ecdysone

Ecdysone is a steroid hormone in arthropods that acts as a prohormone to the more active 20-hydroxyecdysone (20E). It is produced primarily in the prothoracic glands of insects and other arthropods. In target tissues, ecdysone is converted to 20E by a 20-hydroxylase enzyme; 20E then carries the hormonal signal to drive molting and metamorphosis.

Mechanism and action: 20E binds to the ecdysone receptor (EcR), which forms a heterodimer with Ultraspiracle (USP). The EcR/USP complex binds to ecdysone response elements in DNA, activating early genes such as E74, E75, and Broad Complex (BR-C). This triggers a cascade of gene expression that directs tissue remodeling, shedding of the old cuticle, and progression through developmental stages. The outcome of a molt is modulated by juvenile hormone (JH); high JH levels promote replacement of larval structures and maintenance of the larval state, whereas low JH allows metamorphosis.

Distribution and applications: Ecdysone-like compounds are found in many arthropods. Plants also produce ecdysteroids (phytoecdysteroids) that can affect insect herbivores and are studied for other biological effects. In addition to natural ecdysone, synthetic ecdysone agonists such as tebufenozide are used as selective insecticides; they mimic the action of 20E to disrupt development in pest species.

History and notes: The term ecdysone refers to the prohormone class; ecdysone and 20E were among the first ecdysteroids characterized in the mid-20th century from insects. In mammals, ecdysteroids have been investigated for potential biological effects, but they do not function as endogenous hormones.