Wing Discs Of Bombyx Mori Research Articles

DNA Synthesis of Wing Disc Cells and the Effects of Mitomycin C and X Ray Irradiation on the Wing Development of Bombyx mori

The rate of DNA synthesis of wing discs and the effects of X ray irradiation and mitomycin C injection were observed during last larval and early pupal stage of Bombyx mori. The rate of DNA synthesis in wing discs of Bombyx mori was estimated by means of the incorporation of 3H-thymidine during the fifth larval stage. Mitomycin C injection and X ray irradiation were performed during the fifth larval instar and pupal stage to investigate the effects of inhibition of DNA synthesis. The rates of 3H-thymidine incorporation were high on days 0, 1, 2, 4, 5, 7, 8 and 10 of the fifth larval instar. Wings of eclosed adults were affected by injections of mitomycin C between the 7th day of the fifth larval instar and the second day of the pupal stage. Exposing the insects to X rays during the fifth larval instar affected wing and scale formation, and at earlier stages, it had a more deleterious effect. Irradiation at 24–36 hours after pupation inhibited wing expansion and scale formation most among pupal stages. The results suggested that the peaks of 3H-thymidine incorporation during the fifth larval instar and the pupal stage have specific significance for wing development.

Ecdysteroid concentration inducing cell proliferation brings about the imaginal differentiation in the wing disc of Bombyx mori in vitro.

This study was undertaken to evaluate the range of 20-hydroxyecdysone (20HE) concentrations which induce cell proliferation and imaginal differentiation in lepidopteran wing discs in vitro. Wing discs were cultured in medium containing various doses of 20HE. During imaginal differentiation in vitro, wing discs were observed histologically and the number of mitosis was counted every day. Wing discs differentiated adult features in medium containing 0.02-0.2 μg/mL 20HE, and these doses also increased the number of mitosis in disc cells. Wing discs developed the same in vitro as they do in vivo. The concentration of 20HE over 0.2 μg/mL inhibited both mitosis and imaginal differentiation. Cell proliferation, cuticle deposition and tissue elongation were successively observed in vitro the same as observed in vivo. These results suggest that a moderate concentration of ecdysteroid can induce cell proliferation followed by imaginal differentiation.

Accumulation of BmSP1 mRNA in imaginal wing discs ofBombyx moriduring intermolts

Summary A cDNA clone corresponding to an mRNA which accumulated in the wing disc of Bombyx mori has been characterized. The accumulation was restricted to the feeding periods of the intermolts, and the mRNA rapidly disappeared during the larval molt and the spinning period. This accumulation was strongly inhibited by 20-hydroxyecdysone both in vivo and in vitro. The amino acid sequence predicted for the putative protein corresponds to that of the Bombyx mori storage protein 1 (Sakurai et al., 1988). Using in situ hybridization, the mRNA was located in cells associated with trachea formation. Significance of the presence of the mRNA of a storage protein in developing wing disc is discussed.

Genes expressed during the differentiation of the pupal wings are also transiently expressed during the larval moult in Bombyx mori.

By a differential screening of cDNA libraries made with RNAs present in differentiating imaginal wing discs of Bombyx mori, we have isolated clones whose expression is dramatically modified during the formation of the pupal wings. The RNAs corresponding to all but one of these clones are also transiently accumulated in the wing primordia during the last larvo-larval moult and in response to 20-hydroxyecdysone injections. If the injections are made to juvenilized larvae the expression of the same genes is stimulated but the range of the stimulation is reduced. It is suggested that in Bombyx, cells of the wings reach the pupal stage of differentiation by steps corresponding to the phases during which high levels of ecdysteroids are present.