Memory enhancement and formation by atypical PKM activity in Drosophila melanogaster

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Abstract
Synaptic stimulation activates signal transduction pathways, producing persistently active protein kinases. PKMζ is a truncated, persistently active isoform of atypical protein kinase C-ζ (aPKCζ), which lacks the N-terminal pseudosubstrate regulatory domain. Using a Pavlovian olfactory learning task in Drosophila, we found that induction of the mouse aPKMζ (MaPKMζ) transgene enhanced memory. The enhancement required persistent kinase activity and was temporally specific, with optimal induction at 30 minutes after training. Induction also enhanced memory after massed training and corrected the memory defect of radish mutants, but did not improve memory produced by spaced training. The 'M' isoform of the Drosophila homolog of MaPKCζ (DaPKM) was present and active in fly heads. Chelerythrine, an inhibitor of PKMζ, and the induction of a dominant-negative MaPKMζ transgene inhibited memory without affecting learning. Finally, induction of DaPKM after training also enhanced memory. These results show that atypical PKM is sufficient to enhance memory in Drosophila and suggest that it is necessary for normal memory maintenance.