Abstract
BackgroundWing discs of B. mori are transformed to pupal wings during the larva-to-pupa metamorphosis with dramatic morphological and structural changes. To understand these changes at a transcriptional level, RNA-seq of the wing discs from 6-day-old fifth instar larvae (L5D6), prepupae (PP) and pupae (P0) was performed.ResultsIn total, 12,254 transcripts were obtained from the wing disc, out of which 5,287 were identified to be differentially expressed from L5D6 to PP and from PP to P0. The results of comprehensive analysis of RNA-seq data showed that during larvae-to-pupae metamorphosis, many genes of 20E signaling pathway were up-regulated and those of JH signaling pathway were down-regulated. Seventeen transcription factors were significantly up-regulated. Cuticle protein genes (especially wing cuticle protein genes), were most abundant and significantly up-regulated at P0 stage. Genes responsible for the degradation and de novo synthesis of chitin were significantly up-regulated. There were A and B two types of chitin synthases in B. mori, whereas only chitin synthase A was up-regulated. Both trehalose and D-fructose, which are precursors of chitin synthesis, were detected in the hemolymph of L5D6, PP and P0, suggesting de novo synthesis of chitin. However, most of the genes that are related to early wing disc differentiation were down-regulated.ConclusionsExtensive transcriptome and DGE profiling data of wing disc during metamorphosis of silkworm have been generated, which provided comprehensive gene expression information at the transcriptional level. These results implied that during the larva-to-pupa metamorphosis, pupal wing development and transition might be mainly controlled by 20E signaling in B. mori. The 17 up-regulated transcription factors might be involved in wing development. Chitin required for pupal wing development might be generated from both degradation of componential chitin and de novo synthesis. Chitin synthase A might be responsible for the chitin synthesis in the pupal wing, while both trehalose and D-fructose might contribute to the de novo synthesis of chitin during the formation of pupal wing.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-820) contains supplementary material, which is available to authorized users.
Highlights
Wing discs of B. mori are transformed to pupal wings during the larva-to-pupa metamorphosis with dramatic morphological and structural changes
Transcriptome sequencing and statistics of gene expression In total, 4,842,606, 4,741,356 and 4,852,047 clean reads were obtained from the wing disc at 6-day-old fifth instar larvae (L5D6), prepupae (PP) and pupae (P0) stages, respectively
Of the 12,254 assembled transcripts, 9,822 transcripts are commonly shared by the three stages; 607, 373, 312 transcripts are shared by two stages (L5D6 and PP, PP and P0, L5D6 and P0), respectively; 575, 434, 431 transcripts are expressed at L5D6, PP and P0 stage, respectively (Figure 1)
Summary
Wing discs of B. mori are transformed to pupal wings during the larva-to-pupa metamorphosis with dramatic morphological and structural changes. To understand these changes at a transcriptional level, RNA-seq of the wing discs from 6-day-old fifth instar larvae (L5D6), prepupae (PP) and pupae (P0) was performed. 20-hydroxyecdysone (20E) and juvenile hormone (JH) are two major hormones in insects and regulate different biological processes, including growth, molting, and reproduction [7,8]. Both 20E and JH are present at larval stages and they are antagonistic in many aspects. In B. mori, 20E and JH signaling pathways have been found to be involved in normal wing development [19,20,21], but no detailed analyses of the two signaling pathways was performed at the transcriptional level
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