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PubMed1986

Xylosylation and glucuronosylation reactions in rat liver Golgi apparatus and endoplasmic reticulum.

We have studied in rat liver the subcellular sites and topography of xylosylation and galactosylation reactions occurring in the biosynthesis of the D-glucuronic acid-galactose-galactose-D-xylose linkage region of proteoglycans and of glucuronosylation reactions involved in both glycosaminoglycan biosynthesis and bile acid and bilirubin conjugation. The specific translocation rate of UDP-xylose into sealed, "right-side-out" vesicles from the Golgi apparatus was 2-5-fold higher than into sealed right-side-out vesicles from the rough endoplasmic reticulum (RER). Using the above vesicle preparations, we only detected endogenous acceptors for xylosylation in the Golgi apparatus-rich fraction. The specific activity of xylosyltransferase (using silk fibroin as exogenous acceptor) was 50-100-fold higher in Golgi apparatus membranes than in those from the RER. Previous studies had shown that UDP-galactose is translocated solely into vesicles from the Golgi apparatus. In these studies, we found the specific activity of galactosyltransferase I to be 40-140-fold higher in membranes from the Golgi apparatus than in those from the RER. The specific translocation rate of UDP-D-glucuronic acid into vesicles from the Golgi apparatus was 10-fold higher than into those from the RER, whereas the specific activity of glucuronosyltransferase (using chondroitin nonasaccharide as exogenous acceptor) was 12-30-fold higher in Golgi apparatus membranes than in those from the RER. Together, the above results strongly suggest that, in rat liver, the biosynthesis of the above-described proteoglycan linkage region occurs in the Golgi apparatus. The specific activity of glucuronosyltransferase, using bile acids and bilirubin as exogenous acceptor, was 10-25-fold higher in RER membranes than those from the Golgi apparatus. This suggests that transport of UDP-D-glucuronic acid into the RER lumen is not required for such reactions.

Animals↗
PubMed1964

ISOLATION OF THE GOLGI APPARATUS FROM PLANT CELLS.

A method for the isolation of the Golgi apparatus from stem tissues of onion is described. Preparations that consisted mainly of morphologically identifiable Golgi apparatus have been obtained. The best preparations were obtained from tissue homogenized under conditions of minimum shear, and in the presence of sucrose and certain additives which aid in preservation of the integrity of the Golgi membranes. Those additives, which had a pronounced stabilizing effect on the isolated apparatus, included both monovalent and divalent ions (sodium and calcium) and dextran. A large portion of the Golgi apparatus did not appear to change microscopic appearance upon isolation, but were observed to fuse into large aggregate structures not unlike those occurring naturally in certain animal or insect cells (12). Fusion occurred both at the edges of the cisternae and in register, but the integrity of the individual cisternae was not destroyed. The major contaminants of the Golgi apparatus fraction were numerous small and large spherical vesicles. At least some of these vesicles appeared to have been derived from the Golgi apparatus; others may have been fragments of the cell membrane, the endoplasmic reticulum, or other cell debris. By utilizing this procedure, it has been possible to obtain fractions of Golgi apparatus from plant tissues other than onion stem. However, at the present time it is only with onion that the Golgi apparatus has been isolated in a form that would warrant further purification for biochemical analysis.

Animals↗
PubMed1995

Sexual differences in the Golgi apparatus of rat hepatocytes: three-dimensional analysis.

Lipid metabolism takes place in the Golgi apparatus, but at a higher rate in female than in male rats. I therefore examined the Golgi apparatus by morphometric means for differences between the sexes at the light- and electron-microscopic level. The Golgi apparatus was stained in situ by a zinc-iodide-osmium method. The counts of the Golgi apparatus in cross-sections in female hepatocytes by light microscopy were approximately twice that in male hepatocytes. Upon ovariectomy, these counts were greatly reduced but were reestablished after estrogen supplement. To clarify this phenomenon, three-dimensional reconstructions of the Golgi apparatus were produced from electron-microscopic images of serially cut 160-nm sections. The Golgi apparatus of both male and ovariectomized females had the shape of a small ring, whereas it took the form of a large elongated cylinder in normal females and in castrated males after treatment with estrogen. The numerical difference in Golgi apparatus counts by light microscopy of in males and females is, therefore, apparently attributable to the size and shape of the Golgi apparatus, and is controlled by the estrogen level.

