Biomedical subjects

S Yamashiro

Publications and source records attributed to S Yamashiro.

At least 127 records · Page 7Linked to original sources

PubMed1991

Phosphorylation of non-muscle caldesmon by p34cdc2 kinase during mitosis.

One of the profound changes in cellular morphology which occurs during mitosis is a massive alteration in the organization of the microfilament cytoskeleton. This change, together with other mitotic events including nuclear membrane breakdown, chromosome condensation and formation of mitotic spindles, is induced by a molecular complex called maturation promoting factor. This consists of at least two subunits, a polypeptide of relative molecular mass 45,000-62,000 (Mr 45-62K) known as cyclin, and a 34K catalytic subunit which has serine/threonine kinase activity and is known as cdc2 kinase. Non-muscle caldesmon, an 83K actin- and calmodulin-binding protein, is dissociated from microfilaments during mitosis, apparently as a consequence of mitosis-specific phosphorylation. We now report that cdc2 kinase phosphorylates caldesmon in vitro principally at the same sites as those phosphorylated in vivo during mitosis, and that phosphorylation reduces the binding affinity of caldesmon for both actin and calmodulin. Because caldesmon inhibits actomyosin ATPase, our results suggest that cdc2 kinase directly causes microfilament reorganization during mitosis.

Actin Cytoskeleton↗

PubMed1991

Mitosis-specific phosphorylation of caldesmon: possible molecular mechanism of cell rounding during mitosis.

One of the profound changes in cellular morphology during mitosis is a massive alteration in the organization of microfilament cytoskeleton. It has been recently discovered that nonmuscle caldesmon, an actin and calmodulin binding microfilament-associated protein of relative molecular mass Mr = 83,000, is dissociated from microfilaments during mitosis, apparently as a consequence of mitosis-specific phosphorylation. cdc2 kinase, which is a catalytic subunit of MPF (maturation or mitosis promoting factor), is found to be responsible for the mitosis-specific phosphorylation of caldesmon. Because caldesmon is implicated in the regulation of actin myosin interactions and/or microfilament organization, these results suggest that cdc2 kinase directly affects microfilament re-organization during mitosis.

Actin Cytoskeleton↗

PubMed1991

MRI of subarachnoid dissemination of medulloblastoma.

We report two cases with subarachnoid dissemination of medulloblastoma depicted clearly by Gadolinium-DTPA enhanced MRI. We also demonstrate the superiority of Gadolinium-DTPA enhanced MRI over nonenhanced MRI, CT, myelography and postmyelographic CT for diagnosing subarachnoid dissemination and for monitoring the response to therapy.

Brain↗

PubMed1991

Applications of fractal analysis to physiology.

This review describes approaches to the analysis of fractal properties of physiological observations. Fractals are useful to describe the natural irregularity of physiological systems because their irregularity is not truly random and can be demonstrated to have spatial or temporal correlation. The concepts of fractal analysis are introduced from intuitive, visual, and mathematical perspectives. The regional heterogeneities of pulmonary and myocardial flows are discussed as applications of spatial fractal analysis, and methods for estimating a fractal dimension from physiological data are presented. Although the methods used for fractal analyses of physiological data are still under development and will require additional validation, they appear to have great potential for the study of physiology at scales of resolution ranging from the microcirculation to the intact organism.

Animals↗

PubMed1991

The renal histology and ultrastructure in rats given methylmercury and ethanol in combination.

The effects of combined administration of methylmercury (MeHg) and ethanol (EtOH) on renal morphology were examined in the rat. Forty-eight male Wistar rats were divided into 6 groups of 8 rats each as follows: group 1 was given feed ad libitum with no treatment; group 2 was restricted to 70 mL of feed daily with no treatment; groups 3-6 were restricted to 70 mL of feed daily and gavaged with distilled water, MeHg alone, EtOH alone, or MeHg in combination with EtOH, respectively, daily for 45 days. The ingestion of MeHg and EtOH in combination caused severe structural renal lesions which involved the glomerulus and all segments of the uriniferous tubule. Only with this combination treatment (group 6) was glomerular pathology observed; accumulations of platelets and inflammatory cells, fibrosis and thickening of the mesangium were observed in the glomerulus. There was also severe tubulointerstitial nephritis characterized by tubular atrophy, accumulation of inflammatory cells especially neutrophils, and increased collagen deposition in the same group. In contrast, the ingestion of either MeHg or EtOH produced less severe lesions mainly in the proximal tubular epithelium. This study suggests that EtOH enhanced the nephrotoxicity of MeHg.

