Figures & data
Figure 1 Insect moulting is induced by the circulating steroid hormone 20-hydroxyecdysone (20E) whose biosynthesis takes origin from dietary cholesterol. The process is initiated by secretion of the brain neuropeptide prothoracicotropic hormone (PTTH). PTTH acts on the prothoracic glands, triggering the synthesis and secretion of a pre-ecdysteroid which is sequentially converted to active 20E. Cholesterol is converted to 20E thanks to a number of hydroxylation reactions catalysed by cytochrome P450 enzymes of microsomal and/or mitochondrial origin. Then, 20E binds heterodimeric nuclear receptors composed of EcR (Ecdysone Receptor) and Usp (Ultraspiracle), and activates the transcriptional processes underlying the cellular and morphogenetic moulting cascade events. Even if PTTH is the the major tropic hormone driving ecdysone secretion, also insulin-like peptides (ILPs) may induce ecdysteroidogenesis, through stimulation of the prothoracic gland growth. BR (brain); ILPs (insulin-like peptides); PTTH (prothoracicotropic hormone); PG (prothoracic gland); EcR/USP (Ecdysone Receptor/Ultraspiracle).
