Change in corpus allatum function during metamorphosis of the tobacco hornworm Manduca sexta: Regulation at the terminal step in juvenile hormone biosynthesis

Abstract

Changes in activity of the corpora allata (CA) during larval-pupal-adult development of the tobacco hornworm Manduca sexta were studied by transplantation assays, measurements of in vitro juvenile hormone (JH) and JH acid synthesis, and determination of JH acid methyltransferase OHAMT) and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activities.The data from these assays demonstrate that the CA cease to secrete JH by day 4 of the last larval instar (wandering stage). With regard to JH synthesis, they remain inactive throughout the prepupal, pupal, and most of the pharate adult periods. CA of females, but not of males, resume JH synthesis shortly before eclosion. The biochemical basis of the inactivation process is the loss of JHAMT activity. However, prepupal CA produce JH acids, as shown by enzyme and in vitro assays. Pupal and pharate adult CA do not synthesize JH acids although levels of HMG-CoA reductase activity seem to remain relatively high. Radiolabeled JH was recovered from hemolymph of allatectomized prepupae that had been injected with radiolabeled JH acid. These results provide further evidence that certain peripheral tissues (eg, imaginal discs) convert JH acid secreted by the prepupal CA to JH and, thus, that JH acid is a prohormone in the prepupal period. The CA change from hormone secretion to prohormone secretion during larval-prepupal transformation, a unique functional alteration in an endocrine gland.

CYP15A1, the cytochrome P450 that catalyzes epoxidation of methyl farnesoate to juvenile hormone III in cockroach corpora allata

“…Methyl (2E,6E)-farnesoate was metabolized by CYP15A1 to a single product that had the same retention time as JH III on reversedphase HPLC. The reaction did not require the presence of cytochrome b 5 . The HPLC-purified product was analyzed further by GC͞MS.…”

“…In Lepidoptera, epoxidation may precede esterification, and the latter reaction is under strict developmental control (5). The O-methyl transferase activity disappears from the CA of Lepidoptera during metamorphosis but can be found later in some peripheral tissues, most notably in the accessory sex glands of adult male Cecropia moths (6).…”

Juvenile hormone acid methyltransferase: A key regulatory enzyme for insect metamorphosis

“…The CA of M. sexta also lose JHAMT activity at the end of the feeding stage during the last instar (10,13). Similarly, although not directly analyzed, B. mori CA are thought to lose JHAMT activity during the early part of the last instar (14).…”

“…During the last instar JH disappears from the hemolymph, and a surge of small ecdysteroid titer at the end of the feeding stage induces early metamorphic responses, such as wandering behavior and the pupal commitment of the epidermis (1). Toward the end of the feeding period, the CA of M. sexta stops secreting JH and henceforth secretes only JH acid (JHA) thereafter (10)(11)(12). This physiological switching observed in the CA during metamorphosis is considered to be caused by the loss of JHA methyltransferase (JHAMT) activity in the tissue (13).…”

Brain‐controlled synthesis of juvenile hormone in adult insects

“…Lately, it has been suggested that the inactivation of the CA at the end of the last larval instar in M. sexta is due to the loss of JH-methyltransferase activity and not the HMG-CoA reductase activity (Bhaskaran et al, 1986). Interestingly, the methyl transferase is known to be totally lacking in the CA of adult male cecropia moth and is found instead in the accessory sex glands (Shirk et al, 1976).…”