Analysis of proteome dynamics inside the silk gland lumen of Bombyx mori

Abstract

The silk gland is the only organ where silk proteins are synthesized and secreted in the silkworm, Bombyx mori. Silk proteins are stored in the lumen of the silk gland for around eight days during the fifth instar. Determining their dynamic changes is helpful for clarifying the secretion mechanism of silk proteins. Here, we identified the proteome in the silk gland lumen using liquid chromatography–tandem mass spectrometry, and demonstrated its changes during two key stages. From day 5 of the fifth instar to day 1 of wandering, the abundances of fibroins, sericins, seroins, and proteins of unknown functions increased significantly in different compartments of the silk gland lumen. As a result, these accumulated proteins constituted the major cocoon components. In contrast, the abundances of enzymes and extracellular matrix proteins decreased in the silk gland lumen, suggesting that they were not the structural constituents of silk. Twenty-five enzymes may be involved in the regulation of hormone metabolism for proper silk gland function. In addition, the metabolism of other non-proteinous components such as chitin and pigment were also discussed in this study.

Comparative Proteome Analysis Reveals that Cuticular Proteins Analogous to Peritrophin‐Motif Proteins are Involved in the Regeneration of Chitin Layer in the Silk Gland of Bombyx mori at the Molting Stage

“…Over the past few years, proteomic methods have been successfully applied to analyze protein components in the silk gland. However, most studies focused on the fifth instar, and few investigated the silk gland at other larval stages. In this study, LC–MS/MS was used to elucidate the protein differences in the silk gland between the fourth molt and fourth instar.…”

“…Silkworms can spin two kinds of silk: cocoon silk and non‐cocoon silk. Cocoon silk protects the pupa from external environment variations, whereas non‐cocoon silk not only fixes the body to prevent unexpected falling but also helps to cast off old cuticle . Both cocoon and non‐cocoon silk are synthesized by the silk gland, but they are produced at different larval stages: cocoon silk is spun at the end of the fifth larval instar, whereas non‐cocoon silk is produced at the other larval stages .…”

“…Cocoon silk protects the pupa from external environment variations, whereas non‐cocoon silk not only fixes the body to prevent unexpected falling but also helps to cast off old cuticle . Both cocoon and non‐cocoon silk are synthesized by the silk gland, but they are produced at different larval stages: cocoon silk is spun at the end of the fifth larval instar, whereas non‐cocoon silk is produced at the other larval stages . Non‐cocoon silk has a lot of specifically expressed silk proteins relative to cocoon silk, such as BGIBMGA001819 and BGIBMGA011896, and most of these proteins are unknown functional proteins .…”

“…The expression of silk genes in the silk gland is regulated by many factors, leading to the synthesis of silk proteins in a particular space and time. Many researchers have analyzed the proteome of silkworm silk glands at the fifth larval instar and identified many proteins involved in silk synthesis and secretion.…”

Protein Patterns of Silkworm Bombyx mori L. Fed on Leaves of Wild and Cultivated Mulberry Varieties

“…Recent studies concerned with the protein quantification by SDS-PAGE gel electrophoresis were carried out to demonstrate the variability in protein profiles between different mulberry cultivars only (Madhu Babu et al, 2014;Jyothi et al, 2016), on the other hand, the comparative proteomic maps approach was applied to assess many factors that affect the silkworm haemolymph and posterior silkgland protein patterns (Li et al, 2012;Zhang et al, 2014;Dong et al, 2016). Meanwhile the effect of cultivated mulberry varieties on haemolymph protein patterns was investigated by El-Akkad et al (2008).…”