Model for the parallel establishment of the zebrafish embryonic melanocyte lineage and the adult melanocyte stem cell lineage.

<p>Our results indicate that there are two distinct melanocyte lineages that develop in the zebrafish embryo: the embryonic or ontogenetic melanocyte lineage and the regenerative and metamorphic melanocyte lineage. In embryonic development, neural crest cells (squares) give rise to <i>dct+</i> melanoblasts (triangles), which later develop into embryonic melanocytes (black star). The regeneration and metamorphic lineage develops in parallel to embryonic melanocytes, prior to 48 hpf and presumably from the neural crest. The establishment of melanocyte stem cells (MSCs, dark circle) require ErbB signaling to progress from the pre-MSC state (light circle). The MSC can self-renew (circular arrow) and give rise to melanoblasts and melanocytes during metamorphosis or regeneration, when inhibition from embryonic melanocytes (block arrow) is relieved. The MSC–derived melanocytes are sensitive to developmental blockade by ICI-118,551 after the <i>dct</i>+ melanoblast stage. Ectopic expression of <i>kitla</i> can recruit the MSC lineage by either inducing MSCs or pre–MSCs resulting in overproliferation of melanocytes.