Local mRNA expression and translation in axon regrowth

The NeuroSchool PhD Program of Aix-Marseille University (France) has launched its annual calls for PhD contracts for students with a master's degree in a non-French university and for  international co-supervised PhDs.

This project is one of the proposed projects. Not all proposed projects will be funded, check our website for details.

State-of-the-art: The intrinsic inability of injured adult CNS neurons to regenerate their axon is a primary barrier to functional reconnection. Our recent work showed, at the soma level, that mTOR-induced axon regrowth requires translation of specific mRNA subsets, independently of their transcriptional state. In addition, it is known that translation is locally regulated in neuronal compartments such as the axon, a critical process in circuit development and function. However, little is known about local translation in axon regeneration after CNS injury.

Objectives: To unlock CNS axon regrowth, the project focuses on regulation of gene expression in the axon itself. We hypothesize that CNS axon regrowth depends on local translation of regrowth-associated mRNAs, a process that may be defective after injury, contributing to regeneration failure. The specific objectives are to:

1) Characterize the local mRNA content in regrowing axons

2) Characterize mRNA selective translation in regrowing axons

3) Validate axonal localization and translation of candidate mRNAs

4) Validate the functional requirement of candidate mRNAs for axon regrowth.

Methods: To identify locally translated mRNAs, we will study regrowth of injured retinal ganglion cells (RGCs) and compare adult wild-type (WT) RGCs with a regrowth-promoted capacity in adult mTOR-activated RGCs and with a high regrowth capacity in developing (post-natal day 0, P0) WT RGCs. We will use adult retina explant cultures, which offer access to the axonal compartment, RGC specificity and transposability to in vivo testing. Regrowing axons will be isolated from somas using transwell filters, which allow for compartment-specific profiling and ribosome-associated mRNA analysis using RNA-sequencing.

Expected results: This project will identify candidate mRNAs whose axonal translation is required for CNS neuron regrowth. The pool of axonally translated mRNAs differing between P0 WT and adult mTOR-activated axons will provide insight into the specificity of adult CNS axon regrowth. Additionally, any heterogeneity between regrowing axons and within individual axons will allow addressing how local translation contributes to neuronal subpopulation-specific injury responses and to subcompartment gene regulation along the axon.

Feasibility: This project leverages our expertise in adult retina explant cultures (optimized in our previous work), ribosome immunoprecipitation, next-generation sequencing (NGS) analysis and histology. Mouse lines necessary in this project (Pten-floxed, RiboTag) are already available in the lab. We have submitted the project for ethical authorization so the procedures will be approved by the start of the PhD. The project will be conducted at IBDM, which has all essential facilities to carry out experiments.

Complementarity of the two co-supervising laboratories: The PhD candidate will be co-supervised by Julia Schaeffer, who has expertise in axon regeneration and translation regulation; and by Andrew Saurin, who has expertise in NGS design and data analysis. The two laboratories offer a methodology and knowledge complementarity optimal for the project completion. The PhD candidate will also benefit from shared supervision and mentorship.

Within Aix Marseille Université, NeuroMarseille brings together 8 research laboratories and NeuroSchool, a graduate school in neuroscience, to increase the attractiveness of the university, international collaborations, interdisciplinarity, links with the clinical and industrial worlds and the integration of students into professional life. 

Launched in July 2018, NeuroSchool unifies and harmonizes the training of the third year of the Bachelor of Life Sciences (Neuroscience track), the Master's and the PhD in Neuroscience. 

• Master's degree from a non-French university in neuroscience or related field
• Fluent in English

We are looking for a highly motivated candidate with a strong commitment to the project and excellent skills to solve scientific problems, critically discuss experimental results and interact with scientists from distinct backgrounds. The candidate should have a strong interest in cellular and molecular aspects of gene expression regulation. Practical skills in primary cell culture, molecular biology and/or histology are strongly recommended. The project relies heavily on NGS data generation and analysis, for which the candidate should have either experience or a strong motivation to learn. Excellent written and communication skills and English proficiency are required.