Steroid receptors and nervous system metamorphosis in insects.

During CNS metamorphosis, the ecdysteroids evoke diverse neuronal responses including remodeling, maturation, and programmed death. These responses are matched by the equally diverse expression of the two main ecdysone receptor isoforms, EcR-A and EcR-B1. Based on these patterns, it appears that each isoform is associated with a particular program of steroid response: EcR-A with maturation and synaptogenesis and EcR-B1 with synapse loss and process regression. It is proposed that by blending amounts of the two EcRs, neurons adjust the nature of their steroid response to accomodate the developmental needs of the CNS.