Regeneration of a partially amputated fish-nevus. (A) Mosaic integration of mitf-BRAF^V600E promotes fish-nevus development in wild-type zebrafish. Ectopic melanocytes form a fish-nevus in the tail fin (black tissue, ventral portion of tail fin). The red line indicates the line of amputation; the asterisk indicates an additional fish-nevus on the body. (B) Amputation of a portion of the tail fin, removing the distal portion of the fish-nevus (ventral portion of fin) and normal fin tissue (dorsal portion of fin). The regenerating tail fin was imaged at 1-week intervals following amputation. Regrowth of the tail fin at 1 week (C), 2 weeks (D), and 3 weeks (E). Higher-magnification image of the regenerating tail fin pigmentation in the normal tissue of the dorsal portion of the fin (F) and the regenerating fish-nevus (G). Yellow xanthophores and black melanocytes are clearly visible in the tail fin regenerate. (H) Complete tail fin and fish-nevus regeneration at 4 months.

Regenerating fish-nevi develop from an undifferentiated precursor. (A) A zebrafish tail fin with a fish-nevus (asterisks) was partially amputated and regrown in the presence of phenylthiourea (PTU) for 11 days (B). PTU blocks new melanin synthesis (Rawls and Johnson, 2000). Red boxes indicate areas of normal (top) and fish-nevus (bottom) regenerating fin. In the normal and fish-nevus (C and E), the fin regenerates in PTU without pigmentation and the blood vessels are clearly visible. (D and F) After 24 h in fresh water (PTU washout), the melanocytes are clearly visible (red arrows).