Developmental expression of the prothoracicotropic hormone in the CNS of the Tobacco Hornworm Manduca sexta

Abstract

The prothoracicotropic hormone is an insect neuropeptide released into the hemolymph to signal molting and metamorphosis through its stimulation of steroidogenesis. The only known source of the prothoracicotropic hormone in the tobacco hornworm, Manduca sexta, has been a group of lateral cerebral neurosecretory cells, the L-NSC III. In this study, the developmental and spatial distribution of the prothoracicotropic hormone was examined throughout the life cycle of Manduca. In common with many vertebrates and invertebrates in which neuropeptides are located in several regions within the central nervous system (CNS), the prothoracicotropic hormone phenotype in Manduca is expressed by CNS neurons in addition to the L-NSC III. These neurons are located in the brain, frontal ganglion, and subesophageal ganglion. One cerebral neurosecretory cell group, the ventromedial neurons, expresses the prothoracicotropic hormone phenotype and the behavioral neurohormone, eclosion hormone. Whereas the L-NSC III and the ventromedial neurons express the peptide phenotype throughout the life cycle, the other neurons express the peptide only during the embryonic and larval stages. This precise spatial and temporal expression of the prothoracicotropic hormone by different groups of neurosecretory cells raises the possibility that in Manduca the peptide may, in addition to its known neuroendocrine function, play other physiological roles in different ways at different stages of the life cycle.

Testis ecdysiotropin, an insect gonadotropin that induces synthesis of ecdysteroid

“…This distinguished LTE immunoreactivity from that of PTTH, where the lateral NSC of Lepidoptera strongly stain (Mizoguchi et al, 1990, Westbrook et al, 1993. Immunoreactive neurons could be seen leading to immunoreactive cells in the suboesophagial ganglion; stained neurosecretory cell bodies were detected in almost every other ganglion of the ventral nerve cord Fig.1.2-1.4.…”

Expression of theManduca sexta allatotropin gene in cells of the central and enteric nervous systems

“…These FG cells, which also contain FMRFamide-like immunoreactivity (Bhatt et al, 1997) project onto specific muscle fibers near the foregut-midgut boundary (Copenhaver and Taghert, 1991). Immunoreactivity against other neuropeptides have been observed in FG cells in Manduca, including prothoracicotropic hormone (Westbrook et al, 1993), adipokinetic hormone (Copenhaver and Taghert, 1991) and diuretic hormone (DH) (Ž itň an et al, 1993), but it is not known whether these antigens are localized in cells that express the Mas-AT gene.…”

Nervous control of juvenile hormone biosynthesis in Locusta migratoria.

“…In moths, the prothoracicotropes survive the imaginal molt and continue to express the PTTH phenotype (26), possibly stimulating ecdysone production by the ovaries (38). However, it has also been proposed, on the basis of the dense terminal projections ramifying among CA gland cells, that the prothoracicotropes might exert a paracrine influence on CA activity.…”

“…However, it has also been proposed, on the basis of the dense terminal projections ramifying among CA gland cells, that the prothoracicotropes might exert a paracrine influence on CA activity. PTTH itself may play this role (23,26) or other small peptides produced during the processing of the big PTTH precursor molecule (prepro-PTTH) might be involved (23,39). In Manduca sexta an additional 28-kDa peptide unrelated to big PTTH is also produced by the prothoracicotropes and packaged into neurosecretory vesicles, although its function is as yet unclear (40).…”

“…Thus, they may be a source of prothoracicotropic hormone (PTTH), with the CA acting as the release site for this hormone rather than its target. However, PTTH itself or other peptides produced by the prothoracicotropes might also modulate JH production (23,25,26).…”