Figure 8. Model for xanthophore and leucophore development from neural crest.

We propose that xanthophores and leucophores develop from shared progenitors. Sox5 functions to control fate specification of xanthophores in place of leucophores. In the progenitors, which are positive for pax7a, sox5-expressing cells are specified to xanthophore fate whereas pax7a-expressing sox5-negative cells give rise to leucophores. In ml-3 mutants, loss of functional Sox5 causes a failure of xanthophore specification, resulting in all progenitors becoming specified to leucophore fate. The phenotypes of lf-2 (pax7a) and ml-3 (sox5), which are independent of melanophore and iridophore lineages, suggest that xanthophore and leucophore share common progenitors. Mel, melanophore; Iri, iridophore; Xan, xanthophore; Leu, leucophore.