Models for transcriptional regulation of RPE development in mouse versus zebrafish.

<p>(A) In mouse, Otx and Mitf regulate each other's expression and that of other RPE target genes, such that loss of either Mitf or Otx results in insufficient activation to specify RPE cell fate. (B) In contrast, in zebrafish we postulate that Otx is a more important regulator of RPE target genes, and that Otx regulates Mitf expression but not the reverse. Correspondingly, loss of Otx activity results in sub-threshold RPE gene activation and loss of specification, but loss of Mitf alone does not. Loss of both genes produces even lower target gene activation and a more severe phenotype.