• Journal of Life Science
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• v.21 no.10
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• pp.1401-1406
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• 2011

Morphological changes in immune cells occur due to pathogen infection and natural circulation. T cells produce uropod, filopodia, lamellipodia, and microvilli for inflammation, immunosurvelliance, migration, and diapedesis. Short finger-like microvilli cover the surfaces of circulating mammalian immune cells. The surface features of monocytes and neutrophils are quite different, containing membrane ruffles as their predominant structure. In this study, we present the involvement of actin cytoskeleton regarding T lymphocyte microvilli. From analysis of scanning electron micrographs, Jurkat T lymphocyte microvilli was observed to rapidly disassemble when exposed to the actin-sequestering molecule, cytochalasin D. In contrast to cytochalasin D treatment, we found that median microvillar thickness was enlarged on Jurkat T lymphocytes treated with PMA via Lin-11, Isl-1, Mec-3 Kinase (LIMK) and cofilin signaling. In addition, actin cytoskeleton was involved in polarity formation in EL4 T lymphocytes. These results suggest that microvilli formation or polarity of T lymphocytes are involved in actin cytoskeleton dynamics.

• IMMUNE NETWORK
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• v.23 no.1
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• pp.3.1-3.14
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• 2023

Microvilli are outer membrane organelles that contain cross-linked filamentous actin. Unlike well-characterized epithelial microvilli, T-cell microvilli are dynamic similar to those of filopodia, which grow and shrink intermittently via the alternate actin-assembly and -disassembly. T-cell microvilli are specialized for sensing Ags on the surface of Ag-presenting cells (APCs). Thus, these finger-shaped microprotrusions contain many signaling-related proteins and can serve as a signaling platforms that induce intracellular signals. However, they are not limited to sensing external information but can provide sites for parts of the cell-body to tear away from the cell. Cells are known to produce many types of extracellular vesicles (EVs), such as exosomes, microvesicles, and membrane particles. T cells also produce EVs, but little is known about under what conditions T cells generate EVs and which types of EVs are released. We discovered that T cells produce few exosomes but release large amounsts of microvilli-derived particles during physical interaction with APCs. Although much is unanswered as to why T cells use the same organelles to sense Ags or to produce EVs, these events can significantly affect T cell fate, including clonal expansion and death. Since TCRs are localized at microvilli tips, this membrane event also raises a new question regarding long-standing paradigm in T cell biology; i.e., surface TCR downmodulation following T cell activation. Since T-cell microvilli particles carry T-cell message to their cognate partner, these particles are termed T-cell immunological synaptosomes (TISs). We discuss the potential physiological role of TISs and their application to immunotherapies.

• Animal cells and systems
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• v.5 no.1
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• pp.45-50
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• 2001

Rana ovarian follicles consist of oocyte, vitelline envelope, granulosa cells, and theca/epithelial layer. Using scanning electron microscopy, the surface structure of each follicular component was investigated. Changes in oocyte surface during oocyte maturation were also examined. Theca/epithelial layer was almost transparent and some blood vessels and granulosa cells were observed underneath in intact follicle. The number of granulosa cells was estimated to be 6700-7200 per oocyte. The granulosa cells partially overlapped each other and their microvilli penetrated the vitelline membrane via holes present in the vitelline envelope and seemed to be linked to oocyte microvilli. After removal of the vitelline envelope by microforcep, oocyte microvilli were observed on the surface of the devitellined oocyte. The oocyte microvilli formed partial clusters on the surface of white spot area which appears iust before germinal vesicle breakdown (GVBD), whereas they were evenly distributed in other areas. The microvilli became shorter and less dense with oocyte maturation. The lengths of oocyte microvilli in the immature and mature oocyte were 1.5 $\mu$m and 0.6 $\mu$m, respectively. The present study suggests a fundamental structural change occurring on the oocyte surface during maturation.

• Applied Microscopy
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• v.20 no.2
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• pp.117-126
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• 1990

Structural changes of the vitelline envelopes during oogenesis of a polychaete, Nectoneanthes oxypoda, were examined with a scanning electron micrscope. Oocytes grow in the same coelomic fluid to the final stage, but the surface appears to change in the structure during oogenesis. Projections, which were identified to be microvilli, change in shape, number and size. Short microvilli, which cover the surface of oocyte of $33{\mu}m$ diameter densely, grow in length, reaching a maximum at the stage of $73{\mu}m$. The number of microvilli increases with the stages of oogenesis, reaching a plateau at the stage of $82{\mu}m$. The observations suggest that control of material transport including yolk precursor proteins may be correlated with the structural changes in the microvilli.

