title: Transcriptional profiling of midgut immunity response and degeneration in the wandering silkworm, Bombyx mori.
abstract: BACKGROUND
  Lepidoptera insects have a novel development process comprising several metamorphic stages during their life cycle compared with vertebrate animals. Unlike most Lepidoptera insects that live on nectar during the adult stage, the Bombyx mori silkworm adults do not eat anything and die after egg-laying. In addition, the midguts of Lepidoptera insects produce antimicrobial proteins during the wandering stage when the larval tissues undergo numerous changes. The exact mechanisms responsible for these phenomena remain unclear.
  
  
  RESULTS
  We used the silkworm as a model and performed genome-wide transcriptional profiling of the midgut between the feeding stage and the wandering stage. Many genes concerned with metabolism, digestion, and ion and small molecule transportation were down-regulated during the wandering stage, indicating that the wandering stage midgut loses its normal functions. Microarray profiling, qRT-PCR and western blot proved the production of antimicrobial proteins (peptides) in the midgut during the wandering stage. Different genes of the immune deficiency (Imd) pathway were up-regulated during the wandering stage. However, some key genes belonging to the Toll pathway showed no change in their transcription levels. Unlike butterfly (Pachliopta aristolochiae), the midgut of silkworm moth has a layer of cells, indicating that the development of midgut since the wandering stage is not usual. Cell division in the midgut was observed only for a short time during the wandering stage. However, there was extensive cell apoptosis before pupation. The imbalance of cell division and apoptosis probably drives the continuous degeneration of the midgut in the silkworm since the wandering stage.
  
  
  CONCLUSIONS
  This study provided an insight into the mechanism of the degeneration of the silkworm midgut and the production of innate immunity-related proteins during the wandering stage. The imbalance of cell division and apoptosis induces irreversible degeneration of the midgut. The Imd pathway probably regulates the production of antimicrobial peptides in the midgut during the wandering stage.
authors.affiliation: Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China.
authors.forename: Qiuyun
authors.initials: Q
authors.lastname: Xu
authors.forename: Anrui
authors.initials: A
authors.lastname: Lu
authors.forename: Guohua
authors.initials: G
authors.lastname: Xiao
authors.forename: Bing
authors.initials: B
authors.lastname: Yang
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Xuquan
authors.initials: X
authors.lastname: Li
authors.forename: Jingmin
authors.initials: J
authors.lastname: Guan
authors.forename: Qimiao
authors.initials: Q
authors.lastname: Shao
authors.forename: Brenda T
authors.initials: BT
authors.lastname: Beerntsen
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.forename: Chengshu
authors.initials: C
authors.lastname: Wang
authors.forename: Erjun
authors.initials: E
authors.lastname: Ling
mesh_terms: D000818:Animals; D012831:Bombyx / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000276:immunology* / Q000378:metabolism; D007109:Immunity / Q000235:genetics*; D007814:Larva / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008018:Life Cycle Stages; D059467:Transcriptome