title: Identification of the Bombyx red egg gene reveals involvement of a novel transporter family gene in late steps of the insect ommochrome biosynthesis pathway.
abstract: Ommochromes are one of the major pigments involved in coloration of eggs, eyes, and body surface of insects. However, the molecular mechanisms of the final steps of ommochrome pigment synthesis have been largely unknown. The eggs of the silkworm Bombyx mori contain a mixture of ommochrome pigments, and exhibit a brownish lilac color. The recessive homozygous of egg and eye color mutant, red egg (re), whose eggs display a pale orange color instead of normal dark coloration, has been long suggested to have a defect in the biosynthesis of the final ommochrome pigments. Here, we identify the gene responsible for the re locus by positional cloning, mutant analysis, and RNAi experiments. In the re mutants, we found that a 541-bp transposable element is inserted into the ORF of BGIBMGA003497-1 (Bm-re) encoding a novel member of a major facilitator superfamily transporter, causing disruption of the splicing of exon 9, resulting in two aberrant transcripts with frameshifts yielding nonfunctional proteins lacking the C-terminal transmembrane domains. Bm-re function in pigmentation was confirmed by embryonic RNAi experiments. Homologs of the Bm-re gene were found in all insect genomes sequenced at present, except for 12 sequenced Drosophila genomes, which seemed to correlate with the previous studies that have demonstrated that eye ommochrome composition is different from other insects in several Dipterans. Knockdown of the Bm-re homolog by RNAi in the red flour beetle Tribolium castaneum caused adult compound eye coloration defects, indicating a conserved role in ommochrome pigment biosynthesis at least among holometabolous insects.
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan. Electronic address: mfutahashi@nias.affrc.go.jp.
authors.forename: Mizuko
authors.initials: M
authors.lastname: Osanai-Futahashi
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Ken-Ichiro
authors.initials: KI
authors.lastname: Tatematsu
authors.affiliation: Insect Genome Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Kimiko
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Insect Genome Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Narukawa
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Keiro
authors.initials: K
authors.lastname: Uchino
authors.affiliation: Insect Growth Regulation Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kayukawa
authors.affiliation: Insect Growth Regulation Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shinoda
authors.affiliation: Laboratory of Insect Genetic Resources, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Banno
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Tamura
authors.affiliation: Transgenic Silkworm Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Sezutsu
mesh_terms: D000818:Animals; D001483:Base Sequence; D012831:Bombyx / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster; D017344:Genes, Insect / Q000502:physiology*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010640:Phenothiazines / Q000378:metabolism*; D014231:Tribolium / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D019476:Insect Proteins; D010640:Phenothiazines; C002772:ommochrome