MRNA Transport in the Projections of Maturing Hippocampal Neurons

Abstract

Translation of mRNA in axons and dendrites enables a rapid supply of proteins to specific sites of localization within the neuron. Distinct populations of mRNA-containing cargoes, including granules and mitochondrial mRNA, are transported with neuronal projections. The distributions of these cargoes appear to change during neuronal development, but details on the dynamics of mRNA transport during these transitions remain to be elucidated. The goal of this project is to characterize transport of mitochondrial and non-mitochondrial mRNA in neuronal projections during the development of hippocampal neurons. One day old rat hippocampal neurons were cultured for 1, 5, and 7 days, and mRNA transport was examined at each time point. The transport was observed via real-time imaging of SYTO14, a fluorescently labeled marker for mRNA. To differentiate between mitochondrial and granular mRNA, cells were also labeled with MitoTracker. Quantitative analysis was performed by kymograph which gives a graphical representation of spatial position over time. The results suggest differences in the transport pattern of mitochondrial and non-mitochondrial mRNA, and also indicate significant differences in transport parameters at different time points. Unexpectedly, increased bidirectional velocity of mRNA transport was observed from day 1 to day 7, which suggests altered demand for locally synthesized proteins even after maturity. To better understand the logic underlying altered mRNA transport, we are currently investigating whether changes in transport correlate with specific stages of neurite differentiation into axons or dendrites or synaptic contact with other neurons. This work has important implications for the regulation of neuronal plasticity during neuronal growth, maturity, and neurodegeneration.