Transcriptome sequencing reveals potential mechanisms of diapause preparation in bivoltine silkworm Bombyx mori (Lepidoptera: Bombycidae)

In the bivoltine strain of the silkworm, Bombyx mori, embryonic diapause is induced transgenerationally as a maternal effect. Progeny diapause ability is determined by the environmental condition such as temperature and lightness that mothers experience during their own embryonic development. Diapause preparation is a crucial phase of this process; diapause-destined individuals undergo a series of preparatory events before the entry into developmental arrest. However, the molecular regulatory mechanisms of diapause preparation have largely remained unknown. In the present study, we sequenced the transcriptome of bivoltine silkworm Qiufeng's ovaries resulted in laying of diapause destined or non-diapause eggs, using high-throughput RNA-Seq technology. Differential expression analyses identified 183 genes with higher expression, and 106 with lower expression under diapause-inducing conditions. GO and KEGG analysis revealed that the enrichment of several functional terms related to peroxisome, glycerolipid metabolism, steroid biosynthesis, longevity regulating pathway - multiple species, three signaling transductions, insect hormone biosynthesis, and cytoskeleton components. We conducted a detailed comparison of transcript profile data of ovaries from diapause-inducing and non-diapause conditions, the results imply up-regulation of peroxisomal metabolism, triacylglycerides accumulation, cryoprotectant production, and ecdysteroid biosynthesis in diapause-inducing group. Differential expression of genes related to actin cytoskeleton implies the occurrence of shifts in cellular structure and composition between diapause-inducing and non-diapause-inducing groups. The Hippo and FOXO signaling pathways may play an important role in preparing for entering diapause. This study provides an insight into the molecular events of insect diapause, in particular for the preparatory phase.