scholarly journals Studies on the posterior silk gland of the silkworm Bombyx mori. VI. Distribution of microtubules in the posterior silk gland cells.

1976 ◽  
Vol 71 (2) ◽  
pp. 565-574 ◽  
Author(s):  
S Sasaki ◽  
Y Tashiro
Keyword(s):  
Intracellular Transport ◽  
Secretory Granules ◽  
Silk Gland ◽  
Canal System ◽  
Gland Cells ◽  
Apical Cytoplasm ◽  
Radial Microtubule System ◽  
Circular Arrangement ◽  
Silkworm Bombyx Mori ◽  
Posterior Silk Gland

There are two microtubule systems in the posterior silk gland cells. One is a radial microtubule system in which the microtubules run radially from the basal to the apical cytoplasm and in which fibroin globules (secretory granules of fibroin) and mitochondria are arranged along these microtubules, thus composing a "canal system" which is assumed to be responsible for the intracellular transport of fibroin globules. The other is a circular microtubule system in the apical cytoplasm which is composed of bundles of microtubules and microfilaments running in a circular arrangement around the glandular lumen at an interval of approximately 4 mum at the end of the fifth instar. This system is presumably concerned with secretion and/or intraluminal transport of fibroin.

Intracellular transport and secretion of fibroin in the posterior silk gland of the silkworm Bombyx mori

1981 ◽  
Vol 50 (1) ◽  
pp. 19-44 ◽  
Author(s):  
S. Sasaki ◽  
E. Nakajima ◽  
Y. Fujii-Kuriyama ◽  
Y. Tashiro
Keyword(s):  
Intracellular Transport ◽  
Cytochalasin B ◽  
Silk Gland ◽  
Luminal Surface ◽  
Golgi Bodies ◽  
Apical Cytoplasm ◽  
Radial Microtubule System ◽  
Microfilament System ◽  
Silkworm Bombyx Mori ◽  
Posterior Silk Gland

Intracellular transport and secretion of fibroin in the posterior silk gland cells of the silkworm, Bombyx mori, were investigated in relation to the radial microtubule and circular microtubule-microfilament systems of the cells. The silk glands were pulse-labelled for 3 min with [3H]glycine in vitro and then chased in media containing excess cold glycine and in some cases antimitotic reagents (colchicine or vinblastine) or cytochalasin (B or D), and the flow of the label in the glands was investigated by radioautography. It was revealed that the label initially located over the rough endoplasmic reticulum subsequently moves to the Golgi bodies to be condensed there. The secretory granules of fibroin or fibroin globules thus formed are transported via the radial microtubule system to the apical cytoplasm to be secreted there under some regulation by the circular microtubule-microfilament system. In the presence of colchicine or vinblastine, the secretion of fibroin was suppressed an marked accumulation of fibroin globules in the Golgi regions was observed, while in the presence of cytochalasin B or D the secretion was accelerated and extensive invagination of the luminal surface, which was probably due to the serial exocytosis of fibroin globules, was observed. These results suggest that the radial microtubule system and the circular microtubule-microfilament system are responsible for intracellular transport of fibroin globules from Golgi bodies to the apical cytoplasm and secretion by exocytosis at the luminal surface, respectively.

Intracellular electrolyte levels and transport of secretory granules in exocrine gland cells

1998 ◽  
Vol 201 (9) ◽  
pp. 1273-1281
Author(s):  
H Kondo ◽  
B Sakaguchi
Keyword(s):  
Intracellular Calcium ◽  
Intracellular Transport ◽  
Calcium Concentration ◽  
Secretory Granules ◽  
Silk Gland ◽  
Intracellular Calcium Concentration ◽  
Electron Microscopic Autoradiography ◽  
Gland Cells ◽  
Apical Cytoplasm ◽  
Golgi Region

We demonstrate the intracellular transport of secretory granules of a silk protein, fibroin, from the Golgi region to the apical cytoplasm with special reference to microtubule organization, electrolyte concentrations and the acidic intragranular pH of normal and mutant posterior silk gland cells, using the techniques of electrophysiological microelectrode and microprobe analysis and of light and electron microscopic autoradiography. The silk gland cells of a recessive mutant making only flimsy cocoons were defective in the microtubule systems, did not stain with an anti-tubulin antibody in immunofluorescent microscopy, and accumulated intracellular granules in the apical and basal cytoplasm. The increase in intracellular calcium concentration and levels of chloride secretion were also reduced in the mutant cells. A carboxylic ionophore, monensin, which collapsed the granular H+ gradient, induced the transport of chloride and an increase in the intracellular calcium concentration, while it blocked the intracellular transport of granules from the Golgi region to the apical cytoplasm in normal cells. Thus, we conclude that the H+ gradient across the membrane of secretory granules is responsible for the intracellular transport of the secretory granules along the microtubule systems in silk gland cells, while Ca2+ is thought to be required for the exocytosis of the granules.

