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Transcriptomic Analysis of the Anterior Silk Gland in the Domestic Silkworm (Bombyx mori) - Insight into the Mechanism of Silk Formation and Spinning.

Chang H, Cheng T, Wu Y, Hu W, Long R, Liu C, Zhao P, Xia Q - PLoS ONE (2015)

Bottom Line: A total of 7419 genes were found to be expressed in terms of reads per kilobase of exon model per million mapped reads ≥ 5 in at least one sample.The differentially expressed genes were analyzed, and 282 genes were detected as up-regulated in the anterior silk gland, compared with the other parts.In addition, 210 genes were found differently expressed between males and females, which should help to elucidate the mechanism of the quality difference in silk fibers from male and female silkworms.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, China; College of Biotechnology, Southwest University, Beibei, Chongqing, China.

ABSTRACT
Silk proteins are synthesized in the middle and posterior silk glands of silkworms, then transit into the anterior of the silk gland, where the silk fibers are produced, stored and processed. The mechanism of formation and spinning of the silk fibers has not been fully elucidated, and transcriptome analyses specific to the anterior silk gland have not been reported. In the present study, we explored gene expression profiles in five regions of silk gland samples using the RNA-Seq method. As a result, there were 959,979,570 raw reads obtained, of which 583,068,172 reads were mapped to the silkworm genome. A total of 7419 genes were found to be expressed in terms of reads per kilobase of exon model per million mapped reads ≥ 5 in at least one sample. The gene numbers and expression levels of the expressed genes differed between these regions. The differentially expressed genes were analyzed, and 282 genes were detected as up-regulated in the anterior silk gland, compared with the other parts. Functions of these genes were addressed using the gene ontology and Kyoto Encyclopedia of Genes and Genomes databases, and seven key pathways were enriched. It suggested that the ion transportation, energy metabolism, protease inhibitors and cuticle proteins played essential roles in the process of silk formation and spinning in the anterior silk gland. In addition, 210 genes were found differently expressed between males and females, which should help to elucidate the mechanism of the quality difference in silk fibers from male and female silkworms.

No MeSH data available.


Scatter plot of enriched KEGG pathways for the 282 up-regulated genes in the ASG.The “rich factor” shows the ratio of the number of the up-regulated genes to the total gene number in certain pathways. All pathways had FDR ≤ 0.001.
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pone.0139424.g005: Scatter plot of enriched KEGG pathways for the 282 up-regulated genes in the ASG.The “rich factor” shows the ratio of the number of the up-regulated genes to the total gene number in certain pathways. All pathways had FDR ≤ 0.001.

Mentions: KEGG was also used to annotate the up-regulated genes. A total of 96 pathways were enriched (S9 Table), of which nine pathways met the criteria of P-value < 0.05 and FDR < 0.001 (Fig 5), including six pathways for ‘Energy metabolism’, two for ‘pH controlling’ and one for ‘transport’, which was similar to the GO analysis results. The liquid silk proteins, which are synthesized in the PSG and MSG, move to the ASG, and are then spun out. In the ASG, the gel pattern silk proteins were transformed to soliquid—a better status for silk spinning. In this process, the pH gradient and cations play important roles [21, 22]. The pH decreases along the lumen of the PSG to the ASG, and affects the assembly of silk [23]. Lower pH and Ca2+ concentration, and higher potassium ion (K+) concentration, promote the formations of beta-sheets; however, higher pH and Ca2+, and lower K+, maintain the ‘random coil’ conformations of typical silk [24, 25]. A study of six metal elements—K, Ca, sodium (Na), magnesium (Mg), copper (Cu) and zinc (Zn)—at different stages in the silk secretory pathway showed that Mg2+, Cu2+ and Zn2+ induced the conformation transition of silk fibroin to beta-sheets, Ca2+ affected the formation of a stable protein network (gel) and Na+ and K+ broke down the protein network [4]. To obtain a perfect cocoon, the silkworm has to efficiently control pH and cations, and spin the silk proteins out smoothly. The enriched pathways related to transport and energy metabolism in the ASG that were detected in the present study provide an important reference for explaining the mechanism of the silkworm’s control of the internal environment to machine silk fibers.


