A transgenic analysis of G-protein signaling during associative learning in Drosophila

Previously, disruptions of the cyclic adenosine monophosphate (cAMP) signalling pathway have been found to affect olfactory learning in Drosophila. On a neuroanatomical level, the mushroom bodies and central complex have also been implicated in this process. In this study, four P-GAL4 enhancer trap lines were identified, which when used to drive expression of a constitutively activated stimulatory heterotrimeric GTP-binding protein alpha subunit (Gs), were disrupted in their ability to perform an associative olfactory learning task. In three of these lines, expression of activated Gs eliminated learning. In the fourth line, expression of activated Gs reduced learning by about half compared with controls. By contrast, expression of wild type Gs in these P-GAL4 lines had no effect on associative learning. While no P-GAL4 insertion was exclusively expressed in the mushroom bodies, all four showed prominent preferential expression in these structures. In addition, the P-GAL4 insertion producing a partial learning defect was expressed in a restricted subset of mushroom body neurons.;Gross mushroom body morphology was not obviously disrupted in these lines, although more subtle defects in mushroom body morphology or development could not be excluded by this analysis. Expression of activated Gs in components of the central complex had no effect on associative learning, suggesting that such disruption to Gs signalling were insufficient to interfere with olfactory learning. Taken together, these data represent functional evidence that regulated Gs signalling within mushroom body neurons of the Drosophila brain is required for associative olfactory learning.