Central brain postembryonic development in Drosophila: Implication of genes expressed at the interhemispheric junction

Postembryonic brain development of Drosophila has become recently a subject of intense investigations. In particular, the linotte (lio) mutants displa y strong structural defects in the mushroom bodies and the central complex. The Lio kinase is expressed in a glial structure at the interhemispheric j unction of late larval and young pupal brain. With the aim of identifying n ew genes involved in the formation of adult central brain structures, 821 e nhancer-trap Gal4 lines mere generated and screened for late larval express ion. We identified 167 lines showing expression at or near the interhemisph eric junction of third-instar larval brain, an area from which the central complex differentiates. Adult brains from 104 of these 167 lines were analy zed through paraffin sections. This secondary screen allowed the recovery o f five central brain mutants. Of 89 control lines showing various patterns of expression excluding the interhemispheric junction, only one anatomical mutant was isolated, These six mutations, which have been thoroughly charac terized, affect the midline area of the adult brain with phenotypes of spli t central complex structures and/or fused mushroom body lobes. This work op ens the mag for further analysis of the molecular and cellular events invol ved in central brain reorganization during metamorphosis. (C) 2000 John Wil ey & Sons. Inc.