GENES EXPRESSED IN THE RING GLAND, THE MAJOR ENDOCRINE ORGAN OF DROSOPHILA-MELANOGASTER

We have used an enhancer-trap approach to begin characterizing the fun ction of the Drosophila endocrine system during larval development. Fi ve hundred and ten different lethal PZ element insertions were screene d to identify those in which a reporter gene within the P element show ed strong expression in part or all of the ring gland, the major site of production and release of developmental hormones, and which had a m utant phenotype consistent with an endocrine defect. Nine strong candi date genes were identified in this screen, and eight of these are expr essed in the lateral cells of the ring gland that produce ecdysteroid molting hormone (EC). We have confirmed that the genes detected by the se enhancer traps are expressed in patterns similar to those detected by the reporter gene. Two Of the genes encode proteins, protein kinase A and calmodulin, that have previously been implicated in the signali ng pathway leading to EC synthesis and release in other insects. A thi rd gene product, the translational elongation factor EF-1 alpha F-1 co uld play a role in the translational regulation of EC production. The screen also identified the genes couch potato and tramtrack, previousl y known from their roles in peripheral nervous system development, as being expressed in the ring gland. One enhancer trap revealed expressi on of the gene encoding the C subunit of vacuolar ATPase (V-ATPase) in the medial cells of the ring gland, which produce the juvenile hormon e that controls progression through developmental stages. This could r eveal a function of V-ATPase in the response of this part of the ring gland to adenotropic neuropeptides. However, the gene identified by th is enhancer trap is ubiquitously expressed, suggesting that the enhanc er trap is detecting only a subset of its control elements. The result s show that the enhancer trap approach can be a productive way of expl oring tissue-specific genetic functions in Drosophila.