The abnormal-shaped mitochondria in thymus lymphocytes treated with inhibitors of mitochondrial energetics

The Role of Oocyte Organelles in Determining Developmental Competence

The ability of an oocyte to undergo successful cytoplasmic and nuclear maturation, fertilization and embryo development is referred to as the oocyte’s quality or developmental competence. Quality is dependent on the accumulation of organelles, metabolites and maternal RNAs during the growth and maturation of the oocyte. Various models of good and poor oocyte quality have been used to understand the essential contributors to developmental success. This review covers the current knowledge of how oocyte organelle quantity, distribution and morphology differ between good and poor quality oocytes. The models of oocyte quality are also described and their usefulness for studying the intrinsic quality of an oocyte discussed. Understanding the key critical features of cytoplasmic organelles and metabolites driving oocyte quality will lead to methods for identifying high quality oocytes and improving oocyte competence, both in vitro and in vivo.

Immunolocalisation pattern of complex I-V in ageing human retina: Correlation with mitochondrial ultrastructure

Earlier studies reported accumulation of mitochondrial DNA mutations in ageing and age-related macular degeneration. To know about the mitochondrial status with age, we examined immunoreactivity (IR) to markers of mitochondria (anti-mitochondrial antibody and voltage-dependent anion channel-1) and complex I-V (that mediate oxidative phosphorylation, OXPHOS) in donor human retinas (age: 19-94years; N=26; right eyes). In all samples, at all ages, IR to anti-mitochondrial antibody and voltage-dependent anion channel-1 was prominent in photoreceptor cells. Between second and seventh decade of life, strong IR to complex I-V was present in photoreceptors over macular to peripheral retina. With progressive ageing, the photoreceptors showed a decrease in complex I-IR (subunit NDUFB4) at eighth decade, and a weak or absence of IR in 10 retinas between ninth and tenth decade. Patchy IR to complex III and complex IV was detected at different ages. IR to ND1 (complex I) and complex II and V remained unaltered with ageing. Nitrosative stress (evaluated by IR to a nitro-tyrosine antibody) was found in photoreceptors. Superoxide dismutase-2 was found upregulated in photoreceptors with ageing. Mitochondrial ultrastructure was examined in two young retinas with intact complex IR and six aged retinas whose counterparts showed weak to absence of IR. Observations revealed irregular, photoreceptor inner segment mitochondria in aged maculae and mid-peripheral retina between eighth and ninth decade; many cones possessed autophagosomes with damaged mitochondria, indicating age-related alterations. A trend in age-dependent reduction of complex I-IR was evident in aged photoreceptors, whereas patchy complex IV-IR (subunits I and II) was age-independent, suggesting that the former is prone to damage with ageing perhaps due to oxidative stress. These changes in OXPHOS system may influence the energy budget of human photoreceptors, affecting their viability.

Chronological transition of mitochondrial morphology in Chlamydomonas reinhardtii (Chlorophyceae) poststationary phase growth(1)

In Chlamydomonas reinhardtii P. A. Dangeard, mitochondrial morphology has been observed during asexual cell division cycle, gamete and zygote formation, zygote maturation, and meiotic stages. However, the chronological transition of mitochondrial morphology after the stationary phase of vegetative growth, defined as the poststationary phase, remains unknown. Here, we examined the mitochondrial morphology in cells cultured for 4 months on agar plates to study mitochondrial dynamics in the poststationary phase. Fluorescence microscopy showed that the intricate thread-like structure of mitochondria gradually changed into a granular structure via fragmentation after the stationary phase in cultures of about 1 week of age. The number of mitochondrial nucleoids decreased from about 30 per cell at 1 week to about five per cell after 4 months of culture. The mitochondrial oxygen consumption decreased exponentially, but the mitochondria retained their membrane potential. The total quantity of mitochondrial DNA (mtDNA) of cells at 4 months decreased to 20% of that at 1 week. However, the mitochondrial genomic DNA length was unchanged, as intermediate lengths were not detected. In cells in which the total mtDNA amount was reduced artificially to 16% after treatment with 5-fluoro-2-deoxyuridine (FdUrd) for 1 week, the mitochondria remained as thread-like structures. The oxygen consumption rate of these cells corresponded to that of untreated cells at 1 week of culture. This suggests that a decrease in mtDNA does not directly induce the fragmentation of mitochondria. The results suggest that during the late poststationary phase, mitochondria converge to a minimum unit of a granular structure with a mitochondrial nucleoid.

