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Prothoracicotropic hormone in Manduca sexta: localization by a larval assay
The Journal of Experimental Biology
|February 1, 1977
Summary
A new assay for insect prothoracicotropic hormone (PTTH) was developed using Manduca sexta larvae. This method quantizes PTTH by measuring the molting response after injecting brain extracts, identifying its source and properties.
Area of Science:
- Insect Endocrinology
- Developmental Biology
- Neurobiology
Background:
- Insect metamorphosis is regulated by prothoracicotropic hormone (PTTH).
- Accurate quantification of PTTH is essential for understanding insect development.
- Previous PTTH assays were limited in sensitivity and specificity.
Purpose of the Study:
- To develop a novel and sensitive bioassay for insect PTTH.
- To identify the specific source of PTTH within the insect brain.
- To characterize the biochemical properties of PTTH.
Main Methods:
- A neck-ligated larva bioassay was established using fourth instar Manduca sexta larvae.
- Larvae were injected with varying concentrations of brain homogenates.
- PTTH activity was assessed by the induction of molting.
Main Results:
- The bioassay demonstrated a dose-dependent molting response to brain homogenates.
- PTTH activity was localized to the dorsal protocerebrum, specifically lateral neurosecretory cells.
- Partially purified PTTH was found to be water-soluble, heat-stable (boiling for 10 min), and sensitive to proteases (Pronase, trypsin).
Conclusions:
- The developed bioassay provides a reliable method for PTTH quantification.
- The lateral neurosecretory cells in the pupal brain are a primary source of PTTH.
- PTTH is a heat-stable peptide hormone with specific proteolytic cleavage sites.