Animals↗
PubMed2005

Maintenance of Golgi apparatus structure in the face of continuous protein recycling to the endoplasmic reticulum: making ends meet.

I focus here on the Golgi apparatus and the dynamic relationship between the Golgi apparatus, the central organelle of the secretory pathway, and the endoplasmic reticulum (ER). The proteins and lipids of the Golgi apparatus originate in the ER, and cargo proteins and lipids that also originate in the ER are processed and sorted within the Golgi apparatus. The Golgi apparatus is indeed the central organelle of the secretory pathway. Surprisingly, many, if not all, of the proteins and accompanying lipids of the Golgi apparatus cycle continuously between the Golgi and the ER. Neither the Cisternal Maturation nor the Vesicular Transport/Stable Compartment model of Golgi apparatus function predicts continuous cycling of Golgi resident proteins through the ER. Evidence for this cycling comes from multiple experimental approaches, including ER-exit block-revealed accumulation of recycled Golgi resident proteins in the ER, evidence for exchange of green fluorescent protein (GFP)-tagged Golgi proteins or their analogues between Golgi and ER pools, and cisternal rab overexpression-induced redistribution of Golgi resident proteins to the ER. The implications of Golgi protein cycling for the maintenance of Golgi structure in the interphase mammalian cell are discussed. The challenge for the future is to put Golgi resident protein cycling pathway(s) to protein machinery and to characterize the cumulative, weak, dynamic interactions that hold the Golgi apparatus together. In doing so, new paradigms of organelle biogenesis will emerge.

Animals↗
PubMed1990

Fragmentation of the Golgi apparatus of motor neurons in amyotrophic lateral sclerosis revealed by organelle-specific antibodies.

Many studies have established the central involvement of the Golgi apparatus in the transport and processing of plasma membrane, lysosomal, and secreted proteins. The Golgi apparatus of neurons is also involved in the axoplasmic flow of fast-moving macromolecules and in the orthograde, retrograde, and transsynaptic transport of exogenous ligands. Markers of the Golgi apparatus, based on traditional methods of enzyme cytochemistry, are not applicable to human tissues obtained at autopsy. For that reason, the Golgi apparatus of brain cells has not been examined adequately in diseases of the human nervous system. Here we report that an antiserum raised against MG-160, a 160-kDa sialoglycoprotein of medial cisternae of the Golgi apparatus of several rat cells, is a specific and easily reproducible immunocytochemical marker of the Golgi apparatus of human neurons and other cells obtained at autopsy. Application of this probe in amyotrophic lateral sclerosis has shown a fragmentation of the Golgi apparatus in motor neurons similar to that induced by depolymerization of microtubules. We suggest that the fragmentation of the Golgi apparatus of motor neurons in amyotrophic lateral sclerosis has functional implications because significant reductions of secretion of insulin and immunoglobulins have been observed in islet cells and plasma cells, respectively, treated with microtubule-disrupting agents.

Aged↗
PubMed1989

Molecular trapping of a fluorescent ceramide analogue at the Golgi apparatus of fixed cells: interaction with endogenous lipids provides a trans-Golgi marker for both light and electron microscopy.

