Molecular basis of local mRNA translation in neuronal development

During neuronal development, thousands of mRNAs are translated in specific cellular locations to shape the neuron's structure and large network of connections. Mis-regulation of the pathways controlling the local translation of the mRNAs has been linked to severe neurodevelopmental and neurodegenerative diseases, including Fragile X Syndrome, Frontotemporal Degeneration and Amyotrophic Lateral Sclerosis (ALS). A key role in local mRNA translation is played by RNA-binding proteins, which recruit the target mRNA to the transport machinery and regulate its translation. Individual proteins often bind to a large network of targets, and recent work has shown that target selection and regulation is modulated by the methylation of the mRNA during development. This proposal focuses on IGF2 mRNA Binding Protein 1 (IMP1), as a paradigm for RNA-binding proteins that regulate local mRNA translation. IMP1 is a multi-functional RNA-binding protein that is essential for development and plays a key role in defining the complexity of neuronal morphology, including the branching of neurites and the structure of synapses. IMP1 comprise multiple high-affinity RNA-binding units (domains) that are separated by flexible linkers whose phosphorylation acts to regulate RNA binding and is crucial for protein function. We are asking how IMP1 and other RNA-binding proteins recognise and regulate large networks of functionally related mRNA targets, and how this process is controlled during neuronal development. We are also asking whether and how this regulation is coupled to mRNA transport. Finally, we want to understand how the action of IMP1 on individual mRNA targets is integrated to obtain specific morphological changes in the differentiating neuron. Eventually, we aim to provide a mechanistic understanding for the large networks regulated by IMP1 and understand how signalling events can lead to changes in the local morphology of neurons and the creation of new neuronal structures and connections. We examine developmental regulation at different levels, integrating information from several disciplines. Data from structural, biophysical and biochemical methods will explain the physical basis of IMP1-RNA recognition, and how the phosphorylation of a tyrosine residue leads to the release of the bound mRNA. This insight will be integrated with microscopy data in differentiating neurons using modelling and mutations and help understand the process of local mRNA translation. We will use an unbiased AI analysis to understand how the regulation of individual mRNA are integrated to yield larger morphological changes. The results will provide a comprehensive view of the function and regulation of a key RNA-binding protein in neuronal development. Importantly, the concepts and tools developed here will prove useful in the study of other RNA regulators that play major roles in widespread and severe pathologies which are a threat to lifelong human health.