The wing-deficient mutant, flügellos (fl), of the silkworm, lacks four wings in the pupa and the adult. Previous studies have suggested that the fl wing discs lose responsiveness to ecdysteroid during metamorphosis. To test this hypothesis at the molecular level we compared the expression of 12 genes when the wing discs from the wild-type (WT) and fl larvae were cultured in the presence or absence of 20-hydroxyecdysone (20E). Most of the genes tested here, ecdysteroid-inducible (EcR-A, -B1, and E75) and noninducible genes (actin A3, beta-tubulin, apterous (ap), USP, and BHR38) were normally expressed in the fl wing discs. However, the amounts of mRNAs of two ecdysteroid-inducible genes, BHR3 (early-late gene; Bombyx homologue to DHR3 and MHR3) and Urbain (wing-specific late gene), were reduced to about 50% and 20% of WT in the cultured fl wing discs, respectively. We analyzed developmental profiles of these mRNAs during metamorphosis. They also demonstrated decreased BHR3 and Urbain mRNA 2 days after the onset of wandering. This reduction in transcription of BHR3 in the fl mutant was observed only in the wing disc, not in the testis and fatbody. These results imply that the aberrant expression of the fl gene affects the downstream pathway of ecdysteroid signaling specifically in the wing discs and thus leads to a deficiency in wing formation.

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We mapped 633 markers (488 AFLPs, 28 RAPDs, 34 IRSs, 75 ESTs, 4 STSs, and 4 phenotypic markers) for the Medaka Oryzias latipes, a teleost fish of the order Beloniformes. Linkage was determined using a reference typing DNA panel from 39 cell lines derived from backcross progeny. This panel provided unlimited DNA for the accumulation of mapping data. The total map length of Medaka was 1354.5 cM and 24 linkage groups were detected, corresponding to the haploid chromosome number of the organism. Thirteen to 49 markers for each linkage group were obtained. Conserved synteny between Medaka and zebrafish was observed for 2 independent linkage groups. Unlike zebrafish, however, the Medaka linkage map showed obvious restriction of recombination on the linkage group containing the male-determining region (Y) locus compared to the autosomal chromosomes.