We have previously shown that a fluorescent derivative of ceramide, N-(epsilon-7-nitrobenz-2-oxa-1,3-diazol-4-yl-aminocaproyl)-D-eryth ro-sphingosin e (C6-NBD-Cer), vitally stains the Golgi apparatus of cells (Lipsky, N. G., and R. E. Pagano. 1985. Science (Wash. DC). 228:745-747). In the present paper we demonstrate that C6-NBD-Cer also accumulates at the Golgi apparatus of fixed cells and we explore the mechanism by which this occurs. When human skin fibroblasts were fixed with glutaraldehyde and then incubated with C6-NBD-Cer at 2 degrees C, the fluorescent lipid spontaneously transferred into the cells, labeling the Golgi apparatus as well as other intracellular membranes. Subsequent incubations with defatted BSA at 24 degrees C removed excess C6-NBD-Cer from the cells such that fluorescence was then detected only at the Golgi apparatus. Similar results were obtained using other cell types. A method for visualizing the fluorescent lipid at the electron microscopic level, based on the photoconversion of a fluorescent marker to a diaminobenzidine product (Sandell, J. H., and R. H. Masland, 1988. J. Histochem. Cytochem. 36:555-559), is described and evidence is presented that C6-NBD-Cer was localized to the trans cisternae of the Golgi apparatus. While accumulation occurred in cells fixed in various ways, it was inhibited when fixation protocols that extract or modify cellular lipids were used. In addition, Filipin, which forms complexes with cellular cholesterol, labeled the Golgi apparatus of fixed cells and inhibited accumulation of C6-NBD-Cer at the Golgi apparatus. These results are discussed in terms of a simple model based on the physical properties of C6-NBD-Cer and its interactions with endogenous lipids of the Golgi apparatus. Possible implications of these findings for metabolism and transport of (fluorescent) sphingolipids in vivo are also presented.

4-Chloro-7-nitrobenzofurazan↗
PubMed1992

Low density lipoprotein receptor and cation-independent mannose 6-phosphate receptor are transported from the cell surface to the Golgi apparatus at equal rates in PC12 cells.

Efficient transport of cell surface glycoproteins to the Golgi apparatus has been previously demonstrated for a limited number of proteins, and has been proposed to require selective sorting in the endocytic pathway after internalization. We have studied the endocytic fate of several glycoproteins that accumulate in different organelles in a variant clone of PC12, a regulated secretory cell line. The cation-independent mannose 6-phosphate receptor and the low density lipoprotein receptor, both rapidly internalized from the cell surface, and the synaptic vesicle membrane protein synaptophysin, were transported to the Golgi apparatus with equivalent, nonlinear kinetics. Transport to the Golgi apparatus (t1/2 = 2.5-3.0 h) was several times faster than turnover of these proteins (t1/2 greater than or equal to 20 h), indicating that transport of these proteins to the Golgi apparatus occurred on average several times for each protein. In contrast, Thy-1, a protein anchored in the membrane by a glycosylphosphoinositide group, was internalized and transported to the Golgi apparatus more slowly than the three transmembrane proteins. Since each of the transmembrane proteins studied showed the same t1/2 for transport to the Golgi apparatus, we conclude that transport of these proteins from the cell surface to the Golgi apparatus does not require sorting information specific to any one of these proteins. These results suggest that one of the functions of late endosomes is constitutive recycling of cell surface receptors through the Golgi apparatus if they fail to recycle to the cell surface directly from early endosomes, and that the late endosome recycling pathway is followed frequently by many rapidly internalized proteins.

Animals↗
PubMed1983

Relationship between microtubules and Golgi apparatus in hepatocytes: a quantitative study during experimental nephrosis.

In many cell types, microtubules are preferentially associated with the Golgi apparatus. However, the existence of a functional link between these two organelles is still hypothetical. To gain insight into this question, the relationships between microtubules and the Golgi apparatus were studied in rat hepatocytes during experimental nephrosis induced by the aminonucleoside of puromycin. This condition is known to cause prolonged stimulation of plasma protein production by the hepatocytes. Rats were studied 2, 4, 5, 10 and 20 days after aminonucleoside injection. The amount of albumin was measured in serum and hepatic microsomes by laser immunonephelometry. The volume densities of microtubules around the Golgi apparatus and in the remaining cytoplasm were measured by ultrastructural morphometry. Changes of the Golgi apparatus were analysed by measuring the volume density of the whole organelle and the respective proportion of saccules and vesicles. Proteinuria began 5 days after aminonucleoside injection and was accompanied by a decrease in serum albumin and a rise in microsomal albumin. These changes were still more striking after 10 days, but protein and albumin levels were almost back to normal after 20 days. Concomitantly, the volume density of the microtubules increased significantly around the Golgi apparatus (32% after 10 days), and not in the remaining cytoplasm. The Golgi apparatus was enlarged (80% after 10 days) with a higher ratio of secretory vesicle to saccule volume densities. These results show that additional microtubules are present around the Golgi apparatus during the enhanced production of plasma proteins which occurs in nephrosis. They suggest that in hepatocytes, microtubules play a part in the Golgi apparatus function of plasma protein processing.

