Small Multivesicular Bodies Research Articles

Lingual ultrastructure of the long-finned pilot whale (Globicephala melas).

Microscopic studies on the cetacean tongue are limited and, to date, only a few ultrastructural reports on dolphins have been published. This report presents the initial description of the lingual ultrastructure of the long-finned pilot whale. The lingual integumental surface was smooth, lacking papillae, although flaking of outer stratum corneum cells could be observed at high resolution. The keratinocytes of the stratum spinosum of the epidermis resembled those of cetacean skin on other regions of the body. The similarities included the presence of cytoplasmic lipid droplets around the nuclei of stratutm spinosum cells, a lingual feature not seen in terrestrial mammals. Keratin intermediate filaments were numerous and occasionally formed aggregates of circular whorls. At cell surfaces, bundles of keratin intermediate filaments were frequently observed inserting into desmosomal plaques. Pigment granules were not evident and organelles were sparse. Stratum corneal cells contained nuclear remnants (parakeratosis) and small multivesicular bodies, and the corneal layer was approximately 18 cells thick. The nuclei of the stratum basale keratinocytes possessed exceptionally numerous and deep clefts. The dermis was nondistinctive. The skeletal muscle of the tongue was arranged in widely separated fasiculi containing small numbers of muscle fibres. Typical fine structure of skeletal muscle bands and tubular elements was observed by transmission electron microscopy.

Structure of yolk granules in oocytes and eggs of Blattella germanica and their interaction with vitellophages and endosymbiotic bacteria during granule degradation

Oocytes and embryos of the cockroach Blattella germanica were examined by optical and electron microscopy to study yolk granule degradation during embryo development. During vitellogenesis, progressively larger yolk granules are formed in the ooplasm and by chorionogenesis, the mature granules are packed so tightly that their shape is highly distorted. Throughout ovarian development, endosymbiotic bacteria lie at the follicle cell/oocyte interface. Just prior to chorionogenesis the endosymbionts transit the oocyte plasma membrane and cluster at the periphery. Bacteria become more numerous over the ventral region of the egg by day 1 postovulation and begin to invade the interior of the yolk mass from the ventral periphery. At that time, lysis of the nearby yolk granules occurs while those in the central ooplasm remain intact and free of bacteria up to day 4. Vitellophages become evident by day 2 postovulation. These cells are also distributed over the egg's periphery but are most numerous in the ventral region. Vitellophages, in association with the endosymbionts, protrude toward the yolk granules and extend filo- and lamellipodia over the granule surface. Portions of the yolk granules are then engulfed and sequestered as large vacuoles in the vitellophage's cytoplasm. The vacuoles then become vesiculated. As embryo development proceeds, the vesiculated portions partition into smaller multivesicular bodies. This study describes the dynamics of yolk granule-vitellophage interaction in embryos of B. germanica and suggests that yolk utilization entails the cooperative efforts of both vitellophages and endosymbiont bacteria.

Vasopressin- and cAMP-induced changes in ultrastructure of isolated perfused inner medullary collecting ducts

