Analysis of gene expression in the midgut of Bombyx mori during the larval molting stage

Abstract

BackgroundInsects can be models for understanding human intestinal infection and pathology. Molting, a special period during which the old insect cuticle is shed and a new one is produced, is crucial for insect development. Holometabolous insects may experience several larva-to-larva moltings to become larger, a pupal molt and adult eclosion to become adults. During the larval molts, they stop feeding and become quiescent. Although the molting larvae become quiescent, it is not known if changes in microbiome, physiology, development and immunity of midguts occur.ResultsTranscriptome analysis indicated that functions such as metabolism, digestion, and transport may become reduced due to the downregulated expression of many associated genes. During the molting stage, midguts harbor less microflora and DNA synthesis decreases. Both ecdysone and juvenile hormone in the larval midgut likely degrade after entering the larva-to-larva molting stage. However, at 12 h after ecdysis, the feeding larvae of 5th instars that were injected with 20-hydroxyecdysone entered a molting-like stage, during which changes in midgut morphology, DNA synthesis, gene expression, and microflora exhibited the same patterns as observed in the actual molting state.ConclusionThis study is important for understanding insect midgut physiology, development and immunity during a special development stage when no food is ingested. Although the molting larva becomes immobile and quiescent, we demonstrate that numerous changes occur in midgut morphology, physiology, metabolism and microbiome during this period.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3162-8) contains supplementary material, which is available to authorized users.

Transcriptomic analysis at the first instar larval stage of nonmolting Bombyx mori mutant (a42)

“…The silkworm, B. mori , is a typical complete metamorphosis type insect and undergoes six molting stages, which are special periods of the life cycle. There are substantial variations in metabolic pathways and physiological and biochemical characteristics before and after each molting stage, including changes in gene expression, chitin synthesis, cuticle sclerotization and replacement, epidermal staining, midgut cells regeneration and apoptosis (Yang et al, 2016).…”

“…Studies have also shown that the expression of many genes undergoes regulatory changes in the epidermis during molting stages (Yang et al, 2016; J. Zhang, Lu, Kong, Zhang, & Ling, 2014). The gene BmC 1 ‐THF encodes a crucial enzyme in folate metabolism and is important for the synthesis of nucleic acids and proteins as well as DNA methylation and repair (Chen et al, 2018).…”

“…It is possible that in a42 mutants, the decrease of BmAKR2E4 expression leads to observed reductions in the level of 20E, resulting in the upregulation of BmDDC and finally causes high levels of epidermal melanization ( Figure 5). | 9 of 12 synthesis, cuticle sclerotization and replacement, epidermal staining, midgut cells regeneration and apoptosis (Yang et al, 2016).…”

“…Studies have also shown that the expression of many genes undergoes regulatory changes in the epidermis during molting stages (Yang et al, 2016;J. Zhang, Lu, Kong, Zhang, & Ling, 2014).…”

Analysis of the functions of the signal peptidase complex in the midgut of Tribolium castaneum

“…The developmental and tissue expression patterns of the Tribolium SPCs were analyzed by RT‐PCR. Total RNA was isolated from whole insects at various stages by using the TRIZOL REAGENT (Invitrogen, Carlsbad, CA) (Yang et al., ). To assay gene expression in the midgut and carcass (whole body minus gut), 30 individuals were dissected to obtain separate pools of gut and carcass.…”