Ecdysteroids

Definition

A class of polyhydroxylated steroid hormones that regulate molting (ecdysis), metamorphosis, and reproduction in arthropods. These compounds are synthesized from dietary cholesterol via the Halloween gene family of cytochrome P450 enzymes and function through nuclear receptor signaling to coordinate developmental transitions. The prototypical ecdysteroid is 20-hydroxyecdysone (ecdysterone), which acts as the active molting hormone in most insects.

Etymology

From Greek ekdysis (to strip off, shed) + steroid, referring to their role in triggering ecdysis.

Example

In the tobacco hornworm (Manduca sexta), rising titers of 20-hydroxyecdysone trigger the behavioral and physiological changes that initiate pupal ecdysis, including the loosening of old cuticle and the inflation of new wing pads.

Synonyms

• molting hormones
• ecdysones

Related Terms

• Ecdysone
• 20-hydroxyecdysone
• Juvenile hormone
• Ecdysis
• prothoracic gland
• Halloween genes
• nuclear receptor
• steroidogenesis
• Metamorphosis

Usage Notes

The term encompasses both the inactive precursor ecdysone and its active hydroxylated derivatives; specialists often distinguish these by context. Ecdysteroids also occur in plants (phytoecdysteroids) as defensive compounds, but the term in arthropod physiology refers specifically to endogenous hormonal regulators. Concentrations are typically measured in hemolymph or whole-body extracts using radioimmunoassay or LC-MS/MS.