Post-Embryonic Nerve-Associated Precursors to Adult Pigment Cells: Genetic Requirements and Dynamics of Morphogenesis and Differentiation
All images are from early metamorphic (6.2–8.0 SSL) wild-type larvae except for B, L, and M, from erbb3b mutant larvae. (A–C) Transverse confocal projections (collapsing ∼1.5 mm of trunk along the anterior-posterior axis) showing GFP+ cells in living larvae (left side of each larva is shown). Images correspond to Videos S1, S2, S3. (A) mitfa::GFP+ cells in a wild-type fish occur in the hypodermis, between the epidermis (e) and the myotome (m), within the the myotome itself (arrow), and above the spinal cord (sc). Arrowhead, location of the horizontal myoseptum. (B) In erbb3b mutants, most mitfa::GFP+ cells were missing. This image is intentionally overexposed compared to A, revealing faint reflected fluorescence from iridescent iridophores in the hypodermis (arrowhead), which are present in wild-type larvae as well. (C) sox10::GFP+ cells were found in extra-hypodermal locations of wild-type Tg(−4.9sox10:egfp)ba2 larvae . (D–M) Immunohistochemical analyses of fixed specimens. (D) Co-expression of mitfa::GFP (green) and sox10 (red). v, vertebral column. (E) mitfa::GFP+ cells aligned with mbp+ glia (red) along ventral root motor fibers. Arrow, mitfa::GFP+ cells did not co-express mbp. (F) Lateral view showing mitfa::GFP+ cells and foxd3+ cells (red) between Hu+ neurons (blue) of dorsal root ganglia. mitfa::GFP+ and foxd3+ cells were often found close to one another (e.g., arrows) whereas other cells co-expressed mitfa::GFP and foxd3 (arrowhead). (G) Lateral view with superimposed brightfield and fluorescence images showing mitfa::GFP+ and foxd3+ cells along a peripheral nerve fiber stained for acetylated alpha tubulin (blue) within the myotome. Arrows, adjacent mitfa::GFP+ and foxd3+ cells. (H). A nerve plexus near the base of the caudal fin harbored numerous mitfa::GFP+ and foxd3+ cells. (I) Along a peripheral nerve within the myotome some cells co-expressed mitfa::GFP and foxd3 (arrowhead), whereas cells expressing either mitfa::GFP+ or foxd3+ were often juxtaposed (arrows). (J,K) Transverse sections through the dorsal trunk showing sox10+ cells (J) and foxd3+ cells (K) n the hypodermis, within the myotomes, and near the spinal cord. Arrow, lateral line nerve. (L,M) In erbb3b mutant larvae, very few sox10+ (L) or foxd3+ (M) cells were found.