Time-Course Transcriptome Analysis Reveals Global Gene Expression Profiling and Dynamic Developmental Signatures across Complete Life Cycle of Bombyx mori

Background: The silkworm (Bombyx mori) is an important lepidopteran model insect worldwide which undergoes a complete metamorphosis developmental process. Although genome sequencing has been long performed, no transcriptome data covering the complete life cycle are available. Methods: Herein, a total of 10 samples were collected consecutively at four different developmental stages, including eggs of 24 h after oviposition (Ed) and eggs of 24 h after artificial egg-hatching (E); larvae from fist to fifth instar (L1-L5); early and late pupa (P4 and P8); and adult moth (M), were subjected to Illumina RNA-Seq and time-course analysis. Results: The summations of the gene expression of the silkworm ten developmental stages show: at Ed stage, eggs develop towards diapause status, the total gene expression level is relatively low; at E stage, after artificial egg-hatching, the expression level improves rapidly; during larval stages from L1-L5, the expression level rises gradually and reaches a peak at L5 stage; during pupae and moth stages, the total gene expression decline stage by stage. The results revealed a dynamical gene expression profile exhibiting significant differential expressions throughout the silkworm life cycle. Moreover, stage-specific key genes were identified at different developmental stages, suggesting their functions mainly characterized in maintaining insect development and immunity homeostasis or driving metamorphosis. GO annotation and KEGG enrichment analysis further revealed the most significantly enriched and fundamentally biological processes during silkworm growth. Conclusion: Collectively, our omics data depicted the first comprehensive landscape of dynamic transcriptome throughout complete developmental processes of B. mori. Our findings also provide valuable references and novel insights into understanding the molecular developmental remodeling events for other Lepidoptera species.