A Comparison of Co-expression Networks in Silk Gland Reveals the Causes of Silk Yield Increase During Silkworm Domestication.

Long-term domestication and selective breeding have increased the silk yield of the domestic silkworm (Bombyx mori) by several times the amount of the silk yield of its wild ancestor (Bombyx mandarina). However, little is known about the molecular mechanisms behind the increase in silk yield during domestication. Based on dynamic patterns of functional divergence in the silk gland between domestic and wild silkworms, we found that at early and intermediate stages of silk gland development, the up-regulated genes of the domestic silkworm were mainly involved in DNA integration, nucleic acid binding, and transporter activity, which are related to the division and growth of cells. This has led to the posterior silk gland (PSG) of the domestic silkworm having significantly more cells ("factories" of fibroin protein synthesis) than that of the wild silkworm. At the late stage of silk gland development, the up-regulated genes in the domestic silkworm was enriched in protein processing and ribosome pathways, suggesting protein synthesis efficiency is greatly improved during silkworm domestication. While there was an increase in fibroin protein synthesis, the production of sericin protein was simultaneously reduced in the silk gland of the domestic silkworm. This reflects that domestic and wild silkworms have been under different selection pressures. Importantly, we found that the network co-expressed with the silk-coding genes of the domestic silkworm was larger than that of the wild silkworm. Furthermore, many more genes co-expressed with silk-coding genes in the domestic silkworm were subjected to artificial selection than those in the wild silkworm. Our results revealed that the increase of silk yield during silkworm domestication is involved in improvement of a biological system which includes not only expansion of "factories" (cells of PSG) of protein synthesis, but also a high expression of silk-coding genes and silk production-related genes such as biological energy, transport, and ribosome pathway genes.

Zhou QZ ，Fu P ，Li SS ，Zhang CJ ，Yu QY ，Qiu CZ ，Zhang HB ，Zhang Z ... -  《Frontiers in Genetics》

Identification and comparison of long non-coding RNAs in the silk gland between domestic and wild silkworms.

Under long-term artificial selection, the domestic silkworm (Bombyx mori) has increased its silk yield tremendously in comparison with its wild progenitor, Bombyx mandarina. However, the molecular mechanism of silk yield increase is still unknown. Comparative analysis of long non-coding RNAs (lncRNAs) may provide some insights into understanding this phenotypic variation. In this study, using RNA sequencing technology data of silk gland in domestic and wild silkworms, we identified 599 lncRNAs in the silk gland of the silkworm. Compared with protein-coding genes, the silk gland lncRNA genes tend to have fewer exon numbers, shorter transcript length and lower GC-content. Moreover, we found that three lncRNA genes are significantly and differentially expressed between domestic and wild silkworms. The potential targets of two differentially expressed lncRNAs (DELs) (dw4sg_0040 and dw4sg_0483) and the expression-correlated genes with the two DELs are mainly enriched in the related processes of silk protein translation. This implies that these DELs may affect the phenotypic variation in silk yield between the domestic and wild silkworms through the post-transcriptional regulation of silk protein.

Zhou QZ ，Fang SM ，Zhang Q ，Yu QY ，Zhang Z ... -  《-》

Comparative Proteomic Analysis of Posterior Silk Glands of Wild and Domesticated Silkworms Reveals Functional Evolution during Domestication.

Li JY ，Cai F ，Ye XG ，Liang JS ，Li JK ，Wu MY ，Zhao D ，Jiang ZD ，You ZY ，Zhong BX ... -  《-》

Comparative analysis of iTRAQ-based proteomes for cocoons between the domestic silkworm (Bombyx mori) and wild silkworm (Bombyx mandarina).

The domestic silkworm Bombyx mori was domesticated from wild silkworm B. mandarina about 5000 years ago. Long-term domestication and breeding selection have led to the weight of domestic silkworm cocoon being ten times greater than that of wild silkworm cocoon. However, we found that wild silkworm cocoon has significantly much more abundance of sericin proteins than domestic silkworm cocoon. Strikingly, we found that many protease inhibitors have been significantly down-regulated in domestic silkworm cocoon compared with its wild progenitor by using isobaric tag for relative and absolute quantitation (iTraq) approach. Both real-time qPCR experiment and transcriptome data in silk gland also verified these results. In addition, our data indicated that protease inhibitor activity of wild silkworm cocoon was stronger than that of domestic silkworm cocoon, implying that relatively up-regulated protease inhibitors in wild silkworm cocoon may play protection roles against microorganisms. Thus, these protease inhibitors up-regulated in wild silkworm cocoon may have potential values in sericulture and medical practice. SIGNIFICANCE: This study revealed that there is a big difference in abundance of sericin proteins in cocoon between domestic and wild silkworms. Strikingly, many protease inhibitors have been significantly down-regulated in domestic silkworm cocoon compared with its wild progenitor. This may be due to different environments where the two silkworms live. In addition, the results also implied that relatively up-regulated protease inhibitors in wild silkworm cocoon may play protection roles against microorganisms. Thus, these protease inhibitors may have potential values in sericulture and medical practice.

Dai ZJ ，Sun W ，Zhang Z 《-》

Comparative Silk Transcriptomics Illuminates Distinctive Impact of Artificial Selection in Silkworm Modern Breeding.

Zhu K ，Chen Y ，Chen L ，Xiang H ... -  《Insects》