title: Hindgut innate immunity and regulation of fecal microbiota through melanization in insects.
abstract: Many insects eat the green leaves of plants but excrete black feces in an as yet unknown mechanism. Insects cannot avoid ingesting pathogens with food that will be specifically detected by the midgut immune system. However, just as in mammals, many pathogens can still escape the insect midgut immune system and arrive in the hindgut, where they are excreted out with the feces. Here we show that the melanization of hindgut content induced by prophenoloxidase, a key enzyme that induces the production of melanin around invaders and at wound sites, is the last line of immune defense to clear bacteria before feces excretion. We used the silkworm Bombyx mori as a model and found that prophenoloxidase produced by hindgut cells is secreted into the hindgut contents. Several experiments were done to clearly demonstrate that the blackening of the insect feces was due to activated phenoloxidase, which served to regulate the number of bacteria in the hindgut. Our analysis of the silkworm hindgut prophenoloxidase discloses the natural secret of why the phytophagous insect feces is black and provides insight into hindgut innate immunity, which is still rather unclear in mammals.
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 200032, People's Republic of China.
authors.forename: Qimiao
authors.initials: Q
authors.lastname: Shao
authors.forename: Bing
authors.initials: B
authors.lastname: Yang
authors.forename: Qiuyun
authors.initials: Q
authors.lastname: Xu
authors.forename: Xuquan
authors.initials: X
authors.lastname: Li
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Lu
authors.forename: Chengshu
authors.initials: C
authors.lastname: Wang
authors.forename: Yongping
authors.initials: Y
authors.lastname: Huang
authors.forename: Kenneth
authors.initials: K
authors.lastname: Söderhäll
authors.forename: Erjun
authors.initials: E
authors.lastname: Ling
mesh_terms: D000818:Animals; D012831:Bombyx; D004156:Catechol Oxidase / Q000737:chemistry; D004792:Enzyme Precursors / Q000737:chemistry; D005243:Feces; D007107:Immune System; D007113:Immunity, Innate / Q000502:physiology*; D007313:Insecta; D007413:Intestinal Mucosa / Q000378:metabolism*; D042845:Laccase / Q000737:chemistry; D008543:Melanins / Q000737:chemistry*; D054892:Metagenome / Q000502:physiology*; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D009113:Muramidase / Q000737:chemistry; D013997:Time Factors; D014945:Wound Healing
chemical_list: D004792:Enzyme Precursors; D008543:Melanins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D042845:Laccase; D009113:Muramidase