Alcoholic Intoxication↗

PubMed1990

Mitosis-specific phosphorylation causes 83K non-muscle caldesmon to dissociate from microfilaments.

At mitosis in eukaryotic cells there are profound changes of shape and structure whose causes are almost entirely obscure. What is known is that there are changes in the organization of microfilaments, including the disassembly of microfilament bundles during prophases and the accompanying rounding-up of cultured cells; the formation of transient contractile rings during cytokinesis; and, subsequently, the reassembly of microfilament bundles and the respreading of the two daughter cells. As an initial step towards the biochemical understanding of these events, in which the disassembly and reassembly of microfilaments appear to play an important part, we searched for alterations of the molecular constitution of microfilaments during mitosis. We found that non-muscle caldesmon, a protein with a relative molecular mass (Mr) of 83,000 (83K) which binds to actin and calmodulin, is dissociated from microfilaments during mitosis, apparently as a consequence of phosphorylation. This process may contribute to the changes of shape and structure of cells in mitosis, as caldesmon inhibits actomyosin ATPase.

Actin Cytoskeleton↗

PubMed1990

Microinjection of nonmuscle and smooth muscle caldesmon into fibroblasts and muscle cells.

Caldesmon is present in a high molecular mass form in smooth muscle and predominantly in a low molecular mass form in nonmuscle cells. Their biochemical properties are very similar. To examine whether these two forms of caldesmon behave differently in cultured cells, we microinjected fluorescently labeled smooth muscle and nonmuscle caldesmons into fibroblasts. Simultaneous injection of both caldesmons into the same cells has revealed that both high and low relative molecular mass caldesmons are quickly (within 10 min) and stably (over 3 d) incorporated into the same structures of microfilaments including stress fibers and membrane ruffles, suggesting that nonmuscle cells do not distinguish nonmuscle caldesmon from smooth muscle caldesmon. The effect of calmodulin on the incorporation of caldesmon has been examined by coinjection of caldesmon with calmodulin. We have found that calmodulin retards the incorporation of caldesmon into stress fibers for a short period (10 min) but not for a longer incubation (30 min). The behavior of caldesmon in developing muscle cells was also examined because we previously observed that caldesmon disappears during myogenesis (Yamashiro, S., R. Ishikawa, and F. Matsumura. 1988. Protoplasma Suppl. 2: 9-21). We have found that, in contrast to its stable incorporation into stress fibers of fibroblasts, caldesmon is unable to be incorporated into thin filament structure (I-band) of differentiated muscle.

Actins↗

PubMed1990

An ultrastructural study of developing spermatids and associated Sertoli cells during spermiogenesis in the kowari (crest-tailed marsupial rat), Dasyuroides byrnei.

Ultrastructural changes of developing spermatids and associated Sertoli cells during spermiogenesis in the kowari, Dasyuroides byrnei, were observed by transmission electron microscopy. The early round spermatid in the kowari showed an acrosomal vacuole containing sparsely distributed material. The acrosomal vacuole grew to some degree and then collapsed upon itself and decreased in size. After the diminution of the vacuole, flattening and condensation of the nucleus began. At this period, the manchette, nuclear ring and caudal plaque appeared and the ectoplasmic specialization of the Sertoli cell developed in association with the acrosomal region of the spermatid head. Microtubules of the manchette were arranged obliquely or perpendicular to the long axis of the spermatid. As the spermatid developed further, the nucleus displayed a horseshoe shape in cross section and was flattened in longitudinal section. The ectoplasmic specialization which was the most developed at this period appeared like horns protruding from the spermatid nucleus. Immediately before spermiation, the flattened aspect of the spermatid head contacted an apical process of the Sertoli cell. The Sertoli cell apical process extended the spermatid head into the lumen. Long tubulobulbar complexes appeared in the Sertoli cell, after the ectoplasmic specialization had dissociated.

