Induction of embryonic diapause and stimulation of ovary trehalase activity in the silkworm, Bombyx mori, by synthetic diapause hormone

Abstract

Diapause hormones, BomDH-I[19-Cys] and BomDH-I[19-Trp], of the silkworm, Bombyx mori were chemically synthesized and used to confirm the physiological function proposed in our previous experiments performed on the partially purified hormone preparation. Injection of the synthetic hormone into day-4 pharate adults caused the moths to lay diapause eggs and the dose for a half maximal activity was estimated to be 10 pmol/pupa. The induced diapause eggs ceased embryogenesis at stage 8 as observed for natural diapause embryos. Embryogenesis was resumed by chilling at 5°C for 60 days or by HCl treatment, which was effective to break down natural diapause induced by the implantation of an active subesophageal ganglion. Synthetic diapause hormone stimulated trehalase activity in developing ovaries in both in vivo and in vitro conditions according to the same time course. The stimulated activity was comparable to that found in ovaries which developed in situ with the endogenous hormone. This diapause hormone action was suppressed by the addition of cycloheximide and actinomycin D to the incubation medium. Addition of EGTA to the medium reduced the hormonal stimulation of trehalase activity, whereas Ca 2+ addition rescued the hormone action on trehalase activity in ovaries. These results confirmed that diapause hormone is responsible for both the induction of embryonic diapause in laid eggs as well as the stimulation of trehalase activity in developing ovaries of silkworms.