Roles of Panx1 Channels in Larval Zebrafish: From Genes to Visual-Motor Behavior
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Pannexin1 (Panx1) forms ATP-permeable single membrane channels that play a role in the (patho)physiology of the nervous system. Two independent copies of panx1 (i.e., panx1a and panx1b) have been identified in the zebrafish. To evaluate each panx1 copys role in the visual system, we developed zebrafish panx1 knockout models (i.e., panx1a-/-, panx1b-/-, and panx1a-/-/panx1b-/- double knockout; DKO) using TALEN technology. The RNA-seq analysis of 6 days post-fertilization larvae was confirmed by Real-Time PCR and paired with testing visual-motor behaviors. Results demonstrated that both Panx1s contribute to the retinal OFF pathways function, though through different signaling pathways. Panx1a proteins specifically affect the expression of gene classes representing the development of the visual system and visual processing. The molecular and behavioral findings also provide for the first-time evidence that the ablation of panx1a alters dopaminergic signaling and that adenosine signaling links Panx1a proteins to the dopaminergic pathway. Indeed, altered visuomotor behavior in the absence of functional panx1a was simulated through D1/D2 receptor agonist treatment, and rescued applying either D2 receptor antagonist, haloperidol, or adenosine receptor agonist, adenosine. The Panx1b protein emerged as a modulator of the circadian clock system; thereby, affecting diverse biological processes from metabolic pathways to cognition. In terms of vision, loss of panx1b disrupted the retinal response to the abrupt loss of illumination and decreased visual acuity in the dark. Also, it led to cognitive dysfunction, anxiety-related behavior, and difficulty forming visual memory. Interestingly, loss of both panx1 copies in a double knockout resulted in specific transcriptome changes in which biological processes related to the circadian clock were regulated opposite to the changes observed in panx1b-/- larvae. However, these changes did not translate into morphological and behavioral defects in DKO larvae. We concluded that panx1a and panx1b functions are relevant to the retinal OFF-pathways, which support visual-motor functions underlying complex behaviors of freely swimming fish.