Acrosome↗

PubMed1990

The effect of phenyl tert-butyl nitrone (PBN) on CCl4-induced rat liver injury detected by proton magnetic resonance imaging (MRI) in vivo and electron microscopy (EM).

Acute intoxication by CCl4 induces morphological changes in rat liver which are readily detectable by 1H-NMR imaging techniques in situ. Two to four hours after the administration of CCl4, regions of high proton signal intensity are observed in the centrilobular region of the liver. The regions of high signal intensity are attributed to the formation of local edema as a result of CCl4-induced damage. Electron microscopy of the high intensity regions of CCl4 treated liver sections revealed characteristic subcellular changes which include the disapperance of ribosomes from the rough endoplasmic reticulum (RER), the fragmented appearance of the smooth endoplasmic reticulum (SER), formation of vacuoles in the cisternae and swelling of the mitochondria. Pretreatment of rats with alpha-phenyl-tert-butyl nitrone (PBN), a free radical spin trap, prior to halocarbon exposure, was found to reduce the halocarbon-induced edema in the liver. Electron microscopy of the PBN pretreated CCl4 exposed rat liver sections revealed no observable changes in subcellular organization when compared to controls.

Animals↗

PubMed1989

Annealing of gelsolin-severed actin fragments by tropomyosin in the presence of Ca2+. Potentiation of the annealing process by caldesmon.

Previous results from our laboratory have shown that 1) cultured rat cells contain two classes of tropomyosin (TM), one (high Mr TMs) with higher Mr values and greater affinity for actin than the other (low Mr TMs); 2) presaturation of F-actin with high Mr TMs, but not with low Mr TMs, inhibits both actin-severing and actin binding activities of gelsolin; and 3) nonmuscle caldesmon not only enhances the inhibitory effects of high Mr TMs but also makes low Mr TMs capable of inhibiting the severing activity of gelsolin (Ishikawa, R., Yamashiro, S., and Matsumura, F. (1989) J. Biol. Chem. 264, 7490-7497). These results suggest that gelsolin has much lower affinity for F-actin-TM-caldesmon complexes than for pure F-actin. We have therefore examined whether addition of TM and/or caldesmon to gelsolin-severed actin filaments can make gelsolin dissociate from barbed ends of actin filaments, resulting in annealing of short actin filaments into long ones. Flow birefringence and electron microscopic studies have suggested that high Mr TMs slowly and partially anneal gelsolin-severed actin fragments in 3 h, whereas low Mr TMs have no effects. Nonmuscle caldesmon greatly potentiates the effects of high Mr TMs and accelerates the process to 20 min, whereas nonmuscle caldesmon alone shows no effects. Furthermore, nonmuscle caldesmon makes low Mr TMs capable of reversing gelsolin-severing action. Actin binding assay has shown that gelsolin (or a gelsolin-actin complex) is dissociated from these annealed actin filaments. Smooth muscle TM and smooth muscle caldesmon also appear to anneal gelsolin-severed actin fragments as do high Mr TMs and nonmuscle caldesmon. Calmodulin decreases the potentiation effects of caldesmon as calmodulin inhibits actin binding of caldesmon. These results suggest that tropomyosin and caldesmon may regulate both capping and severing activities of gelsolin.

Actins↗

PubMed1989

Differential modulation of actin-severing activity of gelsolin by multiple isoforms of cultured rat cell tropomyosin. Potentiation of protective ability of tropomyosins by 83-kDa nonmuscle caldesmon.

