hagen
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University, Průmyslová 595, Vestec, 252 42, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Tachezy
authors.affiliation: Department of Cell and Molecular Biology, BMC, Uppsala University, Uppsala, Sweden.
authors.forename: Staffan G
authors.initials: SG
authors.lastname: Svärd
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University, Průmyslová 595, Vestec, 252 42, Czech Republic. pavel.dolezal@natur.cuni.cz.
authors.forename: Pavel
authors.initials: P
authors.lastname: Doležal
mesh_terms: D005075:Biological Evolution; D003066:Coenzyme A Ligases / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D016829:Giardia lamblia / Q000166:cytology / Q000378:metabolism*; D007399:Interphase; D008928:Mitochondria / Q000378:metabolism*; D063154:Mitochondrial Dynamics; D000098859:Long-Chain-Fatty-Acid-CoA Ligase
chemical_list: D034281:Dynamins; D003066:Coenzyme A Ligases; D000098859:Long-Chain-Fatty-Acid-CoA Ligase