• Applied Microscopy
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• v.29 no.4
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• pp.437-450
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• 1999

Bile canaliculi are the structure delivering bile secreted by hepatocytes into the bile passage. Bile secretion is mainly controlled by the cytoskeletal elements, mainly of actin in the microvilli, pericanalicular web. Most studies on the bile secretion have been done in viva situation, however, to control the various parameters in vitro culture system seem to be more useful. To set up an in vitro experimental system, the investigator isolated hepatocytes with an enzymatic method using a mixture of collagenase and hyaluronidase from normal Sprague-Dawley rat liver and cultured. Isolated hepatocytes were round and formed cords in culture. Microvilli covered the whole surface of hepatocytes. Bile canaliculi were formed between hepatocytes and were characterized by the presence of microvilli of various lengths and shapes mainly arising from small surface mounds. Actin filament core in the microvilli and pericanalicular actin web were incomplete. After cytochalasin D treatment, cultured hepatocytes were round but the surface were irregular with surfacen blebs, folds and grooves. Microvilli on the surface were scarce. Bile canaliculi were markedly dilated often with the detached junctional complexes. Bile canaliculi lacks microvilli almost completely and extended into the pericanalirular cytoplasm showing complex vacuolar and tubular structures by transmission electron mciroscopy. Pericanalicular actin web, intermediate filaments were hardly identified. Subsurface actin filaments were scattered scarcely under the cell membranes. These results suggest that hepatocytes isolated from rats can survive and form bile canaliculi in culture and the actin filaments are involved in the formation and/or maintenance of the bile canaliculi.

• Applied Microscopy
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• v.9 no.1
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• pp.1-11
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• 1979

Electron microscopic studies were carried out to investigate the fine structure of ommatidia of the compound eyes in Meimuna mongolica D. The crystalline cone appears round, and is composed of four double-membraned cone cells and surrounded by pigment cells having many pigment granules. The rhabdom is a closed type, and is composed of four rhabdomeres Its cross section reveals lamellated microvilli which are oriented in four different directions suggesting that these represent four photoreceptive sites. The microvilli, in a cross sectional view, are hexagonal in shape with a central axis inside. There are usually eight retinular cells arranged radially from the rhabdom, but in some retinular layers seven or nine retinular cells could be observed. The cytoplasm of each retinular cell is interconnected with that of microvilli of the rhabdomere, but the appearance of this interconnection varies depending on the number of retinular cells.'The retinlilar cells neighboring the microvilli seem to have well-developed perirhabdomal vacuoles and mitochondria as well as pigment granules surrounding these vacuoles.

• Korean Journal of Veterinary Research
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• v.39 no.3
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• pp.399-406
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• 1999

The development of uterus in fetuses on 60, 90 and 120 days of gastation and neonates of Korean native goats was investigated by scanning electron microscopy. The results were summarized as follows ; 1. In the 60-day-old fetuses, the short microvilli were sporadically observed on the luminal surface of the endometrium. 2. In the 90-day-old fetuses, the mucosal folds, polygonal microridges, numerous microvilli, flower-like-buds, and domeshaped or crateriform area were also observed on the luminal surface of endometrium. 3. In the 120-day-old fetuses, the primordial caruncles(nodules) of the endometrium were developed conspicuously and long microvilli were developed densely. 4. In the neonates, the caruncles and microvilli of the endometrium were more developed than those of 120-day-old fetuses.