Multiple isoforms of tropomyosin (TM) of rat cultured cells show differential effects on actin-severing activity of gelsolin. Flow birefringence measurements have revealed that tropomyosin isoforms with high Mr values (high Mr TMs) partially protect actin filaments from fragmentation by gelsolin, while tropomyosins with low Mr values (low Mr TMs) have no significant protection even when the actin filaments have been fully saturated with low Mr TMs. We have also examined effect of nonmuscle caldesmon on the severing activity of gelsolin because 83-kDa nonmuscle caldesmon stimulates actin binding of rat cell TMs (Yamashiro-Matsumura, S., and Matsumura, F. (1988) J. Cell Biol. 106, 1973-1983). While nonmuscle caldesmon alone or low Mr TMs alone show no significant protection against fragmentation by gelsolin, the low Mr TMs coupled with 83-kDa protein are able to protect actin filaments. Further, high Mr TMs together with 83-kDa protein appear to block the severing activity completely. Electron microscopic analyses of length distribution of actin filaments have confirmed the results. The average length of control actin filaments is measured as 1.46 +/- microns, and gelsolin shortens the average length to 0.084 +/- 0.039 micron. Similar short average lengths are obtained when gelsolin severs actin complexed with low Mr TMs (0.080 +/- 0.045 micron) or with nonmuscle caldesmon (0.11 +/- 0.072 micron) while longer average length (0.22 +/- 0.18 micron) is measured in the presence of high Mr TMs. The simultaneous addition of nonmuscle caldesmon makes the average length considerably longer, i.e. 0.61 +/- 0.37 micron in the presence of low Mr TMs and 1.57 +/- 0.97 micron in the presence of high Mr TMs. Furthermore, the actin binding of gelsolin is strongly inhibited by co-addition of high Mr TMs and nonmuscle caldesmon. These results suggest that TM and gelsolin share the same binding site on actin molecules and that the differences in the actin affinities between TMs are related to their abilities of protection against gelsolin.

Actin Cytoskeleton↗

PubMed1989

Lymphocytic adenohypophysitis: report of two cases.

Two women with lymphocytic adenohypophysitis not related to pregnancy are reported on. In obtaining a differential diagnosis of lymphocytic adenohypophysitis preoperatively, it is useful to note swelling of the anterior hypophyseal tissue and the existence of a posterior pituitary lobe on sagittal sections of magnetic resonance imaging scans. Hypofunction of the anterior hypophyseal gland is more severe in lymphocytic adenohypophysitis than in pituitary adenomas. Marked adhesion of fibrotic pituitary capsule to the dura is a characteristic observation during surgery for lymphocytic adenohypophysitis.

Adenoma↗

PubMed1989

Morphological demonstration of the failure of Mus caroli trophoblast in the Mus musculus uterus.

A histological study of Mus caroli embryos gestating in the Mus musculus uterus was undertaken at Day 8.5 of gestation, 1 day after such embryos are reported to be normal and 1 day before the earliest events associated with death of the xenogeneic embryos. In comparison to control M. caroli embryos recovered from M. caroli and to control M. musculus embryos recovered from M. musculus, the xenogeneically transferred embryos showed intrauterine growth retardation that was associated with trophoblastic insufficiency. Trophoblast cell degeneration was observed, in the absence of lymphocytic infiltration. Therefore, loss of trophoblast cell function rather than lymphocyte-mediated destruction of trophoblast appears to underlie the death of M. caroli embryos in the M. musculus uterus.

Abortion, Spontaneous↗

PubMed1989

Sites of persistence of feline calicivirus.

Various tissues were collected from eight cats persistently infected with feline calicivirus (FCV) strain 255 to determine the sites of viral persistence. Tissues were tested by virus isolation and an immunohistochemical technique in which infected cells were detected in formalin-fixed, paraffin-embedded tissue sections using rabbit antiserum to FCV 255, a biotinylated second antibody and streptavidin-peroxidase. Virus was detected by one or both techniques in tonsillar tissues of each animal, and not in other samples. Infected cells were detected in samples from six of eight kittens, and in each animal were few in number, and were cells of the superficial tonsillar epithelium or the stratum germinativum of the adjacent fossa mucosa. Transmission electron microscopic examination of tissues from three of the cats revealed calicivirus-like particles in cells similar to those identified immunohistochemically. These results confirm that the tonsillar region is the major site of FCV persistence and indicate that virus replication during persistence is confined to the surface epithelium of the tonsil and adjacent fossa mucosa.

Animals↗

PubMed1989

Three-dimensional structure of some Sertoli cell organelles in the cotton rat and shiba goat.