Features of mitochondrial energetics in living unicellular eukaryote Tetrahymena pyriformis. A model for study of mammalian intracellular adaptation

Tetrahymena pyriformis is used in diverse studies as a non-mammalian alternative due to their resemblance in many main metabolic cycles. However, such basic features of mitochondrial energetics as Delta psi (electrical potential difference across the inner mitochondrial membrane) or maximal stimulation of respiration by uncouplers with different mechanisms of uncoupling, such as DNP (2,4-dinitrophenol) and FCCP (p-trifluoromethoxycarbonylcyanide phenylhydrazone), have not been studied in living ciliates. Tetrahymena pyriformis GL cells during stationary growth phase after incubation under selected conditions were used in this study. Maximal stimulation of cellular respiration by FCCP was about six-fold, thus the proton motive force was high. The DNP uncoupling effect was significantly lower. This suggests low activity of the ATP/ADP-antiporter, which performs not only exchange of intramitochondrial ATP to extramitochondrial ADP, but also helps in the uncoupling process. It participates by a similar mechanism in electrophoretic transport from matrix to cytosol of ATP(4-) and DNP anion, but not FCCP anion. Thus, in contrast with mammalian mitochondria, T. pyriformis mitochondria cannot rapidly supply the cytosol with ATP; possibly the cells need high intramitochondrial ATP. The difference between DNP and FCCP is hypothetically explained by low Delta psi value and/or an increase in concentration of long-chain acyl-CoAs, inhibitors of the ATP/ADP-antiporter. The first suggestion is confirmed by absence of mitochondria with bright fluorescence in T. pyriformis stained with the Delta psi-sensitive probe MitoTracker Red. These data suggest that T. pyriformis cells are useful as a model for study of mitochondrial role in adaptation at the intracellular level.

Plant mitochondria move on F-actin, but their positioning in the cortical cytoplasm depends on both F-actin and microtubules

Mitochondrion movement and positioning was studied in elongating cultured cells of tobacco (Nicotiana tabacum L.), containing mitochondria-localized green fluorescent protein. In these cells mitochondria are either actively moving in strands of cytoplasm transversing or bordering the vacuole, or immobile positioned in the cortical layer of cytoplasm. Depletion of the cell's ATP stock with the uncoupling agent DNP shows that the movement is much more energy demanding than the positioning. The active movement is F-actin based. It is inhibited by the actin filament disrupting drug latrunculin B, the myosin ATPase inhibitor 2,3-butanedione 2-monoxime and the sulphydryl-modifying agent N-ethylmaleimide. The microtubule disrupting drug oryzalin did not affect the movement of mitochondria itself, but it slightly stimulated the recruitment of cytoplasmic strands, along which mitochondria travel. The immobile mitochondria are often positioned along parallel lines, transverse or oblique to the cell axis, in the cortical cytoplasm of elongated cells. This positioning is mainly microtubule based. After complete disruption of the F-actin, the mitochondria parked themselves into conspicuous parallel arrays transverse or oblique to the cell axis or clustered around chloroplasts and around patches and strands of endoplasmic reticulum. Oryzalin inhibited all positioning of the mitochondria in parallel arrays.

Dynamics of mitochondria in living cells: shape changes, dislocations, fusion, and fission of mitochondria

Mitochondria are semi-autonomous organelles which are endowed with the ability to change their shape (e.g., by elongation, shortening, branching, buckling, swelling) and their location inside a living cell. In addition they may fuse or divide. These dynamics are discussed. Dislocation of mitochondria may result from their interaction with elements of the cytoskeleton, with microtubules in particular, and from processes intrinsic to the mitochondria themselves. Morphological criteria and differences in the fate of some mitochondria argue for the presence of more than one mitochondrial population in some animal cells. Whether these reflect genetic differences remains obscure. Emphasis is laid on the methods for visualizing mitochondria in cells and following their behaviour. Fluorescence methods provide unique possibilities because of their high resolving power and because some of the mitochondria-specific fluorochromes can be used to reveal the membrane potential. Fusion and fission often occur in short time intervals within the same group of mitochondria. At sites of fusion of two mitochondria material of the inner membrane, the matrix compartment seems to accumulate. The original arrangement of the fusion partners is maintained for some minutes. Fission is a dynamic event which, like fusion, in most cases observed in vertebrate cell cultures is not a straight forward process but rather requires several "trials" until the division finally occurs. Regarding fusion and fission hitherto unpublished phase contrast micrographs, and electron micrographs have been included.

Schwann cell mitochondrial alterations in peripheral nerves of rabbits treated with 2',3'-dideoxycytidine

2',3'-Dideoxycytidine (ddC) is a nucleoside analogue and reverse-transcriptase inhibitor that is approved for treatment of AIDS patients. A rabbit model of ddC neurotoxicity was developed to help understand the dose-limiting clinical neurotoxicity of ddC. Rabbits with a myelinopathy resulting from treatment with ddC exhibited mitochondrial alterations in Schwann cells of sciatic and tibial nerves and dorsal root ganglia. These changes were initially evident after 16 weeks of oral treatment with 35 mg/kg per day of ddC and were positively correlated with myelin pathology in individual animals. Cup-shaped mitochondria were frequently observed; when these mitochondria occurred in multiple concentric arrays or at various angles to one another, different profiles were formed depending on the plane of section. An increased number of mitochondrial cristae assumed a tubular configuration. It is suggested that the complex aggregations of mitochondria seen in this experiment are an adaptive response to altered mitochondrial function caused by treatment with ddC.