Animals↗
PubMed1992

The signal anchor and stem regions of the beta-galactoside alpha 2,6-sialyltransferase may each act to localize the enzyme to the Golgi apparatus.

The beta-galactoside alpha 2,6-sialyltransferase has been localized to the trans cisternae of the Golgi apparatus and the trans Golgi network where it transfers sialic acid residues to terminal positions on N-linked oligosaccharides. It is a type II transmembrane protein possessing a 9-amino acid amino-terminal cytoplasmic tail, a 17-amino acid signal anchor domain, and a 35-amino acid stem region which tethers the large luminal catalytic domain to the membrane anchor. Previous work has demonstrated that the soluble sialytransferase catalytic domain is rapidly secreted from Chinese hamster ovary cells. These results suggest that the signals for Golgi apparatus localization do not reside in the catalytic domain of the enzyme but must reside in the cytoplasmic tail, signal anchor domain, and/or stem region. To determine which amino-terminal regions are required for Golgi apparatus localization, mutant sialyltransferase proteins were constructed by in vitro oligonucleotide-directed mutagenesis, expressed in Cos-1 cells, and localized by indirect immunofluorescence microscopy. Signal cleavage-sialyltransferase mutants which consist of only the stem and catalytic domain of the enzyme are not rapidly secreted but are retained intracellularly and predominantly localized to the Golgi apparatus. However, deletion of either the stem region or the cytoplasmic tail of the membrane-bound sialyltransferase does not alter its Golgi apparatus localization. In addition, sequential replacement of the amino acids of the sialyltransferase signal anchor domain with amino acids from the signal anchor domain of a plasma membrane protein, the influenza virus neuraminidase does not alter the Golgi apparatus localization of the sialyltransferase. These observations suggest that sequences in the signal anchor region and stem region allow the Golgi apparatus localization of the membrane-bound and soluble forms of the sialytransferase, respectively, and that both regions may contain Golgi apparatus localization signals.

Amino Acid Sequence↗
PubMed1981

Vitamin A effects on hepatic Golgi apparatus architecture.

Effects of dietary vitamin A deficiency and excess on Golgi apparatus architecture were determined for livers of male CDF rats. In deficient animals, Golgi apparatus stacks were reduced in diameter and characterized by small, often highly fenestrated, saccules. Total membrane surface occupied by Golgi apparatus membranes also was less. Golgi apparatus of livers of animals receiving vitamin A in excess were more variable ranging from nearly normal appearance to much larger than normal. Saccules were larger and lacked the numerous fenestrations shown by Gol;gi apparatus of vitamin A deficient animals. Numbers and appearance of secretory vesicles and total number of small vesicular profiles were unaffected by vitamin A status of the animal. Unusual cisternal configurations were encountered much more frequent at the mature face of Golgi apparatus of animals fed vitamin A excess than in animals receiving adequate vitamin A and were absent from Golgi apparatus of animals receiving no vitamin A. Except for slightly swollen mitochondria and a loss of the "zone of exclusion" surrounding the nucleus, both observed in vitamin A excess, the Golgi apparatus response was the only ultrastructural alteration in liver that responded consistently to changes in vitamin A status.

Acid Phosphatase↗
PubMed1997

Purification and characterization of basal apparatuses from a flagellate green alga.

Basal apparatuses consisting of two basal bodies and several attached fibers were isolated from the naked green flagellate Spermatozopsis similis by detergent extraction and mechanical disintegration. Sucrose density centrifugation yielded highly enriched basal apparatuses as shown by electron microscopy. SDS-PAGE revealed the absence of histones, indicating the removal of nuclear contaminations from the isolated basal apparatuses. A mass spectrometric analysis of the carboxyterminal peptides of alpha tubulin documented detyrosination and glutamylation as posttranslational modifications and showed that some 5% of the alpha tubulin carries a polyglutamyl side chain which can reach at least 17 residues in length. Monoclonal antibodies raised against the purified basal apparatuses were used to characterize novel components in the basal apparatus. A 210-kD component identified by mAB BAS (basal apparatus of Spermatozopsis) 1.4 was localized in the flagellar transitional region by immunogold electron microscopy. Antibody BAS 16.4 reacted with two high molecular weight bands (approximately 265 and 240 kD) in Western blotting and decorated a fiber attached to the proximal end of the basal bodies. Immunofluorescence staining of isolated cytoskeletons with these mABs demonstrated that the antigens are also present in the basal apparatuses of Chlamydomonas reinhardtii and Dunahella bioculata. These antibodies are useful tools for the molecular cloning of components from the basal apparatus.

