Induction of Pupation by DNA Broken with Steroid Hormones in Silkworms

The initiation of pupation by larval DNA broken with ecdysterone or cortisone was investigated by using Bombyx mori. A single strand scission (nick) was produced by treating mildly the DNA with the steroid hormone-i-Cu2+ and the nicked DNA was then injected into the posterior part of the ligated prepupa. It was observed that the pupation-inducing action of DNA treated with ecdysterone is stronger than that of DNA treated with cortisone. The pupation by the nicked DNA was, however, not so complete as that by ecdysterone itself. In 3 hr after injection, the degree of nicking produced in DNA of prepupae injected the broken DNA was remarkably low comparing with that produced in DNA of those injected ecdysterone itself. After 24 hr, the nicking degree became much higher and double strand break occurred in both the cases. These observations suggest that the pupation in ligated prepupae injected the nicked DNA is initiated by the synthesis of necessary mRNA.