Panx1b modulates the luminance response and direction of motion in the zebrafish
Pannexin1 (Panx1) can form ATP-permeable integral membrane channels that play roles in the physiology of the visual system. Two independent gene copies of Panx1, panx1a and panx1b, have been identified in the zebrafish with unique and shared properties and tissue expression patterns. Panx1a channels, located in horizontal cells of the outer retina, modulate light decrement detection through an ATP/pH-dependent mechanisms and adenosine/dopamine signaling. Here, we decipher how the strategic localization of Panx1b channels in the inner retina and ganglion cell layer modulates visually evoked motor behavior. We describe a panx1b knockout model generated by TALEN technology. The RNA-seq analysis of 6 days post-fertilization larvae is confirmed by Real-Time PCR and paired with testing of visual-motor behaviors. The Panx1b protein emerges as a modulator of the circadian clock system. The loss of panx1b also disrupts the retinal response to the abrupt loss of illumination and decreases the larval ability to follow leftward direction of motion in the dark. The evidence suggests that in the retina Panx1b contributes to the OFF pathways function, like Panx1a, though through different signaling mechanisms. In this process, the loss of Panx1b channels compromises the final output of luminance as well as direction of motion detector RGCs. In addition, the disruption of the circadian clock system in mutants suggests that Panx1b could participate in non-image forming processes in the inner retina.