A macrophage relay for long distance signaling during post-embryonic tissue remodeling

Macrophages have diverse functions in immunity as well as development and homeostasis. Here we identify a function for these cells in long distance communication during post-embryonic tissue remodeling. Ablation of macrophages in zebrafish prevented melanophores from coalescing into adult pigment stripes. Melanophore organization depends on signals provided by cells of the yellow xanthophore lineage via airinemes, long filamentous projections with vesicles at their tips. We show that airineme extension from originating cells, and vesicle deposition on target cells, depend on interactions with macrophages. These findings identify a role for macrophages in relaying long range signals between non-immune cells. It will be interesting to see if this signaling modality functions in the remodeling and homeostasis of other tissues during normal development and disease.