Fig. S2

Related to Figure 2: Bace2 deficiency leads to increased melanophore cell division.

(A) Schema for testing the mechanism of increased melanophore cell number when Bace2 is loss. WT embryos were treated from 3-5dpF with 300μM PTU and/or 100μM Bace2 inhibitor (PF-06663195). PTU is a tyrosinase inhibitor that prevents new melanin synthesis to allow visualization only of previously pigmented melanophores. (B-C) Schema for two possible scenarios. If Bace2 loss of function induces pigment cell division as shown in (B), co-treatment with the Bace2 inhibitor and PTU would still increase melanophore cell number the same way as Bace2 inhibitor treatment alone. This is because PTU would not affect pre-existing melanin and the newly derived daughter cells would inherit melanin from their mother cell. If Bace2 loss of function induces differentiation of unpigmented precursor cells as shown in (C), co-treatment with the Bace2 inhibitor and PTU would not increase visible melanophores cell number, as PTU would inhibit any new melanin from synthesis. (D-E) Co-treatment with the Bace2 inhibitor and PTU led to an increase in the number of pigmented melanophores, which necessarily must have come from previously pigmented cells division due to the effects of PTU, quantified in (E). The data are from three independent experiments, one-way ANOVA followed by Holm-Sidak's multiple comparisons test; fish number n(DMSO)=53, n(Bace2 inhibitor)=56, n(PTU)=54, n(Bace2 inhibitor+PTU)= 61. **P<0.01, ****P<0.0001. Epinephrine (5mg/ml) was used to aggregate melanin to facilitate cell counting. All bar graphs are presented as mean ± s.e.m. Scale bars, 200μM.