Fig. 5

Genetic fate mapping using a TgBAC(ltk:gfp) construct identifies pigment cells, but also Schwann cells and neurons, as derived from ltk-expressing cells.

a Schematic drawings of reporters. In both constructs, gfp cDNA with polyA site (pA) is inserted at the site of the first methionine. See Methods for details. b Cells labeled by TgBAC(ltk:gfp), shown at 2 dpf (DRG neuron), 3 dpf (melanocyte) or 4 dpf (others). All pigment cells are labeled by GFP or anti-GFP antibody, and observed by differential interference contrast (DIC) and immunofluorescence (GFP) microscopy; combined DIC and fluorescent images also shown (merged). Schwann cell around the posterior lateral line nerve is also detected by anti-GFP antibody (GFP), and pLLn is detected by anti-acetylated tubulin antibody (AcTu). Enteric and DRG sensory neurons are labelled by GFP, with enteric neurons identified by position (revealed by Differential Interference Contrast (DIC)) and anti-Elavl1 staining (Hu)(arrowheads; anti-AcTu also detected), whilst DRGs are identified by position and anti-Elavl1 staining (Hu) and RFP driven by neurog1 promoter (arrows) (see Methods). DRG N, DRG neuron; En, enteric neuron; Ir, Iridophore; Me, melanocyte; pLLn, posterior lateral line nerve; Sc, Schwann cell; Xa, Xanthophore. c Cells labeled by TgPAC(sox10:gfp). In addition to pigment cells and Schwann cells, lower jaw cartilage (Ca), enteric neurons and DRG are also labeled. For quantitation, see Table 2. Scale bar: 50 µm for b and c. d Cyclical Fate Restriction model of pigment cell development. Pigment cells derive from Highly Multipotent Progenitor (HMP) cells, which are envisaged as cycling through multiple sub-states; for simplicity, only two of these (eHMP and ltHMP) are distinguished here, based principally upon the level of expression of ltk (see Fig. 2b). Early and late phase Ltk expression reflects that in the ltHMP and iridoblast/iridophore respectively, with Ltk function (Ltk, boxed) required early for specification of iridophore lineage from ltHMP and late for ongoing differentiation/proliferation. See Fig. 1 legend for key.