Prismatic cristae and paracrystalline inclusions in mitochondria of myocardial cells of the oyster Crassostrea virginica Gmelin

Summary Several types of unusual mitochondrial configurations were found in myocardial cells of the oyster Crassostrea virginica Gmelin. These mitochondria include, in order of frequency, prismatic cristae, filamentous paracrystals in honeycomb and herringbone configurations, and paracrystals composed of rows of electron dense particles. The long, parallel, evenly spaced prismatic cristae are square or rhomboidal in cross section. In the space between the prismatic cristae are rodlike structures (4–6 nm in diameter) that are regularly spaced about 12nm apart and appear to pass between adjacent cristae. Filamentous paracrystals are observed in slender, elongated mitochondria. The filament spacing and form of these paracrystals suggest that they are composed of the intercristal rods. Alternatively, filamentous paracrystals might be tangential sections of prismatic cristae and intercristal rods. Particulate paracrystals which consist of dense lines or rows of particles are the least frequent type of unusual configuration. The particles are triangular, possibly pyramidal, in shape; their bases are 10–12 nm thick and repeat in rows every 17–18 nm. There is a close association between particulate paracrystals and prismatic cristae plus intercristal rods. Although similar mitochondrial configurations have been associated with disease or altered metabolism in a number of species, we have found no such association in the oyster as yet.Supported in part by the Mississippi-Alabama Sea Grant Consortium, through NOAA, Dept. of Commerce under grant no. NA 79AA-D-0049We wish to thank Ms. Barbara M. Hyde, Ms. Patricia A. Vermiere and Mr. Robert Allen for their technical assistance     

Intramitochondrial filamentous bodies in the thick limb of henle of the rat kidney

"Intramitochondrial filamentous bodies" (IMFB) were occasionally found within the matrix of some mitochondria of the thick limb of Henle of the rat kidney, but not elsewhere in the tubular system. Three types were recognized: type I, an accumulation of filaments 55 A thick; type II, a bundle of parallel filaments having the same thickness as those of type I and regular spacing, 87 A apart, from center to center; and type III, consisting of type II with regular light bands of 280 A periodicity and a helical border of prismatic tubular cristae. In addition to these, electron-opaque masses showing variable and faint substructures were found in the matrix of mitochondria. It is suggested that all these IMFB may originate from mitochondrial cristae and that type II IMFB may be an intermediate developmental form between type I and type III. After uranyl acetate staining, IMFB and the membranes of prismatic tubular cristae showed highly increased electron opacity. The literature has been reviewed for reports of intramitochondrial filamentous inclusions in various types of cells. These inclusions have been classified according to their structural characteristics and the localization in the mitochondria and compared with IMFB reported herein.     

The fine structure of mitochondria and the mitochondrial cloud during oogenesis on the sea anemone Actinia

The appearance and arrangement of the mitochondria during all stages of oocyte growth in the sea anemone Actinia fragacea (Cnidaria: Anthozoa) have been examined by electron microscopy. In small oocytes, the mitochondria are generally squat, with a dense matrix and numerous cristae, although a proportion may show an unusual arrangement of prismatic cristae. During early oogenesis, the mitochondria tend to be arranged in aggregates rather than randomly scattered, and may be associated with nuage material. With the onset of vitellogenesis, a large mitochondrial aggregate forms next to the nucleus. During early vitellogenesis this aggregate enlarges and comes to resemble the mitochondrial clouds found in some amphibian oocytes. Within the cloud, many mitochondria appear to be highly elongate and irregular in shape. The cloud begins to fragment and disperse midway through vitellogenesis at about the time when cortical granules appear. In fully grown oocytes, some mitochondria may have a much less dense matrix and fewer cristae than the remainder, which may be related to their state of activity.     

