Ultrastructural changes of the posterior silk gland cells in the early larval instars of the silkworm, Bombyx mori

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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Microtubule Systems and Microtubular Crystals in the Posterior Silk Gland Cells of Bombyx mori

Journal of Electron Microscopy ◽

10.1093/oxfordjournals.jmicro.a050048 ◽

1977 ◽

Keyword(s):

Bombyx Mori ◽

Silk Gland ◽

Gland Cells ◽

Posterior Silk Gland

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STUDIES ON THE POSTERIOR SILK GLAND OF THE SILKWORM, BOMBYX MORI

The Journal of Cell Biology ◽

10.1083/jcb.38.3.574 ◽

1968 ◽

Vol 38 (3) ◽

pp. 574-588 ◽

Cited By ~ 102

Author(s):

Yutaka Tashiro ◽

Takashi Morimoto ◽

Shiro Matsuura ◽

Sunao Nagata

Keyword(s):

Bombyx Mori ◽

Early Stage ◽

Larval Instar ◽

Silk Gland ◽

Exponential Increase ◽

Wet Weight ◽

Rough Er ◽

Electron Microscopical ◽

Silkworm Bombyx Mori ◽

Posterior Silk Gland

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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Lysosomes and Related Structures in the Posterior Silk Gland Cells of Bombyx mori. II. In Prepupal and Early Pupal Stadium

Cell Structure and Function ◽

10.1247/csf.1.223 ◽

1976 ◽

Vol 1 (3) ◽

pp. 223-235 ◽

Cited By ~ 12

Author(s):

Shiro Matsuura ◽

Takeo Shimadzu ◽

Yutaka Tashiro

Keyword(s):

Bombyx Mori ◽

Silk Gland ◽

Gland Cells ◽

Posterior Silk Gland

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Studies on the posterior silk gland of the silkworm Bombyx mori. V. Electron microscope localization of fibroin in the posterior silk gland at the later stage of the fifth instar.

The Journal of Cell Biology ◽

10.1083/jcb.70.3.648 ◽

1976 ◽

Vol 70 (3) ◽

pp. 648-659 ◽

Cited By ~ 14

Author(s):

S Sasaki ◽

Y Tashiro

Keyword(s):

Electron Microscope ◽

Epoxy Resin ◽

Bombyx Mori ◽

Secretory Granules ◽

Silk Gland ◽

Fibrous Materials ◽

Thin Sections ◽

Dense Granules ◽

Silkworm Bombyx Mori ◽

Posterior Silk Gland

Electron microscope observations of thin sections of epoxy resin-embeded posterior silk gland cells at the later stage of the fifth instar revealed that the Golgi vacuoles and the secretory granules (fibroin globules) in the cytoplasm and the glandular lumen contain fine fibrous materials. In frozen thin sections these structures appear as electron-dense granules and electron-dense blocks, or a column, respectively. Immunoelectron microscopy has shown that ferritin particles or products of the peroxidase reaction are localized on these structures. It was concluded that the fine fibrous materials most probably represent native fibroin molecules or their aggregates.

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TREHALASE ACTIVITY IN THE SILK GLANDS OF THE SILKWORM, BOMBYX MORI (LEPIDOPTERA: BOMBYCIDAE)

The Canadian Entomologist ◽

10.4039/ent1071311-12 ◽

1975 ◽

Vol 107 (12) ◽

pp. 1311-1314 ◽

Cited By ~ 10

Author(s):

Shuya Shimada

Keyword(s):

Bombyx Mori ◽

Divalent Cations ◽

Silk Gland ◽

Trehalase Activity ◽

Gland Cells ◽

Silk Glands ◽

Tunica Propria ◽

Silkworm Bombyx Mori ◽

Cu And Zn ◽

Tunica Intima

Abstract(1) Crude extracts prepared from the silk glands of the silkworm, Bombyx mori L. contain trehalase activity. (2) Trehalase in the silk glands has a pH of 5.5 and a Km of 0.71 mM. The activity of the enzyme is inhibited by divalent cations such as Mn, Cu, and Zn. (3) By histochemical methods, it is shown that trehalase is localized in the periphery of the silk gland cells, especially in the tunica propria and tunica intima. (4) Trehalase activity is low in fifth instar and increases greatly in spinning stages, after which the activity decreases.

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Autophagy, apoptosis, and ecdysis-related gene expression in the silk gland of the silkworm (Bombyx mori) during metamorphosis

Canadian Journal of Zoology ◽

10.1139/z10-083 ◽

2010 ◽

Vol 88 (12) ◽

pp. 1169-1178 ◽

Cited By ~ 23

Author(s):

Qingrong Li ◽

Xiaojuan Deng ◽

Wanying Yang ◽

Zhijun Huang ◽

Gianluca Tettamanti ◽

...

Keyword(s):

Bombyx Mori ◽

Receptor Gene ◽

Silk Gland ◽

Apoptotic Bodies ◽

Gland Cells ◽

Cytoplasmic Material ◽

Transcription Factor Genes ◽

Insect Metamorphosis ◽

Apoptosis Pathways ◽

Silkworm Bombyx Mori

Degeneration of larval-specific tissues during insect metamorphosis has been suggested to be the result of apoptosis and autophagy and is triggered by ecdysteroids. However, the relationship between autophagy and apoptosis pathways and the mechanism of regulation by ecdysteroids remain to be elucidated. This study examined the events of autophagy, apoptosis, and the expression of ecdysis-related genes in the silk gland of the silkworm ( Bombyx mori L., 1758) during the larval to pupal transformation. The results indicated that autophagic features appeared in the silk gland at the wandering and spinning stages of the larvae, whereas the apoptotic features such as apoptotic bodies and DNA fragmentation occurred at the prepupal or early-pupal stages. The autophagic granules fused with each other to form large vacuoles where the cytoplasmic material was degraded. Autophagosomes, autolysosomes, and apoptotic bodies were found later in the degenerating silk-gland cells. Expression of the ecdysone receptor gene BmEcR and the transcription factor genes BmE74A and BmBR-C preceded the onset of autophagy and apoptosis, indicating that they may be responsible for triggering these programmed cell death pathways in the silk gland. The results suggest that both autophagy and apoptosis occur in the silk-gland cells during degeneration, but autophagy precedes apoptosis.

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