Transcriptomic Analysis of the Anterior Silk Gland in the Domestic Silkworm (Bombyx mori) - Insight into the Mechanism of Silk Formation and Spinning.

Chang H, Cheng T, Wu Y, Hu W, Long R, Liu C, Zhao P, Xia Q - PLoS ONE (2015)

Scatter plot of enriched KEGG pathways for the 282 up-regulated genes in the ASG.The “rich factor” shows the ratio of the number of the up-regulated genes to the total gene number in certain pathways. All pathways had FDR ≤ 0.001.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4587926&req=5

pone.0139424.g005: Scatter plot of enriched KEGG pathways for the 282 up-regulated genes in the ASG.The “rich factor” shows the ratio of the number of the up-regulated genes to the total gene number in certain pathways. All pathways had FDR ≤ 0.001.
Mentions: KEGG was also used to annotate the up-regulated genes. A total of 96 pathways were enriched (S9 Table), of which nine pathways met the criteria of P-value < 0.05 and FDR < 0.001 (Fig 5), including six pathways for ‘Energy metabolism’, two for ‘pH controlling’ and one for ‘transport’, which was similar to the GO analysis results. The liquid silk proteins, which are synthesized in the PSG and MSG, move to the ASG, and are then spun out. In the ASG, the gel pattern silk proteins were transformed to soliquid—a better status for silk spinning. In this process, the pH gradient and cations play important roles [21, 22]. The pH decreases along the lumen of the PSG to the ASG, and affects the assembly of silk [23]. Lower pH and Ca2+ concentration, and higher potassium ion (K+) concentration, promote the formations of beta-sheets; however, higher pH and Ca2+, and lower K+, maintain the ‘random coil’ conformations of typical silk [24, 25]. A study of six metal elements—K, Ca, sodium (Na), magnesium (Mg), copper (Cu) and zinc (Zn)—at different stages in the silk secretory pathway showed that Mg2+, Cu2+ and Zn2+ induced the conformation transition of silk fibroin to beta-sheets, Ca2+ affected the formation of a stable protein network (gel) and Na+ and K+ broke down the protein network [4]. To obtain a perfect cocoon, the silkworm has to efficiently control pH and cations, and spin the silk proteins out smoothly. The enriched pathways related to transport and energy metabolism in the ASG that were detected in the present study provide an important reference for explaining the mechanism of the silkworm’s control of the internal environment to machine silk fibers.

Bottom Line: A total of 7419 genes were found to be expressed in terms of reads per kilobase of exon model per million mapped reads ≥ 5 in at least one sample.The differentially expressed genes were analyzed, and 282 genes were detected as up-regulated in the anterior silk gland, compared with the other parts.In addition, 210 genes were found differently expressed between males and females, which should help to elucidate the mechanism of the quality difference in silk fibers from male and female silkworms.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, China; College of Biotechnology, Southwest University, Beibei, Chongqing, China.

ABSTRACT
Silk proteins are synthesized in the middle and posterior silk glands of silkworms, then transit into the anterior of the silk gland, where the silk fibers are produced, stored and processed. The mechanism of formation and spinning of the silk fibers has not been fully elucidated, and transcriptome analyses specific to the anterior silk gland have not been reported. In the present study, we explored gene expression profiles in five regions of silk gland samples using the RNA-Seq method. As a result, there were 959,979,570 raw reads obtained, of which 583,068,172 reads were mapped to the silkworm genome. A total of 7419 genes were found to be expressed in terms of reads per kilobase of exon model per million mapped reads ≥ 5 in at least one sample. The gene numbers and expression levels of the expressed genes differed between these regions. The differentially expressed genes were analyzed, and 282 genes were detected as up-regulated in the anterior silk gland, compared with the other parts. Functions of these genes were addressed using the gene ontology and Kyoto Encyclopedia of Genes and Genomes databases, and seven key pathways were enriched. It suggested that the ion transportation, energy metabolism, protease inhibitors and cuticle proteins played essential roles in the process of silk formation and spinning in the anterior silk gland. In addition, 210 genes were found differently expressed between males and females, which should help to elucidate the mechanism of the quality difference in silk fibers from male and female silkworms.

No MeSH data available.