title: Positional cloning of silkworm white egg 2 (w-2) locus shows functional conservation and diversification of ABC transporters for pigmentation in insects.
abstract: The white, scarlet and brown genes of Drosophila melanogaster encode three half-type ATP-binding cassette (ABC) transporters. In Drosophila, precursors of ommochromes and pteridines are transported by White/Scarlet and White/Brown heterodimers, respectively. The white egg 2 (w-2) mutant of the silkworm, Bombyx mori, has white eggs and eyes because of lack of ommochrome granules in the serosa and eyes. Here, we report that the silkworm w-2 locus encodes an ortholog of Drosophila scarlet. Our results indicate that Bombyx Scarlet forms a heterodimer with Bombyx White to transport ommochrome precursors, suggesting that formation of a White/Scarlet heterodimer and its involvement in the transport of ommochrome precursors are evolutionarily ancient and widely conserved traits in insects. Contrary to dipteran insects, white and scarlet were juxtaposed in a head-to-tail orientation in the silkworm genome, suggesting that the origin of white and scarlet was a tandem duplication of their ancestral transporter gene. In Bombyx, White is also essential for the transport of uric acid in larval epidermis. However, our results suggest that a Bombyx White/Scarlet heterodimer is not involved in this process. Our results emphasize the functional conservation and diversification of half-type ABC transporter families in insects, which may contribute to their extremely diverse color patterns.
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Tatematsu
authors.forename: Kimiko
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Keiro
authors.initials: K
authors.lastname: Uchino
authors.forename: Junko
authors.initials: J
authors.lastname: Narukawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Iizuka
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Banno
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.forename: Toru
authors.initials: T
authors.lastname: Shimada
authors.forename: Toshiki
authors.initials: T
authors.lastname: Tamura
authors.forename: Hideki
authors.initials: H
authors.lastname: Sezutsu
authors.forename: Takaaki
authors.initials: T
authors.lastname: Daimon
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000818:Animals; D012831:Bombyx / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D058893:DNA Barcoding, Taxonomic; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling; D056726:Genetic Association Studies; D007313:Insecta / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D010858:Pigmentation / Q000235:genetics*
chemical_list: D018528:ATP-Binding Cassette Transporters