title: LIM-homeodomain transcription factor Awh is a key component activating all three fibroin genes, fibH, fibL and fhx, in the silk gland of the silkworm, Bombyx mori.
abstract: In the silkworm Bombyx mori, three fibroin genes, fibroin-heavy-chain (fibH), fibroin-light-chain (fibL) and fibrohexamerin (fhx), are coexpressed only in the posterior silk gland (PSG) cells, while the sericin genes encoding silk glue proteins are expressed in the middle silk gland (MSG) cells. Silk gland factor-2 (SGF-2) is a PSG-specific activator complex of fibH, composed of a LIM-homeodomain protein, Awh, and its cofactors, Ldb and Lcaf. We investigated whether SGF-2 can activate other fibroin genes using transgenic silkworms. The genes for Ldb and Lcaf were expressed ubiquitously in various tissues, while the gene for Awh was expressed strictly specific in PSG of the wild type silkworms. Misexpression of Awh in transgenic silkworms induced ectopic expression of fibL and fhx as well as fibH in MSG. Coincidently with the induction of fibL and fhx by Awh, binding of SGF-2 to the promoter of fibL and fhx was detected in vitro, and SGF-2 binds directly to the fhx core promoter. Ectopic expression of the fibroin genes was observed at high levels in the middle part of MSG. Moreover, fibL and fhx were induced in the anterior silk gland (ASG) of the transgenic silkworms, but fibH was not. These results indicate that Awh is a key activator of all three fibroin genes, and the activity is probably regulated in conjunction with additional factors.
authors.affiliation: Graduate School of Life Science, Hokkaido University, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Kimoto
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Owashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Tsubota
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Owashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Keiro
authors.initials: K
authors.lastname: Uchino
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Owashi 1-2, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Sezutsu
authors.affiliation: Graduate School of Life Science, Hokkaido University, Japan; Division of Biological Sciences and Center for Genome Dynamics, Faculty of Science, Hokkaido University, North 10, West 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan. Electronic address: takiya@sci.hokudai.ac.jp.
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Takiya
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D012831:Bombyx / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005349:Fibroins / Q000096:biosynthesis / Q000235:genetics*; D006023:Glycoproteins / Q000096:biosynthesis / Q000235:genetics; D018398:Homeodomain Proteins; D017403:In Situ Hybridization; D060850:LIM-Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D007814:Larva; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D060888:Real-Time Polymerase Chain Reaction; D047030:Sericins / Q000378:metabolism; D047011:Silk / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D006023:Glycoproteins; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; D047030:Sericins; D047011:Silk; D014157:Transcription Factors; C418613:fhx protein, Bombyx mori; D005349:Fibroins
keywords: Awh; Bombyx mori; Fibroin; Silk gland; Transgenic