Amino Acid Sequence↗
PubMedDate not supplied

Flagellar apparatus absolute orientations and the phylogeny of the green algae.

The absolute orientation of the flagellar apparatus in green algal motile cells is a feature of considerable value in studies of green algal systematics and phylogeny. The absolute orientation patterns found in those algae for which this feature is known or can be deduced are reviewed. Counterclockwise absolute orientation occurs in all classes except the Chlorophyceae and is considered primitive, while the clockwise absolute orientation present in most members of the Chlorophyceae is the result of progressive clockwise rotation of components during evolution. Extant intermediates documenting this rotation include Hafniomonas vegetative cells, which show counterclockwise absolute orientation, and Chaetopeltis quadriflagellate zoospores, in which the flagellar apparatus is strictly cruciate except for a slight clockwise offset of the microtubular rootlets. The V-shaped arrangement of the basal bodies in the flagellar apparatus, as well as the presence of proximal sheaths and of two layers of scales on the cell body, further identifies the Chaetopeltis zoospore as a primitive cell type within the Chlorophyceae . Trends towards the exsertion of basal bodies from a flagellar pit, either apically or laterally, the elimination of quadriflagellate cells, and, in the Chlorophyceae , an increasing amount of basal body offset, indicate advancement within the classes. Absolute orientation is conserved during flagellar apparatus replication and development. Events after flagellar apparatus division in the algae studied may be subdivided into component assembly, which is universal and preserves phylogenetically-useful features, and component reorientation, which occurs in relatively few green algae and adapts the flagellar apparatus to specialized functions. From these flagellar apparatus orientation studies, a major reevaluation of evolution within the Chlorophyceae is proposed, with weakly- thalloid algae possessing desmoschisis (e.g. Chaetopeltis ) considered primitive, and most other types, including the Volvocales , considered more advanced. The evolution of wall formation does not preclude the formation of scales in primitive chlorophycean genera. In addition, one or more previously undescribed major lineages may exist within the green algae, including one, the Pleurastrum lineage, whose members possess dorsiventrally -flattened motile cells, counterclockwise absolute orientation of the flagellar apparatus, and a phycoplast at cytokinesis. The Chlorophyceae , the Ulvophyceae , and the Pleurastrum lineage are considered to have a common ancestor that resembled the modern genus Pyramimonas , while the Charophyceae is thought to be of more ancient derivation. Th

Chlorophyta↗
PubMed1991

Investigation of germinative cells in generating and renewed anagen hair apparatus in mice using anti-bromodeoxyuridine monoclonal antibody.

To elucidate the cell kinetics in generating and renewed anagen hair apparatus in mice, S-phase cells in dorsal skin of new-born and 14 to 25-day-old mice were labeled with bromodeoxyuridine (BrdU) and stained immunohistochemically using anti-BrdU monoclonal antibody. In primary hair germ, lower and outer cells were positively stained. In hair peg, the positive cells were divided into upper and lower portions. In bulbous hair peg, the lower positive cells gathered at the suprapapillary area, whereas the upper positive cells were located in the outer part of the hair apparatus. The latter positive cells were further divided in the middle and upper parts of the epithelial cord. The upper cells were going to form a sebaceous gland. From the suprapapillary group of germinative cells, hair cortex through the innermost cell layer of the outer root sheath were considered to be produced. The positive cells of the outer middle group may be important for elongation of hair apparatus and produce outer root sheath cells. At the end of anagen phase, first the suprapapillary cells became negative and then the outer root sheath cells became negative. BrdU-positive cells reappeared at the bottom of telogen hair apparatus and formed a secondary hair germ. Then, a similar cell kinetics was repeated in the renewed anagen hair apparatus. The germinative cells were separated into a few groups during the generation and cyclic changes of hair apparatus. Each cell group formed the individual part of the hair apparatus in a coordinate fashion, resulting in dynamic changes of the hair apparatus.

