Debra, a Protein Mediating Lysosomal Degradation, Is Required for Long-Term Memory in Drosophila

A central goal of neuroscience is to understand how neural circuits encode memory and guide behavior changes. Many of the molecular mechanisms underlying memory are conserved from flies to mammals, and Drosophila has been used extensively to study memory processes. To identify new genes involved in long-term memory, we screened Drosophila enhancer-trap P(Gal4) lines showing Gal4 expression in the mushroom bodies, a specialized brain structure involved in olfactory memory. This screening led to the isolation of a memory mutant that carries a P-element insertion in the debra locus. debra encodes a protein involved in the Hedgehog signaling pathway as a mediator of protein degradation by the lysosome. To study debra's role in memory, we achieved debra overexpression, as well as debra silencing mediated by RNA interference. Experiments conducted with a conditional driver that allowed us to specifically restrict transgene expression in the adult mushroom bodies led to a long-term memory defect. Several conclusions can be drawn from these results: i) debra levels must be precisely regulated to support normal long-term memory, ii) the role of debra in this process is physiological rather than developmental, and iii) debra is specifically required for long-term memory, as it is dispensable for earlier memory phases. Drosophila long-term memory is the only long-lasting memory phase whose formation requires de novo protein synthesis, a process underlying synaptic plasticity. It has been shown in several organisms that regulation of proteins at synapses occurs not only at translation level of but also via protein degradation, acting in remodeling synapses. Our work gives further support to a role of protein degradation in long-term memory, and suggests that the lysosome plays a role in this process.