Originally published as Genetics Published Articles Ahead of Print on May 27, 2008.

Genetics, Vol. 179, 875-885, June 2008, Copyright © 2008
doi:10.1534/genetics.107.082784

Positional Cloning of a Bombyx Wingless Locus flügellos (fl) Reveals a Crucial Role for fringe That Is Specific for Wing Morphogenesis

Kaoru Sato*, Tomoko Matsuoka Matsunaga*,1, Ryo Futahashi*, Tetsuya Kojima*, Kazuei Mita{dagger}, Yutaka Banno{ddagger} and Haruhiko Fujiwara*,2

* Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan, {dagger} Laboratory of Insect Genome, National Institute of Agrobiological Sciences, Owashi 1-2, Tsukuba, Ibaraki 305-8643, Japan and {ddagger} 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

Mutations at the flügellos (fl) locus in Bombyx mori produce wingless pupae and moths because of the repressed response of wing discs to ecdysteroid. Four recessive fl alleles occurred spontaneously and were mapped at 13.0 of the silkworm genetic linkage group 10. By positional cloning, we confirmed that the gene responsible for fl is fringe (fng) encoding Fng glycosyltransferase, which is involved in regulating the Notch signaling pathway. In four different fl alleles, we detected a large deletion of the fng gene in flk and nonsense mutations in fl, flo, and fln. In the wild-type (WT) silkworm, fng is expressed actively in the wing discs, brain, and reproductive organs from the fourth to final instars but barely in the other tissues tested. In situ hybridization showed that fng mRNA is expressed in the dorsal layer of the WT wing discs. The wingless (wg) mRNA, a downstream marker of Fng-mediated Notch signaling, is localized at the dorsoventral boundary in the WT wing discs but repressed markedly in the fl wing discs. Although null mutants of Drosophila fng result in postembryonic lethality, loss of fng function in Bombyx affects only wing morphogenesis, suggesting different essential roles for fng in tissue differentiation among insects.