Animals↗
PubMed2005

Evaluation of hydrodynamics in the basket dissolution apparatus using computational fluid dynamics--dissolution rate implications.

The aim of this work was to simulate the fluid flow in the basket dissolution apparatus using computational fluid dynamics (CFD) and to use the resulting velocity data (in combination with velocity data from simulated flow fields of the paddle dissolution apparatus) to relate velocities in the vicinity of a dissolving surface to dissolution rate. A further objective of the work was to compare fluid velocities between the basket and paddle dissolution apparatuses. CFD simulations of the basket apparatus were carried out using Fluent software. Flow field solutions were compared with results from flow visualisation techniques and with published ultrasound-pulse-echo velocity data. Velocity data from the flow field solution revealed velocities within the basket to be of the same order as those at the base of the paddle apparatus at the same rotation speed, supporting equivalent dissolution rate data from these locations. Dissolution rates were obtained for compacts of benzoic acid dissolved in 0.1 M HCl at 37 degrees C in the basket apparatus at 50 rpm. The relationship between maximum velocity in the vicinity of a dissolving surface and dissolution rate data from both the paddle and basket apparatuses was in good agreement with theoretical predictions. Analysis of the dissolution rates suggests a significant contribution from free convection in regions of low velocity at the base of the vessel of the basket apparatus.

Benzoic Acid↗
PubMed2005

Release characterization of dimenhydrinate from an eroding and swelling matrix: selection of appropriate dissolution apparatus.

The objective of this study was to evaluate the effect of various hydrodynamic conditions on drug release from an eroding and gel forming matrix. For this purpose, dimenhydrinate was formulated with hydroxypropyl methyl cellulose and polyethylene oxide into matrix tablets and the drug release in deionized water was evaluated spectrophotometrically, using multiple dissolution methods, namely, compendial USP 27-apparatus I-III, and a modified apparatus II (paddle over mesh). Various hydrodynamic conditions were examined at the agitation rates of 50 and 100 rpm for apparatus I and II, and 5 and 8 dpm for apparatus III. Similarity and difference factors were calculated using compendial apparatus II release data as reference. Among the methods, apparatus I showed the slowest initial release, while the release from apparatus III at 8 dpm was the highest among the methods. This was further compared via the dissolution half-times and calculation of the average release rate for each method. Based on the analysis of difference and similarity factors (f(1) and f(2)), the study clearly demonstrates the significance of hydrodynamics and the choice of a dissolution method and their respective effect on overall release profiles when erodible and swellable matrix systems are involved. Full surface exposure with insertion of mesh device in apparatus II may provide more realistic conditions especially when release data are to be used in developing IVIVCs.

Chemistry, Pharmaceutical↗
PubMed2005

Apparatus bias and the use of light and texture in place conditioning.

In a typical conditioned place preference (CPP) preparation, animals alternately experience drug and vehicle effects in distinct chambers of an apparatus, spending more time in the drug-paired chamber post-conditioning. However, if all animals prefer the same chamber before conditioning, data interpretation may be compromised. Unbiased apparatus has been systematically validated with ethanol in mice ([Cunningham, C.L., Feree, N.K., Howard, M.A. Apparatus bias and place conditioning with ethanol in mice. Psychopharmacology (Berl) 2003;170:409-422]); the present study sought to identify and eliminate bias in a standard black-and-white apparatus and validate that apparatus for CPP with morphine and cocaine in rats. Apparatus bias was assessed in 24 adult female Sprague-Dawley rats. Subjects preferred the black chamber under bright lighting conditions, with no preference in the dark. Subjects then underwent a counterbalanced CPP regimen to 5 mg/kg SC morphine (n=12) or 20 mg/kg IP cocaine (n=12) using only tactile conditioned stimuli. Significant absolute preferences for the drug-paired chamber were produced by both drugs, with no effect of drug-paired chamber assignment on CPP expression; vehicle-treated controls (n=12) showed no preferences. Bias-free CPP to morphine and cocaine using standard apparatus in rats is possible. Implications for place conditioning are discussed, including the potential value of systematically exploiting apparatus bias in addition to eliminating it.

