§ Institute of Biological Sciences, University of Tsukuba, Tsukuba 305, Japan. , # Zoological Institute, University of Basel, Rheinsprung 9, CH-4051 Basel, Switzerland. ,
Mushroom bodies are a pair of neuropil structures that are essential for various higher order functions in the Drosophila brain such as olfactory learning and sexual recognition. We characterize embryonic and post embryonic development of mushroom bodies using several lineage tracers that are specific to mushroom bodies through development. We find that heterogeneity among the mushroom body neuroblasts exist in the late embryonic stages and is established upon hatching. We also present the genetic and molecular map of the locus of an anatomical mutant, mushroom body deranged (mbd), in which the axons of mushroom bodies fail to find the right path leading to abnormally enlarged calyces with degeneration of peduncles and lobes. As a consequence of these anatomical defects, negatively reinforced olfactory learning is completely abolished (Heisenberg et al., 1985). By genetic deficiency mapping, we have delimited the mbd locus at 17B3-6 on the X chromosome and completed DNA walk covering the region 17A-C. Molecular mapping of the chromosomal break points of the deficiency lines delimits the mbd locus in a narrow window of 30 kb in the distal vicinity of the Dwnt-3 gene. A candidate mbd transcription unit, which is broadly expressed in the entire CNS at the late-larval and the prepupal stages, has been isolated as a cDNA clone. Based on these data, we will discuss the molecular structure of the mbd gene (supported by the Univ. Tsukuba and the Swiss NSF).