Steroid hormone secretion in insects comes of age

摘要

The control of molting and metamorphosis in insects first captured the attention of physiologists in the 1920s, when the Polish physiologist Stephan Kopec showed that the brain stimulated molting in larvae of the gypsy moth (1). However, 70 years elapsed before the hormone from the brain, prothoracico-tropic hormone (PTTH), was finally sequenced by groups led by H. Ishizaki and A. Suzuki (2). During the interim, it was shown that the brain's role in causing molting was not direct but was mediated through its action on paired endocrine glands in the thorax, the prothoracic glands (PGs), that then secreted a steroid molting hormone, ecdy-sone. Circulating PTTH acts on these glands to stimulate steroidogenesis via calcium entry and cAMP generation (3) in a manner similar to that seen in some vertebrate steroidogenic systems. Although the control of ecdysone secretion by a circulating tropic hormone has been a central concept in comparative endocrinology for > 40 years, a series of recent articles have revealed that negative factors are also at play (4-6). The article by Yamanaka et al. (7) in a recent issue of PNAS described some novel peptides that exert inhibitory control on the PGs and showed that the pathway by which they exert their effects is through the direct innervation of the glands.