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Fig. 3 kit is expressed by NC-derived melanoblasts and melanocytes during wild-type zebrafish development. (A) Transverse cryosection showing NC cells (arrowheads) expressing kit as they disperse from the neural tube (nt) (18 hours cryosection). (B) Two-color in situ hybridization reveals cells expressing both kit (blue, in B) and nacre (red, in B, B′) in the dorsolateral NC migratory pathway (24 hours whole mount). (C) Lightly pigmented melanocytes expressing kit dorsal to the otocyst (o) (30 hours whole mount). (D) Fully differentiated melanocyte in the dorsal stripe expressing kit (12 day larva, cryosection); m, myotome (treated with PTU to partially inhibit melanin synthesis and better visualize kit staining). (E-K) kit also is expressed by an array of other cell types. (E) kit expression in notochord (arrow) and lateral mesodermal cells that are hematopoietic precursors and will form the intermediate cell mass (arrowhead; Detrich et al., 1995) (14 hours, whole mount dorsal view, anterior to left). (F) Notochord (arrow) and lateral mesodermal staining (arrowhead; 18 hours, transverse cryosection). (G) Notochord staining and staining in the pineal gland (double arrowhead; 17 hours, whole mount). (H) Dispersing, kit-expressing NC cells in the trunk (arrowheads), retinal staining in the eye (small arrow) and posterior notochord staining (large arrow; 22 hours, whole mount). (I) kitexpressing NC cells in the trunk (arrowheads) and branchial arches (inset; whole mount, 30 hours). (J) Zebrafish PGCs were not observed to express kit between 14 hours and 6.5 days. Shown are merged fluorescence and brightfield views of a transverse cryosection with vasastained PGCs (red) that do not stain for kit (blue, in adjacent melanocytes; 42 hours). n, notochord; y, yolk. (K) kit also is expressed in the lateral line sensory system (transverse cryosection, 3 day larva). In contrast to a Xenopus kit-like receptor (Baker et al., 1995) expressed in migrating lateral line primordia, zebrafish kit is expressed in differentiated sensory cells of lateral line neuromasts. Staining with DASPEI (Parichy, 1996a) does not reveal differences in midbody lateral line neuromast number between spab5 and wild type (F1,15=0.77, P=0.4). Scale bars: (A) 10 μm; (B) 5 μm; (C, D) 30 μm; (E) 500 μm; (F) 40 μm; (G, H) 500 μm; (I) 250 μm; (J) 30 μm; (K) 10 μm.