Investigating axonal collateral branching through light induced receptor tyrosine kinases

Abstract

The human brain forms through billions of neurons establishing precise connections. Collateral branches, fine perpendicular axonal projections, are crucial for synaptic connectivity and emerge in response to injury or plasticity. Neurotrophic factors like NGF (high-affinity binding to TrkA) and BDNF (high-affinity binding to TrkB) are shown to induce branch formation, yet the spatiotemporal mechanisms remain unclear. Optogenetic Trk variants provide a precise tool to study receptor-mediated changes. This thesis utilizes Opto-TrkA and Opto-TrkB in chick spinal and DRG neurons to investigate branch formation. Optimizing light intensity revealed an intensity-dependent increase in protrusions. Prolonged stimulation significantly enhanced protrusion density. Localized Opto-TrkA stimulation enabled spatiotemporal control of branching. Additionally, Eps8 knockdown, known to increase protrusions, was examined for its role in stabilizing branches. Increased stable branches were observed. Overall, this thesis establishes an optogenetic framework to study collateral branch formation with spatiotemporal precision.