title: Molecular mechanism underlying juvenile hormone-mediated repression of precocious larval-adult metamorphosis.
abstract: Juvenile hormone (JH) represses precocious metamorphosis of larval to pupal and adult transitions in holometabolous insects. The early JH-inducible gene Krüppel homolog 1 (Kr-h1) plays a key role in the repression of metamorphosis as a mediator of JH action. Previous studies demonstrated that Kr-h1 inhibits precocious larval-pupal transition in immature larva via direct transcriptional repression of the pupal specifier Broad-Complex (BR-C). JH was recently reported to repress the adult specifier gene Ecdysone-induced protein 93F (E93); however, its mechanism of action remains unclear. Here, we found that JH suppressed ecdysone-inducible E93 expression in the epidermis of the silkworm Bombyx mori and in a B. mori cell line. Reporter assays in the cell line revealed that the JH-dependent suppression was mediated by Kr-h1. Genome-wide ChIP-seq analysis identified a consensus Kr-h1 binding site (KBS, 14 bp) located in the E93 promoter region, and EMSA confirmed that Kr-h1 directly binds to the KBS. Moreover, we identified a C-terminal conserved domain in Kr-h1 essential for the transcriptional repression of E93 Based on these results, we propose a mechanism in which JH-inducible Kr-h1 directly binds to the KBS site upstream of the E93 locus to repress its transcription in a cell-autonomous manner, thereby preventing larva from bypassing the pupal stage and progressing to precocious adult development. These findings help to elucidate the molecular mechanisms regulating the metamorphic genetic network, including the functional significance of Kr-h1, BR-C, and E93 in holometabolous insect metamorphosis.
authors.affiliation: Institute of Agrobiological Sciences, National Agriculture and Food Research Organization, Tsukuba 305-8634, Japan kayu@affrc.go.jp.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kayukawa
authors.affiliation: Institute of Agrobiological Sciences, National Agriculture and Food Research Organization, Tsukuba 305-8634, Japan.
authors.forename: Akiya
authors.initials: A
authors.lastname: Jouraku
authors.affiliation: Institute of Agrobiological Sciences, National Agriculture and Food Research Organization, Tsukuba 305-8634, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Ito
authors.affiliation: Institute of Agrobiological Sciences, National Agriculture and Food Research Organization, Tsukuba 305-8634, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shinoda
mesh_terms: D000818:Animals; D001665:Binding Sites; D012831:Bombyx / Q000235:genetics / Q000254:growth & development*; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D016384:Consensus Sequence; D004440:Ecdysone / Q000502:physiology*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D019476:Insect Proteins / Q000235:genetics / Q000502:physiology*; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000502:physiology; D007814:Larva; D008297:Male; D008675:Metamorphosis, Biological / Q000502:physiology*; D008726:Methoprene / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D000072417:Protein Domains; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011679:Pupa; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D019476:Insect Proteins; D051741:Kruppel-Like Transcription Factors; D020033:Protein Isoforms; D014157:Transcription Factors; D004440:Ecdysone; D008726:Methoprene
keywords: E93; Krüppel homolog 1; holometabolous insects; juvenile hormone; metamorphosis