Figure 2.

Macrophage-dependent airineme signalling during pigment pattern formation in zebrafish. Step 1: a macrophage approaches a xanthoblast which has airineme vesicle precursors (=bleb-like structure at the plasma membrane, green circles). Step 2: the macrophage recognizes PtdSer-rich airineme vesicle precursor, Step 3: macrophage nibbles and pulls the precursor (=airineme vesicle). Step 4: the airineme filament elongates as macrophage migrates. Step 5: macrophage recognizes target melanophore and unloads the vesicle. Step 6: the macrophage leaves the target, but the airineme vesicle is stabilized at the surface and activates Notch signalling on the target cell surface. Step 7: the airineme filament retracts but the vesicle is still stabilized on the target cell surface for more than an hour. Step 8: another macrophage approaches the stabilized airineme vesicle on the target cell surface. Step 9: this macrophage engulfs the airineme vesicle. Step 10: the macrophage moves away from the target cell and starts to phagocytose the vesicle. Step 11: the engulfed airineme vesicle is finally degraded. After Notch activation at Step 7, the target melanophore migrates toward the stripes from the interstripe.