Molecular and Genetic Analysis of Synaptic Signaling in Drosophila

by Jackson, Taryn.

Molecular and genetic analysis of synaptic signaling in Drosophila has yielded many insights into nervous system development, properties of synaptic transmission, and how long-lasting changes in neurons occur. Synaptic signaling components required for synaptic transmission and pathways leading to nervous system plasticity are typically conserved from insects to humans. The role of proteins and genes in synaptic function in flies can be analyzed from the level of a single synapse to complex behaviors in the whole organism. Because of a fully sequenced genome and the ease of mutagenesis in flies, genetic screens have been useful in identifying novel regulators of synaptic transmission and long-term memory. In flies, conditional mutations affecting synaptic transmission at nerve terminals often lead to temperature sensitive paralysis. In a screen for mutations that interact with Drosophila shibirets mutants, the stoned gene was identified as a regulator of synaptic vesicle cycling. Stoned encodes two neuronally expressed proteins, stonedA and B, which are required for synaptic vesicle recycling and normal synaptic transmission. However, the exact functions of the two stoned proteins are not fully understood. We investigate distinct roles of the stoned proteins here and show that stoned has a novel role in synaptic growth. Memory in flies can be divided into genetically distinct phases based on the requirement for protein synthesis and activation of the transcription factor CREB. Novel regulators of long-term olfactory avoidance memory were isolated in a mutant screen in 12 flies. Mutants in the Drosophila gene lk6, homologous to the translational regulator MNK, have defects in long-term olfactory avoidance memory. We find that lk6 is highly expressed in the fly nervous system, and is activated by and functions downstream of Ras/ERK signaling in fly neurons. Insights provided here from Drosophila add to the evidence that MNK may be the link between ERK signaling and the regulation of translation in long-term plasticity. Ultimately, understanding synaptic function has therapeutic potential to aid in alleviation of nervous system dysfunction. Insight into the molecular pathways underlying plasticity and long-term memory gained from studies in flies, mollusks, and rodents has been pivotal in the development of potential drugs to aid in memory deficits in humans. 13