Panx1b Modulates the Luminance Response and Direction of Locomotion in the Zebrafish

Pannexin-2 deficiency disrupts visual pathways and leads to ocular defects in zebrafish

Pannexin-2 (Panx2) is a unique ion channel localized to ER-mitochondria contact sites. These specialized microdomains are abundant in neurons and glia and essential for cellular signaling and metabolism. While synaptic interactions are well-studied, the role of intracellular contacts, such as those of ER-mitochondrial junctions, in neuronal function and neurodegeneration remains largely unexplored. To investigate the roles of Panx2 in neuronal communication, we examined its expression pattern in the zebrafish brain and used TALEN technology to generate homozygous Panx2 knockout (Panx2Δ11) zebrafish. Our results demonstrate that panx2 mRNA is present in several brain regions, notably in visual centers such as the optic tectum and the thalamus. In 6 days post fertilization TL (Panx2+/+) larvae, Panx2 expression was observed in the retina and the arborization fields of the optic tract. Transcriptome profiling of Panx2Δ11 larvae by RNA-seq analysis revealed down-regulation of genes involved in visual perception and lens development. Behavioral tests showed that loss of Panx2 leads to an altered ability to interpret visual information, such as changes in ambient illuminations, and respond with the characteristic motor action. Additionally, the knockout larvae displayed significantly impaired optomotor response. Lastly, when we tested the retinal structure of adult zebrafish eyes using optical coherence tomography, Panx2Δ11 fish revealed a longer mean axial length and a negative shift in retinal refractive error (RRE) values. Our findings highlight a distinct, novel function of Panx2 in sensory perception and ocular health, beyond its recognized roles in neurodevelopment and cancer.

Panx1 channels promote both anti- and pro-seizure-like activities in the zebrafish via p2rx7 receptors and ATP signaling

The molecular mechanisms of excitation/inhibition imbalances promoting seizure generation in epilepsy patients are not fully understood. Evidence suggests that Pannexin1 (Panx1), an ATP release channel, modulates the excitability of the brain. In this report, we performed electrophysiological, behavioral, and molecular phenotyping experiments on zebrafish larvae bearing genetic or pharmacological knockouts of Panx1a and Panx1b channels, each homologous to human PANX1. When Panx1a function is lost, or both channels are under pharmacological blockade, seizures with ictal-like events and seizure-like locomotion are reduced in the presence of pentylenetetrazol. Transcriptome profiling by RNA-seq demonstrates a spectrum of distinct metabolic and cell signaling states which correlate with the loss of Panx1a. Furthermore, the pro- and anticonvulsant activities of both Panx1 channels affect ATP release and involve the purinergic receptor P2rx7. Our findings suggest a subfunctionalization of Panx1 enabling dual roles in seizures, providing a unique and comprehensive perspective to understanding seizure mechanisms in the context of this channel.

The Interplay of Cx26, Cx32, Cx37, Cx40, Cx43, Cx45, and Panx1 in Inner-Ear Development of Yotari (dab1−/−) Mice and Humans

We investigated DAB1-protein deficiency in the inner-ear development of yotari in comparison to humans and wild-type (wt) mice by immunofluorescence for the expression of connexins (Cxs) and the pannexin Panx1. The spatial and temporal dynamics of Cx26, Cx32, Cx37, Cx40, Cx43, Cx45, and Panx1 were determined in the sixth and eighth weeks of human development and at the corresponding mouse embryonic E13.5 and E15.5, in order to examine gap junction intercellular communication (GJIC) and hemichannel formation. The quantification of the area percentage covered by positive signal was performed for the epithelium and mesenchyme of the cochlear and semicircular ducts and is expressed as the mean ± SD. The data were analysed by one-way ANOVA. Almost all of the examined Cxs were significantly decreased in the cochlear and semicircular ducts of yotari compared to wt and humans, except for Cx32, which was significantly higher in yotari. Cx40 dominated in human inner-ear development, while yotari and wt had decreased expression. The Panx1 expression in yotari was significantly lower than that in the wt and human inner ear, except at E13.5 in the mesenchyme of the wt and epithelium and mesenchyme of humans. Our results emphasize the relevance of GJIC during the development of vestibular and cochlear functions, where they can serve as potential therapeutic targets in inner-ear impairments.