Zebrafish kit mutation reveals primary and secondary regulation of melanocyte development during fin stripe regeneration

Fin regeneration in adult zebrafish is accompanied by reestablishment of th e pigment stripes. To understand the mechanisms underlying fin stripe regen eration and regulation of normal melanocyte stripe morphology, we investiga ted the origins of melanocytes in the regenerating fin and their requiremen t for the kit receptor tyrosine kinase. Using pre-existing melanin as a lin eage tracer, we show that most fin regeneration melanocytes develop from un differentiated precursors, rather than from differentiated melanocytes. Mut ational analysis reveals two distinct classes of regeneration melanocytes, First, an early regeneration class develops dependent on kit function. In t he absence of kit function and kit-dependent melanocytes, a second class of melanocytes develops at later stages of regeneration, This late kit-indepe ndent class of regeneration melanocytes has little or no role in wild-type fin stripe development, thus revealing a secondary mode for regulation of f in stripes. Expression of melanocyte markers in regenerating kit mutant fin s suggests that kit normally acts after mitf and before dct to promote deve lopment of the primary kit-dependent melanocytes. kit-dependent and kit-ind ependent melanocytes are also present during fin stripe ontogeny in pattern s similar to those observed during regeneration.