Prothoracicotropic Hormone

Publisher Summary This chapter focuses on prothoracicotropic hormone (PTTH), a brain neuropeptide hormone that stimulates the secretion of the molting hormone, ecdysone, from the prothoracic glands. Hardened portions of the cuticle restrict the physical growth of insects; insects solve this problem by periodic molts in which the old cuticle is partly resorbed and partly shed and a new cuticle is laid down, allowing for further growth. In addition, many insects undergo metamorphic molts in which significant changes in structure occur. A suite of hormones controls and coordinates these episodes of rapid developmental change. Physiological, biochemical, and genetic studies on PTTH have shaped our current understanding of how insect molting and metamorphosis are controlled. This chapter reviews the discovery of PTTH followed by sections describing PTTH structure, regulation of PTTH release, and the cellular mechanisms by which PTTH stimulates ecdysteroid secretion. It ends with a brief discussion of developmental changes in the prothoracic glands and of roles played by factors aside from PTTH which have modified our current picture of the regulation of ecdysteroid secretion in insects.