You didn’t stop developing once you were born (or hatched). Our infant selves barely resemble ourselves as adults, thankfully, and stem cells play an important role in this continued development. A recent paper describes the identification of a stem cell niche that generates the melanophores that are responsible for the color patterning in adult zebrafish.
The color patterns that many animal species rely on for natural and sexual selection are generated by differences in melanin synthesis in melanophores. During embryonic development, melanophores are derived from the neural crest. In many species, such as zebrafish, the patterning seen in adults is established well after embryonic development—when the neural crest is no longer present. A recent paper in Development describes the identification of melanophore stem cells that are inactive in the larval stages of zebrafish development, and later activated in juvenile zebrafish. Dooley and colleagues found that the dorsal root ganglia serve as niches for these melanophore stem cells. The melanophore stem cells are established early in embryonic development, and later spread out segmentally to produce the stripes seen on adult zebrafish. These cells depend on the protein ErB for neural crest migration and the gene kit ligand (kitlga) to function as stem cells. In the images above, recovering larval melanophores (green, arrowhead) migrate away from the position of the dorsal root ganglion (asterisk), along the spinal nerves, after morpholino knockdown of the transcription factor mitfa successfully depleted the existing larval melanophores. The blue arrowhead points to a cell that later migrates. This pattern resembles the proximity of melanophores to spinal nerves seen in wild-type juvenile zebrafish.
For a more general description of this image, see my imaging blog within EuroStemCell, the European stem cell portal.
Dooley, C., Mongera, A., Walderich, B., & Nusslein-Volhard, C. (2013). On the embryonic origin of adult melanophores: the role of ErbB and Kit signalling in establishing melanophore stem cells in zebrafish Development, 140 (5), 1003-1013 DOI: 10.1242/dev.087007