Studies were performed to correlate arginine vasopressin (AVP)-induced changes in epithelial ultrastructure with changes in osmotic water permeability in isolated perfused rat terminal inner medullary collecting ducts (tIMCD). The tubules were perfused in three time periods, i.e., a 40-min basal period, a 40-min period with 0.1 nM AVP in the bath, and a 60-min withdrawal period. In each phase, the osmotic water permeability (Pf) was measured, and the perfused tubules were fixed for electron microscopy. AVP caused a four- to eightfold increase in Pf and induced several ultrastructural changes as follows: increased cell height of IMCD cells, expansion of the intercellular spaces, formation of large vacuoles, and increased coated pit density in the apical plasma membrane [from 0.6 +/- 0.2 (n = 6) to 2.9 +/- 0.3 (n = 7) pits/100 microns membrane length]. During AVP withdrawal, Pf decreased toward the basal value in association with partial reversal of the ultrastructural changes including a decrease in coated pit density to 1.0 +/- 0.2 (n = 4). Stimulation with 8-bromoadenosine 3',5'-cyclic monophosphate (8-bromo-cAMP) (0.1 mM) produced similar changes in Pf. Coated pit density increased to 2.1 +/- 0.4 (n = 4) after cAMP stimulation and after cAMP withdrawal decreased to 1.2 +/- 0.2 (n = 6). In contrast to stimulation with AVP, cAMP stimulation did not result in dilated intercellular spaces or formation of large vacuoles. The only ultrastructural feature that directly correlated with the water permeability was the density of coated pits in the apical membrane. Organelles involved in the endocytic pathway were studied with cationized ferritin or albumin-gold in the luminal perfusate. At the end of 40 min basal perfusion or AVP stimulation, luminal tracer was found almost exclusively in large multivesicular bodies (MVB). Tubules perfused with tracer during AVP withdrawal demonstrated rapid tracer accumulation in small vesicles and small MVB within 3-5 min, a time point corresponding to the rapid phase of Pf decrease. Later (30-60 min) the label was mainly confined to large MVB. Occasionally during AVP stimulation or withdrawal, small coated vesicles and smooth vesicles with coated extensions were noted to contain tracer. The data demonstrate AVP-mediated coated pit formation and cellular changes and show very rapid internalization of apical membrane after AVP withdrawal.

Effects of chloroquine on the photosensory membrane turnover and the ultrastructure of lysosome-related bodies of the crayfish photoreceptor.

The effect of chloroquine in combination with bright light on the ultrastructure of crayfish (Orconectes limosus R.) photoreceptors was investigated in vivo. Chloroquine had several effects upon the crayfish retina. Multivesicular bodies (MVB) that are involved in lysosomal degradation of photosensory membrane were altered in ultrastructure. MVB frequently contained smaller MVB in a state of more advanced membrane degradation. Additionally screening pigment-like granules appeared in MVB. MVB accumulated in and filled the retinular cell cytoplasm just proximal or distal to the basement membrane which indicated inhibition of photosensory membrane degradation. Under chloroquine treatment rhabdom degradation appeared to be inhibited, as rhabdom diameter was less reduced under these conditions. Also chloroquine caused accumulation of screening pigment granules in glial cells within the lamina ganglionaris.

Cytochemical evidence for different routes of gonadotropin-releasing hormone processing by large gonadotropes and granulosa cells.

The route and rate of internalization of GnRH were compared in studies of dispersed ovarian granulosa cells and large pituitary gonadotropes from fractions enriched by centrifugal elutriation. GnRH receptors were localized with the use of a biotinylated [D-Lys6]GnRH analog, followed by avidin gold or avidin-biotin-peroxidase complex stains. Both target cell types bound the [biotinyl-D-Lys6]GnRH (Bio-GnRH) in 1 min, and there were multiple patches of label on microvilli and coated or uncoated pits by 3 min. Quantification of the avidin-gold stains showed a significant increase in the number of labeled sites per cell profile at 3 min, followed by a decrease 15 min after exposure. No staining was seen in cells treated with medium only or with Bio-GnRH competing with a 100-fold excess of unlabeled [D-Lys6]GnRH. Internalization of the Bio-GnRH occurred during the first 3 min in both target cell types. However, the initial sites of processing appeared to be different. In granulosa cells, label was in vesicles and receptosomes (endosomes) and a few small multivesicular bodies. No stain was seen in the Golgi region for at least 15 min, at which time the stain was of low intensity. At later times (15-30 min), most of the label appeared in large multivesicular bodies. In contrast, gonadotropes exhibited labeling in Golgi complex cisternae, condensing vesicles, and immature granules as early as 3 min after exposure. Label was also seen on a subpopulation of granules in the cytoplasm and in a few multivesicular bodies. These comparative studies of two different target cells suggest that whereas the rates of internalization of GnRH are similar, the initial sites of processing may be different. Granulosa cells may degrade or separate the ligand from its receptor in multivesicular bodies. Large pituitary gonadotropes appear to use the Golgi complex route, and the processing may be associated with the formation of granules. The staining pattern correlates with early immunocytochemical studies that showed staining for GnRH on gonadotrope granules. We hypothesize that the granules may be sites for degradation of the ligand, separation of the ligand from its receptor, recycling of the receptor to the plasma membrane, or all three.

