title: Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori.
abstract: Pigmentation patterning has long interested biologists, integrating topics in ecology, development, genetics, and physiology. Wild-type neonatal larvae of the silkworm, Bombyx mori, are completely black. By contrast, the epidermis and head of larvae of the homozygous recessive sex-linked chocolate (sch) mutant are reddish brown. When incubated at 30 degrees C, mutants with the sch allele fail to hatch; moreover, homozygous mutants carrying the allele sch lethal (sch(l)) do not hatch even at room temperature (25 degrees C). By positional cloning, we narrowed a region containing sch to 239,622 bp on chromosome 1 using 4,501 backcross (BC1) individuals. Based on expression analyses, the best sch candidate gene was shown to be tyrosine hydroxylase (BmTh). BmTh coding sequences were identical among sch, sch(l), and wild-type. However, in sch the approximately 70-kb sequence was replaced with approximately 4.6 kb of a Tc1-mariner type transposon located approximately 6 kb upstream of BmTh, and in sch(l), a large fragment of an L1Bm retrotransposon was inserted just in front of the transcription start site of BmTh. In both cases, we observed a drastic reduction of BmTh expression. Use of RNAi with BmTh prevented pigmentation and hatching, and feeding of a tyrosine hydroxylase inhibitor also suppressed larval pigmentation in the wild-type strain, pnd(+) and in a pS (black-striped) heterozygote. Feeding L-dopa to sch neonate larvae rescued the mutant phenotype from chocolate to black. Our results indicate the BmTh gene is responsible for the sch mutation, which plays an important role in melanin synthesis producing neonatal larval color.
authors.affiliation: Key Sericultural Laboratory of Agricultural Ministry, Institute of Sericulture and Systems Biology, Southwest University, Chongqing 400716, China.
authors.forename: Chun
authors.initials: C
authors.lastname: Liu
authors.forename: Kimiko
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Ting-Cai
authors.initials: TC
authors.lastname: Cheng
authors.forename: Keiko
authors.initials: K
authors.lastname: Kadono-Okuda
authors.forename: Junko
authors.initials: J
authors.lastname: Narukawa
authors.forename: Shi-Ping
authors.initials: SP
authors.lastname: Liu
authors.forename: Yu
authors.initials: Y
authors.lastname: Han
authors.forename: Ryo
authors.initials: R
authors.lastname: Futahashi
authors.forename: Kurako
authors.initials: K
authors.lastname: Kidokoro
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Noda
authors.forename: Isao
authors.initials: I
authors.lastname: Kobayashi
authors.forename: Toshiki
authors.initials: T
authors.lastname: Tamura
authors.forename: Akio
authors.initials: A
authors.lastname: Ohnuma
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Banno
authors.forename: Fang-Ying
authors.initials: FY
authors.lastname: Dai
authors.forename: Zhong-Huai
authors.initials: ZH
authors.lastname: Xiang
authors.forename: Marian R
authors.initials: MR
authors.lastname: Goldsmith
authors.forename: Kazuei
authors.initials: K
authors.lastname: Mita
authors.forename: Qing-You
authors.initials: QY
authors.lastname: Xia
mesh_terms: D000818:Animals; D012831:Bombyx / Q000201:enzymology* / Q000235:genetics*; D002874:Chromosome Mapping; D017344:Genes, Insect / Q000235:genetics*; D008040:Genetic Linkage; D016678:Genome / Q000235:genetics; D007814:Larva; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D010858:Pigmentation / Q000235:genetics*; D015203:Reproducibility of Results; D012727:Sex Characteristics; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D014446:Tyrosine 3-Monooxygenase