Abstract
Prothoracicotropic hormone (PTTH) is the central cerebral neurohormone in insect development. Its release has been believed for decades to be confined to one (or two) critical moments early in each developmental stage at which time it triggers prolonged activation of the prothoracic glands to synthesize and release the steroid molting hormones (ecdysteroids), which elicit developmental responses in target tissues. We used an in vitro assay for PTTH released from excised brains of the bug Rhodnius prolixus and report that release of PTTH does occur at the expected time on day 6, but that this release is merely the first in a daily rhythm of release that continues throughout most of the 21 days of larval-adult development. This finding, together with reports of circadian control of ecdysteroid synthesis and titer throughout this time, raises significant challenges to several features of the current understanding of the hormonal control of insect development. New questions are raised concerning the function(s) of PTTH, its relationship with the prothoracic glands, and the significance of circadian rhythmicity throughout this endocrine axis. The significance of the reported observations derives from the set of entirely new questions they raise concerning the regulation of insect development.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Bollenbacher W. E., Agui N., Granger N. A., Gilbert L. I. In vitro activation of insect prothoracic glands by the prothoracicotropic hormone. Proc Natl Acad Sci U S A. 1979 Oct;76(10):5148–5152. doi: 10.1073/pnas.76.10.5148. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Cherbas P. The IVth Karlson Lecture: ecdysone-responsive genes. Insect Biochem Mol Biol. 1993 Jan;23(1):3–11. doi: 10.1016/0965-1748(93)90076-5. [DOI] [PubMed] [Google Scholar]
- Huet F., Ruiz C., Richards G. Sequential gene activation by ecdysone in Drosophila melanogaster: the hierarchical equivalence of early and early late genes. Development. 1995 Apr;121(4):1195–1204. doi: 10.1242/dev.121.4.1195. [DOI] [PubMed] [Google Scholar]
- Ishizaki H., Suzuki A. The brain secretory peptides that control moulting and metamorphosis of the silkmoth, Bombyx mori. Int J Dev Biol. 1994 Jun;38(2):301–310. [PubMed] [Google Scholar]
- Lane N. J., Leslie R. A., Swales L. S. Insect peripheral nerves: accessibility of neurohaemal regions to lanthanum. J Cell Sci. 1975 Jun;18(1):179–197. doi: 10.1242/jcs.18.1.179. [DOI] [PubMed] [Google Scholar]
- Orchard I., Steel C. G. Electrical activity of neurosecretory axons from the brain of Rhodnius prolixus: relation of changes in the pattern of activity to endocrine events during the moulting cycle. Brain Res. 1980 Jun 2;191(1):53–65. doi: 10.1016/0006-8993(80)90314-5. [DOI] [PubMed] [Google Scholar]
- Turek F. W. Circadian rhythms. Recent Prog Horm Res. 1994;49:43–90. doi: 10.1016/b978-0-12-571149-4.50007-6. [DOI] [PubMed] [Google Scholar]
- Vafopoulou X., Steel C. G. Circadian regulation of synthesis of ecdysteroids by prothoracic glands of the insect Rhodnius prolixus: evidence of a dual oscillator system. Gen Comp Endocrinol. 1991 Jul;83(1):27–34. doi: 10.1016/0016-6480(91)90102-c. [DOI] [PubMed] [Google Scholar]
- Vafopoulou X., Steel C. G. Developmental and diurnal changes in ecdysteroid biosynthesis by prothoracic glands of Rhodnius prolixus (Hemiptera) in vitro during the last larval instar. Gen Comp Endocrinol. 1989 Jun;74(3):484–493. doi: 10.1016/s0016-6480(89)80046-2. [DOI] [PubMed] [Google Scholar]
- Vafopoulou X., Steel C. G. In vitro photosensitivity of ecdysteroid synthesis by prothoracic glands of Rhodnius prolixus (hemiptera). Gen Comp Endocrinol. 1992 Apr;86(1):1–9. doi: 10.1016/0016-6480(92)90119-5. [DOI] [PubMed] [Google Scholar]