• Applied Microscopy
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• v.14 no.2
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• pp.29-37
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• 1984

Morphological changes of the epithelium of the endometrium by prolonged treatment of $17{\beta}$-estradiol or progesterone in ovariectomized rats was studied at the ultrastructural level. The epithelium of the endometrium in ovariectomized rats was characterized by the appearance of a number of vacuoles which was contained with the membraneous structures, lipid droplets and the others. The epithelium was low cuboidal, and a few short microvilli were present at the cell surface. Secretory granules are rarely found. After estradiol treatment, the epithelium was high columnar in shape. The mitochondria was appeared throughout the cytoplasm, however, long or swelling mitochondria was often found. Golgi apparatus and rER were relatively well-developed. Relatively long and sparse microvilli were present at the cell surface. After progesterone treatment, the epithelium was characterized by the appearance of numerous vesicles at the apical region and numerous lipid droplets at the subnuclear region. At the cell surface a number of short and blunt microvilli were found. These data indicated that the endometrium was dependent on estrogen and progesterone for changes in both its morphological and functional state and suggested that each hormone exerted a unique effect on the epithelial cells.

• Applied Microscopy
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• v.1 no.1
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• pp.27-34
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• 1969

The compound eyes of the adult Drosophila melanogaster were. fixed in 1.25 per cent glutaraldehyde and 1 per cent osmium tetroxide buffered with sodium cacodylate at pH 7.2. Double fixed specimens were dehydrated using the alcohol series and embedded in Epon 812. They were sectioned with porter blum and JUM 5B ultra-microtome and then stained with lead hydrooxide and uranyl acetate. All thin sections were examined with Hitachi HS-7 or HU-11 electron microscope. The rhabdomere of the compound eye is composed of numerous microvilli packed, arranged, and projected from inner edge of each retinal cell. Each microvillus consisted of a centrum, about $82{\AA}$ in diameter, surrounded by the substances, about $105{\AA}$ in width, which were bounded with double membrane about $44{\AA}$ in thickness. In each inner edge of the microvilli, there was a cylinder, about $175{\AA}$ in diameter, in parallel with retinal cells, which contained a cylindrical axis about $583{\AA}$ in diameter. The surface of the outer edges .of .the microvilli was bounded with reticullar substances about $500{\AA}$ in thickness.

• Korean Journal of Animal Reproduction
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• v.17 no.3
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• pp.221-232
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• 1993

Morphological changes in the uterine and vaginal epithelial cells of the Korean native goats were studied in fifteen primiparous goats slaughtered on the day of parturition and on days 1, 3, 10 and 21 postpartum. 15 uterus and vagina from goats were examined by scanning and transmission electron microscopy. The results obtained in this study were summarized as follows : 1. Transmission electron microscopically, long microvilli which sometimes ramified were found until 10 days postpartum, while short microvilli were found at 21 days. The high electron dense irregular-shaped mitochondria were found in the cytoplasm and the crystalline structure of the mitochondrial matrix was also found from 1 day to 10 days postpartum. Well-developed rough-endoplasmic reticulum (rER) with dilated cisternae which contained the proteins materials was observed at 21 days postpartum. These materials were fused each other and then large granules were found in the free surface of the cytoplasm. A few lipid droplets were generally appeared in the cytoplasm, while numerous droplets were found at 21 days postpartum. A moderate number of ribosomes, a few multivesicular bodies, vesicles, lysosomes and macrophages were found. The globule leucocytes were observed from 0 to 3 days postpartum by transmission electron microscopy. The short microvilli, high electron dense cytoplasm and severe indentation of the nuclear enbelope were found in the vaginal epithelium. Numerouos small vesicles and a few vacuoles were observed in the apical cytoplasmic portion of the epithelium. A few mitochondria were high electron dense and irregular in shape. A moderate amounts of microfilaments, loose intercellular space and dilated rER were also found at 21 days postpartum. 2. Scanning electron microscopically, the folds of the uterine mucosa were generally deep. The long microvilli of the epithelium were found until 3 days postpartum, while short microvili were found at 10 and 21 days postpartum. The distinct intercellular boundary was seen. The apporcine secretory profile of the epithelium observed at between 3 and 10 days postpartum and the cells were somewhat protruded into the lumen. The short microvilli were found on the surface of the protruded cells, while polygonal microridge profile of the epithelium and some dome-shaped epithelium were also observed at 21 days postpartum. The folds of the vaginal mucosa were deep and epithelium was polygonal in shape. The microvilli of the epithelium were long until 3 days postpartum, while they were short at 10 and 21 days. The polygonal epithelium was invaginated into the center of the cell surface until 10 days postpartum. The microridge and dome in shape of the epithelium were found at 10 days postpartum, while the polygonal and exfoliating epithelium were observed at 21 days.