Ecdysteroids regulate secretory competence in Inka cells.

Area of Science:

• Insect endocrinology
• Molting physiology
• Developmental biology

Background:

• Ecdysis (molting) in insects is regulated by ecdysteroids and ecdysis-triggering hormone (ETH).
• High ecdysteroid levels initially trigger ETH accumulation, followed by low levels to permit molting behavior onset.
• Inka cells secrete ETH, a key hormone for initiating the molting sequence.

Purpose of the Study:

• To investigate the inhibitory role of high ecdysteroid levels on ETH secretion competence.
• To elucidate the molecular mechanisms by which ecdysteroids regulate the development of Inka cell competence.
• To identify the timing and nature of ecdysteroid action in the molting cascade.

Main Methods:

• In vivo injections of 20-hydroxyecdysone (20E) into Manduca sexta pharate pupae.
• In vitro culture of epitracheal glands to assess competence acquisition.
• Treatment with Actinomycin D to assess transcriptional dependence.
• Analysis of cyclic GMP accumulation in response to eclosion hormone (EH).

Main Results:

• High 20E levels inhibit the acquisition of ETH secretion competence in Inka cells.
• Competence acquisition is dependent on transcriptional events, as shown by Actinomycin D inhibition.
• 20E inhibits an early nuclear event in competence acquisition, preceding Actinomycin D sensitivity.
• Ecdysteroid withdrawal is necessary to permit a late transcriptional event for ETH secretion.

Conclusions:

• High ecdysteroid levels actively suppress the development of competence for ETH secretion.
• Declining ecdysteroid levels are crucial for enabling a late transcriptional step required for molting.
• 20E acts early in the signaling pathway, before EH receptor activation and cyclic GMP accumulation, to regulate transcription.