Date of Award
Scott A. Barbee
FMRP, miRNA, Neuron, P-Body
Changes in synaptic structure in response to neuronal stimulation are believed to underlie the processes of learning and long-term memory. However, the mechanisms for these structural modifications are poorly understood. It is well-known that activity-dependent synaptic modifications rely upon new protein synthesis, and rapid new protein synthesis, at that. Therefore, it is widely believed that pools of messenger RNAs held in a state of translational repression are transcribed in a neuronal cell body prior to stimulation, and transported to the synapse, where they reside until stimulation occurs.
This study investigates the roles and interactions of translational repression mechanisms to better understand how new synaptic growth is repressed or enhanced for the purposes of long-term memory and learning. We found that miRNAs -315, -275, -11 and the miR-9 family are of particular interest for neuronal growth in Drosophila larvae because they are extremely enriched in the larval CNS compared to the adult brain, and are predicted to regulate mRNA targets that significantly contribute to neuronal development. Furthermore, miR-315 and the miR-9 family bind and regulate a Futsch (Drosophila homolog of mammalian MAP1B known to affect synaptic growth) reporter in vitro, and the miR-9 family exhibits an increase in bouton numbers at muscles 6/7 of the NMJ characteristic of an increase in Futsch levels when under-expressed. Curiously, this same effect with seen with miR-9 family overexpression.
While miRNAs are translational repressors and can clearly affect synaptic structure on their own, components of the miRNA pathway further interact with other translational repressors, including the Fragile-X Mental Retardation Protein (FMRP). Although FMRP has been shown to interact with the miRNA pathway, and to regulate Futsch, we could not discern down-regulation of a Futsch reporter from FMRP overexpression in S2 cells, nor an interaction between FMRP and these miRNAs that regulated a Futsch reporter in vitro. However, FMRP did interact with several P-body components, including co-localization with HPat, Twin, and Me31B, as well as co-immunoprecipitation with HPat, Me31B and Dcp1. Genetic interactions between FMRP and HPat and FMRP and Twin produced discernible phenotypes at the Drosophila NMJ, suggesting this interaction is important for synaptic growth.
Symmes, Breanna, "Post-Transcriptional Shaping of Neurons: The Role of miRNAs and FMRP-Interacting P-Body Components in Regulating Neuronal Structure" (2014). Electronic Theses and Dissertations. 636.
Recieved from ProQuest