Precise control of fasciclin II expression is required for adult mushroom body development in Drosophila

Abstract

Fasciclin II (FASII) is a cell adhesion molecule that participates in axonal pathfinding, fasciculation and divergence in the Drosophila nervous system. Here, we examined spatio-temporal control of fasII expression during the development of adult mushroom body (MB) and found that suppression of fasII in α′/β′ neurons is essential for the formation of adult α′/β′ and α/β lobes. Of γ, α′/β′ and α/β neurons, which are derived sequentially from the same four MB neuroblasts, only γ and α/β neurons expressed fasII. When fasII was misexpressed in developing MB neurons, defects resulted, including loss or misdirection of adult α′/ β′ lobes and concurrent misdirection of α/β lobes. Although no gross anatomical defects were apparent in the larval MB lobes, α′/β′ lobes collapsed at the pupal stage when the larval lobe of γ neurons degenerated. In addition, α/β lobes, which developed at this time, were misdirected in close relationship with the collapse of α′/β′ lobes. These defects did not occur when fasII was overexpressed in only γ and α/β neurons, indicating that ectopic expression of fasII in α′/β′ neurons is required for the defects. Our findings also suggest that the α′/β′ lobe play a role in guiding the pathfinding by α/β axons. © 2007 The Authors.