Role of ETH receptors in ecdysis

The growth and development of insects depends on periodic shedding of the exoskeleton through a process called ecdysis. At each transition, the respiratory system is cleared of fluid and inflated, followed by performance of stereotypic behaviors – pre-ecdysis, ecdysis, and post-ecdysis - to shed the old cuticle and proceed to the next stage. This is initiated by circulating ecdysis triggering hormones (ETHs), which act directly on target neurons in the CNS to activate downstream neuropeptide signaling cascades.

New findings revealed the likely identity of ETH receptors (ETHR) in the CNS, and members of a complex CNS signaling cascade that express ETHR. The ecdysis behavioral sequence is induced through direct ETH action on the CNS. ETH receptors (ETHR) in Drosophila are comprised of two subtypes of G-protein coupled receptors ETHR-A and ETHR-B, encoded by the gene CG5911. These two groups of receptors are expressed in mutually exclusive population of neurons through alternate splicing of the 4th exon. Separate populations of ETHR-A and ETHR-B neurons suggest that they play different roles in ecdysis regulation.

Most ETHR-A neurons have been identified as peptidergic leaving behind unsolved questions about ETHR-B. It is hypothesized that ETHR-B controls pre-ecdysis and facilitates switch from pre-ecdysis to ecdysis. This hypothesis will be tested by overexpressing and knocking down the receptor in Drosophila by using molecular and genetic tools. Preliminary results show that overexpression of both subtypes (A and B) of ETHR in ETHR-A neurons, using selective peptide promoters, changes the ecdysis behavioral sequence.