Organized inclusions in astrocytic and amorphous inclusions in neuronal mitochondria of human frontal brain tissue

Brain tissue specimens were obtained early post mortem from the frontal lobe of seven unselected elderly subjects known to have been free of neurologic disease. Electron microscopically, two types of intramitochondrial inclusions were seen in four of seven cases. In two cases a few astrocyte mitochondria of the gyral white matter showed dense, elongated inclusions with an ordered linear substructure. These inclusions were, as a rule, accompanied by a row of prismatic cristae. In three cases some nerve cell mitochondria contained amorphous material of medium density and compact appearance. The globular masses often occupied the whole width of the mitochondrion. A relationship between the observed finding and a particular disease or morbid condition was not apparent. The inclusions are regarded as the morphologic substrate of a nonspecific metabolic change or degenerative process of the mitochondrion.     

Identification of an Arabidopsis thaliana gene for cardiolipin synthase located in mitochondria

Cardiolipin (CL) is an anionic phospholipid with a dimeric structure. In eukaryotes, it is primarily localized in the inner membranes of mitochondria. Although the biosynthetic pathway of CL is well known, the gene for CL synthase has not been identified in any higher organisms. In this study, the CLS gene for a CL synthase has been identified in a higher plant, Arabidopsis thaliana. We have shown that the CLS gene encodes a CL synthase by demonstrating its ability to catalyze the reaction of CL synthesis from CDP-diacylglycerol and phosphatidylglycerol, and that CLS is targeted into mitochondria. These findings demonstrate that CLS is a CL synthase located in mitochondria.     

The biosynthetic pathway for lipoic acid is present in plastids and mitochondria in Arabidopsis thaliana

In eukaryotes, the biosynthetic pathway for lipoic acid is present in mitochondria. However, it has been hypothesized that, in plants, the biosynthetic pathway is present in plastids in addition to mitochondria. In this study, Arabidopsis thaliana LIP1p cDNA for a plastidial form of lipoic acid synthase has been identified. We show that it encodes a lipoic acid synthase by demonstrating its ability to complement an Escherichia coli mutant lacking lipoic acid synthase activity. We also show that LIP1p is targeted to chloroplasts. These findings suggest that the biosynthetic pathway for lipoic acid is present not only in mitochondria but also in plastids.     

Assembly of F1-ATPase in isolated mitochondria

The assembly of the proton-translocating ATPase complex was studied in isolated mitochondria by incubating yeast mitochondria with radiolabeled precursors of mitochondrial proteins which had been made in a cell-free protein synthesis system. Following such an incubation, the ATPase complex (F1F0) was isolated. Newly assembled F1-ATPase was detected by autoradiography of the isolated enzyme, only peptide subunits which had been made in vitro and imported into the isolated mitochondria could be radioactive. Incorporation of radiolabeled ATPase subunits into the enzyme does not occur in the presence of an uncoupler of oxidative phosphorylation or of a divalent metal chelator, nor does it occur in submitochondrial particles rather than intact mitochondria. Incorporation of labeled ATPase subunits into the enzyme can be completed by unlabeled subunits, provided the unlabeled proteins are added before the mitochondria are incubated with radioactive precursors. These findings suggest that F1-ATPase is assembled from a pool of subunits in mitochondria.     

Dart formation in Helix aspersa (Mollusca,Gastropoda)

Summary Dart formation in Helix aspersa has been investigated by SEM of isolated darts at progressive stages in their development, and by histology of dart sacs at the same times. Dart formation begins at the tip of a tubercle where a small group of epithelial cells secrete an organic material filling a small CaCO₃ cone that is the first mineralized part of the shaft. Subsequent secretory activity by an increasing area of the tubercle epithelium results in an increase in the diameter and anterior lengthening of the shaft. Continued secretion by the tubercle and dart sac epithelium produces the flare and finally the corona. A pattern of deposition is also evident in the fine structure of the mineral. In the shaft and vanes there is an inner layer of spherulitic prismatic structure which is covered by a layer of irregular patches of simple prismatic structure. The outermost layer of the shaft and vanes has a continuous simple prismatic structure. Two layers are present in the flare, an inner granular amorphous layer and an outer spherulitic prismatic layer. The corona consists of a single rarefied prismatic layer. A mechanism of dart formation is suggested that involves two types of organic matrix, calcifying and non-calcifying. Measurements of the calcium content of darts, dart sacs, and collars indicate that the hemolymph is the probable source of calcium for the dart.     

