Genetically Encoded Melanin as a Photostable Scattering Contrast for Whole-Brain Tomography

Large-scale brain imaging has traditionally depended on fluorescent reporters, but challenges like photobleaching and inconsistent signals hinder quantitative analysis in intact tissues. In response, we present MelaCAST (melanin-based scattering CAST imaging), a novel genetically encoded scattering method for whole-brain visualization. Using AAV to deliver tyrosinase allows for cell-type-specific melanin synthesis, providing a stable intracellular scattering contrast across the mouse brain. Combining tissue clearing with scattering tomography, MelaCAST offers non-photobleaching, high-throughput volumetric imaging of genetically targeted cell populations in intact brains. This technique establishes melanin as a genetically encoded scattering reporter and broadens whole-organ imaging capabilities beyond traditional fluorescence methods.