INDUCTION OF EMBRYONIC DIAPAUSE AND STIMULATION OF OVARY TREHALASE ACTIVITY IN THE SILKWORM, BOMBYX-MORI, BY SYNTHETIC DIAPAUSE HORMONE

Diapause hormones, BomDH-I[19-Cys] and BomDH-I[19-Trp], of the silkwor m, Bombyx mori were chemically synthesized and used to confirm the phy siological 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 eg gs and the dose for a half maximal activity was estimated to be 10 pmo l/pupa. The induced diapause eggs ceased embryogenesis at stage 8 as o bserved for natural diapause embryos. Embryogenesis was resumed by chi lling at 5-degrees-C for 60 days or by HCl treatment, which was effect ive to break down natural diapause induced by the implantation of an a ctive subesophageal ganglion. Synthetic diapause hormone stimulated tr ehalase activity in developing ovaries in both in vivo and in vitro co nditions according to the same time course. The stimulated activity wa s comparable to that found in ovaries which developed in situ with the endogenous hormone. This diapause hormone action was suppressed by th e addition of cycloheximide and actinomycin D to the incubation medium . Addition of EGTA to the medium reduced the hormonal stimulation of t rehalase activity, whereas Ca2+ 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 develop ing ovaries of silkworms.