Mechanism of the growth and development of the posterior silk gland and silk secretion revealed by mutation of the fibroin light chain in silkworm

Abstract The gene encoding fibroin light chain protein (FibL) is specifically expressed in the posterior silk gland of silkworm and repressed in other tissues. The binding sites of several transcription factors involved in the silk gland transcription specificity of fibl promoter have been recognized, including SGFB, PSGF and BMFA. Here we report the leak expression of the enhanced green fluorescent protein (EGFP) reporter gene in tissues other than the posterior silk gland in vivo when under the control of a shortened fibl promoter with deletion of the 5′ terminal 41 bp sequence, which is located at −650 nt to −610 nt upstream of the fibl transcription starting site. Assay of silk gland specificity of the promoters was performed by observation of green fluorescence in tissues of silkworm larvae following inter-haemocoelic injection of recombinant Autographa californica multiple nuclear polyhedrosis virus carrying the EGFP reporter gene controlled by different lengths of fibl promoters. Our results indicated that availability of the binding sites of several known factors, including SGFB, PSGF and BMFA, is not sufficient for intact silk gland transcription specificity of fibl promoter, and there are possible inhibitor binding sites in the 41 bp sequence (−650 nt to −610 nt) upstream of the transcription starting site which may be required to repress the activity of fibl promoter in other tissues.

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Molecular cloning of the fibroin light chain complementary DNA and its use in the study of the expression of the light chain gene in the posterior silk gland ofBombyx mori

Cellular and Molecular Life Sciences ◽

10.1007/bf01951711 ◽

1985 ◽

Vol 41 (9) ◽

pp. 1167-1171 ◽

Cited By ~ 30

Author(s):

K. Kimura ◽

F. Oyama ◽

H. Ueda ◽

S. Mizuno ◽

K. Shimura

Keyword(s):

Molecular Cloning ◽

Light Chain ◽

Silk Gland ◽

Chain Gene ◽

Light Chain Gene ◽

Complementary Dna ◽

Fibroin Light Chain ◽

Posterior Silk Gland

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

Insects ◽

10.3390/insects12040361 ◽

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.

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STUDIES ON THE POSTERIOR SILK GLAND OF THE SILKWORM BOMBIX MORI

The Journal of Cell Biology ◽

10.1083/jcb.46.1.1 ◽

1970 ◽

Vol 46 (1) ◽

pp. 1-16 ◽

Cited By ~ 28

Author(s):

Yutaka Tashiro ◽

Eiichi Otsuki

Keyword(s):

Guanidine Hydrochloride ◽

Lithium Bromide ◽

Posterior Part ◽

Silk Gland ◽

Sedimentation Equilibrium ◽

Partial Specific Volume ◽

Anterior Portion ◽

Equilibrium Analyses ◽

Fibroin Solution ◽

Posterior Silk Gland

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°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 0.716, the molecular weight of the 10S component of the native fibroin solution was found to be between 3.2 – 4.2 x 105, with a tendency to lie fairly close to 3.7 x 105.

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Participation of the upstream region of the fibroin gene in the formation of transcription complex in vitro

Molecular and Cellular Biology ◽

10.1128/mcb.6.11.3928-3933.1986 ◽

1986 ◽

Vol 6 (11) ◽

pp. 3928-3933

Author(s):

M Tsuda ◽

S Hirose ◽

Y Suzuki

Keyword(s):

Complex Formation ◽

Specific Interaction ◽

Inhibitory Effect ◽

Silk Gland ◽

Upstream Region ◽

Fibroin Gene ◽

Transcription Complexes ◽

Posterior Silk Gland

The addition of exogenous histones has an inhibitory effect on fibroin gene transcription in posterior silk gland extracts. The histones probably disturb a process in complex formation, because when transcription complexes were constructed by preincubation of the templates with the extracts, the inhibitory effect of histones was greatly reduced. Transcription of a fibroin gene construct, pFb5' delta-238, having the upstream region beyond the TATA box was relatively less inhibited than that of pFb5' delta-44 lacking the upstream region. This tendency toward differential inhibition was observed in the silk gland extracts but not in a HeLa cell extract and persisted even after complex formation in the silk gland extracts, suggesting a specific interaction of the upstream region with some factors in the extracts. The complexes formed on pFb5' delta-44 are probably more susceptible to the inhibitory effect of histones. On the basis of these results we propose a participation of the upstream region of the fibroin gene in the formation of stable transcription complexes at the promoter through an interaction with specific factors in the silk gland. Since the transcription-enhancing effect via the upstream region is augmented at a high histone/DNA ratio, it may mimic the in vivo situation in which the fibroin gene can be transcribed in the posterior silk gland even in the presence of excess suppressive materials.

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