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Abstract

In cluA- mutants of Dictyostelium, mitochondria are clustered near the cell center rather than being dispersed throughout the cytoplasm. We have examined two possible mechanisms that could account for this phenotype. First, we sought evidence that the cytoskeleton or a presumptive mitochondrion-cytoskeleton linkage was altered in mutant cells. We found that cytoskeletal structures in cluA- cells appeared normal by immunostaining, and that the distribution of peroxisomes in mutant cells was indistinguishable from that in wild type cells. Treatment of wild type cells with drugs that disrupted microtubules or actin filaments did not mimic the cluA- phenotype. Thus, cytoskeletal defects seemed unlikely to account for the mitochondrial clustering in cluA- cells. Observation of the movement of GFP-tagged mitochondria in wild type cells suggested that mitochondria are transported along microtubules, as in mammalian cells, rather than along actin filaments, as in budding yeast. Therefore, the similar phenotypes of cluA- Dictyostelium cells and clu1delta yeast cells argued against CluA/Clu1p acting as a mitochondrion-cytoskeleton linker. We next examined the ultrastructure of mitochondria in freeze-substituted, thin-sectioned cells. We found that the clustered mitochondria in cluA- cells are interconnected. Often, adjacent mitochondria are linked by narrow membranous strands, although sometimes the mitochondria are partially merged. The presence of narrow constrictions at presumptive division sites argues that the constriction step of division proceeds normally. Our data suggest that cluA- cells may be blocked at a very late step in fission of the outer mitochondrial membrane.

Farnesyl diphosphate synthase, the target for nitrogen-containing bisphosphonate drugs, is a peroxisomal enzyme in the model system Dictyostelium discoideum

“…A typical peroxisomal pattern of fluorescence was observed (Figure 1B). These observations are in agreement with previous reports that both the PTS1 and PTS2 protein import pathways operate in D. discoideum [33–35]. …”

Mitochondrial fission and fusion in Dictyostelium discoideum: a search for proteins involved in membrane dynamics

“…It has been suggested that Dictyostelium cells do carry out mitochondrial fission [23,24], but no actual fission or fusion events have been identified. Thus, we developed an in vivo assay to determine if Dictyostelium cells carry out the processes of mitochondrial fission and fusion and to identify potential molecular players in these pathways.…”

“…Recent work in the model organism, Dictyostelium discoideum, has suggested that the process of mitochondrial fission takes place; however, fixed-cell studies have conclusively demonstrated that Dictyostelium mitochondria are spherical organelles rather than the well studied tubular mitochondria found in most other organisms [20,21,23,24]. The simplicity of these spherical mitochondria suggests that the processes of fission and fusion are not necessary to maintain this organelle morphology.…”

The mitochondrial Ras-related GTPase Miro: views from inside and outside the metazoan kingdom

“…The gemA knockout mutants show impaired cell growth on nutrient media without any obvious defects in cell division, implying that GemA is involved in mitochondrial function (Vlahou et al, 2011). In D. discoideum , mitochondrial transport is primarily mediated by microtubules (Fields et al, 2002; Vlahou et al, 2011). The gemA mutants show no obvious phenotype with respect to mitochondrial size, morphology, or intracellular distribution.…”