Studying the intracellular transdifferentiation of pigment cells using cryo-soft X-ray tomography and spectroscopy

Pigments are found throughout all kingdoms of life, playing key roles such as vision, camouflage and communication. Teleost fish obtain a diverse range of pigment cells, known as chromatophores, including melanophores, xanthophores and iridophores, each producing specific biomolecules that contribute to their characteristic coloration. Recently, a novel pigment cell, termed melanoleucophores (ML), was discovered in zebrafish (Danio rerio). These cells, located at the distal edge of the dorsal fin, have the remarkable ability to transdifferentiate during metamorphosis. In juvenile fish, ML cells transition from melanin- to guanine production. Nevertheless, the exact mechanism underlying this transdifferentiation process, including whether guanine production and melanin degradation occur within the same organelle, remains unknown. Here we propose to utilize soft X-ray tomography, in conjunction with X-ray Absorption Near Edge Structure (XANES) spectro-microscopy to elucidate the molecular and ultrastructural processes involved in the transdifferentiation of ML in zebrafish. We will study ML in four developmental time points (4, 5, 6, and 7 weeks post-fertilization) and fully developed adults (3 months post-fertilization). The combined information will enable us to elucidate the guanine crystal formation and melanin degradation mechanisms and clarify whether these processes occur within the same organelle.