Ecdysone and oocyte morphogenesis in Bombyx mori

Abstract

ECDYSONE, one of the principal hormones of insects, controls the periodic shedding and rebuilding of the cuticle during larval development. (We use “ecdysone” to designate all ecdysoids (in the sense of P. Karlson in ref. 5), or, for the radioimmunoassay, all radioimmunoassay-active ecdysteroid compounds.) It also promotes changes in gene activity observed at the initiation of metamorphosis¹ and influences morphogenetic development of the imaginal disks in pupae. Some reports also indicate that ecdysone is found in adult insects^2–4. Recent work on Drosophila (M.L.D.-R., M. H. Hirn and M. A. Delaage, unpublished), Tenebrio (P. P. Delbecque, M. H. Hirn and M.L.D.-R., unpublished), Locusta⁵ and termites⁶ has shown that a significant level of ecdysone is generally found in adult insects of both sexes and that high titres of ecdysone can be found in ovarian tissues. In Locusta, the ecdysone titre of the ovary increases during each cycle of oocyte maturation⁷, suggesting stimulation by ecdysone, in agreement with observations on Aedes aegypti⁸. This reveals an unexpected aspect of the action of ecdysone. Using a radioimmunoassay to study ecdysone action in Bombyx mori, we have found that not only is ecdysone present in the B. mori ovary during egg production, but that the oocyte itself contains a high concentration of ecdysone. Moreover, this concentration changes during successive phases of oocyte morphogenesis.