THE DROSOPHILA BRAIN REVISITED BY ENHANCER DETECTION

The patterns of gene expression in the Drosophila brain were studied b y using the lacZ reporter gene carried on an enhancer detector element . From the analysis of serial sections fo the heads of 6000 enhancer d etector lines, reporter gene expression in some lines was found to gen erally follow boundaries established by cell type or anatomy, revealin g distinct patterns of lacZ expression restricted to the lamina, the m edulla, mushroom bodies, antennal lobes, or other anatomical subdivisi ons. About 15% of the lines showed ubiquitous expression in most or al l head tissues and 25% of the lines showed expression throughout the C NA. Another quarter of the lines showed widespread expression in the C NA, with large regions of the brain showing expression. This suggests that the majority of detected genes are expressed with little spatial specificity. The expression patterns produced by 12 different insertio ns at the rutabaga locus were found to be extremely similar in the bra in and offer strong evidence that the enhancer detector elements gener ally report the activity oa an adjacent gene. Only 15% of the lines we re judged to have relatively specific expression in one brain region, including those with preferential or specific expression in the mushro om bodies, antennal lobes, lamina, medulla, etc. The cytological inser tion sites for elements showing preferential mushroom body expression were found to be dispersed in the genome at approximately 50 different chromosomal regions. In addition to providing a broad picture of the transcriptional activity in the Drosophila brain, these enhancer detec tor lines offer access to interesting new genes and form a novel colle ction of lines in which identifiable brain cells are marked in a repro ducible way. (C) 1996 John Wiley & Sons, Inc.