fibroblasts/muscle progenitors finetune xanthophore countershading by differentially expressing in embryonic zebrafish.

Animals evolve diverse pigment patterns to adapt to the natural environment. Countershading, characterized by a dark-colored dorsum and a light-colored ventrum, is one of the most prevalent pigment patterns observed in vertebrates. In this study, we reveal a mechanism regulating xanthophore countershading in zebrafish embryos. We found that and mutants altered xanthophore countershading differently: mutants lack ventral xanthophores, while mutants have reduced dorsal xanthophores. Further study revealed that is expressed throughout the trunk, whereas is expressed dorsally. Ectopic expression of or in neurons attracted xanthophores into the spinal cord. Blocking signaling by mutants disrupts spinal cord distribution and normal xanthophores countershading. Single-cell RNA sequencing identified two populations: muscle progenitors and fibroblast progenitors. Ablation of fibroblast and muscle progenitors abolished xanthophore patterns. Our study suggests that fibroblast and muscle progenitors differentially express and to modulate xanthophore patterning, providing insights into the mechanism of countershading.