Diurnal changes of lysosome-related bodies in the crayfish photoreceptor cells.

The effect of illumination on the degradation of microvillar membrane in the invertebrate photoreceptor cell has been correlated with the appearance in the cytoplasm of certain distinct lysosome-related bodies. Three types of organelles were distinguished in the retinula cell cytoplasm of the crayfish, multivesicular bodies (MVB), both large (.20-1.50 micron) and small (1.49-0.30 micron), combination bodies (CB), and lamellar bodies (LB). Under diurnal lighting conditions significant temporal differences were found in the appearance of these three classes of organelles in the retinula cell. Small MVB are present at a consistent level throughout most of the diurnal cycle but show peak numbers at 30 min after light onset and again after 6 h of dark adaptation. Large MVB increase significantly 1 h after light onset and remain elevated through 4 h in the light. After 4 h the large MVB decline gradually for the remaining light period. Combination bodies and LB do not begin to increase until 1 h after light onset and are at peak levels between 4 and 6 h into the light period. The minimum rhabdome diameter coincides with the peak levels of large MVB, CB, and LB. These data support support the hypothesis that light causes microvillar membrane breakdown, resulting in the initial production of MVB which in turn undergo degradation to form CB and finally LB. This primary degradative response appears to be completed within the first 8 h of the light period.

Studies on Regional Fine Structure and Function in the Rabbit Epididymis

The regional fine structure of principal cells in the rabbit epididymal duct is described. Pinocytotic markers and enzyme cytochemistry were used to study pinocytotic mechanisms. Three main segments were defined. The initial segment showed selective micropinocytosis with transfer of surface membrane into large multivesicular bodies. The middle segment showed profuse pinocytosis of opaque material in the lumen and of the pinocytotic markers, and abundant lysosomes. The terminal segment showed some micropinocytosis only with small multivesicular bodies. Iron dextrin only was taken up.There was some evidence of micro‐merocrine protein secretion in the initial segment, but most of the lumenal materials was taken up again in the proximal part of the middle segment. Small vacuoles appeared to form from the Golgi complex in the other segments, too. The possibility is suggested that these vacuoles may represent merocrine secretory vacuoles in all principal cells of the epididymis.Morphological sperm maturation is completed in the proximal half of the middle segment, functional maturation in the proximal third of the terminal segment.

Light and electron microscopic studies of rat kidney after administration of inhibitors of the citric acid cycle in vivo. A morphological and histochemical study of the pars recta during malonate poisoning.

Extensive conglomerations of smooth endoplasmic reticulum (SER) formed in pars recta proximal tubules of rat kidney 15 to 30 minutes after single subcutaneous injections of malonic acid (0.5 M given at 1.0 ml per 100g body weight). Simultaneously rough endoplasmic reticulum (RER) disappeared but within 4 hours the normal ER pattern was restored. During this period numerous large multivesicular bodies (MVB) accumulated. In addition to vesicles many MVB contained mitochondria, cytoplasm and even smaller MVB. Apparent fusion of thinner SER membrane with thicker membrane limiting MVB was observed rarely in both perfusion and immersion fixed tissues. Histochemical studies on altered ER, labelled with thiamine pyrophosphatase and unbuffered osmium staining, failed to demonstrate that MVB vesicles were ER derived or that ER was incorporated into MVB by fusion with the limiting membrane. This must be considered a fixation artifact. Horseradish peroxidase, a pinocytotic tracer, showed MVB to have pinocytotic origin. The vesicles apparently formed by budding of cytoplasm into MVB matrices. Acid phosphatase activity was acquired by MVB as they moved towards mid-cell and the enclosed organelles underwent digestion. It is clear that MVB of pars recta are ambilysosomes digesting both autologous and heterologous materials but there was no evidence that altered ER underwent digestion within them and it is likely that rapid alterations in ER resulted from rearrangements of existing membrane moieties. MVB have been implicated in autophagy in other cell types but their autophagic role in sublethally injured kidney tubules has received little attention.