EAGLE, A MEMBER OF THE STEROID-RECEPTOR GENE SUPERFAMILY, IS EXPRESSED IN A SUBSET OF NEUROBLASTS AND REGULATES THE FATE OF THEIR PUTATIVE PROGENY IN THE DROSOPHILA CNS

We isolated and characterized the eagle gene, encoding a member of the steroid receptor superfamily in Drosophila. In the central nervous sy stem, eagle RNA was expressed in a limited number of cells, During sta ges 10 and 11, eagle RNA expression was observed in four neuroblasts, NB2-4, NB3-3, NB6-4 and NB7-3, Except for NB6-4, eagle RNA expression reached a maximum at the very beginning of expression or in the period of neuroblast delamination, Weak eagle RNA expression was also observ ed in a few putative progeny of NB7-3 during stages, late 11 and 12, A ll eagle RNA in abdominal segments disappeared at stage 13. Using an e agle-kinesin-lacZ fusion gene as a reporter, the division, migration, and axonogenesis in eagle-positive cells and their derivatives were ex amined, At stage 14, several types of neural or glial cells were detec ted which include EG and EW interneurons joining to the anterior and p osterior commissures, respectively, Lack of eagle expression caused al tered axonogenesis in an appreciable fraction of eagle-Kinesin-LacZ-po sitive neurons. Some EG cells failed to acquire the neural fate or und erwent an extremely delayed differentiation, while EW neurons produced neurites in abnormal directions, suggesting that eagle may play a cri tical role in development of the progeny of eagle-positive neuroblasts .