STEROID-HORMONE FLUCTUATIONS REGULATE GANGLIONIC FUSION DURING METAMORPHOSIS OF THE MOTH MANDUCA-SEXTA

We examined the role of the steroid hormone, 20-hydroxyecdysone (20-E) , in regulating ganglionic fusion during metamorphosis of the moth Man duca sexta, At the larval-pupal transition, the first and second abdom inal ganglia begin to migrate anteriorly to coalesce eventually with t he second and third thoracic ganglia, forming the pterothoracic gangli on, Near this time, three fluctuations of ecdysteroids are present: tw o prior to pupation and one after, Ligations posterior to the prothora cic segment isolated the posterior ganglia from the prothoracic glands , a primary source of ecdysteroids, When ligations were performed afte r the first ecdysteroid pulse (commitment pulse), neither pupal cuticl e nor ganglionic fusion was observed, When these abdomens were subsequ ently given a 20-E infusion that mimicked the second pulse (pre-pupal peak), complete pupal abdomens were formed but ganglia did not migrate together and fuse, Only those isolated abdomens given two separate 20 -E infusions (to mimic both the second pulse and third rise) produced fused ganglia, All three ecdysteroid fluctuations, as well as the drop in ecdysteroids between the second pulse and third rise (preadult ris e), were required for normal ganglionic migration and fusion, Fusion-r elated events, and the appearance of other adult characteristics, some times occurred in abdomens that were isolated following pupation, The percentage of abdomens showing adult development was positively correl ated with the time that elapsed between pupation and abdominal isolati on, Using an ecdysteroid radioimmunoassay, we confirmed the presence o f ecdysteroids in isolated abdomens, and demonstrated that isolated ab domens show a temporal pattern of ecdysteroid levels similar to that o f intact insects. Copyright (C) 1996 Elsevier Science Ltd