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A Shimamura

Publications and source records attributed to A Shimamura.

At least 37 records · Page 2Linked to original sources
PubMed1993

The occurrence and fine structure of Merkel cells in the lingual epithelium of the turtle, Clemmys japonica.

Electron microscopic examination of the lingual mucosa of the turtle, Clemmys japonica, revealed the occurrence of Merkel cells that shared many morphological features with Merkel cells in other vertebrates. Merkel cells were located exclusively in the basal portion of the epithelium near the taste buds. We also found occasional Merkel cells devoid of nerve contact. Nerve terminals approaching these non-innervated Merkel cells were occasionally found in the connective tissue just beneath these cells.

Animals↗
PubMed1992

Fine structure of the Herbst corpuscles in the lingual mucosa of the finch, Lonchura striata.

The ultrastructure of Herbst corpuscles in the lingual mucosa of the finch, Lonchura striata var. domestica, was examined by light and electron microscopy. Numerous Herbst corpuscles were found at the top of connective tissue papillae just beneath the dorsal epithelium. The Herbst corpuscle was composed of an outer capsule, inner core and central axon. The central axon was discoid in shape and immunoreactive for NSE-antiserum. The central axon was surrounded by compactly stacked layers of thin lamellae of lamellar cell processes. Since these lamellae did not completely encircle the axon as seen in cross sections, they displayed a symmetrical longitudinal cleft dividing the inner core into bilateral halves. Numerous axonal spines were seen to extend from the Y-axis of the axolemma into the cleft and occasionally into the cytoplasmic invagination of the lamellar cell body in the inner core. A number of clear and dense-cored vesicles were seen in the axoplasm near the base of axonal spines. Further, the omega-shaped coated invaginations were occasionally found on the axolemma near those places. These findings suggest that the area nearby the axonal spine in the central axon of the Herbst corpuscle is a site active both metabolically and functionally.

Animals↗
PubMed1990

Morphological changes of taste buds and fungiform papillae following long-term neurectomy.

Long-term neurectomy of chorda tympani-lingual nerves results in a complete disappearance of taste buds from rabbit fungiform papillae. This supports the view that taste buds of mammalian fungiform papillae are neurally dependent. Furthermore, the covering epithelium of denervated fungiform papillae develops a characteristic keratinization pattern corresponding to that of filiform papillae.

Animals↗
PubMed1989

Assembly and properties of chromatin containing histone H1.

The Xenopus oocyte supernatant (oocyte S-150) forms chromatin in a reaction that is affected by temperature and by the concentration of ATP and Mg. Under optimal conditions at 27 degrees C, relaxed DNA plasmids are efficiently assembled into supercoiled minichromosomes with the endogenous histones H3, H4, H2A and H2B. This assembly reaction is a gradual process that takes four to six hours for completion. Micrococcal nuclease digestions of the chromatin assembled under these conditions generate an extended series of DNA fragments that are, on average, multiples of 180 base-pairs. We have examined the effect of histone H1 in this system. Exogenous histone H1, when added at a molar ratio of H1 to nucleosome of 1:1 to 5:1, causes an increase in the micrococcal nuclease resistance of the chromatin without causing chromatin aggregation under these experimental conditions. Furthermore, the periodically arranged nucleosomes display longer internucleosome distances, and the average length of the nucleosome repeat is a function of the amount of histone H1 added, when this histone is present at the onset of the assembly process. In contrast, no major change in the length of the nucleosome repeat is observed when histone H1 is added at the end of the chromatin assembly process. Protein analyses of the purified minichromosomes show that histone H1 is incorporated in the chromatin that is assembled in the S-150 supplemented with histone H1. The amount of histone H1 bound to chromatin is a function of the total amount of histone H1 added. We define here the parameters that generate histone H1-containing chromatin with native nucleosome repeats from 160 to 220 base-pairs, and we discuss the implications of these studies.

Adenosine Triphosphate↗
PubMed1989

The assembly of regularly spaced nucleosomes in the Xenopus oocyte S-150 extract is accompanied by deacetylation of histone H4.

