THE BRAIN SECRETORY PEPTIDES THAT CONTROL MOLTING AND METAMORPHOSIS OF THE SILKMOTH, BOMBYX-MORI

Progress made toward the elucidation of molecular features of the prot horacicotropic hormone (PTTH) of the silkmoth Bombyx mori is reviewed. PTTH stimulates the prothoracic glands to synthesize and release ecdy sone, and is therefore a key hormone for the regulation of insect moul ting and metamorphosis. Bombyx PTTH is a 30 kDa homodimeric glycoprote in, whose carbohydrate moiety is not essential for the biological func tion. The Bombyx genome contains a single copy of the PTTH gene. PTTH is produced by four dorsolateral neurosecretory cells of brain. Anothe r Bombyxbrain peptide exerting prothoracicotropic activity to a hetero logous moth Samia cynthia ricini but no activity to Bombyx has been id entified and termed bombyxin. Bombyxin is a 5 kDa heterodimeric peptid e that shows a high similarity to insulin in the amino acid sequence. The bombyxin gene structure also shows a high similarity with the insu lin gene structure. The Bombyx genome contains more than 30 copies of the bombyxin gene. Bombyxin is synthesized by eight dorsomedial neuros ecretory cells of brain.