The three-dimensional structure of some Sertoli cell organelles in the cotton rat and shiba goat was observed under a scanning electron microscope using the Osmium-Dimethyl sulfoxide-Osmium method. Mitochondria of the Sertoli trunk in the scanning electron microscopic (SEM) observation appeared much longer and more densely distributed than those in the transmission electron microscopic (TEM) observation and had a different shape from oval mitochondria in the basal region of the Sertoli cell. These rod-shaped mitochondria, 2-3 microns in length, accumulated closely among the ER network. Smooth ER in the Sertoli trunk was composed of continuous small bulges like strings of beads and were connected with each other to form a net-arranged network. Although microtubules which were seen in large numbers in the TEM observation were not preserved in the sample of the present study, a quantity of intermediate filaments was recognized three-dimensionally. These intermediate filaments seemed more crowded in the SEM observation than in the TEM observation. They frequently ramified and formed a meshwork. The accurate configurations of some Sertoli cell organelles, especially the smooth ER network, were obtained from the present study. Each intracellular organelle appeared more densely in the SEM observation than in the TEM observation.

Animals↗

PubMed1987

Platelet alterations in porcine stress syndrome.

Platelets in blood collected from pigs identified as normal (21) or stress susceptible (25) on the basis of their response to halothane challenge, were subjected to electron microscopic examination in order to test whether the ultrastructural features of stress susceptible pigs exhibit any deviation from those of normal. The most striking feature of the platelets from stress susceptible pigs was the extent of dilatation of the open canalicular system (OCS). The difference in platelet morphology between normal and stress susceptible pigs was consistent regardless of the anticoagulants used for blood collection indicating that the platelet alteration may be an inherent component of the porcine stress syndrome.

Animals↗

PubMed1986

The receptors responsible for heat production in brown adipose tissue in the young rabbit.

It is known that adrenergic agonists stimulate thermogenesis in the brown fat of the young rabbit but the receptors responsible for mediating the response have not been identified. The infusion of either noradrenaline or isoproterenol (1-2 micrograms . kg-1 X min-1) produced an increase in subcutaneous temperature (0.93 +/- 0.15 and 1.22 +/- 0.10 degrees C, respectively over the interscapular brown fat. At low doses (0.4 microgram . kg-1 X min-1) only isoproterenol was effective. The thermogenic response to isoproterenol was blocked by atenolol, a beta 1-adrenergic antagonist. Neither salbutamol or terbutaline, both beta 2-agonists, produced a temperature increase. Collectively, these data suggest that stimulation of beta 1-adrenoceptor is primarily responsible for the thermogenic activity of brown fat in the rabbit. However, it was found that 53% of the increase in temperature could be blocked by prazosin, an alpha 1-antagonist. Phentolamine was not effective as a blocker. Although a maximal brown fat thermogenic response can be achieved by stimulating the beta-adrenoceptors, the alpha-adrenoceptors appears to play at least an auxiliary role in young rabbit.

Adipose Tissue, Brown↗

PubMed1986

The noradrenaline content and innervation of brown adipose tissue in the young rabbit.

This work examined the noradrenaline content of brown adipose tissue, the metabolic response to endogenous noradrenaline released during tyramine infusion, and the innervation of brown fat at the electron microscopic level in the young rabbit. The noradrenaline content (ng/g) of the interscapular and cervical fat deposits ranged from 256 +/- 51 to 343 +/- 59 and 399 +/- 18 to 694 +/- 92, respectively, in four groups of rabbits (1-2, 7-8, 12-13, and 25-27 days of age). There was considerable variation amongst animals in each age group, but no evidence of a major increase or decrease in noradrenaline content during the first 4 weeks of life. Intravenous infusion of tyramine (100 micrograms X kg-1 X min-1) increased plasma noradrenaline concentration, oxygen consumption, and blood flow to brown fat. Thus noradrenaline released from endogenous sites, as well as injected noradrenaline, will initiate the thermogenic response of brown fat. Ultrastructurally, unmyelinated axons that were not organized in a fascicle were observed adjacent to the adipocytes in the late gestation fetus. By 1 week of age of axons were surrounded by Schwann cell cytoplasm which formed a fascicle. However, no evidence of myelination was found up to 21 days of age. Collectively, the data indicate that the brown adipocyte is fully responsive at 1-2 days of age even though myelination of the nerves is incomplete, and that the incomplete development of the sympathetic nerves at birth is not a factor in the synthesis of noradrenaline in the very young rabbit. In addition, brown fat of the newborn rabbit is not as thermogenically active as the brown fat of the cold-acclimated rat.

Adipose Tissue↗