Fig. 3

Fig. 3

A sox10-dependent tfec/ltk positive feedback loop is required for iridophore specification.

WISH to detect tfec (A-H) and ltk (I-L) expression at 30 hpf (A-D, I, J) and 48 hpf (E-H, K, L) in WT and mutant embryos, with quantitation (M,N). At 30 hpf, sox10 mutants (B) lack tfec expression in medially migrating iridoblasts (A, arrows) and instead show a striking anteriorly expanded multipotent progenitor domain (B, arrowheads). Both ltk (C) and tfec mutants (D) display a reduced number of medially migrating ib(sp) (horizontal arrows) at 30 hpf, while dorsally located ib(sp) of the posterior trunk and tail (vertical arrows) are only significantly reduced in ltk mutants. At 48 hpf, sox10 (F) and ltk (G) mutants lack tfec-labelling in the position of WT iph (E, asterisks), while tfec mutants (H) display a reduced number of cells in these positions expressing tfec (H, asterisks; N). At both 30 hpf (I, J) and 48 hpf (K, L), tfec mutants lack ltk expression in ib(df) (I, J, arrows) and in iph (K, L, asterisks) locations, with the exception of rare escaper cells. (M) Quantitation of tfec-expressing iridophore lineage cells at 30 hpf. Counts for tfec-positive ib(df) along the dorsal posterior trunk, the migration pathways, and the lateral patches are shown from left to right. (N) Quantitation of tfec-expressing cells along the posterior trunk and tail at 48 hpf. At this stage, scored cells are in iph positions. tfec mutants display almost complete lack of ltk-positive cells both along the dorsal and the ventral stripes compared to their siblings, while tfec positive cells in both regions are partially reduced. p-values given in (M,N) were produced using a two-tailed unpaired t-test to determine the statistical significance of differences between means. ns: p > 0.05. Box-and-whisker plots in M and N show mean, 1^st and 3^rd quartiles and range excluding outliers, which are indicated by dots. (O) Overexpression of WT sox10 mRNA results in an increased number of tfec transcripts, compared to overexpression of null sox10 mRNA. Graph represents 2 biological replicates, each with 3 technical replicates. Error bars indicate respective standard deviations. A-L) Lateral views, head positioned towards the left. Scale bars: 100 μm.