How does ecdysone trigger molting in arthropods?

In arthropods, molting is a complex process hormonally regulated to allow for growth despite the constraints of a rigid exoskeleton. The steroid hormone ecdysone serves as the direct initiator of this process.1

The mechanism generally functions as follows:

• Stimulation: Environmental or internal cues trigger the release of a brain neurohormone, such as prothoracicotropic hormone (PTTH) in insects, which stimulates specific endocrine glands (the prothoracic glands in insects or the Y-organ in crustaceans) to secrete ecdysone into the blood.2345
• Activation: Once in the blood, ecdysone is converted in peripheral tissues into its active form, 20-hydroxyecdysone (20E).24
• Action: This active hormone acts directly on cells to control RNA synthesis and protein synthesis, prompting the epidermis to digest the base of the old exoskeleton and secrete a new one beneath it.216

While ecdysone initiates the molting sequence, the final shedding of the old skeleton—known as ecdysis—is further regulated by additional neuropeptides and hormones, such as ecdysis-triggering hormone.27