Fig. 1

Melanocytes develop from undifferentiated precursor cells and from pigmented melanocytes. (A) Still images of time-lapse microscopy at the onset of melanocyte differentiation. Melanocytes emerge in the dorsal head as highly dendritic and pigmenting cells. Most melanocytes arise de novo from the neural crest and do not divide (melanocytes b,c). A few pigmented melanocytes divide (melanocyte a), becoming rounded before division (to become two cells: a.i, a.ii), which then move away from each other. Scale bar: 100 μm. (B) High-magnification image of pigmented melanocyte a division during a 1.3 hour interval, with cells outlined (broken yellow lines depict the approximate outline of the cells as analyzed through all z-stacks using enhanced contrast techniques). (C) Quantitative analysis of melanocyte development in individual fish (labelled i-ix) over 1-4 dpf show the majority of melanocytes are derived de novo from unpigmented precursor cells (n=166; grey diamonds) and a subpopulation of melanocytes derived from cell division events (n=8; yellow diamonds). Division events were charted for ten other fish examples (fish x-xix) from 3 to 5/6 dpf. Only three new melanocytes were identified during this time, two of which were from division events. Thick grey lines indicate length of each individual time-lapse movie for each embryo.