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 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 Reduced level of secretion and absence of subunit combination for the fibroin synthesized by a mutant silkworm, Nd(2).

1984 ◽  
Vol 99 (6) ◽  
pp. 2005-2010 ◽  
Author(s):  
F Takei ◽  
F Oyama ◽  
K Kimura ◽  
A Hyodo ◽  
S Mizuno ◽  
...  
Keyword(s):  
Electrophoretic Mobility ◽  
Hybrid System ◽  
Disulfide Bond ◽  
Silk Gland ◽  
Subunit Structure ◽  
Present Evidence ◽  
Gland Cells ◽  
Subunit Combination ◽  
Posterior Silk Gland

Fibroin is normally composed of one H chain (350 kd) and one L chain (25 kd) which are connected by disulfide bond(s). However, the small amount of fibroin secreted into the lumen of the posterior silk gland of the Nd(2) (naked pupa) mutant does not contain L chain, although L chain mRNA is present and L chain is synthesized in the posterior silk gland cells of the mutant. In a hybrid silkworm, Nd(2)/Tamanashikasuri, where Tamanashikasuri is a normal producer of fibroin, L chain from the two alleles are distinguishable electrophoretically. It is demonstrated using this system that the L chain from the Nd(2) allele can combine normally with the H chain from Tamanashikasuri and the H-L complex is secreted normally. In another hybrid system, Nd(2)/J-131, where J-131 is a normal producer of fibroin, fibroin derived from the two alleles are distinguishable due to the different electrophoretic mobility of H chain. The fibroin derived from the J-131 allele is composed of H chain and L chain, while the fibroin derived from the Nd(2) allele is devoid of L chain, and its secretion is greatly reduced. We present evidence suggesting that the H chain derived from the Nd(2) allele is structurally abnormal and discuss how the H-L subunit structure is advantageous in the secretion of fibroin.

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.

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 CRISPR-Mediated Endogenous Activation of Fibroin Heavy Chain Gene Triggers Cellular Stress Responses in Bombyx mori Embryonic Cells

Insects ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 552
Author(s):  
Wenbo Hu ◽  
Xiaogang Wang ◽  
Sanyuan Ma ◽  
Zhangchuan Peng ◽  
Yang Cao ◽  
...  
Keyword(s):  
Bombyx Mori ◽  
Heavy Chain ◽  
Stress Responses ◽  
Cellular Stress ◽  
Silk Gland ◽  
Cellular Stress Response ◽  
Molar Ratio ◽  
Chain Gene ◽  
Gland Cells ◽  
Cellular Stress Responses

The silkworm Bombyx mori is an economically important insect, as it is the main producer of silk. Fibroin heavy chain (FibH) gene, encoding the core component of silk protein, is specifically and highly expressed in silk gland cells but not in the other cells. Although the silkworm FibH gene has been well studied in transcriptional regulation, its biological functions in the development of silk gland cells remain elusive. In this study, we constructed a CRISPRa system to activate the endogenous transcription of FibH in Bombyx mori embryonic (BmE) cells, and the mRNA expression of FibH was successfully activated. In addition, we found that FibH expression was increased to a maximum at 60 h after transient transfection of sgRNA/dCas9-VPR at a molar ratio of 9:1. The qRT-PCR analysis showed that the expression levels of cellular stress response-related genes were significantly up-regulated along with activated FibH gene. Moreover, the lyso-tracker red and monodansylcadaverine (MDC) staining assays revealed an apparent appearance of autophagy in FibH-activated BmE cells. Therefore, we conclude that the activation of FibH gene leads to up-regulation of cellular stress responses-related genes in BmE cells, which is essential for understanding silk gland development and the fibroin secretion process in B. mori.

Localization of the genes for silk fibroin in silk gland cells of Bombyx mori

1976 ◽  
Vol 49 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Christian Thomas ◽  
Donald D. Brown
Keyword(s):  
Bombyx Mori ◽  
Silk Fibroin ◽  
Silk Gland ◽  
Gland Cells

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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