Animals↗
PubMed2000

The discovery of the division apparatus of plastids and mitochondria.

Mitochondria and plastids contain distinct genomes and multiply by binary division of existing organelles. Mitochondrial and plastid division can be clearly separated into two main events: division of the organelle nuclei (nucleoids), and subsequent division of the rest of the organelles, the process of organellokinesis. Organellokinesis makes use of organelle dividing apparatuses such as plastid-dividing ring (PD ring) and mitochondrion-dividing ring (MD ring). The plastid-dividing apparatus (PD apparatus) is composed of three electron-dense rings (the outer, middle and inner), while the mitochondrion-dividing apparatus (MD apparatus) is a pair of electron-dense rings in cytoplasm and inner ring in the mitochondrial matrix. The behaviour of both the PD and MD apparatuses throughout organelle division in Cyanidioschyzon merolae has been studied in detail by electron microscopy. When cells enter mitosis, the inner PD ring forms first, followed by the outer and middle rings and finally the MD rings. The PD rings begin to contract before the MD rings. However, the MD rings start to contract at about 4 times the speed of the PD rings and catch up to the PD rings. The cross-sectional areas of both the outer PD and MD rings increase as contraction in the plane of division progress. This suggests that the outer rings of organelle dividing apparatuses (OD apparatus) provide the motive force for contraction. FtsZ protein is located on the bacterial contractile ring at the equator of dividing bacteria, and controls bacterial division. Since FtsZ contains a tubulin motif, and host eukaryotic organisms and chloroplasts evolved from bacteria, there is debate whether that tubulins found in the cytoskeleton and the inner or outer PD ring evolved from FtsZ protein during eukaryogenesis.

Animals↗
PubMed2003

Toward an MRI-based method to measure non-uniform cartilage deformation: an MRI-cyclic loading apparatus system and steady-state cyclic displacement of articular cartilage under compressive loading.

Recent magnetic resonance imaging (MRI) techniques have shown potential for measuring non-uniform deformations throughout the volume (i.e. three-dimensional (3D) deformations) in small orthopedic tissues such as articular cartilage. However, to analyze cartilage deformation using MRI techniques, a system is required which can construct images from multiple acquisitions of MRI signals from the cartilage in both the underformed and deformed states. The objectives of the work reported in this article were to 1) design an apparatus that could apply highly repeatable cyclic compressive loads of 400 N and operate in the bore of an MRI scanner, 2) demonstrate that the apparatus and MRI scanner can be successfully integrated to observe 3D deformations in a phantom material, 3) use the apparatus to determine the load cycle necessary to achieve a steady-state deformation response in normal bovine articular cartilage samples using a flat-surfaced and nonporous indentor in unconfined compression. Composed of electronic and pneumatic components, the apparatus regulated pressure to a double-acting pneumatic cylinder so that (1) load-controlled compression cycles were applied to cartilage samples immersed in a saline bath, (2) loading and recovery periods within a cycle varied in time duration, and (3) load magnitude varied so that the stress applied to cartilage samples was within typical physiological ranges. In addition the apparatus allowed gating for MR image acquisition, and operation within the bore of an MRI scanner without creating image artifacts. The apparatus demonstrated high repeatability in load application with a standard deviation of 1.8% of the mean 400 N load applied. When the apparatus was integrated with an MRI scanner programmed with appropriate pulse sequences, images of a phantom material in both the underformed and deformed states were constructed by assembling data acquired through multiple signal acquisitions. Additionally, the number of cycles to reach a steady-state response in normal bovine articular cartilage was 49 for a total cycle duration of 5 seconds, but decreased to 33 and 27 for increasing total cycle durations of 10 and 15 seconds, respectively. Once the steady-state response was achieved, 95% of all displacements were within +/- 7.42 microns of the mean displacement, indicating that the displacement response to the cyclic loads was highly repeatable. With this performance, the MRI-loading apparatus system meets the requirements to create images of articular cartilage from which 3D deformation can be determined.

Adaptation, Physiological↗