Prothoracic glands of the saturniid moth Samia cynthia ricini possess a circadian clock controlling gut purge timing

Abstract

In the moth Samia cynthia ricini, timing of the release ofprothoracicotropic hormone is controlled by a circadian clock in the cephalic organ (brain); while this hormone release is necessary for gut purge, the final timing of this event is controlled by a circadian clock in the prothoracic glands that gates release of ecdysone. The photoreceptor of the prothoracic gland clock(s) is extraocular and evidently in the glands themselves. Demonstration that the clock and its photoreceptor are in the prothoracic glands is based on a mixture of localized illuminations and the transplantation of glands from one larva to another.

3‐oxoecdysteroid 3β‐reductase in various organs of the European corn borer, Ostrinia nubilalis (Hubner)

“…This series of events is initiated by the release of a brain ecdysiotropin, PTTH* [5], and is influenced by photoperiodic signals [6,7], neural signals [8], juvenile hormone levels [9,10], a hemolymph factor produced and secreted into the blood by the fat body [ll], and by the concentration of ecdysone in the hemolymph [12,13]. Thus, a fairly complex system of external and internal cues including modulating and feedback mechanisms serves to control the production and release of ecdysteroid by the prothoracic glands and thus regulates insect development, metamorphosis, and molting.…”

“…Recently, it has been reported that 3-dehydroecdysone rather than ecdysone is the principal product of some lepidopteran prothoracic glands [l-31, and that the 3-dehydroecdysone produced is rapidly converted to ecdysone by a 3-oxoecdysteroid 3p-reductase (ketoreductase) in hemolymph [ 11. Ecdysone is then metabolized by tissues peripheral to the prothoracic glands to form the principal insect molting hormone, 20-hydroxyecdysone [4]. This series of events is initiated by the release of a brain ecdysiotropin, PTTH* [5], and is influenced by photoperiodic signals [6,7], neural signals [8], juvenile hormone levels [9,10], a hemolymph factor produced and secreted into the blood by the fat body [ll], and by the concentration of ecdysone in the hemolymph [12,13]. Thus, a fairly complex system of external and internal cues including modulating and feedback mechanisms serves to control the production and release of ecdysteroid by the prothoracic glands and thus regulates insect development, metamorphosis, and molting.…”

Mediation of ecdysone synthesis in Manduca sexta by a hemolymph enzyme

“…Although the functioning of the insect neuroendocrine axis, therefore, appears to be explained in simple and straightforward terms, a number of observations in recent years suggest that the details of the control of insect molting are much more complex than first believed. For example, the photoperiod may affect the prothoracic glands directly [4], there may be neural control of gland activity [5], a hemolymph factor stimulates the prothoracic glands in vitro [6], juvenile hormone has direct as well as indirect effects on prothoracic gland activity [7], etc. Very recently an observation was made that adds to the complexity of the overall picture, i.e., the principal ecdysteroid secreted in vitro by the prothoracic glands of Munducu sextu is 3-dehydroecdysone, which is rapidly converted to ecdysone by a factor in the hemolymph [8].…”

Developmental regulation of calmodulin-dependent adenylate cyclase activity in an insect endocrine gland.

“…This pathway could involve the effects of Ca2+/CaM on gland adenylate cyclase that are discussed above. Although the release of PTTH is generally accepted as the principal factor controlling prothoracic gland activity , there is evidence for multiple inputs regulating the precise onset of the commitment peak (Richter, 1989;Mizoguchi and Ishizaki, 1982). The small hemolymph ecdysteroid peak on day 4 of the last larval instar is perhaps one of the most critical points in the development of Manduca, because it signals the cessation of larval feeding and elicits other behavioral changes and the change in commitment required for metamorphosis to the pupa (see Riddiford, 1976 .…”