Ecdysone and gene expressions for chromatin remodeling, histone modification, and Broad Complex in relation to pupal commitment in Bombyx mori.

In the present study, we tried to clarify when and how pupal commitment (PT) better to use PC occurs and what is involved in the PT of Bombyx mori. To clarify this, we examined the responsiveness of a wing disc to ecdysone, referring to metamorphosis-related BR-C, development-related Myc and Wnt, and chromatin remodeling-related genes at around the predicted PT stage of the Bombyx wing disc. Wing disc responsiveness to juvenile hormone (JH) and ecdysone was examined using Methoprene and 20-hydroxyecdysone (20E) in vitro. The body weight of B. mori increased after the last larval ecdysis, peaked at Day 5 of the fifth larval instar (D5L5), and then decreased. The responsiveness of the wing disc to JH decreased after the last larval ecdysis up to D3L5. Bmbr-c (the Broad Complex of B. mori) showed enhanced expression in D4L5 wing discs with 20E treatment. Some chromatin remodeler and histone modifier genes (Bmsnr1, Bmutx, and Bmtip60) showed upregulation after being cultured with 20E in D4L5 wing discs. A low concentration of 20E is suggested to induce responsiveness to 20E in D4L5 wing discs. Bmbr-c, Bmsnr1, Bmutx, and Bmtip60 were upregulated after being cultured with a low concentration of 20E in D4L5 wing discs. The expression of Bmmyc and Bmwnt1 did not show a change after being cultured with or without 20E in D4L5 wing discs, while enhanced expression was observed with 20E in D5L5 wing discs. From the present results, we concluded that PT of the wing disc of B. mori occurred beginning on D4L5 with the secretion of low concentrations of ecdysteroids. Bmsnr1, Bmutx, Bmtip60, and BR-C are also involved.