INVOLVEMENT OF MICROTUBULES IN PROTHORACICOTROPIC HORMONE-STIMULATED ECDYSTEROIDOGENESIS BY INSECT (MANDUCA-SEXTA) PROTHORACIC GLANDS

Secretion of ecdysteroid molting hormones by insect prothoracic glands is stimulated by neuropeptide prothoracicotropic hormones (PTTH). Stu dies reported here were conducted to assess the effects of microfilame nt and microtubule inhibitors on in vitro ecdysteroidogenesis by proth oracic glands of Manduca sexta. Microfilament inhibitors (cytochalasin s B and D) had no effect on basal or big PTTH-stimulated ecdysteroidog enesis. Microtubule inhibitors (colchicine, podophyllotoxin, nocodazol e) had no effect on basal ecdysteroid secretion, but suppressed PTTH-s timulated secretion in a concentration-dependent manner. The effect-of nocodazole was partially reversible, suggesting it was not due to non specific toxicity. Colchicine had no effect on glandular ecdysteroid l evels, indicating that inhibition was not-due solely to blockage of se cretion. The combined results are consistent with the hypothesis that microtubule-mediated transport-of ecdysteroid precursors plays a criti cal role in stimulation of ecdysteroidogenesis by PTTH. (C) 1996 Wiley -Liss, Inc.