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Biomedical subjects

Y Tashiro

Publications and source records attributed to Y Tashiro.

251 records · Page 14Linked to original sources
PubMed1970

Studies on the posterior silk gland of the silkworm Bombix mori. IV. Ultracentrifugal analyses of native silk proteins, especially fibroin extracted from the middle silk gland of the mature silkworm.

Ultracentrifugal analyses of the native silk proteins extracted from the various parts of the middle silk gland of the mature silkworm have revealed that there exist four components with S degrees (20,w) values of 10S, 9-10S, 9S, and 4S in the extract. It is suggested that the fastest 10S component is the native fibroin synthesized in the posterior silk gland and transferred to the middle silk gland to be stored there, while the slower three components probably correspond to inner, middle, and outer sericins which were synthesized in the posterior, middle, and anterior portion of the middle silk gland, respectively. Native fibroin solution was prepared from the most posterior part of the middle silk gland. Ultracentrifugal analyses have shown that the solution contains considerable amounts of aggregates in addition to the main 10S component. Treatment with lithium bromide (LiBr), urea, or guanidine hydrochloride solution up to 6 M all have failed to dissociate the 10S component. From the sedimentation equilibrium analyses and partial specific volume of 0.71(6), the molecular weight of the 10S component of the native fibroin solution was found to be between 3.2 - 4.2 x 10(5), with a tendency to lie fairly close to 3.7 x 10(5).

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PubMed1968

Studies on the posterior silk gland of the silkworm, Bombyx mori. I. Growth of posterior silk gland cells and biosynthesis of fibroin during the fifth larval instar.

Growth of the posterior silk gland and biosynthesis of fibroin during the fifth larval instar of the silkworm, Bombyx mori, have been studied. In accordance with the exponential increase in the wet weight of the gland, the amounts of DNA, RNA, protein, and lipids per animal increased rapidly in the early stage of the fifth instar (0-96 hr). Biosynthesis of fibroin, on the contrary, mainly proceeds in the later stage of the fifth instar (120-192 hr). Electron microscopical observations have shown that, in the very early stage (0-12 hr), a number of free ribosomes exist in the cytoplasm. Rough endoplasmic reticulum (ER) with closely spaced cisternae was also observed. Then rough ER starts to proliferate rapidly, and at the same time lamellar ER is rapidly or gradually transformed into vesicular or tubular forms. In the later stage of the fifth instar (120-192 hr), the cytoplasm is mostly filled with tubular or vesicular ER. Golgi vacuoles, free vacuoles (fibroin globules), and mitochondria are also observed. It is concluded that in the early stage of the fifth instar the cellular structures necessary for the biosynthesis of fibroin are rapidly formed, while in the later stage the biosynthesis of fibroin proceeds at a maximum rate and utilizes these structures.

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PubMed1968

Studies on the posterior silk gland of the silkworm, Bombyx mori. II. Cytolytic processes in posterior silk gland cells during metamorphosis from larva to pupa.

Cytolytic processes in posterior silk gland cells of the silkworm, Bombyx mori, during metamorphosis from larva to pupa have been studied. During this stage, the wet weight and the amounts of RNA and protein of the gland decrease rapidly and markedly, while the amount of DNA decreases slowly and slightly. The ultrastructural changes observed at the beginning of the prepupal stage consist of the appearance or the increase in the number of autophagosomes containing endoplasmic reticulum (ER), or "early autophagosomes" as we have called them, which seem to be gradually transformed to autolysosomes. A number of usual lysosomes, which frequently contain myelin figures, also appear in the cytoplasm. Sometimes they fuse with each other to form large conglomerates. In the middle of the prepupal stage, a number of smooth membrane-bounded vacuoles appear in cytoplasm. Towards the end of the prepupal stage the partition or sequestration of cytoplasm was observed. Thus large autophagosomes containing cytoplasmic organelles such as rough ER and/or mitochondria are formed. The nucleus is partitioned in a similar way by smooth membranes, and then autophagosomes containing condensed chromatin blocks are formed. These various kinds of autophagosomes, or "late autophagosomes" as we have generally called them, are continuously released into the hemolymph until the gland is completely disintegrated.

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PubMed1968

Studies on the posterior silk gland of the silkworm, Bombyx mori. 3. Ultrastructural changes of posterior silk gland cells in the fourth larval instar.

The development of the cells in the posterior silk gland of the silkworm, Bombyx mori, during the fourth larval instar has been studied. In the early stages of this instar, the wet weight of the gland and the amounts of RNA, DNA, and protein per animal increase logarithmically until they reach a stationary state at about 72 hr. At around 96 hr of the fourth instar, the larvae enter the molting state, which lasts for about 24 hr until the fourth ecdysis. Towards the end of the molt stage, the growth of the silk gland is resumed. Electron microscopical observation shows that in the early intermolt stage the cytoplasm is filled with free ribosomes and with rough endoplasmic reticulum (ER), first of the lamellar type (0-6 hr) and then of the vesicular or tubular type. The Golgi apparatus also is well developed. At the beginning of the molt stage (90-96 hr), however, most of the ER becomes lamellar in type, concentric lamellar structures being occasionally observed, and the Golgi vacuoles disappear. Autophagosomes and lysosomes increase markedly and the apical portion of the cytoplasm becomes extensively vacuolated; this suggests that the secretory activities are completely depressed, and pronounced degenerative changes appear during the molt stage. Towards the end of the molt stage, large lamellar ER elements are fragmented into smaller lamellae and there is a pronounced increase in the number of free ribosomes.

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PubMedDate not supplied

Calcium distribution and mobilization during depolarization in single cochlear hair cells. Imaging microscopy and fura-2.

Intracellular distribution of cytoplasm-free Ca2+ concentrations ((Ca2+)i) and dynamic changes during stimulation of viable hair cells were studied using digital imaging microscopy and the Ca2(+)-sensitive dye fura-2. (Ca2+)i was visualized on pseudo-colour images and three-dimensional computer graphics. In the resting state, the intra-cellular distribution of (Ca2+)i in both the outer and inner hair cells was heterogeneous, and the amount of (Ca2+)i in most of the peripheral cytoplasm just beneath the plasma membrane was greater than that throughout the entire cytoplasm. Cell depolarization, induced by elevated K+, led to an increase in (Ca2+)i in the outer hair cells. The increase in (Ca2+)i was not observed under conditions of depolarization in Ca2(+)-free medium. These observations are interpreted to mean that the increase in (Ca2+)i is induced by depolarization with the result that there is an influx of extracellular Ca2+ into the cytoplasm. When Mn2+ was applied during depolarization, a fluorescence quenching occurred. By such means the site of Ca2+ channels was elucidated.

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