Originally published as Genetics Published Articles Ahead of Print on October 14, 2008.

Genetics, Vol. 180, 1995-2005, December 2008, Copyright © 2008
doi:10.1534/genetics.108.096388

yellow and ebony Are the Responsible Genes for the Larval Color Mutants of the Silkworm Bombyx mori

Ryo Futahashi^*,,1, Jotaro Sato^,1, Yan Meng^,1, Shun Okamoto^*, Takaaki Daimon, Kimiko Yamamoto, Yoshitaka Suetsugu, Junko Narukawa, Hirokazu Takahashi, Yutaka Banno, Susumu Katsuma, Toru Shimada, Kazuei Mita and Haruhiko Fujiwara^*,2

^* Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba 277-8562, Japan, Laboratory of Insect Genome, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8643, Japan, Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Science, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan and Laboratory of Insect Genetic Resources, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan

² Corresponding author: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Bldg. 501, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
E-mail: haruh{at}k.u-tokyo.ac.jp

Many larval color mutants have been obtained in the silkworm Bombyx mori. Mapping of melanin-synthesis genes on the Bombyx linkage map revealed that yellow and ebony genes were located near the chocolate (ch) and sooty (so) loci, respectively. In the ch mutants, body color of neonate larvae and the body markings of elder instar larvae are reddish brown instead of normal black. Mutations at the so locus produce smoky larvae and black pupae. F₂ linkage analyses showed that sequence polymorphisms of yellow and ebony genes perfectly cosegregated with the ch and so mutant phenotypes, respectively. Both yellow and ebony were expressed in the epidermis during the molting period when cuticular pigmentation occurred. The spatial expression pattern of yellow transcripts coincided with the larval black markings. In the ch mutants, nonsense mutations of the yellow gene were detected, whereas large deletions of the ebony ORF were detected in the so mutants. These results indicate that yellow and ebony are the responsible genes for the ch and so loci, respectively. Our findings suggest that Yellow promotes melanization, whereas Ebony inhibits melanization in Lepidoptera and that melanin-synthesis enzymes play a critical role in the lepidopteran larval color pattern.

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