家蚕驯化过程中组蛋白修饰对丝蛋白合成的调控研究

The silkworm Bombyx mori is an economically important insect, which is domesticated from the wild silkworm Bombyx mandarina. Compared to B. mandarina, many economic characteristics such as silk production and quality have been improved in the B. mori. The mechanism on the regulation of silk protein synthesis by artificial domestication, however, is largely unknown. It has been recently reported that the changes of DNA methylation in the silk gland of B. mori and B. mandarina could regulate the expression of genes artificially selected, which implied that the epigenetic regulation may play a very important role in the domestication. The level of DNA methylation in silkworm, however, is very low, and the role of DNA methylation is also confused at present. In this project, we thus focus on histone modification, another epigenetic marker, in order to explore its role in the domestication. We use the methods of RNA-seq and ChIP-seq to obtain the differential expression genes and differential histone modification profiles in the silk gland of B. mori and B. mandarina, and find the positive genes corresponded to the changes of histone modifications. RNAi-mediated silencing or knockout of enzyme genes responsible for histone modifications is further performed to confirm its role in the regulation of candidate genes. We are expected to understand the relationship between the epigenetics and silk protein synthesis during the domestication of silkworm.

家蚕是重要的经济昆虫，是野桑蚕经过长期的人工驯化培育而来。相比较于野桑蚕，家蚕的多种重要经济性状如蚕丝产量和品质都达到了显著的改善。但是，人工驯化过程如何影响家蚕丝腺的丝蛋白合成并不清楚。在最近的研究中发现，家蚕丝腺DNA甲基化修饰变化影响了受人工选择基因的表达，暗示表观遗传学改变很可能在家蚕的人工驯化过程中发挥了重要的作用。然而，家蚕DNA甲基化水平很低且功能未知。因此，本项目从另一个重要的表观遗传学标记－组蛋白修饰出发，来探讨组蛋白修饰在家蚕人工驯化过程中的作用。通过转录组测序和染色质免疫共沉淀测序来鉴定家蚕和野桑蚕丝腺组织中的差异表达基因和差异组蛋白修饰谱，综合比较分析获得受组蛋白修饰变化而变化的人工选择基因，并利用RNAi或基因敲除技术验证组蛋白修饰在目标基因表达中的调控作用。研究结果将有助于揭示在人工驯化过程中表观遗传变化与丝腺丝蛋白合成的关系。

本项目以家蚕和野桑蚕为对象，研究了家蚕从野桑蚕在人工驯化过程中的表观遗传变化，取得的主要结果有：（1）通过转录组测序技术分析了家蚕和野桑蚕丝腺组织中的差异表达基因，发现有上千个基因发生上调或下调表达；（2）通过染色质免疫共沉淀测序技术分析了家蚕和野桑蚕丝腺组织中的组蛋白H3K4me3和H3K27me3的差异修饰谱，发现有4640个基因存在H3K4me3修饰以及969个基因存在H3K27me3修饰；（3）对组蛋白修饰H3K4me3和H3K27me3的目标基因进行了表达分析，发现H3K4me3修饰基因主要是高表达量基因，而H3K27me3则更多富集于低量表达基因中；（4）通过RNAi基因沉默技术研究了组蛋白修饰H3K4me3和H3K27me3对目标基因的调控机制，发现H3K4me3主要促进基因表达，而H3K27me3主要抑制基因表达。相关研究结果将为未来通过表观遗传变化实现对家蚕丝蛋白合成的调控奠定基础。