scholarly journals EXTRUSION OF NUCLEAR MATERIALS INTO CYTOPLASM IN THE POSTERIOR SILK GLAND CELLS OF SILKWORM, BOMBYX MORI

1968 ◽  
Vol 36 (3) ◽  
pp. C5-10 ◽  
Author(s):  
Yutaka Tashiro ◽  
Shiro Matsuura ◽  
Takashi Morimoto ◽  
Sunao Nagata
Keyword(s):  
Bombyx Mori ◽  
Silk Gland ◽  
Nuclear Materials ◽  
Gland Cells ◽  
Silkworm Bombyx Mori ◽  
Posterior Silk Gland

scholarly journals 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.

1976 ◽  
Vol 70 (3) ◽  
pp. 648-659 ◽  
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.

scholarly journals Further evidence for importance of the subunit combination of silk fibroin in its efficient secretion from the posterior silk gland cells.

1987 ◽  
Vol 105 (1) ◽  
pp. 175-180 ◽  
Author(s):  
F Takei ◽  
Y Kikuchi ◽  
A Kikuchi ◽  
S Mizuno ◽  
K Shimura
Keyword(s):  
Silk Fibroin ◽  
Silk Gland ◽  
Chain Gene ◽  
Structural Abnormality ◽  
Wild Type ◽  
Disulfide Linkage ◽  
Gland Cells ◽  
Subunit Combination ◽  
Silkworm Bombyx Mori ◽  
Posterior Silk Gland

A locus responsible for the Nd-s mutation of the silkworm, Bombyx mori, has been mapped very close to or within the fibroin light (L) chain gene on the 14th chromosome (Takei, F., K. Kimura, S. Mizuno, T. Yamamoto, and K. Shimura, 1984, Jpn. J. Genet., 59:307-313). A strain of B. mori carrying the homozygous Nd-sD mutation (Nd-sD/Nd-sD; Nd-sD is allelic to Nd-s) secretes less than 0.3% of fibroin into the lumen of the posterior silk gland compared with a strain carrying the homozygous wild-type alleles (+/+). The small amount of fibroin that is secreted in the Nd-sD/Nd-sD strain consists of the heavy (H) chain only and lacks the L chain, although the L chain mRNA and the proteins that are cross-reactable with the anti-L chain serum are present in the posterior silk gland cells. In the hybrid silkworm, Nd-sD/+, the H chain derived from either the Nd-sD or + allele forms disulfide linkage with the L chain derived from the + allele and these fibroins are secreted into the lumen with an equal efficiency, but the L chain derived from the Nd-sD allele remains in the cell unbound to the H chain. Some evidence suggesting structural abnormality of the L chain derived from the Nd-sD allele is presented. These results, together with the previous results on the effect of the H chain gene-linked Nd(2) mutation (Takei, F., F. Oyama, K. Kimura, A. Hyodo, S. Mizuno, and K. Shimura, 1984, J. Cell Biol., 99:2005-2010), strongly suggest that the H-L subunit combination of silk fibroin is important for its efficient secretion.

scholarly journals Enhanced Myc Expression in Silkworm Silk Gland Promotes DNA Replication and Silk Production

Insects ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 361
Author(s):  
Wenliang Qian ◽  
Yan Yang ◽  
Zheng Li ◽  
Yuting Wu ◽  
Xuechuan He ◽  
...  
Keyword(s):  
Dna Replication ◽  
Cell Growth ◽  
Silk Gland ◽  
Biological Functions ◽  
Gland Cells ◽  
Silk Production ◽  
Myc Gene ◽  
Cell Growth And Proliferation ◽  
Silkworm Silk ◽  
Posterior Silk Gland

Silkworm is an economically important insect that synthetizes silk proteins for silk production in silk gland, and silk gland cells undergo endoreplication during larval period. Transcription factor Myc is essential for cell growth and proliferation. Although silkworm Myc gene has been identified previously, its biological functions in silkworm silk gland are still largely unknown. In this study, we examined whether enhanced Myc expression in silk gland could facilitate cell growth and silk production. Based on a transgenic approach, Myc was driven by the promoter of the fibroin heavy chain (FibH) gene to be successfully overexpressed in posterior silk gland. Enhanced Myc expression in the PSG elevated FibH expression by about 20% compared to the control, and also increased the weight and shell rate of the cocoon shell. Further investigation confirmed that Myc overexpression increased nucleus size and DNA content of the PSG cells by promoting the transcription of the genes involved in DNA replication. Therefore, we conclude that enhanced Myc expression promotes DNA replication and silk protein expression in endoreplicating silk gland cells, which subsequently raises silk yield.

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

1968 ◽  
Vol 38 (3) ◽  
pp. 574-588 ◽  
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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