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Zabelina V, Takasu Y, Sehadova H, Yonemura N, Nakajima K, Sezutsu H, Sery M, Zurovec M, Sehnal F, Tamura T. Mutation in Bombyx mori fibrohexamerin (P25) gene causes reorganization of rough endoplasmic reticulum in posterior silk gland cells and alters morphology of fibroin secretory globules in the silk gland lumen. Insect Biochem Mol Biol 2021; 135:103607. [PMID: 34102294 DOI: 10.1016/j.ibmb.2021.103607] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 05/30/2021] [Accepted: 05/31/2021] [Indexed: 06/12/2023]
Abstract
Larvae of many lepidopteran species produce a mixture of secretory proteins, known as silk, for building protective shelters and cocoons. Silk consists of a water-insoluble silk filament core produced in the posterior silk gland (PSG) and a sticky hydrophilic coating produced by the middle silk gland (MSG). In Bombyx mori, the fiber core comprises three proteins: heavy chain fibroin (Fib-H), light chain fibroin (Fib-L) and fibrohexamerin (Fhx, previously referred to as P25). To learn more about the role of Fhx, we used transcription activator-like effector nuclease (TALEN) mutagenesis and prepared a homozygous line with a null mutation in the Fhx gene. Our characterization of cocoon morphology and silk quality showed that the mutation had very little effect. However, a detailed inspection of the secretory cells in the posterior silk gland (PSG) of mid-last-instar mutant larvae revealed temporary changes in the morphology of the endoplasmic reticulum. We also observed a morphological difference in fibroin secretory globules stored in the PSG lumen of Fhx mutants, which suggests that their fibroin complexes have a slightly lower solubility. Finally, we performed an LC-MS-based quantitative proteomic analysis comparing mutant and wild-type (wt) cocoon proteins and found a high abundance of a 16 kDa secretory protein likely involved in fibroin solubility. Overall, our study shows that whilst Fhx is dispensable for silk formation, it contributes to the stability of fibroin complexes during intracellular transport and affects the morphology of fibroin secretory globules in the PSG lumen.
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Affiliation(s)
- Valeriya Zabelina
- National Agriculture and Food Research Organization, 1-2 Owashi, Tsukuba, Ibaraki, 305-8634, Japan; Biology Centre of the Czech Academy of Sciences and Faculty of Sciences, University of South Bohemia, 370 05, České Budějovice, Czech Republic
| | - Yoko Takasu
- National Agriculture and Food Research Organization, 1-2 Owashi, Tsukuba, Ibaraki, 305-8634, Japan
| | - Hana Sehadova
- Biology Centre of the Czech Academy of Sciences and Faculty of Sciences, University of South Bohemia, 370 05, České Budějovice, Czech Republic; Faculty of Science, University of South Bohemia, Branisovska 31, 370 05, Ceske Budejovice, Czech Republic
| | - Naoyuki Yonemura
- National Agriculture and Food Research Organization, 1-2 Owashi, Tsukuba, Ibaraki, 305-8634, Japan
| | - Kenichi Nakajima
- National Agriculture and Food Research Organization, 1-2 Owashi, Tsukuba, Ibaraki, 305-8634, Japan
| | - Hideki Sezutsu
- National Agriculture and Food Research Organization, 1-2 Owashi, Tsukuba, Ibaraki, 305-8634, Japan
| | - Michal Sery
- Biology Centre of the Czech Academy of Sciences and Faculty of Sciences, University of South Bohemia, 370 05, České Budějovice, Czech Republic
| | - Michal Zurovec
- Biology Centre of the Czech Academy of Sciences and Faculty of Sciences, University of South Bohemia, 370 05, České Budějovice, Czech Republic; Faculty of Science, University of South Bohemia, Branisovska 31, 370 05, Ceske Budejovice, Czech Republic.
| | - Frantisek Sehnal
- Biology Centre of the Czech Academy of Sciences and Faculty of Sciences, University of South Bohemia, 370 05, České Budějovice, Czech Republic.
| | - Toshiki Tamura
- Institute of Sericulture, Iikura 1053, 300-0324, Ami-machi, Ibaraki, Japan.
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