Histone proteins, which were assembled into chromatin using the Xenopus oocyte S-150 extract, were analyzed on acid-urea gels and Triton-acid-urea gels to determine their state of modification. We find that histone H4, which is present in a diacetylated form in the oocyte S-150, gradually loses its acetate groups as the DNA is packaged into chromatin. Thus, this process parallels the one observed in vivo during chromatin formation in growing eucaryotic cells. Histone H4 deacetylation in the oocyte S-150 is a DNA-dependent reaction. This reaction is blocked when butyrate (an inhibitor of histone deacetylase) is added at the onset of the chromatin assembly process. When butyrate is added at the end of the assembly process, no de novo acetylation of the nucleosomal histone H4 is observed. Chromatin with regularly spaced nucleosomes, displaying periodicities ranging from 160 to 220 base pairs, can be assembled in vitro with the oocyte S-150 (Rodríguez-Campos, A., Shimamura, A., and Worcel, A. (1989) J. Mol. Biol., in press). This chromatin may contain either deacetylated histone H4 when assembled under standard conditions or diacetylated H4 when assembled in the presence of butyrate. Both types of chromatin display identical structures upon digestion with nucleases. The potential applications of this system toward the study of the naturally occurring diacetylated histone H4 are discussed.

Acetylation↗
PubMed1989

Use of 13C-n.m.r. spectroscopy for the quantitative estimation of 3-O- and 3,6-di-O-substituted D-glucopyranosyl residues in alpha-D-glucans formed by the D-glucosyltransferases of Streptococcus sobrinus.

The 13C-n.m.r. spectra of the three alpha-D-glucans from Streptococcus sobrinus and the dextran from Leuconostoc mesenteroides, which differ widely in the ratios of omega (terminal, nonreducing) D-glucopyranosyl groups: 3-:6-:3,6-linked D-glucopyranosyl (Glc) residues, were measured in 0.5M NaOH at 22 degrees. The C-1 signals of 3-O-substituted Glc in a linear sequence, 6-O-substituted Glc in a linear sequence, 3,6-di-O-substituted Glc in a (1----6)-linked sequence, and Glc attached to O-3 of 3,6-di-O-substituted Glc were distinguished from each other. The C-3 signal of 3,6-linked Glc appeared downfield by 0.6 to 1.0 p.p.m. compared to the C-3 signal of 3-linked Glc in a linear sequence. The C-6 signals of omega-terminal, 3-linked, 6-linked, and 3,6-linked Glc were also assigned. The C-2 signal of 3-linked Glc in a linear sequence appeared separately, at 73.76 p.p.m. Based on these assignments, the various D-glucopyranosyl residues of the S. sobrinus alpha-D-glucans were quantitatively estimated from the signal areas of the C-2 atom of 3-linked Glc, the C-3 atom of 3-linked and 3,6-linked Glc, the C-6 atom of 6-linked and 3,6-linked Glc, and the C-6 atom of the omega-Glc groups and 3-linked Glc residues. The figures thus derived for the linkage ratios were close to those obtained by methylation analysis.

Carbohydrate Conformation↗
PubMed1989

Purification and characterization of extracellular glucosyltransferase synthesizing water-insoluble glucan from Streptococcus rattus.

An extracellular glucosyltransferase synthesizing water-insoluble glucan (GTF-I) was purified from the culture supernatant of Streptococcus rattus strain BHT (mutans serotype b) by hydroxylapatite chromatography, DEAE-Toyopearl chromatography and preparative isoelectric focusing. The Mr of GTF-I was 155,000 by SDS-PAGE and the isoelectric point was pH 4.9. The specific activity, the optimum pH and the Km value for sucrose were 10.0 i.u. (mg protein)-1, 6.5 and 2.4 mM, respectively. The enzyme synthesized a water-insoluble glucan consisting of 69.4 mol% 1,3-alpha-linked glucose, 23.6 mol% 1,6-alpha-linked glucose, 2.6 mol% 1,3,6-alpha-branched glucose and 4.4 mol% non-reducing terminal glucose, and also a small amount (3% of the total glucan) of soluble glucan with 82.4 mol% 1,6-alpha-linked glucose. The Mr and pI values of purified GTF-I were identical with those of the enzyme in the culture supernatant.

Chromatography, Gel↗
PubMed1989

Purification and characterization of cell-associated glucosyltransferase synthesizing insoluble glucan from Streptococcus mutans serotype c.

Streptococcus mutans Ingbritt (serotype c) was shown to have a significant amount of cell-associated glucosyltransferase activity which synthesizes water-insoluble glucan from sucrose. The enzyme was extracted from the washed cells with SDS, renatured with Triton X-100, adsorbed to 1,3-alpha-D-glucan gel, and then eluted with SDS. The enzyme preparation was electrophoretically homogeneous, and the specific activity was 7.3 i.u. (mg protein)-1. The enzyme had an Mr of 158,000 as determined by SDS-PAGE, and was a strongly hydrophilic protein, as judged by its amino acid composition. The enzyme gradually aggregated in the absence of SDS. The enzyme had an optimum pH of 6.5 and a Km value of 16.3 mm for sucrose. Activity was stimulated 1.7-fold by dextran T10, but was not stimulated by high concentrations of ammonium sulphate. Below a sodium phosphate buffer concentration of 50 mm, activity was reduced by 75%. This enzyme synthesized an insoluble D-glucan consisting of 76 mol% 1,3-alpha-linked glucose and 24 mol% 1,6-alpha-linked glucose.

