GAL4 causes neuronal death in Drosophila

CAROLINA REZÁVAL Y M. FERNANDA CERIANI

Mar del Plata, Argentina

Congreso; I Congreso Conjunto de Sociedades Biomédicas; 2004

Rest-activity cycles display daily fluctuations that accompany cycles of light and dark in a characteristic pattern. In Drosophila, the lateral neurons (LNs) play a central role in the control of locomotor rhythms.  To expand our understanding about this behavior we employed the GAL4/UAS system, a widely used tool for targeting gene expression to different cell types in Drosophila.  During the course of our work we observed that transgenic lines overexpressing the transcriptional factor GAL4 specifically in the LNs (pdf-gal4) displayed abnormal locomotor rhythms.  The extensive application of this driver line prompted us to investigate the cause underlying such phenotype.  We found that increased GAL4 accumulation positively correlated with a decrease in behavioral rhythmicity, which in turn was associated with a reduction in the number of LNs.  Overexpression of HSP70 and baculovirus p35 rescued the arrhythmic phenotype, strongly suggesting the LNs were undergoing cell death.  Confocal analysis of PDF neurons showed colocalization of PDF and tunel staining (a marker of nuclear fragmentation), clearly indicating the accumulated GAL4 protein triggers cell death via apoptosis.  Programmed cell death as a result of GAL4 accumulation is not a result of a special sensitivity of this neuronal circuit, since similar results were obtained in parallel following GAL4 continuous expression in the developing eye.  The GAL4/UAS system has been used to introduce human disease genes into Drosophila, express them in specific neural structures and determine whether this expression confers a phenotype that resembles the human disorder. In several examples to date, as the Drosophila model of Parkinson (Nature 2000 404: 394), Alzheimer (Science 2001 293:711) and Huntington (Neuron 1998 633:642), the similarity to the modeled human pathology has been remarkable. Our data suggests that high level of GAL4 has per se deleterious effects on cell viability, which should be taken into account when employing this strategy to model neurodegenerative diseases.