COMPARTMENTALIZED SECOND MESSENGER SIGNALING DURING RETINAL GANGLION CELL AXON GUIDANCE: A COMPUTATIONAL MODELING STUDY

During embryonic development, retinal ganglion cells (RGCs) extend axons from the retina to specific dorsal brain targets under the guidance of extracellular cues such as EphrinA5 and Slit1. These cues regulate growth cone behavior through second messengers including cAMP, cGMP, and calcium. Recent experimental work has demonstrated that EphrinA5 and Slit1 trigger spatially distinct second messenger signals within subcellular nanodomains of the growth cone, highlighting subcellular localization as a key mechanism for signaling specificity. However, the biochemical mechanisms underlying this compartmentalization remain poorly understood. We developed compartmentalized computational models of growth cone signaling in which EphrinA5 signaling is confined to lipid raft microdomains, while Slit1 signaling occurs in non-raft regions. Several model architectures were constructed based on biological hypotheses regarding the localization and regulation of signaling components. The models were calibrated using experimental FRET measurements of cAMP, cGMP, and calcium dynamics before and after exposure to guidance cues (S. Baudet et al., 2023, Nature Communications). Bayesian model selection was used to evaluate the different model architectures and identify candidate isoforms of adenylyl cyclases, guanylyl cyclases, and phosphodiesterases operating within each compartment, as well as candidate mechanisms involved in calcium dynamics. These models establish a quantitative framework to explore how the spatial organization of signaling components shapes second messenger dynamics in response to EphrinA5 and Slit1. By linking subcellular localization to signaling dynamics, this approach aims to generate testable hypotheses and guide future experiments investigating the molecular mechanisms underlying RGCs axon guidance.