Analyses of the Molecular Mechanisms Associated with Silk Production in Silkworm by iTRAQ-Based Proteomics and RNA-Sequencing-Based Transcriptomics

Silkworm
is used as a model organism to analyze two standard complex
traits, which are high and low silk yields. To understand the molecular
mechanisms of silk production, the posterior silk glands aged to the
third day of the fifth instar were analyzed from the ZB strain with
low silk production and from the control strain Lan10. Using isobaric
tags for relative and absolute quantification (iTRAQ) quantitative
shotgun proteomics and RNA-sequencing-based transcriptomics, 139 proteins
and 630 transcripts were identified as novel in the ZB strain compared
with the Lan10 strain, indicating that these results significantly
expand the coverage of proteins and transcripts of the posterior silk
glands in the silkworm. Of the 89 differently changed proteins, 23
were increased, and 66 were decreased. Of the 788 transcripts, 779
were upregulated, and 9 were downregulated. These results confirm
that decreased energy utilization/protein translation and enhanced
protein degradation are the key factors in lower silk production.
Moreover, this study provides novel insight into the molecular changes
that may result in lower silk production, namely, a combination of
impaired transcription activity, missed protein folding/transport,
and lowered yields of the main components of fibroin, along with weakened
growth/development of the posterior silk gland.

家蚕（Silkworm）被用作模式生物，用于分析两项标准化复杂性状——高蚕丝产量与低蚕丝产量。为解析蚕丝生成的分子机制，本研究对产丝量较低的ZB品系以及对照品系Lan10的五龄第三天后部丝腺开展了分析。采用同量异位素相对与绝对定量（isobaric tags for relative and absolute quantification, iTRAQ）定量鸟枪法蛋白质组学及基于RNA测序的转录组学技术，相较于对照品系Lan10，ZB品系中鉴定出139种全新蛋白质与630个全新转录本，该结果显著拓展了家蚕后部丝腺的蛋白质与转录本覆盖范围。在89种差异表达蛋白质中，23种表达上调，66种表达下调；在788个转录本中，779个表达上调，仅9个表达下调。上述结果证实，能量利用/蛋白质翻译水平降低以及蛋白质降解增强是导致蚕丝产量降低的关键因素。此外，本研究为蚕丝产量降低相关的分子变化提供了全新视角：即转录活性受损、蛋白质折叠/运输缺陷、丝素主要组分合成量减少，以及后部丝腺生长发育减弱共同作用所致。