MORPHOLOGY OF ISOLATED RABBIT HEART MUSCLE MITOCHONDRIA AND THE OXIDATION OF EXTRAMITOCHONDRIAL REDUCED DIPHOSPHOPYRIDINE NUCLEOTIDE

The morphology of rabbit heart muscle mitochondria isolated in several media has been compared by electron microscopy. The internal structure of isolated mitochondria differs from that of in situ mitochondria, with the type and degree of alteration depending on the isolation medium. Examination of the isolated mitochondria after incubation revealed that additional morphological changes occurred during incubation, but these changes were less pronounced when the incubation was conducted in a complete medium containing substrate. The isolated mitochondria have been shown to be capable of catalyzing a slow aerobic oxidation of extramitochondrial reduced diphosphopyridine nucleotide. The rate of DPNH oxidation observed is sufficient to account for the ability of the mitochondria to oxidize lactate in the presence of catalytic amounts of DPNH. The suspensions used were essentially free of mitochondrial fragments, which are known to oxidize DPNH. Possible relationships of these findings to metabolism in situ are discussed. The results indicate the desirability of correlating biochemical activities with the morphology of isolated mitochondria.     

CONVERGENT SHELL MORPHOLOGY IN INTERTIDAL GASTROPODS

The functional morphology of shell infrastructure in 2 speciesof intertidal trochid was compared with that in 2 species ofnerite. The shell of Monodonta constrictais typical of the majorityof trochids. The shell is composed of 4 layers: a distal layer(calcite), anouter prismatic layer (aragonite), a nacreous layer(aragonite), and an oblique prismatic layer (aragonite). Monodontalabio lacks a distal layer and an oblique prismatic layer. Theoblique prismatic layer is replaced by an inner prismatic layerwhich forms an apertural ridge as a result of deposition andresorption. The shells of Nerita versicolor and N. tessellataconsistof 3 layers: an outer prismatic layer (calcite), a crossedlamellar layer (aragonite), and a complex crossed lamellar layer(aragonite). The complex crossed lamellar layer is covered withinclined platelets which superficially resemble the surfaceof the ique prismatic layer of trochids. In addition, the complexcrossed lamellar layer forms an apertural ridge which is similarin appearance to that of Monodonta labio. The outer surfaceof the mantle of Nerita versicolor and N. tessellata is throwninto a series of large folds which lie in contact with the inclinedplatelets of the omplex crossed lamellar layer. The interactionof the mantle folds with the inclined platelets is thought toserve as a rachet mechanism to aid in extension of themantle;a similar function has previously been proposed for trochids.The apertural ridges of Monodonta labio and Nerita are thoughtto prevent excessive desiccation when these gastropodsare exposedat low tide. ¹Contribution No. 56 of the Tallahassee, Sopchoppy & GulfCoast Marine Biological Association (Received 6 July 1979;     

Mitochondria–plasma membrane interactions and communication

Mitochondria are known as the powerhouses of eukaryotic cells; however, they perform many other functions besides oxidative phosphorylation, including Ca²⁺ homeostasis, lipid metabolism, antiviral response, and apoptosis. Although other hypotheses exist, mitochondria are generally thought as descendants of an α-proteobacteria that adapted to the intracellular environment within an Asgard archaebacteria, which have been studied for decades as an organelle subdued by the eukaryotic cell. Nevertheless, several early electron microscopy observations hinted that some mitochondria establish specific interactions with certain plasma membrane (PM) domains in mammalian cells. Furthermore, recent findings have documented the direct physical and functional interaction of mitochondria and the PM, the organization of distinct complexes, and their communication through vesicular means. In yeast, some molecular players mediating this interaction have been elucidated, but only a few works have studied this interaction in mammalian cells. In addition, mitochondria can be translocated among cells through tunneling nanotubes or by other mechanisms, and free, intact, functional mitochondria have been reported in the blood plasma. Together, these findings challenge the conception of mitochondria as organelles subdued by the eukaryotic cell. This review discusses the evidence of the mitochondria interaction with the PM that has been long disregarded despite its importance in cell function, pathogenesis, and evolution. It also proposes a scheme of mitochondria–PM interactions with the intent to promote research and knowledge of this emerging pathway that promises to shift the current paradigms of cell biology.     

