title: Krüppel Homolog 1 Inhibits Insect Metamorphosis via Direct Transcriptional Repression of Broad-Complex, a Pupal Specifier Gene.
abstract: The Broad-Complex gene (BR-C) encodes transcription factors that dictate larval-pupal metamorphosis in insects. The expression of BR-C is induced by molting hormone (20-hydroxyecdysone (20E)), and this induction is repressed by juvenile hormone (JH), which exists during the premature larval stage. Krüppel homolog 1 gene (Kr-h1) has been known as a JH-early inducible gene responsible for repression of metamorphosis; however, the functional relationship between Kr-h1 and repression of BR-C has remained unclear. To elucidate this relationship, we analyzed cis- and trans elements involved in the repression of BR-C using a Bombyx mori cell line. In the cells, as observed in larvae, JH induced the expression of Kr-h1 and concurrently suppressed 20E-induced expression of BR-C. Forced expression of Kr-h1 repressed the 20E-dependent activation of the BR-C promoter in the absence of JH, and Kr-h1 RNAi inhibited the JH-mediated repression, suggesting that Kr-h1 controlled the repression of BR-C. A survey of the upstream sequence of BR-C gene revealed a Kr-h1 binding site (KBS) in the BR-C promoter. When KBS was deleted from the promoter, the repression of BR-C was abolished. Electrophoresis mobility shift demonstrated that two Kr-h1 molecules bound to KBS in the BR-C promoter. Based on these results, we conclude that Kr-h1 protein molecules directly bind to the KBS sequence in the BR-C promoter and thereby repress 20E-dependent activation of the pupal specifier, BR-C. This study has revealed a considerable portion of the picture of JH signaling pathways from the reception of JH to the repression of metamorphosis.
authors.affiliation: From the Insect Growth Regulation Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan,. Electronic address: kayu@affrc.go.jp.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kayukawa
authors.affiliation: From the Insect Growth Regulation Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan,; Laboratory of Applied Entomology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo, Tokyo 113-8657, Japan, and.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Nagamine
authors.affiliation: From the Insect Growth Regulation Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Ito
authors.affiliation: Department of Biological Science and Center for Genome Dynamics, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Nishita
authors.affiliation: Laboratory of Applied Entomology, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo, Tokyo 113-8657, Japan, and.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ishikawa
authors.affiliation: From the Insect Growth Regulation Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shinoda
mesh_terms: D000818:Animals; D012831:Bombyx / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015536:Down-Regulation; D004441:Ecdysterone / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D007605:Juvenile Hormones / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism*; D007814:Larva / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D008675:Metamorphosis, Biological; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011679:Pupa / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D015398:Signal Transduction; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D007605:Juvenile Hormones; D051741:Kruppel-Like Transcription Factors; D014157:Transcription Factors; D004441:Ecdysterone
keywords: development; endocrinology; hormone; insect; signaling