title: Hormonal regulation and developmental role of Krüppel homolog 1, a repressor of metamorphosis, in the silkworm Bombyx mori.
abstract: Juvenile hormone (JH) has an ability to repress the precocious metamorphosis of insects during their larval development. Krüppel homolog 1 (Kr-h1) is an early JH-inducible gene that mediates this action of JH; however, the fine hormonal regulation of Kr-h1 and the molecular mechanism underlying its antimetamorphic effect are little understood. In this study, we attempted to elucidate the hormonal regulation and developmental role of Kr-h1. We found that the expression of Kr-h1 in the epidermis of penultimate-instar larvae of the silkworm Bombyx mori was induced by JH secreted by the corpora allata (CA), whereas the CA were not involved in the transient induction of Kr-h1 at the prepupal stage. Tissue culture experiments suggested that the transient peak of Kr-h1 at the prepupal stage is likely to be induced cooperatively by JH derived from gland(s) other than the CA and the prepupal surge of ecdysteroid, although involvement of unknown factor(s) could not be ruled out. To elucidate the developmental role of Kr-h1, we generated transgenic silkworms overexpressing Kr-h1. The transgenic silkworms grew normally until the spinning stage, but their development was arrested at the prepupal stage. The transgenic silkworms from which the CA were removed in the penultimate instar did not undergo precocious pupation or larval-larval molt but fell into prepupal arrest. This result demonstrated that Kr-h1 is indeed involved in the repression of metamorphosis but that Kr-h1 alone is incapable of implementing normal larval molt. Moreover, the expression profiles and hormonal responses of early ecdysone-inducible genes (E74, E75, and Broad) in transgenic silkworms suggested that Kr-h1 is not involved in the JH-dependent modulation of these genes, which is associated with the control of metamorphosis.
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Takumi
authors: T
authors: Kayukawa
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Mika
authors: M
authors: Murata
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Isao
authors: I
authors: Kobayashi
authors: Faculty of Agriculture and Life Sciences, Hirosaki University, Hirosaki 036-8561, Japan.
authors: Daisuke
authors: D
authors: Muramatsu
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Chieko
authors: C
authors: Okada
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Keiro
authors: K
authors: Uchino
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Hideki
authors: H
authors: Sezutsu
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Makoto
authors: M
authors: Kiuchi
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors: Toshiki
authors: T
authors: Tamura
authors: Faculty of Agriculture and Life Sciences, Hirosaki University, Hirosaki 036-8561, Japan.
authors: Kiyoshi
authors: K
authors: Hiruma
authors: Laboratory of Applied Entomology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors: Yukio
authors: Y
authors: Ishikawa
authors: National Institute of Agrobiological Sciences, Ohwashi 1-2, Tsukuba, Ibaraki 305-8634, Japan. Electronic address: shinoda@affrc.go.jp.
authors: Tetsuro
authors: T
authors: Shinoda
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D012831:Bombyx / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D004440:Ecdysone / Q000737:chemistry; D026461:Ecdysteroids / Q000737:chemistry; D005260:Female; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism*; D007814:Larva / Q000235:genetics / Q000378:metabolism; D008297:Male; D008675:Metamorphosis, Biological; D016366:Open Reading Frames; D015398:Signal Transduction
chemical_list: D026461:Ecdysteroids; D019476:Insect Proteins; D051741:Kruppel-Like Transcription Factors; D004440:Ecdysone
keywords: Ecdysone-inducible gene; Ecdysteroid; Juvenile hormone; Krüppel homolog 1; Metamorphosis; Molt