The Km of NADH dehydrogenase is decreased in mitochondria of cystic fibrosis cells

The kinetic properties of the NADH dehydrogenase of the mitochondrial respiratory chain, assayed as NADH-dependent rotenone-sensitive cytochrome c reductase have been studied in mitochondria isolated from mononuclear white blood cells in patients affected by cystic fibrosis. Data reported here show that the apparent Km of the enzyme for NADH is significantly decreased in cystic fibrosis mitochondria. These findings are independent of the age or the clinical state of the disease and have also been obtained with mitochondria isolated from cultured skin fibroblasts. These observations support the notion that cystic fibrosis is possibly accompanied by alterations of intracellular membranes and these are evident also in circulating cells and cultured fibroblasts.     

Autophagy and the degradation of mitochondria

The cellular process of macromolecular degradation known as macroautophagy has long been known to play a role in the elimination of mitochondria. Over the past decade, much progress has been made in the development of systems by which the nature and mechanism of mitochondria degradation may be studied. Recent findings imply that the degradation of mitochondria via autophagy may be more specific and more tightly regulated than originally thought, and have led to designation of this specific type of autophagy as “mitophagy”. In this review we provide a brief history of the development of mitophagy models and their associated discoveries.     

Differential processing of cytosolic and mitochondrial caspases

The mitochondria have been shown to play a key role in the initiation of caspase activation during apoptosis. Recently, some caspases have been shown to be associated with mitochondria. In this study, we used Jurkat T-lymphoblasts to show that caspases -2 and -3 are located in the mitochondrial intermembrane space, associated with the inner membrane. Caspase-9 is associated with the outer membrane and is exposed to the cytosolic compartment. Caspase activation took place predominantly in the cytosol in response to Fas ligation, but staurosporine treatment led to caspase activation in both cytosol and mitochondria. In response to both Fas and staurosporine treatment, caspase processing could be detected earlier in cytosol than in mitochondria, but this could reflect the limits of sensitive detection by immunoblotting. Only trace amounts of Apaf-1 were found in association with the mitochondria. However, staurosporine treatment led to preferential auto-processing of caspase-9 associated with mitochondria. These findings suggest that mitochondrial caspases are regulated independently of the cytosolic pool of caspases. The data are also consistent with the notion of a caspase nucleation site associated with mitochondria. Using a stable transfected CEM cell line, we show that Bcl-2 suppressed caspase processing in both cytosolic and mitochondrial compartments in response to both staurosporine and Fas ligation.     

Die Mikro- und Ultrastruktur abgedeckter Hohlelemente und die Conellen des Ammoniten-Gehäuses

Hollow floored spines in the shell ofKosmoceras (Kosmoceras) spinosum (Sow.) and the hollow floored keel ofEleganticeras elegantulum (Young & Bird) have been studied with the scanning electron microscope. In both cases the shell wall is complete in so far as it consists of the outer prismatic layer, the nacreous layer and at least the distal zones of the inner prismatic layer. Both types of hollow shell elements are separated from the lumen of the whorl by a floor which is made up by the proximal zones of the inner prismatic layer. This explains why conellae occur, with preference, along the floors of hollow spines and keels. The origin of primary aragonitic conellae and of secondary calcitic conellae is discussed as well as their dependence on structural properties of the corresponding shell layer, which is the inner prismatic layer. An attempt is made to reconstruct the way of formation of the floored hollow spines and the floored hollow keels by the mantle epithelium.     

Homogeneous longitudinal profiles and synchronous fluctuations of mitochondrial transmembrane potential

This study reports for the first time (a) the longitudinal profile of the transmembrane potential (mDeltapsi) of single mitochondria using a Nernstian fluorescent probe and (b) the distribution of mDeltapsi fluctuations of mitochondria undergoing permanent depolarization. Our findings show that (1) mitochondria in different energetic conditions coexist in the same cell, (2) mDeltapsi is rather homogeneous along the entire length of single mitochondria, (3) mDeltapsi is not influenced by the surrounding cytoplasmic environment and (4) mDeltapsi fluctuations occur simultaneously in groups of mitochondria connected in a network. Taken together, these findings provide further evidence for a functional relationship between mitochondrial arrangement and energetic condition.     

