Foxq2 determines blue cone identity in zebrafish

Abstract

AbstractMost vertebrate lineages retain a tetrachromatic visual system, which is supported by a functional combination of spectrally distinct multiple cone photoreceptors, UV, blue, green, and red cones. The blue cone identity is ensured by selective expression of blue (sws2) opsin, and the mechanism is poorly understood becauseSWS2gene has been lost in mammalian species such as mouse, whose visual system has been extensively studied. Here we pursued loss-of-function studies on transcription factors expressed predominantly in zebrafish cone photoreceptors and identified Foxq2 as a core factor drivingsws2gene expression.foxq2is expressed only in the blue cone, and loss offoxq2selectively abolishessws2expression. Comparative genomic analysis revealed that a wide range of vertebrate species retain bothFOXQ2andSWS2genes. We propose that FOXQ2-dependentSWS2expression is a prevalent regulatory mechanism that was acquired at the early stage of vertebrate evolution