Bacterial Proteins↗
PubMed1989

Histone H1 represses transcription from minichromosomes assembled in vitro.

We have previously shown that transcription from a Xenopus 5S rRNA gene assembled into chromatin in vitro can be repressed in the absence of histone H1 at high nucleosome densities (one nucleosome per 160 base pairs of DNA) (A. Shimamura, D. Tremethick, and A. Worcel, Mol. Cell. Biol. 8:4257-4269, 1988). We report here that transcriptional repression may also be achieved at lower nucleosome densities (one nucleosome per 215 base pairs of DNA) when histone H1 is present. Removal of histone H1 from the minichromosomes with Biorex under conditions in which no nucleosome disruption was observed led to transcriptional activation. Transcriptional repression could be restored by adding histone H1 back to the H1-depleted minichromosomes. The levels of histone H1 that repressed the H1-depleted minichromosomes failed to repress transcription from free DNA templates present in trans. The assembly of transcription complexes onto the H1-depleted minichromosomes protected the 5S RNA gene from inactivation by histone H1.

Animals↗
PubMed1989

Scanning electron microscopic study on the lingual papillae of the Japanese insectivora.

The tongue and lingual papillae of the Japanese Insectivora, the Shinto shrew (Sorex caecuiens saevus), the long-clawed shrew (S. unguiculatus), the dsinezumi shrew (Crocidura dsinezumi dsinezumi) and the Japanese water shrew (Chimarrogale himalyica platycephala), were observed by scanning electron microscope. The tongue of these animals had two vallate papillae. In two species of the Sorex a papilla in the vallate papilla was surrounded by two separated trenches, but in the other species it was surrounded by only a continuous trench and a clear vallum. The fungiform papillae in the Sorex were less developed than those of the other species. In the Sorex and Crocidura, there was no filiform papilla on the lingual apex. These genera, however, have papillary projections in the margin of the lingual apex. The results of this investigation suggest that the Sorex and Crocidura indicate an ancient form of the mammalian tongue. These characters, furthermore, were compared among seven species in six genera added three species observed by Kobayashi et al. (1983) to this study.

Animals↗
PubMed1988

Streptococcus mutans gtfA gene specifies sucrose phosphorylase.

The ethanol-insoluble product formed from sucrose by purified enzyme encoded by the gtfA gene from Streptococcus mutans, expressed in recombinant Escherichia coli, was analyzed by 13C and 31P nuclear magnetic resonance. The product was identified as alpha-D-glucose-1-phosphate, and it was concluded that the GTF-A enzyme is sucrose phosphorylase (sucrose:orthophosphate alpha-D-glucosyltransferase [EC 2.4.1.7]).

DNA, Bacterial↗
PubMed1988

Characterization of the repressed 5S DNA minichromosomes assembled in vitro with a high-speed supernatant of Xenopus laevis oocytes.

We describe an in vitro system, based on the Xenopus laevis oocyte supernatant of Glikin et al. (G. Glikin, I. Ruberti, and A. Worcel, Cell 37:33-41, 1984), that packages DNA into minichromosomes with regularly spaced nucleosomes containing histones H3, H4, H2A, and H2B but no histone H1. The same supernatant also assembles the 5S RNA transcription complex; however, under the conditions that favor chromatin assembly, transcription is inhibited and a phased nucleosome forms over the 5S RNA gene. The minichromosomes that are fully loaded with nucleosomes remain refractory to transcriptional activation by 5S RNA transcription factors. Our data suggest that this repression is caused by a nucleosome covering the 5S RNA gene and that histone H1 is not required for regular nucleosome spacing or for gene repression in this system.

Animals↗
PubMed1988

An immunohistochemical demonstration of neuron-specific enolase in the Merkel cells of the frog taste organ.

The Merkel cells in the taste organ of the frog were investigated by immunohistochemistry using neuron-specific enolase (NSE) antiserum. NSE-immunoreactivity was found exclusively in the Merkel cells lying at the base of the taste organ. The distribution and the profiles of the NSE-immunoreactive Merkel cells coincided with serotonin-containing cells previously reported at the same place.

Animals↗