Unravelling the physiological function of a highly conserved HNRNPA1 splice variant

点击翻译按钮获取中文摘要

My research program is dedicated to studying the molecular mechanisms that govern RNA binding protein (RBP) function in neurons, in both stressed and physiological conditions. Due to their highly polarized nature, neurons rely on numerous RBPs to support neuronal function, plasticity and survival. HNRNPA1 (heterogeneous ribonucleoprotein A1) encodes for two isoforms: hnRNP A1 and hnRNP A1B. These two proteins are identical, except for the inclusion of an additional 52 residues in the C-terminal glycine-rich domain in hnRNP A1B, owing to a highly conserved alternative splicing event. While hnRNP A1 is a well-known regulator of splicing, virtually nothing is known about the longer and phylogenetically ancestral isoform, hnRNP A1B. Using a custom antibody to selectively recognize hnRNP A1B, we have uncovered that hnRNP A1B is developmentally regulated such that its initial broad expression becomes restricted to motor neurons in adulthood. In addition, we have observed that unlike hnRNP A1, hnRNP A1B displays a granular cytoplasmic pattern in spinal motor neurons, in neurites of primary neurons and in a neuronal-like human cell line. We now have completed immunoprecipitation/mass spectrometry experiments to probe hnRNP A1B specific interactions in the CNS. These data indicate that hnRNP A1B may function in mRNA transport and local translational control, processes that are highly relevant to neurons. Moreover, we have observed that hnRNP A1B expression can be modulated by environmental stress, suggesting that it may play a role in the neuronal response to adverse conditions. As there are a limited number of motor proteins, but ~1500 RBPs, it is speculated that many of them function to improve transport specificity, serving as adaptors to link mRNAs with the transport machinery. Transported mRNAs are either translationally suppressed or co-translated following specific stimuli. Upon neuronal stimulation/activation (such as occurs in response to injury), distally-localized mRNAs are translated. Thus, RBPs effectively mediate spatial and temporal protein synthesis. The full repertoire of RBPs involved in these processes is not known. Our hypothesis is that hnRNP A1B plays a critical role in cytoplasmic RNA metabolic processes including axonal transport and localized translation that is essential for neuronal homeostasis in basal and stressed conditions. The aims are: Aim 1: Does hnRNP A1B contribute to the intracellular trafficking of mRNA in neurons? Aim 2: What is the function of hnRNP A1B in localized translation in neurons? Aim 3: Is hnRNP A1B upregulation a physiological response to insult/stimuli? Perspectives: This work will generate mechanistic insights on the physiological function of this understudied isoform in neurons and expand our knowledge of RBP regulation of neuronal response to insult. This information is critical to understand the diversity of neuronal functions and regulation of synaptic plasticity events.