Fate of melanocytes in sparse mutant larvae. (A,B) At 11 days, melanocytes persist in wild type (A), but are virtually absent from spab5 mutants (B). (C,D) sparse mutant larvae recover melanocytes during the larval-to-adult transition. Thus, both wild-type (C) and spab5 (D) adult zebrafish exhibit dark stripes of melanocytes and iridophores, alternating with light stripes of xanthophores and iridophores. Small arrow in D indicates the dorsal region where scale melanocytes are present in wild-type but absent in spab5. (E,F) In 7 day wild-type and sparse mutant larvae, cross sections (3 mm) of plasticembedded specimens reveal a difference in melanocyte localization. In wild type (E), melanocytes (arrowhead) are spread beneath the epidermis; in spab5 mutants (F), however, melanocytes are rounded within the plane of the epidermis (f, fin; e, epidermis; m, myotome). (G,H) sparse mutant melanocytes undergo apoptosis. TUNEL+ melanocytes are rounded and bulging outwards from the epidermis; this melanocyte morphology is not observed in wild-type larvae. Corresponding bright-field (G) and fluorescence (H) images of a spab5 mutant, TUNEL+ melanocyte rounded within the epidermis near the base of the fin fold (5.5 days). (I,J) sparse mutant melanocytes are extruded from the epidermis as revealed by capture on nylon membranes. Membranes beneath free-swimming wild-type larvae is unmarked (I), whereas membranes beneath free-swimming spab5 mutant larvae (J) collect spots of melanin (arrow) of the same size as melanocytes remaining in sparse larvae (inset: same magnification image showing melanocytes on sparse larva dried onto membrane). Scale bars: (A,B) 1 mm; (C,D) 8 mm; (E,F) 20 μm; (G,H) 12 μm; (I,J) 250 μm.
|