Do mammalian cells synthesize lipoic acid? Identification of a mouse cDNA encoding a lipoic acid synthase located in mitochondria

Lipoic acid is a coenzyme essential to the activity of enzymes such as pyruvate dehydrogenase, which play important roles in central metabolism. However, neither the enzymes responsible for biosynthesis nor the biosynthetic event of lipoic acid has been reported in mammalian cells. In this study, a mouse mLIP1 cDNA for lipoic acid synthase has been identified. We have shown that the cDNA encodes a lipoic acid synthase by its ability to complement a mutant of Escherichia coli defective in lipoic acid synthase and that mLIP1 is targeted into the mitochondria. These findings suggest that mammalian cells are able to synthesize lipoic acid in mitochondria.     

Biogenesis of peroxisomes and mitochondria: linked by division

Peroxisomes and mitochondria are metabolically linked organelles, which are crucial to human health and development. The search for components involved in their dynamics and maintenance led to the interesting finding that mitochondria and peroxisomes share components of their division machinery. Recently, it became clear that this is a common strategy used by mammals, fungi and plants. Furthermore, a closer interrelationship between peroxisomes and mitochondria has been proposed, which might have an impact on functionality and disease conditions. Here, we briefly highlight the major findings, views and open questions concerning peroxisomal formation, division, and interrelationship with mitochondria. Presented at the 50th Anniversary Symposium of the Society for Histochemistry, Interlaken, Switzerland, October 1–4, 2008.     

Aragonitic dendritic prismatic shell microstructure in Thracia (Bivalvia,Anomalodesmata)

The shells of most anomalodesmatan bivalves are composed of an outer aragonitic layer of either granular or columnar prismatic microstructure, and an inner layer of nacre. The Thraciidae is one of the few anomalodesmatan families whose members lack nacreous layers. In particular, shells of members of the genus Thracia are exceptional in their possession of a very distinctive but previously unreported microstructure, which we term herein “dendritic prisms.” Dendritic prisms consist of slender fibers of aragonite which radiate perpendicular to, and which stack along, the axis of the prism. Here we used scanning and transmission electron microscopical investigation of the periostracum, mantle, and shells of three species of Thracia to reconstruct the mode of shell calcification and to unravel the crystallography of the dendritic units. The periostracum is composed of an outer dark layer and an inner translucent layer. During the free periostracum phase the dark layer grows at the expense of the translucent layer, but at the position of the shell edge, the translucent layer mineralizes with the units typical of the dendritic prismatic layer. Within each unit, the c‐axis is oriented along the prismatic axis, whereas the a‐axis of aragonite runs parallel to the long axis of the fibers. The six‐rayed alignment of the latter implies that prisms are formed by {110} polycyclically twinned crystals. We conclude that, despite its distinctive appearance, the dendritic prismatic layer of the shell of Thracia spp. is homologous to the outer granular prismatic or prismatic layer of other anomalodesmatans, while the nacreous layer present in most anomalodesmatans has been suppressed.     

Phospholipase activity in rat liver mitochondria studied by the use of endogenous substrates

The hydrolysis of endogenous phosphatidyl ethanolamine and lecithin in rat liver mitochondria has been studied by using mitochondria from rats injected with ethanolamine-1,2-(14)C or choline-1,2-(14)C. A phospholipase A-like enzyme has been demonstrated, which catalyzes the hydrolysis of one fatty acid ester linkage in phosphatidyl ethanolamine and lecithin. Phosphatidyl ethanolamine is hydrolyzed in preference to lecithin and the main reaction products are free fatty acids and lysophosphatidyl ethanolamine. The further breakdown of lysophospholipids appears to be limited in mitochondria, which indicates that lysophospholipase activity is mainly located extramitochondrially. The enzymic system is greatly stimulated by calcium ions, and also slightly by magnesium ions, while EDTA inhibits it almost completely. These findings are discussed in relation to previous observations on the effect of calcium and of EDTA on the functions of mitochondria. The possible function of the mitochondrial phospholipase for the formation of phospholipids with special fatty acids at the alpha- and -position is discussed.